JPH05168606A - MR spectroscopic imaging method and imaging apparatus thereof - Google Patents

Abstract

(57) [Abstract] [Purpose] In MRSI, the spatial resolution is set according to a region of interest such as a lesion before data collection, and signals from other than the region of interest are prevented from being mixed into voxel data as much as possible. [Configuration] An MR image of ¹ H or the like is obtained, and the MR image and the rectangular ROI are displayed in a superimposed manner. Next, the operator is made to adjust the ROI to specify the minimum area including the lesion. Next, the gradient magnetic field strength for phase encoding is set from the vertical and horizontal dimensions of the final ROI, and a 3D-MRSI scan such as ³¹ P is performed. Furthermore, after the MR spectrum data is obtained as the voxel luminance data by Fourier transform, the matrix image (luminance data), the MR image, and the ROI are displayed, and the primary phase shift is performed based on the positional deviation between the grid and the ROI of the matrix image. Is performed to obtain voxel data matched to the position of ROI. Further, the spectrum data in the designated ROI is obtained from the Fourier transform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an MR spectroscopic imaging method and an imaging apparatus therefor, and more particularly to an imaging method capable of obtaining an MR spectrum whose spatial resolution is preset.

[0002]

2. Description of the Related Art MRSI (Magnetic Reso-nance Spectroscopic), which is a type of magnetic resonance imaging (MRI),
Imaging) encodes spatial information into the initial phase of the signal in the time domain by means of a pulsed linear gradient magnetic field, collects MR signals without adding a readout gradient magnetic field, and then performs Fourier transform to obtain position information. It is also used for quantitative analysis of samples (eg, Brown TR et al, NMR Chemical Shift).
Imaging in three dimensions, Proc. Natl. Acad. Sc
i. USA, 1982; 79: 3523-3526 ,, BD Ross et al,
Metabolic Re-sponse of Glioblastoma to Adoptive I
mmunotherapy: Detection by Phospho-rus MR Spectros
copy, J. of Computer Assisted Tomography, 13 (2): 18
9-193,1989). There are various MRSIs depending on the number of phase encodes. Among these, two-dimensional phase encoding is performed (in addition, the unit of chemical shift is added),
A pulse sequence and acquisition matrix of 3D-MRSI are shown in FIGS. MRSI such as ³¹ P
Then, from the relationship between the S / N ratio and the collection time, 8 × 8 or 16
A collection matrix of about × 16 is used, and each voxel size is set to about 20 to 40 mm.

[0003]

However, even in the above-mentioned MRSI, it is required that the diagnostic conditions of MRI, that is, the spatial resolution and the concentration resolution are excellent, and in order to improve the spatial resolution, the size of voxel is required. Is desired to be as small as possible. On the other hand, in order to improve the density resolution, it is desirable to make the S / N ratio per voxel as high as possible. However, if the voxels are reduced in order to improve the spatial resolution, the S / N ratio deteriorates, and it has been difficult to achieve both high spatial resolution and high density resolution. Therefore, as a compromise between spatial resolution and density resolution, conventionally, one side is 20 to 4
The voxel size of 0 mm was set, but it cannot be said that this voxel size is sufficiently smaller than the measurement target such as a tumor. As shown in FIG. 12, in the voxel covering the measurement target OB, the measurement target OB There may be a large area OT other than. That is, in such a case, there is a problem in that a large amount of signals from other than the interested portion OB are mixed in the spectrum data obtained by the MRSI, and a highly accurate MR spectrum cannot be obtained for the measurement target OB. It was

The present invention has been made in view of such a conventional problem, and in MR spectroscopic imaging, the spatial resolution can be set in advance and arbitrarily, and a signal from a portion other than a portion of interest is mixed. It is an object of the present invention to provide an imaging method and apparatus capable of obtaining a reduced MR spectrum.

[0005]

In order to achieve the above object, the imaging method of the present invention is such that an MR image of a desired region of a subject is acquired in advance, and the acquired MR image is
A rectangular ROI whose position and size can be adjusted by the operator
, And then the ROI set by the operator
The same size as the imaging voxel size is determined, the gradient magnetic field strength for phase encoding is determined based on the determined voxel size, and then MR spectroscopic imaging is performed based on the determined gradient magnetic field strength. A first data processing step of obtaining a matrix image in which spectral data due to chemical shift is reflected, and the MR
After collecting the data by spectroscopic imaging, the MR image and the RO set by the operator were again used.
I and the matrix image are displayed, the positional deviation between the ROI and the grid of the matrix image is calculated, and thereafter,
A second data processing step of reconstructing the spectral data in the ROI based on the calculated value of the positional deviation.

