JP2002085376A - Nuclear magnetic resonance imaging device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal correction method for acquiring a practical, high- quality single-shot EPI image with an open type MRI having relatively large static field nonuniformities. SOLUTION: In this method, the step of collecting and processing signal correction data, the step of collecting and processing image formation data, and a corrective step for correcting the image formation data according to the signal correction data are carried out for the formation of an image through an image reconfiguration process upon detection of a magnetic resonance signal from a subject placed in a static magnetic field. In this case, the signal correction data is comprised of signals with a smaller number of phase encoding than that of the image formation data so as to obtain an image with a low spatial frequency. The number of data for that image is interpolated to match the number of image formation data so as to produce a map of nonuniformities of the static magnetic field. Using the map, the image formation data are corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures nuclear magnetic resonance (hereinafter, referred to as "NMR") signals from hydrogen, phosphorus, and the like in a subject, and visualizes nuclear density distribution, relaxation time distribution, and the like. The present invention relates to a nuclear magnetic resonance imaging (MRI) device.

[0002]

2. Description of the Related Art In recent years, MRI has made remarkable technological progress in both hardware and software, and the speed and strength of the gradient magnetic field have been increased, the imaging speed has been increased, and the static magnetic field magnet has been opened. As a result, in addition to conventional morphological imaging, functional imaging, intraoperative monitoring, etc.
MRI is beginning to be used. In particular, recent open MRI systems have improved image quality and performance.
(Interventional / Intraoperative MRI) applications are being studied in advanced medical institutions.

[0003] A typical high-speed imaging is an EPI (Echo Planer Imager) that acquires a plurality of echoes by one excitation.
ng) and split EPI are known, and an open MRI system incorporating this is also being developed. Normally, the EPI is susceptible to the influence of magnetic field non-uniformity, which causes a problem of deterioration of image quality. In order to solve this problem, phase correction using prescan data is generally performed.

For example, Japanese Patent Application Laid-Open No. 5-31095 discloses an EPI
A technique has been disclosed in which prescan data of one echo train is acquired in imaging, and the data of the main measurement is phase corrected using the data. However, 1-echo rain data is data to which one phase encoding is applied or no phase encoding is applied, and when this is applied to the main measurement data of all phase encoding, a good image quality is not necessarily obtained. Absent. In particular, when the static magnetic field is not uniform, the image quality deteriorates.

[0005] As a method of improving this, a method of performing pre-scanning a plurality of times and correcting it is known (author name:
Xin Wan, Grant T. Gullberg, Dennis L. Parker,
Gengsheng L. Zeng, title: Reduction of Geometric a
nd Intensity Distortions in Echo-Planar Imaging Us
ing a Multireference Scan, Magazine Name: Magn Reson Med
37, 932-944 (1997)).

In this method, image distortion due to non-uniformity of a static magnetic field is removed by using multi-reference scan data obtained by performing a plurality of prescans as phase correction data. The method can correct for non-uniform magnetic fields caused by changes in the magnetic susceptibility of the subject, in particular, geometric and signal strength distortions occurring at the boundary between soft tissue and air, the boundary between soft tissue and bone, and the like. .

However, in the multi-reference scan, an ordinary spin echo (S
E) The same number of scans as the sequence (for example, 64 shots on an EPI with 64 echo trains, EP on a 128 echo train)
I requires 128 shots) and the acquisition time is long. Therefore, the advantage of the high speed of the EPI is significantly impaired. As a result, it has not been widely used in general clinical practice.

[0008]

Therefore, the present invention provides an EPI
It is an object of the present invention to provide an MRI apparatus capable of accurately performing a phase in a short time even when there is non-uniformity of a static magnetic field when applying the method. Another object of the present invention is to provide an MRI apparatus that enables application of EPI in open-type MRI and can acquire an MR image with excellent image quality in a short time.

