JPS63279831A - Mri image pickup method and apparatus - Google Patents

Abstract

PURPOSE:To obtain a good NMR image having no geometrical strain, by correcting the image strain contained in the NMR image without restricting the direction of the coordinates axes constituting an image surface. CONSTITUTION:The constitution correcting the strain mixed in the image of an object to be examined consists of a calculation system 23b for calculating the distribution of a static magnetic field and that of the magnetic field distribution in the coordinates axis direction of a reference coordinates system and a strain correction system 24b for correcting the strain of an obliquely cut image. The calculation system 23b for calculating the distribution of the static magnetic field and that of the inclined magnetic field in the coordinates axis direction of the reference coordinates system consists of calculation systems 27b, 30b, 26b, 31b for calculating the distribution of strain quantities in the axial directions of the coordinates axes (x), (y), (z) of the reference coordinates system and a static magnetic field distribution calculation system 32b. The strain correction system 24b of the obliquely cut image consists of a coordinates converting system 34b, a strain quantity calculation system 35b and a strain correction system 36b.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a nuclear magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus), and in particular to an MRI apparatus suitable for correcting image distortion thereof.
The present invention relates to an imaging method and apparatus.

[Conventional technology]

In an MRI device, the distribution of nuclear spin inside the object to be inspected,
Images representing parameters related to the spin-lattice relaxation constant, spin-spin relaxation constant, and tissue structure in combination can be measured. In an MRI device, an object to be examined is placed in a fairly uniform static magnetic field, and a gradient magnetic field and a high-frequency magnetic field are applied according to a preset time order to calculate an NMR image (also called an MR image). Measure the NMR signal of.

The gradient magnetic field is combined with a high-frequency magnetic field and irradiated onto an object to be inspected placed in a static magnetic field in order to add spatial information to the NMR signal generated from the object to be inspected. Therefore, if there is no uniformity in the static magnetic field or linearity in the gradient magnetic field,
Errors are mixed into the spatial information of the NMR signal, and local positional deviations, that is, image distortions occur in the NMR signal. As a method for correcting image distortion caused by the non-uniformity of the gradients of the static magnetic field and the gradient magnetic field, the distribution of image distortion caused by the non-uniformity of the static magnetic field and the non-linearity of the gradient magnetic field within the field of view is A method has been adopted in which measurements are taken in advance and the data is used to correct each point on the image obtained under the above-mentioned static magnetic field and gradient magnetic field.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into consideration the arbitrariness of the direction of the coordinate axes that constitute the imaging plane, and the amount of image distortion for an arbitrary oblique image is measured in advance as data.

There is a problem with saving the table of distortion amount distribution, which becomes large in size.

An object of the present invention is to provide a method and apparatus for correcting image distortion contained in an NMR image without limiting the direction of the coordinate axes that constitute the image plane, and obtaining a good NMR image free of geometric distortion. It is in.

[Means for solving problems]

The main point of the present invention is that in an inspection apparatus that performs imaging using a direct measurement method, a static magnetic field within a field of view and a rectangular coordinate system (
The intensity distribution of the gradient magnetic field in each axis direction of the reference coordinate system (hereinafter referred to as the reference coordinate system) is measured in advance, and this data is used to calculate the intensity distribution of the gradient magnetic field in each axis direction of an arbitrary orthogonal coordinate system. Images obtained under a static magnetic field and a gradient magnetic field are
This is because the correction is made for each point on the image.

Taking a two-dimensional case as an example, a method for measuring the intensity distribution of the static magnetic field within the field of view and the gradient magnetic field in each axial direction of the reference coordinate system will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows an improved sequence of the spin warp method. The data measured using this sequence is C(Xs
y) is the distribution of target nuclei, E (x.

y) is the deviation of the static magnetic field distribution from the reference amount, Gx.