Further, the imaging apparatus of the present invention has means for preliminarily acquiring an MR image of a desired region of the subject and a rectangular shape for which the operator can adjust the position and size of the MR image acquired by this means. Of the ROI, the means for determining the imaging voxel size of the same size as the ROI set by the operator, and the gradient magnetic field strength for phase encoding based on the voxel size determined by the voxel size determining means. And means for obtaining a matrix image reflecting spectral data due to chemical shift by performing MR spectroscopic imaging based on the gradient magnetic field strength determined by the magnetic field strength determining means. After data collection by MR spectroscopic imaging, again before MR images, the operator has set R
Means for displaying the OI and the matrix image, and the RO
It is provided with means for calculating the positional deviation between I and the grid of the matrix image, and means for reconstructing the spectral data in the ROI based on the positional deviation value calculated by the calculating means.

[0007]

According to the imaging method and apparatus of the present invention, first, a high-resolution MR image (for example, an axial image of a head) of a desired region of the subject (for example, an axial image of the head) is scanned before performing the MR spectroscopic imaging scan. ¹ H proton density distribution image) is collected in advance. Thereby, morphological information such as the position and size of the lesion area can be obtained.
This MR image is displayed on the monitor together with a rectangular ROI whose position and size can be adjusted by the operator. afterwards,
The operator adjusts the position of the ROI to the lesion of interest on the MR image, and adjusts the size of the rectangle so that the ROI circumscribes the lesion, for example.
After this adjustment is completed, the operator determines the imaging voxel size that is the same as the ROI that is finally set, and the gradient magnetic field strength for phase encoding is determined based on the determined voxel size. , MR spectroscopic imaging is performed on the basis of the gradient magnetic field strength, and a matrix image reflecting spectral data due to the electron shielding effect is obtained. When this matrix image is obtained, the MR image, the ROI set by the operator, and the matrix image are displayed again on the monitor, and the positions of the ROI and the grid of the matrix image (the boundary line between voxels forming the matrix image) are displayed. The deviation is calculated, and the ROI is calculated based on the calculated value of the positional deviation by using, for example, a first-order phase shift method on the k space.
The spectral data in is reconstructed. As a result, the spectrum data of the minimum necessary area including the lesion can be obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

The MR spectroscopic imaging apparatus shown in FIG. 1 is capable of performing the MRSI of the present invention, and includes a magnet unit for generating a static magnetic field and a gradient magnetic field generating gradient for giving positional information to the static magnetic field. Magnetic field part, excitation and NM
It functionally has a transmitting / receiving unit for receiving the R signal and a control / arithmetic unit for system control and data processing.

Specifically, the magnet section includes, for example, a superconducting magnet 1 and a static magnetic field power supply 2 for exciting the magnet 1, and a static magnetic field is provided in the z-axis direction of the opening into which the subject P is inserted. H
Generates ₀ . Further, the gradient magnetic field unit is composed of three pairs of gradient magnetic field coils 4 ... 4 incorporated in the magnet 1 in the x, y and z directions.
(Only part of which is shown), and these gradient coil 4 ...
Drive circuit 5 and gradient magnetic field control device 6 for supplying current to 4
And a gradient magnetic field power source. Gradient magnetic field controller 6
Activates the drive circuit 5 according to the pulse sequence supplied from the main controller 7. As a result, a gradient magnetic field in which a linear magnetic field is superimposed on the static magnetic field H ₀ is formed, and position information for imaging is added. The transmission / reception unit includes a transmission / reception high-frequency coil 8 arranged to face the subject P in the opening of the magnet 1, and a transmitter 9 and a receiver 10 connected to the high-frequency coil 8. .. Transmitter 9
Radio frequency (RF) for exciting nuclear magnetic resonance (NMR)
The pulse is generated based on a command from the control device 7. Receiver 10
Is subjected to processing such as detection and amplification of the NMR signal collected by the high frequency coil 8 and sends the processed signal to the storage device 11.