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied the factors that degrade the image quality of single-shot EPI in a medium magnetic field (0.3 T) open MRI apparatus. As a result, the ratio between the static magnetic field inhomogeneity, which is a measure of EPI image quality degradation, and the gradient magnetic field strength of the medium magnetic field (0.3 T) open MRI apparatus is about 2 times that of the high magnetic field (1.5 T) cylindrical MRI apparatus. It was confirmed that the quality of the image was easily deteriorated twice and that the main cause of the magnetic field inhomogeneity of the medium magnetic field open MRI system was the spatial inhomogeneity of the static magnetic field created by the static magnetic field magnet. The spatial non-uniformity of the static magnetic field has a comparatively gentle distribution of convex shapes. Therefore, if this is expressed in terms of spatial frequency, the static magnetic field inhomogeneity map contains many low spatial frequency components and few high spatial frequency components. In view of the static magnetic field inhomogeneity characteristics in such a medium magnetic field open MRI apparatus, the present invention obtains low spatial frequency component data as a static magnetic field inhomogeneous map for phase correction, thereby making it suitable for a medium magnetic field open MRI apparatus. This makes it possible to perform accurate phase correction and reduce the time required to acquire phase correction data.

That is, an MRI apparatus according to the present invention comprises: a static magnetic field generating means for generating a static magnetic field in a space where a subject is placed; a gradient magnetic field generating means for generating a gradient magnetic field in the space; High-frequency generating means for generating a high-frequency magnetic field that causes a magnetic field, detecting means for detecting a nuclear magnetic resonance signal generated from the subject, and signal processing means for reconstructing an image of the subject using the nuclear magnetic resonance signal And an MRI apparatus including a control unit for controlling the gradient magnetic field generation unit, a high frequency generation unit, a detection unit and a signal processing unit, wherein the control unit excites a subject tissue once or once.
After the application of a set of high-frequency magnetic fields, perform control to acquire a plurality of nuclear magnetic resonance signals to which different phase encodings have been added,
Nuclear magnetic resonance signals of the number of phase encodes (N) required for image formation are acquired as the main measurement data, and a desired phase encode is applied after one or a set of high-frequency magnetic fields for exciting the subject tissue. The acquisition of the plurality of nuclear magnetic resonance signals is repeated a number of times (M) less than the number of phase encodings (N) while changing the amount of phase encoding, and acquiring a nuclear magnetic resonance signal for phase correction as correction data, The signal processing means interpolates the correction data to obtain data having the same number of matrices as the main measurement data, and then uses the data for phase correction of the main measurement data.

The MRI method of the present invention is a method of detecting a magnetic resonance signal from a subject placed in a static magnetic field and creating an image by image reconstruction processing. Alternatively, after applying a set of high-frequency magnetic fields, control is performed to acquire a plurality of nuclear magnetic resonance signals with different phase encodings, and the nuclear magnetic resonance signals of the number of phase encodings (N) required for image formation are measured. Obtaining as, and after applying one or a set of high-frequency magnetic fields to excite the subject tissue, obtaining a plurality of nuclear magnetic resonance signals to which a desired phase encoding is applied, while changing the amount of phase encoding A step of repeating the number of times (M) less than the number of phase encodes (N) to obtain a nuclear magnetic resonance signal for phase correction as correction data; and obtaining an acquisition time using the correction data. Creating a low spatial resolution image for each different nuclear magnetic resonance signal, creating a magnetic field inhomogeneity map from the low spatial resolution image, each of the main measurement data using the magnetic field inhomogeneity map Correcting the phase for each signal.

