U.S. patent application number 17/101591 was filed with the patent office on 2021-05-27 for motion correction and motion reduction during dedicated magnetic resonance imaging.
This patent application is currently assigned to Siemens Healthcare GmbH. The applicant listed for this patent is Siemens Healthcare GmbH. Invention is credited to David Grodzki, Carmel Hayes, Rene Kartmann, Mario Zeller.
Application Number | 20210156945 17/101591 |
Document ID | / |
Family ID | 1000005325655 |
Filed Date | 2021-05-27 |
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United States Patent
Application |
20210156945 |
Kind Code |
A1 |
Grodzki; David ; et
al. |
May 27, 2021 |
MOTION CORRECTION AND MOTION REDUCTION DURING DEDICATED MAGNETIC
RESONANCE IMAGING
Abstract
In a method and system for reducing motion artifacts in magnetic
resonance image data acquired from a facial region of a patient,
the patient is positioned in an imaging region of a magnetic
resonance imaging device configured to perform a magnetic resonance
measurement of the facial region of the patient, the magnetic
resonance measurement is performed to acquire magnetic resonance
image data of the facial region of the patient, and a motion
correction technique is employed exploiting an accessibility to the
facial region of the patient during the magnetic resonance
measurement. The motion correction technique advantageously reduces
an influence of a patient motion on the magnetic resonance image
data.
Inventors: |
Grodzki; David; (Erlangen,
DE) ; Zeller; Mario; (Erlangen, DE) ; Hayes;
Carmel; (Muenchen, DE) ; Kartmann; Rene;
(Nuernberg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Siemens Healthcare GmbH |
Erlangen |
|
DE |
|
|
Assignee: |
Siemens Healthcare GmbH
Erlangen
DE
|
Family ID: |
1000005325655 |
Appl. No.: |
17/101591 |
Filed: |
November 23, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62941163 |
Nov 27, 2019 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/7214 20130101;
G01R 33/543 20130101; A61B 5/4547 20130101; G01R 33/5608 20130101;
A61B 2090/3912 20160201; A61B 2090/3954 20160201; G01R 33/283
20130101; G01R 33/30 20130101; A61B 5/70 20130101; G01R 33/56509
20130101; A61C 5/007 20130101; A61B 2576/02 20130101; A61B 5/055
20130101 |
International
Class: |
G01R 33/565 20060101
G01R033/565; G01R 33/30 20060101 G01R033/30; G01R 33/28 20060101
G01R033/28; G01R 33/54 20060101 G01R033/54; G01R 33/56 20060101
G01R033/56; A61B 5/055 20060101 A61B005/055; A61B 5/00 20060101
A61B005/00; A61C 5/00 20060101 A61C005/00 |
Claims
1. A method for reducing motion artifacts in magnetic resonance
image data acquired from a facial region of a patient, the method
comprising: positioning the patient in an imaging region of a
magnetic resonance imaging (MRI) device configured to perform a
magnetic resonance (MR) measurement of the facial region of the
patient; performing the MR measurement to acquire MR image data of
the facial region of the patient; and employing a motion correction
technique exploiting an accessibility to the facial region of the
patient during the MR measurement, wherein the motion correction
technique reduces an influence of a patient motion on the MR image
data.
2. The method according to claim 1, wherein: the facial region
comprises a teeth region and/or jaw region of the patient; and the
motion correction technique comprises positioning a mouth guard in
an intraoral region of the patient to suppress movement of the
teeth region and/or the jaw region of the patient while performing
the MR measurement.
3. The method according to claim 2, wherein: the mouth guard
comprises a suction pipe; and the motion correction technique
comprises draining saliva from the intraoral region of the patient
via the suction pipe while performing the MR measurement to reduce
a need for swallowing.
4. The method according to claim 2, wherein: the mouth guard
comprises a magnetic resonance visible marker; the motion
correction technique comprises detecting the MR visible marker
during the MR measurement; and the motion correction technique
comprises a prospective and/or retrospective correction of the MR
image data in dependence of a displacement of the MR visible marker
due to motion of the patient.
5. The method according to claim 3, wherein: the mouth guard
comprises a magnetic resonance visible marker; the motion
correction technique comprises detecting the MR visible marker
during the MR measurement; and the motion correction technique
comprises a prospective and/or retrospective correction of the MR
image data in dependence of a displacement of the MR visible marker
due to motion of the patient.
6. The method according to claim 1, wherein the motion correction
technique comprises: positioning a mechanical element in contact
with the facial region of the patient, the mechanical element
including a motion sensor; determining a displacement of the
mechanical element due to motion of the patient while performing
the MR measurement; and performing a prospective and/or
retrospective correction of the MR image data based on the
displacement of the mechanical element.
7. The method according to claim 1, wherein the motion correction
technique comprises: acquiring optical image data of the facial
region of the patient using an optical sensor while performing the
MR measurement; and performing a prospective and/or retrospective
correction of the MR image data based on the optical image
data.
8. The method according to claim 7, wherein the facial region of
the patient is an eye region of the patient and wherein the optical
image data is acquired from the eye of the patient.
9. The method according to claim 8, wherein the motion correction
technique comprises a prospective and/or retrospective correction
of the MR image data based on a detected motion of a pupil of the
eye of the patient.
10. The method according to claim 2, wherein: the MR measurement
comprises acquiring separate MR image data from a lower jaw and an
upper jaw of the teeth region and/or jaw region; and the motion
correction technique comprises a prospective and/or retrospective
correction of the MR image data based on a rigid model of the lower
jaw and the upper jaw of the patient.
11. The method according to claim 2, further comprising: acquiring
a projection image of the facial region of the patient, the motion
correction technique including adjusting a projection direction
based on a detected motion of the facial region of the patient.
12. The method according to claim 11, further comprising:
performing a navigator measurement of the facial region of the
patient to acquire navigator data, the motion correction technique
including detecting a displacement of a characteristic feature in
the navigator data and prospectively and/or retrospectively
correcting the MR image data based on the displacement of the
characteristic feature.
13. The method according to claim 2, further comprising: performing
a navigator measurement of the facial region of the patient to
acquire navigator data, the motion correction technique including
detecting a displacement of a characteristic feature in the
navigator data and prospectively and/or retrospectively correcting
the MR image data based on the displacement of the characteristic
feature.
14. A computer program which includes a program and is directly
loadable into a memory of the MRI device, when executed by a
processor of the MRI device, causes the processor to perform the
method as claimed in claim 1.
15. A non-transitory computer-readable storage medium with an
executable program stored thereon, that when executed, instructs a
processor to perform the method of claim 1.
16. A magnetic resonance imaging (MRI) system, comprising: a
magnetic resonance (MR) scanner configured to perform a magnetic
resonance (MR) measurement of a facial region of a patient; and a
controller that is configured to: position a patient in an imaging
region of the MR scanner; control the MR scanner to perform the MR
measurement to acquire MR image data of the facial region of the
patient; and preform a motion correction technique exploiting an
accessibility to the facial region of the patient during the MR
measurement, wherein the motion correction technique reduces an
influence of a patient motion on the MR image data.
17. The MRI system according to claim 16, wherein the controller is
further configured to control the MR scanner to acquire a
projection image of the facial region of the patient, wherein the
motion correction technique includes adjusting a projection
direction based on a detected motion of the facial region of the
patient.
18. The MRI system according to claim 17, wherein the controller is
further configured to control the MR scanner to perform a navigator
measurement of the facial region of the patient to acquire
navigator data, wherein the motion correction technique includes
detecting a displacement of a characteristic feature in the
navigator data and prospectively and/or retrospectively correcting
the MR image data based on the displacement of the characteristic
feature.
19. The MRI system according to claim 16, wherein the controller is
further configured to control the MR scanner to perform a navigator
measurement of the facial region of the patient to acquire
navigator data, wherein the motion correction technique includes
detecting a displacement of a characteristic feature in the
navigator data and prospectively and/or retrospectively correcting
the MR image data based on the displacement of the characteristic
feature.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims priority to, and the benefit
of, U.S. Provisional Patent Application No. 62/941,163, filed Nov.
27, 2019, which is incorporated herein by reference in its
entirety.
BACKGROUND
Field
[0002] The disclosure relates to a method for reducing motion
artifacts in magnetic resonance image data acquired from a facial
region of a patient, a magnetic resonance imaging system,
comprising a magnetic resonance imaging device and a processor,
wherein the processor is configured to coordinate and execute an
inventive method by means of the magnetic resonance imaging
device.
Related Art
[0003] The facial region accommodates a number of important sensory
organs and bodily functions which are important, for example, for
communication, ingestion and perception. The facial region of the
body may be affected by a multitude of different diseases, which
may drastically affect the way of living of an individual.
Typically, diseases of different parts of the facial region are
diagnosed using different diagnostic techniques. For example,
diseases of the teeth and the periodontium, such as caries or
periodontitis, are typically diagnosed with X-ray-based imaging
methods. For this purpose, conventional or digital X-ray projection
methods, and recently also three-dimensional (3D) X-ray methods,
are used. An example of a three-dimensional X-ray method is digital
volume tomography, which can be used for imaging of the teeth and
the viscerocranium.
