JP2002017707A - Image pickup face determining method and mri device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine an image pickup face for photographing the MR image of nerve fiber. SOLUTION: MR image data is collected in pulse sequence that does not impress the diffusion emphasizing gradient magnetic field (S1), and MR image data is collected in pulse sequence that impresses the diffusion emphasizing gradient magnetic field in six or more different impressing patterns (S2). A diffusion tensor of each of a large number of reference points is obtained on the basis of the pixel value of an MR image formed on the basis of the obtained MR image data (S3), and the characteristic vector of the diffusion tensor of each reference point is obtained (S4). A characteristic vector map image mapping the characteristic vectors is formed and displayed on a screen (S5). At least one of the characteristic vectors is selected by an operator (S6), and the image pickup face is determined on the basis of the selected characteristic vector information (S7). The MR image of the nerve fiber can thereby be easily photographed on the image pickup face coinciding with the anatomical position of nerve fiber to permit the best description of the nerve fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining an imaging plane and an MRI (Magnetic Resonance Imaging) apparatus, and more particularly, to easily determine an imaging plane for satisfactorily capturing an MR image of a nerve fiber. The present invention relates to a method for determining an imaging plane and an MRI apparatus.

[0002]

2. Description of the Related Art Conventionally, when an MR image of a nerve fiber is taken, an operator estimates a traveling direction of the nerve fiber to determine an imaging plane.

[0003]

However, since the estimation of the operator and the actual running direction of the nerve fiber often do not coincide with each other, in order to obtain a better MR image of the nerve fiber, imaging such as changing the oblique angle is required. The current situation is that the surface is frequently modified. Therefore, an object of the present invention is to provide an imaging plane determination method and an MRI apparatus that can easily determine an imaging plane for satisfactorily capturing an MR image of a nerve fiber.

[0004]

According to a first aspect of the present invention, a zeroth MR image data is acquired by a pulse sequence in which a diffusion-enhancing gradient magnetic field is not applied, and the diffusion-enhancing gradient magnetic field is set to X, Y. , Z-axis with k (≧ 6) different application patterns in the k-th pulse sequence and the first to k-th pulse sequences.
Of the 0th to kth MR images.
A diffusion tensor for each of a number of reference points on the MR image is obtained based on pixel values of the 0th to kth MR images generated based on the image data, and an eigenvector of the diffusion tensor for each reference point is obtained. An eigenvector map image in which eigenvectors are mapped in correspondence with the MR image is generated and displayed on a screen, at least one of the eigenvectors on the eigenvector map image is selected by an operator, and an imaging surface is selected based on the selected eigenvector information. Is determined, and an imaging plane determination method is provided.

It is known that the diffusion characteristic of water in nerve fibers is represented by a 3 × 3 matrix diffusion tensor. It is also known that the direction of the eigenvector having the largest eigenvalue among the three eigenvectors of the diffusion tensor matches the running direction of the nerve fiber. The explanation about the eigenvector of such a diffusion tensor and the running direction of the nerve fiber is as follows.
For example, "Microstructural and Physiological Features
of Tissues Elucidatedby Quantitative-Diffusion-Te
nsor MRI: PETER J. BASSER AND CARLO PIERPAOLI: JOU
RNAL OF MAGNETIC RESONANCE Series B 111, 209-219 (1
996) ”and“ Diffusion Anisotropy -2D and 3D Images of Brain White Matter Fiber Group- ”: Kyoto Prefectural University of Medicine, Department of Radiology, Yasuomi Kinosada: The 30th MR Imaging Society, Heisei 10
September 4 (Sapporo) ".

[0006] In the imaging plane determination method according to the first aspect, the operator selects at least one of the eigenvectors on the eigenvector map image displayed on the screen, and determines the imaging plane based on the information of the selected eigenvector. However, as described above, since the eigenvector of the diffusion tensor is an index indicating the traveling direction of the nerve fiber, the determined imaging plane matches the anatomical position of the nerve fiber corresponding to the selected eigenvector and its MR image This is the optimal imaging surface for capturing the image. Therefore, it is possible to easily determine an imaging surface for satisfactorily capturing an MR image of a nerve fiber. Note that the term “eigenvector” simply refers to the one having the largest eigenvalue among the three eigenvectors that can exist for the diffusion tensor.

