U.S. patent application number 17/223762 was filed with the patent office on 2021-08-12 for methods and apparatus for patient positioning in magnetic resonance imaging.
This patent application is currently assigned to Hyperfine Research, Inc.. The applicant listed for this patent is Hyperfine Research, Inc.. Invention is credited to Jeremy Christopher Jordan, Christopher Thomas McNulty, Anne Michele Nelson, Michael Stephen Poole.
Application Number | 20210244306 17/223762 |
Document ID | / |
Family ID | 1000005553099 |
Filed Date | 2021-08-12 |
United States Patent
Application |
20210244306 |
Kind Code |
A1 |
Nelson; Anne Michele ; et
al. |
August 12, 2021 |
METHODS AND APPARATUS FOR PATIENT POSITIONING IN MAGNETIC RESONANCE
IMAGING
Abstract
According to some aspects, a magnetic resonance imaging system
capable of imaging a patient is provided. The magnetic resonance
imaging system comprising at least one B0 magnet to produce a
magnetic field to contribute to a B0 magnetic field for the
magnetic resonance imaging system and a member configured to engage
with a releasable securing mechanism of a radio frequency coil
apparatus, the member attached to the magnetic resonance imaging
system at a location so that, when the member is engaged with the
releasable securing mechanism of the radio frequency coil
apparatus, the radio frequency coil apparatus is secured to the
magnetic resonance imaging system substantially within an imaging
region of the magnetic resonance imaging system.
Inventors: |
Nelson; Anne Michele;
(Guilford, CT) ; McNulty; Christopher Thomas;
(Guilford, CT) ; Jordan; Jeremy Christopher;
(Cromwell, CT) ; Poole; Michael Stephen;
(Guilford, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hyperfine Research, Inc. |
Guilford |
CT |
US |
|
|
Assignee: |
Hyperfine Research, Inc.
Guilford
CT
|
Family ID: |
1000005553099 |
Appl. No.: |
17/223762 |
Filed: |
April 6, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16554479 |
Aug 28, 2019 |
11006851 |
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17223762 |
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16516373 |
Jul 19, 2019 |
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16554479 |
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62811361 |
Feb 27, 2019 |
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62700711 |
Jul 19, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/055 20130101;
A61B 5/70 20130101; G01R 33/34007 20130101; A61B 6/04 20130101;
G01R 33/543 20130101; A61B 90/14 20160201; G01R 33/4833 20130101;
G01R 33/307 20130101 |
International
Class: |
A61B 5/055 20060101
A61B005/055; G01R 33/30 20060101 G01R033/30; G01R 33/34 20060101
G01R033/34; A61B 90/14 20060101 A61B090/14 |
Claims
1-20. (canceled)
21. A magnetic resonance imaging system comprising: a B.sub.0
magnet configured to produce a B.sub.0 magnetic field for the
magnetic resonance imaging system, the B.sub.0 magnet comprising:
at least one first B.sub.0 magnet to produce a first magnetic field
to contribute to the B.sub.0 magnetic field for the magnetic
resonance imaging system; and at least one second B.sub.0 magnet to
produce a second magnetic field to contribute to the B.sub.0
magnetic field for the magnetic resonance imaging system; and a
coupling member attached to the B.sub.0 magnet of the magnetic
resonance imaging system, such that the coupling member is disposed
between the at least one first B.sub.0 magnet and the at least one
second B.sub.0 magnet, wherein the coupling member is configured to
engage with a securing mechanism of a radio frequency coil
apparatus, the securing mechanism for securing the radio frequency
coil apparatus to and releasing the radio frequency coil apparatus
from the coupling member, so that, when the coupling member is
engaged with the securing mechanism of the radio frequency coil
apparatus, the radio frequency coil apparatus is secured to the
magnetic resonance imaging system.
22. The magnetic resonance imaging system of claim 21, wherein the
coupling member is attached to the at least one second B.sub.0
magnet.
23. The magnetic resonance imaging system of claim 22, wherein the
coupling member comprises a first portion having a first diameter
and a second portion having a second diameter larger than the first
diameter.
24. The magnetic resonance imaging system of claim 23, wherein the
first diameter is selected so that the coupling member can fit
within a receptacle of the securing mechanism of the radio
frequency coil apparatus.
25. The magnetic resonance imaging system of claim 24, wherein a
height of the first portion of the coupling member is configured to
allow at least a portion of the securing mechanism forming the
receptacle to fit underneath the second portion of the coupling
member.
26. The magnetic resonance imaging system of claim 23, wherein the
second portion of the coupling member comprises at least one recess
configured to accommodate the securing mechanism of the radio
frequency coil apparatus to prevent rotation of the radio frequency
coil apparatus about the coupling member.
27. The magnetic resonance imaging system of claim 22, wherein the
B.sub.0 magnetic field has a magnetic field strength of less than
or equal to 0.2 Tesla (T) and greater than or equal to 20 mT.
28. The magnetic resonance imaging system of claim 27, wherein the
B.sub.0 magnetic field has a magnetic field strength of less than
or equal to 0.1 T and greater than or equal to 50 mT.
29. The magnetic resonance imaging system of claim 21, wherein the
magnetic resonance imaging system is configured to image a patient
at least partially supported by a hospital bed comprising
ferromagnetic material.
30. The magnetic resonance imaging system of claim 21, further
comprising the securing mechanism of the radio frequency coil
apparatus.
31. A magnetic resonance imaging system comprising: a B.sub.0
magnet configured to produce a B.sub.0 magnetic field for the
magnetic resonance imaging system, the B.sub.0 magnet comprising:
at least one first B.sub.0 magnet to produce a first magnetic field
to contribute to the B.sub.0 magnetic field for the magnetic
resonance imaging system; and at least one second B.sub.0 magnet to
produce a second magnetic field to contribute to the B.sub.0
magnetic field for the magnetic resonance imaging system; and a
coupling member attached to the B.sub.0 magnet of the magnetic
resonance imaging system, such that the coupling member is disposed
between the at least one first B.sub.0 magnet and the at least one
second B.sub.0 magnet, and wherein the coupling member is
configured to engage with a securing mechanism of a patient
handling apparatus configured to secure to a radio frequency coil
apparatus, the securing mechanism for securing the patient handling
apparatus to and releasing the patient handling apparatus from the
coupling member, so that, when the coupling member is engaged with
the securing mechanism of the patient handling apparatus, the radio
frequency coil secured to the patient handling apparatus is secured
to the magnetic resonance imaging system.
32. The magnetic resonance imaging system of claim 31, wherein the
coupling member is attached to the at least one second B.sub.0
magnet.
33. The magnetic resonance imaging system of claim 32, wherein the
coupling member comprises a first portion having a first diameter
and a second portion having a second diameter larger than the first
diameter.
34. The magnetic resonance imaging system of claim 33, wherein the
first diameter is selected so that the coupling member can fit
within a receptacle of the securing mechanism of the patient
handling apparatus.
35. The magnetic resonance imaging system of claim 33, wherein a
height of the first portion of the coupling member is configured to
allow at least a portion of the securing mechanism forming the
receptacle to fit underneath the second portion of the coupling
member.
36. The magnetic resonance imaging system of claim 31, wherein the
B.sub.0 magnetic field has a magnetic field strength of less than
or equal to 0.2 Tesla (T) and greater than or equal to 20 mT.
37. The magnetic resonance imaging system of claim 36, wherein the
B.sub.0 magnetic field has a magnetic field strength of less than
or equal to 0.1 T and greater than or equal to 50 mT.
38. The magnetic resonance imaging system of claim 31, further
comprising the securing mechanism of the patient handling
apparatus.
39. A method for facilitating imaging using a magnetic resonance
imaging system, the method comprising: positioning a portion of
anatomy of a patient within the magnetic resonance imaging system;
and acquiring at least one magnetic resonance image of the portion
of the anatomy of the patient while the portion of the anatomy of
the patient is within the magnetic resonance imaging system,
wherein positioning the portion of the anatomy of the patient
comprises engaging a securing mechanism of a radio frequency coil
apparatus to a coupling member attached to the magnetic resonance
imaging system at a location between first and second B.sub.0
magnets of the magnetic resonance imaging system, the securing
mechanism for securing the radio frequency coil apparatus to the
coupling member and releasing the radio frequency coil apparatus
from the coupling member, so that, when the coupling member is
engaged with the securing mechanism of the radio frequency coil
apparatus, the radio frequency coil apparatus is secured to the
magnetic resonance imaging system.
40. The method of claim 39, wherein acquiring the at least one
magnetic resonance image of the portion of the anatomy of the
patient is performed while the patient is at least partially
supported by a medical bed comprising at least some ferromagnetic
material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn. 120
and is a continuation (CON) of U.S. patent application Ser. No.
16/516,373 filed Jul. 19, 2019 and titled "Methods and Apparatus
for Patient Positioning in Magnetic Resonance Imaging," which
claims priority under 35 U.S.C. .sctn. 119 to U.S. Provisional
Application Ser. No. 62/700,711 filed Jul. 19, 2018 and titled
"Methods and Apparatus for Patient Positioning in Magnetic
Resonance Imaging," and U.S. Provisional Application Ser. No.
62/811,361 filed Feb. 27, 2019 and titled "Methods and Apparatus
for Patient Positioning in Magnetic Resonance Imaging," each
application of which is herein incorporated by reference in its
entirety.
BACKGROUND
[0002] Magnetic resonance imaging (MRI) provides an important
imaging modality for numerous applications and is widely utilized
in clinical and research settings to produce images of the inside
of the human body. As a generality, MRI is based on detecting
magnetic resonance (MR) signals, which are electromagnetic waves
emitted by atoms in response to state changes resulting from
applied electromagnetic fields. For example, nuclear magnetic
resonance (NMR) techniques involve detecting MR signals emitted
from the nuclei of excited atoms upon the re-alignment or
relaxation of the nuclear spin of atoms in an object being imaged
(e.g., atoms in the tissue of the human body). Detected MR signals
may be processed to produce images, which in the context of medical
applications, allows for the investigation of internal structures
and/or biological processes within the body for diagnostic,
therapeutic and/or research purposes.
[0003] MRI provides an attractive imaging modality for biological
imaging due to the ability to produce non-invasive images having
relatively high resolution and contrast without the safety concerns
of other modalities (e.g., without needing to expose the subject to
ionizing radiation, e.g., x-rays, or introducing radioactive
material to the body). Additionally, MRI is particularly well
suited to provide soft tissue contrast, which can be exploited to
image subject matter that other imaging modalities are incapable of
satisfactorily imaging. Moreover, MR techniques are capable of
capturing information about structures and/or biological processes
that other modalities are incapable of acquiring. However, there
are a number of drawbacks to MRI that, for a given imaging
application, may involve the relatively high cost of the equipment,
limited availability and/or difficulty in gaining access to
clinical MRI scanners and/or the length of the image acquisition
process.
[0004] The trend in clinical MRI has been to increase the field
strength of MRI scanners to improve one or more of scan time, image
resolution, and image contrast, which, in turn, continues to drive
up costs. The vast majority of installed MRI scanners operate at
1.5 or 3 tesla (T), which refers to the field strength of the main
magnetic field B.sub.0. A rough cost estimate for a clinical MRI
scanner is approximately one million dollars per tesla, which does
not factor in the substantial operation, service, and maintenance
costs involved in operating such MRI scanners.
[0005] Additionally, conventional high-field MRI systems typically
require large superconducting magnets and associated electronics to
generate a strong uniform static magnetic field (B.sub.0) in which
an object (e.g., a patient) is imaged. The size of such systems is
considerable with a typical MRI installment including multiple
rooms for the magnet, electronics, thermal management system, and
control console areas. The size and expense of MRI systems
generally limits their usage to facilities, such as hospitals and
academic research centers, which have sufficient space and
resources to purchase and maintain them. The high cost and
substantial space requirements of high-field MRI systems results in
limited availability of MRI scanners. As such, there are frequently
clinical situations in which an MRI scan would be beneficial, but
due to one or more of the limitations discussed above, is not
practical or is impossible, as discussed in further detail
below.
SUMMARY
[0006] Some embodiments include a patient handling apparatus
configured to facilitate positioning a patient within a magnetic
resonance imaging device, the patient handling apparatus comprising
a patient support having a surface adapted to be positioned between
the patient and a bed so that, when positioned, the surface of the
patient support is underneath at least a portion of the patient's
body, and a securing portion comprising at least one first
releasable securing mechanism configured to engage with a radio
frequency component to secure the radio frequency component to the
securing portion, and at least one second releasable securing
mechanism configured to engage with the magnetic resonance imaging
device to secure the securing portion to the magnetic resonance
imaging device.
[0007] Some embodiment include a helmet configured to accommodate a
patient's head during magnetic resonance imaging, the helmet
comprising at least one radio frequency transmit and/or receive
coil, and at least one first releasable securing mechanism
configured to engage with a member attached to a magnetic resonance
imaging system at a location such that, when the at least one
securing mechanism engages with the member, the helmet is
positioned within the imaging region of the magnetic resonance
imaging system.
[0008] Some embodiments include a helmet configured to accommodate
a patient's head during magnetic resonance imaging, the helmet
comprising at least one radio frequency transmit and/or receive
coil, at least one first releasable securing mechanism configured
to engage with a member of the magnetic resonance imaging system
such that, when the at least one securing mechanism engages with
the member, the at least one securing mechanism resists translation
of the helmet relative to the cooperating member, and at least one
second securing mechanism configured to, when engaged with a
cooperating portion of the member, prevent rotation of the helmet
about the member.
[0009] Some embodiments include a magnetic resonance imaging system
capable of imaging a patient at least partially supported by a
support comprising ferromagnetic material, the magnetic resonance
imaging system comprising at least one first B.sub.0 magnet to
produce a first magnetic field to contribute to a B.sub.0 magnetic
field for the magnetic resonance imaging system, the B.sub.0
magnetic field having a field strength of less than or equal to 0.2
T, at least one second B.sub.0 magnet to produce a second magnetic
field to contribute to the B.sub.0 magnetic field for the magnetic
resonance imaging system, wherein the at least one first B.sub.0
magnet and the at least one second B.sub.0 magnet are arranged
relative to one another so that an imaging region is provided there
between, and a member configured to engage with a releasable
securing mechanism of a radio frequency coil apparatus, the member
attached to the magnetic resonance imaging between the at least one
first B.sub.0 magnet and the at least one second B.sub.0 magnet at
a location so that, when the member is engaged with the releasable
securing mechanism of the radio frequency coil apparatus, the radio
frequency coil apparatus is secured to the magnetic resonance
imaging system substantially within the imaging region.
[0010] Some embodiments include a magnetic resonance imaging system
capable of imaging a patient at least partially supported by a
support comprising ferromagnetic material, the magnetic resonance
imaging system comprising at least one first B.sub.0 magnet to
produce a first magnetic field to contribute to a B.sub.0 magnetic
field for the magnetic resonance imaging system, the B.sub.0
magnetic field having a field strength of less than or equal to 0.2
T, at least one second B.sub.0 magnet to produce a second magnetic
field to contribute to the B.sub.0 magnetic field for the magnetic
resonance imaging system, wherein the at least one first B.sub.0
magnet and the at least one second B.sub.0 magnet are arranged
relative to one another so that an imaging region is provided there
between, and a member configured to engage with a releasable
securing mechanism of a patient handling apparatus configured to
secure a radio frequency coil apparatus, the member attached to the
magnetic resonance imaging between the at least one first B.sub.0
magnet and the at least one second B.sub.0 magnet at a location so
that, when the member is engaged with the releasable securing
mechanism of the patient handling apparatus, the radio frequency
coil secured to the patient handling apparatus is positioned
substantially within the imaging region.
[0011] Some embodiments include a method, comprising releasably
securing a support to a magnetic resonance imaging device so as to
facilitate magnetic resonance imaging of a patient, the support
disposed between the patient and a standard medical bed.
[0012] Some embodiments include a method comprising positioning a
portion of anatomy of a patient within an imaging region of a
magnetic resonance imaging system while the patient is at least
partially supported by a standard medical bed, and acquiring at
least one magnetic resonance image of the portion of the anatomy of
the patient while the patient is at least partially supported by
the standard medical bed.
[0013] Some embodiments include an apparatus for imaging a foot,
the apparatus comprising at least one housing configured to
accommodate a patient's foot during magnetic resonance imaging, at
least one radio frequency transmit and/or receive coil, and at
least one first releasable securing mechanism configured to engage
with a member attached to a magnetic resonance imaging system at a
location such that, when the at least one securing mechanism
engages with the member, the apparatus is positioned within the
imaging region of the magnetic resonance imaging system.
[0014] Some embodiments include an apparatus for imaging a foot,
the apparatus comprising at least one radio frequency transmit
and/or receive coil, and at least one housing configured to
accommodate a patient's foot during magnetic resonance imaging, the
at least one housing tilted at an angle relative to a vertical
axis
[0015] Some embodiments include a bridge adapted for attachment to
a magnetic resonance imaging system and configured to facilitate
positioning a patient within the magnetic resonance imaging system,
the bridge comprising a support having a surface configured to
support at least a portion of the patient, the support being
moveable between an up position and a down position, wherein the
surface is substantially vertical in the up position and
substantially horizontal in the down position, a hinge configured
to allow the support to be moved from the up position to the down
position and vice versa, and a base configured to attach the bridge
to the magnetic resonance imaging system.
[0016] Some embodiments include a magnetic resonance imaging system
comprising a B.sub.0 magnet configured to generate a magnetic field
suitable for magnetic resonance imaging, a conveyance mechanism
configured to allow the magnetic resonance imaging system to be
moved to different locations, and a bridge configured to facilitate
positioning a patient within the magnetic resonance imaging system,
the bridge comprising a support having a surface configured to
support at least a portion of the patient, the support being
moveable between an up position and a down position, wherein the
surface is substantially vertical in the up position and
substantially horizontal in the down position, a hinge configured
to allow the support to be moved from the up position to the down
position and vice versa, and a base attaching the bridge to the
magnetic resonance imaging system.
[0017] Some embodiments include a method of imaging a portion of
anatomy of a patient while the patient is at least partially
supported by a standard medical bed, the method comprising
positioning a magnetic resonance imaging system and the bed
proximate one another, moving a bridge attached to the magnetic
resonance imaging system from a vertical position to a horizontal
position so that the bridge overlaps a portion of the bed,
positioning the patient via the bridge so that the portion of
anatomy of the patient is within an imaging region of the magnetic
resonance imaging system, and acquiring at least one magnetic
resonance image of the portion of the anatomy of the patient while
the patient is at least partially supported by the bed and at least
partially supported by the bridge.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Various aspects and embodiments of the disclosed technology
will be described with reference to the following figures. It
should be appreciated that the figures are not necessarily drawn to
scale.
