U.S. patent application number 13/930107 was filed with the patent office on 2014-09-11 for magnetic resonance apparatus and method for preparing a sensitivity map.
The applicant listed for this patent is GE Medical Systems Global Technology Company, LLC. Invention is credited to Janeiro Aguilar, Ken Arai, Yusuke Asaba, Mitsuhiro Bekku, Miho Nagasawa.
Application Number | 20140253123 13/930107 |
Document ID | / |
Family ID | 49777451 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140253123 |
Kind Code |
A9 |
Asaba; Yusuke ; et
al. |
September 11, 2014 |
MAGNETIC RESONANCE APPARATUS AND METHOD FOR PREPARING A SENSITIVITY
MAP
Abstract
A magnetic resonance apparatus configured to select a coil mode
that includes a combination of coil elements to be used when a
subject is scanned from within a plurality of coil elements and
configured to execute a predetermined scan for acquiring data on
the subject using the selected coil mode is provided. The magnetic
resonance apparatus includes a coil device having n coil modes, a
selecting unit configured to select, from within the n coil modes,
a candidate for the selected coil mode, a scanning unit configured
to execute a first scan for acquiring the data on the subject using
the candidate, and a sensitivity map preparing unit configured to
prepare a sensitivity map of the candidate based on data obtained
by the first scan.
Inventors: |
Asaba; Yusuke; (Toyko,
JP) ; Arai; Ken; (Toyko, JP) ; Aguilar;
Janeiro; (Tokyo, JP) ; Bekku; Mitsuhiro;
(Tokyo, JP) ; Nagasawa; Miho; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GE Medical Systems Global Technology Company, LLC |
Waukesha |
WI |
US |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20140002083 A1 |
January 2, 2014 |
|
|
Family ID: |
49777451 |
Appl. No.: |
13/930107 |
Filed: |
June 28, 2013 |
Current U.S.
Class: |
324/318 |
Current CPC
Class: |
G01R 33/34084 20130101;
G01R 33/3415 20130101; G01R 33/32 20130101; G01R 33/543
20130101 |
Class at
Publication: |
324/318 |
International
Class: |
G01R 33/32 20060101
G01R033/32 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2012 |
JP |
2012-146767 |
Claims
1. A magnetic resonance apparatus configured to select a coil mode
that includes a combination of coil elements to be used when a
subject is scanned from within a plurality of coil elements and
configured to execute a predetermined scan for acquiring data on
the subject using the selected coil mode, the magnetic resonance
apparatus comprising: a coil device having n coil modes; a
selecting unit configured to select, from within the n coil modes,
a candidate for the selected coil mode; a scanning unit configured
to execute a first scan for acquiring the data on the subject using
the candidate; and a sensitivity map preparing unit configured to
prepare a sensitivity map of the candidate based on data obtained
by the first scan.
2. The magnetic resonance apparatus of claim 1, wherein said
scanning unit is configured to execute the first scan such that
although a gradient magnetic field is applied to each of sections
crossing the subject in a frequency encoding direction, the
gradient magnetic field is not applied in a phase encoding
direction using the candidate, and said sensitivity map preparing
unit is configured to prepare projection data that includes data
which has been projected in the phase encoding direction by section
of the subject based on data obtained by the first scan, and
configured to prepare the sensitivity map using the projection
data.
3. The magnetic resonance apparatus of claim 2, wherein said
scanning unit is configured to execute the first scan using an RF
coil built into a magnet, and said sensitivity map preparing unit
is configured to prepare projection data when the RF coil has been
used based on data obtained by the first scan using the RF coil,
and configured to prepare the sensitivity map using the projection
data when the RF coil has been used and the projection data when
the candidate has been used.
4. The magnetic resonance apparatus of claim 1, further comprising:
a data preparing unit configured to prepare sensitivity data that
includes sensitivities of the n coil modes in respective
predetermined directions, wherein said selecting unit is configured
to select the candidate from within the n coil modes based on the
sensitivity data.
5. The magnetic resonance apparatus of claim 2, further comprising:
a data preparing unit configured to prepare sensitivity data that
includes sensitivities of the n coil modes in respective
predetermined directions, wherein the selecting unit is configured
to select the candidate from within the n coil modes based on the
sensitivity data.
6. The magnetic resonance apparatus of claim 3, further comprising:
a data preparing unit configured to prepare sensitivity data that
includes sensitivities of the n coil modes in respective
predetermined directions, wherein the selecting unit is configured
to select the candidate from within the n coil modes based on the
sensitivity data.
7. The magnetic resonance apparatus of claim 4, wherein said
selecting unit is configured to select the candidate from within
the n coil modes based on a threshold value of the sensitivity
data.
8. The magnetic resonance apparatus of claim 4, wherein said
scanning unit is configured to execute a second scan such that
although a gradient magnetic field is applied to sections crossing
the subject in a frequency encoding direction, the gradient
magnetic field is not applied in a phase encoding direction using
one of the n coil modes, and said data preparing unit is configured
to prepare projection data that includes data which has been
projected in the phase encoding direction based on data obtained by
the second scan, and configured to prepare sensitivity data using
the projection data.
9. The magnetic resonance apparatus of claim 7, wherein the
scanning unit is configured to execute a second scan such that
although a gradient magnetic field is applied to sections crossing
the subject in a frequency encoding direction, the gradient
magnetic field is not applied in a phase encoding direction using
one of the n coil modes, and said data preparing unit is configured
to prepare projection data that includes data which has been
projected in the phase encoding direction based on data obtained by
the second scan, and configured to prepare sensitivity data using
the projection data.
10. The magnetic resonance apparatus of claim 8, wherein said
scanning unit is configured to execute the second scan using an RF
coil built into a magnet, and said data preparing unit is
configured to prepare project data when the RF coil has been used
based on data obtained by the second scan using the RF coil, and
configured to prepare the sensitivity data using the project data
when the RF coil has been used and the project data when the one of
the n coil modes has been used.
11. The magnetic resonance apparatus of claim 1, further
comprising: a display unit configured to display the sensitivity
map.
12. The magnetic resonance apparatus of claim 11, further
comprising: a sensitivity score calculating unit configured to
calculate a sensitivity score indicating a sensitivity in a
predetermined range of the sensitivity map.
13. The magnetic resonance apparatus of claim 12, wherein the
predetermined range of the sensitivity map is a range of an imaging
view field of the predetermined scan.
14. The magnetic resonance apparatus of claim 12, wherein said
selecting unit is configured to select a plurality of candidates
for the coil mode, said sensitivity map preparing unit is
configured to prepare a sensitivity map for each of the candidates,
said sensitivity score calculating unit is configured to calculate
a sensitivity score of each sensitivity map, and said display unit
is configured to display a sensitivity map which is the highest in
sensitivity score.
15. The magnetic resonance apparatus of claim 13, wherein said
selecting unit is configured to select a plurality of candidates
for the coil mode, said sensitivity map preparing unit is
configured to prepare a sensitivity map for each of the candidates,
said sensitivity score calculating unit is configured to calculate
a sensitivity score of each sensitivity map, and said display unit
is configured to display a sensitivity map which is the highest in
sensitivity score.
