JPH09508A - Magnetic resonance imaging method - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a magnetic resonance imaging method capable of eliminating aliasing. [Structure] The present invention follows a single high-frequency excitation pulse,
A magnetic resonance imaging method in which a plurality of echo signals are generated using a plurality of high-frequency inversion pulses, and a series of operations of performing phase encoding of different magnitudes on the plurality of echo signals is performed at least once, in a first direction. A first gradient magnetic field having a gradient along with a high-frequency excitation pulse, and a second gradient magnetic field having a gradient along a second direction with a high-frequency inversion pulse, and a finite direction in the second direction. By performing an operation of selectively reversing the phase advance / delay relationship of the transverse magnetization existing in the second region having the width of, the echo signal is generated only from the common region of the first region and the second region. It is characterized by generating.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a magnetic resonance imaging apparatus.

[0002]

2. Description of the Related Art Spin Echo method (SE
Method), Fast Spin Echo method (also called FSE method, RARE method), Gradient and Spin Echo method (GRASE method), Ec
The ho Planar Imagimg method (EPI method) is available. Especially FS
Since the E method, GRASE method, and EPI method can obtain an image having the same image quality in a shorter time than the SE method, the T ₁ weighted image, T ₁
Even in normal inspections (routine inspections) such as _2- weighted images, three-dimensional imaging, which is generally considered to have a long imaging time, is becoming possible. Hereinafter, this three-dimensional imaging method is abbreviated as “3DFT” or simply “3D”.

FIG. 15 shows the definition of each coordinate in the K space (spatial frequency space) and the range for collecting data in the case of three-dimensional discrete Fourier imaging. Fig. 16 shows the so-called Ramp
FIG. 17 and FIG. 18 show pulse sequence charts of the 3D-FSE method of a circular encoded (Ge1) array in the K space of the data obtained by the pulse sequence of FIG. Also, FIG. 19 schematically shows how the signal intensity of each data changes due to T ₂ relaxation of the magnetization spin of the imaging target in the pulse sequence of FIG. 16, and FIG. 19A shows the first phase. Encoding direction ke
1 shows the signal strength change along the line 1, and FIG. 19B shows the signal strength change along the second phase encoding direction ke2.

In FIG. 16, 90 ° is a high frequency excitation pulse and 180 ° is a high frequency inversion pulse. Gs is a gradient magnetic field in the slice direction, Ge1 is a gradient magnetic field in the first phase encoding direction, Ge is a gradient magnetic field in the second phase encoding direction, and Gr is a gradient magnetic field in the readout direction. The second phase encoding direction is equal to the slice direction, and the gradient magnetic field waveforms of the gradient magnetic field Gs in the slice direction are actually superimposed.

In this example, the number of echoes is 5, the number of steps in the first phase encoding direction is 20, and the number of steps in the second phase encoding direction is 21. The waveforms in both phase encode directions each have a portion having a plurality of intensities, which is a TR of 1 Shot sequence.
It shows that the intensity is changed along the arrow each time the cycle is repeated in [seconds]. If the execution of one sequence from the application of the high frequency excitation pulse to the fifth echo is called “shot”, there are 4 types of Ge1 waveforms and 21 types of Ge2 waveforms. Even if it is 1, 84 shots are required for one shooting.

FIG. 17 shows data in the K space obtained by the pulse sequence of FIG. 16 with ke2 = 0. E1 to E5 on the left side show what number of echo data the echo data in the area surrounded by each solid line is, where E1 is the first echo and E2 is the second echo. Echo, E3 is the third echo, E4 is the fourth echo, and E5 is the fifth echo. Similarly, FIG. 18 shows the case where kr = 0. As can be seen from FIGS. 17 and 18, echo data having different echo times are arranged in the ke1 direction. Therefore, as shown in FIG. 19A, T ₂ relaxation of the magnetization spin of the imaging target is performed in the ke space in the ke1 direction. The signal strength will change.

When the repetition time TR is twice or more as long as the length of the sequence for one shot, multi-slab imaging is also possible for the purpose of increasing the number of matrices in the slice direction.

