JP5697925B2 - Magnetic resonance imaging apparatus, slice position setting method, and program - Google Patents

Description

  The present invention relates to a magnetic resonance imaging apparatus for imaging a disc of a subject, a slice position setting method, and a program.

  2. Description of the Related Art Conventionally, a method for automatically determining a slice position of an intervertebral disc and photographing the intervertebral disc has been known (see, for example, Patent Document 1).

JP 7-51248 A

  If the slice position deviates from the intervertebral disc, it is difficult to make a medical diagnosis of the intervertebral disc. Therefore, it is desirable to set the intervertebral disc slice position so as to cross as close to the center of the intervertebral disc as possible. However, the intervertebral disc is thin, and depending on the subject, the intervertebral disc may be deformed, and in some cases, the slice position may be displaced from the intervertebral disc. In order to make the slice position coincide with the intervertebral disc, the operator may set the slice position manually. Therefore, it is desired to improve the accuracy of the slice position without taking as much trouble as possible to the operator.

A first aspect of the present invention is a magnetic resonance imaging apparatus for imaging an intervertebral disc of a subject,
A frequency spectrum creating means for creating a frequency spectrum based on a magnetic resonance signal collected from the subject;
An intervertebral disc interval calculating means for calculating an intervertebral disc interval based on the frequency spectrum;
Landmark interval adjusting means for adjusting the interval between a plurality of landmarks included in the reference model of cerebrospinal fluid based on the interval between the intervertebral discs;
A reference model positioning means for deforming the reference model in which the interval between the landmarks is adjusted according to the cerebrospinal fluid of the subject and positioning the reference model with respect to the cerebrospinal fluid of the subject;
Landmark displacement means for displacing each of the plurality of landmarks;
Profile creation means for creating a profile for a magnetic resonance signal on a line crossing each of the plurality of landmarks;
A reference point setting means for setting a reference point for positioning the slice position of the intervertebral disc on the intervertebral disc based on the profile;
Slice positioning means for positioning a slice position with respect to the intervertebral disc based on the reference point.

A second aspect of the present invention is a slice position setting method for setting a slice position of an intervertebral disc of a subject,
A frequency spectrum creating step for creating a frequency spectrum based on a magnetic resonance signal collected from the subject;
An intervertebral disc interval calculating step for calculating an intervertebral disc interval based on the frequency spectrum;
A landmark interval adjustment step of adjusting the interval between a plurality of landmarks of the reference model of cerebrospinal fluid based on the interval between the intervertebral discs;
A reference model positioning step in which the reference model in which the interval between the landmarks is adjusted is deformed according to the cerebrospinal fluid of the subject and positioned with respect to the cerebrospinal fluid of the subject;
A landmark displacement step of displacing each of the plurality of landmarks;
Creating a profile for magnetic resonance signals on a line across each of the plurality of landmarks;
A reference point setting step for setting a reference point for positioning a slice position of the intervertebral disc on the intervertebral disc based on the profile;
A slice positioning step for positioning a slice position with respect to the intervertebral disc based on the reference point;
Is a slice position setting method.

A third aspect of the present invention is a program for a magnetic resonance imaging apparatus for imaging a subject's intervertebral disc,
A frequency spectrum creating process for creating a frequency spectrum based on the magnetic resonance signal collected from the subject;
Intervertebral disc interval calculation processing for calculating the disc interval based on the frequency spectrum;
Landmark interval adjustment processing for adjusting the interval between a plurality of landmarks of the reference model of cerebrospinal fluid based on the interval between the intervertebral discs;
A reference model positioning process in which the reference model in which the interval between the landmarks is adjusted is deformed according to the cerebrospinal fluid of the subject and positioned with respect to the cerebrospinal fluid of the subject;
Landmark displacement processing for displacing each of the plurality of landmarks;
A profile creation process for creating a profile relating to a magnetic resonance signal on a line crossing each of the plurality of landmarks;
A reference point setting process for setting a reference point for positioning a slice position of the intervertebral disc on the intervertebral disc based on the profile;
A slice positioning process for positioning a slice position with respect to the intervertebral disc based on the reference point;
Is a program for causing a computer to execute.

  Since the intervals between the plurality of landmarks included in the reference model of cerebrospinal fluid are adjusted based on the interval between the intervertebral discs of the subject, the slice position can be set according to the interval between the intervertebral discs of the subject.

1 is a schematic diagram of a magnetic resonance imaging apparatus according to a first embodiment of the present invention. 3 is a diagram illustrating an example of a processing flow of the MRI apparatus 100. It is a figure which shows the slice position when a coronal scan is performed. It is a figure which shows an example of the coronal image IC which the operator 13 selected. It is an example of the frequency spectrum obtained by carrying out the Fourier transform of the coronal image IC. It is a figure explaining the detection method of the position of a spine. It is a figure which shows the sagittal surface SA scanned. It is a figure which shows an example of sagittal image data SI. It is explanatory drawing of the preparation procedure of the reference | standard model MC of cerebrospinal fluid. The spacing of the landmark M _i of the reference model MC cerebrospinal fluid is a diagram showing the manner in which adjustment based on the interval SP disc. FIG. 4 is an explanatory diagram when the cerebrospinal fluid reference model MC is deformed in accordance with the cerebrospinal fluid of the subject 12 and positioned with respect to the cerebrospinal fluid of the subject 12. Is a diagram illustrating the signal intensity profiles on line crossing the landmark M _1. Is a diagram illustrating the signal intensity profiles on line crossing the landmark M _2. It is a schematic diagram showing a signal intensity profile obtained for each landmark M ₁ ~M _x. It is a diagram showing a signal intensity profile when displacing the position of the landmark M _1. The disc DK _1, an illustration of the time for setting a reference point for positioning the slice position. All disc DK ₁ ~DK _x, is a diagram showing a state where a reference point for positioning the slice position has been set. It is a diagram illustrating the major axis _LD 1 to Ld _x of each disc _DK 1 _{~DK x.} It is a figure which shows a slice position. It is a diagram showing a slice position _SL 1 to SL _x in in the sagittal image data SI. It is the schematic of the MRI apparatus 200 of a 2nd form. It is a figure which shows an example of the processing flow of the MRI apparatus. Is a diagram showing the integrated value Int to each signal strength of the signal intensity profile P ₁ to P _x. It is a figure showing a plurality of landmarks after being displaced. It is a diagram illustrating a landmark _M 1 ~M _x after displacement (open circles) signal intensity profile _P 1 crosses the 'to P _x'. It is a diagram showing the integrated value Int 'of each of the signal strength of the signal intensity profile P _1' ~P x _'. It is explanatory drawing of the adjustment method of the position of a landmark.