16. The magnetic resonance apparatus of claim 11, wherein the
predetermined scan is a localizer scan for acquiring localizer
image data to be used when a slice position is set, and said
display unit is configured to display the sensitivity map and the
localizer image data one upon another.
17. The magnetic resonance apparatus of claim 11, wherein the
predetermined scan is a main scan for acquiring image data on a
part to be imaged of the subject, and said display unit is
configured to display the sensitivity map and the image data one
upon another.
18. The magnetic resonance apparatus of claim 2, wherein in the
first scan, said frequency encoding direction is set in a plurality
of directions for each of a plurality of sections crossing the
subject.
19. The magnetic resonance apparatus of claim 18, wherein a
sagittal plane, an axial plane and a coronal plane are included in
the plurality of sections, and in the first scan the frequency
encoding direction is set in an SI direction and an AP direction
for the sagittal plane, the frequency encoding direction is set in
the AP direction and an RL direction for the axial plane, and the
frequency encoding direction is set in the RL direction and the SI
direction for the coronal plane.
20. A method for preparing a sensitivity map of a coil device
having n coil modes, said method comprising: selecting a coil mode
that includes a combination of coil elements from within a
plurality of coil elements; executing a predetermined scan for
acquiring data on the subject using the selected coil mode;
selecting, from within the n coil modes, a candidate for the
selected coil mode; executing a first scan for acquiring the data
on the subject using the candidate; and preparing a sensitivity map
of the candidate based on data obtained by the first scan.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Japanese Patent
Application No. 2012-146767 filed Jun. 29, 2012, which is hereby
incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a magnetic resonance
apparatus that selects a coil mode, and a method for preparing a
sensitivity map of a coil device having n coil modes.
[0003] A technique of automatically recognizing a combination of
coil elements to be used when a subject is scanned is known (see,
for example, Japanese Patent Application Laid-Open No.
2011-156096).
[0004] In a general technique of automatically recognizing a
combination of coil elements, a coil installation position is
fixed. Thus, there is such a disadvantage that coils which can be
used are limited.
[0005] On the other hand, although a magnetic resonance apparatus
in which a position of an Anterior coil is detected by using a
positioning sensor which is called IntelliTouch is known, it is
necessary for an operator to operate the positioning sensor and
hence there is such a problem that a workload on the operator is
increased in this magnetic resonance apparatus.
[0006] In addition, the Anterior coil is made of a soft material so
as to be deformable in many cases, and hence the shape of the
Anterior coil changes depending on the body shape of a subject. As
the shape of the Anterior coil is deformed, sensitivity is changed
accordingly, so that there is such a problem that it becomes
difficult to select an optimum coil.
[0007] Further, it becomes also important to select a combination
of coil elements suited for imaging in a short time from the
viewpoint of reducing an imaging time.
[0008] For reasons as mentioned above, it is desired to select the
combination of coil elements suited for scanning the subject in a
short time with as little the load on the operator as possible.
BRIEF DESCRIPTION OF THE INVENTION
[0009] In one aspect, a magnetic resonance apparatus is provided.
The magnetic resonance apparatus selects a coil mode indicating a
combination of coil elements to be used when a subject is scanned
from within a plurality of coil elements, and executes a
predetermined scan for acquiring data on the subject by using the
selected coil mode, the magnetic resonance apparatus having a coil
device having n coil modes, a selecting unit selecting a candidate
for the coil mode to be used when the predetermined scan is
executed from within the n coil modes, a scanning unit executing a
first scan for acquiring the data on the subject by using the
candidate for the coil mode and a sensitivity map preparing unit
preparing a sensitivity map of the candidate for the coil mode on
the basis of the data obtained by the first scan.
[0010] In another aspect, a program of a magnetic resonance
apparatus is provided. The program selects a coil mode indicating a
combination of coil elements to be used when a subject is scanned
from within a plurality of coil elements, and executes a
predetermined scan for acquiring data on the subject by using the
selected coil mode, the program making a computer execute a
selecting process of selecting a candidate for a coil mode to be
used when the predetermined scan is executed from within n coil
modes and a sensitivity map preparing process of preparing a
sensitivity map of the candidate for the coil mode.
[0011] Since the sensitivity map of the coil mode is prepared, the
sensitivity map according to the shape of the coil can be obtained
regardless of deformation of the shape of the coil. Thus, it
becomes possible to select a coil mode suited for a predetermined
scan. In addition, since the candidate for the coil mode to be used
for the predetermined scan is selected before preparation of the
sensitivity map, there is no need to perform a first scan using
each of the n coil modes and it becomes possible to select the coil
mode suited for the predetermined scan in a short time.
[0012] Advantages of the embodiments described herein will be
apparent from the following description as illustrated in the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic diagram of a magnetic resonance
apparatus of one embodiment.
[0014] FIGS. 2A and 2B are diagrams showing structures of a front
array coil and a rear array coil.
[0015] FIG. 3 is an explanatory diagram of coil modes.
[0016] FIG. 4 is a diagram showing scans executed in the exemplary
embodiment.
[0017] FIG. 5 is a diagram schematically showing a part to be
imaged.
[0018] FIG. 6 is a chart showing a flow when a subject is
imaged.
[0019] FIG. 7 is a diagram showing a state where the front array
coil has been attached to the subject.
[0020] FIG. 8 is a diagram showing an example of a landmark LM.
[0021] FIG. 9 is a diagram showing a state after the part to be
imaged has been conveyed into an imageable region.
[0022] FIG. 10 is a diagram showing one example of a scan A.
[0023] FIG. 11 is an explanatory diagram of scans A.sub.0 to
A.sub.4.
[0024] FIG. 12 is a diagram showing one example of a pulse sequence
used in the scans A.sub.0 to A.sub.4.
[0025] FIG. 13 is a diagram schematically showing projection data
P.sub.0 of an RF coil.
[0026] FIG. 14 is a diagram schematically showing projection data
P.sub.1 to P.sub.4 prepared for respective coil modes Set1 to
Set4.
[0027] FIG. 15 is an explanatory diagram when coverage data are
prepared.
[0028] FIG. 16 is an explanatory diagram when a coil mode having a
high sensitivity in the imageable region is detected from within
the coil modes Set1 to Set4.
[0029] FIG. 17 is a diagram showing one example of a scan B.
[0030] FIG. 18 is a diagram schematically showing prepared
projection data Q.sub.01 to Q.sub.06.
[0031] FIG. 19 is a diagram schematically showing projection data
Q.sub.11 to Q.sub.16, Q.sub.21 to Q.sub.26, and Q.sub.31 to
Q.sub.36 prepared for respective scans B.sub.1 to B.sub.3 for
sensitivity maps.
[0032] FIG. 20 is an explanatory diagram when a sensitivity map is
prepared.
[0033] FIG. 21 is an explanatory diagram of one example of a method
of preparing a sensitivity map M.sub.1.
[0034] FIG. 22 is a diagram schematically showing sensitivity maps
M.sub.1 to M.sub.8 of the coil modes Set1 to Set3.
[0035] FIG. 23 is a diagram schematically showing one example of an
imaging view field FOV1 which has been set within the imageable
region.
[0036] FIG. 24 is an explanatory diagram when sensitivity scores
are calculated.