Further, the control / calculation unit includes a control device 7 connected to the transmitter 9, the receiver 10 and the gradient magnetic field control device 6, a storage device 11 for storing processed data, and a calculation device for data calculation. 12 and a display device 13 for display. An input device 14 such as a keyboard, a trackball, a mouse or a joystick is connected to the control device 7. The arithmetic unit 12 subjects the stored NMR signal to an enormous amount of arithmetic processing including Fourier transform and the like to process it into image data. This image data is displayed on the display device 13 as needed.

The built-in memory of the control device 7 stores a procedure for controlling from a predetermined photographing plan to the main photographing as one of fixed data, and the procedure is stored in the work area when the system is started. Be called. And
While performing the shooting according to the called procedure,
A message is displayed on the display device 13, a necessary dialogue is performed with the operator, and a predetermined procedure is digested based on the result.

The MR spectroscopic imaging device is capable of adjusting the frequencies of the electromagnetic waves to be transmitted and received, so that the magnetic resonance imaging for normal nuclei and the MR spectroscopic imaging can be performed by the same device. ing.

Next, the operation of this embodiment will be described with reference to FIGS.

The control unit 7 carries out the series of processing shown in FIG. 2 upon activation thereof. That is, step 2 of FIG.
0 waits while judging whether or not MRSI is ready to be performed.
If it is determined that the preparation is completed based on the command sent through step S21, the process proceeds to step 21.

In this step 21, MRS such as ³¹ P
Normal MR imaging (MRI) such as the spin echo method is performed on the site where I will be performed. As a result, for example, a ¹ H high resolution MR image (for example, 25 H
A 6 × 256 matrix with a resolution of about 1 mm) is collected in advance, and its MR data is stored in the storage device 11.
Next, the control device 7 displays the acquired MR image on the display device 13 as shown in FIG. 3, for example, in the process of step 22. Thereby, the operator obtains the morphological information of the affected area (for example, the position and size of the tumor OB in the head as shown in FIG. 3).

Next, the control device 7 shifts to the processing of step 23, and a rectangular ROI (region of interest) with a preset initial size is set in the already displayed MR image at its initial position as shown in FIG. It is superimposed and displayed. This ROI functions as a marker.

Next, the control unit 7 performs steps 24-26.
Is processed. That is, in step 24, it is determined based on the command from the input device 14 whether or not the operator has finally determined the position and size of the ROI. N in this judgment
If it is O, it is finally undecided, so step 25
Then, the operator uses the input device 14 to input an adjustment signal for the position and size of the ROI to be given to the apparatus. Further, in step 26, the ROI of the adjusted position and size is superimposed and displayed on the MR image in near real time. After this, the process returns to step 24, and finally R
The above process is repeated until it is determined that the position and size of the OI have been determined.

That is, the operator observes the MR image such as ¹ H and adjusts the ROI according to the position of the lesion of interest.
And the ROI of the minimum necessary rectangle (arbitrary size) in which the lesion enters is set. Thereby, for example, as shown in FIG. 5, the ROI having a size circumscribing the tumor OB of the head is set as a voxel size described later.

When the ROI is finally set in this way, YES is determined in step 24, and then the processing from step 27 onward is sequentially executed by the control device 7. Of these, the RO finally set in step 27
The vertical and horizontal sizes x and y of I (see FIG. 5) are read, and in step 28, the maximum strengths Gxmax and Gymax of the MRSI phase encoding gradient magnetic field (that is, from the minimum value to the maximum value of the phase encoding gradient magnetic field). Swing width [G / m
m]: see FIG. 6), that is, the spatial resolution in the X and Y directions is set based on the following two equations.

Γ · Gxmax · x · τ = 2π γ · Gymax · y · τ = 2π where γ: is the gyromagnetic ratio of the nuclide for MRSI,
For example, in the case of ³¹ P, γ = 1.084 × 10 ⁴ [rad / S ・
G], x, y: voxel size [mm] set by ROI, τ: application time [s] of phase encoding gradient magnetic field. The calculation of these two equations is based on the pulse sequence of 3D-MRSI shown in FIG.

Here, the magnitude of the maximum strengths Gxmax and Gymax of the phase encoding gradient magnetic field at each step will be exemplified. For example, when the target nuclide is ³¹ P and the voxel size x in the X direction (that is, the size of the ROI in the X direction) = 30 [mm], if τ = 2.0 [ms], then Gxmax = 2π / (γ · x · τ) = 9.6 × 10 ⁻³ [G /
mm]. Therefore, assuming that the number of matrices = 8, the gradient magnetic field strength per step of phase encoding is approximately Gxmax / 8 = 1.2 × 10 ⁻³ [G / mm] (see FIG. 6).