Further, the MRI method of the present invention is a nuclear magnetic resonance imaging method for detecting a magnetic resonance signal from a subject placed in a static magnetic field and creating an image by image reconstruction processing. (1) for collecting and processing the data of step (1), step (2) for collecting and processing data for image generation, and correction step (3) for correcting the data for image generation using the data for signal correction. The step (1) of collecting and processing the data for signal correction includes:
Applying a first RF irradiation magnetic field for generating transverse magnetization to the subject (11), applying a first phase encoding magnetic field (12), reversing the polarity of the first readout gradient magnetic field (13) generating the first echo signal group in synchronization with the generation timing of the first readout gradient magnetic field (14); repeating the RF while changing the phase encoding amount (15) repeating the generation of the irradiation magnetic field, the generation of the readout magnetic field, and the signal detection, and the step of generating an image with a relatively low spatial resolution for each generation timing from a group of echo signals of different phase encoding for each generation timing ( 16) and a step (17) of extracting information reflecting the magnetic field map for each generation timing from the low spatial resolution image, Serial step of collecting and processing the data for image creation, the step of applying a second RF irradiation magnetic field for generating the transverse magnetization in the subject (2
1), a step of repeatedly applying a second phase encoding magnetic field in a stepwise manner (22), a step of continuously generating a second readout gradient magnetic field while reversing the polarity in synchronization with the application of the phase encoding magnetic field ( 23) a step (24) of detecting a second echo signal in synchronization with each generation timing of the readout gradient magnetic field, and the correcting step (3) is performed for each generation timing obtained in the step (24). A step (31) of correcting each echo signal using the magnetic field map for each generation timing obtained in the step (17), and a step (32) of forming a relatively high spatial resolution image from the corrected echo signal ).

According to the MRI apparatus and method of the present invention, since a static magnetic field map of a relatively low frequency component is created as data for signal correction, the number of echoes to be measured can be reduced, and signal acquisition is performed. Can significantly reduce the time required for pre-scanning.

The use of such a low-frequency component static magnetic field map enables accurate phase correction in a medium magnetic field MRI apparatus. Open M single-shot EPI with high image quality and low degradation
This can be realized by an RI device.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 4 shows a typical MRI to which the present invention is applied.
FIG. 2 is a diagram illustrating a configuration of an apparatus. This MRI apparatus is used for the subject 401
A magnet 402 for generating a static magnetic field in the space where
A gradient magnetic field coil 403 for generating a gradient magnetic field in this space;
RF coil 4 for generating a high-frequency magnetic field in the imaging region of the subject 401
04, an RF probe 405 for detecting an MR signal generated by the subject 401, and a bed 412 for transporting the subject 401 to the static magnetic field space.

The magnet 402 is an open type composed of a pair of upper and lower magnets sandwiching a space where the subject 401 is placed, and generates a substantially uniform static magnetic field in the vertical direction in the figure. Static magnetic field magnet
The spatial inhomogeneity of the static magnetic field created by the 402 has a comparatively gentle distribution in a convex shape.

The gradient magnetic field coil 403 is constituted by gradient magnetic field coils in three directions of X, Y and Z, and generates a gradient magnetic field in accordance with a signal from the gradient magnetic field power supply 409.

The RF coil 404 generates a high-frequency magnetic field according to the signal of the RF transmission unit 410. The signal of the RF probe 405 is detected by the signal detection unit 406, and the signal is processed by the signal processing unit 407.
It is converted into an image signal by calculation. The image is displayed on the display unit 40
Displayed as 8.

The gradient magnetic field power supply 409, the RF transmitter 410, and the signal detector 406 are controlled by the controller 411, and the application of a high-frequency magnetic field pulse, a gradient magnetic field pulse, and the measurement of an NMR signal are controlled according to a time chart called a pulse sequence. You. Various kinds of pulse sequences that differ depending on the purpose of photographing are incorporated in the memory of the control unit 411 as programs in advance. In the MRI apparatus of the present embodiment, an EPI pulse sequence including phase correction is incorporated as the pulse sequence.

Next, a photographing method will be described. FIG. 1 is a diagram showing an outline of an MRI method of the present invention. This imaging method is roughly divided into steps of collecting and processing data for signal correction (1) and steps of collecting and processing data for image creation. (2) and a correction step (3) for correcting the image creation data using the signal correction data.

