U.S. patent application number 14/276942 was filed with the patent office on 2015-03-19 for superconductor rf coil array.
This patent application is currently assigned to Time Medical Holdings Company Limited. The applicant listed for this patent is Time Medical Holdings Company Limited. Invention is credited to Erzhen Gao, Qiyuan Ma.
Application Number | 20150077116 14/276942 |
Document ID | / |
Family ID | 43302905 |
Filed Date | 2015-03-19 |
United States Patent
Application |
20150077116 |
Kind Code |
A1 |
Ma; Qiyuan ; et al. |
March 19, 2015 |
Superconductor RF Coil Array
Abstract
A superconducting RF coil array which may be used in whole body
MRI scanners and/or in dedicated MRI systems. Some embodiments
provide a superconducting RF coil array for at least one of
receiving signals from and transmitting signals to a sample during
magnetic resonance analysis of the sample, the superconducting RF
coil array comprising a thermally conductive member configured to
be cryogenically cooled, and a plurality of coils elements
comprising superconducting material, wherein each coil element is
thermally coupled to the thermally conductive member and is
configured for at least one of (i) receiving a magnetic resonance
signal from a spatial region that is contiguous with and/or
overlaps a spatial region from which at least one other of the
plurality of coil elements is configured to receive a signal and
(ii) transmitting a radiofrequency signal to a spatial region that
is contiguous with and/or overlaps a spatial region to which at
least one other of the plurality coil elements is configured to
transmit a radiofrequency signal.
Inventors: |
Ma; Qiyuan; (Millburn,
NJ) ; Gao; Erzhen; (Millburn, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Time Medical Holdings Company Limited |
Hong Kong |
|
CN |
|
|
Assignee: |
Time Medical Holdings Company
Limited
Hong Kong
CN
|
Family ID: |
43302905 |
Appl. No.: |
14/276942 |
Filed: |
May 13, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12887474 |
Sep 21, 2010 |
8723522 |
|
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14276942 |
|
|
|
|
61244132 |
Sep 21, 2009 |
|
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Current U.S.
Class: |
324/322 |
Current CPC
Class: |
G01R 33/3403 20130101;
G01R 33/3415 20130101; G01R 33/34023 20130101; G01R 33/34007
20130101 |
Class at
Publication: |
324/322 |
International
Class: |
G01R 33/34 20060101
G01R033/34 |
Claims
1. A superconducting RF coil array for receiving signals from a
sample during magnetic resonance analysis of the sample, the
superconducting RF coil array comprising: a thermally conductive
member configured to be cryogenically cooled; a plurality of coils
elements each comprising a high temperature superconducting coil,
wherein each coil element is thermally coupled to said thermally
conductive member and is configured to provide a respective
electrical channel for receiving a magnetic resonance signal from a
spatial region that is contiguous with and/or overlaps a spatial
region from which at least one other of the plurality of coil
elements is configured to receive a signal; and wherein the high
temperature superconducting coils of neighboring coil elements are
separate with respect to electrical conductivity and partially
overlap spatially.
2. The superconducting RF coil array according to claim 1, wherein
the high temperature superconducting coil of each coil element
comprises a thin film high temperature superconducting coil, and
each coil element comprises the thin film high temperature
superconducting coil disposed on a thermally conductive
substrate.
3. The superconducting RF coil array according to claim 2, wherein
the thermally conductive substrate comprises at least one of
alumina and sapphire, and said thermally conductive member is an
alumina or sapphire plate.
4. The superconducting RF coil array according to claim 2, wherein
the thermally conductive substrate of each coil element is directly
or indirectly thermally coupled to said thermally conductive
member.
5. The superconducting RF coil array according to claim 4, wherein
a plurality of the thermally conductive substrates are each
directly thermally coupled to said thermally conductive member, and
each of at least one other of said thermally conductive substrates
is indirectly and not directly thermally coupled to said thermally
conductive member.
6. The superconducting RF coil array according to claim 5, wherein
each of said at least one other thermally conductive substrates is
directly thermally coupled to at least one of the thermally
conductive substrates that are directly thermally coupled to said
thermally conductive member, thereby being indirectly thermally
coupled to said thermally conductive member.
7. The superconducting RF coil array according to claim 5, wherein
one or more of said at least one other thermally conductive
substrates is thermally coupled to said thermally conductive member
via a thermally conductive spacer member, thereby being indirectly
thermally coupled to said thermally conductive member.
8. The superconducting RF coil array according to claim 1, wherein
the high temperature superconducting coils of neighboring coil
elements are disposed on or above a common surface of the thermally
conductive member.
9. The superconducting RF coil array according to claim 1, wherein
the high temperature superconducting coils of neighboring coil
elements are disposed on or above opposing surfaces of the
thermally conductive member.
10. The superconducting RF coil array according to claim 1, wherein
the coil elements are configured as a linear array.
11. The superconducting RF coil array according to claim 1, wherein
the coil elements are configured as a two-dimensional array.
12. The superconducting RF coil array according to claim 1, wherein
each coil element comprises a thermally conductive substrate that
is thermally coupled to (i) the high temperature superconducting
coil of the coil element and (ii) said thermally conductive
member.
13. The superconducting RF coil array according to claim 12,
wherein the thermally conductive substrate of each coil element is
configured as a generally cylindrical structure having an outer
surface upon which the high temperature superconducting coil is
disposed.
14. The superconducting RF coil array according to claim 1, wherein
the number of said coil elements is at least five.
15. The superconducting RF coil array according to claim 1, wherein
the thermally conductive member is configured as a generally
cylindrical structure having an outer surface upon which said high
temperature superconducting coils are disposed such that
neighboring superconducting coils are displaced and overlap
circumferentially about the cylindrically-shaped thermally
conductive member.