[0019] FIG. 1 illustrates exemplary components of a magnetic
resonance imaging system;
[0020] FIGS. 2A and 2B illustrate a portable low-field MRI system,
in accordance with some embodiments.
[0021] FIG. 3 illustrates a portable MRI system, in accordance with
some embodiments;
[0022] FIGS. 4A-I illustrate a patient handling apparatus that
facilitates MRI of a patient from a standard hospital bed, in
accordance with some embodiments;
[0023] FIGS. 5A-F illustrate aspects of a securing portion of a
patient handling apparatus, in accordance with some
embodiments;
[0024] FIGS. 6A-B illustrate a releasable securing mechanism, in
accordance with some embodiments;
[0025] FIGS. 7A-B illustrate aspects of a releasable securing
mechanism of a radio frequency coil apparatus, in accordance with
some embodiments.
[0026] FIGS. 8A-B illustrate aspects of a releasable securing
mechanism of a radio frequency coil apparatus, in accordance with
some embodiments;
[0027] FIGS. 9A-B illustrate a see-through radio frequency helmet,
in accordance with some embodiments;
[0028] FIGS. 10-D illustrate view of a foot coil, in accordance
with some embodiments;
[0029] FIG. 11 illustrates a foot coil configured to accommodate a
wider foot, in accordance with some embodiments; and
[0030] FIGS. 12A-D illustrate a foot coil positioned within a
magnetic resonance imaging device, in accordance with some
embodiments;
[0031] FIG. 13A illustrates a fold-up bridge shown in a vertical or
up position, in accordance with some embodiment;
[0032] FIG. 13B illustrates the fold-up bridge illustrated in FIG.
13A in a horizontal or down position, in accordance with some
embodiments.
[0033] FIG. 14 illustrates components of a fold-up bridge, in
accordance with some embodiments;
[0034] FIG. 15A illustrates a model of a bridge, in accordance with
some embodiments;
[0035] FIG. 15B illustrates a stress plot of the model of the
bridge illustrated in FIG. 15A;
[0036] FIG. 15C illustrates a deflection plot of the model of the
bridge illustrated in FIG. 15A.
[0037] FIG. 15D is Figure A.19 from the IEC 60601-1 illustrating
the human body mass distribution for patient support surfaces;
[0038] FIGS. 16A and 16B illustrate components of a fold-up bridge
with a counter-balance mechanism, in accordance with some
embodiments;
[0039] FIG. 17A illustrates a portable MRI system with a bridge in
the vertical position;
[0040] FIG. 17B illustrates a portable MRI system with a bridge in
the horizontal position;
[0041] FIG. 17C illustrates a patient positioned within a portable
MRI system and supported by a fold-out bridge.
DETAILED DESCRIPTION
[0042] The MRI scanner market is overwhelmingly dominated by
high-field systems, and particularly for medical or clinical MRI
applications. As discussed above, the general trend in medical
imaging has been to produce MRI scanners with increasingly greater
field strengths, with the vast majority of clinical MRI scanners
operating at 1.5 T or 3 T, with higher field strengths of 7 T and 9
T used in research settings. As used herein, "high-field" refers
generally to MRI systems presently in use in a clinical setting
and, more particularly, to MRI systems operating with a main
magnetic field (i.e., a B.sub.0 field) at or above 1.5 T, though
clinical systems operating between 0.5 T and 1.5 T are often also
characterized as "high-field." Field strengths between
approximately 0.2 T and 0.5 T have been characterized as
"mid-field" and, as field strengths in the high-field regime have
continued to increase, field strengths in the range between 0.5 T
and 1 T have also been characterized as mid-field. By contrast,
"low-field" refers generally to MRI systems operating with a
B.sub.0 field of less than or equal to approximately 0.2 T, though
systems having a B.sub.0 field of between 0.2 T and approximately
0.3 T have sometimes been characterized as low-field as a
consequence of increased field strengths at the high end of the
high-field regime. Within the low-field regime, low-field MRI
systems operating with a B.sub.0 field of less than 0.1 T are
referred to herein as "very low-field" and low-field MRI systems
operating with a B.sub.0 field of less than 10 mT are referred to
herein as "ultra-low field."
[0043] As discussed above, conventional MRI systems require
specialized facilities. An electromagnetically shielded room is
required for the MRI system to operate and the floor of the room
must be structurally reinforced. Additional rooms must be provided
for the high-power electronics and the scan technician's control
area. Secure access to the site must also be provided. In addition,
a dedicated three-phase electrical connection must be installed to
provide the power for the electronics that, in turn, are cooled by
a chilled water supply. Additional HVAC capacity typically must
also be provided. These site requirements are not only costly, but
significantly limit the locations where MRI systems can be
deployed. Conventional clinical MRI scanners also require
substantial expertise to both operate and maintain. These highly
trained technicians and service engineers add large on-going
operational costs to operating an MRI system. Conventional MRI, as
a result, is frequently cost prohibitive and is severely limited in
accessibility, preventing MRI from being a widely available
diagnostic tool capable of delivering a wide range of clinical
imaging solutions wherever and whenever needed. Typically, patient
must visit one of a limited number of facilities at a time and
place scheduled in advance, preventing MRI from being used in
numerous medical applications for which it is uniquely efficacious
in assisting with diagnosis, surgery, patient monitoring and the
like.
[0044] As discussed above, high-field MRI systems require specially
adapted facilities to accommodate the size, weight, power
consumption and shielding requirements of these systems. For
example, a 1.5 T MRI system typically weighs between 4-10 tons and
a 3 T MRI system typically weighs between 8-20 tons. In addition,
high-field MRI systems generally require significant amounts of
heavy and expensive shielding. Many mid-field scanners are even
heavier, weighing between 10-20 tons due, in part, to the use of
very large permanent magnets and/or yokes. Commercially available
low-field MRI systems (e.g., operating with a B.sub.0 magnetic
field of 0.2 T) are also typically in the range of 10 tons or more
due to the large amounts of ferromagnetic material used to generate
the B.sub.0 field, with additional tonnage in shielding. To
accommodate this heavy equipment, rooms (which typically have a
minimum size of 30-50 square meters) have to be built with
reinforced flooring (e.g., concrete flooring), and must be
specially shielded to prevent electromagnetic radiation from
interfering with operation of the MRI system. Thus, available
clinical MRI systems are immobile and require the significant
expense of a large, dedicated space within a hospital or facility,
and in addition to the considerable costs of preparing the space
for operation, require further additional on-going costs in
expertise in operating and maintaining the system.
[0045] In addition, currently available MRI systems typically
consume large amounts of power. For example, common 1.5 T and 3 T
MRI systems typically consume between 20-40 kW of power during
operation, while available 0.5 T and 0.2 T MRI systems commonly
consume between 5-20 kW, each using dedicated and specialized power
sources. Unless otherwise specified, power consumption is
referenced as average power consumed over an interval of interest.
For example, the 20-40 kW referred to above indicates the average
power consumed by conventional MRI systems during the course of
image acquisition, which may include relatively short periods of
peak power consumption that significantly exceeds the average power
consumption (e.g., when the gradient coils and/or RF coils are
pulsed over relatively short periods of the pulse sequence).
Intervals of peak (or large) power consumption are typically
addressed via power storage elements (e.g., capacitors) of the MRI
system itself. Thus, the average power consumption is the more
relevant number as it generally determines the type of power
connection needed to operate the device. As discussed above,
available clinical MRI systems must have dedicated power sources,
typically requiring a dedicated three-phase connection to the grid
to power the components of the MRI system. Additional electronics
are then needed to convert the three-phase power into single-phase
power utilized by the MRI system. The many physical requirements of
deploying conventional clinical MRI systems creates a significant
problem of availability and severely restricts the clinical
applications for which MRI can be utilized.
[0046] Accordingly, the many requirements of high-field MRI render
installations prohibitive in many situations, limiting their
deployment to large institutional hospitals or specialized
facilities and generally restricting their use to tightly scheduled
appointments, requiring the patient to visit dedicated facilities
at times scheduled in advance. Thus, the many restrictions on high
field MRI prevent MRI from being fully utilized as an imaging
modality. Despite the drawbacks of high-field MRI mentioned above,
the appeal of the significant increase in SNR at higher fields
continues to drive the industry to higher and higher field
strengths for use in clinical and medical MRI applications, further
increasing the cost and complexity of MRI scanners, and further
limiting their availability and preventing their use as a
general-purpose and/or generally-available imaging solution.
[0047] The low SNR of MR signals produced in the low-field regime
(particularly in the very low-field regime) has prevented the
development of a relatively low cost, low power and/or portable MRI
system. Conventional "low-field" MRI systems operate at the high
end of what is typically characterized as the low-field range
(e.g., clinically available low-field systems have a floor of
approximately 0.2 T) to achieve useful images. Though somewhat less
expensive than high-field MRI systems, conventional low-field MRI
systems share many of the same drawbacks. In particular,
conventional low-field MRI systems are large, fixed and immobile
installments, consume substantial power (requiring dedicated
three-phase power hook-ups) and require specially shielded rooms
and large dedicated spaces. The challenges of low-field MRI have
prevented the development of relatively low cost, low power and/or
portable MRI systems that can produce useful images.
[0048] The inventors have developed techniques enabling portable,
low-field, low power and/or lower-cost MRI systems that can improve
the wide-scale deployability of MRI technology in a variety of
environments beyond the current MRI installments at hospitals and
research facilities. As a result, MRI can be deployed in emergency
rooms, small clinics, doctor's offices, in mobile units, in the
field, etc. and may be brought to the patient (e.g., bedside) to
perform a wide variety of imaging procedures and protocols. Some
embodiments include very low-field MRI systems (e.g., 0.1 T, 50 mT,
20 mT, etc.) that facilitate portable, low-cost, low-power MRI,
significantly increasing the availability of MRI in a clinical
setting.
[0049] There are numerous challenges to developing a clinical MRI
system in the low-field regime. As used herein, the term clinical
MRI system refers to an MRI system that produces clinically useful
images, which refers to images having sufficient resolution and
adequate acquisition times to be useful to a physician or clinician
for its intended purpose given a particular imaging application. As
such, the resolutions/acquisition times of clinically useful images
will depend on the purpose for which the images are being
obtained.
[0050] Among the numerous challenges in obtaining clinically useful
images in the low-field regime is the relatively low SNR.
Specifically, the relationship between SNR and B.sub.0 field
strength is approximately B.sub.0.sup.5/4 at field strength above
0.2 T and approximately B.sub.0.sup.3/2 at field strengths below
0.1 T. As such, the SNR drops substantially with decreases in field
strength with even more significant drops in SNR experienced at
very low field strength. This substantial drop in SNR resulting
from reducing the field strength is a significant factor that has
prevented development of clinical MRI systems in the very low-field
regime. In particular, the challenge of the low SNR at very low
field strengths has prevented the development of a clinical MRI
system operating in the very low-field regime. As a result,
clinical MRI systems that seek to operate at lower field strengths
have conventionally achieved field strengths of approximately the
0.2 T range and above. These MRI systems are still large, heavy and
costly, generally requiring fixed dedicated spaces (or shielded
tents) and dedicated power sources.
[0051] The inventors have developed low-field and very low-field
MRI systems capable of producing clinically useful images, allowing
for the development of portable, low cost and easy to use MRI
systems not achievable using state of the art technology. According
to some embodiments, an MRI system can be transported to the
patient to provide a wide variety of diagnostic, surgical,
monitoring and/or therapeutic procedures, generally, whenever and
wherever needed. There are challenges to providing an MRI system
that can be transported to the patient and/or operated outside
specialized facilities (e.g., outside secure and shielded rooms), a
number of which are addressed using the techniques described in
U.S. patent Ser. No. 10/222,434 (hereinafter, "the '434 patent"),
titled "Portable Magnetic Resonance Imaging Methods and Apparatus,"
issued Mar. 5, 2019, which patent is herein incorporated by
reference in its entirety.
[0052] Another challenge involves positioning the patient within
the MRI system for imaging. As discussed above, conventional MRI is
confined to specialized facilities, including a room for the device
itself that is outfitted with extensive shielding and must meet
stringent safety regulations, including requiring the room to be
secure and free from ferrous material due to the high field
strengths involved in conventional clinical MRI. Standard hospital
beds are constructed using ferrous material, often steel,
prohibiting there use with conventional clinical MRI systems. As a
result, a patient must be brought to the specialized facility
dedicated to the MRI system and transferred to a custom bed
designed for use with the MRI system.
[0053] For patients that are ambulatory, this may mean requiring
the patient to enter the secure room housing the MRI device and
positioning themselves on a MRI-safe bed integrated with the MRI
device. For patients that are not ambulatory or are otherwise
immobilized, the patient may need to be first transferred to a
customized MRI-safe bed to be transported to the secure room and
then transferred to the integrated bed of the MRI system. Such
requirements limit the circumstances in which a patient can undergo
MRI and in some cases prohibits the use of MRI entirely. For
example, transfer of non-ambulatory and/or immobile patients to an
MRI safe bed or wheel chair to transport the patient into the
secure room and, potentially, another transfer to the integrated
bed or patient support of the MRI system is difficult and, in some
circumstances, not feasible for medical safety reasons.
Additionally, MRI safe beds are costly and not widely
available.
[0054] The inventors have developed techniques that allow MRI to be
performed in conjunction with a standard patient support, such as a
standard hospital bed or standard wheelchair, thereby eliminating
the requirement of transferring patients one or more times, as well
eliminating costs and availability issues associated with
specialized MRI safe transports (e.g., beds, wheelchairs, etc.).
Additionally, techniques that allow MRI to be performed, for
example, from a standard hospital bed, facilitate point-of-care
MRI. According to some embodiments, MRI is performed at field
strengths that are low enough to allow for imaging to be performed
on a patient positioned on or in a standard patient support, for
example, a patient lying on a standard hospital bed or seated in a
standard wheelchair. As used herein, a standard hospital bed or
standard wheelchair refers to a patient support that has not been
outfitted for use with conventional high-field MRI. Standard
hospital beds or wheelchairs will often be constructed of
ferromagnetic material, such as steel, that prevents there use with
high-field MRI.
[0055] To image a patient from, for example, a standard hospital
bed, certain MRI imaging procedures may require positioning target
anatomy of the patient within an MRI system moved to a location,
for example, the bed on which the patient is currently lying. The
inventors have developed techniques for facilitating the
positioning of a patient within an MRI system for imaging of
desired anatomy of the patient. According to some embodiments, a
patient handling system that can be secured to the MRI system is
used to support the patient and position the desired anatomy of the
patient within the MRI system.
[0056] Conventional MRI systems typically include an integrated bed
or support for the patient that is constructed using non-ferrous
material to satisfy stringent regulatory requirements (e.g.,
regulations promulgated to ensure both patient and clinician
safety) and so as to not disturb the magnetic fields produced by
the MRI system. This customized MRI-safe bed is generally
configured to be slid into and out of the bore of the system and
typically has mounts that allow the appropriate radio frequency
coil apparatus to be connected over the portion of the anatomy to
be imaged. When preparing a patient for imaging, the patient is
positioned on the bed outside the magnet bore so that the radio
frequency coil apparatus can be positioned and attached to the
cooperating mounts on the bed. For example, for a brain scan, a
radio frequency head coil apparatus is positioned about the
patient's head and attached to cooperating mounts fixed to the bed.
After the radio frequency coil apparatus is attached and positioned
correctly, the bed is moved inside the B.sub.0 magnet so that the
portion of the anatomy being imaged is positioned within the image
region of the MRI system.
[0057] The inventors have recognized that this conventional process
is not applicable to portable or point-of-care MRI, nor can this
process be used to image a patient from a standard medical bed or
wheelchair. For example, standard medical beds are not equipped
with mounts to which a radio frequency coil apparatus can be
attached, nor are radio frequency coil apparatus configured to be
attached to standard medical beds. In addition, a standard medical
bed or wheelchair cannot be positioned within the imaging region of
an MRI system. To facilitate imaging from, for example, a standard
medical bed, the inventors have developed radio frequency coil
apparatus adapted to accommodate target anatomy of a patient and
configured to engage with a cooperating member attached to the MRI
system so that when the radio frequency coil apparatus is engaged
with the member, the target anatomy is positioned within the
imaging region of the MRI system. In this way, the radio frequency
coil apparatus can be positioned about the patient and then
attached to a portable MRI system so that the patient can be imaged
from a standard medical bed or wheelchair, allowing the MRI system
to be brought to the patient or the patient wheeled to an available
MRI system and imaged from the standard medical bed. Such
point-of-care MRI allows MRI to be utilized in a wide variety of
medical situations where conventional MRI is not available (e.g.,
in the emergency room, intensive care unit, operating rooms,
etc.).
[0058] According to some embodiments, a radio frequency helmet
comprising one or more radio frequency coils is adapted to
accommodate a patient's head. The radio frequency helmet comprises
a releasable securing mechanism configured to secure the helmet to
a member attached to the MRI system at a location so that whenever
the radio frequency helmet is secured to the member, the helmet is
substantially within the imaging region of the MRI system. In
particular, when the helmet accommodates a patient's head and is
secured to the member, the patient's head is positioned within the
imaging region of the MRI system. According to some embodiments, a
radio frequency coil apparatus comprising one or more radio
frequency coils adapted to accommodate an appendage, such as a leg
or an arm, is equipped with such a releasable securing mechanism so
that when the radio frequency coil apparatus is secured to the
member, the radio frequency coil apparatus is substantially within
the imaging region of the MRI system so that the appendage
positioned for imaging.
[0059] FIG. 1 is a block diagram of typical components of a MRI
system 100. In the illustrative example of FIG. 1, MRI system 100
comprises computing device 104, controller 106, pulse sequences
store 108, power management system 110, and magnetics components
120. It should be appreciated that system 100 is illustrative and
that a MRI system may have one or more other components of any
suitable type in addition to or instead of the components
illustrated in FIG. 1. However, a MRI system will generally include
these high level components, though the implementation of these
components for a particular MRI system may differ vastly, as
discussed in further detail below.