FIG. 2 (step (2)) and FIG. 3 (step (1)) show specific examples of the pulse sequence executed in steps (1) and (2). These pulse sequences are respectively incorporated in the control unit of the MRI apparatus of the present invention as described above.

First, the pulse sequence shown in FIG. 2 is a gradient echo (GrE) type EPI sequence for acquiring an echo signal for forming a tomographic image of the subject, and the execution of this sequence causes step 2 (FIG. 1). Steps 21 to 24) are performed.

FIG. 3 shows a pulse sequence for acquiring an echo signal including phase information for performing phase correction of the echo signal acquired in the EPI sequence. The imaging using this pulse sequence is called a pre-scan, and is performed before or after the imaging (main measurement) for obtaining a tomographic image of the subject.
Is executed.

The EPI sequence for the main measurement shown in FIG. 2 is a sequence well known to those skilled in the art. Is applied, and a slice to be imaged is selected. Next, pulse 20 that gives the phase encoding offset
A pulse 205 for giving an offset of 3 and the readout gradient magnetic field is applied. Thereafter, a readout gradient magnetic field pulse 206 that is continuously inverted is applied.

The gradient magnetic field pulse 206 is trapezoidal. In synchronization with the gradient magnetic field pulse 206, the phase encoding gradient magnetic field pulse 204 is discretely applied in a blip shape. Since the echo signal 207 of each phase encode is generated in time series within each cycle of the inverted read gradient magnetic field 206,
Sample each time during 08 to get time series data. For example, the number of data is 64 in the reading direction (kx) and 64 in the phase encoding direction (ky). The time ranges 208 are typically on the order of 1 ms each. Through a series of operations 209, all echoes (main measurement data) required for image reconstruction are collected.

The prescan is performed in order to obtain phase correction information of each echo signal when reconstructing an image using the data obtained by such actual measurement. The sequence for the pre-scan shown in FIG. 3 is the same as the sequence of the main measurement shown in FIG. 2 in terms of the RF pulse, the intensity of the readout gradient magnetic field, the application timing, and the like. However, unlike the pulse sequence of FIG. 2, the phase encoding pulse is applied as a single rectangular pulse before the first pulse of the readout gradient magnetic field.

Scanning is repeated while changing the area of the rectangular pulse, that is, the pulse intensity and / or application time, to obtain a plurality of sets of signals having different phase encodes. The number of repetitions is, for example, 16.

This data or the complex image data obtained by Fourier transforming the data is stored in a memory so as to be used for signal correction of the main measurement data to be subsequently obtained. As described above, the number of repetitions of the pre-scan (the number of scans) 16 is determined by the imaging matrix of the main measurement (here
64) is a feature of the present invention.

Next, a procedure for preparing data for phase correction from such pre-scan data (steps 16 and 17) and a procedure for correcting the phase of the main measurement data using the data for phase correction (step 3) will be described. I do. Here, the case of creating phase correction data using complex image data obtained by performing two-dimensional Fourier transform of prescan data is shown.
This will be described with reference to FIG.

First, two-dimensional Fourier transform is performed on data obtained by the above-described pre-scan of 16 scans (FIG. 1: step 16). As a result, a complex image of 64 × 16 pixels, that is, a low spatial frequency is obtained for each time phase. The phase component of the complex image reflects the static magnetic field distribution.

Next, 64 × 16 two-dimensional image data for each time phase is interpolated to create an image having the same number of matrices as 64 × 64 as the actual measurement matrix (FIG. 5: step 51). The interpolation may be a first-order approximation, which is the simplest interpolation, but it is preferable to use a quadratic function in order to increase the accuracy. Fitting a quadratic function is sufficient to find the static magnetic field distribution of open MRI, but if necessary, it is possible to adopt a more accurate interpolation technique, for example, a gridding algorithm using the sinc function. is there.