Gy is the magnitude of the gradient of the gradient magnetic field in the phase encoding direction and readout direction, respectively, ax (xt y) tεy
(x, y) is the X direction, the amount of deviation from the straight line that depends on the shape of the gradient magnetic field coil in the X direction, Gx・Ex(xIy) gG
If y°εy (x, y) is the component that deviates from the straight line of the gradient magnetic field in the X direction and the
(Gy(y+εy(x,y))to+(E(xty)+
Gx(x+εx(x,y)))tx)]dxdy (
1). Note that the relaxation term is ignored here. Further, γ is the nuclear gyromagnetic ratio, and tx and ty are the times during which the gradient magnetic fields are applied in the X direction and the X direction, respectively.

When converted according to
p [-2πj y(Gy-y'・to+Gx-x'・
tx)]dx'dy'. Here, Also, here, ft(x'yy'Lf2(x' r
! ') is the result of solving equation (2) inversely, X = f 1
(X' t V' Ly = f 2 (x'
ty').

J(x,y) is y It is.

Normally, it can be regarded as
)lf2(X'+'/')) (6).

Now, when the measurement data 5 (tx, ty) is subjected to two-dimensional inverse Fourier transform, C'(x'yy') is obtained. This C'
(x'+y') can be calculated from any distribution C(x) using equation (6).

It is equivalent to the coordinate transformation of y) according to equation (2).

That is, the image is subjected to distortion shown by equation (2) due to the gradient magnetic field and static magnetic field distribution in the X-axis direction, which is the readout direction, and due to the gradient magnetic field distribution in the y-axis direction, which is the phase encoding direction. According to the distortion correction method previously proposed by the present inventors, the amount of distortion shown in equation (7) can be obtained.

However, as can be seen from equation (7), the distribution of the gradient magnetic field and the static magnetic field in the X-axis direction cannot be determined separately from the strain amount in the X-axis direction determined by the above method. Therefore, a method for obtaining the distributions of the gradient magnetic field and the static magnetic field separately will be explained below.

FIG. 2 shows the sequence of FIG. 1 with the readout direction and phase encoding direction exchanged. In the case of this sequence, the amount of distortion corresponding to equation (7) is vx' (x, y) = Cx
It is indicated by (x + y). Therefore, (7), (8
) The static magnetic field distribution can be determined from each strain amount in the above two sequences shown in the equation. It is also clear from equations (7) and (8) that the gradient magnetic field distribution in each direction has been determined.

In the above, a two-dimensional case has been taken as an example to simplify the explanation, but it is also possible to expand to three dimensions and obtain the static magnetic field distribution and gradient magnetic field distribution in the viewing space.

Next, a method for determining the distribution of the gradient magnetic field in an arbitrary direction from the distribution of the gradient magnetic field in each axis direction of the reference coordinate system will be explained. Third
The x, y, and z axes in the figure are the axes of the basic coordinate system, and P+rtS
The axis is an axis of a coordinate system that can be taken arbitrarily by the angle O2φ.

Incidentally, since the magnetic field directions of the gradient magnetic fields are all the same, a gradient magnetic field in any direction can be generated by linear addition of gradient magnetic fields in the X, y, and Z directions. Taking the gradient magnetic field in the p-axis direction in Figure 3 as an example, a point in an arbitrary coordinate system (P+P+S
) is the magnitude of the gradient magnetic field at Gp(p1εp(
py r, 5) = Gp [ax'(x(py r, s) + 1x(p, r
, s)) 1ay'(y(p, r, S)+εy(P+ r
, s)) 10az・(z(P+ r, s) 1εz(p,
r, s))] (9). Here, Gp is the magnitude of the gradient magnetic field in the p-axis direction, and ax, ay, and az are θ
, φ, represents the ratio of the gradient magnitude of the gradient magnetic field in the x, y, and z axis directions determined by φ, and
P+ r'+ 5)tZ(P+ P+ S) is the point (
Coordinates (x+ y+
z). From equation (9), the magnitude of the gradient magnetic field in the x, y, and z axis directions is Gp-ax, Gp'a'/+G, respectively.
p, aZ. Also, i p(P+ P+ S)+ E
X(P+ P+ S)+ ty(P+ P+ S)+
εZ(P+P+S) is the amount of deviation of the gradient magnetic field from the straight line in the P+X,'lr Z-axis direction. Therefore, from equation (9), the amount of deviation of the gradient magnetic field in the p-axis direction from the straight line is [P(PI r, 5)=ax't x(p+r+s)
+a y′t y(p+r*s) 10az·εz(p+rts) (n). From the above, the amount of deviation of the gradient magnetic field from the straight line in any direction is calculated using equation (11).