[0037] FIG. 25 is a diagram schematically showing the sensitivity
map M1 of the coil mode Set1 which has been displayed on a display
unit.
[0038] FIG. 26 is a diagram schematically showing localizer image
data obtained by a localizer scan.
[0039] FIG. 27 is a diagram schematically showing one example of an
imaging view field FOV2 which has been set.
[0040] FIG. 28 is a diagram showing sensitivity scores V.
[0041] FIG. 29 is a diagram schematically showing the sensitivity
map M2 of the coil mode Set2 which has been displayed on the
display unit.
[0042] FIG. 30 is a diagram schematically showing a state that
localizer image data are superimposed on sensitivity distributions
in windows.
[0043] FIG. 31 is a graph showing experimental results.
[0044] FIGS. 32A and 32B are graphs showing experimental
results.
DETAILED DESCRIPTION OF THE INVENTION
[0045] Although exemplary embodiments will be described in the
following, the disclosure is not limited to the following exemplary
embodiments.
[0046] FIG. 1 is a schematic diagram of a magnetic resonance
apparatus according to one embodiment.
[0047] A magnetic resonance apparatus (hereinafter, referred to as
an "MR apparatus") 100 has a magnet 2, a table 3, a positioning
light 4, the front array coil 40, the rear array coil 41 and the
like.
[0048] The magnet 2 has a bore 21 in which a subject 11 is
contained, a superconductive coil 22, a gradient coil 23, and the
RF coil 24. The superconductive coil 22 forms a static magnetic
field, the gradient coil 23 generates a gradient magnetic field,
and the RF coil 24 transmits an RF pulse. Incidentally, a permanent
magnet may be used in place of the superconductive coil 22.
[0049] The positioning light 4 is disposed on a front face of the
magnet 2. The positioning light 4 sets the landmark which will
serve as a mark when the subject 11 is to be conveyed into the bore
21.
[0050] The table 3 has a cradle 3a for supporting the subject 11.
The cradle 3a is configured to be movable within the bore 21. The
subject 11 is conveyed into the bore 21 by the cradle 3a.
[0051] The front array coil 40 is attached to the abdomen of the
subject 11. In addition, the rear array coil 41 is embedded in the
cradle 3a. A combination of the front array coil 40 and the rear
array coil 41 corresponds to a coil device. Structures of the front
array coil 40 and the rear array coil 41 will be described
later.
[0052] The MR apparatus 100 also has a transmitter 5, a gradient
magnetic field power source 6, a receiver 7, a control unit 8, an
operation unit 9, the display unit 10 and the like.
[0053] The transmitter 5 supplies a current to the RF coil 24, and
the gradient magnetic field power source 6 supplies a current to
the gradient coil 23.
[0054] The receiver 7 executes signal processing such as wave
detection and the like on signals received from the front array
coil 40 and the rear array coil 41. Incidentally, a combination of
the magnet 2, the transmitter 5 and the gradient magnetic field
power source 6 corresponds to a scanning unit.
[0055] The control unit 8 controls operations of respective parts
of the MR apparatus 100 so as to implement various operations of
the MR apparatus 100 such as an operation of transferring required
information to the display unit 10, an operation of reconstructing
an image on the basis of data received from the receiver 7 and
others. The control unit 8 is configured by, for example, a
computer. The control unit 8 has a data preparing unit 81 to a
sensitivity score calculating unit 84 and others.
[0056] The data preparing unit 81 prepares coverage data (see FIG.
15) of coil modes. The coil modes will be described later.
[0057] A coil mode candidate selecting unit 82 selects candidates
for coil modes used in a localizer scan LS and a main scan MS1 (see
FIG. 4).
[0058] A sensitivity map preparing unit 83 prepares sensitivity
maps of the coil modes.
[0059] The sensitivity score calculating unit 84 calculates
sensitivity scores of the coil modes.
[0060] The control unit 8 is one example configuring the data
preparing unit 81 to the sensitivity score calculating unit 84 and
functions as these units by executing a predetermined program.
[0061] The operation unit 9 is operated by an operator to input
various pieces of information into the control unit 8. The display
unit 10 displays various pieces of information.
[0062] The MR apparatus 100 is configured as mentioned above. Next,
the structures of the front array coil 40 and the rear array coil
will be described (see FIGS. 2A and 2B).
[0063] FIGS. 2A and 2B are diagrams showing the structures of the
front array coil 40 and the rear array coil 41.
[0064] FIG. 2A is a perspective view of the front array coil 40 and
the rear array coil 41, and FIG. 2B is a side view of the front
array coil 40 and the rear array coil 41.
[0065] The front array coil 40 is a coil which is attached to a
part to be imaged (the abdomen in the exemplary embodiment) of the
subject. The front array coil 40 is configured by a plurality of
coil elements.
[0066] The rear array coil 41 is a coil which is embedded in the
cradle 3a. The rear array coil 41 is also configured by a plurality
of coil elements.
[0067] When the subject is to be imaged, a coil element which is
used for a scan is selected from within the coil elements that the
front array coil 40 and the rear array coil 41 have in accordance
with imaging conditions (see FIG. 3).
[0068] FIG. 3 is an explanatory diagram showing combinations of
coil elements which can be used when the subject is scanned in the
exemplary embodiment.
[0069] In the exemplary embodiment, the rear array coil 41 is
divided into two parts (a rear array 41a and a rear array 41b) so
as to set such that the coil modes Set1 to Set4 described as
follows can be used.
[0070] (1) The coil mode Set1: the front array coil 40+the rear
array 41a
[0071] (2) The coil mode Set2: the front array coil 40+the rear
array 41b
[0072] (3) The coil mode Set3: the rear array 41a
[0073] (4) The coil mode Set4: the rear array 41b
[0074] When the subject is to be imaged, a coil mode conforming to
the imaging conditions is selected from within the coil modes Set1
to Set4. How the coil mode is selected will be described later.
Incidentally, although the coil mode is configured by the plurality
of coil elements in the above mentioned example, the coil mode may
be configured by only one coil element.
[0075] FIG. 4 is a diagram showing scans executed in the exemplary
embodiment, and FIG. 5 is a diagram schematically showing a part to
be imaged.
[0076] In the exemplary embodiment, the scan A for coverage data,
the scan B for sensitivity maps, the localizer scan LS and the main
scan MS1 are executed.
[0077] The scan A for coverage data is a scan to be executed to
prepare later described coverage data. The scan A for coverage data
will be described in detail later.
[0078] The scan B for sensitivity maps is a scan to be executed to
prepare later described sensitivity maps. The scan B for
sensitivity maps will be also described in detail later.
[0079] The localizer scan LS is a scan for acquiring localizer
image data to be used when a slice position is set.
[0080] The main scan MS1 is a scan for collecting image data on a
part including the liver. The main scan MS1 is a scan for
collecting, for example, T1 emphasized image data and T2 emphasized
image data.
[0081] In the following, a flow when the subject is imaged by
executing the scans shown in FIG. 4 will be described.
[0082] FIG. 6 is a chart showing the flow when the subject is
imaged.