FIG. 20 shows a modification of FIG. 16, which is so-called Low.
The pulse sequence chart of 3D-FSE method of a pass-like encoding (Ge1) arrangement is shown. 21 and 22 show the positions of the data obtained by the pulse sequence of FIG. 20 in the K space. Also, FIG. 23 schematically shows how the signal intensity of each data changes due to T ₂ relaxation of the magnetization spin of the imaging target in the pulse sequence of FIG.

FIG. 24 schematically shows a conventional procedure from reconstruction to display of a three-dimensional image. Since the number of matrices in the first phase encoding direction cannot generally be made too small for the purpose of avoiding aliasing artifacts, which will be described later, the matrix in the second phase encoding direction having no problem of aliasing artifacts can be used in order to shorten the photographing time as much as possible. Set less. Therefore, the three-dimensional image data is divided by the plane including the read direction and the first phase encoding direction, and the images of the respective sections obtained by the division are sequentially displayed on the screen according to the position in the second phase encoding direction. Or overwrite and display in order.

Such a conventional 3DET has the following problems. (A) Compared to the sensitivity area of the RF coil, the imaging area (Field of
View; FOV) is small, and if there is a signal source in a portion other than the FOV in the sensitivity region of the RF coil, aliasing (folding artifact) occurs due to the property of the discrete Fourier transform.

FIG. 25 schematically shows the aliasing phenomenon of an MR image due to this aliasing. FIG. 25 (a) is a diagram showing the relationship between the imaging target and the FOV, and FIG. 25 (b) is
The obtained reconstructed image is shown. As shown in this figure, the object to be imaged is FOV in the direction of phase encoding pe1 or pe2.
If it is more protruding than that, and if the protruding portion is in the sensitivity region of the RF coil, aliasing occurs in the reconstructed image.

For this reason, the images of two different parts are overlapped with each other, and the image quality is significantly deteriorated. This problem needs to be taken into consideration when determining the position or direction of the imaging cross section and the FOV, and there is a problem that setting the imaging conditions is troublesome and the imaging time itself increases.

(B) The size (degree) of the blur of the image differs depending on the direction in the image. As shown in FIGS. 19 and 23, T
₂ Gpe1 (ke
In the direction of 1), the image blurring is severe, and the degree of blurring is read out and the gradient magnetic field direction Gr and the second phase encoding direction Gpe are read.
Since it is larger than 2, it is inconvenient in use when the cross-section display in various directions is performed as post-processing because the size of the blur varies depending on the direction of the image.

Usually, when performing three-dimensional imaging by a high-speed imaging method such as FSE, there are many cases in which a pulse sequence with a very long echo train number is used because of a request to perform imaging with a large number of matrices in the shortest time possible ( For example, 12
8 echoes). Therefore, it can be said that this problem is particularly serious in the case of three-dimensional imaging.

(C) In 3D imaging, when the number of matrices in the slice direction is relatively large, multislab imaging is performed.
For pulse sequences with very long echo trains,
Due to time constraints, the number of multi-slabs cannot be increased so much.

In FSE and GRASE, the number of multi-slabs is similarly limited in terms of exposure to RF. Therefore, there is a problem that the imaging time is extended because the imaging is performed several times.

(D) As shown in FIG. 26 (a), when there are two elements having different resonance frequencies in the object to be imaged and having two different resonance frequencies, such as water and fat, an image is displayed as shown in FIG. If this is done, there is a problem that the relative positional relationship between the substances becomes incorrect as shown in FIG. 26B due to the difference in resonance frequency due to the chemical shift, which may lead to misdiagnosis.

(E) The 3D imaging setting method and display method need to consider the above problems and skillfully set a large number of parameters, require some experience, and require high throughput as a routine inspection. It is difficult to operate while maintaining.

[0019]

SUMMARY OF THE INVENTION A first object of the present invention is to provide a magnetic resonance imaging method capable of eliminating aliasing. The second object of the present invention is to suppress the difference in the degree of blurring depending on the direction of the image.
A magnetic resonance imaging method for three-dimensional imaging is provided. A third object of the present invention is to provide a magnetic resonance imaging method for three-dimensional imaging capable of increasing the number of multi-slabs in a relatively short imaging time. A fourth object of the present invention is to provide a magnetic resonance imaging method of three-dimensional imaging that eliminates relative positional shift between substances due to chemical shift.