  Hereinafter, although the form for inventing is demonstrated, this invention is not limited to the following forms.

(1) First Embodiment FIG. 1 is a schematic diagram of a magnetic resonance imaging apparatus according to a first embodiment of the present invention.
A magnetic resonance imaging apparatus (MRI apparatus MRI: Magnetic Resonance Imaging) 100 includes a magnetic field generator 2, a table 3, a receiving coil 4, and the like.

  The magnetic field generator 2 includes a bore 21 in which the subject 12 is accommodated, a superconducting coil 22, a gradient coil 23, and a transmission coil 24. The superconducting coil 22 applies a static magnetic field B0, and the gradient coil 23 applies a gradient magnetic field. The transmission coil 24 transmits an RF pulse. In place of the superconducting coil 22, a permanent magnet may be used.

  The table 3 has a cradle 31 for supporting the subject 12. The cradle 31 is configured to be movable to the bore 21. The subject 12 is transported to the bore 21 by the cradle 31.

  The receiving coil 4 is attached from the chest to the abdomen of the subject 12 and receives a magnetic resonance signal.

  The MRI apparatus 100 further includes a sequencer 5, a transmitter 6, a gradient magnetic field power source 7, a receiver 8, a central processing unit 9, an input device 10, and a display device 11.

  Under the control of the central processing unit 9, the sequencer 5 sends information for executing a pulse sequence to the transmitter 6 and the gradient magnetic field power supply 7. Specifically, under the control of the central processing unit 9, the sequencer 5 sends RF pulse information (center frequency, bandwidth, etc.) to the transmitter 6, and gradient magnetic field information (gradient magnetic field strength, etc.). Send to gradient magnetic field power supply 7.

  The transmitter 6 outputs a drive signal for driving the RF coil 24 based on the information sent from the sequencer 5.

  The gradient magnetic field power supply 7 outputs a drive signal for driving the gradient coil 23 based on the information sent from the sequencer 5.

  The receiver 8 processes the magnetic resonance signal received by the receiving coil 4 and transmits it to the central processing unit 9.

  The central processing unit 9 implements various operations of the MRI apparatus 100 such as transmitting necessary information to the sequencer 5 and the display unit 11 and reconstructing an image based on a signal received from the receiver 8. The operation of each unit of the MRI apparatus 100 is controlled. The central processing unit 9 is constituted by a computer, for example. The central processing unit 9 includes frequency spectrum creation means 9A to slice positioning means 9J.

  The frequency spectrum creating means 9A creates a frequency spectrum related to the coronal image data IC (see FIG. 4).

  The spine detection unit 9B detects where the spine of the subject 12 is located based on the frequency spectrum FS (see FIG. 5) created by the frequency spectrum creation unit 9A.

  The intervertebral disc interval calculating means 9C calculates the intervertebral disc interval SP of the subject 12 based on the frequency spectrum FS (see FIG. 5).

The landmark interval adjusting means 9D adjusts the intervals δ _{i, i + 1} of the plurality of landmarks M _{1 to} M _{x included} in the reference model MC of cerebrospinal fluid based on the calculated intervertebral disc interval SP (see FIG. 10). ).

  The reference model positioning unit 9E deforms the reference model MC with the landmark interval adjusted according to the cerebrospinal fluid of the subject 12, and positions the reference model MC with respect to the cerebrospinal fluid of the subject 12 (see FIG. 11). ).

Landmarks displacement means 9F displaces each of the plurality of landmarks _M 1 ~M _x.
The profile creation means 9G creates a profile related to the magnetic resonance signal on a line that crosses each of the plurality of landmarks.

  The reference point setting unit 9H sets a reference point for positioning the slice position of the intervertebral disc on the intervertebral disc based on the profile created by the profile creating unit 9G.

The major axis direction detecting means 9I detects the major axis direction of the intervertebral disc.
The slice positioning unit 9J positions the slice position of the intervertebral disc based on the reference point set by the reference point setting unit 9H and the long axis direction of the intervertebral disc detected by the long axis direction detecting unit 9I.

  The central processing unit 9 is an example of the frequency spectrum creation unit 9A to the slice positioning unit 9J, and functions as these units by executing a predetermined program.

  The input device 10 inputs various commands to the central processing unit 9 according to the operation of the operator 13. The display device 11 displays various information.

  The MRI apparatus 100 is configured as described above. Next, a processing flow of the MRI apparatus 100 will be described.

FIG. 2 is a diagram illustrating an example of a processing flow of the MRI apparatus 100.
In step S1, a scan for obtaining a plurality of coronal images (hereinafter referred to as “coronal scan”) is executed.