[0060] As illustrated in FIG. 1, magnetics components 120 comprise
B.sub.0 magnet 122, shim coils 124, RF transmit and receive coils
126, and gradient coils 128. Magnet 122 may be used to generate the
main magnetic field B.sub.0. Magnet 122 may be any suitable type or
combination of magnetics components that can generate a desired
main magnetic B.sub.0 field. As discussed above, in the high field
regime, the B.sub.0 magnet is typically formed using
superconducting material generally provided in a solenoid geometry,
requiring cryogenic cooling systems to keep the B.sub.0 magnet in a
superconducting state. Thus, high-field B.sub.0 magnets are
expensive, complicated and consume large amounts of power (e.g.,
cryogenic cooling systems require significant power to maintain the
extremely low temperatures needed to keep the B.sub.0 magnet in a
superconducting state), require large dedicated spaces, and
specialized, dedicated power connections (e.g., a dedicated
three-phase power connection to the power grid). Conventional
low-field B.sub.0 magnets (e.g., B.sub.0 magnets operating at 0.2
T) are also often implemented using superconducting material and
therefore have these same general requirements. Other conventional
low-field B.sub.0 magnets are implemented using permanent magnets,
which to produce the field strengths to which conventional
low-field systems are limited (e.g., between 0.2 T and 0.3 T due to
the inability to acquire useful images at lower field strengths),
need to be very large magnets weighing 5-20 tons. Thus, the B.sub.0
magnet of conventional MRI systems alone prevents both portability
and affordability.
[0061] Gradient coils 128 may be arranged to provide gradient
fields and, for example, may be arranged to generate gradients in
the B.sub.0 field in three substantially orthogonal directions (X,
Y, Z). Gradient coils 128 may be configured to encode emitted MR
signals by systematically varying the B.sub.0 field (the B.sub.0
field generated by magnet 122 and/or shim coils 124) to encode the
spatial location of received MR signals as a function of frequency
or phase. For example, gradient coils 128 may be configured to vary
frequency or phase as a linear function of spatial location along a
particular direction, although more complex spatial encoding
profiles may also be provided by using nonlinear gradient coils.
For example, a first gradient coil may be configured to selectively
vary the B.sub.0 field in a first (X) direction to perform
frequency encoding in that direction, a second gradient coil may be
configured to selectively vary the B.sub.0 field in a second (Y)
direction substantially orthogonal to the first direction to
perform phase encoding, and a third gradient coil may be configured
to selectively vary the B.sub.0 field in a third (Z) direction
substantially orthogonal to the first and second directions to
enable slice selection for volumetric imaging applications. As
discussed above, conventional gradient coils also consume
significant power, typically operated by large, expensive gradient
power sources, as discussed in further detail below.
[0062] MRI is performed by exciting and detecting emitted MR
signals using transmit and receive coils, respectively (often
referred to as radio frequency (RF) coils). Transmit/receive coils
may include separate coils for transmitting and receiving, multiple
coils for transmitting and/or receiving, or the same coils for
transmitting and receiving. Thus, a transmit/receive component may
include one or more coils for transmitting, one or more coils for
receiving and/or one or more coils for transmitting and receiving.
Transmit/receive coils are also often referred to as Tx/Rx or Tx/Rx
coils to generically refer to the various configurations for the
transmit and receive magnetics component of an MRI system. These
terms are used interchangeably herein. In FIG. 1, RF transmit and
receive coils 126 comprise one or more transmit coils that may be
used to generate RF pulses to induce an oscillating magnetic field
Bi. The transmit coil(s) may be configured to generate any suitable
types of RF pulses.
[0063] Power management system 110 includes electronics to provide
operating power to one or more components of the low-field MRI
system 100. For example, as discussed in more detail below, power
management system 110 may include one or more power supplies,
gradient power components, transmit coil components, and/or any
other suitable power electronics needed to provide suitable
operating power to energize and operate components of MRI system
100. As illustrated in FIG. 1, power management system 110
comprises power supply 112, power component(s) 114,
transmit/receive switch 116, and thermal management components 118
(e.g., cryogenic cooling equipment for superconducting magnets).
Power supply 112 includes electronics to provide operating power to
magnetic components 120 of the MRI system 100. For example, power
supply 112 may include electronics to provide operating power to
one or more B.sub.0 coils (e.g., B.sub.0 magnet 122) to produce the
main magnetic field for the low-field MRI system. Transmit/receive
switch 116 may be used to select whether RF transmit coils or RF
receive coils are being operated.
[0064] Power component(s) 114 may include one or more RF receive
(Rx) pre-amplifiers that amplify MR signals detected by one or more
RF receive coils (e.g., coils 126), one or more RF transmit (Tx)
power components configured to provide power to one or more RF
transmit coils (e.g., coils 126), one or more gradient power
components configured to provide power to one or more gradient
coils (e.g., gradient coils 128), and one or more shim power
components configured to provide power to one or more shim coils
(e.g., shim coils 124).
[0065] In conventional MRI systems, the power components are large,
expensive and consume significant power. Typically, the power
electronics occupy a room separate from the MRI scanner itself. The
power electronics not only require substantial space, but are
expensive complex devices that consume substantial power and
require wall mounted racks to be supported. Thus, the power
electronics of conventional MRI systems also prevent portability
and affordability of MRI.
[0066] As illustrated in FIG. 1, MRI system 100 includes controller
106 (also referred to as a console) having control electronics to
send instructions to and receive information from power management
system 110. Controller 106 may be configured to implement one or
more pulse sequences, which are used to determine the instructions
sent to power management system 110 to operate the magnetic
components 120 in a desired sequence (e.g., parameters for
operating the RF transmit and receive coils 126, parameters for
operating gradient coils 128, etc.). As illustrated in FIG. 1,
controller 106 also interacts with computing device 104 programmed
to process received MR data. For example, computing device 104 may
process received MR data to generate one or more MR images using
any suitable image reconstruction process(es). Controller 106 may
provide information about one or more pulse sequences to computing
device 104 for the processing of data by the computing device. For
example, controller 106 may provide information about one or more
pulse sequences to computing device 104 and the computing device
may perform an image reconstruction process based, at least in
part, on the provided information. In conventional MRI systems,
computing device 104 typically includes one or more high
performance work-stations configured to perform computationally
expensive processing on MR data relatively rapidly. Such computing
devices are relatively expensive equipment on their own.
[0067] As should be appreciated from the foregoing, currently
available clinical MRI systems (including high-field, mid-field and
low-field systems) are large, expensive, fixed installations
requiring substantial dedicated and specially designed spaces, as
well as dedicated power connections. As discussed above, the
inventors have developed low power, portable low-field MRI systems
that can be deployed in virtually any environment and that can be
brought to the patient who will undergo an imaging procedure. In
this way, patients in emergency rooms, intensive care units,
operating rooms and a host of other locations can benefit from MRI
in circumstances where MRI is conventionally unavailable. The
exemplary portable MRI systems described below in connection with
FIGS. 2A, 2B and 3A are capable of being moved to locations at
which MRI is needed (e.g., emergency and operating rooms, primary
care offices, neonatal units, intensive care units, specialty
departments, hospital rooms, recovery units, etc.), facilitating
point-of-care MRI operable in proximity to standard hospital
equipment such as hospital beds, wheelchairs, other medical
devices, computing equipment, life support systems, etc.
Additionally, the exemplary portable MRI systems described herein,
including the systems described in the '434 patent, allow for the
deployment of the MRI system in virtually any location so that a
patient can be easily brought to the MRI system (e.g., transported
using a standard hospital bed or wheelchair) to achieve
point-of-care MRI.
[0068] FIGS. 2A and 2B illustrate a low power, portable low-field
MRI system, in accordance with some embodiments. Portable MRI
system 200 comprises a B.sub.0 magnet 205 including at least one
first permanent magnet 210a and at least one second permanent
magnet 210b magnetically coupled to one another by a ferromagnetic
yoke 220 configured to capture and channel magnetic flux to
increase the magnetic flux density within the imaging region (field
of view) of the MRI system. Permanent magnets 210a and 210b may be
constructed using any suitable technique, (e.g., using any of the
techniques, designs and/or materials described in the '434 patent).
Yoke 220 may also be constructed using any of the techniques
described herein (e.g., using any of the techniques, designs and/or
materials described in the '434 patent). It should be appreciated
that, in some embodiments, B.sub.0 magnet 205 may be formed using
electromagnets using any of the electromagnet techniques described
herein (e.g., using any of the techniques, designs and/or materials
described in the '434 patent). B.sub.0 magnet 205 may be encased or
enclosed in a housing 212 along with one or more other magnetics
components, such as the system's gradient coils (e.g., x-gradient,
y-gradient and z-gradient coils) and/or any shim components (e.g.,
shim coils or permanent magnetic shims), B.sub.0 correction coils,
etc.
[0069] B.sub.0 magnet 205 may be coupled to or otherwise attached
or mounted to base 250 by a positioning mechanism 290, such as a
goniometric stage (examples of which are described in the '434
patent), so that the B.sub.0 magnet can be tilted (e.g., rotated
about its center of mass) to provide an incline to accommodate a
patient's anatomy as needed. In FIG. 2A, the B.sub.0 magnet is
shown level without an incline and, in FIG. 2B, the B.sub.0 magnet
is shown after undergoing a rotation to incline the surface
supporting the patient's anatomy being scanned. Positioning
mechanism 290 may be fixed to one or more load bearing structures
of base 250 arranged to support the weight of B.sub.0 magnet
205.
[0070] In addition to providing the load bearing structures for
supporting the B.sub.0 magnet, base 250 also includes an interior
space configured to house the electronics 270 needed to operate the
portable MRI system 200. For example, base 250 may house the power
components to operate the gradient coils (e.g., X, Y and Z) and the
RF transmit/receive coils. The inventors have developed generally
low power, low noise and low cost gradient amplifiers configured to
suitably power gradient coils in the low-field regime, designed to
be relatively low cost, and constructed for mounting within the
base of the portable MRI system (i.e., instead of being statically
racked in a separate room of a fixed installment as is
conventionally done). Examples of suitable power components to
operate the gradient coils are described in further detail below
(e.g., the power components described in connection with FIGS.
20-34). According to some embodiments, the power electronics for
powering the gradient coils of an MRI system consume less than 50 W
when the system is idle and between 100-300 W when the MRI system
is operating (i.e., during image acquisition). Base 250 may also
house the RF coil amplifiers (i.e., power amplifiers to operate the
transmit/receive coils of the system), power supplies, console,
power distribution unit and other electronics needed to operate the
MRI system, further details of which are described below.
[0071] According to some embodiments, the electronics 270 needed to
operate portable MRI system 200 consume less than 1 kW of power, in
some embodiments, less than 750 W of power and, in some
embodiments, less than 500 W of power (e.g., MRI systems utilizing
a permanent B.sub.0 magnet solution). Techniques for facilitating
low power operation of an MRI device are discussed in further
detail below. However, systems that consume greater power may also
be utilized as well, as the aspects are not limited in this
respect. Exemplary portable MRI system 200 illustrated in FIGS. 2A
and 2B may be powered via a single power connection 275 configured
to connect to a source of mains electricity, such as an outlet
providing single-phase power (e.g., a standard or large appliance
outlet). Accordingly, the portable MRI system can be plugged into a
single available power outlet and operated therefrom, eliminating
the need for a dedicated power source (e.g., eliminating the need
for a dedicated three-phase power source as well as eliminating the
need for further power conversion electronics to convert three
phase power to single phase power to be distributed to
corresponding components of the MRI system) and increasing the
availability of the MRI system and the circumstances and locations
in which the portable MRI system may be used.
[0072] Portable MRI system 200 illustrated in FIGS. 2A and 2B also
comprises a conveyance mechanism 280 that allows the portable MRI
system to be transported to different locations. The conveyance
mechanism may comprise one or more components configured to
facilitate movement of the portable MRI system, for example, to a
location at which MRI is needed. According to some embodiments,
conveyance mechanism comprises a motor 286 coupled to drive wheels
284. In this manner, conveyance mechanism 280 provides motorized
assistance in transporting MRI system 200 to desired locations.
Conveyance mechanism 280 may also include a plurality of castors
282 to assist with support and stability as well as facilitating
transport.
[0073] According to some embodiments, conveyance mechanism 280
includes motorized assistance controlled using a controller (e.g.,
a joystick or other controller that can be manipulated by a person)
to guide the portable MRI system during transportation to desired
locations. According to some embodiments, the conveyance mechanism
comprises power assist means configured to detect when force is
applied to the MRI system and to, in response, engage the
conveyance mechanism to provide motorized assistance in the
direction of the detected force. For example, rail 255 of base 250
illustrated in FIGS. 2A and 2B may be configured to detect when
force is applied to the rail (e.g., by personnel pushing on the
rail) and engage the conveyance mechanism to provide motorized
assistance to drive the wheels in the direction of the applied
force. As a result, a user can guide the portable MRI system with
the assistance of the conveyance mechanism that responds to the
direction of force applied by the user. The power assist mechanism
may also provide a safety mechanism for collisions. In particular,
the force of contact with another object (e.g., a wall, bed or
other structure) may also be detected and the conveyance mechanism
will react accordingly with a motorized locomotion response away
from the object. According to some embodiments, motorized
assistance may be eliminated and the portable MRI system may be
transported by having personnel move the system to desired
locations using manual force.
[0074] Portable MRI system 200 includes slides 260 that provide
electromagnetic shielding to the imaging region of the system.
Slides 260 may be transparent or translucent to preserve the
feeling of openness of the MRI system to assist patients who may
experience claustrophobia during conventional MRI performed within
a closed bore. Slides 260 may also be perforated to allow air flow
to increase the sense of openness and/or to dissipate acoustic
noise generated by the MRI system during operation. The slides may
have shielding 265 incorporated therein to block electromagnetic
noise from reaching the imaging region. According to some
embodiments, slides 260 may also be formed by a conductive mesh
providing shielding 265 to the imaging region and promoting a sense
of openness for the system. Thus, slides 260 may provide
electromagnetic shielding that is moveable to allow a patient to be
positioned within the system, permitting adjustment by personnel
once a patient is positioned or during acquisition, and/or enabling
a surgeon to gain access to the patient, etc. Thus, the moveable
shielding facilitates flexibility that allows the portable MRI
system to not only be utilized in unshielded rooms, but enables
procedures to be performed that are otherwise unavailable.
Exemplary slides providing varying levels of electromagnetic
shielding are discussed in further detail below.
[0075] According to some embodiments, a portable MRI system does
not include slides, providing for a substantially open imaging
region, facilitating easier placement of a patient within the
system, reducing the feeling of claustrophobia and/or improving
access to the patient positioned within the MRI system (e.g.,
allowing a physician or surgeon to access the patient before,
during or after an imaging procedure without having to remove the
patient from the system). As an example, FIG. 3 illustrates an
exemplary portable low-field magnetic resonance imaging system that
can be moved to and operated at the point of care. MRI system 300
may be similar to one or more of the portable MRI systems described
in the '434 patent, comprising a B.sub.0 magnet 322 that includes
at least one first magnet 322a and at least one second magnet 322b
magnetically coupled to one another by a ferromagnetic yoke 320
configured to capture and channel magnetic flux to increase the
magnetic flux density within the imaging region (field of view) of
the MRI system. Magnets 322a and 322b may be constructed using any
suitable technique, including any of the techniques described in
the '434 patent. For example, B.sub.0 magnet 322 may include
permanent magnet(s), electromagnet(s), printed magnetics, or any
thereof. MRI system 300 further comprises gradient coils 328a and
328b to provide X-gradient, Y-gradient and Z-gradient coils for
spatial encoding of MR signals.
[0076] B.sub.0 magnet 322 may be coupled to or otherwise attached
or mounted to base 350 to support the B.sub.0 magnet. Base 350
includes housing 302 configured to house the electronics needed to
operate the portable MRI system 300 (e.g., as described in detail
in the '434 patent). To facilitate transporting the system to the
point of care, MRI system 300 may include a conveyance mechanism.
In FIG. 3, wheels or castors 382 allow the MRI system to be wheeled
to desired locations. According to some embodiments, MRI system 300
includes motorized assist to facilitate maneuvering the system,
some examples of which are described in the '434 patent. For
example, the conveyance mechanism may include a motor to drive
wheels/castors 382 provide motorized assistance in transporting MRI
system 300 to desired locations. According to some embodiments, the
conveyance mechanism may include motorized assistance controlled
using a controller (e.g., a joystick or other controller that can
be manipulated by a person) to guide the portable MRI system during
transportation to desired locations. According to some embodiments,
the conveyance mechanism comprises power assist means configured to
detect when force is applied to the MRI system by an operator and
to, in response, engage the conveyance mechanism to provide
motorized assistance in the direction of the detected force,
examples of which are described in further detail in the '434
patent.
[0077] As shown, MRI system 300 may have a maximum horizontal width
W that facilitates the maneuverability of the system within the
facilities in which the MRI system is used. According to some
embodiments, the maximum horizontal dimension of a portable MRI
system is in a range between 40 and 60 inches and, more preferably,
in a range between 35 and 45 inches. For example, exemplary MRI
system 300 has a maximum horizontal width of approximately 40
inches. As a result, MRI system 300 can be brought to locations in
which the MRI is needed, including to the bedside of a patient to
be imaged. MRI system 300 also includes bridge 373 that is mounted
to the MRI system to facilitate positioning a patient within the
imaging region of the MRI system. Bridge 373 may be configured to
be attached to different locations around the base to allow a
patient to be positioned within the imaging region from different
directions and/or orientations. According to some embodiments,
bridge 373 is attached to the MRI system 300 so that it can be
moved around the perimeter of the B.sub.0 magnet. According to some
embodiments, bridge 373 is configured to be removed and reattached
at different locations around the perimeter of the B.sub.0 magnet.
According to some embodiments, the bridge may be configured to
attach to yoke 320, base 350 or any other suitable portion of MRI
system 300, as the aspects are not limited in this respect.
[0078] The exemplary low-field MRI systems discussed above and in
the '434 patent can be used to provide point-of-care MRI, either by
bringing the MRI system directly to the patient or bringing the
patient to a relatively nearby MRI system (e.g., by wheeling the
patient to the MRI system in a standard hospital bed, wheelchair,
etc.). To facilitate imaging of patients using the exemplary
systems discussed herein, the inventors have developed techniques
to allow a patient to be positioned such that the target anatomy is
located correctly within the imaging region of the MRI system,
including techniques that allow the patient to be positioned from a
standard medical bed, wheelchair or other patient support, even
when the patient has limited or no mobility (e.g., the patient is
unconscious, sedated or anesthetized, or otherwise has limited
autonomous motion).
[0079] Following below are more detailed descriptions of various
concepts related to, and embodiments of, allowing for point-of-care
MRI using a portable low-field MRI. It should be appreciated that
the embodiments described herein may be implemented in any of
numerous ways. Examples of specific implementations are provided
below for illustrative purposes only. It should be appreciated that
the embodiments and the features/capabilities provided may be used
individually, all together, or in any combination of two or more,
as aspects of the technology described herein are not limited in
this respect.