[0020]

According to a first aspect of the invention, a plurality of echo signals are generated by using a plurality of high frequency inversion pulses after one high frequency excitation pulse, and the plurality of echo signals are different from each other. In a magnetic resonance imaging method in which a series of operations of performing phase encoding of a magnitude is performed at least once, a first gradient magnetic field having a gradient along a first direction is applied together with the high frequency excitation pulse,
A first region having a finite width in the first direction is selectively excited, and a second gradient magnetic field having a gradient along a second direction is applied together with the radio frequency inversion pulse; By performing an operation of selectively reversing the advance / lag relationship of the phase of the transverse magnetization existing in the second region having a finite width in the direction of 2, the first region and the second region are It is characterized in that the echo signal is generated only from the common area of.

According to the invention of claim 7, a plurality of echo signals are generated by using a plurality of high-frequency inversion pulses after one high-frequency excitation pulse, and phase echoes of different magnitudes are respectively generated in the plurality of echo signals. In a magnetic resonance imaging method in which a series of operations of applying is performed a plurality of times, phase encoding is applied so that echo times of echo signals equidistant from the coordinate axis in the read direction in the K space are the same. To do.

According to an eighth aspect of the invention, a plurality of echo signals are generated by using a plurality of high frequency inversion pulses after one high frequency excitation pulse, and phase encodings having different magnitudes are generated for each of the plurality of echo signals. In a magnetic resonance imaging method in which a series of operations are performed a plurality of times, a plurality of echo signals having the same echo time are used as a cylinder having a coordinate axis in the read direction on the K space as a central axis, a cylinder having a rectangular or square cross section. It is characterized in that it is phase-encoded so as to be arranged in a rectangular area.

[0023]

According to the first aspect of the present invention, by performing selective excitation in two directions, the excited region, that is, the region where the echo signal is generated is limited, and aliasing is eliminated.
Further, when determining the position or direction of the imaging cross section, it is not necessary to consider folding artifacts, and it is not necessary to set the direction of the lead, the number of multi-slabs, the number of matrices per slab, etc., and the condition setting for 3D imaging is performed. Simplifies. Furthermore, the imaging time itself becomes short.

Further, according to the invention of claim 4, by forming a two-dimensional image with respect to a plane consisting of two phase encoding directions, that is, by forming a plurality of two-dimensional images along the lead-out direction, imaging is performed. The number of matrices can be increased without spending time. That is, the number of slices can be increased according to the data sampling interval. Further, since the multi-slab imaging is not necessary and the imaging need not be performed in several times, RF exposure is reduced and the imaging time is shortened. Further, an image having no positional shift due to chemical shift can be obtained.

According to the invention of claim 7 and the invention of claim 8, since the echo time of echo signals equidistant from the coordinate axis in the read direction in the K space is the same, 3D imaging in which a plurality of phase encode directions are set. Even in the normal method, the blurring of the image due to T ₂ relaxation is substantially equal in the phase encoding directions.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a magnetic resonance imaging apparatus (MRI apparatus) according to the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of the MRI apparatus according to this embodiment. Generally, the pulse sequence calculation means 1 using a host computer calculates the application timing and intensity of the high frequency pulse of the pulse sequence described later, the waveform of the gradient magnetic field of each channel, and the like. Pulse sequence calculation means 1
The gradient magnetic field pulse waveform and the high frequency pulse waveform are generated in the pulse sequence waveform generation means 2 as the sequence controller according to the calculation result of These waveforms are amplified by the gradient magnetic field power supply 3 and the high frequency amplifier 4,
The gradient magnetic field coil 6 and the high frequency coil 7 placed in the static magnetic field generated by the static magnetic field magnet 5 apply the magnetic field to the imaging target. The nuclide element (mainly proton) contained in the imaging target is excited to generate an echo signal (weak high-frequency signal) at the timing shown in a pulse sequence chart described later. This echo signal is received again by the high frequency coil 7, detected by the phase detector 8, converted into a digital value by the analog-digital converter (A / D converter) 9, reconstructed by the reconstruction calculation means 10, and image processed. The image is processed by the means 11 and visually displayed as a magnetic resonance image by the image display means 12 including, for example, a CRT display.