Similarly, the voxel size in the Y direction is 40 [m
m], Gymax = 7.2 × 10 ⁻³ [G / mm] Gymax / 8 = 0.9 × 10 ⁻³ [G / mm] (see FIG. 6).

When the phase-encoding gradient magnetic field is obtained as described above, 3D is obtained in the process of step 29 in FIG.
The MRSI scan is performed as shown in FIG. 6, and the spectrum data due to the electron shielding effect is obtained. Then
In step 30, the data obtained by this 3D-MRSI pulse sequence is Fourier transformed in the direction of Kx, Ky (the number of steps of phase encoding in the X and Y directions: integer) and time t, and each spectrum of the matrix in space is calculated. Is obtained as luminance data. For example, in the case of a matrix in space = 8 × 8, -3 ≦ Kx ≦ 4 and -3 ≦ Ky ≦ 4. Therefore, the spectral data of 8 × 8 = 64 voxels in space is the integral of the spectrum. It is obtained as brightness data corresponding to the value.

After that, in step 31, the image thus obtained is divided and displayed on the display device 13. That is, the brightness value of the spectrum data obtained in step 30 is displayed as one of the divided screens (see FIG. 7), and the MR image such as ¹ H and the ROI superimposed image set by the operator are displayed as another screen. Displayed at the same time.

The size of each voxel in FIG. 7 is the same as the size x, y of the ROI set in FIG. However, since the position of each voxel and the position of the ROI are determined or set independently of each other, when the object is used as a reference except when it happens to be coincident, as shown in FIG. The position of the two does not match.

Therefore, in the processing of the next step 32, in order to obtain the spectrum data within the ROI finally set by the operator, the positional deviation Δx between the position of the ROI and the boundary line between each voxel (called a grid), Δy (see FIG. 8) is calculated by the control device 7. Next, in step 33, one ROI set by the operator is set.
Re-set the voxels of the whole matrix so that fits exactly in the first square of the matrix (one voxel). That is, using the shifts Δx and Δy calculated in step 32, the original data S _{(Kx, Ky, t)} after scanning obtained in step 29 is used for _{Kx, Ky} on the k space based on the following equation. A first-order phase shift (phase rotation) is performed on the to obtain spectrum data S ′ _{(Kx, Ky, t)} .

S ' _{(Kx, Ky, t)} = S _{(Kx, Ky, t)} ^{.multidot.e-i.gamma.A} However, where n is the number of matrices (eg, 8), A = (Gxmax / n) .Kx.delta.x.tau. + (Gymax / n)
・ Ky ・ Δy ・ τ. In the real space, this phase shift corresponds to redrawing the grid as shown in FIG. 9 so that the grid shown in FIG. 7 matches the ROI.

After that, the process proceeds to step 34 and the spectrum data S '(Kx, Ky, t) subjected to the primary phase shift is used.
Is again Fourier transformed. Therefore, this time, a matrix-like luminance value that forms a grid for accommodating the ROI set by the operator in the first cell is obtained. This allows
The brightness value of the voxel at the position of the ROI designated by the operator corresponds to the spectrum data in the ROI to be obtained.

For this reason, the voxel at the ROI position (same for other voxels) is originally set by the operator to the required minimum size in accordance with a lesion such as a tumor. Signal contamination (in this case noise) for the spectral data from is minimized. Therefore, it is possible to obtain a highly accurate MR spectrum of a lesion area by localized MRSI, and it is possible to obtain an advantage that the diagnostic ability is significantly improved as compared with the conventional method.

The MRSI of the above-described embodiment has been shown in the case where the FID (free induction attenuation) signal is collected as the MR signal by performing the two-dimensional phase encoding (3D-MRSI), but the present invention is such. It is not limited to the embodiment. For example, instead of slice selection, Z
It can also be applied to the case of so-called 4D-MRSI in which phase encoding is performed in the direction (body axis direction). Further, the MR signal is not the FID signal, but can be applied to the case of collecting in the form of spin echo after the 180 ° pulse application.