FIG. 3 is a diagram illustrating a slice position when a coronal scan is executed.
The MRI apparatus 100 automatically sets coronal slice planes CP _{1 to} CP _n according to preset conditions, and executes a coronal scan. By executing the coronal scan, it is possible to collect magnetic resonance signals of coronal images in the slice planes CP _{1 to} CP _n . The coronal scan may be a 3D scan or a 2D scan. The magnetic resonance signal is received by the receiving coil 4 (see FIG. 1) and transmitted to the receiver 8. The receiver 8 performs predetermined signal processing including digital processing on the signal transmitted from the receiving coil 4 and outputs the result to the central processing unit 9. In the central processing unit 9, a plurality of coronal images are reconstructed based on the signal obtained from the receiver 8. The operator 13 displays a plurality of reconstructed coronal images on the display device 11, and selects a coronal image crossing the spine from the plurality of coronal images. FIG. 4 shows an example of the coronal image IC selected by the operator 13. When the operator 13 selects the coronal image IC, the process proceeds to step ST2.

  In step ST2, the frequency spectrum creation means 9A (see FIG. 1) Fourier transforms the coronal image data IC selected by the operator 13 in the z-axis direction to create a frequency spectrum (see FIG. 5).

  FIG. 5 is an example of a frequency spectrum obtained by Fourier transforming the coronal image IC. FIG. 5A shows a coronal image IC, and FIG. 5B shows a frequency spectrum FS.

  The frequency spectrum FS is represented by a three-dimensional graph. The horizontal axis of the frequency spectrum FS is the position of the coronal image IC in the x-axis direction, and the vertical axis is the frequency f. In addition, the vertical direction on the paper surface of the graph of the frequency spectrum FS represents the spectrum intensity. After creating the frequency spectrum FS, the process proceeds to step ST3.

  In step ST3, the spine detection means 9B (see FIG. 1) detects where the spine of the subject 12 is located on the x-axis based on the frequency spectrum FS created in step ST2. Below, the detection method of the position of a spine is demonstrated (refer FIG. 6).

FIG. 6 is a diagram illustrating a method for detecting the position of the spine.
6 (a) is the same diagram as FIG. 5, and FIGS. 6 (b), (c), and (d) show frequency spectra FS1, FS2, and x3 at positions x = x1, x2, and x3, respectively. It is a figure which shows FS3.

  In the spine, since the intervertebral discs are arranged in the z-axis direction, a periodicity in which the intervertebral discs appear repeatedly in the z-axis direction is observed. Therefore, a peak Q in which the spectrum intensity increases due to the periodicity of the intervertebral disc appears in the frequency spectrum at the position of the spine. On the other hand, since such periodicity is not seen in the region around the spine, the peak Q at which the spectrum intensity increases is less likely to appear in the frequency spectrum. Therefore, it is possible to detect the position of the spine by obtaining the peak Q of the spectrum intensity for each frequency spectrum at each position in the x-axis direction and detecting the position in the x-axis direction when the peak Q reaches the maximum value. it can.

  For example, FIG. 6 shows a frequency spectrum FS1 at x = x1, a frequency spectrum FS2 at x = x2, and a frequency spectrum FS3 at x = x3 as the frequency spectrum at each position in the x-axis direction. A peak Q (= Q1) appears in the frequency spectrum FS1, a peak Q (= Q2) appears in the frequency spectrum FS2, and a peak Q (= Q3) appears in the frequency spectrum FS3. Comparing these peaks Q1, Q2, and Q3, peak Q2 is the largest. Therefore, among x = x1, x2, and x3, the position x2 where the peak Q2 appears is most likely the position of the spine. In the above description, only the peak Q of the frequency spectrum at the positions x = x1, x2, and x3 is described. However, the peak Q is also obtained for the frequency spectrum at positions other than x = x1, x2, and x3. The position of the spine can be detected by detecting the maximum value of the peak Q from the obtained peak Q.

  In the first embodiment, it is assumed that the maximum peak Q (= Q2) appears in the frequency spectrum FS2 at the position x2 in the x-axis direction. Therefore, the spine detection means 9B detects x = x2 as a position on the x-axis of the spine (note that the peak of the spectral intensity at the frequency f = 0 appears irrespective of the periodicity of the intervertebral disc. Excluded from the peaks considered when detecting). After detecting the position x2 on the x-axis of the spine of the intervertebral disc, the process proceeds to step ST4.

  In step ST4, a sagittal scan including the position x2 on the x-axis detected in step ST3 (hereinafter referred to as “sagittal scan”) is executed.

FIG. 7 is a diagram showing a sagittal plane SA to be scanned.
A magnetic resonance signal obtained by scanning the sagittal plane SA is received by the receiving coil 4 (see FIG. 1) and transmitted to the receiver 8. The receiver 8 performs predetermined signal processing including digital processing on the signal transmitted from the receiving coil 4 and outputs the result to the central processing unit 9. The central processing unit 9 creates sagittal plane image data (hereinafter referred to as “sagittal image data”) based on the signal obtained from the receiver 8. FIG. 8 shows an example of sagittal image data SI. After the sagittal scan is completed, the process proceeds to step ST5.

In step ST5, the intervertebral disc interval calculation means 9C (see FIG. 1) calculates the intervertebral disc interval SP of the subject 12 based on the frequency spectrum FS (see FIG. 6). In the frequency spectrum FS2 at the position x2 in the x-axis direction, a peak Q (= Q2) in which the spectrum intensity increases due to the periodicity of the intervertebral disc appears. Therefore, using the frequency f2 when the peak Q2 appears, The interval SP can be calculated. However, since the actual intervertebral discs are not arranged at regular intervals and have some variation, the value of the intervertebral disc spacing SP is a value when it is considered that the intervertebral discs are arranged at regular intervals. Calculated. In addition, in the frequency spectrum FS2 at the position x2 in the x-axis direction, another peak appears in addition to the peak Q2 (for example, the peak Q21) due to the periodicity of the intervertebral disc. Therefore, in addition to the frequency f2 at the peak Q2, the frequency SP21 at another peak Q21 may be used to calculate the disc space SP. In the first embodiment, the spacing SP of the calculated discs, and a SP = SP _0. After calculating the intervertebral disc spacing SP (= SP ₀ ), the process proceeds to step ST6.