Next, a method for correcting distortion of arbitrary oblique images will be explained. FIG. 4 shows a sequence for taking an oblique image. In Fig. 3, the S axis is the slice direction during oblique imaging, the r axis is the phase encoding direction, and the r axis is the readout direction, c (p + re s) is the distribution of the object, GP (P + EP (p + rt 5)) r
If Gr (r+i r (p+ r, s)) is the r-axis, a gradient magnetic field in the r-axis direction, and E (p+ r, s) is a nonuniform component of the static magnetic field, the data measured using this sequence is S (tp+Gr)=/C(p, r, 5o)exp[-
2ij y(Gp (p + i p(p+rtso)
)to+(E(p+r+5o))10Gr(r+t r
(p, r, 5o)) tr) ldpdr, (12
) corresponds to equation (1). Here, so indicates the slice position on the imaging plane. Furthermore, by performing coordinate transformation using equation (13), equation (12) &yo, 5(tp, 0r) = fC
(p', r'5o)exp[2πjy(Gp-r'・t
o+Gr-r'·tr)]dxdy. Here (1
Equation 3) corresponds to equation (2) thick, (14) ni, and equation (3). In addition, as the strain amount corresponding to equation (7), the strain amount in the p + r axis direction is vp (p * r, so), vr (P + r
e SO), then the above strain amount is the ratio of the gradient magnetic fields in the X, y, and z directions to generate the gradient magnetic field in the p+r axis direction, respectively.
p X s a P Y g a p Z s a r
By putting X + arylarz, it can be written as from equation (11).

[Effect]

By the above means, the coordinate axis of the reference orthogonal coordinate system, that is, x
, the distributed force of the gradient magnetic field in the y- and z-axis directions 1 and the like (16) are used to calculate the strain amounts yp and vr, and using the above-mentioned yp and Vr, the measurement data 5 (tp, Or) is subjected to two-dimensional inverse Fourier transformation. From C'(p'+1-', so) obtained as follows, the distribution C(P tr + so) can be found.

〔Example〕

An embodiment of the present invention will be described below.

FIG. 5 is a block diagram showing the overall configuration of the magnetic resonance imaging apparatus according to the present invention. This nuclear magnetic resonance imaging apparatus obtains a tomographic image of a subject using nuclear magnetic resonance (NMR) development, and includes a static magnetic field generating magnet 1,
It consists of a central processing unit (CPU) 2, a sequencer 3, a transmission system 4, a magnetic field gradient generation system 5, a reception system 6, and a signal processing system 7. The static magnetic field generating magnet 1 generates a strong and uniform static magnetic field in the direction of the body axis of the subject 22 or in a direction perpendicular to the body axis, and has a certain extent around the subject 22. A permanent magnet type, normal conduction type, or superconducting type magnetic field generating means is arranged in the space. The sequencer No. 3 operates under the control of the CPU 2 and sends various commands necessary for data collection of tomographic images of the subject 22 to the transmission system 4, magnetic field gradient generation system 5, and reception system 6. The transmission system 4 includes a high frequency oscillator 8 and a modulator 9
The high frequency pulse output from the high frequency oscillator 8 is amplitude-modulated by the modulator 9 according to the commands of the sequencer 3, and the amplitude-modulated high-frequency pulse is generated by the high-frequency amplifier. 10
The subject 22 is irradiated with electromagnetic waves by amplifying the electromagnetic waves and then supplying the electromagnetic waves to a high-frequency coil lla placed close to the subject 22. The magnetic field gradient generating system 5 is X.