[0004] A major disadvantage of X-ray-based imaging methods is
constituted by the need for an application of ionizing radiation
for imaging. Magnetic resonance tomography is an imaging method
that avoids using ionizing radiation. Furthermore, magnetic
resonance tomography typically provides an enhanced soft tissue
contrast in comparison to X-ray-based imaging methods and natively
supports three-dimensional imaging of an examination object. Thus,
magnetic resonance tomography represents a potential alternative to
known X-ray methods for imaging teeth and/or jaws of the
examination object as well as diagnosing dental diseases. However,
other regions of the head of the patient may also benefit from
magnetic resonance tomography. For example, imaging of the eyes is
currently performed with dedicated cameras, providing essentially a
front-view image of the eye. Magnetic resonance tomography may
facilitate the diagnosis of eye diseases by providing
three-dimensional information on the orbit and the eye cavity.
[0005] Magnetic resonance tomography represents a prominent imaging
method for acquiring images of an interior of the examination
object. In order to carry out a magnetic resonance measurement, the
examination object is positioned in a strong and homogeneous,
static magnetic field (B0 field) of a magnetic resonance device.
The static magnetic field may comprise magnetic field strengths of
0.2 Tesla to 7 Tesla in order to align nuclear spins within the
examination object with the static magnetic field. For triggering
so-called nuclear spin resonances, radiofrequency excitation pulses
are emitted into the examination subject. Each radiofrequency
excitation pulse causes a magnetization of nuclear spins within the
examination object to deviate from the static magnetic field by an
amount which is known as the flip angle. A radiofrequency
excitation pulse may be provided via a high frequency magnetic
field alternating with a frequency which corresponds to the Larmor
frequency at the respective static magnetic field strength. Excited
nuclear spins may exhibit a rotating and decaying magnetization
(magnetic resonance signal), which can be detected using dedicated
radiofrequency antennas. For spatial encoding of measured data,
rapidly switched magnetic gradient fields are superimposed on the
static magnetic field.
[0006] The received nuclear magnetic resonances are typically
digitized and stored as complex values in a k-space matrix. This
k-space matrix provides a basis for a reconstruction of magnetic
resonance images and for determining spectroscopic data. A magnetic
resonance image is typically reconstructed by means of a
multi-dimensional Fourier transformation of the k-space matrix.
[0007] In avoiding ionizing radiation, magnetic resonance
tomography is particularly suitable for continuous or repetitious
diagnostic monitoring of dental diseases and/or tooth development,
for example within the framework of a longitudinal imaging study.
Longitudinal imaging studies may comprise carrying out a plurality
of imaging examinations in order to determine a progression of a
disease or a success of a therapeutic treatment over an elongated
period of time. A disadvantage usually associated with magnetic
resonance tomography is the amount of time required for performing
the magnetic resonance measurement in comparison to other imaging
methods. This poses a challenge for acquiring magnetic resonance
image data of the patient, particularly the face region of the
patient, as this region is associated with frequent, often
unintentional movement such as blinking or swallowing. Patient
motion may cause image artifacts like diffuse image noise or
ghosting effects, thus compromising a quality of acquired magnetic
resonance images as well as the diagnosis based thereon.
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
[0008] The accompanying drawings, which are incorporated herein and
form a part of the specification, illustrate the embodiments of the
present disclosure and, together with the description, further
serve to explain the principles of the embodiments and to enable a
person skilled in the pertinent art to make and use the
embodiments.
[0009] FIG. 1 is a schematic representation of a magnetic resonance
imaging system according to an exemplary embodiment of the
disclosure.
[0010] FIG. 2 is a schematic representation of a magnetic resonance
imaging system according to an exemplary embodiment of the
disclosure.
[0011] FIG. 3 is a schematic representation of a headrest according
to an exemplary embodiment of the disclosure.
[0012] FIG. 4 is a schematic representation of a mouth guard
according to an exemplary embodiment of the disclosure.
[0013] FIG. 5 is a flowchart of a method for reducing motion
artifacts according to an exemplary embodiment of the
disclosure.
[0014] The exemplary embodiments of the present disclosure will be
described with reference to the accompanying drawings. Elements,
features and components that are identical, functionally identical
and have the same effect are--insofar as is not stated
otherwise--respectively provided with the same reference
character.
DETAILED DESCRIPTION
[0015] In the following description, numerous specific details are
set forth in order to provide a thorough understanding of the
embodiments of the present disclosure. However, it will be apparent
to those skilled in the art that the embodiments, including
structures, systems, and methods, may be practiced without these
specific details. The description and representation herein are the
common means used by those experienced or skilled in the art to
most effectively convey the substance of their work to others
skilled in the art. In other instances, well-known methods,
procedures, components, and circuitry have not been described in
detail to avoid unnecessarily obscuring embodiments of the
disclosure. The connections shown in the figures between functional
units or other elements can also be implemented as indirect
connections, wherein a connection can be wireless or wired.
Functional units can be implemented as hardware, software or a
combination of hardware and software.
[0016] It is therefore an object of the disclosure to reduce an
influence of patient motion on magnetic resonance image data.
[0017] This object is achieved by a method, a magnetic resonance
imaging system and a computer program product according to the
disclosure.
[0018] The inventive method reduces motion artifacts in magnetic
resonance image data acquired from a facial region of a patient. A
motion artifact may represent any blurring, streaking, smearing
and/or shading as well as diffuse image noise and/or ghosting in
magnetic resonance images caused by a movement of the patient
during a magnetic resonance measurement. The movement may comprise
voluntary and/or involuntary movement. Examples for common patient
movements are, amongst others, tilting or turning a head, blinking,
swallowing, rolling an eye, moving a tongue, moving a cheek, moving
a lip, moving a jaw, but also respiratory motion and so forth.
[0019] In one step of the inventive method, the patient is
positioned in an imaging region of a magnetic resonance imaging
device configured to perform a magnetic resonance measurement of
the facial region of the patient. An imaging region may represent a
volume wherein the patient is positioned in order to perform a
magnetic resonance measurement of the patient. The imaging region
is at least partially encompassed by a magnetic field generator of
the magnetic resonance imaging device. For example, the imaging
region may be confined by the magnetic field generator in at least
one spatial direction, at least two spatial directions or at least
three spatial directions. It is also conceivable, that the imaging
region is encompassed by the magnetic field generator in a
circumferential direction. The magnetic field generator may be
configured to provide a homogenous, static magnetic field
(B0-field), a magnetic gradient field and/or a high frequency
magnetic field (B1-field) inside the imaging region of the magnetic
resonance imaging device. In an exemplary embodiment, the magnetic
field generator is configured to provide an imaging volume within
the imaging region, the imaging volume being characterized by a
particularly homogenous magnetic field or an approximately linear
magnetic gradient field. The imaging volume may be an isocenter of
the magnetic resonance imaging device. In one embodiment, a
dimension of the imaging volume may correspond to a dimension of
the diagnostically relevant area. It is conceivable, that the
magnetic resonance imaging device encloses at least a part of the
head of the patient, when the patient is positioned in the imaging
region. Positioning the head of the patient in the imaging region
may comprise locking the head of the patient in a predefined
relative position to the magnetic resonance imaging device. For
example, the magnetic resonance imaging device may comprise
adjustable mechanical elements and/or fasteners configured to fix
the head of the patient in a predefined position, thus preventing
the head from moving during the magnetic resonance measurement.
[0020] In a further step of the inventive method, the magnetic
resonance measurement is performed to acquire magnetic resonance
image data of the facial region of the patient. A magnetic
resonance measurement may comprise performing an imaging sequence
which may be characterized by a plurality of imaging parameters.
The plurality of imaging parameters may determine, for example, a
size and/or position of the imaging volume, a property and/or
temporal succession of the magnetic gradient field and/or the high
frequency magnetic field, as well as a time for readout of magnetic
resonance signals from the imaging volume. Examples for commonly
used imaging parameters are a repetition time, an echo time, a
field of view, a spatial resolution and the like. In an exemplary
embodiment, the imaging sequence is configured to provide a high
signal intensity or a bright contrast of the diagnostically
relevant area of the patient. For example, the imaging sequence may
comprise a short echo time in order to account for a short
T2-relaxation time associated with dentine or enamel of a tooth of
the patient. A short echo time may be lower than 150 .mu.s or lower
than 70 .mu.s. Examples of imaging sequences with a short echo time
are FLASH (fast low-angle shot) sequences and UTE (ultra-short echo
time) sequences. However, it is also conceivable to image dentine
or enamel of teeth with an imaging sequence comprising a longer
echo time, such as a TSE (turbo spin echo) sequence. In using
longer echo times, teeth may be characterized via a particularly
low signal intensity or a dark contrast. Thus, the dentine or
enamel of teeth may easily be differentiated from surrounding
tissue comprising a bright contrast. Of course, the imaging
sequences presented are to be understood as examples and other
imaging sequences may be employed to acquire magnetic resonance
imaging signals from a diagnostically relevant region of the face
of the patient. In particular, imaging sequences may be configured
to provide an appropriate contrast of specific parts of the facial
region. The facial region may comprise one or more of the following
body parts of the patient: one eye or both eyes, an eyeball, an eye
cavity, a retina, a jaw region, a jawbone, a gingiva, an enamel, a
dental arch, a dentine, a dental root of the patient. Posterior or
inaccessible parts of the head of the patient, such as a brain, a
back of the head or a part of a spinal cord, are not considered to
be parts of the facial region of the patient. Magnetic resonance
imaging of such posterior or inaccessible parts of the head are
therefore explicitly excluded from a scope of the proposed
inventive method.