  In step ST6, the landmark interval adjusting means 9D (see FIG. 1) adjusts the interval between the plurality of landmarks included in the reference model of cerebrospinal fluid based on the intervertebral disc interval SP calculated in step ST5. The cerebrospinal fluid reference model is created in advance before imaging the subject 12. The procedure for creating a reference model for cerebrospinal fluid is described below.

FIG. 9 is an explanatory diagram of a procedure for creating a reference model MC for cerebrospinal fluid.
Reference model MC cerebrospinal fluid have been prepared on the basis of the data _DC 1 to DC _n cerebrospinal fluid of multiple subject _SU 1 to SU _n. Data DC ₁ of cerebrospinal fluid has a plurality of landmarks _LM i (i = 1~x). The landmark LM _i represents the feature point of the cerebrospinal fluid of the subject SU ₁ . Here, the position a _i (i = 1 to x) adjacent to the intervertebral disc DK _i (i = 1 to x) in the cerebrospinal fluid region of the subject SU ₁ is used as a feature point of the cerebrospinal fluid. . Therefore, the landmarks LM _{1 to} LM _x are arranged at the same interval as the intervertebral discs DK _{1 to} DK _x .

In the above description has described data DC ₁ of cerebrospinal fluid of the subject SU _1, also data _DC 2 to DC _n cerebrospinal fluid of other subject _SU 2 to SU _n, of the subject SU ₁ Brain Similar to the spinal fluid data DC ₁ , the landmark LM _i representing the characteristic point of the cerebrospinal fluid is included.

Reference model MC cerebrospinal fluid have been prepared on the basis of the data _DC 1 to DC _n cerebrospinal fluid of multiple subject _SU 1 to SU _n. A landmark included in the reference model MC of cerebrospinal fluid is represented by a symbol “M _i (i = 1 to x)”, and an interval between adjacent landmarks M _i and M _{i + 1} is represented by a symbol “δ _{i, i + 1.} Is represented. For example, the interval between adjacent landmarks M ₁ and M ₂ is “δ _1,2 ”, and the interval between adjacent landmarks M _k and M _{k + 1} is “δ _{k, k + 1} ”. Landmark interval adjusting means. 9D, the distance between landmarks M _i of the reference model MC cerebrospinal fluid that is created as described above, is adjusted based on the interval SP disc which was calculated in step ST5 (Fig. 10 reference).

10, the distance between landmarks M _i of the reference model MC cerebrospinal fluid is a diagram showing the manner in which adjustment based on the interval SP disc.

10 (a) it is, represents a reference model prior to adjusting the distance the landmark M _i, FIG. 10 (b) represents the reference model after adjusting the spacing of the landmark M _i.

In the first embodiment, the interval of the landmark M _i is adjusted so that the interval δ _{i, i + 1} between the adjacent landmarks M _i and M _{i + 1} coincides with the intervertebral disc interval SP calculated in step ST5. In step ST5, since SP = SP ₀ is calculated, the interval between the landmarks M _i is adjusted so that δ _{i, i + 1} = SP ₀ . After adjusting the spacing of the landmark _{M i,} the process proceeds to step ST7.

In step ST7, the reference model positioning means 9E is, the reference model MC cerebrospinal fluid space of the landmark M _i is adjusted, deformed in accordance with the cerebrospinal fluid of a subject 12, cerebrospinal fluid of a subject 12 (See FIG. 11).

  FIG. 11 is an explanatory diagram when the reference model MC of cerebrospinal fluid is deformed in accordance with the cerebrospinal fluid of the subject 12 and positioned with respect to the cerebrospinal fluid of the subject 12.

  FIG. 11A schematically shows a state before the cerebrospinal fluid reference model MC is deformed to match the cerebrospinal fluid of the subject 12, and FIG. 11B shows a cerebrospinal fluid reference model. It is a figure which shows roughly the mode after deform | transforming MC according to the cerebrospinal fluid of the subject 12, and positioning with respect to the cerebrospinal fluid of the subject 12.

Reference model positioning means. 9E, the reference model MC cerebrospinal fluid space of the landmark M _i is adjusted, if deformed in accordance with the cerebrospinal fluid of a subject 12, a sagittal image data SI obtained in step ST4 Is used. Since the sagittal image data SI includes the cerebrospinal fluid of the subject 12, the reference model MC can be deformed according to the cerebrospinal fluid of the subject 12 by using the sagittal image data SI. . As a method of deforming the cerebrospinal fluid reference model MC in accordance with the cerebrospinal fluid of the subject 12, affine transformation or the like can be used. After the cerebrospinal fluid reference model MC is deformed in accordance with the cerebrospinal fluid of the subject 12 and positioned with respect to the cerebrospinal fluid of the subject 12, the process proceeds to step ST8.

In step ST8, the profile creation means 9G (see FIG. 1) creates a signal intensity profile on a line crossing the landmarks M _{1 to} M _x . Hereinafter, the signal intensity profile will be described.

Figure 12 is a diagram illustrating the signal intensity profiles on line crossing the landmark M _1. FIG. 12 shows the positional relationship between the intervertebral discs DK _{1 to} DK _x and the landmarks M _{1 to} M _x of the subject 12 shown in FIG.

Profile generation means 9G, first, defining a line _{L 1} intersecting the landmark _{M 1.} Line _{L 1} is defined to be perpendicular to the line segment _{LS 12} connecting the landmark _{M 2} landmark _{M 1} and neighbor. The profile creation unit 9G creates a signal intensity profile _{P 1} on the line _{L 1.} Signal intensity profile P ₁ is shown to the right of the line L _1. Since the intervertebral disc DK ₁ has a higher signal intensity than the surrounding tissue, the portion of the signal intensity profile P ₁ where the signal intensity is high represents the signal intensity of the portion C ₁ where the line L ₁ and the intervertebral disc DK ₁ intersect. Yes. The longer the length of the portion C ₁ crossing, the width W ₁ of the large portion of the signal strength in the signal intensity profile P ₁ is spread while the shorter portion C ₁ is the length crossing, the width W ₁ is Narrow. Note that the signal intensity profile P _1, the signal intensity of cerebrospinal fluid are omitted.