It consists of a gradient magnetic field coil 12 wound in the three axial directions of Y and Z, and a gradient magnetic field power source 13 that drives each coil, and drives the gradient magnetic field power source 13 of each coil in accordance with the command from the sequencer 3. Accordingly, x, y,
The gradient magnetic fields Gx, Gy, and Gz in the three axial directions of z are applied to the object 22.
It is designed to be applied to A slice plane for the subject 22 can be set by applying this gradient magnetic field. The receiving system 6 includes a high frequency coil 11b on the receiving side.
, amplifier 14 , quadrature phase detector 15 , and A/D converter 16
The electromagnetic waves (NMR
signal) is detected by a high frequency coil llb which is designed to be close to the subject 22, and is detected by an amplifier 14 and a quadrature phase detector 15.
15) is input to the A/D converter 16 and converted into a digital quantity,
Furthermore, two series of collected data are sampled by the quadrature phase detector 15 at timings according to commands from the sequencer 3, and the signals are sent to the signal processing system 7. This signal processing system 7 includes a CPU 2, a two-dimensional memory 17, a two-dimensional FFT unit 18, a two-dimensional memory 19,
(a).

(b) It consists of a distortion correction calculation unit 20 and an image display device 21, and the signal intensity distribution of an arbitrary cross section of the subject 22 or the distribution obtained by performing appropriate calculations on a plurality of collected data is used as image data. The image data is stored in the dimensional memory 19(a), and the distortion correction calculation section 20 performs distortion correction on this image data. The obtained results are stored in the two-dimensional memory 19(b).
Store in. The stored data is displayed on the image display device 21 as an NMR image without distortion. In addition, in FIG. 5, the high-frequency coil l on the transmitting side and the receiving side
la, llb and the gradient magnetic field coil 12 are arranged in the magnetic field space of the static magnetic field generating magnet 1 arranged in the space around the subject 22.

Next, a method and apparatus for correcting the non-uniformity of the static magnetic field and the non-linearity of the gradient magnetic field in this nuclear magnetic resonance imaging apparatus will be described.

FIG. 6(a) shows a correction processing procedure when the present invention is applied to a two-dimensional NMR image.

The processing procedure can be roughly divided into two steps.

That is, one of them is the process 23 (a
), and the other is the process 24 (a) of actually taking an oblique image of the subject, calculating the distortion amount distribution on the imaging plane from the imaging conditions, and correcting the distortion mixed into the image of the subject. ).

6(b) is a block diagram showing the overall configuration of the correction processing procedure shown in FIG. 6(a), in which the calculation system 23 ( b)
and an oblique image distortion correction system 24(b). Gradient magnetic field distribution calculation system 2 in the coordinate axis direction of the static magnetic field and reference coordinate system
3 (b) is the coordinate axis x, y, z axis direction strain distribution calculation system 27 (b), 30 (b), 26 (b) of the reference coordinate system.
), 31(b), and a static magnetic field distribution calculation system 32(b). Also, the oblique image distortion correction system 24. (b) consists of a coordinate transformation system 34 (b), a distortion amount calculation system 35 (b), and a distortion correction system 36 (b). Below, Section 6 (a) and (b)
) The main parts of the present invention will be explained in detail in the figures.

In the phantom photography 25 (a) of the above process 23 (a), a grid-like phantom is used, and the sequence is the first one.
Use the one shown in the figure. The above sequence is based on the improved spin warp method, and the Z-axis direction is the slicing direction, the X-axis direction is the readout direction, and the y-axis direction is the phase encoding direction.

From equation (7), the gradient magnetic field distribution is determined from the amount of distortion in the phase encoding direction, and the gradient magnetic field distribution plus the static magnetic field distribution is determined from the amount of distortion in the readout direction.

Therefore, using the phantom image obtained by the phantom imaging 25 (a), the gradient magnetic field distribution εy (X+ y+ z) in the y-axis direction is determined from the y-axis strain distribution calculation 26 (a). Further, using the above-mentioned Frantom image, from the X-axis direction strain distribution calculation 27 (a), the strain amount vx(X.

yyz) is found.