FIG. 2 shows a pulse sequence chart of the 3D fast SE method (three-dimensional fast spin echo method). FIG.
Should be referred to in comparison with FIG. Although the 3D high-speed SE method will be described as an example here, three-dimensional EP
The same can be applied to the I method and the three-dimensional GRASE method. In the 3D high-speed SE method, echo signals are phase-encoded in two directions. One of them is the first
And the other is the second phase encoding direction Ge2. First phase encoding direction Ge
1 and the second phase encoding direction Ge2 are set to be orthogonal to the read direction Gr and not orthogonal to each other. The second phase encoding direction Ge2 is assumed to be the same as the slice direction Gs.

As shown in FIG. 2, the high frequency excitation pulse (90
Pulse) is applied together with the gradient magnetic field (first gradient magnetic field) in the first phase encoding direction Ge1. For this reason,
Only nuclides existing in a region (first region) having a finite width in the first phase encoding direction Ge1 are excited and transverse magnetization is generated. Following one high-frequency excitation pulse, a plurality of echo signals are generated while repeatedly applying a plurality of high-frequency inversion pulses (180 ° pulses) as in the conventional case. The high frequency inversion pulse is applied together with the gradient magnetic field (second gradient magnetic field) in the second phase encoding direction Ge2. As a result, only the magnetization spins in the region (second region) having a finite width in the second phase encoding direction Ge2 are phase-inverted, and the lateral magnetization is refocused.

The frequency band of the high-frequency excitation pulse and the high-frequency inversion pulse are arranged so that the common region between the first region and the second region fits within the imaging region in the first phase encoding direction and the second phase encoding direction. The frequency band, the strength of the first gradient magnetic field and the strength of the second gradient magnetic field are adjusted.

Regarding the first and second phase encode directions, it is a common area, and regarding the read direction, only the portion of the echo signal within the band of the reception filter of the phase detector 8 appears as a reconstructed image. Therefore, if there is an object that produces an echo signal outside this common area, and if the high-frequency coil 7 has sensitivity in that area as well, the aliasing artifacts shown in FIG.

Therefore, it is not necessary to increase the number of slices and matrices in the encoding direction more than necessary, and the imaging time can be shortened. 3D high speed S
The other pulse sequence chart of E method is shown. FIG.
See FIG. 20 in comparison with the related art.

FIG. 4 shows another pulse sequence chart of the 3D high-speed SE method. In FIG. 5A, ke2 = 0 kr ×
5B shows the data order of the cross section of ke1, and FIG. 5B shows the data order of the cross section of ke1 × ke2 in the case of arbitrary kr. Figure 6
7 and FIG. 7 show the correspondence relationship between the area values (time integration values) of the phase-encoding gradient magnetic field pulses in each shot, and FIG. 6 shows from the first shot to the 42nd shot, the 43rd shot in FIG. To the 84th shot
Up to. FIG. 8A shows how the signal strength changes due to T ₂ relaxation of the imaging target in the ke1 direction (ke2 = 0) when kr is arbitrary. FIG. 8B shows how the signal intensity changes due to T ₂ relaxation of the imaging target in the ke2 direction (ke1 = 0) when kr is arbitrary.

The areas E1 to E5 in FIGS. 5A and 5B are respectively occupied by the echo signals E1 to E5 having different echo times TE as shown in FIG. Phase encoding is performed so that the echo times of echo data at symmetrical positions with respect to the coordinate axis in the read direction on the kr × ke1 surface and the ke1 × ke2 surface of the K space are the same. Further, the phase encoding is performed such that the echo data having a shorter echo time TE is located closer to the center of the K space, and the echo data having a longer echo time TE is located near the center of the K space. The data in the area covered by each echo in the K space may be collected in any order. The number of shots taken for each data can be set independently in each echo area. FIG. 6 and FIG. 7 show one example thereof, as in the conventional case, when the number of echoes is 5, the number of steps in the first phase encoding direction is 20, and the number of steps in the second phase encoding direction is 21, as shown in S11 to S25 of FIG. It shows how the area value (time integration value) of the phase-encoding gradient magnetic field should be changed for each shot.