As described above, it is possible to obtain a signal intensity profile P ₁ on the line L ₁ intersecting the landmark M _1. Next, a description will be given signal intensity profiles on line crossing the landmark M _2.

Figure 13 is a diagram illustrating the signal intensity profiles on line crossing the landmark M _2.

Profile creating means 9G is, to define the line _{L 2} across the land mark _{M 2.} Line _{L 2} is defined to be perpendicular to the line segment _{LS 13} connecting the landmark _{M 1} and _{M 3} on both sides of the landmark _{M 2.} The profile creation unit 9G creates a signal intensity profile _{P 2} on the line _{L 2.} Signal intensity profile P ₂ is shown to the right of the line L _2. Since the intervertebral disc DK ₂ has a higher signal strength than the surrounding tissue, the portion of the signal strength profile P ₂ where the signal strength is high represents the signal strength of the portion C ₂ where the line L ₂ and the intervertebral disc DK ₂ intersect. Yes. The longer the length of the intersecting portion C ₂ is, the wider the width W ₂ of the portion of the signal strength profile P ₂ where the signal intensity is large, while the shorter the length of the intersecting portion C ₂ is, the width W ₂ is. Narrow. Note that the signal intensity profile P _2, the signal strength of the cerebrospinal fluid is omitted.

As described above, it is possible to obtain a signal intensity profile P ₂ on the line L ₂ crossing the landmark M _2. Similarly, in accordance with the method shown in FIG. 12 or FIG. 13, a signal intensity profile on a line crossing the other landmarks M _{3 to} M _x is created (see FIG. 14).

FIG. 14 is a schematic diagram showing signal strength profiles obtained for each of the landmarks M _{1 to} M _x .

Line _L 3 _{~L x-1} across the landmark _M 3 _{~M x-1,} similar to the line _{L 2} crossing the landmark _{M 2,} landmarks on both sides of each of the landmark _M 3 _{~M x-1} It is defined as a line perpendicular to the line segment connecting. The line _{L x} crossing the landmark _{M x} is defined to be perpendicular to the line segment _{LS x-1, x} connecting the landmark _{M x-1} landmark _{M x} and neighbor. The profile creation means 9G creates signal intensity profiles P _{1 to} P _x on the lines L _{1 to} L _x . After creating the signal intensity profiles P _{1 to} P _x , the process proceeds to step ST9.

At step ST9, to displace the respective landmarks M ₁ ~M _x, to create a signal strength profile on line across the landmark after displacement. In this embodiment, first, the landmark M ₁ is displaced, creating a signal strength profile on line across the landmark after displacement (see Figure 15).

Figure 15 is a diagram showing a signal intensity profile when displacing the landmark M _1.

First, the landmark displacement means 9F (see FIG. 1), to displace the landmark _{M 1.} In this embodiment, the landmark M ₁ is displaced by Δx in the direction perpendicular to the line L ₁ . In FIG. 15, the landmarks after displacement are indicated by reference signs “M _1a ”, “M _1b ”, “M _1c ”, and “M _1d ”. In FIG. 15, for convenience of explanation, the number of landmarks after displacement is four, but the number of landmarks after displacement may be less than four or more than four. After displacing the landmark _{M 1,} the profile creating unit 9G define landmarks _M 1a after _{displacement,} M _{1b, M 1c,} and a line _L 1a _{~L 1d} across each of _{M 1d.} Then, to create a signal intensity profile _P 1a _{to P 1d} on each line _L 1a _{~L 1d.} Therefore, in addition to the signal intensity profile _{P 1} before displacing landmark _{M 1,} the signal intensity profile _P 1a _{to P 1d} after displacing the landmark _{M 1} is obtained. After creating the signal strength profile, the process proceeds to step ST10.

In step ST10, the reference point setting unit 9H (see FIG. 1) determines the slice position on the disc based on the signal intensity profile before the landmark is displaced and the signal intensity profile after the landmark is displaced. Set the reference point for positioning. Here, first, the signal intensity profile _{P 1} before displacing landmark _{M 1} shown in FIG. 15, on the basis of the signal intensity profile _P 1a _{to P 1d} after displacing the landmark _{M 1,} disc DK _1, sets a reference point for positioning the slice position (see FIG. 16).

FIG. 16 is an explanatory diagram for setting a reference point for positioning the slice position on the intervertebral disc DK ₁ .

In order to set the reference point in the intervertebral disc DK ₁ , the reference point setting unit 9H first shows a portion with a large signal intensity for each of the signal intensity profiles P ₁ , P _1a , P _1b , P _1c , and P _1d. Judge whether or not. Of the signal intensity profiles P ₁ , P _1a , P _1b , P _1c , and P _1d , the signal intensity profiles P ₁ , P _1a , P _1b , and P _1c cross the intervertebral disc DK ₁ , so the signal intensity A large part of appears. However, since the signal intensity profile P _1d does not cross the intervertebral disc DK ₁ , a portion having a large signal intensity does not appear. Therefore, in the reference point setting unit 9H, a portion having a large signal strength appears for the signal strength profiles P ₁ , P _1a , P _1b , and P _1c , but a signal strength profile P _1d has a high signal strength. Judge that the part does not appear. As an example of a method for determining whether or not a portion having a large signal strength appears in each of the signal strength profiles P ₁ , P _1a , P _1b , P _1c , and P _1d , the threshold of the signal strength is previously set. A method may be considered in which a value is determined and a judgment is made based on whether or not a portion having a signal strength greater than the threshold value appears in the signal strength profiles P ₁ , P _1a , P _1b , P _1c , and P _1d. It is done.