[0083] In step ST1, the subject 11 is laid down on the cradle 3a
and then the front array coil 40 is attached onto it. FIG. 7
schematically shows a state that the front array coil 40 has been
attached onto the subject 11. In the exemplary embodiment, since
the abdomen of the subject 11 will be imaged, the operator attaches
the front array coil 40 onto the abdomen of the subject 11. After
the front array coil 40 has been attached, the flow proceeds to
step ST2.
[0084] In step ST2, the operator sets the landmark to be served as
a mark when the subject 11 is carried into the bore 21 by using
light from the positioning light 4. One example of the set landmark
LM is shown in FIG. 8. The operator moves the cradle 3a until the
abdomen of the subject 11 is positioned under the positioning light
4 and sets the landmark LM. An example in which the landmark LM has
been set on a central position of the front array coil 40 is shown
in FIG. 8.
[0085] The operator moves the cradle 3a such that the abdomen of
the subject is conveyed into the imageable region 25 in the bore 21
after the landmark LM has been set. The imageable region 25
indicates a region in which the static magnetic field exhibits
favorable uniformity and the gradient magnetic field exhibits
favorable linearity, and an image of good quality can be acquired.
The imageable region 25 can be defined, for example, by setting an
isocenter indicating the center of the gradient magnetic field as a
reference. A state after the part to be imaged has been conveyed
into the imageable region 25 is shown in FIG. 9. After the part to
be imaged has been conveyed into the imageable region 25 in the
bore 21, the flow proceeds to step ST3.
[0086] In step ST3, the scan A for coverage data (see FIG. 4) is
performed to select candidates for coil modes to be used in the
localizer scan LS and the main scan MS1 from within the coil modes
Set1 to Set4. In description of the step ST3, the scan A for
coverage data will be described first.
[0087] FIG. 10 is a diagram showing one example of the scan A for
coverage data.
[0088] In the exemplary embodiment, the scan A for coverage data
has five scans A.sub.0 to A.sub.4. In the following, the scans
A.sub.0 to A.sub.4 will be described.
[0089] FIG. 11 is an explanatory diagram of the scans A.sub.0 to
A.sub.4.
[0090] The scans A.sub.0 to A.sub.4 are scans in which although the
gradient magnetic field is applied to a sagittal plane SG within a
screening region 26 in a frequency encoding direction (in FIG. 11,
an SI (superior-inferior) direction), the gradient magnetic field
is not applied in a phase encoding direction. One example of a
pulse sequence used in the scans A.sub.0 to A.sub.4 is shown in
FIG. 12. The screening region 26 is set to be wider than the
imageable region 25. The length of the screening region 26 is 1.5
times the length of the imageable region 26. Incidentally, coils
used to receive a magnetic resonance signal on the sagittal plane
SG are different from one another in the scans A.sub.0 to A.sub.4.
The coils to be used for receiving the magnetic resonance signal on
the sagittal plane SG in the scans A.sub.0 to A.sub.4 are as
follows.
[0091] (0) The scan A.sub.0: the RF coil 24
[0092] (1) The scan A.sub.1: the coil mode Set1 (the front array
coil 40+the rear array 41a)
[0093] (2) The scan A.sub.2: the coil mode Set2 (the front array
coil 40+the rear array 41b)
[0094] (3) The scan A.sub.3: the coil mode Set3 (the rear array
41a)
[0095] (4) The scan A.sub.4: the coil mode Set4 (the rear array
41b)
[0096] In step ST3, the above mentioned scans A.sub.0 to A.sub.4
are executed to select the candidates for the coil modes to be used
in the localizer scan LS and the main scan MS1 from within the coil
modes Set1 to Set4 on the basis of data obtained by the respective
scans A.sub.0 to A.sub.4. In the following, respective sub-steps
ST31 to ST34 executed in step ST3 will be described in order.
[0097] In sub-step ST31, the scan A.sub.0 is executed using the RF
coil 24. The magnetic resonance signal received by the RF coil is
sent to the control unit 8 via the receiver 7. In the control unit
8, the data preparing unit 81 (see FIG. 1) prepares projection data
when the RF coil 34 has been used on the basis of data obtained by
the scan A.sub.0. Projection data P0 when the RF coil 24 has been
used is schematically shown in FIG. 13. Since the scan A.sub.0 is a
scan that although the gradient magnetic field is applied to the
sagittal plane SG within the screening region 26 in the frequency
encoding direction (the SI direction), the gradient magnetic field
is not applied in the phase encoding direction, the projection data
P.sub.0 indicating data which has been projected in the phase
encoding direction is obtained by executing the scan A.sub.0. Since
the frequency direction is the SI direction, the projection data
P.sub.0 indicates a relation between a position in the SI direction
and a signal value. After the scan A.sub.0 has been executed, the
flow proceeds to sub-step ST32.
[0098] In sub-step ST32, the scans A.sub.1 to A.sub.4 using the
coil modes Set1 to Set4 are executed. The data preparing unit 81
prepares projection data when the coil modes Set1 to Set4 have been
used on the basis of data obtained by the scans A.sub.1 to A.sub.4.
Projection data P.sub.1 to P.sub.4 when the coil modes Set1 to Set4
have been used are schematically shown in FIG. 14. Since the scans
A.sub.1 to A.sub.4 are scans that although the gradient magnetic
field is applied to the sagittal plane SG within the screening
region 26 in the frequency encoding direction (the SI direction),
the gradient magnetic field is not applied in the phase encoding
direction, the projection data P.sub.1 to P.sub.4 indicating the
data projected in the phase encoding direction are obtained by
executing the scans A.sub.1 to A.sub.4. Since the frequency
encoding direction is the SI direction, the projection data P.sub.1
to P.sub.4 each indicate a relation between a position in the SI
direction and a signal value. After the scans A.sub.1 to A.sub.4
have been executed, the flow proceeds to sub-step ST33.
[0099] In sub-step ST33, the data preparing unit 81 prepares
sensitivity data (hereinafter, referred to as "coverage data")
indicating sensitivities of the coil modes Set1 to Set4 in the SI
direction (see FIG. 15).
[0100] FIG. 15 is an explanatory diagram when the coverage data are
prepared.
[0101] The data preparing unit 81 prepares coverage data C.sub.1 to
C.sub.4 by dividing respective signal values of the projection data
P.sub.1 to P.sub.4 when the coil modes Set1 to Set4 have been used
by the signal value of the projection data P.sub.0 when the RF coil
24 has been used. Since the sensitivity of the RF coil 24 can be
regarded to be uniform within the imageable region 25, the
influence of a difference among the signal values caused by a
difference among the human tissues can be reduced by dividing the
signal values of the projection data P.sub.1 to P.sub.4 by the
signal value of the projection data P.sub.0. After the coverage
data C1 to C4 have been prepared, the flow proceeds to sub-step
ST34.
[0102] In sub-step ST34, a coil mode candidate selecting unit 82
(see FIG. 1) selects a coil mode having a high sensitivity in the
imageable region 25 from within the coil modes Set1 to Set4 on the
basis of the coverage data C.sub.1 to C.sub.4.
[0103] FIG. 16 is an explanatory diagram of one example when the
coil mode having the high sensitivity within the imageable region
25 is selected.