By performing the above-described phase encoding, as shown in FIGS. 8A and 8B, the intensity (degree) of change in the amplitude of the echo signal is the same in both phase encoding directions. Becomes Conventional FIG. 23 (a),
See (b) for comparison. In the present embodiment, the difference in the change in the amplitude of the echo signal in the K space depending on the phase encoding direction is smaller than that in the conventional example. This means that the degree of blurring of an image is the same in each phase encoding direction, and the image quality is improved particularly when displaying an arbitrary cross section.

Next, another phase encoding method will be described. FIG. 9, FIG. 10 and FIG. 11 show data arrays on the ke1 × ke2 surface according to the three types of phase encoding methods. Note that the shaded area in FIG. 10 is the area where a value of 0 is entered without actually collecting. 9 is based on a rectangular area, and FIGS. 10 and 11 are based on a circular area. A plurality of echo signals having the same echo time are subjected to phase encoding so as to be arranged in a cylindrical region having a cross section of a cylinder, a rectangle, or a square with the coordinate axis in the read direction in the K space as a central axis. . In addition, the area including the center of the K space is the echo E with the shortest echo time TE.
The phase encoding is performed so that the data of No. 1 is carried and the data of the echo E5 (or E4) having a longer TE is carried in the region farther from the center. That is, an example is shown in the order of E1 → E2 → E3 → E4 → E5 from the center of the K space to the periphery.
On the contrary, E5 → E4 → E3 → E2 → E1 or E1 → E2 →
The order may be arbitrarily changed like E5 → E4 → E3.

Next, a method of image reconstruction will be described with reference to FIG. Please refer to FIG. 24 for comparison. 3
Three-dimensional reconstructed image data can be obtained by a reconstructing method such as a three-dimensional inverse Fourier transform. What is important here is that data is divided into two-dimensional planar data having the same position in the lead direction,
A three-dimensional image to the first and second phase encoding directions ke1, k
It is composed of a surface of xe1 × xe2 corresponding to e2, and is multi-sliced in the direction of xr corresponding to the read direction kr. Also, a two-dimensional image is arranged and displayed along xr.

When such a display method is performed, the first phase encode direction and the second phase encode direction are formed, and in other words, the two-dimensional image is not formed in the read direction (frequency encode direction) and the multi-slice direction is formed. Therefore, as shown in FIG.
There is no positional shift between different substances such as water and fat due to chemical shift in the three-dimensional image. Further, image distortion due to non-uniformity of the static magnetic field does not occur.

When this display method is compared with the conventional multi-slice imaging method, the conventional multi-slice imaging method is 1sho.
Due to the relationship between the sequence length per t and the repetition time,
While the number of slices was limited by the imaging time, this embodiment is characterized in that the number of slices can be increased in principle by shortening the data sampling interval. For example, when a pulse sequence having a sequence length of 400 ms per one shot at TR = 4000 ms is performed for the purpose of heavy T ₂ -weighted contrast, when imaging is performed by the conventional multi-slice imaging method, only 10 slices at the maximum are obtained. Can not be removes. On the other hand, when an image is picked up as in the present embodiment, as long as the sampling interval can be set, an arbitrary number of slices (for example, 1024) can be obtained while the imaging time remains constant.

However, the number of echoes per one shot and s
The product of the hot number and the horizontal direction of xe1 of the two-dimensional image and xe2
Must be equal to the product of the number of matrices in the vertical direction. It can be said that this method is particularly suitable for the case where the number of slices is larger than the number of matrices in the vertical and horizontal directions, for example, for imaging a rod-shaped (square columnar) imaging region.