Next, the reference point setting unit 9H has the widths W ₁ , W _1a , W _{1 of} the portions with high signal strength for the signal strength profiles P ₁ , P _1a , P _1b , and P _1c where the portions with high signal strength appear. _1b and _W1c are calculated. Then, the reference point setting unit 9H specifies a profile having the widest width W of the portion having the large signal intensity from the signal intensity profiles P ₁ , P _1a , P _1b , and P _1c . Here, it is assumed that the width W _1a is the maximum value among the widths W ₁ , W _1a , W _1b , and W _1c . Therefore, the reference point setting unit 9H has a signal intensity profile P _1a, the width W is specified as the widest signal intensity profile.

After specifying the signal strength profile P _1a , the reference point setting unit 9H obtains an intermediate position V _1a of the width W _1a . Since the signal intensity profile P _1a is a profile on the line L _1a , the position V _1a corresponding to the position V _1a on the line L _1a is specified by _obtaining an intermediate position V _1a of the width W _1a. be able to. Reference point setting means 9H is the position _{V 1a} on the line _{L 1a,} sets a reference point _{R 1} when positioning the slice position. The position of the reference point _{R 1} does not necessarily need an intermediate position _{V 1a} width _{W 1a,} a position shifted from the middle position _{V 1a} width _{W 1a,} even if the position of the reference point _{R 1} Good. After setting the reference point _{R 1,} the process proceeds to step ST11.

In step ST11, it is determined whether or not a reference point for positioning the slice position has been set for all the intervertebral discs. Here, still, since only a reference point _{R 1} disc DK ₁ is not set, the flow returns to step ST9.

At step ST9, to displace the next landmark M _2, obtains the signal intensity profile across the landmark M ₂ after displacement. Then, the process proceeds to step ST10, in the same manner as when setting the reference point _{R 1} in the disc DK _1, sets a reference point _{R 2} in the disc DK _2. After setting the reference point R _2, the process proceeds to step ST11, all of the disc, it is determined whether the reference point for positioning the slice position has been set. Similarly, the loop of steps ST9 to ST11 is repeatedly executed until it is determined in step ST11 that the reference points for positioning the slice positions are set for all the intervertebral discs.

FIG. 17 is a diagram showing a state when the reference points for positioning the slice positions are set in all the intervertebral discs DK _{1 to} DK _x .

As shown in FIG. 17, when the reference points R _{1 to} R _x are set for all the intervertebral discs DK _{1 to} DK _x, it is determined in step ST11 that the reference points are set for all the intervertebral discs, and the process proceeds to step ST12.

In step ST12, the major axis direction detecting means 9I (see FIG. 1) detects the major axis direction of each of the intervertebral discs DK _{1 to} DK _x . The longitudinal direction of the intervertebral disc can be detected, for example, by principal component analysis (PCA). FIG. 18 shows major axis directions LD _{1 to} LD _x of the intervertebral discs DK _{1 to} DK _x . After detecting the longitudinal direction of the intervertebral disc, the process proceeds to step ST13.

In step ST13, the slice positioning means 9J (see FIG. 1), and the reference point _R 1 to R _x disc _DK 1 to Dk _x, based on the long axis direction _LD 1 to Ld _x disc, disc _DK 1 ~ The slice position of DK _x is positioned (see FIG. 19).

FIG. 19 is a diagram showing slice positions.
The slice positioning means 9J sets the lines extending through the reference points R _{1 to} R _x in the longitudinal direction LD _{1 to} LD _x of the intervertebral disc as slice positions SL _{1 to} SL _{x of the} intervertebral disc. FIG. 20 shows slice positions SL _{1 to} SL _x in the sagittal image data SI. When the slice positions SL _{1 to} SL _x are positioned, the process proceeds to step ST14, the main scan is executed according to the slice positions SL _{1 to} SL _x , and the flow ends.

In this embodiment, a frequency spectrum of the spine is created, and the interval between the intervertebral discs is calculated based on the frequency spectrum. Then, after the intervals of the plurality of landmarks M _{1 to} M _x of the reference model MC of cerebrospinal fluid are made to coincide with the calculated interval of the intervertebral disc, the reference model MC is deformed according to the cerebrospinal fluid of the subject 12. ing. Therefore, the plurality of landmarks M _{1 to} M _x can be set in the vicinity of the intervertebral discs DK _{1 to} DK _x . Moreover, the landmark M ₁ ~M _x is displaced near the disc DK ₁ to Dk _x, the signal strength on line crossing the signal intensity profiles on line across the landmark before the displacement, the landmark after displacement Creating profiles and. Therefore, based on the obtained signal intensity profile, a reference point for positioning the slice position can be set in the intervertebral discs DK _{1 to} DK _x . In this embodiment, after specifying the coronal image IC (see FIG. 4) specified by the operator, the slice positions of the intervertebral discs DK _{1 to} DK _x can be automatically positioned according to steps ST2 to ST13. Therefore, it is possible to reduce the work burden on the operator.

In addition, since the interval between the landmarks M _{1 to} M _x of the reference model MC of the cerebrospinal fluid is made coincident with the calculated interval between the intervertebral discs of the subject 12, the optimal interval is determined according to the interval between the intervertebral discs of the subject 12. The slice position can be positioned at the position.

  In the first embodiment, the long axis direction detecting means 9I is provided. However, if the slice position of the intervertebral disc can be set with high accuracy, it is not always necessary to include the major axis direction detecting means 9I.

  In the first embodiment, the profile creating means 9G creates a signal intensity profile. However, if the slice position can be set in the intervertebral disk with sufficient accuracy, a profile related to the magnetic resonance signal different from the signal intensity profile may be created.