In a second aspect, the present invention provides a method for determining an imaging plane having the above-described configuration, wherein when a plurality of eigenvectors whose directions are parallel or substantially parallel are selected on the eigenvector map image, the direction of the eigenvectors is determined. An imaging surface determination method is provided, wherein a plane having the closest direction is determined as an imaging surface. In the imaging plane determination method according to the second aspect, when a plurality of eigenvectors are selected, an imaging plane optimal for imaging a nerve fiber traveling in a direction corresponding to the eigenvectors is determined.

[0008] In a third aspect, the present invention provides a method for determining an imaging plane having the above configuration, wherein when one eigenvector that is not perpendicular or substantially perpendicular to the imaging plane corresponding to the eigenvector map image is selected, the eigenvector is included. In addition, there is provided an imaging surface determination method characterized by determining a plane perpendicular to the imaging surface corresponding to the eigenvector map image as the imaging surface. In the imaging plane determination method according to the third aspect, by selecting only one eigenvector, an imaging plane optimal for imaging a nerve fiber traveling in a direction corresponding to the eigenvector is determined.

In a fourth aspect, the present invention provides a method for determining an imaging plane having the above structure, wherein when an eigenvector having a second eigenvector is selected, a plane including the eigenvector and the second eigenvector is determined as an imaging plane. And a method of determining an imaging plane. In addition, "2nd
The “eigenvector” refers to the eigenvector having the second largest eigenvalue among the three eigenvectors that can exist for the diffusion tensor. When there is a plate-like nerve fiber, the eigenvector having the largest eigenvalue indicates the running direction of the nerve fiber, the eigenvector having the second largest eigenvalue indicates the spreading direction of the nerve fiber, and the eigenvector having the smallest eigenvalue is the nerve fiber. 3 shows the thickness direction. Therefore, in the imaging plane determination method according to the fourth aspect, only by selecting one eigenvector, a plate-like nerve fiber that runs in the direction corresponding to the eigenvector and spreads in the direction corresponding to the second eigenvector is imaged. The optimal imaging plane is determined.

According to a fifth aspect, the present invention provides a method of acquiring zeroth MR image data in a pulse sequence in which no diffusion-enhancing gradient magnetic field is applied, and setting the diffusion-enhancing gradient magnetic field to X,
MR image data acquisition means for acquiring first to k-th MR image data in k pulse sequences applied in k (≧ 6) different application patterns on the Y and Z axes; k generated based on the k MR data
A diffusion tensor calculating means for obtaining a diffusion tensor for each of a large number of reference points on the MR image based on pixel values of the k-th MR image, an eigenvector calculating means for obtaining an eigenvector of the diffusion tensor for each of the reference points, An eigenvector map image generating means for mapping the eigenvector in correspondence with an image to generate an eigenvector map image; an image display means for displaying the eigenvector map image on a screen; and at least one of the eigenvectors on the displayed eigenvector map image. An MRI apparatus comprising: an operation unit for causing an operator to select an imaging surface; and an imaging surface determination unit that determines an imaging surface based on information of a selected eigenvector. In the MRI apparatus according to the second aspect, the imaging surface determination method according to the first aspect can be suitably implemented.

According to a sixth aspect, the present invention provides an M
In the RI apparatus, when a plurality of eigenvectors whose directions are parallel or substantially parallel are selected on the eigenvector map image, the imaging plane determination means determines a plane having a direction closest to the direction of the eigenvectors as the imaging plane. An MRI apparatus is provided. In the MRI apparatus according to the sixth aspect, the imaging surface determination method according to the second aspect can be suitably implemented.

According to a seventh aspect, the present invention provides an M
In the RI apparatus, the imaging plane determination means includes, when one eigenvector that is not perpendicular or substantially perpendicular to the imaging plane corresponding to the eigenvector map image is selected, includes the eigenvector and is perpendicular to the imaging plane corresponding to the eigenvector map image. An MRI apparatus characterized in that a simple plane is determined as an imaging plane. In the MRI apparatus according to the seventh aspect, the imaging surface determination method according to the third aspect can be suitably implemented.