[0021] In one step of the inventive method, a motion correction
technique exploiting an accessibility to the facial region of the
patient during the magnetic resonance measurement is employed,
wherein the motion correction technique reduces an influence of a
patient motion on the magnetic resonance image data. A motion
correction technique may comprise techniques that mechanically
limit or restrict the motion of the patient. For example, the
magnetic resonance imaging device may comprise a mechanical means,
such as a fastener, which is configured to arrest the head of the
patient in a predefined position in order to limit a movement of
the patient's head. However, the mechanical means may also
represent a separate component or device, which may be oriented or
aligned in a relative position to the magnetic resonance device
when performing a magnetic resonance measurement of the facial
region of the patient. In one example, the mechanical means may
comprise a separate chair or a stand with a head cover configured
to receive at least the head of the patient and to fix the head of
the patient in a predefined position in order to prevent movement
during the magnetic resonance measurement.
[0022] However, the motion correction technique may also comprise
techniques for determining and/or quantifying a motion of the
patient during the magnetic resonance measurement. In particular,
the motion correction may comprise techniques for correcting
acquired magnetic resonance image data in dependence of the
determined and/or quantified patient motion. This concept is
referred to as retrospective correction of the magnetic resonance
image data. It is also conceivable, that the motion correction
technique comprises adjusting imaging parameters of an imaging
sequence in real-time during the magnetic resonance measurement in
order to prospectively correct the acquired magnetic resonance
image data. The patient motion may be determined by employing a
sensor, such as a motion sensor and/or an optical sensor, which is
configured to acquire information on a movement of the patient
during the magnetic resonance measurement. The motion correction
technique may further comprise using algorithms, particularly image
processing algorithms, configured to compensate for patient
movement by processing or manipulating the acquired magnetic
resonance image data or the reconstructed magnetic resonance images
in dependence of information acquired via the sensor.
[0023] The motion correction technique exploits an accessibility to
the facial region of the patient during the magnetic resonance
measurement. The accessibility to the facial region of the patient
may be provided via a physical access, such as an entry, a
clearance and/or an unobstructed view, which may be used to apply a
mechanical sensor and/or acquire an optical image with an optical
sensor configured for detecting a motion of the patient. In
particular, the accessibility may comprise a clearance for a
mechanical element, such as a fixation element and/or a mouth guard
configured for positioning within an intraoral region of the
patient. However, the accessibility to the facial region may
further relate to the fact, that the magnetic resonance imaging
device is a dedicated scanner, configured to acquire magnetic
resonance image data from a specific facial region of the
patient.
[0024] By reducing an influence of a patient motion on the magnetic
resonance image data, an occurrence of motion artifacts in magnetic
resonance images can advantageously be reduced or avoided. Thus, a
quality of magnetic resonance images can be increased and a risk
for misdiagnosis of magnetic resonance images and/or a need for
repetition of the magnetic resonance measurement can advantageously
be decreased.
[0025] In one embodiment of the inventive method, the facial region
comprises a teeth region and/or jaw region of the patient, wherein
the motion correction technique comprises positioning a mouth guard
in an intraoral region of the patient to suppress movement of the
teeth region and/or the jaw region of the patient while performing
the magnetic resonance measurement. A mouth guard may be shaped in
such a way, that the mouth guard may be positioned between an upper
dental arch and a lower dental arch inside an oral cavity of the
patient. For example, the shape of the mouth guard may comprise a
U-shape approximating the shape of a lower dental arch and/or an
upper dental arch of the patient. It is conceivable, that the shape
of the mouth guard is designed to fit a target group of patients.
However, the mouth guard may also comprise adjustable elements in
order to adjust the shape or a dimension of the mouth guard to the
mouth cavity or a dental arch of an individual patient. For
example, the mouth guard may be a gum shield, a removable brace or
any other element shaped in such a way, that it can be positioned
in the oral cavity of the patient and limit movement of at least
one jaw. In an exemplary embodiment, the mouth guard consists of a
biocompatible material. A biocompatible material may be configured
to avoid undesirable side effects on the patient. For example, a
biocompatible material may comprise a high cell and blood
compatibility and may be histopathologically harmless. Possible
examples of biocompatible materials are plastics such as silicones,
polyethers, polyamides, polycarbonates, but also polymers of
various natural substances such as proteins, saccharides, peptides
and the like. Ceramics, such as aluminum oxide, gypsum or
hydroxyapatite are further examples of suitable biocompatible
materials. The mouth guard may be configured to provide a spacing
between the upper dental arch and the lower dental arch of the
patient, when positioned in the oral cavity of the patient. Thus,
the upper dental arch and the lower dental arch may be held apart,
preventing a relative motion of the two dental arches. However, the
patient may also be instructed or required to bite upon the mouth
guard during magnetic resonance measurement.
[0026] In providing a mouth guard to prevent a relative motion of
the lower dental arch and the upper dental arch of the patient
during the magnetic resonance measurement, motion artifacts due to
movement of the jaws can favorably be reduced or avoided.
[0027] According to one embodiment of the inventive method, the
mouth guard comprises a suction pipe, wherein the motion correction
technique comprises saliva being drained from the intraoral region
of the patient via the suction pipe while the magnetic resonance
measurement is performed in order to reduce a need for swallowing.
The suction pipe may represent a channel or a cavity in the mouth
guard. The channel or cavity may comprise at least one opening in
the oral cavity of the patient and at least one opening connected
to a vacuum system. For example, the suction pipe may be connected
to a pump or a compressor configured to provide a vacuum for
draining saliva from the oral cavity of the patient. The suction
pipe may also be embedded within the mouth guard, protruding from a
surface of the mouth guard in such a way, that it may drain the
saliva from underneath a tongue of the patient. For this purpose,
in an exemplary embodiment, the suction pipe consists of a
flexible, biocompatible material. In a further embodiment, the
suction pipe may also be used to fill the patient's mouth with a
fluid configured to enhance and/or change a contrast in a magnetic
resonance image. For example, the suction pipe may be configured to
provide an inflow of water covering the teeth of the patient in
order to provide a predetermined contrast with respect to the teeth
of the patient.
[0028] In providing a suction pipe integrated into the mouth guard,
saliva can be drained from the oral cavity of the patient. Thus, a
patient's urge for swallowing can advantageously be reduced, as
well as an associated swallowing motion causing artifacts in the
magnetic resonance images.
[0029] In a further embodiment of the inventive method, the
magnetic resonance measurement comprises acquiring separate
magnetic resonance image data from a lower jaw and an upper jaw of
the teeth region and/or jaw region, wherein the motion correction
technique comprises a prospective and/or retrospective correction
of the magnetic resonance image data in dependence of a rigid model
of the lower jaw and the upper jaw of the patient. The rigid model
of the lower jaw and the upper jaw of the patient may be derived,
for instance, from magnetic resonance images of the patient (e.g.
via segmentation) and/or from a database storing models, which may
be adjusted to an individual patient via parameterization. It is
conceivable, that the lower jaw and the upper jaw of the patient
may be treated as rigid bodies when correcting the acquired
magnetic resonance image data for patient movement, thus allowing
for an increase of an accuracy of the motion correction (e.g. up to
a sub .mu.m accuracy). For this purpose, a separate correction of
the acquired data may be performed, depending on a time of
acquisition, a respective motion state and/or relative position of
the lower jaw and the upper jaw of the patient. The individual
k-space-lines may be transferred to an image space before
correction. For example, based on the rigid model, a translational
motion of the lower jaw and/or the upper jaw may be corrected by
applying a phase change to the acquired magnetic resonance image
data. In order to compensate for rotational movement of the head of
the patient 15, non-Cartesian reconstruction methods may be
applied. In an exemplary embodiment, an imaging parameter of the
magnetic resonance measurement is adjusted when acquiring magnetic
resonance image data of the upper jaw or the lower jaw in
dependence of the rigid model. For this purpose, a movement of a
patient's jaw may be determined via correlation of a position of
the rigid model with a position of the patient's jaw. In order to
prospectively reduce an influence of the patient motion, an
encoding gradient of the imaging sequence may be rotated in
accordance with a rotational movement of a patient's jaw, whereas a
translational movement may be accounted for by changing a frequency
and/or phase of the radiofrequency excitation pulse. Depending on
the diagnostically relevant region, the magnetic resonance
measurement may be optimized to acquire magnetic resonance signals
from the upper jaw or the lower jaw, if only one jaw is of
interest. It is also conceivable, however, that the magnetic
resonance measurement is optimized to acquire magnetic resonance
image data from parts of the upper jaw and/or the lower jaw.