(2) Second Embodiment FIG. 21 is a schematic diagram of an MRI apparatus 200 of the second embodiment.
In the second embodiment, the central processing unit 9 includes feature amount calculation means 9K. The feature amount calculation unit 9K calculates the feature amount of the profile created by the profile creation unit 9G. The reference model positioning unit 9E adjusts the position of the landmark of the reference model MC based on the feature amount calculated by the feature amount calculation unit 9K. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  Next, the operation of the MRI apparatus 200 of the second embodiment configured as described above will be described.

FIG. 22 is a diagram illustrating an example of a processing flow of the MRI apparatus 200.
Steps ST1 to ST8 are the same as those in the first embodiment, and a description thereof will be omitted. In step ST8, signal intensity profiles P _{1 to} P _x are created (see FIG. 14), and then the process proceeds to step ST81.

In step ST81, the feature quantity calculating means 9K (see FIG. 21) calculates the feature quantities of each of the signal intensity profiles P _{1 to} P _x . In the second mode, the integral value Int of each signal strength of the signal strength profiles P _{1 to} P _x is calculated as a feature amount (see FIG. 23).

FIG. 23 is a diagram illustrating an integrated value Int of signal strengths of the signal strength profiles P _{1 to} P _x .

In FIG. 23, the integrated values Int of the signal intensity profiles P _{1 to} P _x are represented by Int = Int1 to Intx. After calculating the integral values Int1 to Intx, the process proceeds to step ST82.

In step ST82, the landmark displacing means 9F (see FIG. 21) keeps the intervals δ _{i, i + 1} of the plurality of landmarks M _{1 to} M _x equal to the interval SP ₀ of the intervertebral discs, while maintaining the plurality of landmarks M ₁ to M M _x is displaced (see FIG. 24).

FIG. 24 is a diagram illustrating a plurality of landmarks after being displaced.
In FIG. 24, a plurality of landmarks M _{1 to} M _x before displacement are indicated by black circles, while a plurality of landmarks M _{1 to} M _x after displacement are indicated by white circles. The interval between the landmarks M _{1 to} M _x (white circles) after the displacement is held at “SP0”, similarly to the interval between the landmarks M _{1 to} M _x (black circles) before the displacement. The amount of displacement of the landmark is, for example, about several pixels. After the landmark is displaced, the process proceeds to step ST83.

In step ST83, signal intensity profiles P ₁ ′ to P _x ′ crossing the landmarks M _{1 to} M _x (white circles) after displacement are obtained in the same procedure as in step ST8. FIG. 25 shows signal intensity profiles P ₁ ′ to P _x ′ crossing the landmarks M _{1 to} M _x (white circles) after displacement. After obtaining the signal intensity profiles P ₁ ′ to P _x ′, the process proceeds to step ST84.

In step ST84, the feature amount (signal intensity integral value Int ′) of each of the signal intensity profiles P ₁ ′ to P _x ′ is calculated in the same procedure as in step ST81. FIG. 26 shows the integrated values Int ′ = Int1 ′ to Intx ′ of the signal strengths of the signal strength profiles P ₁ ′ to P _x ′. After calculating the integral value Int ′, the process proceeds to step ST85.

In step ST85, the reference model positioning means 9E (see FIG. 21) uses a plurality of landmarks M _{1 to} M of the reference model MC based on the integral value Int (see FIG. 23) and the integral value Int ′ (see FIG. 26). Adjust the position of _x . Hereinafter, this adjustment method will be described with reference to FIG.

FIG. 27 is an explanatory diagram of a landmark position adjustment method.
Reference model positioning means 9E, first, the signal intensity profile _P 1 to P _x integral value Int1~Intx of the sum ADD = alpha, the signal intensity profile _P 1 '~P _x' integrated value Int1'～Intx 'of The addition value ADD = α ′ is calculated. Then, the addition values α and α ′ are compared, and if the addition value α is larger, the reference model positioning unit 9E adjusts the landmarks M _{1 to} M _x to the positions indicated by the black circles. On the other hand, when the added value α ′ is larger, the reference model positioning unit 9E adjusts the landmarks M _{1 to} M _x to the positions indicated by white circles. In the second embodiment, it is assumed that α ′> α. Therefore, the reference model positioning unit 9E adjusts the landmarks M _{1 to} M _x to the positions indicated by white circles. After the landmarks M _{1 to} M _x are adjusted to positions indicated by white circles, the process proceeds to step ST9.

  Steps ST9 to ST14 are the same processing as in the first embodiment, and thus description thereof is omitted. In this way, the flow ends.

In the second embodiment, the signal intensity profile _P 1 to P and the added value ADD = alpha integrated value Int1~Intx of _x, the added value ADD integral value Int1'～Intx 'of the signal intensity profile _P 1' ~P _x ' = Α ′ is calculated, and the landmarks M _{1 to} M _x are adjusted to positions where the added value ADD becomes large. By adjusting the positions of the landmarks M _{1 to} M _{x in} this way, the positions of the landmarks M _{1 to} M _x can be adjusted to a more optimal position with respect to the intervertebral disc.

In the second embodiment, the addition value ADD of the integral value is calculated, but instead of the addition value ADD, the average value of the integral value is calculated, and the landmark is calculated based on the comparison result of the average value of the integral value. it may adjust the position of the M ₁ ~M _x.

In the second embodiment, only one combination of landmarks is defined as a combination of landmarks after displacement (see white circles shown in FIGS. 24 to 27). However, a plurality of combinations of landmarks may be defined as the combination of landmarks after displacement. In this case, the addition value ADD is obtained for each combination, and the positions of the landmarks M _{1 to} M _x may be adjusted to the position where the addition value ADD is maximized.

  Furthermore, in the second embodiment, the integral value of the signal intensity is calculated as the feature amount of the profile. However, if the slice position can be set with sufficient accuracy in the intervertebral disc, another feature amount is calculated. May be.