According to an eighth aspect, the present invention provides an M
In the RI apparatus, the imaging plane determining means determines an plane including the eigenvector and the second eigenvector as an imaging plane when an eigenvector having a second eigenvector is selected. . In the MRI apparatus according to the eighth aspect, the imaging surface determination method according to the fourth aspect can be suitably performed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited by this. FIG. 1 is a block diagram showing an MRI apparatus according to one embodiment of the present invention. In this MRI apparatus 100, the magnet assembly 1
Has a space (hole) for inserting a subject inside, a permanent magnet 1p for applying a constant main magnetic field to the subject so as to surround this space, and an X-axis, a Y-axis, A gradient magnetic field coil 1g for generating a Z-axis gradient magnetic field, a transmission coil 1t for applying an RF pulse for exciting spins of nuclei in the subject, and a receiving coil 1r for detecting an NMR signal from the subject. Is arranged. The gradient coil 1g, the transmission coil 1t, and the reception coil 1r
Are connected to a gradient magnetic field driving circuit 3, an RF power amplifier 4 and a preamplifier 5, respectively.

The sequence storage circuit 8 operates the gradient magnetic field drive circuit 3 based on the stored pulse sequence in accordance with a command from the computer 7 to generate a gradient magnetic field from the gradient magnetic field coil 1g of the magnet assembly 1 and The gate modulation circuit 9 is operated to modulate the carrier wave output signal of the RF oscillation circuit 10 into a pulse signal having a predetermined timing and a predetermined envelope shape, which is added to the RF power amplifier 4 as an RF pulse. After power amplification, the power is applied to the transmission coil 1t of the magnet assembly 1 to selectively excite a desired imaging surface.

The preamplifier 5 includes a magnet assembly 1
The NMR signal from the subject detected by the receiving coil 1r is amplified and input to the phase detector 12. Phase detector 12
Uses the carrier output signal of the RF oscillation circuit 10 as a reference signal, performs phase detection on the NMR signal from the preamplifier 5, and
/ D converter 11. The A / D converter 11 converts the analog signal after phase detection into digital data and inputs the digital data to the computer 7.

The computer 7 reads digital data from the A / D converter 11 and performs an image reconstruction operation to generate an MR image of the imaging plane. Further, the computer 7 is responsible for overall control such as receiving information input from the console 13. Further, the computer 7 performs an imaging plane determination process described later with reference to FIG. The display device 6 displays the MR image and an eigenvector map image described later.

FIG. 2 is a flowchart showing the imaging plane determination processing by the MRI apparatus 100. In step S1,
The zeroth MR image data is collected using an arbitrary imaging surface using a pulse sequence that does not apply a diffusion-weighted gradient magnetic field. This pulse sequence is illustrated in FIG. In step S2, the diffusion-enhancing gradient magnetic field MPG is set to X, Y,
The first to k-th MRs are performed using k (≧ 6) different pulse patterns applied to the Z axis in k different pulse sequences.
Obtain image data. Fig. 4 shows six pulse sequences.
9 to FIG. 4 is on the XY axis, FIG. 5 is on the YZ axis,
6 applies the ZX axis, FIG. 7 applies the −XY axis, FIG. 8 applies the −YZ axis, and FIG. 9 applies the diffusion-enhancing gradient magnetic field MPG to the −ZX axis.

In step S3, first, the 0th to k-th M
The 0th to kth MR images are generated from the R image data.
Next, using the pixel values of the 0th to kth MR images, a diffusion tensor is determined for each of a large number of preset reference points by a known algorithm (see the above-mentioned document). The reference point is, for example, an MR image of 512 × 51.
When it is composed of two pixels, 100 grid points are selected and set for every 50 pixels vertically and horizontally. In step S4, eigenvectors are obtained from the diffusion tensors of a large number of reference points by a known algorithm (see the above-mentioned data).

In step S4, as shown in FIG.
An eigenvector map image Mo in which eigenvectors are mapped on the 0th MR image is generated and displayed. Specifically, for each reference point on the 0th MR image, only when the absolute value of the corresponding eigenvector is equal to or greater than a predetermined threshold, the eigenvector is projected onto the 0th MR image and an appropriate drawing length is set. The direction bars A, B, and C created by converting to are drawn. Although the direction bars A and B look like dots,
This means that the corresponding eigenvector is perpendicular to the screen.