[0030] By using a rigid model of the upper jaw and/or the lower jaw
of the patient, correcting the magnetic resonance image data for
motion of the patient can be carried out in a robust and
reproducible fashion.
[0031] In an exemplary embodiment of the inventive method, the
motion correction technique comprises positioning a mechanical
element in contact with the facial region of the patient, wherein
the mechanical element comprises a motion sensor, wherein the
motion correction technique comprises determining a displacement of
the mechanical element due to motion of the patient while
performing the magnetic resonance measurement and wherein the
motion correction technique comprises a prospective and/or
retrospective correction of the magnetic resonance image data in
dependence of the displacement of the mechanical element. The
motion sensor is configured to determine a displacement of the
mechanical element in order to quantify a movement of the patient.
For this purpose, the motion sensor may comprise a gyroscope, a
pressure gauge, an accelerometer and the like. Possible examples of
mechanical elements are a chinrest, a headrest, a mouth guard or
any fixating and/or supporting structure in contact with the facial
region of the patient, particularly the jaw region of the patient.
In accordance with the example of a mouth guard, the motion sensor
and/or the mechanical element may be positioned within the oral
cavity of the patient during the magnetic resonance
measurement.
[0032] The mechanical element may consist of a non-rigid material
or comprise non-rigid elements. For example, the mechanical element
may comprise elastic elements, such as a spring element, an
expansion member, a flexible element and the like, which may be
deformed as a consequence of movement of the patient. Thus, a
movement of the patient may be determined in dependence of a
deformation of the elastic element via a pressure gauge and/or a
strain gauge.
[0033] In an exemplary embodiment, the mechanical element comprises
a chinrest or a headrest. In one example, the mechanical element
may be a simple holder, such as a supportive chinrest. In another
example, the mechanical element comprises a more sophisticated
structure, wherein the head of the patient may be positioned or be
embedded. The mechanical element may at least partially encompass
at least a part of the patient's head. It is also conceivable, that
the mechanical element encompasses the patient's head in a
circumferential direction. A motion sensor integrated into the
mechanical element may be configured to determine a motion of the
head or the facial region and provide feedback to the magnetic
resonance imaging device in real-time. For example, the determined
motion may be represented by motion data comprising time-related,
positional information on the head of the patient and/or the facial
region of the patient. A function of the motion sensor may be
similar to a function of a motion sensor of a gimbal in a drone or
a hand-held camera. However, the motion correction technique may
further comprise adjusting an imaging parameter, such as a property
of a radiofrequency excitation pulse and/or an orientation of an
encoding gradient, in dependence of the motion data in real-time
during the magnetic resonance measurement. It is also conceivable,
that an information on the determined motion is fed back to an
image reconstruction algorithm in order to correct the magnetic
resonance image data for motion of the patient retrospectively.
[0034] A motion sensor integrated into a mechanical element of the
magnetic resonance imaging device favorably allows for a
particularly cost-efficient implementation of a motion correction
technique.
[0035] According to one embodiment of the inventive method, the
motion correction technique comprises employing an optical sensor
to acquire optical image data of the facial region of the patient
while performing the magnetic resonance measurement, wherein the
motion correction technique comprises a prospective and/or
retrospective correction of the magnetic resonance image data in
dependence of the optical image data. The optical sensor may
comprise a camera, such as a two-dimensional (2D) camera, an
infrared camera or a 3D camera, which is configured to acquire
optical image data of the patient's head and/or face during the
magnetic resonance measurement. However, the camera may also be
used for preparation and/or positioning of the patient before the
magnetic resonance measurement. The camera may comprise a processor
configured to process the acquired optical image data and determine
motion data of the patient's head and/or face. For example, motion
data may characterize and/or quantify a movement and/or a current
orientation of the patient's head and/or the face of the patient.
It is also conceivable, that the camera is configured to transmit
the acquired optical image data and/or motion data to a separate
processor, e.g. a processor of the magnetic resonance imaging
device. Thus, the magnetic resonance imaging device may be able to
quantify a movement of the patient during the magnetic resonance
measurement and/or during preparation for the magnetic resonance
measurement. In an exemplary embodiment, the processor of the
magnetic resonance imaging device is configured to determine motion
data related to the patient's head and/or face in dependence of
optical image data received from the optical sensor.
[0036] It is conceivable, that one or more cameras are used in
order to acquire optical image data and/or motion data of the
patient. The one or more cameras may be positioned in an
examination space comprising the magnetic resonance imaging device,
in front of the patient's face and/or within the oral cavity of the
patient. In an exemplary embodiment, the optical sensor may be
configured to detect facial landmarks of the patient. For example,
facial landmarks may be used to determine a tilting of the head, a
swallowing motion, a blinking motion, a jaw movement, an eye
movement or any other movement of the head and/or face during a
predefined time period. During this time period, the magnetic
resonance measurement may be suspended in order to avoid image
artifacts when reconstructing a magnetic resonance image. However,
it is also conceivable, that the acquired magnetic resonance image
data of this time period is disregarded when reconstructing a
magnetic resonance image. Analogous to an embodiment described
above, the motion data derived from the optical image data may be
used to adjust an imaging parameter during the magnetic resonance
measurement and/or to correct the acquired magnetic resonance image
data for motion of the patient.
[0037] In one embodiment, the use of an optical sensor is combined
with an artificial intelligence-based training. For example, in a
learning phase, a movement of the facial landmarks is correlated
with an actual movement of the jaws. For this purpose, a motion
sensor, e.g. integrated into a mouth guard or a brace, may be
applied in order to determine a relative position of the upper jaw
and the lower jaw. Thus, the movement of facial landmarks may be
correlated with an expected movement of the jaws. In an applying
phase, the expected movement of the jaws may be correlated with a
movement of facial landmarks determined via the optical sensor.
This is particularly advantageous, as some motion sensors may not
be compatible with magnetic fields and cannot easily be positioned
in proximity to the imaging volume of the magnetic resonance
imaging device.
[0038] In using an optical sensor, the movement of the patient can
be determined from a distance. Thus, a positioning of a sensor in
direct proximity to the magnetic field of the magnetic resonance
imaging device can advantageously be avoided.
[0039] According to one embodiment of the inventive method, the
facial region of the patient is an eye region of the patient and
optical image data is acquired from an eye of the patient. It is
conceivable, that the magnetic resonance imaging device is a
dedicated eye scanner configured to acquire magnetic resonance
signals from the eye region of the patient. In an exemplary
embodiment, the eye scanner comprises one or more optical sensors,
for example one or more cameras, configured to track a motion of at
least one eye of the patient. The one or more cameras may be
configured in such a way, that a field of view provided by the one
or more cameras is focused on the at least one eye of the
patient.
[0040] In one embodiment, the magnetic resonance imaging device
comprises a processor configured to process optical image data
provided by an optical sensor. The processor may comprise a
detection and/or tracking algorithm configured to track, for
instance, a position and/or a motion of a pupil of the eye of the
patient during the magnetic resonance measurement. As a relative
position of the eyes and the head of the patient is constant, it
may be sufficient to derive rotational coordinates only. In one
embodiment, the patient's head may freely be moved within the
imaging region of the magnetic resonance imaging device. In this
case, a plurality of cameras may be used to track the total head
motion of the patient. For example, the processor may be configured
to separately process head related motion data and eye related
motion data. The processor may further be configured to take into
account the head related motion data and/or the eye related motion
data when reconstructing a magnetic resonance image as described
above. It is conceivable, that the detected motion is used to
prospectively correct the magnetic resonance image data, i.e. by
adjusting an imaging parameter, such as a field of view, a slice
center and/or an excitation pulse frequency, for a next acquired
k-space line. For example, a determined rotation of the head of the
patient may be used to rotate an encoding gradient, whereas a
determined translation may be used to adjust transmit and receive
frequency and phase. However, the detected motion may also be used
to retrospectively correct the magnetic resonance image data.
[0041] In a further embodiment, a camera is used for triggering a
magnetic resonance measurement. For example, magnetic resonance
image data may be acquired only when the patient focuses a target
region and discarded at other times. A focus of the patient may be
determined via one or more cameras directed at an eye of the
patient.
[0042] Of course, the inventive methods may also be employed in a
conventional magnetic resonance imaging device instead of a
dedicated eye scanner. In this case, the cameras and/or optical
sensors may be carried by a dedicated eye coil or a conventional
head coil. It is also conceivable, that the camera tracking
described above may be used for other ophthalmological
examinations.