[0104] In the exemplary embodiment, first, a range in which a
signal value becomes larger than a threshold value S.sub.th is
detected from within the imageable region 25 for each of the
coverage data C.sub.1 to C.sub.4 to calculate a length L=L.sub.1 to
L.sub.4 of the detected range in the SI direction. Incidentally,
the threshold value S.sub.th may be a fixed value which has been
determined in advance or may be obtained on the basis of the signal
values of the coverage data C.sub.1 to C.sub.4.
[0105] Next, whether the following relational expression is
established between the length L=L.sub.1 to L.sub.4 and a length
L.sub.0 of the imageable region 25 in the SI direction is
determined.
L.gtoreq.k. L.sub.0 (1)
[0106] A coefficient k in the expression (1) is a value of
0<k<1, and for example, k=0.5. If the expression (1) is
satisfied, the coil mode will be determined to have a high
sensitivity within the imageable region 25. On the other hand, if
the expression (1) is not satisfied, the coil mode will be
determined not to have the high sensitivity within the imageable
region 25.
[0107] Here, it is supposed that although L.sub.1, L.sub.2 and
L.sub.3 satisfy the expression (1), L.sub.4 does not satisfy the
expression (1). Thus, three coil modes Set1, Set2 and Set3 are
selected as the coil modes having high sensitivities from within
the coil modes Set1 to Set4. The coil modes Set1, Set2 and Set3
which have been so selected are selected as the candidates for the
coil modes used in the localizer scan LS and the main scan MS1.
After the coil modes Set1, Set2 and Set3 have been selected, the
flow proceeds to step ST4.
[0108] In step ST4, the scan B for sensitivity maps (see FIG. 4) is
performed to prepare the sensitivity maps of the coil modes Set1,
Set2 and Set3 selected in step ST3 in the imageable region 25. In
description of step ST4, first, the scan B for sensitivity maps
will be described.
[0109] FIG. 17 is a diagram showing one example of the scan B for
sensitivity maps.
[0110] In the exemplary embodiment, the scan B for sensitivity maps
has four scans B.sub.0 to B.sub.3. In the following, first, the
scan B.sub.0 will be described.
[0111] The scan B.sub.0 includes six scans b1 to b6. The scans b1
to b6 are scans as described in the following.
[0112] (1) The scan b1: a scan that although the gradient magnetic
field is applied to the sagittal plane SG within the imageable
region 25 in the frequency encoding direction (the S1
(superior-inferior) direction), the gradient magnetic field is not
applied in the phase encoding direction
[0113] (2) The scan b2: a scan that although the gradient magnetic
field is applied to the sagittal plane SG within the imageable
region 25 in a frequency encoding direction (an AP
(anterior-posterior) direction), the gradient magnetic field is not
applied in the phase encoding direction
[0114] (3) The scan b3: a scan that although the gradient magnetic
field is applied to an axial plane AK within the imageable region
25 in the frequency encoding direction (the AP direction), the
gradient magnetic field is not applied in the phase encoding
direction
[0115] (4) The scan b4: a scan that although the gradient magnetic
field is applied to the axial plane AK within the imageable region
25 in a frequency encoding direction (an RL (right-left)
direction), the gradient magnetic field is not applied in the phase
encoding direction
[0116] (5) The scan b5: a scan that although the gradient magnetic
field is applied to a coronal plane CO within the imageable region
25 in the frequency encoding direction (the RL direction), the
gradient magnetic field is not applied in the phase encoding
direction
[0117] (6) The scan b6: a scan that although the gradient magnetic
field is applied to the coronal plane CO within the imageable
region 25 in the frequency encoding direction (the SI direction),
the gradient magnetic field is not applied in the phase encoding
direction
[0118] That is, in the scan B.sub.0, the six scans b1 to b6 are
executed. As a pulse sequence in the scans b1 to b6, the same pulse
sequence as that in FIG. 12 can be used. Incidentally, the above
mentioned scans b1 to b6 are executed also in the scans B.sub.1,
B.sub.2 and B.sub.3 as in the scan B.sub.0. However, the scans
B.sub.0 to B.sub.3 are different from one another in coil used for
receiving the magnetic resonance signal. In the scans B.sub.0 to
B.sub.3, the coils used for receiving the magnetic resonance signal
are as follows.
[0119] (0) The scan B.sub.0: the RF coil 24
[0120] (1) The scan B.sub.1: the coil mode Set1 (the front array
coil 40+the rear array 41a)
[0121] (2) The scan B.sub.2: the coil mode Set2 (the front array
coil 40+the rear array 41b)
[0122] (3) The scan B.sub.3: the coil mode Set3 (the rear array
41a)
[0123] In step ST4, the above mentioned scans B.sub.0 to B.sub.3
are executed to prepare the sensitivity maps of the coil modes
Set1, Set2 and Set3 which have been selected in step ST3 on the
basis of data obtained by the respective scans B.sub.0 to B.sub.3.
In the following, respective sub-steps ST41 to ST43 executed in
step ST4 will be described.
[0124] In sub-step ST41, the scan B.sub.0 (the scans b1 to b6) is
executed using the RF coil 24. The magnetic resonance signal
received by the RF coil 24 is sent to the control unit 8 via the
receiver 7. In the control unit 8, the sensitivity map preparing
unit 83 prepares projection data when the RF coil 24 has been used
on the basis of data obtained by the scan B.sub.0. Projection data
Q.sub.01 to Q.sub.06 when the RF coil has been used are
schematically shown in FIG. 18.
[0125] The projection data Q.sub.01 indicates a relation between
each position on the sagittal plane SG in the SI direction and a
signal value. The projection data Q.sub.02 indicates a relation
between each position on the sagittal plane SG in the AP direction
and a signal value.
[0126] The projection data Q.sub.03 indicates a relation between
each position on the axial plane AK in the AP direction and a
signal value. The projection data Q.sub.04 indicates a relation
between each position on the axial plane AK in the RL direction and
a signal value.
[0127] The projection data Q.sub.05 indicates a relation between
each position on the coronal plane CO in the RL direction and a
signal value. The projection data Q.sub.06 indicates a relation
between each position on the coronal plane CO in the SI direction
and a signal value.
[0128] After the scan B.sub.0 has been executed, the flow proceeds
to sub-step ST42.
[0129] In sub-step ST42, the scans B.sub.1 to B.sub.3 are executed.
The scans b1 to b6 are executed also in the scans B.sub.1 to
B.sub.3 as in the scan B.sub.0. However, in the scans B.sub.1 to
B.sub.3, the magnetic resonance signal is received respectively by
using the coil modes Set1 to Set3. The magnetic resonance signals
received by the coil modes Set1 to Set3 are sent to the control
unit 8 via the receiver 7. In the control unit 8, the sensitivity
map preparing unit 83 prepares projection data when the coil modes
Set1 to Set3 have been used on the basis of data obtained by the
scans B.sub.1 to B.sub.3. Projection data Q.sub.11 to Q.sub.16,
Q.sub.21 to Q.sub.26, and Q.sub.31 to Q.sub.36 when the coil modes
Set1 to Set3 have been used are schematically shown in FIG. 19.
[0130] After the scans B.sub.1 to B.sub.3 have been executed, the
flow proceeds to sub-step ST43.
[0131] In sub-step ST43, the sensitivity map preparing unit 83
prepares sensitivity maps indicating sensitivities of the coil
modes Set1 to Set3 in the imageable region 25 (see FIG. 20).