[0080] FIG. 4A illustrates a patient handling apparatus that
facilitates performing MRI on a patient from a standard hospital
bed. FIG. 4A shows a first step of positioning target anatomy of
patient 499 within imaging region 415 of MRI system 400 (successive
steps are illustrated in FIGS. 4B-4I discussed in further detail
below). In particular, a patient 499 for which MRI is desired may
be confined to a bed 490 for convenience, comfort or stabilization
and/or because the patient is unconscious, immobilized or otherwise
is not ambulatory or cannot be safely moved. Bed 490 may be a
standard medical or hospital bed of the type typically used in
emergency rooms, operating rooms, intensive care units, etc. Such
standard hospital beds are typically constructed using
ferromagnetic, often steel, that prohibits there use with
conventional clinical MRI systems. In addition, hospital beds often
have motorized components for raising and lowering different
portions of the bed that also often contain material not permitted
to be located near a conventional clinical MRI system.
[0081] As used herein, the term standard hospital or medical bed
refers generally to any bed that has not been manufactured to be
MRI-safe according to regulations for current high-field MRI and/or
that has not been customized for use with conventional high-field
clinical MRI systems (e.g., manufactured to be free of any
ferromagnetic material). Therefore, standard medical or hospital
bed includes not only general purpose hospital beds, but also beds
that have been configured for specific medical purposes other than
customized beds manufactured to be compliant with current
regulatory requirements for use with conventional high field MRI.
Thus, beds that are constructed of ferrous or ferrite material
(e.g., ferromagnetic material such as iron, steel, etc.) or other
material prohibited from being used in restricted areas of
conventional clinical MRI are considered standard hospital beds,
even though they may be customized for specific purposes.
[0082] For conventional clinical MRI, exemplary bed 490 may
comprise a steel frame 495 so that, in addition to needing to be
transported to a dedicated MRI facility, the patient would be need
to be transferred to an integrated bed of the MRI system and/or
transferred to an MRI safe bed (e.g., a specially made bed using
aluminum or other non-magnetic material), or both. Such
requirements limit the circumstances in which a patient can undergo
MRI and in some cases prohibits the use of MRI entirely. In FIG. 4,
low-field MRI system 400 has been transported bed-side to the
patient to perform point-of-care MRI. Alternatively, low-field MRI
system 400 may be a local installation deployed in an emergency
room, operating room, intensive care unit, doctor's office, etc.
and bed 490 can be wheeled to the MRI system (i.e., MRI system 400
need not be portable). Because of the low-field strengths of MRI
system 400, bed 490 can be safely brought into close proximity to
B.sub.0 magnet 422 of MRI system 400. Additionally, low-field MRI
techniques are more robust to perturbations that may be caused by
ferromagnetic materials of the bed or in the environment of the MRI
system, allowing MRI system 400 to be operated adjacent bed 490 and
proximate other equipment in the vicinity that may include
ferromagnetic material.
[0083] In the embodiment illustrated in FIG. 4A, patient handling
apparatus 440 is provided to assist in moving patient 499 into
position within imaging region 435 of MRI system 400. The imaging
region or field of view defines the volume in which the B.sub.0
magnetic field produced by the B.sub.0 magnet (e.g., B.sub.0 magnet
422 comprising upper B.sub.0 magnet 422a, lower B.sub.0 magnet 422b
and yoke 420 illustrated in FIG. 4A) is suitable for imaging. More
particularly, the imaging region or field of view corresponds to
the region for which the B.sub.0 magnetic field is sufficiently
homogeneous at a desired field strength that detectable MR signals
are emitted by an object positioned therein in response to
application of radio frequency excitation (e.g., a suitable radio
frequency pulse sequence). In exemplary MRI system 400, B.sub.0
magnet 422 comprises an upper B.sub.0 magnet 422a and a lower
B.sub.0 magnet 422b, each producing a magnetic field to contribute
to the B.sub.0 magnetic field produced by B.sub.0 magnet 422. Upper
B.sub.0 magnet 422a and a lower magnet 422b are arranged in a
bi-planar arrangement to form imaging region 435 between them.
B.sub.0 magnet 422 also comprises yoke 420 to direct magnetic flux
from upper B.sub.0 magnet 422a and lower B.sub.0 magnet 422b to
imaging region 415 to increase the magnetic flux density
therein.
[0084] Patient handling apparatus 440 comprises a support portion
442 configured to support at least a portion of the patient while
the patient is positioned for imaging and a securing portion 445
configured to releasably secure the patient handling apparatus to a
radio frequency coil apparatus (e.g., a radio frequency helmet) and
to releasably secure the patient handling apparatus to MRI system
400, some embodiments of which are described in further detail
below. Securing portion 445 includes at least one releasable
securing mechanism configured to secure the patient handling
apparatus to a member 429 attached to the MRI system. In the
embodiment illustrated in FIG. 4A, member 429 is attached to lower
B.sub.0 magnet 422b of B.sub.0 magnet 422 at a location so that
when the patient handling apparatus 440 is secured to member 429,
the patient handling apparatus is positioned between upper B.sub.0
magnet 422a and lower B.sub.0 magnet 422b of the B.sub.0 magnet.
When a member to which a securing mechanism is configured to engage
with is described as being attached to B.sub.0 magnet 422b, it
means the member is attached to the cover or housing of the B.sub.0
magnet, any structure contained within the cover or housing for the
B.sub.0 magnet and/or attached to the B.sub.0 magnet itself.
[0085] As discussed in further detail below, securing portion 445
may also include at least one releasable securing mechanism to
secure patient handling apparatus 440 to a radio frequency coil
apparatus such that when the patient handling apparatus 440 is
secured to the radio frequency coil apparatus and to member 429,
the radio frequency coil apparatus is positioned at least partially
in and, more preferably, substantially within the imaging region of
MRI system 400. As a result, when target anatomy of a patient is
positioned within the radio frequency coil secured to the patient
handling apparatus 400, and the patient handling apparatus 400 is
secured to member 429, the target anatomy is positioned within
imaging region 415 of MRI system 400 for image acquisition.
[0086] As discussed above, patient handling apparatus comprises a
support portion 442 configured to support at least a portion of the
patient's body to facilitate positioning the patient within the
imaging region of the MRI system. Support portion 442 may include a
fold or hinge 442a that allows patient handling apparatus to be
folded to make the patient handling apparatus more compact, for
example, during storage and/or transport and unfolded, for example,
during use. Support portion 442 may be constructed from a molded
plastic, such as polyethylene or polypropylene. Fold 442a may be a
living hinge, a piano hinge, or any other suitable hinge that
facilitates the folding of support portion 442. It should be
appreciated that support portion 442 may include multiple folds to
increase compactness, or may not include a fold at all, as the
aspects are not limited in this respect.
[0087] As shown in FIG. 4A, a bridge 473 may be mounted to MRI
system 400 to facilitate positioning patient handling apparatus 400
within MRI system 400 to secure the securing portion 445 to member
429 via the at least one releasable securing mechanism. According
to some embodiments, bridge 473 is configured to mount to bed 490
instead of MRI system 400. According to some embodiments, bridge
472 may be configured to be mountable to either the bed, the MRI
system, or both, as the aspects are not limited in this respect.
Bridge 473 may be made of material that reduces friction between
patient handling apparatus 400 and the bridge, such as a smooth
plastic, to facilitate sliding the patient support 440 across the
bridge so that securing portion 445 can be secured to member 429
via the at least one releasable securing mechanism. Examples of
releasable securing mechanisms for securing and releasing a patient
handling apparatus to and from a radio frequency coil apparatus and
to secure the patient handling apparatus to the MRI system, in
accordance with some embodiments, are described in further detail
below.
[0088] FIG. 5A illustrates a securing portion of a patient handling
apparatus, in accordance with some embodiments. Securing portion
545 may be similar or the same as securing portion 445 of patient
handling apparatus 440 illustrated in FIG. 4. In FIG. 5A, the
bottom surface (underside) of securing portion 545 is shown (i.e.,
the surface opposite the surface on which the patient is
supported). That is, when the patient handling apparatus to which
securing portion 545 is coupled is positioned for use, surface 545a
will face down towards the bed in the direction of the floor. In
FIG. 5A, securing portion 545 is engaged with member 429 of a
magnetic resonance imaging system and a member 531 of a radio
frequency coil apparatus to illustrate techniques for securing a
patient handling apparatus to the radio frequency coil apparatus
and magnetic resonance imaging system to facilitate positioning a
patient within the magnetic resonance imaging system, in accordance
with some embodiments.
[0089] Securing portion 545 comprises a first releasable securing
mechanism 543 configured to engage with a radio frequency coil
apparatus to secure the securing portion 545 (and thus the patient
handling apparatus) to the radio frequency coil apparatus. In the
exemplary embodiment illustrated in FIG. 5A, the first releasable
securing mechanism 543 comprises a retention member 543a and a
keyhole slot 543b to engage with member 531 of a radio frequency
coil apparatus (e.g., a radio frequency helmet) to secure the
patient handling apparatus to the radio frequency coil apparatus.
Keyhole slot 543b includes a larger diameter portion 543b' and a
smaller diameter portion 543b'' dimensioned so that member 531 can
be inserted into larger diameter portion 543b' in a first direction
along axis 505c (i.e., in a direction out of the page of the
drawing) and slid into smaller diameter portion 543b'' where the
smaller diameter prevents member 531 from exiting keyhole slot 543b
in a second direction along axis 505c (i.e., in a direction
opposite the direction member 531 was inserted into keyhole slot
543b). Securing portion 545 may include additional keyhole slots
549a and 549b, each with respective larger and smaller diameter
portions (e.g., larger diameter portions 549a' and 549b', and
smaller diameter portions 549a'' and 549b'', respectively.
Additional keyhole slots may be included to assist in securing the
radio frequency coil apparatus to the securing portion, an example
of which is illustrated in FIGS. 5B and 5C.
[0090] Retention member 543a is configured to allow member 531 to
be moved into smaller diameter portion 543b'' (i.e., in a first
direction along axis 505a) and to snap into place to retain member
531 in smaller diameter portion 543b'' (i.e., retention member 543a
resists movement of member 531 in a second direction along axis
505a out of the smaller diameter portion into the larger diameter
portion). Accordingly, once member 531 has been moved from larger
diameter portion 543b' to smaller diameter portion 543b'', smaller
diameter portion 543b'' and retention member 543a secure the radio
frequency coil apparatus to the securing portion 545. To disengage
the radio frequency coil apparatus from securing portion 545 of a
patient handling apparatus, a force may be applied against
retention mechanism 543a so that retention mechanism 543a moves
aside to allow member 531 to be moved into larger diameter portion
543b of keyhole slot 543b so that the radio frequency coil
apparatus can be lifted away from securing portion 545. For
example, a force applied to the radio frequency coil apparatus in
the second direction along axis 505a causes retention mechanism
543b to slip so that member 531 is allowed to slide into the larger
diameter portion of the keyhole.
[0091] This process of securing a patient handling apparatus to,
and releasing it from, a radio frequency helmet, is described in
further detail below in connection with FIGS. 5B and 5C. In
particular, FIGS. 5B and 5C illustrate the underside of a patient
handling apparatus 540 comprising a support portion 542 and
securing portion 545 as it is engaging with radio frequency helmet
530. Radio frequency helmet 530 is configured to accommodate the
head of a patient and comprises one or more radio frequency coils
configured to transmit magnetic resonance pulse sequences and/or
detect MR signals emitted from the patient in response to a
transmitted pulse sequence. The radio frequency coils may be, for
example, any of the radio frequency coils and geometries thereof
described in U.S. application Ser. No. 15/152,951, filed on May 31,
2016 and titled "Radio Frequency Coil Methods and Apparatus." Radio
frequency helmet 530 comprise member 53 configured to engage with
securing mechanism 543 of securing portion 545 of patient handling
apparatus 540, and members 533a and 533b configured to engage with
keyhole slots 549a and 549b.
[0092] In FIG. 5B, members 531, 533a and 533b have been inserted
into respective keyhole slots 543b, 549a and 549b and, more
particularly, have been inserted through the respective larger
diameter portions of the respective keyhole slots that are
dimensioned to allow the respective member to be inserted into the
respective keyhole slot. By moving the radio frequency coil
apparatus 530 in the direction indicated by arrow 505 (or moving
the patient handling apparatus in the opposite direction), members
531, 533a and 533b can be moved from the larger diameter portion to
the smaller diameter portion of the respective keyhole slot. For
example, member 531 can be moved from larger diameter portion 543b'
(see FIG. 5C) to the smaller diameter portion 543b'' (see FIG. 5B)
of keyhole slot 543b. The result of this movement is illustrated in
FIG. 5C.
[0093] As shown in FIG. 5C, radio frequency helmet 530 has been
secured to patient handling apparatus 540. Because the smaller
diameter portions of the keyhole slots are dimensioned to be
smaller than the diameter of the portion of the member inserted
through the larger diameter portion of the keyhole slot, radio
frequency helmet 530 cannot be lifted from the securing portion 545
of patient handling apparatus 540 without first being returned to
the large diameter portions. As also shown in FIG. 5c, retention
member 543 snaps into place to resist movement of the member 531
back into the larger diameter portion 543b' of keyhole slot 543b.
That is, retention member resists movement of radio frequency coil
apparatus 530 in the direction indicated by arrow 505'. However,
the resistance of retention member 543a can be overcome by
providing a strong enough force in the direction of arrow 505' to
return the radio frequency coil apparatus 530 to the position
illustrated in FIG. 5B so that the radio frequency helmet 530 can
moved away from or lifted off of securing portion 545, thereby
disengaging radio frequency helmet 530 from patient handling
apparatus 540. In this manner, securing mechanism 543 releasably
secures radio frequency helmet 530 to patient handling apparatus
540 (e.g., by providing sufficient force to overcome the resistance
of the retention member, the secured helmet can be released from
the releasable securing mechanism 543).
[0094] FIGS. 6A and 6B illustrates a cross-sectional view of a
radio frequency coil apparatus 630 secured within a keyhole slot of
a releasable securing mechanism of a securing portion 645 of a
patient handling apparatus. Radio frequency coil apparatus 630
comprises a member 631 configured to engage with a keyhole slot of
securing portion 645. Member 631 comprises portions 631a, 631b and
631c dimensioned differently so that member 631 can be inserted
into the keyhole slot and slid into a secured position. Foot
portion 631a is dimensioned to be sufficiently small so that it can
be inserted into the larger diameter portion (not visible in FIGS.
6A and 6B, but see e.g., larger diameter portion 543b' illustrated
in FIGS. 5A and 5C) of the keyhole slot and sufficiently large so
it cannot be inserted into or removed from the smaller diameter
portion 643b'' of the keyhole slot (see also smaller diameter
portion 543b'' illustrated in FIGS. 5A and 5B).
[0095] Neck portion 631b is dimensioned to be sufficiently small so
that it can be accommodated by the smaller diameter portion 643b''
of the keyhole slot so that, after foot portion 631a is inserted in
the larger portion of the keyhole slot, member 631 can be moved
into the smaller diameter portion 643b''. Body portion 631c is
dimensioned to be sufficiently large so that it cannot be
accommodated by either the smaller or the larger diameter portions
of the keyhole slot. Neck portion 631b has height (e.g., its
dimension in the direction of arrow 605c) so that when body portion
631c prevents further insertion of member 631 into the keyhole slot
(i.e, further movement in the direction of arrow 605c is prevented
by body portion 631c), foot portion 631a has been positioned
through the large diameter portion of the keyhole slot so that
member 631 can be slid into the smaller diameter portion 643b'' to
the secured position illustrated in FIGS. 6A and 6B. Because foot
portion 631a is larger than the smaller diameter portion 643b'',
member 631 cannot be lifted from securing portion 645 in the
direction of arrow 605c' without first being transitioned back into
the larger diameter portion of the keyhole slot.
[0096] Referring again to FIG. 5A, according to some embodiments,
retention member 543a is made from plastic and is formed into a
flat serpentine geometry. For example, retention member 543a may be
a flat plastic spring, having a fixed end 543a' and a free end
543a'' that can move to allow member 531 to be slid into smaller
diameter portion 543b'' and return to position to resist movement
of member 531 back into larger diameter portion 543b'. The free end
543a'' may be located in window 503. The depth of window 503 (i.e.,
generally corresponding to the thickness of securing portion 545 in
the direction along axis 505c) may be relatively small. As a
result, retention member 543a may also have a relatively small
thickness in directions along axis 505c (i.e., the thickness of the
material forming the retention member, for example, the thickness
of the plastic may be required to be relatively thin). That is,
retention member 543a may be constructed to be flat so that the
member does not extend beyond surface 545a (or extend beyond the
top surface of securing portion 545 on which the radio frequency
apparatus rests when engaged). According to some embodiments,
retention member comprises a flat plastic spring with a thickness
less than or equal to approximately 0.5 inches. According to some
embodiments, retention member comprises a flat plastic spring with
a thickness less than or equal to approximately 0.25 inches. In
this way, the retention mechanism can be contained within the
thickness of the securing portion 545.
[0097] Securing portion 545 may further comprise a second
releasable securing mechanism 547 configured to engage with a
magnetic resonance imaging system to secure the securing portion
545 (and thus the patient handling apparatus) to the magnetic
resonance imaging system. According to some embodiments, second
releasable securing mechanism 547 comprises tapered lead-in
portions 547a that allows a member 429 attached to the magnetic
resonance imaging system to enter receptacle portion 547e, and
comprises retention portions 547b that prevent member 429 from
exiting receptacle 547d. Pulls 547d allow a user to retention
portions 547b to allow member 549 to exit receptacle 547d. Springs
547c allow the releasable securing mechanism to be actuated, either
by utilizing pulls 547d or under the force of member 429 pushing
against tapered lead-in portions 547a. It should be appreciated
that the underside of member 429 is illustrated in FIG. 5A to show
how releasable securing mechanism 547 engages with member 429, but
that surface 429' of member 429 is the surface that is attached to
the magnetic resonance imaging system, for example, attached to
lower B.sub.0 magnet 422b as shown in FIG. 4A.