[0032]

As described above, the M according to the present invention
According to the R spectroscopic imaging method and apparatus, the MR image of the desired region of the subject acquired in advance is
A rectangular ROI whose position and size can be adjusted by the operator
Is displayed together with, and then R set by the operator
A voxel size for imaging having the same size as the OI is determined, a gradient magnetic field intensity for phase encoding is determined based on the determined voxel size, and M is determined based on the gradient magnetic field intensity.
R spectroscopic imaging is performed. further,
After collecting the data by the MR spectroscopic imaging, the MR image and the R set by the operator were set again.
It is assumed that the OI and the matrix image are displayed, the positional deviation between the ROI and the grid of the matrix image is calculated, and the spectral data in the ROI is reconstructed based on the calculated value of the positional deviation. Therefore, the size of each voxel (that is, the spatial resolution) of the matrix image becomes the same as the size of the rectangular ROI set by the operator, so that the shape of the lesion part that appeared in the MR image before the operator scans the MRSI. The size of ROI (that is, spatial resolution) can be arbitrarily set according to the above. Therefore, the operator can set the ROI circumscribing the lesion area to eliminate the spectrum data mixed from the tissue other than the lesion area as much as possible, and obtain the MR spectrum that more accurately reflects the spectrum data of the lesion area. The diagnostic ability can be remarkably improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an MR spectroscopic imaging apparatus according to the present invention.

FIG. 2 is a schematic flowchart showing an example of a processing procedure of a control device.

FIG. 3 is an explanatory diagram showing an example of MR images acquired in advance.

FIG. 4 is an explanatory diagram showing an ROI superimposed and displayed on an MR image.

FIG. 5 is an explanatory diagram showing a state in which an ROI is circumscribed on a lesion area on an MR image.

FIG. 6 is a timing chart illustrating a pulse sequence of 3D-MRSI.

FIG. 7 is an explanatory diagram showing an example of a 3D-MRSI matrix image.

FIG. 8 is an explanatory diagram showing a positional deviation between a matrix image grid and an ROI set by an operator.

FIG. 9 is an explanatory diagram showing a state where the matrix is reset according to the ROI.

FIG. 10: 3D- cited for explaining the prior art.
The timing chart which shows the pulse sequence of MRSI.

FIG. 11: 3D- cited for explaining the prior art.
Explanatory drawing explaining the acquisition matrix obtained by MRSI.

FIG. 12 is an explanatory diagram for explaining an inconvenience of a conventional technique of MRSI.

[Description of Reference Signs] 1 magnet 2 static magnetic field power supply 4 gradient magnetic field coil 5 driving circuit 6 gradient magnetic field control device 7 control device 8 high frequency coil 9 transmitter 10 receiver 11 storage device 12 arithmetic device 13 display device 14 input device

Claims (2)

[Claims] 1. An ROI set by an operator after acquiring an MR image of a desired region of a subject in advance, displaying the acquired MR image together with a rectangular ROI whose position and size can be adjusted by the operator. The same size as the voxel size for imaging is determined, and the gradient magnetic field strength for phase encoding is determined based on the determined voxel size,
After that, after the first data processing step of performing MR spectroscopic imaging based on the determined gradient magnetic field strength to obtain a matrix image reflecting the spectral data, and after collecting the data by the MR spectroscopic imaging, , The MR image, the ROI set by the operator, and the matrix image are displayed.
A positional deviation between the OI and the grid of the matrix image is calculated, and then the ROI is calculated based on the calculated value of the positional deviation.
A second data processing step of reconstructing spectral data in the MR spectroscopic imaging method. 2. A means for preliminarily acquiring an MR image of a desired region of a subject and a rectangular R whose operator can adjust the position and size of the MR image acquired by this means.
A means for displaying together with the OI, a means for determining an imaging voxel size of the same size as the ROI set by the operator, and a gradient magnetic field strength for phase encoding based on the voxel size determined by the voxel size determining means. The MR spectroscopic imaging is provided with a means for determining and a means for obtaining a matrix image reflecting the spectral data by performing MR spectroscopic imaging based on the gradient magnetic field strength determined by the magnetic field strength determining means. After collecting the data, the MR image and the R set by the operator
Means for displaying the OI and the matrix image, and the RO
An MR comprising: means for calculating the positional deviation between I and the grid of the matrix image; and means for reconstructing the spectral data in the ROI based on the positional deviation value calculated by the calculating means. Spectroscopic imaging system.