16. The superconducting RF coil array according to claim 1, wherein
at least one of the coil elements is configured as a multiple
resonance radiofrequency coil element operable to receive signals
corresponding to different magnetic resonance frequencies at the
same magnetic field.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/887,474, filed Sep. 21, 2010, which claims the benefit of
U.S. Provisional Application No. 61/244,132, filed Sep. 21, 2009,
each of which is hereby incorporated herein by reference in its
entirety.
TECHNICAL FIELD
[0002] The present invention relates generally to magnetic
resonance imaging and spectroscopy, and, more particularly, to
superconductor coil arrays comprising a plurality of coil elements
configured as a surface or volume coil array for receiving signals
from and/or transmitting signals to a sample to be examined
according to magnetic resonance techniques, and, further, to
magnetic resonance imaging and/or spectroscopy apparatus and/or
methods employing such a superconductor coil array.
BACKGROUND
[0003] Magnetic Resonance Imaging (MRI) technology is commonly used
today in larger medical institutions worldwide, and has led to
significant and unique benefits in the practice of medicine. While
MRI has been developed as a well-established diagnostic tool for
imaging structure and anatomy, it has also been developed for
imaging functional activities and other biophysical and biochemical
characteristics or processes (e.g., blood flow,
metabolites/metabolism, diffusion), some of these magnetic
resonance (MR) imaging techniques being known as functional MRI,
spectroscopic MRI or Magnetic Resonance Spectroscopic Imaging
(MRSI), diffusion weighted imaging (DWI), and diffusion tensor
imaging (DTI). These magnetic resonance imaging techniques have
broad clinical and research applications in addition to their
medical diagnostic value for identifying and assessing pathology
and determining the state of health of the tissue examined.
[0004] During a typical MRI examination, a patient's body (or a
sample object) is placed within the examination region and is
supported by a patient support in an MRI scanner where a
substantially constant and uniform primary (main) magnetic field is
provided by a primary (main) magnet. The magnetic field aligns the
nuclear magnetization of precessing atoms such as hydrogen
(protons) in the body. A gradient coil assembly within the magnet
creates a small variation of the magnetic field in a given
location, thus providing resonance frequency encoding in the
imaging region. A radio frequency (RF) coil is selectively driven
under computer control according to a pulse sequence to generate in
the patient a temporary oscillating transverse magnetization signal
that is detected by the RF coil and that, by computer processing,
may be mapped to spatially localized regions of the patient, thus
providing an image of the region-of-interest under examination.
[0005] In a common MRI configuration, the static main magnetic
field is typically produced by a solenoid magnet apparatus, and a
patient platform is disposed in the cylindrical space bounded by
the solenoid windings (i.e. the main magnet bore). The windings of
the main field are typically implemented as a low temperature
superconductor (LTS) material, and are super-cooled with liquid
helium in order to reduce resistance, and, therefore, to minimize
the amount of heat generated and the amount of power necessary to
create and maintain the main field. The majority of existing LTS
superconducting MRI magnets are made of a niobium-titanium (NbTi)
and/or Nb.sub.3Sn material which is cooled with a cryostat to a
temperature of 4.2 K.
[0006] As is known to those skilled in the art, the magnetic field
gradient coils generally are configured to selectively provide
linear magnetic field gradients along each of three principal
Cartesian axes in space (one of these axes being the direction of
the main magnetic field), so that the magnitude of the magnetic
field varies with location inside the examination region, and
characteristics of the magnetic resonance signals from different
locations within the region of interest, such as the frequency and
phase of the signals, are encoded according to position within the
region (thus providing for spatial localization). Typically, the
gradient fields are created by current passing through coiled
saddle or solenoid windings, which are affixed to cylinders
concentric with and fitted within a larger cylinder containing the
windings of the main magnetic field. Unlike the main magnetic
field, the coils used to create the gradient fields typically are
common room temperature copper windings. The gradient strength and
field linearity are of fundamental importance both to the accuracy
of the details of the image produced and to the information on
tissue chemistry (e.g., in MRSI).
[0007] Since MRI's inception, there has been a relentless pursuit
for improving MRI quality and capabilities, such as by providing
higher spatial resolution, higher spectral resolution (e.g., for
MRSI), higher contrast, and faster acquisition speed. For example,
increased imaging (acquisition) speed is desired to minimize
imaging blurring caused by temporal variations in the imaged region
during image acquisition, such as variations due to patient
movement, natural anatomical and/or functional movements (e.g.,
heart beat, respiration, blood flow), and/or natural biochemical
variations (e.g., caused by metabolism during MRSI). Similarly, for
example, because in spectroscopic MRI the pulse sequence for
acquiring data encodes spectral information in addition to spatial
information, minimizing the time required for acquiring sufficient
spectral and spatial information to provide desired spectral
resolution and spatial localization is particularly important for
improving the clinical practicality and utility of spectroscopic
MRI.
[0008] Several factors contribute to better MRI image quality in
terms of high contrast, resolution, and acquisition speed. An
important parameter impacting image quality and acquisition speed
is the signal-to-noise ratio (SNR). Increasing SNR by increasing
the signal before the preamplifier of the MRI system is important
in terms of increasing the quality of the image. One way to improve
SNR is to increase the magnetic field strength of the magnet as the
SNR is proportional to the magnitude of the magnetic field. In
clinical applications, however, MRI has a ceiling on the field
strength of the magnet (the US FDA's current ceiling is 3T
(Tesla)). Other ways of improving the SNR involve, where possible,
reducing sample noise by reducing the field-of-view (where
possible), decreasing the distance between the sample and the RF
coils, and/or reducing RF coil noise.