[0132] FIG. 20 is an explanatory diagram when the sensitivity maps
are prepared. Incidentally, although in FIG. 20, a method of
preparing the sensitivity map of the coil mode Set1 in the coil
modes Set1-Set3 will be described representatively, the sensitivity
maps of the other coil modes Set2 and Set3 can be also prepared by
the method which will be described in the following.
[0133] First, the sensitivity map preparing unit 83 divides the
signal values of the projection data Q.sub.11 to Q.sub.16 when the
coil mode Set1 has been used by signal values of the projection
data Q.sub.01-Q.sub.06 when the RF coil 24 has been used. Owing to
this, the influence of the difference among the signal values
caused by the difference among the human tissues can be reduced. In
FIG. 20, the projection data Q.sub.11 to Q.sub.16 of the coil mode
Set1 after divided by the projection data Q.sub.01 to Q.sub.06 of
the RF coil 24 are designated by numerals "Q.sub.11'" to
"Q.sub.16'".
[0134] Next, the sensitivity map preparing unit 83 prepares a
sensitivity map M.sub.1 of the coil mode Set1 in the imageable
region 25 on the basis of the obtained projection data Q.sub.11' to
Q.sub.16' (see FIG. 21).
[0135] FIG. 21 is an explanatory diagram of one example of a method
of preparing the sensitivity map M.sub.1.
[0136] The sensitivity at a coordinate point (x.sub.1, y.sub.1,
z.sub.1) of the sensitivity map M.sub.1 is obtained by multiplying
together signal values of respective coordinates x.sub.1, y.sub.1
and z.sub.1 of the projection data Q.sub.11' to Q.sub.16', and is
also obtained by multiplying together the signal values of the
respective coordinates of the projection data Q.sub.11' to
Q.sub.16' similarly with respect to other coordinate points.
[0137] The sensitivity map M1 of the coil mode Set1 in the
imageable region 25 can be prepared from the projection data
Q.sub.11' to Q.sub.16' in the above mentioned manner.
[0138] Incidentally, sensitivity maps of the coil modes Set2 and
Set3 can be also prepared in the same order. The sensitivity maps
M.sub.1 to M.sub.3 of the coil modes Set1 to Set3 are schematically
shown in FIG. 22. After the sensitivity maps M.sub.1 to M.sub.3
have been prepared, the flow proceeds to step ST5.
[0139] In step ST5, a coil mode which is considered to be the most
suited for the localizer scan LS (see FIG. 4) is specified from
within the coil modes Set1 to Set3 for which the sensitivity maps
M.sub.1 to M.sub.3 have been prepared. In the following, respective
sub-steps ST51 to ST54 of the step ST5 will be described.
[0140] In sub-step ST51, an imaging view field when the localizer
scan LS is executed is set within the imageable region 25 (see FIG.
23).
[0141] FIG. 23 is a diagram schematically showing one example of an
imaging view field FOV1 set within the imageable region 25.
[0142] The operator makes the display unit 10 display the
sensitivity maps M.sub.1 to M.sub.3 prepared in step ST4. Then,
FOV1 when the localizer scan LS is executed is set while referring
to the sensitivity maps M.sub.1 to M.sub.3 displayed on the display
unit 10. After FOV1 has been set, the flow proceeds to sub-step
ST52. Incidentally, in the case that FOV1 when the localizer scan
LS is executed is set in advance by default, sub-step ST51 is
skipped and the flow proceeds to sub-step ST52.
[0143] In sub-step ST52, the sensitivity score calculating unit
(see FIG. 1) calculates a sensitivity score indicating a
sensitivity in FOV1 for each of the sensitivity maps M.sub.1 to
M.sub.3 of the coil modes Set1 to Set3 (see FIG. 24).
[0144] FIG. 24 is an explanatory diagram when the sensitivity score
is calculated.
[0145] A sensitivity score V can be calculated, for example, as a
mean value of sensitivities at respective positions in FOV1. In
FIG. 24, the sensitivity scores V of the coil modes Set1, Set2 and
Set3 are designated by V.sub.1, V.sub.2 and V.sub.3. After the
sensitivity scores have been calculated, the flow proceeds to step
ST53.
[0146] In step ST53, a coil mode which is the largest in
sensitivity score is obtained from within the coil modes Set1 to
Set3. Here, it is supposed that V.sub.1 has a maximum value in the
sensitivity scores V.sub.1, V.sub.2 and V.sub.3. Thus, the coil
mode Set1 is selected. After the coil mode Set1 which is the
largest in sensitivity score has been selected, the flow proceeds
to sub-step ST54.
[0147] In sub-step ST54, the sensitivity map M.sub.1 of the coil
mode Set1 is displayed on the display unit 10 (see FIG. 25).
[0148] FIG. 25 is a diagram schematically showing the sensitivity
map M.sub.1 of the coil mode Set1 displayed on the display unit
10.
[0149] On the display unit 10, three windows W1, W2 and W3 and
others are displayed.
[0150] The window W1 is a window for displaying a sensitivity
distribution on the sagittal plane SG of the sensitivity map
M.sub.1. The window W2 is a window for displaying a sensitivity
distribution on the axial plane AK of the sensitivity map M.sub.1.
The window W3 is a window for displaying a sensitivity distribution
on the coronal plane CO of the sensitivity map M.sub.1.
[0151] The operator can move the positions of the sagittal plane
SG, the axial plane AK and the coronal plane CO of the sensitivity
map M.sub.1 respectively in the RL direction, the SI direction and
the AP direction as required. Thus, the operator can visually
confirm the sensitivity map M.sub.1 of the coil mode Set1 within
the imageable region 25 before executing the localizer scan LS by
observing the sensitivity distributions of the respective windows
W1, W2 and W3. Owing to this, the operator can confirm to which
extent of sensitivity the coil mode Set1 has to the part to be
imaged by the localizer scan LS.
[0152] In addition, the operator can make the display unit 10
display not only the sensitivity map M.sub.1 of the coil mode Set1
but also the sensitivity map M.sub.2 of the coil mode Set2 and the
sensitivity map M.sub.3 of the coil mode Set3 by operating the
operation unit 9. Thus, the operator can recognize not only the
sensitivity map M.sub.1 of the coil mode Set1 but also the
sensitivity map M.sub.2 of the coil mode Set2 and the sensitivity
map M.sub.3 of the coil mode Set3.
[0153] The operator confirms the sensitivity map M.sub.1 of the
coil mode Set1 displayed on the display unit 10 and determines
whether the localizer scan LS is to be executed by using the coil
mode Set1. When it has been determined to execute the localizer
scan LS by using the coil mode Set1, the operator operates the
operation unit 9 to input an instruction for executing the
localizer scan LS. When this instruction is input, the flow
proceeds to step ST6 and the localizer scan LS using the coil mode
Set1 is executed.
[0154] On the other hand, when the operator has thought that
execution of the localizer scan LS by using a coil mode other than
the coil mode Set1 would be desirable, the operator operates the
operation unit 9 to input an instruction for changing the coil
mode. For example, when it has been thought that execution of the
localizer scan LS using the coil mode Set2 would be desirable, the
operation unit 9 is operated to input an instruction for changing
the coil mode from Set1 to Set2. After the instruction for changing
the coil mode has been input, an instruction for executing the
localizer scan LS is input. When this instruction is input, the
flow proceeds to step ST6 and the localizer scan LS using the coil
mode Set2 is executed.