The 64 × 64 image after the interpolation is returned to the data in the measurement space again by the two-dimensional Fourier transform (FIG. 5: step 52). The data in the measurement space is 64 × 64. That is, reference data (data for phase correction) supplementing 48 echoes that are not actually measured is obtained. The reference data is information reflecting a magnetic field map for each generation timing (time phase) of the echo signal.

Next, the main measurement data is phase corrected using the reference data thus obtained (FIG. 5: Steps 53 to 5).
5). Here, the reference data is p (i, j, k), and the main measurement data is q (i, j, k). Here, i and j are position coordinates in the measurement space, that is, i is a frequency encoding amount and j is a phase encoding amount. k is a phase encoding amount, and in this example, corresponds to the measurement time sequence (time phase) of the echo.

First, the influence of the magnetic field non-uniformity due to the difference in the generation time of the echo signal, that is, the effect of the magnetic field non-uniformity with time variation is determined (FIG. 5: step 53). Assuming that the reference data for the phase correction among the reference data, for example, the first measured data is p (i, j, kb), the effect of the magnetic field inhomogeneity with time variation is p (i, j, kb). And p (i, j, k). That is, the change in the phase component is

[0036]

(Equation 1) And the change in the absolute value component is

[0037]

(Equation 2) (FIG. 5: Step 54).

Therefore, by correcting these measurement data using these values, an image free of the influence of the non-uniform magnetic field can be obtained (FIG. 5: step 55). That is,

[0039]

(Equation 3) Get.

The phase-corrected image can be obtained by performing the two-dimensional Fourier transform on the main measurement data thus corrected (FIG. 5: step 56). As described above, one feature of the present invention is that signal correction is performed using the above-described phase map for each time phase before the two-dimensional Fourier transform.

In this example, a case has been described in which the prescan data is interpolated as real space data and corrected using data returned to the measurement space. However, in one direction (readout direction), the real space is used. In one direction (phase encoding direction), correction may be performed on data in a hybrid space that is a measurement space.

In any case, by performing such a correction, in an open MRI in which the static magnetic field non-uniformity is as large as 10 ppm or more, a single shot EPI free from image distortion and strong Nyquist artifact due to the magnetic field non-uniformity can be obtained.
It can be realized with a short pre-measurement time.

For example, in the prior art, 64 shots of pre-measurement data are required, but in this example, correction can be made with 16 shots of pre-measurement data, so that the time required for pre-measurement can be reduced to 1/4. . This is equivalent to a time reduction of 96 s when the repetition time of the pre-measurement is 2 s. In addition, since the measurement data before acquisition is obtained by signal estimation (interpolation), there is no deterioration in correction accuracy.

In the above example, the main measurement data is a 64 × 64 matrix, and the prescan data is 16 shot data. However, the number of matrixes of the main measurement data and the number of prescan shots are not limited thereto.

By the way, as a photographing method using the EPI, a dynamic EPI that performs continuous photographing and obtains a time-series continuous image.
The phase correction of the present invention can be applied to such a dynamic EPI. In general, the magnetic field fluctuation caused by the apparatus does not change with each imaging, so if the imaging target is a part such as the brain where there is no large change in position, the prescan needs to be performed only once, and the subsequent series Same correction factor for data of

[0046]

(Equation 4) Can be used to correct the signal. This avoids unnecessary extension of the prescan data measurement.

Such a dynamic single shot
The EPI is suitable for, for example, contrast enhanced perfusion (perfusion) imaging of the brain. FIG. 6 shows an example of the imaging timing applied to the contrast perfusion. A typical imaging sequence is a single shot GrE-EPI, the imaging matrix is 128 × 128, the imaging field is 200 mm, the slice thickness is 7 mm, the number of multi-slices is 15, and the dynamic interval is 2 s. TR at the time of acquiring the correction data is 2 s. A plurality of correction data are acquired corresponding to each slice of the main imaging.