[0009] Despite the relentless efforts and many advancements for
improving MRI, there is nevertheless a continuing need for yet
further improvements in MRI, such as for providing greater
contrast, improved SNR, higher acquisition speeds, higher spatial
and temporal resolution, and/or higher spectral resolution.
[0010] Additionally, a significant factor affecting further use of
MRI technology is the high cost associated with high magnetic field
systems, both for purchase and maintenance. Thus, it would be
advantageous to provide a high quality MRI imaging system that is
capable of being manufactured and/or maintained at reasonable cost,
permitting MRI technology to be more widely used.
SUMMARY OF INVENTION
[0011] Various embodiments of the present invention provide a
superconducting RF coil array which may be used in whole-body MRI
scanners and/or in dedicated MRI systems. Some embodiments of the
invention provide a superconducting RF coil array for at least one
of receiving signals from and transmitting signals to a sample
during magnetic resonance analysis of the sample, the
superconducting RF coil array comprising a thermally conductive
member configured to be cryogenically cooled, and a plurality of
coils elements comprising superconducting material, wherein each
coil element is thermally coupled to the thermally conductive
member and is configured for at least one of (i) receiving a
magnetic resonance signal from a spatial region that is contiguous
with and/or overlaps a spatial region from which at least one other
of the plurality of coil elements is configured to receive a signal
and (ii) transmitting a radiofrequency signal to a spatial region
that is contiguous with and/or overlaps a spatial region to which
at least one other of the plurality coil elements is configured to
transmit a radiofrequency signal.
[0012] In some embodiments, each coil element may comprise a thin
film superconducting coil disposed on a thermally conductive
substrate. The thermally conductive substrate may comprise at least
one of alumina and sapphire, and the thermally conductive member
may be implemented as an alumina or sapphire plate. In various
embodiments, the thermally conductive substrate of each coil
element may be directly or indirectly thermally coupled to the
thermally conductive member. For instance, in some embodiments, a
plurality of the thermally conductive substrates are each directly
thermally coupled to the thermally conductive member, and each of
at least one other of the thermally conductive substrates is
indirectly and not directly thermally coupled to said thermally
conductive member. Such other thermally conductive substrates may
be directly thermally coupled to at least one of the thermally
conductive substrates that are directly thermally coupled to the
thermally conductive member, such other thermally conductive
substrates thereby being indirectly thermally coupled to the
thermally conductive member. Thermally conductive spacer members
(e.g., standoffs) may alternatively or additionally be used to
thermally couple such other thermally conductive substrates to the
thermally conductive member, thereby providing indirect thermal
coupling between such other thermally conductive substrates and the
thermally conductive member.
[0013] In some embodiments, one or more of the superconducting
coils may comprise a high temperature superconductor, which may be
implemented, for example, as a thin film and/or with high
temperature superconducting tape. Alternatively or additionally,
neighboring superconducting coils may be configured such that they
are separate with respect to electrical conductivity and overlap
spatially. Such neighboring overlapping coils may be disposed on or
above a common surface of the thermally conductive member and/or
disposed on opposing surfaces of the thermally conductive
member.
[0014] In various embodiments, the superconducting RF coil array
may be configured as a linear array or a two-dimensional array or a
volumetric array. Coils may be implemented as receive-only,
transmit-only, or transmit-and-receive.
[0015] In some embodiments, each coil element comprises at least
one high temperature superconducting coil and a thermally
conductive substrate that is thermally coupled to (i) the at least
one high temperature superconducting coil and (ii) the thermally
conductive member. The thermally conductive substrate may be
configured as a generally cylindrical structure having an outer
surface upon which at least one superconducting coil is disposed.
For example, each thermally conductive substrate may (i) be
generally ring-shaped, having a small height relative to diameter,
and (ii) have one superconducting coil disposed about the outer
surface thereof.
[0016] In some embodiments, the superconducting RF coil array may
further comprise at least one thermally conductive substrate that
is thermally coupled to the thermally conductive member, and
wherein each coil element comprises a high temperature
superconducting coil. In some such embodiments, each of the at
least one thermally conductive substrate may be configured as a
generally cylindrical structure having an outer surface upon which
at least one of the high temperature superconducting coils is
disposed.
[0017] In various such implementations, each of the at least one
thermally conductive substrate includes at least two of the
superconducting coils configured such that neighboring
superconducting coils (i) are separate with respect to electrical
conductivity and (ii) are displaced and overlap along the axial
direction of the cylindrically-shaped thermally conductive
substrate. In some of these implementations, the thermally
conductive member may be generally planar and the RF coil array may
comprise two of the generally cylindrical thermally conductive
substrates, each having one axial end thereof thermally coupled to
a common surface of the thermally conductive member, and wherein
the dimensions of the thermally conductive substrates and their
separation are configured to provide the RF coil array as a
dedicated breast-imaging RF coil array.
[0018] In other various such implementations, the thermally
conductive substrate may include at least two of the
superconducting coils configured such that neighboring
superconducting coils (i) are separate with respect to electrical
conductivity and (ii) are displaced and overlap circumferentially
about the cylindrically-shaped thermally conductive substrate. The
number of circumferentially displaced and overlapping
superconducting coils may, for example, be at least four.
[0019] In some embodiments, each of the plurality of coil elements
may comprise a high temperature superconducting coil, and the
thermally conductive member may be configured as a generally
cylindrical structure having an outer surface upon which the high
temperature superconducting coils are disposed such that
neighboring superconducting coils (i) are separate with respect to
electrical conductivity and (ii) are displaced and overlap
circumferentially about the cylindrically-shaped thermally
conductive member.
[0020] In various embodiments, at least one of the coil elements
may be configured as a multiple resonance radiofrequency coil
element operable to receive signals corresponding to different
magnetic resonance frequencies at the same magnetic field.