[0155] Here, it is supposed that the operator has determined to
execute the localizer scan LS using the coil mode Set1. Thus, the
localizer scan LS using the coil mode Set1 is executed in step ST6.
Localizer image data obtained by the localizer scan is
schematically shown in FIG. 26. In the exemplary embodiment,
localizer image data D1 on the sagittal plane SG, localizer image
data D2 on the axial plane AK and localizer image data D3 on the
coronal plane CO are acquired. After execution of the localizer
scan LS, the flow proceeds to step ST7.
[0156] In step ST7, a coil mode which is thought to be the most
suited for the main scan MS1 (see FIG. 4) is selected from within
the coil modes Set1 to Set3 for which the sensitivity maps M.sub.1
to M.sub.3 have been prepared. In the following, respective
sub-steps ST71 to ST74 in the step ST7 will be described.
[0157] In sub-step ST71, an imaging view field when the main scan
MS1 is to be executed is set (see FIG. 27).
[0158] FIG. 27 is a diagram schematically showing one example of an
imaging view field FOV2 which has been set.
[0159] The operator sets a slice position and the imaging view
field FOV2 when the main scan MS1 is to be executed while referring
to the localizer image data acquired in step ST6. After FOV2 has
been set, the flow proceeds to sub-step ST72.
[0160] In sub-step ST72, the sensitivity score calculating unit 84
calculates the sensitivity score indicating the sensitivity in FOV2
for each of the sensitivity maps M.sub.1 to M.sub.3 of the coil
modes Set1 to Set3. The sensitivity score V is shown in FIG. 28.
Incidentally, since the method of calculating the sensitivity score
is the same as the method in sub-step ST52 (see FIG. 24),
description thereof will be omitted.
[0161] In sub-step ST73, a coil mode which is the largest in
sensitivity score is obtained from within the coil modes Set1 to
Set3. Here, it is supposed that V.sub.2 has a maximum value in the
sensitivity scores V.sub.1, V.sub.2 and V.sub.3. Thus, the coil
mode Set2 is selected. After selection of the coil mode Set2 which
is the largest in sensitivity score V, the flow proceeds to
sub-step ST74.
[0162] In step ST74, the sensitivity map M.sub.2 of the coil mode
Set2 is displayed on the display unit 10 (see FIG. 29).
[0163] FIG. 29 is a diagram schematically showing the sensitivity
map M.sub.2 of the coil mode Set2 which has been displayed on the
display unit 10.
[0164] The three windows W1, W2 and W3 and others are displayed on
the display unit 10.
[0165] The window W1 is a widow for displaying the sensitivity
distribution on the sagittal plane SG of the sensitivity map
M.sub.2. The window W2 is a window for displaying the sensitivity
distribution on the axial plane AK of the sensitivity map M.sub.2.
The window W3 is a window for displaying the sensitivity
distribution on the coronal plane CO of the sensitivity map
M.sub.2.
[0166] The operator can move the positions of the sagittal plane
SG, the axial plane AK and coronal plane CO of the sensitivity map
M.sub.2 respectively in the RL direction, the SI direction and the
AP direction as required. Thus, the operator can visually confirm
the sensitivity map M.sub.2 of the coil mode Set2 before executing
the main scan MS1 by observing the sensitivity distributions in the
respective windows W1, W2 and W3. Owing to this, the operator can
confirm to which extent of sensitivity the coil mode Set2 has to
the part to be imaged before executing the main scan MS1.
[0167] Incidentally, the operator may display the localizer image
data (see FIG. 26) acquired in step ST6 by superimposing them on
the sensitivity distributions in the windows W1, W2 and W3 on the
display unit 10 (see FIG. 30).
[0168] FIG. 30 is a diagram schematically showing a state that the
localizer image data are superimposed on the sensitivity
distributions in the windows.
[0169] A corresponding relation between the localizer image data
and the sensitivity distribution can be visually recognized by
superimposing the localizer image data on the sensitivity
distribution in the window. Thus, the operator can know in more
detail the relation between the part which is being displayed in
the localizer image data and the sensitivity.
[0170] In addition, the operator can make the display unit 10
display not only the sensitivity map M.sub.2 of the coil mode Set2
but also the sensitivity map M.sub.1 of the coil mode Set1 and the
sensitivity map M.sub.3 of the coil mode Set3 by operating the
operation unit 9. Thus, the operator can confirm not only the
sensitivity map M.sub.2 of the coil mode Set2 but also the
sensitivity map M.sub.1 of the coil mode Set1 and the sensitivity
map M.sub.3 of the coil mode Set3.
[0171] The operator confirms the sensitivity map M.sub.2 of the
coil mode Set2 which is being displayed on the display unit 10 and
determines whether the main scan MS1 is to be executed by using the
coil mode Set2. When it has been determined to execute the main
scan MS1 by using the coil mode Set2, the operator operates the
operation unit 9 to input an instruction for executing the main
scan MS1. When this instruction is input, the flow proceeds to step
ST8 and the main scan MS1 using the coil mode Set2 is executed.
[0172] On the other hand, when the operator has thought that
execution of the main scan MS1 by using a coil mode other than the
coil mode Set2 would be desirable, the operation unit 9 is operated
to input an instruction for changing the coil mode. For example,
when it has been thought that execution of the main scan MS1 using
the coil mode Set1 would be desirable, the operation unit 9 is
operated to input an instruction for changing the coil mode from
Set2 to Set1. After the instruction for changing the coil mode has
been input, an instruction for executing the main scan MS1 is
input. When this instruction is input, the flow proceeds to step
ST8 and the main scan MS1 using the coil mode Set1 is executed, by
which the flow comes to an end.
[0173] In the exemplary embodiment, before execution of the
localizer scan LS, the coil modes Set1 to Set3 which are large in
sensitivity in the SI direction are selected from within the coil
modes Set1 to Set4 (sub-step ST34). Then, the sensitivity maps of
the coil modes Set1-Set3 are prepared to obtain the coil mode Set1
which is maximized in sensitivity score within FOV1 of the
localizer scan LS from within the coil modes Set1-Set3. Thus, it
becomes possible to automatically detect the coil mode Set1 which
is suited for the localizer scan LS. In addition, since the
sensitivity map of the coil mode Set1 is displayed on the display
unit 10, the operator can visually confirm to which extent of
sensitivity the coil mode Set1 has to the part to be imaged by the
localizer scan LS before execution of the localizer scan LS.
Further, the operator can display also the sensitivity maps of the
coil modes Set2 and Set3 other than the coil mode Set1 on the
display unit 10 and hence can visually confirm also the sensitivity
maps of the coil mode Set1 and Set3. Thus, the operator can compare
the sensitivity maps of the coil modes Set1-Set3 with one another
before execution of the localizer scan LS. In addition, when the
operator has thought that execution of the localizer scan LS not
using the coil mode Set1 but using another coil mode (for example,
Set2) would be better, the operator can change the coil mode of his
own will, so that execution of the localizer scan LS that the
operator would desire becomes possible.