[0043] In providing a method for acquiring motion data of an eye of
the patient, a diagnostic capability of magnetic resonance imaging
can favorably be increased. Thus, a distribution of dedicated
magnetic resonance imaging devices for specific body regions can be
enhanced and patients can benefit from three-dimensional imaging
techniques.
[0044] In a further embodiment, the inventive method comprises the
step of acquiring a projection image of the facial region of the
patient, wherein the motion correction technique comprises
adjusting a projection direction in dependence of a detected motion
of the facial region of the patient. Projection imaging may
represent a magnetic resonance measurement without gradient
encoding in one spatial direction. Thus, an essentially 2D
projection image of a 3D imaging volume within the patient may be
obtained. In an exemplary embodiment, projection imaging is
employed for dental imaging. In order to reduce an influence of the
patient's motion, the motion correction technique may comprise
adjusting a projection direction according to a detected motion of
the patient's teeth. For this purpose, a slice-following technique
may be employed. The movement of the patient may be detecting via
an optical sensor and/or a motion sensor as described above.
[0045] In comparison to X-ray based acquisition techniques for
dental imaging, magnetic resonance imaging provides a unique
advantage of being completely flexible with regard to the direction
of acquired projections for a Radon transformation. If, for
example, the patient tilts the head backwards during acquisition of
image data, an X-ray projection imaging device may not allow for a
movement according to the tilting of the patient's head. For
magnetic resonance imaging, following a patient's movement can
favorably be realized by choosing an imaging rotation matrix equal
to the patient's matrix.
[0046] According to a further embodiment, the inventive method
comprises the step of performing a navigator measurement of the
facial region of the patient to acquire navigator data, wherein the
motion correction technique comprises detecting a displacement of a
characteristic feature in the navigator data and prospectively
and/or retrospectively correcting the magnetic resonance image data
in dependence of the displacement of the characteristic feature.
When performing the navigator measurement, an essentially
one-dimensional image area, such as a linear or pencil-like image
area, may be selected. In an exemplary embodiment, the image area
is oriented approximately perpendicular to an expected moving
direction of the patient or a moving body part of the patient. It
is conceivable, that the image area comprises regions with varying
contrasts in order to permit an accurate detection of a movement of
the patient. In an exemplary embodiment, the image area comprises a
region with high T2(*) variations. An example for such a region is
a border between a tooth and other tissue (e.g. soft tissue) within
the oral cavity of the patient. A characteristic feature may
represent a high signal intensity provided by a tooth within the
image area when using an imaging sequence with a short echo time.
However, a characteristic feature may also be represented by other
anatomical structures, tissue or any other volume within the
patient comprising a prominent or characteristic signal intensity.
A displacement of the characteristic feature may be determined via
a shift or relocation of an area with high signal intensity within
a static image area of the navigator measurement. In analogy to an
embodiment described above, the displacement of the characteristic
feature may be used to adjust an imaging parameter during the
magnetic resonance measurement and/or to correct the acquired
magnetic resonance image data for motion of the patient.
[0047] By performing a navigator measurement in an image area
comprising at least a part of a tooth, navigator data with a
particularly high contrast differences may be obtained. Thus, a
detection of movement can be facilitated and/or an accuracy of a
detection of movement can favorably be increased.
[0048] In a further embodiment of the inventive method, the mouth
guard comprises a magnetic resonance visible marker, wherein the
motion correction technique comprises detecting the magnetic
resonance visible marker during the magnetic resonance measurement
and wherein the motion correction technique comprises a prospective
and/or retrospective correction of the magnetic resonance image
data in dependence of a displacement of the magnetic resonance
visible marker due to motion of the patient. By providing a mouth
guard with magnetic resonance visible markers, the magnetic
resonance visible markers may be positioned in the oral cavity of
the patient. For this purpose, in an exemplary embodiment, the
magnetic resonance visible markers consist of a biocompatible
material. For example, a magnetic resonance visible marker may be a
capsule comprising Vitamin D, Vitamin E or cod liver oil. One or
more capsules may be attached to a mouth guard or removable braces
which may be positioned in the oral cavity of the patient before
the magnetic resonance measurement.
[0049] In an exemplary embodiment, the magnetic resonance visible
marker is configured to provide a high intensity magnetic resonance
signal. Such a signal may be detected and used for determining a
movement of the patient during the magnetic resonance measurement.
For example, a displacement of the magnetic resonance visible
marker due to motion of the patient may be determined via a shift
or relocation of an area with high signal intensity within the
acquired magnetic resonance image data and/or reconstructed
magnetic resonance images. Similar to an embodiment described
above, the displacement of the magnetic resonance visible marker,
i.e. when the patient moves a jaw, may be used to adjust an imaging
parameter of the magnetic resonance measurement in real-time and/or
be used to correct for movement of the patient when performing a
reconstruction of magnetic resonance images.
[0050] In one embodiment, the magnetic resonance visible markers
may be earbuds configured for positioning in an ear of a patient.
In this embodiment, the magnetic resonance visible markers may
advantageously be combined with headphones, which may be used for
communication with the patient. In positioning earbuds with
magnetic resonance visible markers in opposite ears of the patient,
a motion of the patient's head may favorably be detected in
dependence of a tilt of an imaginary axis connecting the earbuds.
In a further embodiment, magnetic resonance markers are positioned
on a surface of the head of the patient. For this purpose, the
magnetic resonance visible markers may be glued or clamped to a
surface of the head region of the patient. The glue may provide a
temporary attachment, which may become detached after a
predetermined period of time and/or be easily detachable by
applying water or other solvents.
[0051] Magnetic resonance visible markers may be deployed with
minimal effort, thus enabling a time-efficient preparation of the
magnetic resonance measurement. Due to a high magnetic resonance
visibility of said magnetic resonance visible markers, a time
efficient and reliable detection of patient motion can be achieved,
even when applying low magnetic field strengths.
[0052] The inventive magnetic resonance imaging system comprises
magnetic resonance imaging device and a processor which is
configured to coordinate and execute an inventive method by means
of the magnetic resonance imaging device. In order to acquire,
process and/or store data, such as magnetic resonance image data,
optical image data or motion data, the magnetic resonance imaging
system may comprise components such as a controller, a processor, a
logic unit, a memory, an internal and/or an external storage unit,
as well as a suitable interface configured to transmit and receive
data and/or convert data into a desired data format. The processor
may comprise a controller, a microcontroller, a CPU, a GPU and the
like. The memory and/or the internal storage unit may comprise a
RAM, ROM, PROM, EPROM, EEPROM, flash memory, as well as an HDD, an
SSD and the like. However, the processor may also have access to an
external data storage, i.e. an external server or a cloud storage,
connected to the processor via a suitable network connection. The
data may be transported between components via analog and/or
digital signals using suitable signal connections. The magnetic
resonance imaging system may further comprise at least one motion
sensor and/or at least one optical sensor configured to determine
and/or quantify a movement of a patient positioned in an imaging
region of the magnetic resonance imaging device. In an exemplary
embodiment, the at least one motion sensor and/or the at least one
optical sensor are configured to transmit motion data and/or
optical image data to the processor via a suitable signal
connection. It is conceivable, that the processor is configured to
quantify a movement of the patient in dependence of the motion data
and/or the optical image according to an embodiment of the
inventive method described above. The processor may further be
configured to adjust an imaging parameter of a current magnetic
resonance measurement and/or to correct a reconstruction of
magnetic resonance image data in dependence of the motion data
and/or the optical image data in order to account for a movement of
the patient during the magnetic resonance measurement. It is also
conceivable, that the processor is configured to acquire a
projection image and/or navigator data of the facial region of the
patient by means of the magnetic resonance imaging device.
[0053] In an exemplary embodiment, the magnetic resonance device is
a dedicated scanner configured to acquire magnetic resonance image
data of a specific body region of the patient. For example, the
magnetic resonance imaging device may be configured to perform a
magnetic resonance measurement of an eye region and/or a jaw region
of the patient. Thus, an imaging volume of the magnetic resonance
imaging device may be tailored to match a diagnostically relevant
area, such as an eye, both eyes, a tooth, several teeth, a jaw, a
dental arch or both dental arches of the patient. Particularly, the
imaging region of the dedicated scanner may be configured to match
the specific body region of the patient, such as the facial region
of the patient.
[0054] In providing a processor configured to correct for a
movement of the patient in dependence of motion data and/or optical
image data, a quality of magnetic resonance image data acquired
from the facial region of the patient can be increased
advantageously. Furthermore, in providing a magnetic resonance
imaging system including integrated motion sensors and/or optical
sensors, a movement of the patient can be determined in a reliable
and robust fashion.
[0055] The inventive computer program product can be loaded into a
memory of a programmable processor of a magnetic resonance imaging
system and comprises program code means to perform a method
according to the disclosure when the computer program product is
executed in the processor of the magnetic resonance imaging system.