Such a multi-slice dynamic
FIG. 7 shows the procedure of correction in EPI. Also in this procedure, the steps 71 to 74 for obtaining the influence of the magnetic field non-uniformity with the time variation from the pre-scan data are the same as the procedure of FIG. However, in multi-slice imaging, such steps 71 to 74 are performed.
Is performed for all slices to obtain correction data for each slice. The set of correction data thus obtained is applied to the main measurement data (step 75), and images for the number of slices are obtained (step 76). At this time, since a set of correction data can be applied to the main measurement data at each time when images are continuously taken, it is unnecessary to repeatedly calculate most of the correction calculation, and the correction time can be reduced. it can.

The embodiment of the present invention has been described above. Here, an echo (first echo) measured first after excitation by a high-frequency magnetic field is used as data (reference data) as a reference of time variation of a magnetic field non-uniformity. Although the case has been described, the reference echo is not limited to the first echo, and a desired echo can be used as the reference data. The echo time TE (time from excitation to measurement of the echo signal) of the reference echo is the effective TE of the corrected data. Therefore, the reference echo can be selected so as to be a suitable execution TE according to the purpose of the image. For example, by using a reference echo with a TE of 40 ms, a T2 * -weighted image can be obtained, and fMRI (functional MRI)
And image contrast suitable for contrast-enhanced MRI. Further, the image contrast is affected by the TR at the time of acquiring the correction data. Therefore, although slightly different from the pure EPI image contrast (TR = infinity), in practice, TR = 500-2000 ms may be set.

In this embodiment, a GrE-type EPI sequence has been exemplified as a sequence for acquiring the image creation data and the pre-scan data. May be added as a spin echo type single shot EPI, which can be selected according to the desired image contrast. That is, by using the spin echo component as the reference echo, the image contrast of the EPI becomes equivalent to the spin echo. Further, by using the non-spin echo component, the image contrast of the EPI becomes the same as the offset spin echo image.

In the embodiment, the single shot EPI has been described, but a multi shot EPI may be used. In this case, in operation 209 of FIG. 2, only part of the phase-encoded data is obtained, and then the operation 209 is repeated while changing the pulse 203 that gives the phase-encoding offset, to obtain the remaining echo signal 207.

In addition, as the pulse sequence, EPI
In addition, the same can be applied to a GRSE (gradient and spin echo) sequence or a spiral scan. It can also be applied to 3D EPI and 3D GRSE.

[0053]

According to the present invention, signal correction data corresponding to the magnetic field characteristics of a medium magnetic field open MRI apparatus is obtained and created, and the image creation data is corrected by this. Therefore, it is necessary to obtain the correction data. Time can be reduced and a high quality image can be obtained. As a result, clinically practical EPI can be realized in an open MRI apparatus.

[Brief description of the drawings]

FIG. 1 is a diagram showing a processing flow of an MRI method of the present invention.

FIG. 2 is a diagram showing an example of an MRI imaging sequence to which the present invention is applied.

FIG. 3 is a view showing an MRI imaging sequence according to an embodiment of the present invention.

FIG. 4 is an overall view of an MRI apparatus to which the present invention is applied.

FIG. 5 is a diagram showing an example of a correction processing flow according to the MRI method of the present invention.

FIG. 6 is a diagram showing an application example of the MRI method of the present invention to perfusion imaging.