[0174] In addition, in the scan A for coverage data and the scan B
for sensitivity maps, scans that a phase encoding amount is not
changed are executed. Thus, a scan time taken for the scan A for
coverage data and a scan time taken for the scan B for sensitivity
map can be reduced.
[0175] In addition, in the exemplary embodiment, the coil mode Set2
which is maximized in sensitivity score in FOV2 for the main scan
MS1 is obtained from within the coil modes Set1-Set3 before
execution of the main scan MS1. Thus, it becomes possible to
automatically detect the coil mode Set2 which is suited for the
main scan MS1. In addition, since the sensitivity map of the coil
mode Set2 is displayed on the display unit 10, the operator can
visually confirm to which extent of sensitivity the coil mode Set2
has to the part to be imaged by the main scan MS1 before execution
of the main scan MS1. Further, the operator can display also the
sensitivity maps of the coil modes Set1 and Set3 other than the
coil mode Set2 on the display unit 10 and hence can visually
confirm the sensitivity maps of the coil modes Set1 and Set3. Thus,
the operator can also compare the sensitivity maps of the coil
modes Set1-Set3 with one another before execution of the main scan.
In addition, when the operator has thought that execution of the
main scan MS1 not using the coil mode Set2 but using another coil
mode (for example, Set1) would be better, the operator can change
the coil mode of his own will, so that execution of the main scan
MS1 that the operator would desire becomes possible.
[0176] Incidentally, when another main scan MS2 is to be executed
after execution of the main scan MS1, step ST7 is executed to
select a coil mode to be used in execution of another main scan
MS2. Then, the main scan MS2 may be executed using the selected
coil mode. However, when the position of a part to be imaged by the
main scan MS2 is greatly separated from the position of the part
which has been imaged by the main scan MS1, step ST7 may be
executed to select a coil mode to be used in execution of the main
scan MS2 after setting again the position of the landmark returning
to step ST2 and then executing step ST3 and step ST4.
[0177] In the exemplary embodiment, the coil modes Set1, Set2 and
Set3 which are large in sensitivity in the SI direction are
selected as the candidates for the coil modes to be used in the
localizer scan LS and the main scan MS1 (step ST3) before execution
of the localizer scan LS. Thus, since exclusion of the coil mode
Set4 which is small in sensitivity in the SI direction from the
candidates for the coil modes to be used in the localizer scan LS
and the main scan MS1 is possible, there is no need to perform a
scan using the coil mode Set4 in step ST42, and it becomes possible
to promote scan time reduction.
[0178] In addition, in the exemplary embodiment, the projection
data are acquired from the mutually intersecting three planes (the
sagittal plane SG, the axial plane AK and the coronal plane CO) to
prepare the sensitivity maps. However, the sensitivity maps may be
prepared by acquiring the projection data from three or more
planes. Further, the sensitivity maps may be prepared by acquiring
the projection data from a plurality of parallel-arrayed planes, in
place of acquiring the projection data from a plurality of mutually
intersecting planes.
[0179] Incidentally, it is described that the coil modes Set1-Set3
which are high in sensitivity in the SI direction can be
distinguished from the coil mode Set4 which is low in sensitivity
in the SI direction by the coverage data C.sub.1-C.sub.4 in step
ST3. Thus, a simple experiment for verifying that this distinction
is possible was made. In the following, experimental results will
be shown.
[0180] FIG. 31 is a graph showing the experimental results.
[0181] In the experiment, a phantom was installed on the cradle 3a
and the front array coil 40 was installed on the phantom. Then, the
coverage data were prepared in accordance with the procedures of
step ST3. Referring to FIG. 31, a distinct difference in signal
value between the coverage data C1-C3 of the coil modes Set1-Set3
and the coverage data C4 of the coil mode Set4 is observed. Thus,
it is found that distinction between the coil modes Set1-Set3 which
are high in sensitivity in the SI direction and the coil mode Set4
which is low in sensitivity in the SI direction is possible.
[0182] In addition, in step ST4, the sensitivity maps are prepared
on the basis of the projection data. Thus, a simple experiment for
verifying to which extent of quality the sensitivity maps prepared
on the basis of the projection data have was made. In the
following, experimental results will be shown.
[0183] FIGS. 32A and 32B are graphs showing the experimental
results.
[0184] In the experiment, a phantom was installed on the cradle 3a
and the front array coil 40 was installed on the phantom. Then, the
sensitivity map of the coil mode Set1 and the sensitivity map of
the coil mode Set3 were prepared in accordance with the procedures
of step ST4. FIG. 32A shows the sagittal plane, the coronal plane
and the axial plane of the sensitivity map of the coil mode Set1,
and FIG. 32B shows the sagittal plane, the coronal plane and the
axial plane of the sensitivity map of the coil mode Set3. In
addition, a localizer image of a corresponding section is shown on
the right side of each sensitivity map. Comparison of the
sensitivity map with the localizer image shows that the sensitivity
map exhibits a tendency toward contrasts of light against dark
which would be the same as that of the localizer image and hence it
is found that the reliability of the sensitivity map is high.
[0185] Incidentally, in the exemplary embodiment, the following
coil modes are set as available coil modes.
[0186] (1) The coil mode Set1: the front array coil 40+the rear
array 41a
[0187] (2) The coil mode Set2: the front array coil 40+the rear
array 41b
[0188] (3) The coil mode Set3: the rear array 41a
[0189] (4) The coil mode Set4: the rear array 41b
[0190] However, available coil modes are not limited to Set1-Set4.
In the following, other examples of the available coil modes will
be shown.
[0191] (1) The coil mode Set1: the front array coil+the rear array
41a
[0192] (2) The coil mode Set2: the front array coil 40+the rear
array 41b
[0193] (3) The coil mode Set3: the rear array 41a
[0194] (4) The coil mode Set4: the rear array 41b
[0195] (5) A coil mode Set5: the rear array 41a+the rear array
41b
[0196] In this example, the coil mode Set5 is added in addition to
the coil modes Set1-Set4. Thus, in step ST3, a scan A.sub.5 using
the coil mode Set5 may be executed in addition to the scans
A.sub.1-A.sub.4 using the coil modes Set1-Set4. Since it is
possible to prepare projection data of the coil mode Set5 by the
scan A4 using the coil mode Set5, coverage data of the coil mode
Set5 can be obtained by dividing it by the projection data of the
RF coil. Incidentally, since the coil mode Set5 is configured by
the coil modes Set3 and Set4, the projection data of the coil mode
Set5 may be estimated from the projection data of the coil mode
Set3 and the projection data of the coil mode Set4. In the case
that the projection data of the coil mode Set5 is estimated from
the projection data of the coil mode Set3 and the projection data
of the coil mode Set4, a scan using the coil mode Set5 is not
needed and hence it becomes possible to prevent the scan time taken
in step ST3 from being increased.
[0197] Many widely different embodiments may be configured without
departing from the spirit and the scope of the disclosure. It
should be understood that the disclosure is not limited to the
specific embodiments described in the specification, except as
defined in the appended claims.
[0198] The disclosure is directed to the magnetic resonance
apparatus which prepares the sensitivity map of the coil mode, and
the apparatus can select a coil mode suited for a predetermined
scan.
* * * * *