[0021] It will be appreciated by those skilled in the art that the
foregoing brief description and the following detailed description
are exemplary and explanatory of the present invention, but are not
intended to be restrictive thereof or limiting of the advantages
which can be achieved by this invention. Additionally, it is
understood that the foregoing summary of the invention is
representative of some embodiments of the invention, and is neither
representative nor inclusive of all subject matter and embodiments
within the scope of the present invention. Thus, the accompanying
drawings, referred to herein and constituting a part hereof,
illustrate embodiments of this invention, and, together with the
detailed description, serve to explain principles of embodiments of
the invention. Aspects, features, and advantages of embodiments of
the invention, both as to structure and operation, will be
understood and will become more readily apparent when the invention
is considered in the light of the following description made in
conjunction with the accompanying drawings, in which like reference
numerals designate the same or similar parts throughout the various
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Aspects, features, and advantages of embodiments of the
invention, both as to structure and operation, will be understood
and will become more readily apparent when the invention is
considered in the light of the following description made in
conjunction with the accompanying drawings, in which like reference
numerals designate the same or similar parts throughout the various
figures, and wherein:
[0023] FIGS. 1A and 1B schematically depict a plan view and side
view, respectively, of an illustrative superconducting RF coil
array comprising generally circular coils, in accordance with some
embodiments of the present invention;
[0024] FIGS. 2A and 2B schematically depict a plan view and side
view, respectively, of an illustrative superconducting RF coil
array comprising generally rectangular coils, in accordance with
some embodiments of the present invention;
[0025] FIGS. 3A, 3B, and 3C schematically illustrate a top view,
side view, and oblique view, respectively, of a two-dimensional
array of overlapping coil elements, in accordance with some
embodiments of the present invention;
[0026] FIG. 4A and FIG. 4B schematically depict a plan view and a
cross-sectional side view, respectively, of an illustrative
superconducting RF coil array which employs high temperature
superconductor (HTS) tape for the coils, in accordance with some
embodiments of the present invention;
[0027] FIG. 5A and FIG. 5B schematically depict a plan view and a
side view, respectively, of an illustrative superconducting RF coil
array configured for breast imaging in a horizontal main magnetic
field, in accordance with some embodiments of the present
invention;
[0028] FIG. 6A and FIG. 6B schematically depict a plan view and a
side view, respectively, of an illustrative superconducting RF coil
array configured for breast imaging in a vertical main magnetic
field, in accordance with some embodiments of the present
invention;
[0029] FIG. 7A and FIG. 7B schematically depict a plan view and a
side view, respectively, of an illustrative superconducting RF coil
array configured for breast imaging in a vertical main magnetic
field, in accordance with some embodiments of the present
invention;
[0030] FIG. 7C and FIG. 7D schematically depict a plan view and a
side view, respectively, of an illustrative superconducting RF coil
array configured for breast imaging, in accordance with some
embodiments of the present invention;
[0031] FIGS. 8A and 8B schematically depict an HTS tape coil array
comprising a generally cylindrical thermally conductive support and
circumferentially disposed overlapping HTS coils, in accordance
with some embodiments of the present invention; and
[0032] FIGS. 9A and 9B show simulated results of the RF signal
profile associated with one HTS coil (FIG. 9B) and with a linear
array of five overlapping HTS coils according to some embodiments
of the present invention.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0033] The ensuing description discloses various embodiments of a
cryogenically cooled superconducting RF coil array which may be
used in whole-body MRI scanners and/or in dedicated MRI systems
(e.g., head-dedicated, limb-dedicated, breast-dedicated,
pediatric-dedicated, spine-dedicated, etc.). As will be further
understood in view of the ensuing description, embodiments of the
present invention include surface and volume coil array designs
and, in various implementations, two or more superconducting coil
array modules (e.g., two or more substantially planar coil array
modules, such as one or two dimensional surface coil array modules)
such as the herein described embodiments (and variations thereof)
may be used together (e.g., by independently positioning them
and/or by mounting them in a fixed spatial relationship with
respect to each other, such as by mechanically coupling them,
directly to each other or via one or more intervening support
structures) to essentially form a larger array. For example, two or
more superconducting surface coil array modules may be configured
to surround an extremity (e.g., thigh, head, etc.) or the torso
(e.g., for cardiac imaging) to provide for imaging over a desired
region of interest (ROI) (e.g., the desired field of view
(FOV)).
[0034] As will also be further understood in view of the ensuing
description, each superconducting coil array embodiment having a
certain general overall geometry (e.g., a substantially planar one
(e.g., linear) or two dimensional array, a generally cylindrical
array, etc.) may be configured according to various embodiments for
any of a variety of applications, such as for whole-body imaging,
head-dedicated imaging, extremity-dedicated imaging,
pediatric-dedicated imaging, etc.
[0035] According to the application for which the coil array may be
applied or intended, however, particular design parameters of the
coil array of a given general overall geometry may be varied. Such
design parameters may include, for example, dimensions of the
overall geometric configuration, the dimensions and/or geometry
(e.g., circular, square, hexagonal, etc.) and/or number of the coil
elements in the array, etc. By way of example, a generally
cylindrical array geometry may be applicable for whole-body
imaging, head-dedicated imaging, and breast-dedicated imaging;
however, if the array is particularly intended for one of these
applications, then its design parameters may be determined
accordingly (e.g., cylinder length and radius, number and
dimensions of coil elements, type of coil elements, spatial
arrangement of coil elements about the generally cylindrical
geometry, etc.). By way of further example in the context of
cylindrical geometries, a cylindrical array intended for
head-dedicated applications may be arranged such that the
cylindrical structure is open at both ends, whereas for
breast-dedicated applications one end of the cylindrical structure
may be closed (e.g., allowing for a cryocooler to be disposed
adjacent to the closed end).