In phantom photography 28 (a) and 29 (a), a grid-like phantom is used as the phantom, and a sequence based on the improved spin warp method is used, as in the above-mentioned phantom photography 25 (a). Further, the x and z directions are respectively taken as phase encoding directions. Above y-axis direction strain distribution calculation 26
(a) Same x and z direction strain distribution calculation 29 (a), 30
In (a), the above phantom photographing 28 (a), 2'9
Using the phantom image in (a), the gradient magnetic field distribution in the x and z directions εX (Xe)'+Z)t εZ (X, y
, Z).

Next, in static magnetic field distribution calculation 32 (a), the strain amount v calculated in the above X-direction strain distribution calculation 27 (a), 30 (a)
By using x (x, y, z) and εX (XI 3'l Z), the static magnetic field distribution is calculated based on equation (9).

A detailed diagram of the static magnetic field distribution calculation system 32(b), which is the means of the static magnetic field distribution calculation 23(a), is illustrated in FIG. The two-dimensional memory 38 stores vx (x, y, z) obtained from the X-axis direction strain distribution calculation 27, and
9, the gradient magnetic field distribution εx (xt yt z
) is stored.

vx (xt yt z) stored in the memory 38
ε stored in the memory 39 using the subtractor 40 from
Subtract X (XI yt Z). The multiplier 41 multiplies the gradient Gx of the gradient magnetic field stored in the register 42 in advance by the above subtraction result. The above multiplication result is obtained in the two-dimensional memory 43.

Next, the method of process 24(a) in FIG. 6(a) will be explained. First, an oblique image of the subject is photographed according to the sequence shown in FIG. Coefficients bxr and bxp are determined by the oblique angles θ and φ, which are the above-mentioned photographing conditions.

bxs, byr, byp, bys, bzr, bzp.

Coordinate transformation 34 using bzs. Do (a) and (10
), the coordinates (p, r, so) of a point on the imaging plane are converted into coordinates (XI ytZ) in the reference coordinate system.

FIG. 8 illustrates a detailed diagram of the coordinate transformation system, which is the means of the coordinate transformation 34 (a), and the X coordinate calculation means will be explained.

Pixel position p generated from counter 44 (a), (b)
, r are input to multipliers 45 (a) and (b). The registers 46(a) and 46(b) stored the coefficients bxp and bxr of Par in the conversion formula regarding the X coordinate of equation (10), and the register 46(c) stored bxso. Here, since the slice position S is a constant value (set as so) on the image plane, the third term bxs-5 on the right side of the conversion equation regarding the X coordinate is set as bxso. Further, in FIG. 8, the contents of the registers 46 (a), (b), and (c) correspond to the upper row of each register. Integrator 45(a).

bxp-p and bxP-r are calculated by (b), and the above calculation results are input to the adder 47. The result of the above squaring is added in an adder 47 to calculate bxp-p+bxr-r. Furthermore, the above addition result is sent to the adder 48 as bxso
By performing an addition operation with , the X coordinate is calculated and stored in the register 49. Next, the y and z coordinate calculation means will be explained. The y, z coordinate calculating means is the register 46 (a
) to (c), the coefficients shown in the lower row are stored in place of the coefficients shown in the upper row, and the calculation is performed using the same procedure as the X coordinate calculation. Here, byso, bzs.

Similarly to bxso, represents the third term on the right side of the conversion equation regarding the 3'+Z coordinate in equation (10).

In the strain amount calculation 35, the gradient magnetic field distribution εX(
XI Vr Z) * εy(Xt'/+Z)t ε
2(xt yt z), the gradient ratio apx:apy' of the gradient magnetic field in the X, y, and z axis directions determined by the above oblique angles θ and φ
:apz, arx:ary:arz to point (p*r,
εP(P+r+so), [r(p,
r, so), and the above calculation result εP (p* r'
+ S O) + E r (p+ reso), the static magnetic field distribution "(xt Vr Z) and the gradient Gr of the gradient magnetic field in the readout direction at the point (P+r+so) (16
) The amount of distortion vp (ptr, 5o) vr (p, r
, so).