Next, the image processing will be described with reference to FIGS. 13 and 14. The rectangles in the figure schematically show a side view of a slice (slice) obtained by dividing a three-dimensional image into a plurality of two-dimensional images. The arrows in the figure indicate addition processing or averaging processing. A plurality of two-dimensional images that are adjacent along the read direction (xr corresponding to the read direction) are added or averaged between frames. FIG. 13A shows addition or averaging processing between two frames. The position of the image to be added or averaged can be shifted as shown in FIG. In addition, the number of images (the number of frames) to be subjected to addition or averaging processing can be adjusted as shown in FIG. As shown in FIG. 13D, the shift adjustment and the number adjustment can be performed at the same time.
Further, as shown in FIGS. 14A to 14C, the images to be added or averaged can be overlapped, and the number of overlaps can be adjusted. The image display may be performed again each time the adjustment amount of the image processing is changed. Of course, the present invention is not limited to the above-described embodiments, and can be variously modified and implemented.

[0041]

According to the first aspect of the present invention, by performing selective excitation in two directions, the excited region, that is, the region where the echo signal is generated is limited, and aliasing is eliminated. In addition, when determining the position or direction of the imaging cross section,
It is not necessary to consider folding artifacts, and it is not necessary to set the direction of the lead, the number of multi-slabs, the number of matrices per slab, and the like, which simplifies the condition setting for 3D imaging. Furthermore, the imaging time itself becomes short.

Further, according to the invention of claim 4, by forming a two-dimensional image with respect to a plane consisting of two phase encoding directions, that is, by forming a plurality of two-dimensional images along the lead-out direction, imaging is performed. The number of matrices can be increased without spending time. That is, the number of slices can be increased according to the data sampling interval. Further, since the multi-slab imaging is not necessary and the imaging need not be performed in several times, RF exposure is reduced and the imaging time is shortened. Further, an image having no positional shift due to chemical shift can be obtained.

According to the invention of claim 7 and the invention of claim 8, since echo times of echo signals equidistant from the coordinate axis in the read direction in the K space are the same, 3D imaging in which a plurality of phase encode directions are set. Even in the normal method, the blurring of the image due to T ₂ relaxation is substantially equal in the phase encoding directions.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a magnetic resonance imaging apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a pulse sequence chart of the 3D high-speed SE method according to the present embodiment.

FIG. 3 is a diagram showing another pulse sequence chart of the 3D high-speed SE method according to the present embodiment.

FIG. 4 is a diagram showing still another pulse sequence chart of the 3D high-speed SE method according to the present embodiment.

FIG. 5 is a diagram showing a data order of a cross section of kr × ke1 where ke2 = 0, and a data array of a cross section of ke1 × ke2 when kr is arbitrary.

FIG. 6 is a diagram showing a correspondence relationship between area values (time integrated values) of gradient magnetic field pulse for phase encoding in each shot from the first shot to the 42nd shot.

FIG. 7 is a diagram showing a correspondence relationship between area values (time integrated values) of gradient magnetic field pulse for phase encoding in each shot from the 43rd shot to the 84th shot.

FIG. 8 is a ke1 direction (ke2 = 0) when kr is arbitrary.
Of the change in signal intensity due to T ₂ relaxation of the imaging target of
Figure showing changes in signal strength due to the T ₂ relaxation of the imaging subject ke2 direction when kr is arbitrary (ke1 = 0).

FIG. 9 is a ke1 depending on how the first type of phase encoding is performed.
The figure which shows the data array of xke2 surface.

FIG. 10 shows ke according to how to perform the second type phase encoding.
The figure which shows the data array of 1xke2 surface.

FIG. 11 is a diagram showing how ke depends on how the third type of phase encoding is performed.
The figure which shows the data array of 1xke2 surface.

FIG. 12 is an explanatory diagram of an image reconstruction method.

FIG. 13 is an explanatory diagram of an image processing method.

FIG. 14 is an explanatory diagram of another image processing method.

FIG. 15 is a diagram showing a definition of each coordinate in K space and a range for collecting data in the 3D-FSE method.

FIG. 16 is a diagram showing a pulse sequence chart of a 3D-FSE method of a conventional Ramp-shaped encode (Ge1) array.

17 is a diagram showing the arrangement of data obtained by the pulse sequence of FIG. 16 on the kr × ke1 plane of the K space.

FIG. 18 is a diagram showing an arrangement of data obtained by the pulse sequence of FIG. 16 on a ke1 × ke2 plane of a K space.