As a result, the method according to the disclosure can be carried
out quickly, and in a robust and repeatable manner. The computer
program product is configured in such a way that it can carry out
the method steps according to the disclosure by means of the
processor. The processor must in each case comprise the
prerequisites such as a corresponding main memory, a corresponding
graphics card or a corresponding logic unit, so that the respective
method steps can be carried out efficiently.
[0056] The computer program product is, for example, stored on a
computer-readable medium or stored on a network, a server or a
cloud, from where it can be loaded into the processor of a local
processor. The local processor can be directly connected to the
magnetic resonance imaging system or designed as part of the
magnetic resonance imaging system. Furthermore, control information
of the computer program product can be stored on an electronically
readable medium. The control information on the electronically
readable medium can be designed in such a way that, when the medium
is used, it carries out a method according to the disclosure in a
processor of the magnetic resonance imaging system. Examples of an
electronically readable medium are a DVD, a magnetic tape or a USB
stick on which electronically readable control information, in
particular software, is stored. If this control information is read
from the medium and stored in a control and/or processor of a
magnetic resonance imaging system, all embodiments of the inventive
method described above can be carried out.
[0057] FIG. 1 shows an embodiment of a magnetic resonance imaging
system 11 according to the disclosure. The magnetic resonance
imaging system 11 comprises a magnetic resonance (MR) device (MR
scanner) 13 with a static field magnet 17 that provides a
homogenous, static magnetic field 18 (B0 field). The static
magnetic field 18 comprises an isocenter 38 and a cylindrical
imaging region 36 for receiving a patient 15. The imaging region 36
is surrounded by the magnet arrangement 30 in a circumferential
direction. The patient support 16 is configured to transport the
patient 15 into the imaging region 36. In particular, the patient
support 16 may transport a diagnostically relevant region of the
patient 15 into an imaging volume defined by the isocenter 38 of
the magnetic resonance imaging device 13. In an exemplary
embodiment, the magnetic resonance device 13 is screened from an
environment by a housing shell 31.
[0058] The magnetic resonance device 13 further comprises a
gradient magnet arrangement 19 configured to provide magnetic
gradient fields used for spatial encoding of magnetic resonance
signals during the magnetic resonance measurement. The gradient
magnet arrangement 19 is activated by a gradient controller 28 via
an appropriate current signal.
[0059] The magnetic resonance device 13 further comprises a
radiofrequency antenna 20 (body coil), which may be integrated into
the magnetic resonance device 13. The radiofrequency antenna 20 is
operated via a radiofrequency controller 29 that controls the
radiofrequency antenna 20 to generate a high frequency magnetic
field and emit radiofrequency excitation pulses into an examination
space, which is essentially formed by the imaging region 36. The
magnetic resonance imaging system 11 may further comprises a local
coil 21, which is positioned on or in proximity to the
diagnostically relevant region of the patient 15. The local coil 21
may be configured to emit radiofrequency excitation pulses into the
patient 15 and/or receive magnetic resonance signals from the
patient 15. It is conceivable, that the local coil 21 is controlled
via the radiofrequency controller 29.
[0060] The magnetic resonance imaging system 11 further comprises a
controller 23 configured to control the magnetic resonance imaging
system 11. The controller 23 may comprise a processor 24 configured
to process magnetic resonance signals and reconstruct magnetic
resonance images. The processor 24 may also be configured to
process input from a user of the magnetic resonance imaging device
13 and/or provide an output to the user. For this purpose, the
processor 24 and/or the controller 23 can be connected to a display
unit 25 and an input unit 26 via a suitable signal connection. For
a preparation of a magnetic resonance measurement, preparatory
information, such as imaging parameters or patient information, can
be provided to the user via the display unit 25. The input unit 26
may be configured to receive information and/or imaging parameters
from the user. The display unit 25 and the input unit 26 may also
be implemented as a combined interface, such as a touch interface.
In an exemplary embodiment, the controller 23 includes processor
circuitry that is configured to perform one or more functions
and/or operations of the controller 23, including controlling the
MR imaging system 11 and/or the MR device 13, processing magnetic
resonance signals, reconstructing magnetic resonance images,
processing input from the user of the magnetic resonance imaging
device 13 and/or providing an output to the user.
[0061] Of course, the magnetic resonance imaging system 11 may
comprise further components that magnetic resonance imaging systems
usually have. The general operation of a magnetic resonance imaging
system 11 is known to those skilled in the art, so a more detailed
description is not deemed necessary.
[0062] FIG. 2 depicts a further embodiment of a magnetic resonance
imaging device 13 according to the disclosure. The magnetic
resonance imaging device 13 comprises a C-shaped magnet arrangement
30 partially encompassing the head of the patient 15 in a
circumferential direction. The isocenter 38 provided by the magnet
arrangement 30 is positioned in the eye region of the patient 15.
It is conceivable, that the magnetic resonance imaging device 13
may be moved relative to the patient 15 along the Z-direction, the
Y-direction and/or the X-direction in order to adjust the position
of the isocenter 38 to a diagnostically relevant region of the
patient 15. It is also conceivable, that the magnetic resonance
imaging device 13 may be tilted or turned with respect to the
patient 15.
[0063] In one example, a diagnostically relevant region may
comprise the jaw region of the patient 15. In an exemplary
embodiment, the magnet arrangement 30 is configured in such a way,
that a shape of the isocenter 38 is matched with a target anatomy
of the patient 15. For covering a dental arch of the patient 15,
the isocenter 38 may comprise a U-shape or an ellipsoid shape. In
other examples, the shape of the isocenter 38 may be ovoid,
polygonal, prismatic or any combination thereof. In FIG. 2, the
isocenter 38 comprises an ellipsoid shape in order to cover both
eyes of the patient 15 during the magnetic resonance measurement.
However, the magnetic arrangement 30 may also be configured to
provide an approximately spherical isocenter 38 which covers only
one eye of the patient 15.
[0064] In the depicted embodiment, the magnetic resonance imaging
system 11 comprises two cameras 31a and 31b, which are configured
to acquire optical image data from the eyes of the patient 15. The
cameras 31a and 31b are oriented in such a way, that optical image
data of the eyes, particularly of the pupils, can be acquired. The
acquired optical image data is transmitted to the processor 24 of
the magnetic resonance imaging system 11 via a suitable signal
connection. For example, the image data may comprise analog and/or
digital signals transferred via a cable connection or a wireless
connection such as WLAN, Bluetooth, infrared and so forth. The
processor 24 is configured to process the acquired optical image
data, as well as magnetic resonance image data and perform a motion
correction technique according to one of the embodiments described
above. In order to reduce a movement of the patient 15 during the
magnetic resonance measurement, the head of the patient 15 is
positioned in a headrest 32. The headrest 32 may be configured to
suppress tilting and/or turning of the head. For this purpose, the
head of the patient 15 may also be fixed in the headrest via
suitable fasteners (not shown).
[0065] FIG. 3 depicts a schematic representation of a headrest 32
according to the disclosure. The headrest 32 comprises a chinrest
32b for resting a chin of the patient 15 and a supporting element
32a for supporting the back of the head of the patient 15. The
headrest 32 may be configured to limit movement of the patient 15
during the magnetic resonance measurement. However, in order to
increase patient comfort, the headrest 32 may also allow for a
predefined degree of motion. For this purpose, the headrest 32 may
comprise motion sensors 33a and 33b, which are configured to
determine a movement of the head of the patient 15. For example,
the motion sensors 33a and 33b may comprise a spring configured to
accommodate a motion of the head. A mechanical force exerted on the
spring may be determined via the motion sensors 32a and 32b. In one
embodiment, the supporting element 32a and the chinrest 32b may
comprise strain gauges 33a and 33b embedded in an elastic material,
such as a foam or bolster, of the headrest 32. The strain gauges
33a and 33b are configured to transmit a signal representing the
mechanical force and/or pressure exerted on the headrest 32 to the
processor 24 via a suitable signal connection. The processor 24 may
be configured to determine motion data in dependence of the signal
provided via the motion sensors 33a and 33b. Of course, the
magnetic resonance imaging system 11 may comprise other sensors,
such as a camera 31 or further optical and/or motion sensors (not
shown), to determine the motion of the patient 15. In the depicted
embodiment, the camera 31 may be configured to determine an eye
motion of the patient 15. The optical image data acquired via the
camera 31 may be transmitted to the processor 24, which may be
configured to trigger a magnetic resonance measurement and/or
reject acquired magnetic resonance image data in dependence of a
position of a pupil of an eye of the patient. As can be seen in
FIG. 2 and FIG. 3, an access for a camera 31 and/or a chinrest 32b
to the facial region of the patient 15 is provided during the
magnetic resonance measurement, which can be exploited by the
motion correction technique.