FIG. 9 illustrates details of the manual distortion amount calculation system 35(b) of the distortion amount calculation 35(a). In this means, the above step 2
Gradient magnetic field distribution in x, y, and z directions calculated by 3(b) εX (X+ Vr Z)+ Ey(x+3'+Z)+
εz(X+VzZ) and Shizumoto memory 50 (a)
-(c) 51, and the gradient Gr of the gradient magnetic field in the readout direction, which is the imaging condition, is stored in the register 52. The coordinates (p) of the imaging plane are calculated by the coordinate transformation system 34 (b) and stored in the registers 49 (a) to (Q).

The coordinates (XHyr2) of r, so) in the reference coordinate system are input into the three-dimensional memories 50 (a) to (c) and 51. EX(
X, y, z), ε'/ (X+ Vr Z) + εZ (
Read X+ 'I+ Z)+E (X+'/p Z). Above εX (X+ Y+ Z)+ Ey(X+
'/+ ZLεz (X+ yr Z) is input to the deviation amount calculation system 53 (a), (b) of the gradient magnetic field (phase encode, read direction) from the straight line, and is phase encoded.

The amount of deviation of the gradient magnetic field in the readout direction from the straight line εp(P+
P+ S O)+ E r (P+ P+
S O) is calculated. Amount of deviation from the straight line of the gradient magnetic field in the phase encoding direction Ep (P+ r, s o)
From equation (15), the amount of image distortion v in the phase encoding direction is
As equivalent to p(P+r,so), register 54
It is stored in (a). Further, the shift amount εr (p +, r + s o) of the gradient magnetic field in the readout direction is input to the adder 55 . Then, E(X+'/l Z) read from the memory 51 is input to the divider 56 and divided by Gr stored in the register 52 in advance. The above calculation result E (X + 3' r Z ) / G r
is input to the adder, and the previously input εr (P+ P
+so). The above calculation result is stored in the register 5 as the image distortion amount vr (p, r, SO) in the read direction.
4 (b).

Next, the means for calculating the amount of deviation of the gradient magnetic field in the phase emboard direction from the straight line 53 (a) is shown in FIG. 10 and will be described. Register 57 (a).

(b) and (Q) show the gradient ratios ap
Store y and apz. In FIG. 10, each register is shown in the upper row. Memory 50 (a) in FIG. 9 above
EX (X+ '/+ Z)+ read from (c)
Ey(X+'/+Z)+fZ(X+yrZ)
is input to the multipliers 58 (a) to (c), and the multiplier 58
(a) to (c) are the registers 57 (a), respectively.
apx stored in ~(c).

Perform a product operation with aPy+aPZ. Above calculation result aPX
' EX (x+ Vr Z) + aPy'E3'
(X+y+z) is input to the adder 59 and subjected to a post-addition operation, and the output result is apx·εx(xyy+z)+apy·E
y (x + y + z) is input to adder 60 . The other terminal of the adder 60 receives the multiplication result apz·ε2.
(x+yr z) and apx'εX
(X r yrz) + apy・ε'/ (XI '/
+ Z) and outputs the amount of deviation εp (P+ r, so) of the gradient magnetic field in the phase encoding direction. Calculation system 53 for the amount of deviation of the gradient magnetic field in the readout direction from the straight line
The means in (b) is a calculation system 53 for calculating the amount of deviation of the gradient magnetic field from the straight line in the phase encoding direction in FIG. 10. The register 57 in the means in (a) is changed from the upper row to the lower row. However, since the remaining processing can be carried out in the same manner as in the phase encoding direction, detailed explanation will be omitted.

Furthermore, in the distortion correction 36 (a), the distortion amount calculation 35 (
Distortion amount VP (p+r+so), v calculated in a)
By using r (p, r, so), the coordinates p1. Find rT and perform distortion correction.