In step S5, the operator selects at least one of the eigenvectors on the eigenvector map image. Specifically, the operator operates a pointing device such as a trackball to designate a desired direction bar on the screen.

In step S6, the imaging plane is determined based on the information of the selected eigenvector. For example, the imaging plane is determined as follows. (1) As shown in FIG. 11, a plurality of direction bars D, E, F
Is designated, the plane passing through the reference points corresponding to them or passing through their nearest neighbors and having a direction closest to the direction of the corresponding eigenvectors d, e, f is determined as the imaging plane SP. Note that the operator needs to specify a plurality of direction bars whose directions are parallel or substantially parallel (for example, in FIG. 10, A and B may be specified, but A and C are specified. must not). (2) As shown in FIG. 12, when only one direction bar G is specified, a plane including the eigenvector g corresponding thereto and perpendicular to the imaging plane (Mo) of the 0th MR image is defined as the imaging plane S.
Decide on P. It should be noted that the operator has to input the 0th MR image (M
A direction bar that is perpendicular or almost perpendicular to o) must not be specified (for example, in FIG. 10, C may be specified, but A and B must not be specified). (3) As shown in FIG. 13, when only one direction bar H is designated, a plane including the corresponding eigenvector h1 and its second eigenvector h2 is determined as the imaging plane SP. This method is effective when the nerve fiber is planar and a second eigenvector is obtained. After determining the imaging plane, the process ends.

After the above-described imaging plane determination processing, MR image data is collected by applying a pulse sequence for imaging the determined imaging plane without applying a diffusion-enhancing gradient magnetic field and generating an MR image. Alternatively, a diffusion-weighted MR magnetic field is collected by applying a diffusion-weighted gradient magnetic field corresponding to the direction of the selected eigenvector and collecting MR image data by a pulse sequence for photographing the determined imaging surface.

According to the MRI apparatus 100, the image can be taken on the imaging plane in the direction closest to the direction of the selected eigenvector. However, since the direction of the eigenvector represents the running direction of the nerve fiber, it is eventually selected. Thus, the nerve fiber corresponding to the eigenvector obtained can be photographed on the imaging surface that can best image the nerve fiber.

For example, assuming that a positive diffusion gradient magnetic field of a positive polarity is applied to the X-axis and the Y-axis and no diffusion-weighted gradient magnetic field is applied to the Z-axis is represented by (+, +, 0). ~
In FIG. 9, (0, 0, 0), (+, +, 0), (0,
+, +), (+, 0, +), (-, +, 0), (0,
−, +), (+, 0, −) as shown in FIG. Other examples include (0,0,0),
(+, 0, 0), (0, +, 0), (0, 0, +),
(+, +, 0), (0, +, +), (+, 0, +),
A gradient magnetic field for diffusion emphasis may be applied as (-, +, 0), (0,-, +), (+, 0,-).

[0026]

According to the imaging plane determination method and the MRI apparatus of the present invention, it is possible to easily determine an imaging plane for satisfactorily capturing an MR image of a nerve fiber. That is, it is possible to easily capture an image on an imaging surface that matches the anatomical position of the nerve fiber and can best render the nerve fiber.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an MRI apparatus according to one embodiment of the present invention.

FIG. 2 is a flowchart showing an imaging plane determination process by the MRI apparatus of FIG. 1;

FIG. 3 is an exemplary diagram of a pulse sequence in which a gradient field for diffusion emphasis is not applied.

FIG. 4 is an illustration of a pulse sequence for applying a diffusion-weighted gradient magnetic field to the X and Y axes.

FIG. 5 is an exemplary diagram of a pulse sequence for applying a diffusion-weighted gradient magnetic field to the Y and Z axes.

FIG. 6 is an illustration of a pulse sequence for applying a diffusion-weighted gradient magnetic field to the Z and X axes.

FIG. 7 is an exemplary diagram of a pulse sequence for applying a diffusion-weighted gradient magnetic field to the -X and Y axes.

FIG. 8 is an exemplary diagram of a pulse sequence for applying a diffusion-weighted gradient magnetic field to the −Y and Z axes.