[0066] FIG. 4 holds a schematic representation of a mouth guard 34
according to the disclosure. The mouth guard 34 is positioned
inside the oral cavity of the patient 15. In an exemplary
embodiment, the mouth guard 34 provides a spacing between the lower
dental arch and the upper dental arch of the patient 15 in such a
way, that movement of the lower jaw is prevented unless the patient
15 deliberately opens the mouth. Thus, the mouth guard 34
effectively limits the movement in the jaw region of the patient
15. The mouth guard 34 may comprise magnetic resonance visible
markers 35, which may be detected by the magnetic resonance imaging
device 13. In particular, a motion correction technique according
to the disclosure may be used to determine a position of the
magnetic resonance visible marker 35 by means of the magnetic
resonance image data (k-space data). The motion correction
technique may further comprise correcting for motion of the patient
15 in dependence of a position of magnetic resonance visible
markers 35 determined from the magnetic resonance image data. It is
also conceivable, that the mouth guard 34 comprises a motion sensor
33 (not shown), such as an accelerometer and/or a gyro sensor,
configured to determine a movement of the jaw region of the patient
15. The motion sensor 33 may be embedded in the mouth guard 34 or
attached to a surface of the mouth guard 34. Signals acquired from
the motion sensor 33 may be transmitted to the processor 24 via a
wireless or corded signal connection. In the latter case, the
signal connection may be carried by or attached to a suction pipe
40 configured to drain saliva from the oral cavity of the patient
15. In the depicted embodiment, the suction pipe 40 is connected to
a vacuum system 41 configured to provide a vacuum in the suction
pipe 40 in order to drain saliva from the oral cavity of the
patient 15.
[0067] In order to determine a motion of the patient 15, the
magnetic resonance system may further comprise cameras 31a and 31b.
The cameras 31a and 31b may be 2D or 3D cameras configured to
detect landmarks on the facial region of the patient 15. The
optical image data acquired via the cameras 31a and 31b are
transmitted to the processor 24, which is configured to determine a
motion of the patient 15 in dependence of a position of a landmark
in the optical image data. Of course, the number of cameras 31 used
for detection of motion may vary.
[0068] FIG. 5 depicts a flowchart of an inventive method for
reducing motion artifacts in magnetic resonance image data acquired
from a facial region of the patient 15.
[0069] In a step S1, the patient 15 is positioned in an imaging
region 36 of the magnetic resonance imaging device 13 configured to
perform a magnetic resonance measurement of the facial region of
the patient 15. For this purpose, the patient 15 may be positioned
on the patient support 16, which is configured to carry the patient
15 into the imaging region 16 either automatically or in dependence
of a control instruction provided by a user of the magnetic
resonance imaging device 13. However, as shown in FIG. 2, the
magnetic resonance imaging device 13 may also be configured in such
a way, that the patient 15 is able to autonomously enter the
imaging region 36. It is also conceivable, that the magnet
arrangement 30 of the magnetic resonance imaging device 13 is
positioned relative to the patient 15 in order to match the
isocenter 38 with a diagnostically relevant region. When
positioning the patient 15 in the imaging region 36, at least the
head of the patient 15 may be supported and/or fixed in a headrest
32, a chin rest 32b or a suitable fastening system in order to
reduce a movement of the patient 15 during the magnetic resonance
measurement.
[0070] In a step S2, a magnetic resonance measurement is performed
to acquire magnetic resonance image data of the facial region of
the patient 15. Acquiring magnetic resonance image data may
comprise performing at least one imaging sequence dedicated to a
specific region of the face of the patient 15. In particular, the
at least one imaging sequence may be suitable for acquiring
magnetic resonance signals of a jaw region, a dental region or an
eye region of the patient 15.
[0071] In one embodiment, performing the magnetic resonance
measurement may comprise acquiring separate magnetic resonance
image data from a lower jaw and/or an upper jaw of the teeth region
and/or the jaw region of the patient. For this purpose, a plurality
of imaging sequences, such as at least two imaging sequences, may
be performed. It is conceivable that imaging parameters of the at
least two imaging sequences are adjusted to enhance a signal
intensity, a signal-to-noise ratio, a resolution and/or an
acquisition time of magnetic resonance image data of the lower jaw
and/or upper jaw.
[0072] In an exemplary embodiment, optical image data and/or motion
data is acquired from the patient 15 via at least one optical
sensor 31 and/or at least one motion sensor 33 while the magnetic
resonance measurement is performed. In one example, the motion
sensor 33 may be integrated into a mechanical element, such as a
chinrest 32b and/or a supporting element 32a of the magnetic
resonance imaging device 13. The optical sensor 31 may be a camera
31 configured to acquire optical image data from the facial region
of the patient 15. In an exemplary embodiment, the optical image
data and/or motion data is transferred to the processor 24 of the
magnetic resonance imaging device 13, which is configured to derive
motion data comprising for instance time-related, positional
information on the head of the patient and/or the facial region of
the patient. In dependence of the motion data, the processor 24 may
perform a motion correction technique according to an embodiment
described above. It is also conceivable, that a position of a
magnetic resonance visible marker 35 is detected via the motion
correction technique when performing the magnetic resonance
measurement. Thus, the inventive method may comprise several ways
or options for determining a motion of the patient 15 during the
magnetic resonance measurement.
[0073] In one embodiment, a magnetic resonance visible marker 35 is
positioned in the facial region of the patient 15. For example,
when performing a magnetic resonance measurement of the teeth or
jaw region of the patient 15, one or more capsules comprising
Vitamin E may be positioned in the oral cavity of the patient 15.
The one or more capsules may simply be deposited in the patient's
mouth, e.g. in a cheek area and/or below the tongue. In an
exemplary embodiment, however, the magnetic resonance visible
marker(s) 35 are attached to or embedded in a mouth guard 34, a
removable brace or any other carrier element shaped in such a way,
that it can be positioned in the oral cavity of the patient 15. In
one embodiment, the magnetic resonance visible marker(s) may also
be positioned on a surface of the face of the patient 15, e.g. via
use of a soluble adhesive and/or clamps. It is also conceivable,
that a magnetic resonance visible marker 35 is integrated in an
earbud which may be positioned in the patient's ear.
[0074] In an optional step S3, a projection image of the facial
region of the patient 15 is acquired via the magnetic resonance
imaging device 13. A projection image may be derived from a
magnetic resonance measurement wherein gradient encoding is not
performed in one spatial direction in order to acquire a 2D
projection of a 3D imaging volume of at least a part of the facial
region of the patient.
[0075] In a further optional step S4, a navigator measurement may
be performed via the magnetic resonance imaging device in order to
acquire navigator data of the facial region of the patient 15. The
navigator measurement may comprise an essentially one-dimensional
image area, such as oriented approximately perpendicular to an
expected moving direction of the patient 15 or a moving part of the
facial region of the patient 15.
[0076] In a step S5, a motion correction technique exploiting an
accessibility to the facial region of the patient during the
magnetic resonance measurement is employed, wherein the motion
correction technique reduces an influence of a patient motion on
the magnetic resonance image data. In one embodiment, the motion
correction technique comprises positioning a mouth guard 34 in the
intraoral region of the patient 15 in order to suppress movement of
the teeth region and/or jaw region. In an exemplary embodiment, the
mouth guard 34 is positioned in the oral cavity of the patient 15
before the magnetic resonance measurement is started. Thus, a
relative motion of the upper jaw and the lower jaw of the patient
15 may be avoided or reduced while the magnetic resonance
measurement is performed. In a further embodiment, the mouth guard
34 comprises a suction pipe 40, wherein the suction pipe 40 is
configured to continuously or discontinuously drain saliva from the
intraoral region of the patient 15. As a result, the motion
correction technique reduces a patient's need for swallowing while
the magnetic resonance measurement is performed.
[0077] According to one embodiment, the motion correction technique
comprises a prospective and/or retrospective correction of the
magnetic resonance image data in dependence of a rigid model of the
lower jaw and the upper jaw of the patient 15. For deriving the
rigid model of the lower jaw and the upper jaw of the patient 15,
an initial magnetic resonance measurement may be performed to
acquire magnetic resonance image data from the lower jaw and the
upper jaw of the patient 15. The rigid model may then be created
via segmentation of the magnetic resonance image data or any other
image recognition technique. However, it is also conceivable, that
the rigid model is derived from an existing model of a lower jaw
and/or an upper jaw stored in a storage unit (memory) 27, which may
be adapted to the patient 15. The adaption of the rigid model to
the patient 15 may involve using segmented magnetic resonance
images acquired from the lower jaw and/or the upper jaw, as well as
parameterization of the rigid model in dependence of patient
information (e.g. patient data stored in the storage unit 27 and/or
patient data entered via the input unit 26). For example, a
dimension of the lower jaw and/or the upper jaw derived from a
segmented magnetic resonance image may be transferred to a
corresponding dimension of the rigid model. The motion correction
technique may comprise performing a separate correction of the
acquired magnetic resonance image data depending on a time of
acquisition and a respective motion state or relative position of
the lower jaw and the upper jaw. For this purpose, the individual
k-space-lines may be transferred to an image space before
correction. Based on the rigid model, a translational motion of the
lower jaw and/or the upper jaw may be corrected by applying a phase
change to the acquired magnetic resonance image data. In order to
compensate for rotational movement of the head of the patient 15,
non-Cartesian reconstruction methods may be applied.