[0036] Similarly, those skilled in the art will understand in view
of the ensuing description that the various design parameters and
particular configuration of superconducting coil array according to
embodiments of the present invention may also vary according to the
overall magnetic resonance system in which the coil will be used
(e.g., size, open, closed, number of RF channels available, etc.,
of the MR system).
[0037] Additionally, as will be further understood by those skilled
in the art in view of the ensuing description, a
cryogenically-cooled superconducting RF coil array coil according
to various embodiments of the present invention may be implemented
in myriad magnetic resonance imaging and spectroscopy systems, such
as systems employing conventional copper gradient coils, systems
employing superconducting gradient coils (e.g., such as disclosed
in U.S. patent application Ser. No. 12/416,606, filed Apr. 1, 2009,
and in Provisional Application No. 61/170,135, filed Apr. 17, 2009,
each of which is hereby incorporated by reference in its entirety),
whole body systems, dedicated head-only systems, systems with a
vertically or horizontally oriented main magnetic field, open or
closed systems, etc. Similarly, it will also be understood by those
skilled in the art that while various portions of the ensuing
description may be set forth in the context of an MRI system that
may be used for structural examination of a sample (e.g., an
individual such as a patient, an animal such as a dog or a rat, a
tissue sample, or an other living or non-living object), various
embodiments of the present invention may be employed in connection
with magnetic resonance (MR) systems operated and/or configured for
other modalities, such as functional MRI, diffusion weighted and/or
diffusion tensor MRI, MR spectroscopy and/or spectroscopic imaging,
etc. Additionally, as used herein, MRI includes and embraces
magnetic resonance spectroscopic imaging, diffusion tensor imaging
(DTI), as well as any other imaging modality based on nuclear
magnetic resonance.
[0038] Those skilled in the art will also understand from the
ensuing description that superconducting coil arrays according to
embodiments of the present invention may be configured or adapted
for use as receive-only, or transmit-only, or
transmit-and-receive.
[0039] FIGS. 1A and 1B schematically depict a plan view (with the
contours of underlying features depicted for clarity) and side
view, respectively, of an illustrative superconducting RF coil
array 10, in accordance with some embodiments of the present
invention. More specifically, FIGS. 1A and 1B illustrate a
configuration of five superconducting RF coil elements 14a-14e
(also referred to herein as coils 14a-14e, and collectively as
superconductor RF coil elements 14 or coils 14) arranged in two
layers to provide a linear array.
[0040] As shown, coil elements 14a, 14c, and 14e (referred to,
collectively, for convenience as the "lower coil elements") are
each disposed in direct thermal contact with a heat conducting
substrate (plate) 12, and coil elements 14b and 14d (referred to,
collectively, for convenience as the "upper coil elements") are
disposed above the lower coil elements and are thermally coupled to
the lower coil elements and to the plate 12 via standoffs 16a and
16b (referred to collectively as standoffs 16), respectively. Epoxy
and/or thermal grease/compound (which are not shown) may be
provided between the coils 14 and plate 12 and/or standoffs 16 to
provide thermal and mechanical contact therebetween.
[0041] Heat conducting plate 12 and each heat conducting standoff
16 may be formed, for example, of any of one or more high thermal
conductivity materials, such as sapphire or alumina, or other
non-metallic high thermal conductivity material, such as high
thermal conductivity ceramic. As further described hereinbelow,
heat conducting plate 12 is thermally coupled (not shown herein) to
a cryogenic cooling system, and superconducting coil array 10 is
enclosed within a housing that maintains array 10 within a vacuum
(e.g., at least a low vacuum). In various alternative embodiments,
heat conducting plate 12 may be narrower than the diameter of the
coil elements and, in some embodiments, plate 12 may be implemented
as two separate, parallel elongated members that each contact a
backside portion of coil elements 14a, 14c, 14e.
[0042] In FIGS. 1A and 1B, each coil element 14 comprises a
substrate 15 (e.g., a sapphire wafer) and a thin film
superconducting coil 17 (also referred to as a trace 17). In the
embodiment of FIGS. 1A and 1B, thin film traces 17 are formed on
the upper surface (facing away from plate 12) of substrates 15,
though in various alternative embodiments the traces may be
disposed on the lower surface (facing plate 12) of substrates
15.
[0043] More particularly, in accordance with some embodiments of
the present invention, the trace 17 of each RF coil element 14a-14e
may be implemented as a high temperature superconductor (HTS), such
as YBCO and/or BSCCO, etc. (e.g., using an HTS thin film or HTS
tape), though a low temperature superconductor (LTS) may be used in
various embodiments. For example, in some embodiments, each of RF
coil elements 14a-14e is an HTS thin film spiral coil and/or an HTS
thin film spiral-interdigitated coil on a substrate such as
sapphire or lanthanum aluminate. The design and fabrication of such
coils is further described in and/or may be further understood in
view of, for example, Ma et al., "Superconducting RF Coils for
Clinical MR Imaging at Low Field," Academic Radiology, vol. 10, no.
9, September 2003, pp. 978-987; Gao et al., "Simulation of the
Sensitivity of HTS Coil and Coil Array for Head Imaging,"
ISMRM-2003, no. 1412; Fang et al., "Design of Superconducting MRI
Surface Coil by Using Method of Moment," IEEE Trans. on Applied
Superconductivity, vol. 12, no. 2, pp. 1823-1827 (2002); and Miller
et al., "Performance of a High Temperature Superconducting Probe
for In Vivo Microscopy at 2.0 T," Magnetic Resonance in Medicine,
41:72-79 (1999), each of which is incorporated by reference herein
in its entirety. Accordingly, in some embodiments, superconducting
RF coil array 10 is implemented as an HTS thin film RF coil
array.