[0098] FIGS. 5D-F illustrate the operation of an exemplary
releasable securing mechanism 547. FIG. 5D illustrates releasable
securing mechanism 547 in a closed position in which springs 547c
are in repose and tapered portions 547a and retentions portion 547b
extend into receptacle 547e. Releasable securing mechanism 547 can
be opened by applying a force on pulls 547d in the directions shown
by arrows 505b and 505b' or by applying a force to tapered portions
547a in the direction shown by arrows 505a to move securing
mechanism 547 to the open position shown in FIG. 5E. When
releasable securing mechanism 547 is opened, springs 547c are
compressed and tapered portions 547a and retention portions 547b
separate to allow entry and/or exit of member 439 into receptacle
547e. When the force applied to open securing mechanism 547 is
removed, springs 547c return to their repose position, forcing
tapered portions 547a and retention portions 547b towards each
other to close the path for 439 into and out of receptacle 547e,
returning the releasable securing mechanism 547 to the position
illustrated in FIG. 5D.
[0099] Force in the direction shown by arrows 505a may be applied
by pushing the tapered portions 547a against member 429, thereby
compressing springs 547c and opening the securing mechanism to
allow member 429 to enter receptacle 547e. After member 429 enters
receptacle 547e, springs 547C return to their repose position and
retention portions 547b close behind member 429 to secure securing
portion 545 of patient handling apparatus 540 to the magnetic
resonance imaging system, as illustrated in FIG. 5F. As shown in
FIG. 5F, member 429 may include a smaller diameter portion 429a
dimensioned to fit within receptacle 547e, and a larger diameter
portion 429b dimensioned to be larger than receptacle 547e.
Securing portion 545 is dimensioned so that at least the portions
forming receptacle 547e fit underneath larger diameter portion 429b
so that when securing portion 545 is engaged with member 429 as
shown FIG. 5F, the larger diameter portion 429b prevents patient
handling apparatus 540 from being lifted away from the magnetic
resonance imaging system, while retention portions 547b retain
member 429 within receptacle 547e of releasable securing mechanism
547. In particular, for exemplary member 429 illustrated in FIG.
5F, the smaller diameter portion 429a has a height that allows
those portions of securing portion 545 forming receptacle 547e to
fit underneath larger diameter portion 429b to hold securing
portion 545 to the surface to which member 429 is attached.
[0100] To release patient handling apparatus from the magnetic
resonance imaging system, a user can apply a force to pulls 547d in
the directions shown by arrows 505b and 505b' to open releasable
securing mechanism 547 (e.g., to place releasable securing
mechanism 547 in the open position illustrated in FIG. 5E). With
the path out of receptacle 547e for member 429 opened, patient
handling apparatus 540 can be disengaged from the magnetic
resonance imaging system. According to some embodiments, pulls 547d
are configured to operate independently of one another so that both
sides need to be pulled to open securing mechanism 547d. According
to some embodiments, pulling on either of pulls 547d engages both
sides so that only one pull needs to be used to open securing
mechanism 547.
[0101] Referring again to FIG. 4A, member 429 may be attached to
MRI system 400 at a location such that when releasable securing
mechanism 547 engages member 429 (e.g., as shown in FIGS. 5A and
5F), a radio frequency coil apparatus that has been secured to the
patient handling apparatus is located substantially within the
imaging region of the MRI system. For example, when radio frequency
helmet 530 is secured to securing portion 545 of patient handling
apparatus 540 via releasable securing mechanism 543 and second
releasable securing mechanism 547 is engaged with member 429, radio
frequency helmet 530 is positioned substantially within the imaging
region of the MRI system (e.g., as shown in FIG. 4I). As a result,
when target anatomy is positioned within the radio frequency coil
apparatus, the target anatomy is within imaging region 415 of MRI
system 400.
[0102] FIGS. 4A-4I illustrate exemplary steps that allow a patient
to be imaged from a standard hospital bed, in accordance with some
embodiments. In FIG. 4A, a patient handling apparatus 440 may be
positioned on bed 490 proximate patient 499 patient to begin the
process of positioning the patient within MRI system 400. As shown
in FIG. 4B, patient 499 may be rolled to the side or partially
lifted so that patient handling apparatus can be moved towards the
center of bed 490 and/or generally aligned with MRI system 400.
Patient 499 can then be rolled back or released so that patient
handling apparatus 440 is positioned between bed 490 and patient
499 and at least a portion of patient 499 is supported by support
442 of patient handling apparatus 440, as shown in FIG. 4C. The
head of patient 499 may be positioned generally over securing
portion 445 of patient handling apparatus 440, which itself may be
positioned proximate bridge 473 to facilitate positioning patient
499 within MRI system 400.
[0103] As shown in FIG. 4D, a radio frequency helmet 430 may be
positioned on bridge 473 or otherwise positioned to engage with
securing portion 445 of patient handling apparatus 440. Radio
frequency helmet 430 may then be secured to securing portion 435 of
patient handling apparatus 440 with the patient's head positioned
within the radio frequency helmet 430, as shown in FIG. 4E. For
example, radio frequency helmet 430 may be secured by engaging a
releasable securing mechanism of securing portion 435 with a
cooperating member or members of radio frequency helmet 430, as
discussed in connection with FIGS. 5A-C and FIGS. 6A-B. Patient
handling apparatus 440, with radio frequency helmet 430 secured, is
ready to be moved over bridge 473 to engage with member 429 to
secure the patient handling apparatus to MRI system 400, as shown
in FIG. 4F.
[0104] FIG. 4G illustrates patient handling apparatus 440 as the
entrance to a releasable securing mechanism of securing portion 445
approaches member 429 (e.g., approaches the entrance to a
receptacle of the releasable securing mechanism). As shown, radio
frequency helmet 430, which is accommodating or holding the
patient's head, has entered imaging region 415 of MRI system 400.
At the stage illustrated in FIG. 4H, member 429 engages with
tapered lead-in portions of a releasable securing mechanism (e.g.,
tapered lead-in portions 547a of releasable securing mechanism 547
illustrated in FIGS. 5A and 5D-F) causing the releasable securing
mechanism to open to allow member 429 to enter a receptacle of the
releasable securing mechanism (e.g., receptacle 547e illustrated in
FIGS. 5A-F). Once member 429 has passed into the receptacle beyond
the tapered lead-in portions, the releasable securing mechanism
closes and retention portions of releasable securing mechanism
prevent member 439 from exiting the receptacle, as shown in FIG.
4I. In this position, patient handling apparatus 440 is secured to
MRI system 400 and radio frequency helmet 430 and the patient's
head are positioned correctly with imaging region 415 so that one
or more image acquisition processes may be performed.
[0105] As shown in FIGS. 4A-4I, point-of-care MRI may be performed
by bringing a portable low field MRI system (e.g., MRI system 400)
to the patient (or wheeling a patient to the MRI system in the
patient's bed) so that MRI can be performed on the patient from the
patient's bed, even under circumstances where the patient has
limited or no mobility (e.g., the patient is injured, unconscious
or otherwise has limited mobility). As a result, MRI may be made
available in numerous circumstances where it was previously
unavailable. As discussed above, because of the relatively low
field strengths involved in low-field MRI, MRI can be performed on
the patient without needing to transfer the patient to an MRI-safe
bed, allowing for imaging of the patient from whatever bed the
patient is positioned on, opening up MRI to emergency rooms,
operating rooms, intensive care units, doctor's offices and
clinics, etc.
[0106] According to some embodiments, a radio frequency coil
apparatus may be configured to be directly secured to an MRI system
without first being secured to a patient handling apparatus. FIG.
7A illustrates a radio frequency helmet configured to engage
directly with the MRI system to secure the radio frequency helmet
within the imaging region of the MRI system to position the patient
for imaging, in accordance with some embodiments. In particular,
FIG. 7A illustrates the underside of a radio frequency helmet 730
equipped with a releasable securing mechanism 735 configured to
engage with and grip a member 729 attached to the MRI system.
Member 729 may be similar or the same as member 429 in that it is
attached to the MRI system at a location such that when radio
frequency helmet 730 is secured to member 729, the radio frequency
helmet 730 is positioned within the imaging region of the MRI
system. Member 729 may also include a smaller diameter portion 729a
and a larger diameter portion 729b configured to cooperate with
releasable securing mechanism 735 to secure radio frequency helmet
730, as discussed in further detail below.
[0107] Releasable securing mechanism 735 comprises a receptacle
dimensioned to accommodate member 729 and a retention portion 737
configured to resist movement of the cooperating member 729 once
the member has been positioned within the receptacle, as shown in
FIG. 7A. Exemplary retention portion 737 comprises two arm portions
737a and 737b forming a portion of the receptacle and configured to
grip member 729 when member 729 is positioned within the
receptacle. According to some embodiments, arm portions 737a and
737b include protrusions 733a and 733b, respectively, configured to
resist movement of member 729 after it has been inserted into the
receptacle of releasable securing mechanism 735. Protrusions 733a
and 733b comprise respective outward facing sides 733a' and 733b'
and respective inward facing sides 733a'' and 733b'' dimensioned to
facilitate engaging with member 729 to secure radio frequency
helmet 730 to the MRI system. According to some embodiments, the
angle of the outward facing sides of protrusions 733a and 733b and
the angle of the inward facing sides of protrusions are configured
such that less forced is required to allow member 729 to enter into
the receptacle of securing mechanism 735 than to allow member 729
to exit from the receptacle. For example, the relative angles of
the outward and inward facing sides may be selected so that a
relatively small force on the outward facing sides is needed to
part arm portions 737a and 737b to allow member 729 to enter the
receptacle of releasable securing mechanism 735 and a larger force
on the inward facing sides is needed to part arm portion 737a and
737b to allow member 729 to be released from the receptacle of
securing mechanism 735. It should be appreciated that protrusions
733a and 733b may be dimensioned in any way to achieve desired
forces needed to engage and disengage member 729 with securing
mechanism 735, as the aspects are not limited in this respect.
Thus, radio frequency helmet 730 can be secured to and released
from member 729 by applying a force in the appropriate direction.
That is, securing mechanism 735 is releasable because after arm
portions 737a and 737b grip member 729, the grip can be released by
providing sufficient force on helmet 730 so that member 729 parts
the arm portions 737a and 737b and releases the member.
[0108] As discussed above, the view in FIG. 7A is of the underside
of the radio frequency helmet 730 and member 729 so that surface
729' is visible. However, this surface is attached to the MRI
system at a location so that when radio frequency helmet 730 is
engaged with the member, the helmet and target anatomy of the
patient are positioned with the imaging region of the MRI system
(e.g., as shown in FIGS. 4A-4I). FIG. 7B illustrates a top view of
releasable securing mechanism 735 engaged with member 729 of an MRI
system. As shown, arm portions 737a and 737b fit underneath larger
diameter portion 729b and protrusions 733a and 733b grip smaller
diameter portion 729a. In this manner, larger diameter portion 729b
prevents radio frequency helmet 730 from being lifted away from
member 729. That is, larger diameter portion 729b restricts
movement of radio frequency helmet 730 in the direction indicated
by arrow 705a. In addition, arms 737a and 737b restrict movement of
radio frequency helmet 730 in the directions illustrated by arrows
705b and 705c (securing mechanism 735 restricts movement of member
727 in the plane of the top surface 729'' of member 729). While the
resistance to movement of radio frequency helmet 730 out of
securing mechanism 735 can be overcome by applying sufficient force
to the helmet as discussed above, absent such a force,
translational movement of radio frequency helmet 730 is generally
prevented in all directions. However, releasable securing mechanism
735 may be configured to allow radio frequency helmet to be rotated
about member 729 (e.g., about the axis along arrow 705a). By
allowing radio frequency helmet 730 this degree of freedom, radio
frequency coil can be oriented as desired about the center of the
MRI system, providing flexibility as to the directions in which the
patient can be inserted into the MRI system. According to some
embodiments, an additional securing mechanism is provided to
prevent rotation after a desired orientation has been reached, as
discussed in further detail in connection with FIGS. 8A and 8B.
[0109] FIGS. 8A and 8B illustrate an example of a releasable
securing mechanism that allows for rotation of the radio frequency
coil apparatus about a securing member of the MRI system to provide
the above discussed flexibility, and that comprises an additional
securing mechanism to hold the radio frequency coil apparatus in
place once a desired orientation has been reached, in accordance
with some embodiments. FIG. 8A illustrates a cross-sectional view
of a radio frequency helmet 830 comprising a releasable securing
mechanism 835 configured to engage member 829 to secure the radio
frequency helmet 830 to an MRI system. Releasable securing
mechanism 835 may be similar to releasable securing mechanism 735
illustrated in FIGS. 7A and 7B. In particular, releasable securing
mechanism 835 may include arm portions 837a and 837b (shown in FIG.
8B) configured to grip member 829 to resist translational movement
of radio frequency helmet 830, but allow for rotation about member
829. In addition, a second securing mechanism 831 is provided to
hold radio frequency helmet 830 at a particular orientation about
the member 829. For example, securing mechanism 831 may be a peg,
pin or post configured to cooperate with at least one recess 829c
(e.g., a slot, notch or other recess) provided in larger diameter
portion 829b of member 829. When radio frequency helmet 830 engages
with member 829, the helmet can be rotated until the securing
mechanism 831 finds recess 829c to hold the helmet at the fixed
orientation of the recess. In this manner, helmet 830 can be
secured to member 829 and quickly rotated and held in place at a
corresponding desired orientation. It should be appreciated that
member 829 may be provided with as many recesses around its
perimeter as desired to allow a radio frequency helmet to be
secured to an MRI system at the different corresponding
orientations.
[0110] FIGS. 9A and 9B illustrate a see-through radio frequency
helmet 930 to assist medical personnel in properly positioning a
patient within helmet 930. According to some embodiments, helmet
930 comprises an outer housing 930a and a coil support 930b for
transmit and/or receive coils, both made of see-through material.
The term see-through refers to structure or material that is
transparent or semitransparent (e.g., translucent) so that the
location of a patient's head can be viewed through the helmet. That
is, see-through material refers to material that is sufficiently
transparent to allow medical personnel to visually assess whether a
patient is positioned correctly by looking through the helmet. Coil
support 930b may be adapted to accommodate a patient's head and
provide a surface to which the transmit and/or receive coils are
disposed. Exemplary coil support 930b provides a surface for
transmit coil(s) 990a and receive coils 990b. It should be
appreciated that any configuration or geometry of transmit and/or
receive coils may be used, as the aspects are not limited in this
respect.
[0111] Exemplary housing 930a may contain electronics 970 that are
used in the operation of transmit/receive coils 930a and 930b,
though such electronic may be positioned outside the housing, as
the aspects are not limited in this respect. Housing 930a may be
attached to base 950 comprising a releasable securing mechanism 935
according to any one or more of the techniques described herein to
releasably secure helmet 930 to a magnetic resonance imaging system
within the imaging region of the system. FIG. 9B illustrates a
radio frequency helmet 930 with a patient 999 positioned within
coil support 930b. Because outer housing 930a and coil support 930b
are see-through (e.g., constructed from a transparent or
semitransparent plastic material), the patient's head can be viewed
through helmet 930, thus facilitating proper positioning of patient
999 within helmet 930. It should be appreciated that while
exemplary helmet 930 comprises a housing and a coil support, this
is not a requirement. For example, according to some embodiments, a
radio frequency helmet may consist of a single surface on which
transmit/receive coils are provided, and this surface may be made
from see-through material to assist medical personnel in
positioning a patient properly within the helmet.
[0112] As discussed above, techniques for providing a releasable
securing mechanism may also be applied to a radio frequency coil
apparatus comprising one or more radio frequency coils adapted to
accommodate an appendage, such as a leg or an arm, or a portion of
an appendage such as an ankle, foot, wrist, hand, etc. FIGS. 10A-D
illustrate aspects of a foot coil adapted to accommodate a foot and
configured to secure the foot coil to an MRI system so that the
foot is positioned within the imaging region of the MRI system
(e.g., within the imaging region of the exemplary low-field MRI
systems described in the foregoing). According to some embodiments,
a radio frequency apparatus is adapted to accommodate a foot and
configured to be secured within the imaging region of an MRI system
having a bi-planar B.sub.0 magnet configuration in which the space
between upper and lower B.sub.0 magnets may be limited, some
examples of which are described in further detail below.
[0113] FIG. 10A illustrates a view of a radio frequency apparatus
1030 (referred to generally herein as a "foot coil," adapted to
accommodate a foot for one or more MRI procedures. Foot coil 1030
comprises transmit/receive housings or supports 1030t/r on or
within which transmit and/or receive coils for the radio frequency
apparatus are provided. According to some embodiments, foot coil
1030 comprises a transmit housing for transmit coils and a receive
housing for receive coils, examples of which are illustrated in
FIGS. 10B and 10C, respectively, discussed in further detail below.
According to some embodiments, the transmit and receive coils may
be provided on or within the same housing (e.g., transmit coils and
receive coils may be provided on the same side of a shared housing,
on outer and inner sides of the same housing and/or one or more
coils may be used for both transmit and receive), as the aspects
are not limited in this respect.
[0114] Exemplary foot coil 1030 also comprises an outer housing
1030a to at least partially cover transmit/receive housing(s)
1030t/r and to form a volume 1030c adapted to accommodate a foot.
As illustrated in FIG. 10A, volume 1030c has a height h and a w
that allows a foot to be inserted into the interior of foot coil
1030. In the embodiment illustrated in FIG. 10A, foot coil 1030 is
constructed at an angle .theta. relative to the vertical axis. The
inventors have recognized that angling the foot coil relative to
the vertical axis (e.g., generally pointing the toes away from the
vertical axis) may provide a number of advantages over a vertical
orientation. For example, a foot coil set at an angle relative to
the vertical (i.e., with a podal axis greater than zero degrees)
facilitates accommodating larger feet within the imaging region of
the MRI system. In particular, the distance between the upper and
lower B.sub.0 magnets in the bi-planar configuration described in
the foregoing places a limit on the height h of the foot coil
(e.g., the distance D labeled in FIG. 4G constrains the height of
the foot coil that can be accommodated by the MRI system). As shown
in FIG. 10A, axis 1039 is tilted from vertical by an angle .theta..
Axis 1039, referred to herein as the podal axis, is the principal
axis of the foot coil that is aligned with the foot when inserted
into volume 1030c and the angle .theta. defines the angle of the
podal axis away from the vertical axis 1025 in the direction of the
longitudinal axis 1041. That is, the podal axis refers to the axis
that is aligned in the direction from the bottom of the foot coil
where the heel of the foot is positioned towards the toes of the
foot when placed within the foot coil. A podal axis at zero degrees
from the vertical axis 1025 in the direction of the longitudinal
axis 1041 (i.e., .theta.=0.degree.) is aligned with the vertical
axis in this respect, and a podal axis of 90 degrees from the
vertical axis 1025 in the direction of the longitudinal axis 1041
(i.e., .theta.=90.degree.) is aligned with the longitudinal axis in
this respect. Exemplary foot coil 1030 has a podal axis 1039 of
approximately 45 degrees from the vertical axis in the direction of
the longitudinal axis.