[0078] In a further embodiment, the motion correction technique
comprises positioning a mechanical element 32b in contact with the
facial region of the patient 15, wherein the mechanical element 32b
comprises a motion sensor 33b, wherein the motion correction
technique comprises determining a displacement of the mechanical
element 32b due to motion of the patient 15 while performing the
magnetic resonance measurement. Due to movement of the patient 15,
the position of the diagnostically relevant region may vary within
the imaging region 36. The movement of the patient 15 may cause a
translative movement of the mechanical element 32b detected via
motion sensor 33, thus displacing the mechanical element 32b. The
motion correction technique further comprises a prospective and/or
retrospective correction of the magnetic resonance image data in
dependence of the displacement of the mechanical element 32b. In
order to compensate for the translative movement, the frequency
and/or phase of the radiofrequency excitation pulse emitted via the
radiofrequency antenna 20 is adjusted in real-time in such a way,
that the imaging volume tracks the diagnostically relevant region
of the patient 15 during the magnetic resonance measurement. In a
similar fashion, one or more motion sensors 33 may also detect a
rotational movement of the patient's head. In this case, an
encoding gradient of the imaging sequence may be rotated in order
to account for the detected movement.
[0079] In one embodiment, the motion correction technique comprises
employing an optical sensor to acquire optical image data of the
facial region of the patient while performing the magnetic
resonance measurement and a prospective and/or retrospective
correction of the magnetic resonance image data in dependence of
the optical image data. As described above, the processor 24 may be
configured to derive motion data of the patient 15 in dependence of
optical image data acquired via a camera 31 (see FIGS. 2 to 4). The
motion data may be used to adjust a field of view, a slice center
and/or an excitation pulse frequency for a next acquired k-space
line in real-time during the magnetic resonance measurement. For
example, encoding gradients of the imaging sequence may be rotated
in accordance with a rotational movement of the patient's head,
whereas a translational movement may be accounted for by changing a
frequency of the radiofrequency excitation pulse. However, the
motion data may also be fed back to an image reconstruction
algorithm in order to correct the magnetic resonance image data for
motion of the patient retrospectively. As described above, this may
comprise applying a phase change to the acquired magnetic resonance
image data in order to compensate for translational motion and/or
applying non-Cartesian reconstruction methods for correcting
rotational motion. In particular, the prospective and/or
retrospective correction of the magnetic resonance image data may
be carried out in dependence of a detected motion of a pupil of an
eye of the patient 15.
[0080] In one embodiment, the motion correction technique comprises
adjusting a projection direction in dependence of a detected motion
of the facial region of the patient 15. For example, a projection
image may comprise a front view or a side view of a dental arch of
the patient 15. The projection direction may be adjusted in
real-time in dependence of motion data derived from a signal of an
optical sensor 31 and/or a motion sensor 33. In particular, the
projection direction may be adjusted in accordance with a turning
and/or tilting motion of the head in order to maintain an initial
projection trajectory with respect to the patient's head. This
adjustment may be performed according to one of the embodiments
described above.
[0081] According to one embodiment, the motion correction technique
comprises detecting a displacement of a characteristic feature in
the navigator data and prospectively and/or retrospectively
correcting of the magnetic resonance image data in dependence of
the displacement of the characteristic feature. In an exemplary
embodiment, the navigator measurement comprises an essentially
one-dimensional image area. The image area may be positioned in
such a way, that it covers a region with high T2(*) variations,
e.g. a border of a tooth of the patient 15, wherein the
characteristic feature may be represented by a border of a tooth of
the patient 15. A movement of the patient 15 may be determined
based on a shift or relocation of the characteristic feature within
the image area of the navigator data. An adjustment of an imaging
parameter of the magnetic resonance measurement and/or a correction
of the magnetic resonance image data may be performed in dependence
of the displacement of the characteristic feature according to any
of the embodiments described above. For example, the frequency and
phase of the radiofrequency excitation pulse is changed in
accordance a movement displacement of the characteristic feature in
the image area of the navigator measurement in order to
prospectively correct for translational movement of the patient
15.
[0082] In a further embodiment, the motion correction technique
comprises a prospective and/or retrospective correction of the
magnetic resonance image data in dependence of a displacement of a
magnetic resonance visible marker 35 due to motion of the patient
15. In an exemplary embodiment, a magnetic resonance visible marker
35 provides a high signal intensity which may provide a
characteristic contrast of pictures elements (pixels) in a
reconstructed magnetic resonance image. A displacement of such a
characteristic contrast between a plurality of magnetic resonance
images may be used to quantify a motion of the patient 15 and
correct for the detected motion as described above.
[0083] The embodiments described above are to be recognized as
examples. Individual embodiments may be extended by features of
other embodiments. In particular, a sequence of the steps of the
inventive methods are to be understood as exemplary. The individual
steps can also be carried out in a different order or overlap
partially or completely in time.
[0084] To enable those skilled in the art to better understand the
solution of the present disclosure, the technical solution in the
embodiments of the present disclosure is described clearly and
completely below in conjunction with the drawings in the
embodiments of the present disclosure. Obviously, the embodiments
described are only some, not all, of the embodiments of the present
disclosure. All other embodiments obtained by those skilled in the
art on the basis of the embodiments in the present disclosure
without any creative effort should fall within the scope of
protection of the present disclosure.
[0085] It should be noted that the terms "first", "second", etc. in
the description, claims and abovementioned drawings of the present
disclosure are used to distinguish between similar objects, but not
necessarily used to describe a specific order or sequence. It
should be understood that data used in this way can be interchanged
as appropriate so that the embodiments of the present disclosure
described here can be implemented in an order other than those
shown or described here. In addition, the terms "comprise" and
"have" and any variants thereof are intended to cover non-exclusive
inclusion. For example, a process, method, system, product or
equipment comprising a series of steps or modules or units is not
necessarily limited to those steps or modules or units which are
clearly listed, but may comprise other steps or modules or units
which are not clearly listed or are intrinsic to such processes,
methods, products or equipment.
[0086] References in the specification to "one embodiment," "an
embodiment," "an exemplary embodiment," etc., indicate that the
embodiment described may include a particular feature, structure,
or characteristic, but every embodiment may not necessarily include
the particular feature, structure, or characteristic. Moreover,
such phrases are not necessarily referring to the same embodiment.
Further, when a particular feature, structure, or characteristic is
described in connection with an embodiment, it is submitted that it
is within the knowledge of one skilled in the art to affect such
feature, structure, or characteristic in connection with other
embodiments whether or not explicitly described.
[0087] The exemplary embodiments described herein are provided for
illustrative purposes, and are not limiting. Other exemplary
embodiments are possible, and modifications may be made to the
exemplary embodiments. Therefore, the specification is not meant to
limit the disclosure. Rather, the scope of the disclosure is
defined only in accordance with the following claims and their
equivalents.
[0088] Embodiments may be implemented in hardware (e.g., circuits),
firmware, software, or any combination thereof. Embodiments may
also be implemented as instructions stored on a machine-readable
medium, which may be read and executed by one or more processors. A
machine-readable medium may include any mechanism for storing or
transmitting information in a form readable by a machine (e.g., a
computer). For example, a machine-readable medium may include read
only memory (ROM); random access memory (RAM); magnetic disk
storage media; optical storage media; flash memory devices;
electrical, optical, acoustical or other forms of propagated
signals (e.g., carrier waves, infrared signals, digital signals,
etc.), and others. Further, firmware, software, routines,
instructions may be described herein as performing certain actions.
However, it should be appreciated that such descriptions are merely
for convenience and that such actions in fact results from
computing devices, processors, controllers, or other devices
executing the firmware, software, routines, instructions, etc.
Further, any of the implementation variations may be carried out by
a general-purpose computer.
[0089] For the purposes of this discussion, the term "processor
circuitry" shall be understood to be circuit(s), processor(s),
logic, or a combination thereof. A circuit includes an analog
circuit, a digital circuit, state machine logic, data processing
circuit, other structural electronic hardware, or a combination
thereof. A processor includes a microprocessor, a digital signal
processor (DSP), central processor (CPU), application-specific
instruction set processor (ASIP), graphics and/or image processor,
multi-core processor, or other hardware processor. The processor
may be "hard-coded" with instructions to perform corresponding
function(s) according to aspects described herein. Alternatively,
the processor may access an internal and/or external memory to
retrieve instructions stored in the memory, which when executed by
the processor, perform the corresponding function(s) associated
with the processor, and/or one or more functions and/or operations
related to the operation of a component having the processor
included therein.
[0090] In one or more of the exemplary embodiments described
herein, the memory is any well-known volatile and/or non-volatile
memory, including, for example, read-only memory (ROM), random
access memory (RAM), flash memory, a magnetic storage media, an
optical disc, erasable programmable read only memory (EPROM), and
programmable read only memory (PROM). The memory can be
non-removable, removable, or a combination of both.
* * * * *