2 Magnetic field generator 3 Table 4 Receiving coil 5 Sequencer 6 Transmitter 7 Gradient magnetic field power supply 8 Receiver 9 Central processing unit 10 Input device 11 Display device 12 Subject 21 Bore 22 Superconducting coil 23 Gradient coil 24 Transmitting coil 31 Cradle 9A Frequency Spectrum creation means 9B Spine detection means 9C Intervertebral disk interval calculation means 9D Landmark interval adjustment means 9E Reference model positioning means 9F Landmark displacement means 9G Profile creation means 9H Reference point setting means 9I Long axis direction detection means 9J Slice positioning means 9K Features Calculation means

Claims (13)

A magnetic resonance imaging apparatus for imaging an intervertebral disc of a subject,
An intervertebral disc interval calculating means for calculating an intervertebral disc interval based on magnetic resonance signals collected from the subject;
Landmark interval adjusting means for adjusting the interval between a plurality of landmarks included in the reference model of cerebrospinal fluid based on the interval between the intervertebral discs;

A reference model positioning means for deforming the reference model in which the interval between the landmarks is adjusted according to the cerebrospinal fluid of the subject and positioning the reference model with respect to the cerebrospinal fluid of the subject;

Landmark displacement means for displacing each of the plurality of landmarks after positioning by the reference model positioning means ;

A profile generating means for generating a profile of the magnetic resonance signals on the that side cutting each transection Ri disc of the plurality of landmarks line,

A reference point setting means for setting a reference point for positioning the slice position of the intervertebral disc on the intervertebral disc based on the profile;

Slice positioning means for positioning a slice position with respect to the intervertebral disc based on the reference point;
A magnetic resonance imaging apparatus. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the intervertebral disc interval calculating unit calculates the intervertebral disc interval based on a frequency spectrum created based on the magnetic resonance signal.
The profile created by the profile creation means includes a profile on a line that crosses the intervertebral disc across the landmark before and after the displacement in the landmark displacement means, and is parallel to each other between the landmarks. 3. A magnetic resonance imaging apparatus according to 2.
In the profile creation means, a line crossing each of the plurality of landmarks and crossing the intervertebral disc is a line segment connecting the landmark and the adjacent landmark, or a line segment connecting the landmarks adjacent to the landmark. The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance imaging apparatus is defined to be vertical.
Long axis direction detecting means for detecting the long axis direction of the intervertebral disc,
The magnetic resonance imaging apparatus according to claim 1, wherein the slice positioning unit positions a slice position of the intervertebral disc based on the reference point and the major axis direction.
The profile is the a signal intensity profile representing the signal strength of the magnetic resonance signals, the magnetic resonance imaging apparatus according to any one of claims 1-5.
A feature amount calculating means for calculating a feature amount of each of the plurality of profiles created by the profile creating means;
The reference model positioning means includes
Based on the feature quantity of each of the plurality of profiles, to adjust the position of the landmark, a magnetic resonance imaging apparatus according to any one of claims 1-6.
The magnetic resonance imaging apparatus according to claim 7 , wherein the feature amount is an integral value of signal intensity. The magnetic resonance imaging apparatus according to claim 8 , wherein the reference model positioning unit adjusts the position of the landmark by using an added value of integral values of signal intensities of the plurality of profiles.
Having spine detection means for detecting the position of the spine;
The reference model positioning means uses the sagittal image data obtained by scanning a sagittal plane including the position of the spine to determine the reference model in which the interval between the landmarks is adjusted as the cerebrospinal cord of the subject. The magnetic resonance imaging apparatus according to claim 1 , wherein the magnetic resonance imaging apparatus is positioned with respect to the liquid.
The magnetic resonance imaging apparatus according to claim 2 , wherein the frequency spectrum is created based on coronal image data of the subject.
A slice position setting method for setting a slice position of an intervertebral disc of a subject,
An intervertebral disc interval calculating step for calculating an intervertebral disc interval based on magnetic resonance signals collected from the subject;
A landmark interval adjustment step of adjusting the interval between a plurality of landmarks of the reference model of cerebrospinal fluid based on the interval between the intervertebral discs;

A reference model positioning step in which the reference model in which the interval between the landmarks is adjusted is deformed according to the cerebrospinal fluid of the subject and positioned with respect to the cerebrospinal fluid of the subject;

A landmark displacement step of displacing each of the plurality of landmarks after positioning by the reference model positioning means ;

A profile creating step of creating a profile of the magnetic resonance signals on the that side cutting each transection Ri disc of the plurality of landmarks line,

A reference point setting step for setting a reference point for positioning a slice position of the intervertebral disc on the intervertebral disc based on the profile;

A slice positioning step for positioning a slice position with respect to the intervertebral disc based on the reference point;
A slice position setting method. A program of a magnetic resonance imaging apparatus for imaging an intervertebral disc of a subject,
Intervertebral disc interval calculation processing for calculating the disc interval based on magnetic resonance signals collected from the subject;
Landmark interval adjustment processing for adjusting the interval between a plurality of landmarks of the reference model of cerebrospinal fluid based on the interval between the intervertebral discs;

A reference model positioning process in which the reference model in which the interval between the landmarks is adjusted is deformed according to the cerebrospinal fluid of the subject and positioned with respect to the cerebrospinal fluid of the subject;

Landmark displacement processing for displacing each of the plurality of landmarks after positioning by the reference model positioning means ;

A profile creating processing for creating a profile of the magnetic resonance signals on the that side cutting each transection Ri disc of the plurality of landmarks line,

A reference point setting process for setting a reference point for positioning a slice position of the intervertebral disc on the intervertebral disc based on the profile;

A slice positioning process for positioning a slice position with respect to the intervertebral disc based on the reference point;
A program that causes a computer to execute.