FIG. 9 is an exemplary diagram of a pulse sequence for applying a diffusion-weighted gradient magnetic field to the −Z and X axes.

FIG. 10 is an illustration of an eigenvector map image.

FIG. 11 is a first exemplary diagram of a determined imaging surface.

FIG. 12 is a second illustration of the determined imaging plane.

FIG. 13 is a third exemplary diagram of the determined imaging surface.

[Explanation of symbols]

 Reference Signs List 100 MRI apparatus 1 Magnet assembly 1g Gradient magnetic field coil 6 Display device 7 Calculator 8 Sequence storage circuit 13 Operation console

Claims (8)

[Claims] 1. A zero-order MR image data is collected in a pulse sequence in which a diffusion-enhancing gradient magnetic field is not applied, and k (≧ 6) different application patterns of the diffusion-enhancing gradient magnetic field on the X, Y, and Z axes are provided. Pixel data of the 0th to kth MR images generated based on the 0th to kth MR image data by collecting the 1st to kth MR image data with k kinds of pulse sequences applied in A diffusion tensor for each of a large number of reference points on the MR image is obtained based on the above, an eigenvector of the diffusion tensor for each of the reference points is obtained, an eigenvector map image in which each eigenvector is mapped in correspondence with the MR image is generated and displayed on a screen. Displaying an image, allowing the operator to select at least one of the eigenvectors on the eigenvector map image, and determining an imaging plane based on information on the selected eigenvector. Surface determination method. 2. The imaging plane determination method according to claim 1, wherein when a plurality of eigenvectors whose directions are parallel or substantially parallel are selected on the eigenvector map image, the eigenvector has a direction closest to the direction of the eigenvectors. An imaging surface determination method, wherein a plane is determined as an imaging surface. 3. The imaging plane determination method according to claim 1, wherein when one eigenvector perpendicular or substantially perpendicular to the imaging plane corresponding to the eigenvector map image is selected, the eigenvector map image includes the eigenvector and includes the eigenvector map image. A method for determining an imaging surface, wherein a plane perpendicular to a corresponding imaging surface is determined as an imaging surface. 4. The imaging plane determination method according to claim 1, wherein when an eigenvector having a second eigenvector is selected, a plane including the eigenvector and the second eigenvector is determined as an imaging plane. Imaging surface determination method to be performed. 5. A method for acquiring data of the 0th MR image in a pulse sequence in which no diffusion-enhancing gradient magnetic field is applied, and applying k (≧ 6) different application patterns of the diffusion-enhancing gradient magnetic field on the X, Y, and Z axes. And MR data acquisition means for acquiring the first to k-th MR image data in k pulse sequences applied in the step (b), and the 0th to kth MR image data generated based on the 0th to kth MR image data. a diffusion tensor calculating means for calculating a diffusion tensor for each of a large number of reference points on the MR image based on pixel values of the MR image of k; an eigenvector calculating means for calculating an eigenvector of the diffusion tensor for each of the reference points; An eigenvector map image generating means for mapping the eigenvectors to generate an eigenvector map image, and displaying the eigenvector map image on a screen Image display means, operating means for allowing an operator to select at least one of the eigenvectors on the displayed eigenvector map image, and imaging surface determination means for determining an imaging surface based on information on the selected eigenvector. An MRI apparatus, comprising: 6. The MRI apparatus according to claim 5, wherein
When a plurality of eigenvectors whose directions are parallel or substantially parallel are selected on the eigenvector map image, the imaging plane determination means determines a plane having a direction closest to the direction of the eigenvectors as the imaging plane. MRI
apparatus. 7. The MRI apparatus according to claim 5, wherein
When one eigenvector that is not perpendicular or substantially perpendicular to the imaging surface corresponding to the eigenvector map image is selected, the imaging surface determination unit captures a plane that includes the eigenvector and that is perpendicular to the imaging surface corresponding to the eigenvector map image. An MRI apparatus characterized by determining a plane. 8. The MRI apparatus according to claim 5, wherein
An MRI apparatus, wherein, when an eigenvector having a second eigenvector is selected, the imaging plane determination means determines a plane including the eigenvector and the second eigenvector as an imaging plane.