[0115] By angling the foot coil (i.e., tilting the podal axis away
from the vertical axis), a longer foot can be accommodated within
the imaging region of, for example, the exemplary MRI systems
described herein (e.g., MRI systems having the bi-planar
configuration shown in FIGS. 2-4). That is, the length of a foot
that can be accommodated by the foot coil is greater than the
height of the foot coil in the vertical direction (i.e., L>h as
shown in FIG. 10A). The more that foot coil 1030 is angled relative
to the vertical axis, the longer the foot that can be accommodated
within the same vertical height (i.e., the greater the length L is
relative to the height h). Because the human foot tends to rest
with the toes pointed away from the vertical axis (i.e., rather
than having the toes straight above the heal), a foot coil that
generally mimics the natural repose of the foot may improve patient
comfort during an imaging procedure. Specifically, the angled or
tilted foot coil may obviate the need for the patient to orient and
hold their foot straight up and down, which may cause discomfort or
pain, particularly in circumstances where the foot is injured from
disease, infection or trauma. Though large angles (e.g., angles
between 60 and 75 degrees) may compromise the comfort of the
patient in certain circumstances, such angles may be used to
construct a foot coil capable of accommodating longer feet.
[0116] To accommodate even larger feet, the foot coil may
additionally be tilted away from the vertical axis in a direction
towards the latitudinal axis. That is, the podal axis may be tilted
by an angle .phi. away from the vertical axis 1025 in the direction
of latitudinal axis 1043 illustrated in FIG. 10A. The different
tilt angles (i.e., tilt angles .theta. and .phi.) may be used alone
or in combination to accommodate a wide variety of foot sizes. A
podal axis at zero degrees from the vertical axis 1025 in the
direction of the latitudinal axis 1043 (i.e., .phi.=0.degree.) is
aligned with the vertical axis in this respect, and a podal axis of
90 degrees from the vertical axis 1025 in the direction of the
latitudinal axis 1043 (i.e., .phi.=90.degree.) is aligned with the
latitudinal axis in this respect.
[0117] It should be appreciated that the podal axis may be chosen
as desired to suit the needs of the imaging application and/or the
patient and multiple foot coils may be manufactured with different
podal axes and dimensions to facilitate MRI of a wide variety of
feet under differing circumstances and conditions. According to
some embodiments, the foot coil is tilted relative to vertical in
the direction of the longitudinal axis at an angle between 5
degrees and 60 degrees (i.e., a podal axis with an angle .theta.
between 5 and 60 degrees), more preferably between 15 degrees and
50 degrees and, more preferably between 30 and 45 degrees (e.g., as
illustrated by podal axis 1039 for exemplary foot coil 1030
illustrated in FIG. 10A). According to some embodiments, the foot
coil is tilted relative to vertical in the direction of the
latitudinal axis at an angle between 5 degrees and 60 degrees
(i.e., a podal axis with an angle .phi. between 5 and 60 degrees),
more preferably between 15 degrees and 50 degrees and, more
preferably between 30 and 45 degrees, or at an angle of
approximately zero degrees as illustrated in FIG. 10A. It should be
appreciated that a foot coil may be tilted to have a .theta.
component, a .phi. component, or both. As discussed above, it
should be appreciated that different foot coils may be constructed
at different angles to accommodate a wide variety of feet under a
wide variety of different conditions and circumstances, and the
exemplary podal axis and dimensions described herein are not
limiting.
[0118] Foot coil 1030 also comprises back portion 1030b that houses
the electronics for the foot coil when connected with bottom
portion 1030b'. For example, the electronics forming portions of
the radio frequency signal chain (e.g., the transmit/receive
circuitry) for operating the transmit and receive coils may be
housed in back portion 1030b, 1030b', as discussed in further
detail below. Bottom portion 1030b' further comprises a terminal
connection for cable bundle 1076 which carries power, control
and/or data (e.g., MR signal data) from the MRI system to the
transmit/receive circuitry housed in the back portion. In the
embodiment illustrated in FIG. 10A, the interface to the MRI system
comprises board 1072 for providing power, control and/or data
between the radio frequency apparatus and the MRI system and an
adapter 1074 constructed to prevent board 1072 from being connected
to the MRI system in an incorrect orientation. In this manner, foot
coil 1030 can be easily and simply connected to, operated by, and
disconnected from the MRI system. Foot coil 1030 further comprises
a base 1050 coupled to a releasable mechanism that allows the foot
coil to engage with and disengage from the MRI system. For example,
as described in further detail in connection with FIGS. 10C and
10D, base 1050 may be affixed to or otherwise coupled to a
releasable mechanism that engages with a cooperating member
situated within the imaging region of the MRI system.
[0119] FIG. 10B illustrates another view of foot coil 1030 showing
the nested structure of the exemplary foot coil. In particular,
FIG. 10B illustrates receive housing 1030r and transmit housing
1030t before insertion into outer housing 1030a. In the exemplary
foot coil illustrated in FIG. 10B, receive coil housing 1030r
(which supports receive coils 1090b, 1090b' described below) is
configured as the inner most housing providing the volume 1030c
adapted to accommodate the foot. Transmit housing 1030t is adapted
to fit over received housing 1030r and the nested transmit/receive
housing 1030t/r is configured to be inserted into outer housing
1030a. However, it should be appreciated that the order of the
nesting may be switched and/or a single housing may be provided to
support or carry both the transmit and receive coils, as discussed
in further detail below.
[0120] As visible in the view shown in FIG. 10B, transmit coil(s)
1090a are provided on transmit housing 1030t and, more
particularly, provided on an outside surface of the transmit
housing. Alternatively or additionally, transmit coil(s) 1090a may
be provided on an inner surface of transmit housing 1030t, provided
in grooves or contours fabricated into the housing or otherwise
integrated into transmit housing 1030t. Transmit coil(s) 1090a may
comprise one or more conductors arranged in a three-dimensional
geometry about volume 1030c to produce radio frequency pulses
configured to cause MR signals to be emitted from a patient's foot
positioned within volume 1030c when foot coil 1030 is engaged with
and operated by the MRI system. According to some embodiments,
transmit coil 1090a comprises a single conductor provided about
transmit housing 1030t in a number of turns over one or more
surfaces of the transmit housing. Alternatively, transmit coil
1090a may comprise multiple separate conductors provided over one
or more surfaces of transmit housing 1030t.
[0121] In the embodiment illustrated in FIGS. 10A-D, transmit
coil(s) 1090a operate as transmit only coils and the receive coils
are provided as a separate receive coil array, as discussed in
further in detail in connection with FIG. 10C. However, according
to some embodiments, radio frequency coil(s) 1090a may also operate
as one or more receive coils configured to detect MR signals
emitted from a foot being imaged in response to a selected pulse
sequence produced, at least in part, by the same coils operating in
transmit mode. In such embodiments, radio frequency coil(s) 1090a
operate as transmit and receive coils. The geometry of transmit
coil(s) 1090a (e.g., the relative spacing of the turns, the
geometry of the contours, etc., may be determined to generally
optimize characteristics of the radio frequency pulses emitted
based on the geometry of volume 1030c using, for example, any of
the techniques described in U.S. Patent Publication No.
2016/0334479, published Nov. 17, 2016 and titled "Radio Frequency
Coil Methods and Apparatus." For example, a magnetic model may be
used to determine a geometry for transmit coil(s) 1090a that
generally optimize the magnetic pulses delivered to volume
1030c.
[0122] As discussed above, receive housing 1030r may be configured
to fit within transmit housing 1030t. As visible in the view shown
in FIG. 10B, a plurality of receive coils 1090b and 1090b'
configured to detect magnetic resonance signals emitted from the
foot of a patient in response to radio frequency pulses emitted by
the transmit coils (e.g., transmit coil(s) 1090a) are provided on
receive housing 1030r. As with the transmit coils, receive coils
may alternatively or additionally be provided on an inner surface
of receive housing 1030r or otherwise integrated within the
housing. In the embodiment illustrated in FIGS. 10B and 10C, the
receive coils comprise eight separate receive coils; six receive
coils 1090b (e.g., three overlapping receive coils on each side of
receive housing 1030r) and two receive coils 1090b' (e.g., a
receive coil provided at least partially on top and bottom portions
of the receive housing).
[0123] In the exemplary configuration illustrated in FIGS. 10B and
10C, the receive coils 1090b are positioned in an overlapping
arrangement to reduce the inductive coupling between the coils.
Spatially, receive coils 1090b are stacked in the vertical
direction (e.g., in the direction of the B.sub.0 magnetic field
illustrated generally by arrow 1025) with the same characteristic
tilt of the foot coil. That is, the receive coils may be aligned
with the podal axis of the foot coil so that each successive
receive coil is offset from the adjacent receive coil in a
horizontal direction (e.g., in the longitudinal direction. With
this arrangement, receive coils are configured to detect MR signals
emitted from a patient's foot in directions along an axis
orthogonal to the B.sub.0 magnetic field generated, for example, by
the exemplary MRI systems illustrated and described in the
foregoing. Receive coils 1090b' are positioned on the top and
bottom sides of receive housing 1030r to generally detect magnetic
resonance imaging signals emitted in directions along another axis
orthogonal to the B.sub.0 magnetic field. In this manner, the
receive coils can be configured approximately as quadrature coils
to generally optimize the detection of MR signals. It should be
appreciated that receive coils 1090b and 1090b' are merely
exemplary and any number of coils in any suitable arrangement may
be used, as the aspects are not limited in this respect.
[0124] As shown in FIG. 10C, receive housing 1030r includes a
backside 1032r having electronic connections to electronics 1070 on
bottom portion 1030b' that, when connected, allow power, control
and/or data (e.g., MR signal data) to be exchanged between the MRI
system and the foot coil (e.g., between the MRI system and transmit
coils 1090a and receive coils 1090b, 1090b'). Specifically, power,
control and/or data may be exchanged via the connection cable 1076
and board 1072 when adapter 1074 is connected to the MRI system in
the manner discussed above in connection with FIG. 10A.
[0125] The view in FIG. 10C shows base 1050 that supports the radio
frequency coil housings and releasable securing mechanism 1035
that, when assembled, is coupled to the bottom of base 1050.
According to some embodiments, releasable securing mechanism 1035
includes a retention portion 1037 configured to grip a cooperating
member affixed to the MRI system within the imaging region in a
manner similar to or the same as the securing mechanism discussed
above in connection with the radio frequency helmet described in
FIGS. 7A-B and 8A-B. An example of one embodiment of securing
mechanism 1035 is described in further detail in connection with
the bottom view of foot coil 1030 illustrated in FIG. 10D.
[0126] FIG. 10D illustrates a bottom view of foot coil 1030 showing
securing mechanism 1035 configured to engage directly with an MRI
system equipped with a cooperating member to secure foot coil 1030
within the imaging region of the MRI system, in accordance with
some embodiments. In particular, in the embodiment illustrated in
FIG. 10D, the outer housing 1030a may be coupled to base 1050 which
in turn may be coupled to releasable securing mechanism 1035
configured to engage with and grip a cooperating member (e.g.,
member 729 illustrated in FIGS. 7A and 7B) attached to the MRI
system at a location so that, when foot coil 1030 is engaged with
the cooperating member, foot coil 1030 is positioned within the
imaging region of the MRI system. In this manner, a patient's foot
positioned within foot coil 1030 when attached to the MRI system is
properly positioned for imaging.
[0127] Exemplary releasable securing mechanism 1035 comprises a
circular receptacle portion dimensioned to accommodate the
cooperating member attached to the MRI system and a retention
portion 1037 configured to resist movement of the cooperating
member once the member has been positioned within the receptacle.
Exemplary retention portion 1037 comprises two arm portions 1037a
and 1037b, respectively forming a portion of the receptacle and
configured to grip the cooperating member when positioned within
the receptacle. According to some embodiments, arm portions 1037a
and 1037b include protrusions 1033a and 1033b, respectively,
configured to resist movement of the cooperating member after it
has been inserted into the receptacle of releasable securing
mechanism 1035. Protrusions 1033a and 1033b comprise respective
outward facing sides 1033a' and 1033b' and respective inward facing
sides 1033a'' and 1033b'' dimensioned to facilitate securing the
cooperating member of the MRI system to foot coil 1030.
[0128] According to some embodiments, the angle of the outward
facing sides of protrusions 1033a and 1033b and the angle of the
inward facing sides of the protrusions are configured such that
less forced is required to allow the cooperating member to enter
into the receptacle of securing mechanism 1035 than is required to
allow the cooperating member to exit the receptacle (e.g., it
requires less force to engage with the cooperating member than to
disengage with the cooperating member). For example, as discussed
above in connection with radio frequency helmet 735, the relative
angles of the outward and inward facing sides may be selected so
that a relatively small force on the outward facing sides is needed
to part arm portions 1037a and 1037b to allow the cooperating
member to enter the receptacle of releasable securing mechanism
1035 and a larger force on the inward facing sides is needed to
part arm portions 1037a and 1037b to allow foot coil 1030 to be
released from the cooperating member (e.g., to allow the
cooperating member to be released from the receptacle of securing
mechanism 1035).
[0129] It should be appreciated that protrusions 1033a and 1033b
may be dimensioned in any way so that desired forces achieve
engaging and disengaging securing mechanism 1035 with the
cooperating member, as the aspects are not limited in this respect.
Thus, foot coil 1030 can be secured to and released from the MRI
system by applying a force in the appropriate direction. That is,
securing mechanism 1035 is releasable because following engagement
of arm portions 1037a and 1037b with the cooperating member, foot
coil 1030 can released by providing sufficient force on the foot
coil so that the cooperating member forces the arm portions 1037a
and 1037b outward and releases the foot coil from the cooperating
member. According to some embodiments, the cooperating member is
similar to or the same as member 829 illustrated in FIGS. 8A and 8B
that includes a recess (e.g., recess 829c) and the securing
mechanism 1035 includes a pin or post (e.g., similar to or the same
as pin 831 illustrated in FIGS. 8A and 8B) so that the foot coil
can be rotated about the cooperating member until the pin finds the
recess and prevents further rotation.
[0130] FIG. 11 illustrates a foot coil adapted for a larger foot,
for example, a swollen foot resulting from disease such as diabetes
or complications that causes edema (e.g., congestive heart failure,
kidney or liver disease, etc.), swelling that results from
infection or trauma, or the foot of a larger person. Foot coil 1130
may be similar in many respects to foot coil 1030 illustrated in
FIG. 10A. However, foot coil 1130 is constructed to have a width W
that is greater than the width w of coil 1030 illustrated in FIG.
10A to accommodate a larger foot and, more particularly, a larger
width foot characteristic of disease or edema, thus providing a
larger volume 1130c for the foot coil 1130. As discussed above, the
angle at which foot coil is tilted relative to vertical may be
selected based on patient comfort, to accommodate larger feet, to
accommodate other circumstances or imaging conditions, etc.
Similarly, the podal axis of foot coil 1130 illustrated in FIG. 11
may also be varied for comfort and/or to accommodate longer feet.
Similarly, different foot coils may be manufactured at different
angles so that a wide variety of patients and imaging conditions
can be accommodated.
[0131] FIG. 12A illustrates a foot coil 1230 engaged with a
cooperating member of MRI system 1200 so that the foot coil 1230
and the right foot positioned therein is within the imaging region
of MRI system 1200 and positioned correctly for imaging. FIGS. 12B
and 12C illustrate different views of the foot coil 1230 positioned
with MRI system 1200. FIG. 12D illustrates foot coil 1230
accommodating the left foot. Also, FIG. 12D shows support 1231
(also visible in FIGS. 12A-12C) inserted within foot coil 1230 to
support and provide comfort to the foot during an imaging
procedure.
[0132] As discussed above, imaging a patient using MRI from, for
example, a standard hospital bed typically requires positioning
target anatomy of the patient within an MRI system located
proximate the hospital bed on which the patient is lying. As
discussed in connection with FIGS. 4A-I, the inventors have
developed techniques for facilitating the positioning of a patient
within the MRI system for imaging of desired anatomy of the patient
from the patient's bed. For example, FIG. 4A illustrates a portable
low-field MRI system 400 that has been moved into position
proximate a standard hospital bed 490 to perform MRI on a patient
499 who may be confined to the bed for convenience, comfort or
stabilization and/or because the patient is unconscious,
immobilized or otherwise is not ambulatory or cannot be safely
moved. Portable MRI system 400 may be a local installation deployed
in an emergency room, operating room, intensive care unit, doctor's
office, etc. that can be moved to bed 490, or in some cases, bed
490 can be wheeled to the MRI system. As discussed in detail in the
foregoing, because of the low-field strengths of MRI system 400,
bed 490 can be safely positioned in close proximity to MRI system
400.
[0133] To bridge the gap between bed 490 and MRI system 100, the
MRI system may be equipped with a bridge 473 mounted to MRI system
100 to facilitate positioning patient 199 within the imaging region
of MRI system 100. Specifically, bridge 473 provides a surface 474
over which patient 499 can be moved so that the patient's anatomy
being imaged (e.g., the patient's head) can be positioned within
the imaging region of the MRI system. However, the inventors have
recognized that exemplary bridge 473 illustrated in FIG. 4A may be
improved in a number of ways. For example, bridge 473 may be
designed to work in cooperation with patient support 440 so that as
long as the bridge 473 has dimension suitable to allowed the
patient support to be transitioned over its surface, the dimensions
of the bridge are sufficient. However, in some embodiments, a
patient may be positioned within MRI system 400 without the
assistance of a patient support. In such embodiments, it may be
preferable to employ a larger dimensioned bridge both to facilitate
ease and comfort of positioning the patient and to accommodate
larger and heavier patients. The inventors have developed bridges
adapted to facilitate patient positioning that are generally
optimized for use either with or without a patient support.
[0134] As illustrated in FIG. 4A, fixed bridge 473 protrudes out
from the MRI system, thereby increasing the footprint of the
system. As a result, navigating the MRI system down hallways and
through doorways is more difficult. Additionally, the useable
surface of bridge 473 is limited and the construction of the bridge
may not be suitable for heavier patients, particularly in cases
where the patient is being positioned without the aid of a patient
support. As a result, bridge 473 may be difficult to use with
larger and/or heavier patients and may not be rated to support the
heaviest patients. However, increasing the dimensions of the bridge
to facilitate patient positioning without a patient support and/or
to support heavier or larger patient, results in a bridge that
protrudes even further from the MRI system and requires more robust
construction.