[0044] The design of each coil element (e.g., trace diameter,
number of turns) may depend on the application, and may include
considerations of homogeneity, signal-to-noise ratio, and field of
view (FOV). Similar considerations may factor into determining the
number of coil elements that will be employed (e.g., while five
coil elements are shown in the embodiment of FIGS. 1A and 1B, a
linear array may include fewer or more coil elements). As depicted
in FIGS. 1A and 1B, the traces 17 of neighboring coil elements 14
overlap, with this overlap being provided by vertically displacing
neighboring coil elements. Those skilled in the art will understand
that the amount of overlap between neighboring coils may be
optimized with respect to decoupling.
[0045] As indicated, standoffs 16 may assist in thermal conduction
(e.g., between upper coils and plate 12) and in mechanical support
(e.g., assisting support of the upper coils). Using standoffs 16a
disposed over the traces of the lower coil elements may also assist
in preventing damage that may occur to these traces if the upper
coil elements directly contacted the lower coil elements. In
various embodiments, standoffs 16a may include a narrow recessed
region that is disposed over the underlying trace of the lower coil
elements such that the lower trace is not mechanically contacted by
the overlying standoff 16a.
[0046] It will be understood that in various alternative
embodiments, one or more (e.g., all) of the standoffs 16 may be
eliminated. For example, some embodiments may include the standoffs
16a between lower and upper coil elements while not employing
standoffs 16b between plate 12 and upper coil elements 14b, 14d, as
the inter-coil element standoffs 16a may provide sufficient thermal
conduction for cooling the upper coil elements. Additionally or
alternatively, various embodiments may include an additional high
thermal conductivity plate in direct contact with upper coil
elements 14b and 14d.
[0047] By way of non-limiting example, for illustrative purposes,
in some embodiments, plate 12 may have a thickness of about 3-5 mm,
each coil element trace 17 may have a diameter of about 1 cm to
about 10 cm or greater, each coil element substrate 15 may have a
thickness of about 0.3 mm to about 0.6 mm, and standoffs 16a may
have a thickness of about 0.1 mm to about 0.5 mm.
[0048] While not shown in FIGS. 1A and 1B, an electronics module
for each coil element may be disposed on plate 12 and/or substrates
15, and may include at least a preamplifier, and may also include
additional circuitry, such as for impedance matching, decoupling,
etc.
[0049] As indicated above, superconducting RF coil array 10
depicted in FIGS. 1A and 1B is disposed in a vacuum chamber and is
cooled by plate 12 being thermally coupled with a cryogenic cooling
system. In various embodiments, the coils elements 14a-14e may be
cooled to a temperature in the range of about 4K to 100K, and more
particularly, to a temperature below the critical temperature of
the superconducting material (e.g., in some embodiments, below the
critical temperature of a high temperature superconductor (HTS)
material used for the RF coils 17). In various embodiments, the
cryogenic cooling system may comprise a cryocooler implemented as
any of various single stage or multi-stage cryocoolers, such as,
for example, a Gifford McMahon (GM) cryocooler, a pulse tube (PT)
cooler, a Joule-Thomson (JT) cooler, a Stirling cooler, or other
cryocooler. In various alternative embodiments, the superconductor
RF coil array 10 may be configured for cooling such that coils 17
are cooled by a cryogen, such as liquid helium and liquid
nitrogen.
[0050] While not shown herein, the vacuum chamber may be
implemented, for example, as a double-walled Dewar structure. More
specifically, in accordance with some embodiments of the present
invention, the vacuum chamber may comprise a double-walled Dewar
made of glass and/or other non-conductive, mechanically strong
material(s), such as G10, RF4, plastic, and/or ceramic. In various
embodiments, a double-walled Dewar may be implemented in accordance
with, or similar to, the hermetically sealed double-walled
structures (and vacuum thermal isolation housing) described in U.S.
application Ser. No. 12/212,122, filed Sep. 17, 2008, in U.S.
application Ser. No. 12/212,147, filed Sep. 17, 2008, and in U.S.
Provisional Application No. 61/171,074, filed Apr. 20, 2009, each
of which is herein incorporated by reference in its entirety. While
not discussed in detail hereinbelow, it will be understood that the
embodiments presented below are also implemented within a vacuum
chamber and are thermally coupled for cryogenic cooling.
[0051] It will be understood that two or more linear arrays such
as, or in accordance with, the linear array depicted in FIGS. 1A
and 1B may be combined to provide a two or three dimensional array
assembly. For example, in some embodiments, eight linear arrays
(e.g., each having two or more linearly arranged coil elements) may
be assembled into a generally cylindrical, octagonal arrangement,
with each linear array extending longitudinally, and azimuthally
displaced by about 45 degrees. Such a configuration may be
implemented similarly to embodiments of the superconductor RF head
coil array disclosed in Provisional Application No. 61/171,074,
filed Apr. 20, 2009, which is herein incorporated by reference in
its entirety.
[0052] As understood in view of the foregoing description, in
accordance with various embodiments of the present invention,
superconducting RF coil array 10 may be implemented as a
receive-only array, with an RF transmitter being implemented as a
separate RF coil (not shown), which in various embodiments may be a
conventional (e.g., non-superconducting, such as a conventional
copper RF coil) RF transmitter coil or a superconducting RF
transmitting coil. In some embodiments, superconducting RF coil
array 10 may be implemented as a transmit and receive coil array (a
transceiver array), with each superconducting RF coil element 14
being used for both transmission and reception of RF signals.
[0053] In accordance with various embodiments of the present
invention, one or more of the superconducting RF coil elements 14
may be implemented as a multiple resonance RF coil element (e.g.,
comprising two or more receiving coils having different resonant
frequencies, such as for detecting sodium and hydrogen resonances
at a given magnetic field (e.g., at 3 Tesla (T)).