FIG. 7 is a diagram showing an example of a correction processing flow in the imaging of FIG. 6;

[Explanation of symbols]

401 ... subject, 402 ... magnet, 403 ... gradient coil, 404 ...
RF coil, 405… RF probe, 406… Signal detector, 407…
Signal processing unit, 411 ... Control unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01N 24/08 510Y

Claims (3)

[Claims] 1. A static magnetic field generating means for generating a static magnetic field in a space where a subject is placed, a gradient magnetic field generating means for generating a gradient magnetic field in the space, and a high frequency magnetic field for causing nuclear magnetic resonance in the subject. A high-frequency generating means for generating, a detecting means for detecting a nuclear magnetic resonance signal generated from the subject, a signal processing means for reconstructing an image of the subject using the nuclear magnetic resonance signal, and the gradient magnetic field generation Means, a high-frequency generation means, a nuclear magnetic resonance imaging apparatus comprising a control means for controlling the detection means and the signal processing means, the control means, after the application of one or a set of high-frequency magnetic fields to excite the subject tissue Acquiring a plurality of nuclear magnetic resonance signals to which different phase encodings are applied, acquiring nuclear magnetic resonance signals of the number of phase encodings (N) required for image formation as main measurement data, To excite the subject tissue 1
After the application of one or a set of high-frequency magnetic fields, the acquisition of a plurality of nuclear magnetic resonance signals to which a desired phase encoding is applied is repeated (M) times smaller than the number of phase encodings (N) while changing the amount of phase encoding. Performing control to acquire a nuclear magnetic resonance signal for phase correction as correction data, the signal processing means performs interpolation on the correction data, and after obtaining the same number of matrices as the main measurement data, A nuclear magnetic resonance imaging apparatus used for phase correction of main measurement data. 2. A nuclear magnetic resonance imaging method for detecting a magnetic resonance signal from a subject placed in a static magnetic field and creating an image by image reconstruction processing, comprising: After applying a set of high-frequency magnetic fields, control is performed to acquire a plurality of nuclear magnetic resonance signals with different phase encodings, and the nuclear magnetic resonance signals with the number of phase encodings (N) required for image formation are used as the main measurement data. Acquiring, and after applying one or a set of high-frequency magnetic fields to excite the subject tissue, acquiring a plurality of nuclear magnetic resonance signals to which a desired phase encoding has been applied, while changing the amount of phase encoding A step of repeating the number of times (M) less than the number of phase encodes (N) to obtain a nuclear magnetic resonance signal for phase correction as correction data; and obtaining the data using the correction data. Creating a low-spatial-resolution image for each nuclear magnetic resonance signal at a different time; creating a magnetic field inhomogeneity map from the low spatial resolution image; and Performing a phase correction. 3. A magnetic resonance signal is detected from a subject placed in a static magnetic field, and an image is created by image reconstruction processing.
A nuclear magnetic resonance imaging method, comprising: collecting and processing data for signal correction (1).
And the step of collecting and processing data for image creation (2)
And a correction step (3) of correcting the image creation data using the signal correction data. The step (1) of collecting and processing the signal correction data includes generating transverse magnetization in the subject. Applying a first high-frequency magnetic field for applying the first phase encoding magnetic field (1)
2) Step of continuously generating the first readout gradient magnetic field while reversing the polarity (13). In synchronization with the generation timing of the first readout gradient magnetic field,
Detecting the first echo signal group (14), repeating the generation of the high-frequency magnetic field, the generation of the readout gradient magnetic field, and the signal detection while changing the amount of phase encoding (15); different phase encoding for each generation timing Creating an image with a relatively low spatial resolution for each generation timing from the echo signal group of (16), and extracting information reflecting a magnetic field map for each generation timing from the low spatial resolution image (17) The step of collecting and processing the data for image creation includes the step of applying a second high-frequency magnetic field for generating transverse magnetization to the subject (21); (22) repeatedly applying the second readout gradient magnetic field in synchronization with the application of the phase encoding magnetic field. (23) to generate continuously while inverting the polarity, in synchronization with each generation timing of the readout gradient magnetic field,
The correction step (3) comprises the steps of: detecting each echo signal for each generation timing obtained in the step (24); and correcting each echo signal for each generation timing obtained in the step (17). A nuclear magnetic resonance imaging method, comprising: a step (31) of correcting using a magnetic field map; and a step (32) of creating an image having a relatively high spatial resolution from the corrected echo signal.