[0135] The inventors have recognized the benefits of patient
support bridge capable of supporting larger and heavier patients
and have appreciated the benefits of such a bridge that can
accommodate a range of gaps between the MRI system and a patient
bed and/or that provide more overlap between the bridge and the
bed. Specifically, for patient comfort, safety and/or to facilitate
more convenient positioning of a patient, particularly larger
and/or heavier patients, it is desirable to equip a portable MRI
system with relatively large dimensioned bridges capable of safely
supporting a wide range of patients. However, there are a number of
issues associated with the design and development of relatively
large dimensioned bridges capable of supporting the weight of
larger patients.
[0136] For example, as mentioned above, larger bridges increase the
footprint of the MRI system even further, making it more difficult
(or impossible) to transport the MRI system down hallways and to
fit the MRI system through the doorways of the health care
facilities in which they are deployed. To address the problem of
increased footprint for the MRI system, the inventors have
developed a fold-out bridge that can be folded-down to facilitate
positioning the patient within the imaging region of the MRI system
and to support the patient during an imaging procedure and that can
be folded-up during transport of the MRI system so that the MRI
system can be more easily moved down hallways and through doorways
to the patient.
[0137] Additionally, providing a bridge capable of safely
supporting larger, heavier patients requires robust construction.
Typically, such patient supports would be constructed using large
amounts of metal material capable of withstanding the significant
stresses resulting from supporting the weight of heavier patients.
However, significant quantities of metal may negatively impact the
operation of the magnetic resonance imaging system to which the
bridge is attached by distorting the main magnetic field and/or
producing substantial eddy currents during operation of the
magnetic resonance imaging system that negatively impact image
quality. To mitigate this problem, some embodiments include a
fold-up bridge in which the metal composition of the bridge is
minimized to the extent possible to provide a bridge capable of
supporting heavier patient while minimizing the impact on the
operation of the magnetic resonance imaging system. Thus, the
exemplary fold-up bridges described herein may be capable of
supporting large and/or heavy patients safely and securely, thus
taking advantage of the benefits of larger dimensioned bridges
without significantly impacting the ability to move the MRI system
down hallways and through doorways.
[0138] Following below are more detailed descriptions of various
concepts related to, and embodiments of, a fold-out bridge that can
be moved from a vertical position for stowing during transport of a
portable low-field MRI system or when the MRI system is not in use
to a horizontal position to facilitate positioning of the patient
for point-of-care MRI. It should be appreciated that the
embodiments described herein may be implemented in any of numerous
ways. Examples of specific implementations are provided below for
illustrative purposes only. It should be appreciated that the
embodiments and the features/capabilities provided may be used
individually, all together, or in any combination of two or more,
as aspects of the technology described herein are not limited in
this respect or to the specific combinations described.
[0139] FIGS. 13A and 13B illustrate an exemplary fold-out bridge
for supporting a patient during positioning and imaging, in
accordance with some embodiments. Bridge 1300 is configured to be
placed in a stowed or "folded-up" position (also referred to simply
as the "up" or "vertical" position) or placed in an operational or
"folded-down" position (also referred to simply as the "down" or
"horizontal" position), respectively. Bridge 1300 includes a
support 1310 configured to bridge a gap between the MRI system to
which the bridge is attached and, for example, a hospital bed to
which the MRI system is proximately located. Support 1310 comprises
a surface 1310a designed to support the patient during positioning
and imaging when the bridge is placed in the down position shown in
FIG. 13B.
[0140] When bridge 1300 is in the down position, surface 1310a of
support 1310 is substantially horizontal to provide support for the
patient. Support 1310, and particularly surface 1310a, may be made
of material that reduces friction between a patient and the bridge,
such as a smooth plastic, to facilitate positioning of the patient
within the imaging region of the MRI system without producing eddy
currents during operation of the system. As shown in FIG. 13A, when
bridge 1300 is in the up position, surface 1310a (which is visible
in FIG. 13B) of support 1310 is substantially vertical so that the
support does not add substantially, if at all, to the dimensions of
the magnetic resonance imaging system (e.g., when the bridge is in
the up position, the bridge does not increase the outer perimeter
or footprint of the system).
[0141] Bridge 1300 comprises a hinge 1350 that allows support 1310
to pivot from the up position to the down position and vice versa
(e.g., hinge 1350 allows bridge 1300 to be moved between the
positions illustrated in FIGS. 13A and 13B). According to some
embodiments, hinge 1350 comprises a shaft 1355 that allows support
1310 to pivot or rotate from the vertical position shown in FIG.
13A to the horizontal position shown in FIG. 13B and vice versa.
Specifically, exemplary bridge 1300 comprises a base 1352 and a
pivot portion 1358 through which shaft 1355 passes to allow the
pivot portion 1358 to rotate about the shaft when folding up and
folding down the bridge. Base 1352 is configured to attach to the
MRI system and includes stop 1353 (see FIG. 13A) and stop 1354 (see
FIG. 13B) that provide end stops to prevent further pivoting of the
bridge when the horizontal position and vertical position are
reached, respectively.
[0142] Base 1352 further comprises counter-bores 1345 (e.g., bores
1345a, 1345b and 1345c) to accommodate bolts that allow bridge 1300
to be securely attached to the MRI system. For example, according
to some embodiments, base 1352 is constructed with three
counter-bores to accommodate respective M8 bolts that securely
attach the base of the bridge directly to the B.sub.0 magnet of the
MRI system (e.g., as shown in FIGS. 17A-17C discussed below).
Bolting the bridge to the MRI system in this manner contributes to
the bridge being able to withstand the torque produced by the
weight of a patient.
[0143] As discussed above, the inventors have recognized the
benefits of providing a bridge that can accommodate larger (e.g.,
wider) and heavier patients and that can bridge larger gaps between
a patient bed and the MRI system and/or that provide additional
overlap with the patient bed when placed in the down position.
According to some embodiments, a fold-out bridge is constructed
having a width of between 12 and 36 inches and a length of between
8 and 24 inches. For example, exemplary bridge 1300 has a width W
of at least 24 inches and a length L of at least 12 inches to
provide a relatively large surface to accommodate a variety of
patients and to bridge a variety of gaps. The length of the bridge
refers to the dimension generally in a direction outward from the
MRI system. By increasing the length of the bridge, larger gaps can
be bridged and/or larger overlaps with a patient bed can be
achieved.
[0144] The width of the bridge refers to the dimension generally in
a direction tangent to the MRI system. By increasing the width of
the bridge, wider patients may be more comfortably accommodated and
supported. Hospital equipment for acute care is often rated to
accommodate patients weighing 500 lbs. (e.g., hospital beds are
often rated to support 500 lb. patients). According to some
embodiments, bridge 1300 is also rated for 500 lb. patients and may
be constructed to have a safety factor of at least 2.5 (i.e., that
have a yield strength of at least 2.5 times the rating). According
to some embodiments, bridge 1300 is rated for 500 lb. patients and
is constructed to have a safety factor of 4.0 or more, examples of
which are described in further detail below.
[0145] FIG. 14 illustrates components of a fold-out bridge 1400 to
illustrate exemplary construction details, in accordance with some
embodiments. Similar to bridge 1300 described above, bridge 1400
includes a support 1310 having a surface 1310a configured to
support a patient during positioning and imaging. Bridge 1400
further includes a hinge 1350 comprising base 1352 and pivot
portion 1358 that, when coupled together via shaft 1355, allows
support 1310 to pivot from a vertical position to a horizontal
position and vice versa. For exemplary bridge 1400, support 1310
may be coupled to pivot portion 1358 using a tongue-and-groove
interface. Specifically, support 1310 includes a groove 1317
configured to receive tongue 1357, which extends out from pivot
portion 1358. To couple the support to the pivot portion, tongue
1357 may be inserted into groove 1317 and screwed or bolted into
place to secure support 1310 to pivot portion 1358.
[0146] To construct hinge 1350, pivot portion 1358 comprises
shoulders 1359a and 1359b between which is provided gap 1363 sized
to accommodate base 1352. Shoulders 1359a, 1359b and stop 1354 of
base 1352 include cooperating bores 1365 through which shaft 1355
is inserted to allow support 1310 to pivot between the up and down
positions. When constructed, shaft 1355 is secured within bores
1365 of the base and pivot portions with nuts 1366a and bolts 1366b
at both ends of the shaft. Thus, pivot portion 1358 is allowed to
rotate about the shaft so that support 1310 can be moved from the
vertical position (i.e., in which planar surface 1310a is
substantially vertical) when not in use to the horizontal position
(i.e., in which the planar surface 1310a is substantially
horizontal) to facilitate positioning a patient within the imaging
region of the MRI system and to support the patient during imaging.
As discussed above, bridge 1400 can be bolted to the MRI system via
bolt holes 1345a-c (e.g., bolted to the lower B.sub.0 magnet of the
MRI system so that it is level with the patient surface within the
imaging region of the MRI system as shown in FIGS. 6A-C discussed
below).
[0147] Bridge 1400 may further include ball plungers 1380a and
1380b that facilitate holding the bridge in the vertical position
when the bridge is not being used. For example, ball or spring
plungers 1380a and 1380b may be positioned on either side of base
1352 to interact with shoulders 1359a and 1359b of pivot portion
1358. Specifically, to move bridge 1400 from the vertical to the
horizontal position, the shoulders of the pivot portion must first
overcome the resistance provided by the spring loaded ball plungers
(i.e., to pivot bridge 1400 out of the vertical position, shoulders
1359a and 1359b must first move over the ball plungers, which
provide a counter-resistance to the initial rotation of the pivot
portion). Accordingly, because an initial force exceeding the
resistance of the ball plungers is needed to move the bridge out of
the vertical position, a measure of safety is provided by reducing
the chances that bridge 1400 will unintentionally fall from the
vertical position to the horizontal position. Bridge 1400 may also
include rubber stoppers 1393 configured to fit within corresponding
holes provided in stop 1353 of base 1352 to reduce noise produced
when shoulders 1359a, 1359b contact stop 1353 when the bridge is
moved to the down position and/or to absorb some of the impact of
the bridge should the bridge fall or if the bridge is roughly
handled during transition to the horizontal position.
[0148] FIG. 15A illustrates a model of a fold-out bridge 1500
constructed to support larger and/or heavier patients, in
accordance with some embodiments. The model illustrated in FIG. 15A
was used to perform a number of performance tests on exemplary
bridge 1500 designed to provide a relatively large surface to
facilitate patient positioning and constructed to support heavier
patients (e.g., to achieve a 500 lb. rating). The following
dimensions, materials and construction details are provided merely
as description of exemplary bridge 1500 on which stress tests were
performed and do not limit the aspects of a fold-out bridge in this
respect. In particular, different dimensions, materials and designs
may be used to construct a fold-out bridge and different aspects of
a fold-out bridge discussed herein may be used in different
combinations. Bridge 1500 merely illustrates one example of a
suitable fold-out bridge capable of supporting larger and/or
heavirt patients and that provides a relatively large surface to
facilitate patient positioning and support.
[0149] Bridge 1500 is provided with a support 1310 having a
relatively large surface area, for example, a width of 24 inches
and a length of 14.4 inches measured from the far side of support
1310 to the center of the curved interface of base 1352 where
bridge 1500 is bolted to the MRI system (i.e., at counter-bore
1345b). Support 1310 is formed, at least in part, by a 1 inch thick
plastic platform that provides a surface 1310a over which a patient
can be moved to position the patient within the MRI system. Similar
to the construction of exemplary bridge 1400, pivot portion 1358 is
coupled to support 1310 via a tongue-and-groove interface and
coupled to the base via a 16 mm diameter shaft 1355 inserted
through shoulder portions 1359a and 1359b. For exemplary bridge
1500, shoulders 1359a and 1359b are constructed of metal (e.g.,
aluminum) and tongue portion 1357 is constructed of plastic (or
other non-metallic material). Base 1352 for exemplary bridge 1550
is constructed of metal, such as steel, and comprises three
counter-bores 1345a-c for bolting bridge 1500 to the B.sub.0 magnet
of the MRI system (e.g., using three corresponding M8 bolts). In
this way, components of bridge 1500 that undergo the greatest
amount of stress may be constructed of metal and components that
undergo less stress may be made of plastic (or other non-metallic
material) to minimize eddy current production when the MRI system
is operated, while providing a bridge with a robust
construction.
[0150] To evaluate the performance of exemplary bridge 1500, stress
tests were simulated on the model of bridge 1500 to ensure that the
design achieves a 500 lb. rating with a safety factor suitable for
patient support equipment. In particular, using the above described
construction details, a mesh was applied to the model of bridge
1500 as shown in FIG. 15A and the stresses resulting from the
weight of a patient were simulated via finite element analysis. The
weight that bridge 1500 is required to support for a 500 lb.
patient was obtained from the International Electrotechnical
Commission (IEC) 60601-1 International Standard. Specifically, IEC
60601-1 establishes a number of safety requirements and performance
standards for medical equipment.
[0151] Figure A.19 of IEC 60601-1, which is reproduced herein as
FIG. 15D, shows an example of human body mass distribution that was
used to determine how the weight of a 500 lb. patient is
distributed over the patient support surface of the exemplary
bridges described herein. As shown in FIG. 15D, Figure A.19 of IEC
60601-1 specifies the length dimension (in millimeters) and the
percent of a patient's body mass that is contributed by significant
segments of the human body lying in a supine position.
Specifically, the head accounts for 7.4% of the mass of the
patient, the torso accounts for 40.7%, the upper arms together
account for 7.4% and the lower arms another 7.4%, the upper legs
account for 22.2% and the lower legs account for 14.8%. When a
patient is positioned within a portable MRI system, the head lies
within the imaging region and is supported by the MRI system (e.g.,
by the helmet on which the transmit/receive coils are located) so
that the bridge need support at least some portion of the torso,
shoulder and arm portions of the body. The full contribution of the
torso and the upper arms is approximately 50% (48.1%) of the body
mass of the patient. Accordingly, in approximate numbers, for a
bridge having a 500 lb. rating and a safety factor of 1, the bridge
would be required to support 250 lbs. (i.e., 50% of the patient's
total weight). For a safety factor of 2.5, the bridge would need to
support 625 lbs (i.e., 50% of the patient's weight times 2.5) and,
for a safety factor of 4, the bridge would need to support 1000
lbs. (i.e., 50% of the patients weight times 4).
[0152] To evaluate bridge 1500 for a 500 lb. rating, the stresses
on bridge 1500 resulting from a 500 lb. patient were simulated by
distributing 250 lbs. of weight over the surface of the bridge
(i.e., 50% of the patient's weight that the bridge needs to
support), as shown by the downward arrows in FIGS. 15A-15C. Using
the materials and dimensions discussed above, this distributed
weight produced the stress plot shown in FIG. 15B. A maximum stress
of 6,981 psi resulted at the corners of the base indicated by
arrows 1553a and 1553b. The yield strength of exemplary bridge 1500
was also assessed to evaluate the maximum stress that bridge 1500
can withstand. The yield strength of bridge 1500 was determined to
be 30,000 psi. Thus, exemplary bridge 1500 achieves a 500 lb.
rating with a safety factor of 4.3. Specifically, the yield
strength of the bridge is 4.3 times greater than the maximum stress
resulting from simulating the forces applied on bridge 1500 by a
500 lb. patient.
[0153] FIG. 15C illustrates a deflection plot showing the
deformation of the bridge under the 250 lb. simulated weight. The
maximum deflection of the bridge resulting from the simulation was
1.5 mm at the far end of support 1310. In particular, the arrows
show the location of the bridge without the simulated force
applied. In FIGS. 15B and 15C, the displacement resulting from the
applied 250 lbs. is shown at 36.4 scale to exaggerate the
displacement so that it can be visualized (i.e., the actual
displacement is 36.4 times smaller than it appears in the plots
shown in FIGS. 15B and 15C.). Thus, a 250 lb. weight distributed
across bridge 1500 to simulate the stresses resulting from a 500
lb. patient resulted in a maximum displacement of 1.5 mm at end
1310b of support 1310.
[0154] The inventors have recognized that some embodiments of a
fold-out bridge may be relatively large and heavy, particularly
when dimensioned and constructed to facilitate positioning and
support of larger, heavier patients. For example, an exemplary
bridge may be dimensioned to have a length of between 1 and 2 feet
or more and a width of between 1.5 and 2.5 feet or more, resulting
in bridges that can weigh between 8 and 15 lbs. or more. Larger,
heavier bridges have the potential to injure if the bridge
accidentally falls from the vertical position. To prevent a bridge
from being able to free fall, the inventors have developed a
counter-balance mechanism configured to slow the rate at which the
bridge can transition from the up position to the down position.
The counter-balance mechanism provides an additional safety
precaution that protects patients and medical personnel from
possible injury, as discussed in further detail below.
[0155] FIGS. 16A and 16B illustrate components for a bridge 1600,
in accordance with some embodiments. Exemplary fold-out bridge 1600
may comprise many of the same components described in connection
with bridge 1400 illustrated in FIG. 14 and/or bridge 1500
illustrated in FIGS. 15A-C. However, bridge 1600 includes a
counter-balance mechanism configured to slow the rate at which
fold-out bridge 1600 can pivot to the horizontal position.
According to some embodiments, the counter-balance mechanism
comprises torsion springs 1375a and 1375b. Torsion springs 1375a
and 1375b are configured to fit over respective ends of shaft 1655.
Each torsion spring 1375a, 1375b is configured with end portions
1376a and 1376b that protrude out from the spring in the direction
of the shaft's longitudinal axis, as can be seen best in the
magnified portion of one end of the counter-balance component
illustrated in FIG. 16B.
[0156] In particular, end portions 1376a are arranged in the
direction of the axis of shaft 1655 and positioned on the perimeter
of the respective torsion spring and are configured to fit into a
corresponding indexing hole 1378 provided in indexing components
1377a, 1377b. End portions 1376b are similarly arranged and
configured to fit into respective indexing holes 1378 provided in
shoulders 1659a and 1659b of pivot portion 1658. Specifically,
indexing components 1377a, 1377b comprise a plurality of indexing
holes 1378 around the perimeter (see e.g., exemplary indexing holes
1378a and 1378b illustrated in FIG. 16B) to accommodate end
portions 1376a. Shoulders 1659a and 1659b comprise notches 1656a
and 1656b to accommodate respective torsion springs. Notches 1656a
and 1656b comprise bores 1365 through which shaft 1655 passes and
further comprise indexing holes 1378 into which end portions 1376b
are inserted (as best seen by indexing hole 1378d provide next to
bore 1365 within notch 1656b). For example, end portion 1376b of
each torsion spring 1375a, 1375b fits into the respective indexing
holes 1378c and 1378d so that the torsion spring is coupled to
indexing component 1377 at one end and pivot component 1658 at the
other end.