[0054] Referring now to FIGS. 2A and 2B, shown are a plan view
(with the contours of underlying features depicted for clarity) and
side view, respectively, of an illustrative superconducting RF coil
array 20, in accordance with some embodiments of the present
invention. More specifically, FIGS. 2A and 2B illustrate a
configuration of five superconducting RF coil elements 24a-24e
(referred to herein collectively as superconductor RF coil elements
24 or coils 24) arranged in two layers to provide a linear array,
similar to the linear array of FIGS. 1A and 1B, formed on a heat
conducting plate 22. Compared to the linear array of FIGS. 1A and
1B, the linear array of FIGS. 2A and 2B includes substantially
rectangular (thin film HTS) traces 27 and substantially rectangular
substrates 25. Rectangular substrates 25 may be formed by cutting
or scribing a circular substrate, such as a circular sapphire or
alumina substrate. Rectangular shaped traces may provide for
improved image reconstruction due to the substantially constant
trace overlap distance. Rectangular coil elements may also be
better suited than circular coil elements for forming
two-dimensional arrays.
[0055] For example, FIGS. 3A-3C illustrate a two-dimensional
(2.times.5) rectangular array 30 of substantially rectangular coil
elements 34a1, 34b1 . . . 34e1, 34a2, 34b2 . . . 34e2, having
substantially rectangular substrates and substantially rectangular
traces 37, assembled in four layers using a standoff element 36
directly coupled between heat conducting plate 32 and the coil
elements of the second uppermost layer (comprising elements 34a2,
34c2, and 34e2), thereby providing thermal conduction and
mechanical support for the elements of the second uppermost layer
and those of the overlying uppermost layer (comprising elements
34b2, 34d2). More specifically, FIG. 3A is a top view (with the
contours of underlying features depicted for clarity), FIG. 3B is a
side view, and FIG. 3C is an oblique view (with the contours of
underlying features depicted for clarity). As shown, the traces 37
of each adjacent coil element overlap each other (i.e., a coil
element trace overlaps the traces of its nearest neighbors and
next-nearest neighbors (i.e., diagonally disposed neighbors). It
will be understood that in various implementations, standoff disk
elements may also be included to directly couple elements of the
lowermost layer (comprising elements 34a1, 34c1, 34e1) and elements
of the second uppermost layer (comprising elements 34a2, 34c2, and
34e2) in regions where the lowermost layer elements and second
uppermost layer elements overlap. It will also be understood that
rather than employing an elongated standoff element 36, separate
standoff disks may be disposed between plate 32 and each of coil
elements 34a2, 34c2, and 34e2. Those skilled in the art will
understand that such a four-layer construction as depicted in the
embodiment of FIGS. 3A-3C may be used to provide a two-dimensional
array of overlapping coil elements of arbitrary dimension (e.g.,
3.times.5, 4.times.5, 4.times.8, 8.times.8, etc.).
[0056] Referring now to FIG. 4A and FIG. 4B, shown are a plan view
(with the contours of underlying features depicted for clarity) and
a cross-sectional side view (sectioned along the diameter of coil
elements), respectively, of an illustrative superconducting RF coil
array 40 which employs high temperature superconductor (HTS) tape
for the coils, in accordance with some embodiments of the present
invention. As shown, array 40 comprises three linearly arranged
coil elements 44a, 44b, 44c, alternately disposed on opposite
surfaces of heat conducting plate 42. Each coil element comprises a
thermally conductive (e.g., alumina) supporting ring 43, an HTS
coil 47, and an electrical circuit 49. As shown, thermally
conductive (e.g., alumina) supporting ring 43 is thermally coupled
to heat conducting (e.g., alumina or sapphire) plate 42, and HTS
tape 47 is wrapped circumferentially around alumina supporting ring
43 and may be fixed in place by attachment (e.g., soldering) of
electrical circuit 49. Epoxy and/or thermal grease may also be used
to thermally couple and affix tape 47 to the circumferential
surface of supporting ring 43. Electrical circuit 49 may include at
least a preamplifier, and may also include additional circuitry,
such as for impedance matching, decoupling, etc. By way of
non-limiting example, for purposes of illustration, ring 43 may
have a diameter between about 2.5 cm to about 25 cm or greater, and
may have a height (along cylindrical axis) of about 5 mm to about
25 mm; HTS tape 47 may have a thickness of about 0.1 mm to about
0.5 mm and a width of about 5 mm to about 13 mm and may be wrapped
a single loop around alumina ring 43.
[0057] Referring now to FIG. 5A and FIG. 5B, shown are a plan view
(with the contours of underlying features depicted for clarity) and
a side view, respectively, of an illustrative superconducting RF
coil array 50 which employs high temperature superconductor (HTS)
tape for the coils and is configured for breast imaging in a
horizontal main magnetic field (i.e., orthogonal to the
longitudinal axis of the generally cylindrically shaped coil
elements), in accordance with some embodiments of the present
invention. The construction of coil array 50 is similar to coil
array 40 at least insofar as the coil elements are implemented as
HTS tape mounted about a generally cylindrical thermally conductive
(e.g., alumina) support ring which is thermally coupled to a heat
conducting plate. More specifically, as shown, each generally
cylindrical coil element of array 50 comprises a thermally
conductive (e.g., alumina) supporting ring 53, an HTS coil 57, and
an electrical circuit 59. As shown, thermally conductive (e.g.,
alumina) supporting ring 53 is thermally coupled to heat conducting
(e.g., alumina or sapphire) plate 52, and HTS tape 57 is wrapped
circumferentially around alumina supporting ring 53 in a coil
configuration for use with a horizontal magnetic field, and may be
fixed in place by attachment (e.g., soldering) of electrical
circuit 59. Epoxy and/or thermal grease may also be used to
thermally couple and affix tape 57 to the circumferential surface
of supporting ring 53. Electrical circuit 59 may include at least a
preamplifier, and may also include additional circuitry, such as
for impedance matching, decoupling, etc. By way of non-limiting
example, for purposes of illustration, ring 43 may have a diameter
of about 15 cm to about 25 cm or greater, and may have a height
(along cylindrical axis) of about 15 cm to about 25 cm or
greater.