19 is a diagram schematically showing how the signal intensity of each data changes due to T ₂ relaxation of the magnetization spin of the imaging target in the pulse sequence of FIG.

FIG. 20 is a diagram showing a pulse sequence chart of a 3D-FSE method of a conventional Low Pass-like encoding (Ge1) array.

21 is a diagram showing an arrangement of data obtained by the pulse sequence of FIG. 20 on the kr × ke1 plane of the K space.

22 is a diagram showing the arrangement of data obtained by the pulse sequence of FIG. 20 on the ke1 × ke2 plane of the K space.

23 is a diagram schematically showing how the signal intensity of each data changes due to T ₂ relaxation of the magnetization spin of the imaging target in the pulse sequence of FIG. 20.

FIG. 24 is a diagram schematically showing a conventional procedure from reconstruction to display of a three-dimensional image.

FIG. 25 is a diagram schematically showing an aliasing phenomenon of an MR image due to aliasing.

FIG. 26 is an explanatory diagram of a positional shift between water and fat due to a chemical shift.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pulse sequence calculation means, 2 ... Pulse sequence waveform generation means, 3 ... Gradient magnetic field power supply, 4 ... High frequency amplifier, 5 ... Static magnetic field magnet, 6 ... Gradient magnetic field coil, 7 ... High frequency coil, 8 ... Phase detector, 9 ... A / D converter, 10 ... Reconstruction calculation means, 11 ... Image processing calculation means, 12 ... Image display means.

Claims (8)

[Claims] 1. A series of operations in which a plurality of high-frequency inversion pulses are used to generate a plurality of echo signals following a single high-frequency excitation pulse, and the plurality of echo signals are subjected to phase encoding of different magnitudes. In the magnetic resonance imaging method of performing at least once, a first gradient magnetic field having a gradient along a first direction is applied together with the high frequency excitation pulse, and a first magnetic field having a finite width in the first direction is applied. Region is selectively excited, a second gradient magnetic field having a gradient along a second direction is applied together with the high frequency inversion pulse, and a second region having a finite width in the second direction is applied. The echo signal is generated only from the common region of the first region and the second region by performing an operation of selectively reversing the relationship of the advance / delay of the phase of the transverse magnetization existing in 1. When The magnetic resonance imaging method that. 2. The magnetic resonance imaging method according to claim 1, wherein the echo signal is phase-encoded in a plurality of directions. 3. The magnetic resonance imaging method according to claim 2, wherein the first direction and the second direction are orthogonal to the lead direction and are not parallel to each other. 4. A plurality of two-dimensional images are formed on a plane composed of two phase encoding directions based on three-dimensional data obtained by reconstructing the plurality of echo data. Magnetic resonance imaging method. 5. A plurality of two-dimensional images that are adjacent in the lead direction among the plurality of two-dimensional images are added between frames to arbitrarily change the thickness of the two-dimensional image in the cross-sectional direction. Alternatively, the magnetic resonance imaging method may be performed by averaging. 6. The frequency band of the high-frequency excitation pulse, the frequency band of the high-frequency inversion pulse, the intensity of the first gradient magnetic field, and the second gradient magnetic field so that the common region falls within the imaging region in the direction of the phase encoding. The magnetic resonance imaging method according to claim 1, wherein the intensity of the gradient magnetic field is adjusted. 7. A series of operations for generating a plurality of echo signals by using a plurality of high frequency inversion pulses after one high frequency excitation pulse and subjecting the plurality of echo signals to phase encoding of different magnitudes. In a magnetic resonance imaging method for performing a plurality of times, phase encoding is performed so that echo times of echo data at symmetrical positions with respect to the coordinate axis of the read direction in the K space are the same. Method. 8. A series of operations for generating a plurality of echo signals by using a plurality of high frequency inversion pulses following a single high frequency excitation pulse, and subjecting the plurality of echo signals to phase encoding of different magnitudes. In the magnetic resonance imaging method of performing multiple times, multiple echo signals having the same echo time are arranged in a cylindrical region having a cross section of a cylinder, a rectangle, or a square with the coordinate axis in the read direction in the K space as the central axis. A magnetic resonance imaging method, wherein the phase encoding is performed as described above.