[0157] Shaft 1655 includes flats 1655a and 1655b configured to fit
into respective indexing components 1377a and 1377b. Specifically,
flats 1655a and 1655b are configured to be inserted into slots 1379
provided in respective indexing components 1377a, 1377b (as seen
best in the magnified view shown in FIG. 16B) and secured by screws
1666a and 1666b at opposite ends of shaft 1655. To facilitate
operation of the counter-balance mechanism, corresponding screw
holes 1336a and 1336b are provided through stop 1354 of base 1352
and into shaft 1655, respectively, to accommodate screw 1335 to
hold shaft 1355 in place. Specifically, screw 1335 is inserted
through screw hole 1336a in the base and into screw hole 1336b in
shaft 1655 to prevent the shaft from rotating when pivot portion
1658 rotates during transitions between the up and down positions.
Preventing shaft 1355 from rotating ensures that rotation of pivot
portion 1658 causes the torsion springs 1375a, 1375b to wind-up or
tighten to slow the rate at which pivot portion 1658 can rotate, as
discussed in further detail below. Sleeves 1360a and 1360b cover
respective torsion springs 1375a and 1375b when the bridge is
assembled.
[0158] When constructed as described above, shaft 1655 is fixed in
place and prevented from rotating by inserting the shaft through
bores 1365 and into slots 1379 of the respective indexing portions
1377a, 1377b and screwing the shaft in place via screws 1666a,
1666b and 1335. By inserting end portions 1376a and 1376b of the
torsion springs 1375a, 1375b into the indexing portions 1377a,
1377b and pivot portion 1658, respectively, rotation of pivot
portion 1658 from the vertical position to the horizontal position
causes the torsion springs to tighten due to the fixed connection
between end portions 1376a and the indexing components 1377a, 1377b
(which does not rotate) and the fixed connection between end
portions 1376b and the indexing holes 1378c, 1378d in notches
1656a, 1656b, respectively, by which end portions 1376b are rotated
along with the pivot portion 1658. That is, because indexing holes
1378c and 1378d and end portions 1376b are aligned in the direction
of the shaft axis but are positioned off-axis, the rotation of the
pivot portion causes the torsion spring to tighten as indexing
holes 1378c and 1378d rotate about the axis of the shaft. Thus,
when the bridge pivots from a vertical to a horizontal position,
the twisting of the torsion springs slows the rotation of support
1310 to prevent the bridge from rotating in free fall. The spring
constant of the torsion springs can be selected to achieve the
desired level of control of the rate at which the bridge is allowed
to transition between the up and down positions. In this manner,
bridge 1600 includes a counter-balance mechanism providing an
additional safety mechanism to reduce the chances of injury when
using a fold-out bridge.
[0159] As discussed above, the exemplary fold-out bridges described
herein are configured to attach to a portable magnetic resonance
imaging system to facilitate positioning and supporting a patient
during point-of-care MRI. FIGS. 17A, 17B and 17C illustrate a
portable low-field MRI system to which the exemplary fold-out
bridges described herein can be attached. Specifically, portable
low-field MRI system 10000 can be deployed in virtually any
environment to image patients, for example, from a standard
hospital bed located in emergency rooms, intensive care units,
operating rooms, neonatal units, clinics, primary care offices,
recovery units, etc. where conventional MRI is typically not
available. Exemplary fold-out bridge may be configured to
facilitate positioning and support of large, heavy patients without
substantially increasing the footprint of the MRI system by virtue
of being capable of being stowed in the vertical position during
transport or when not in use and folded-down when needed to
perform, for example, point-of-care MRI.
[0160] In particular, to facilitate transporting portable MRI
system 10000 to locations at which MRI is needed, portable MRI
system 10000 is equipped with a fold-out bridge 1700, which may
include any one or more of the features of a fold-out bridge
described herein. FIG. 17A illustrates bridge 1700 configured in
its up position so that support 1710 is substantially vertical and
does not add significantly (or at all) to the footprint of the MRI
system. As a result, bridge 1700 does not impede moving the
portable MRI system down hallways and through doorways. FIG. 17A
also illustrates a deployable guard 10040 in its deployed position
to indicate the 5-Gauss line for the MRI system as its being
transported or when it is stored away or otherwise not in use. As
discussed in U.S. application Ser. No. 16/389,004, titled
"Deployable Guard for Portable Magnetic Resonance Imaging Device,"
filed on Apr. 19, 2019, and which is herein incorporated by
reference in its entirety, the guard can be deployed to demarcate
the physical boundary within which the magnetic field is above a
specified field strength to provide a visual signal regarding the
magnetic field when the MRI system is being moved to a different
location. In addition, as illustrated in FIG. 17B, when bridge 1700
is up, the bridge provides a barrier to the imaging region of the
MRI system where the magnetic field is strongest.
[0161] FIG. 17B illustrates portable MRI system 10000 with bridge
1700 configured in the down position and FIG. 17C illustrates
bridge 1700 deployed in the down position to bridge the gap between
a patient bed 490 and MRI system 10000 to allow patient 499 to be
positioned within the imaging region of the MRI system and to
support patient 499 during imaging. As discussed above, bridge 1700
may be bolted to the B.sub.0 magnet to secure the bridge to the MRI
system. For example, as shown in FIG. 17B, portable MRI system
10000 comprises a B.sub.0 magnet 10005 that includes at least one
first permanent B.sub.0 magnet 10010a and at least one second
permanent B.sub.0 magnet 10010b magnetically coupled to one another
by a ferromagnetic yoke 10020 configured to capture and channel
magnetic flux to increase the magnetic flux density within the
imaging region 10065 (field of view) of the MRI system. For
exemplary MRI system 10000, bridge 1700 is bolted to the lower
magnet 10010b so that when it is deployed (i.e., positioned in the
down position as shown in FIGS. 17B and 17C), support 1710 provides
a continuation of the planar surface 10015 of the magnet housing to
facilitate positioning the patient within imaging region 10065 and
providing relatively level support to the patient during imaging.
FIG. 17B also illustrates a conveyance mechanism 10080 of MRI
system 10000 that facilitates moving the MRI system from one
location to another, as discussed in further detail below.
[0162] FIG. 17C illustrates patient 499 positioned within the
imaging region of MRI system 1000 for imaging of the patient's head
from hospital bed 490. As shown, once the patient is positioned
with the imaging region and during the imaging process, the
patient's head is supported by helmet 10030 (which comprises radio
frequency transmit and receive coils), at least a portion of the
patient's torso and arms are supported by fold-out bridge 1700 and
the remainder of the patient's weight is supported by patient bed
490. As discussed above, some embodiments of a fold-out bridge are
dimensioned and constructed to support large and heavy patients.
For example, bridge 1700 may be rated for a 500 lb. patient with a
safety factor of 2.5 or more. According to some embodiments, bridge
1700 may be rated for a 500 lb. patient with a safety factor of 4.0
or more (e.g., a safety factor of 4.3), for example, using the
various exemplary bridge constructions described above in
connection with any of exemplary bridges 1400, 1500 or 1600.
[0163] As discussed above, portable MRI system 10000 includes a
conveyance mechanism configured to allow the portable MRI system to
be transported to desired locations. Referring to FIG. 17B,
portable MRI system 10000 comprises a conveyance mechanism 10080
having a drive motor 10086 coupled to drive wheels 10084.
Conveyance mechanism 10080 may also include a plurality of castors
1082 to assist with support and stability as well as to facilitate
transport of the MRI system. In this manner, conveyance mechanism
10080 provides motorized assistance in transporting MRI system
10000 to desired locations.
[0164] According to some embodiments, conveyance mechanism 10080
includes motorized assistance controlled using a controller (e.g.,
a joystick or other controller that can be manipulated by a person)
to guide the portable MRI system during transportation to desired
locations. According to some embodiments, the conveyance mechanism
comprises power assist means configured to detect when force is
applied to the MRI system and to engage the conveyance mechanism to
provide motorized assistance in the direction of the detected
force. For example, rail 10050 illustrated in FIG. 17B may be
configured to detect when force is applied to the rail (e.g., by
personnel pushing on the rail) and engage the drive motor to
provide motorized assistance to drive the wheels in the direction
of the applied force. As a result, a user can guide the portable
MRI system with the assistance of the conveyance mechanism that
responds to the direction of force applied by the user. The drive
motor may be operated in other ways, such as via buttons, roller
ball or other suitable mechanism located on the MRI system, or
using touch screen controls on a mobile computing device 10025
communicatively coupled to the MRI system, as the aspects of
motorized control is not limited in this respect.
[0165] Thus, low-field MRI system 10000 equipped with fold-out
bridge 1700 can be used to perform point-of-care MRI on a patient,
including large and heavy patients. For example, to perform
point-of-care MRI on a patient from a standard medical bed, the MRI
system and the bed can be positioned proximate one another. In some
embodiments, the MRI system is portable and can be moved into
position near the hospital bed by medical personnel pushing the MRI
system into place and/or using a motor drive conveyance system to
move the MRI system into position. In some instances, the MRI
system may need to be transported from another room or unit within
the hospital. In other instances, the MRI system may already be
located in the same room as the patient and need only be moved next
to the bed of the patient. In other circumstances, a hospital bed
is transported to the MRI system and moved into place proximate the
MRI system for imaging. During the positioning of the MRI system
and the patient bed near one another, a fold-out bridge attached to
the MRI system may be positioned in the vertical or up position
(e.g., in the vertical position illustrated in FIG. 17A) to
facilitate transport of the system down hallways and/or through
doorways and/or to facilitate positioning the MRI system and the
bed in close proximity (e.g., positioning the MRI system and the
foot or head of the bed adjacent one another).
[0166] Once the MRI system and the bed are positioned proximate one
another, the fold-out bridge may be moved from the vertical
position to a horizontal position so that the bridge at least
partially overlaps the bed (e.g., the fold-out bridge 1700 may be
moved from the vertical position illustrated in FIG. 17A to the
horizontal position illustrated in FIGS. 17B and 17C). The fold-out
bridge then provides a surface that bridges the gap between the MRI
system and the bed over which the patient can be moved. For
example, the portion of anatomy of the patient to be imaged may be
positioned within an imaging region of the MRI system via the
bridge and the bridge may provide support for the patient during
and after positioning the patient within the imaging region. After
positioning the patient within the MRI system, at least one
magnetic resonance image of the portion of the anatomy of the
patient may be acquired while the patient is at least partially
supported by the bed and at least partially support by the bridge
(e.g., as shown in FIG. 17C). In this way, point-of-care MRI may be
performed.
[0167] Having thus described several aspects and embodiments of the
technology set forth in the disclosure, it is to be appreciated
that various alterations, modifications, and improvements will
readily occur to those skilled in the art. Such alterations,
modifications, and improvements are intended to be within the
spirit and scope of the technology described herein. For example,
those of ordinary skill in the art will readily envision a variety
of other means and/or structures for performing the function and/or
obtaining the results and/or one or more of the advantages
described herein, and each of such variations and/or modifications
is deemed to be within the scope of the embodiments described
herein. Those skilled in the art will recognize, or be able to
ascertain using no more than routine experimentation, many
equivalents to the specific embodiments described herein. It is,
therefore, to be understood that the foregoing embodiments are
presented by way of example only and that, within the scope of the
appended claims and equivalents thereto, inventive embodiments may
be practiced otherwise than as specifically described. In addition,
any combination of two or more features, systems, articles,
materials, kits, and/or methods described herein, if such features,
systems, articles, materials, kits, and/or methods are not mutually
inconsistent, is included within the scope of the present
disclosure.
[0168] The above-described embodiments can be implemented in any of
numerous ways. One or more aspects and embodiments of the present
disclosure involving the performance of processes or methods may
utilize program instructions executable by a device (e.g., a
computer, a processor, or other device) to perform, or control
performance of, the processes or methods. In this respect, various
inventive concepts may be embodied as a computer readable storage
medium (or multiple computer readable storage media) (e.g., a
computer memory, one or more floppy discs, compact discs, optical
discs, magnetic tapes, flash memories, circuit configurations in
Field Programmable Gate Arrays or other semiconductor devices, or
other tangible computer storage medium) encoded with one or more
programs that, when executed on one or more computers or other
processors, perform methods that implement one or more of the
various embodiments described above. The computer readable medium
or media can be transportable, such that the program or programs
stored thereon can be loaded onto one or more different computers
or other processors to implement various ones of the aspects
described above. In some embodiments, computer readable media may
be non-transitory media.
[0169] The terms "program" or "software" are used herein in a
generic sense to refer to any type of computer code or set of
computer-executable instructions that can be employed to program a
computer or other processor to implement various aspects as
described above. Additionally, it should be appreciated that
according to one aspect, one or more computer programs that when
executed perform methods of the present disclosure need not reside
on a single computer or processor, but may be distributed in a
modular fashion among a number of different computers or processors
to implement various aspects of the present disclosure.
[0170] Computer-executable instructions may be in many forms, such
as program modules, executed by one or more computers or other
devices. Generally, program modules include routines, programs,
objects, components, data structures, etc. that perform particular
tasks or implement particular abstract data types. Typically the
functionality of the program modules may be combined or distributed
as desired in various embodiments.
[0171] Also, data structures may be stored in computer-readable
media in any suitable form. For simplicity of illustration, data
structures may be shown to have fields that are related through
location in the data structure. Such relationships may likewise be
achieved by assigning storage for the fields with locations in a
computer-readable medium that convey relationship between the
fields. However, any suitable mechanism may be used to establish a
relationship between information in fields of a data structure,
including through the use of pointers, tags or other mechanisms
that establish relationship between data elements.
[0172] The above-described embodiments of the present invention can
be implemented in any of numerous ways. For example, the
embodiments may be implemented using hardware, software or a
combination thereof. When implemented in software, the software
code can be executed on any suitable processor or collection of
processors, whether provided in a single computer or distributed
among multiple computers. It should be appreciated that any
component or collection of components that perform the functions
described above can be generically considered as a controller that
controls the above-discussed function. A controller can be
implemented in numerous ways, such as with dedicated hardware, or
with general purpose hardware (e.g., one or more processor) that is
programmed using microcode or software to perform the functions
recited above, and may be implemented in a combination of ways when
the controller corresponds to multiple components of a system.
[0173] Further, it should be appreciated that a computer may be
embodied in any of a number of forms, such as a rack-mounted
computer, a desktop computer, a laptop computer, or a tablet
computer, as non-limiting examples. Additionally, a computer may be
embedded in a device not generally regarded as a computer but with
suitable processing capabilities, including a Personal Digital
Assistant (PDA), a smartphone or any other suitable portable or
fixed electronic device.
[0174] Also, a computer may have one or more input and output
devices. These devices can be used, among other things, to present
a user interface. Examples of output devices that can be used to
provide a user interface include printers or display screens for
visual presentation of output and speakers or other sound
generating devices for audible presentation of output. Examples of
input devices that can be used for a user interface include
keyboards, and pointing devices, such as mice, touch pads, and
digitizing tablets. As another example, a computer may receive
input information through speech recognition or in other audible
formats.
[0175] Such computers may be interconnected by one or more networks
in any suitable form, including a local area network or a wide area
network, such as an enterprise network, and intelligent network
(IN) or the Internet. Such networks may be based on any suitable
technology and may operate according to any suitable protocol and
may include wireless networks, wired networks or fiber optic
networks.
[0176] Also, as described, some aspects may be embodied as one or
more methods. The acts performed as part of the method may be
ordered in any suitable way. Accordingly, embodiments may be
constructed in which acts are performed in an order different than
illustrated, which may include performing some acts simultaneously,
even though shown as sequential acts in illustrative
embodiments.
[0177] All definitions, as defined and used herein, should be
understood to control over dictionary definitions, definitions in
documents incorporated by reference, and/or ordinary meanings of
the defined terms.
[0178] The indefinite articles "a" and "an," as used herein in the
specification and in the claims, unless clearly indicated to the
contrary, should be understood to mean "at least one."
[0179] The phrase "and/or," as used herein in the specification and
in the claims, should be understood to mean "either or both" of the
elements so conjoined, i.e., elements that are conjunctively
present in some cases and disjunctively present in other cases.
Multiple elements listed with "and/or" should be construed in the
same fashion, i.e., "one or more" of the elements so conjoined.
Other elements may optionally be present other than the elements
specifically identified by the "and/or" clause, whether related or
unrelated to those elements specifically identified. Thus, as a
non-limiting example, a reference to "A and/or B", when used in
conjunction with open-ended language such as "comprising" can
refer, in one embodiment, to A only (optionally including elements
other than B); in another embodiment, to B only (optionally
including elements other than A); in yet another embodiment, to
both A and B (optionally including other elements); etc.
[0180] As used herein in the specification and in the claims, the
phrase "at least one," in reference to a list of one or more
elements, should be understood to mean at least one element
selected from any one or more of the elements in the list of
elements, but not necessarily including at least one of each and
every element specifically listed within the list of elements and
not excluding any combinations of elements in the list of elements.
This definition also allows that elements may optionally be present
other than the elements specifically identified within the list of
elements to which the phrase "at least one" refers, whether related
or unrelated to those elements specifically identified. Thus, as a
non-limiting example, "at least one of A and B" (or, equivalently,
"at least one of A or B," or, equivalently "at least one of A
and/or B") can refer, in one embodiment, to at least one,
optionally including more than one, A, with no B present (and
optionally including elements other than B); in another embodiment,
to at least one, optionally including more than one, B, with no A
present (and optionally including elements other than A); in yet
another embodiment, to at least one, optionally including more than
one, A, and at least one, optionally including more than one, B
(and optionally including other elements); etc.
[0181] Also, the phraseology and terminology used herein is for the
purpose of description and should not be regarded as limiting. The
use of "including," "comprising," or "having," "containing,"
"involving," and variations thereof herein, is meant to encompass
the items listed thereafter and equivalents thereof as well as
additional items.
[0182] In the claims, as well as in the specification above, all
transitional phrases such as "comprising," "including," "carrying,"
"having," "containing," "involving," "holding," "composed of," and
the like are to be understood to be open-ended, i.e., to mean
including but not limited to. Only the transitional phrases
"consisting of" and "consisting essentially of" shall be closed or
semi-closed transitional phrases, respectively.
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