[0058] Referring now to FIG. 6A and FIG. 6B, shown are a plan view
(with the contours of underlying features depicted for clarity) and
a side view, respectively, of an illustrative superconducting RF
coil array 60 which employs high temperature superconductor (HTS)
tape for the coils and is configured for breast imaging in a
vertical main magnetic field (i.e., parallel to the longitudinal
axis of the generally cylindrically shaped coil elements), in
accordance with some embodiments of the present invention. As
shown, each generally cylindrical coil element of array 60
comprises a thermally conductive (e.g., alumina) supporting ring
63, an HTS coil 67, and an electrical circuit 69, and the thermally
conductive (e.g., alumina) supporting ring 63 is thermally coupled
to heat conducting (e.g., alumina or sapphire) plate 62. The
construction of coil array 60 is similar to coil array 50; however,
HTS coils 67 are wound in a configuration suitable for use in a
vertical field (e.g., a saddle coil configuration).
[0059] Referring now to FIG. 7A and FIG. 7B, shown are a plan view
(with the contours of underlying features depicted for clarity) and
a side view, respectively, of an illustrative superconducting RF
coil array 70 which employs high temperature superconductor (HTS)
tape for the coils and is configured for breast imaging in a
vertical main magnetic field (i.e., parallel to the longitudinal
axis of the generally cylindrically shaped coil elements), in
accordance with some embodiments of the present invention. As
shown, each generally cylindrical coil element of array 70
comprises a thermally conductive (e.g., alumina) supporting ring
73, HTS tape 77, and an electrical circuit 79, and the thermally
conductive (e.g., alumina) supporting ring 73 is thermally coupled
to heat conducting (e.g., alumina or sapphire) plate 72. The
construction of coil array 70 is similar to coil array 60; however,
the HTS tape 77 associated with each supporting ring is implemented
as two overlapping coils to provide a coil array for each generally
cylindrical element. More specifically, as shown, overlapping HTS
coils 77a1 (upper) and 77b1 (lower) are wound on one common
supporting ring 73, and overlapping HTS coils 77a2 (upper) and 77b2
(lower) are wound on the other common supporting ring 73, with each
coil 77a1, 77b1, 77a2, 77b2 wound in a configuration suitable for
use in a vertical field (e.g., a saddle coil configuration).
Electrical insulators 71 are disposed where the upper and lower
coils overlap to separate the overlapping upper and lower coils.
The coil group 77a1/77b1 and group 77a2/77b2 can be arranged such
that their respective associated fields (B1 field) are orthogonal
with each other to minimize the coupling between them, as shown in
FIG. 7C and FIG. 7D.
[0060] FIGS. 8A and 8B schematically depict an HTS tape coil array
comprising a generally cylindrical thermally conductive support
(e.g., alumina tube) 83 and HTS coils (87) implemented as HTS tape
and formed on the alumina tube directly or through a thin plastic
sheet, in accordance with some embodiments of the present
invention. More specifically, FIG. 8B depicts the overlapping six
element coil array configuration that is circumferentially disposed
about support 83. As noted, high temperature superconductor (HTS)
tape is used for the coils, in accordance with various embodiments.
Additionally, as shown, electrical insulators (dielectric spacers)
81 are disposed where the coils overlap to separate the overlapping
coils.
[0061] FIGS. 9A and 9B show simulated results of the RF signal
profile associated with one HTS coil (FIG. 9A) and with a linear
array of five overlapping HTS coils, illustrating the uniformity
that may be provided by such arrays.
[0062] Additionally, as indicated above, it is understood that
according to some embodiments of the present invention, a
cryogenically-cooled superconducting RF coil array coil according
to various embodiments of the present invention may be implemented
in a magnetic resonance imaging system that employs superconducting
gradient coils such as those disclosed in U.S. patent application
Ser. No. 12/416,606, filed Apr. 1, 2009, and in Provisional
Application No. 61/170,135, filed Apr. 17, 2009, each of which is
hereby incorporated by reference in its entirety.
[0063] The present invention has been illustrated and described
with respect to specific embodiments thereof, which embodiments are
merely illustrative of the principles of the invention and are not
intended to be exclusive or otherwise limiting embodiments.
Accordingly, although the above description of illustrative
embodiments of the present invention, as well as various
illustrative modifications and features thereof, provides many
specificities, these enabling details should not be construed as
limiting the scope of the invention, and it will be readily
understood by those persons skilled in the art that the present
invention is susceptible to many modifications, adaptations,
variations, omissions, additions, and equivalent implementations
without departing from this scope and without diminishing its
attendant advantages. For instance, except to the extent necessary
or inherent in the processes themselves, no particular order to
steps or stages of methods or processes described in this
disclosure, including the figures, is implied. In many cases the
order of process steps may be varied, and various illustrative
steps may be combined, altered, or omitted, without changing the
purpose, effect or import of the methods described. It is further
noted that the terms and expressions have been used as terms of
description and not terms of limitation. There is no intention to
use the terms or expressions to exclude any equivalents of features
shown and described or portions thereof. Additionally, the present
invention may be practiced without necessarily providing one or
more of the advantages described herein or otherwise understood in
view of the disclosure and/or that may be realized in some
embodiments thereof. It is therefore intended that the present
invention is not limited to the disclosed embodiments but should be
defined in accordance with the claims that follow.
* * * * *