The means of distortion correction system 36 (b) of the above distortion correction 36 (a),
It is shown in FIG. Subject photographing 33 in Fig. 6(b) (b
) is stored in the memory 61 in advance, and the slice position SO is input into the memories 61 and 63.The counter 44 (a), (b)
The Par generated by the above is input to the adders 62 (a), (b) and the memory 63. In addition, the adder 62 (a)
, (b), the phase encode obtained from the Pyr by the coordinate transformation system 34 (b) and the distortion amount calculation system 35 (b), and the distortion amount VP of the image in the readout direction.
(P+ P+ So) + Vr (Pt P+ S
o) is input, and the adders 62 (a) and (b) add p
.

An addition operation with r is performed. The above output results are input to the memory 61 as pixel positions p' and r' before correction, and C'(p' + r' so) specified by the previously input slice position so and the above P'yr' is read out. The read C'(p',r' so) is input as C (p, r, so) to the address specified by the previously input p' + r' HSo.

By executing the above procedure for P+r over the entire image plane, the correction of the image C'(p' + r' so) is completed, and a distortion-free image c (pt r, so) is obtained in the memory 63.

〔Effect of the invention〕

According to the present invention, image distortion included in an NMR image is corrected without limiting the direction of the coordinate axes that constitute the image plane.
A good NMR image without geometric distortion can be obtained.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing the sequence for determining the gradient magnetic field and static magnetic field distribution in the y"x direction. Figure 3 is a diagram showing the relationship between basic coordinates and arbitrary coordinate systems. Figure 4 5 is a diagram showing the sequence for oblique tomographic imaging, FIG. 5 is a block diagram of the MRI apparatus, FIG. 6(a) is a diagram showing the processing procedure of the distortion correction method of the present invention, and FIG. 6(b) The figure is a block diagram of the overall configuration of the distortion correction device of the present invention, Figure 7 is a circuit diagram for calculating static magnetic field distribution, and Figure 8 is a circuit diagram for converting coordinates in an arbitrary oblique image to coordinates in a reference coordinate system. , FIGS. 9 and 10 are circuit diagrams for calculating the amount of distortion in arbitrary oblique tomographic images, and FIG. 11 is a circuit diagram for correcting distortion in arbitrary oblique tomographic images. 1. Static magnetic field generating magnet, 2 ...Central processing unit, 3.
...Sequencer, 4...Transmission system, 5...Magnetic field gradient generation system, 6...Reception system, 7...Signal processing system, 17...
・Two-dimensional memory, rate l Figure 2 Figure 3 Figure 4 Nichijo 7 Koutei 10 Ward /l Figure C (erSo)

Claims (1)

[Claims] 1. A step of generating each magnetic field of a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, a step of detecting a nuclear magnetic resonance signal from an object to be examined, and a step of detecting the inside of the object to be examined using the detection signal. In a nuclear magnetic resonance imaging method comprising a step of reconstructing to obtain an image related to composition and a step of correcting distortion of the obtained image, there is a step of correcting the distortion in three axial directions of a reference coordinate system. calculating the distribution of the amount of distortion of an image on an arbitrary oblique section from the distribution of the gradient magnetic field and static magnetic field in the three axes of the reference coordinate system; MR comprising the step of correcting an image regarding the internal composition of the object to be examined using
Imaging method of I. 2. Means for generating each magnetic field of a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, a means for detecting a nuclear magnetic resonance signal from an object to be examined, and a means for obtaining an image regarding the internal composition of the object to be examined using the detection signal. In the MRI imaging apparatus, the means for correcting distortion of the obtained image includes means for calculating gradient magnetic fields and static magnetic field distribution in three axes of a reference coordinate system. and a means for calculating the distribution of the amount of distortion of an image on an arbitrary oblique section from the gradient magnetic field and static magnetic field distribution in the three-axis directions of the reference coordinate system, and correcting the image regarding the internal composition of the inspection object using the amount of distortion. An MRI imaging device characterized by comprising means for.