JP5360757B2 - Magnetic resonance imaging and magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging method capable of appropriately suppressing the influence of a local gradient magnetic field present in an X direction and a Y direction within a slice plane. <P>SOLUTION: Every time the position of a sampling window 20 in a size equivalent to target resolution within a full K space 30 is set over a plurality of times, frequency information equivalent to a part of the full K space 30 is acquired. By Fourier transforming each of two or more pieces of the frequency information, a plurality of MRI images 40 corresponding to each of the frequency information are acquired. For each of a plurality of pixels within the slice plane, the MRI image 40 whose index correlated to the strength of an MRI signal has a maximum is selected from the plurality of acquired MRI images 40, the strength of the MRI signal in the MRI image 40 selected corresponding to the pixel is used for the contrast data of each pixel, and magnetic resonance images are reconstructed on the basis of the contrast data. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a magnetic resonance imaging method and a magnetic resonance imaging apparatus.

  Magnetic resonance imaging (hereinafter may be abbreviated as “MRI”) is widely used in the medical field as a precision examination method for the human body, and many documents on MRI have already been published (for example, Patent Document 1).

  In recent years, a magnetic resonance functional imaging method (functional MRI; hereinafter, sometimes abbreviated as “fMRI”) that measures brain activity using MRI has attracted attention (see, for example, Patent Document 2). In this fMRI, activities in the human brain can be evaluated non-invasively with millimeter-level spatial resolution, and it is said that higher-order functions of the human brain that are difficult to evaluate by animal experiments can be known appropriately.

  In particular, the echo planar imaging (EPI) method is the most popular high-speed MRI imaging method and is an indispensable tool in the fMRI method for brain function research.

  However, signal attenuation due to the presence of a local gradient magnetic field in the EPI-specific voxel is a weak point of the EPI method, and various efforts have been made to deal with such problems.

  For example, in order to cancel a local gradient magnetic field in the slice direction (hereinafter sometimes abbreviated as “Z direction”), a compensation pre-pulse is applied to recover signal attenuation due to the influence of the local gradient magnetic field in the Z direction. A method (hereinafter referred to as “Z-shimming method”) has been devised (see, for example, Non-Patent Document 1).

JP 2002-165774 A JP 2007-190120 A

Frahm, J et al., Direct FLASH MR Imaging of Magnetic Field Inhomogeneities by Gradient Compensation, MAGNETIC RESONANCE IN MEDICINE 6,474-480 (1988)

  The present inventor is working on research and development that can visualize human brain mechanisms using fMRI technology based on EPI imaging scan.

  In the process of this research and development, the slice plane (in plane) lead-out direction (also referred to as the frequency encoding direction; hereinafter, sometimes referred to as “X direction”) and the phase encoding method (hereinafter referred to as “Y direction”) We paid attention to the problem of local gradient magnetic field existing in some cases. In other words, the present inventor uses the change in the magnetic susceptibility of blood moglobin between the time of brain activation and the rest when the BOLD (Blood Oxygen Level Dependent) effect, which is the mainstream of the fMRI measurement method, Thus, it is considered that the local gradient magnetic field in the slice plane is closely related to the attenuation of the BOLD signal. In particular, the attenuation of the BOLD signal should be a problem at sites that are susceptible to brain structures, such as the temporal lobe in the lower frontal lobe that contacts the paranasal sinuses and mastoid honeycomb. Furthermore, as the magnetic field is increased, the attenuation of the BOLD signal due to the above causes becomes more significant, and this is considered to be a factor that impedes the application of the high magnetic field of 7 T or higher with high sensitivity to the fMRI technique. .

  Based on the above situation, the present inventor succeeded for the first time in devising a method capable of appropriately suppressing the influence of the local gradient magnetic field existing in the X and Y directions in the slice plane. In this specification, such a method is referred to as an “XY-shimming method”, and details of the “XY-shimming method” will be described later. In addition, it has been experimentally verified that the attenuation of the BOLD signal due to the local gradient magnetic field in the slice plane created intentionally can be recovered by the fMRI technique using the “XY-shimming method”. To do.

  The present invention has been made in view of such circumstances, and magnetic resonance imaging that can appropriately suppress the influence of local gradient magnetic fields existing in the X and Y directions in the slice plane, and An object of the present invention is to provide a magnetic resonance imaging apparatus capable of displaying a magnetic resonance image using magnetic resonance imaging.

In order to solve the above problems, the present invention is a magnetic resonance imaging method for constructing a magnetic resonance image based on a K space obtained by imaging scanning larger than a target resolution,
The frequency information corresponding to a part of the K space is acquired each time the sampling window having a size corresponding to the target resolution in the K space is set a plurality of times.
By Fourier transforming each of the plurality of frequency information, a plurality of magnetic resonance images corresponding to each of the frequency information is acquired,
For each of the plurality of pixels in the slice plane, from among the plurality of acquired magnetic resonance images, select a magnetic resonance image that maximizes the index correlated with the intensity of the magnetic resonance signal,
Using the intensity of the magnetic resonance signal in the magnetic resonance image selected corresponding to the pixel for the contrast data of each pixel,
Magnetic resonance imaging is provided that reconstructs a magnetic resonance image based on the contrast data.

Further, the present invention provides a static magnetic field generating means capable of generating a uniform static magnetic field in a space where a subject is placed,
A gradient magnetic field generating means capable of generating a gradient magnetic field in three orthogonal directions in the space;
High-frequency pulse generating means capable of irradiating a high-frequency pulse causing nuclear magnetic resonance to protons in a static magnetic field constituting the subject's living tissue;
Detecting means for detecting a magnetic resonance signal depending on a magnetic moment state of protons in a slice plane in which the nuclear magnetic resonance has occurred;
There is also provided a magnetic resonance imaging apparatus comprising: an image processing apparatus that displays the reconstructed magnetic resonance image.

In the magnetic resonance imaging method of the present invention, the index may be BOLD sensitivity (BS) formulated by the following formula (1).

BS = TE × I (1)

Where TE: effective echo time, I: intensity of magnetic resonance signal (pixel value)

  With the above configuration, since the influence of the local gradient magnetic field in the slice plane can be appropriately suppressed in the post-process (image processing) stage, it is only necessary to acquire the K space by a single imaging scan. Appropriate contrast data with little attenuation of BOLD sensitivity can be obtained for each pixel. Therefore, in the magnetic resonance imaging apparatus of the present embodiment, a magnetic resonance image can be reconstructed based on such contrast data, and the magnetic resonance image (contrast image) can be displayed on the image processing apparatus.

  Therefore, it is possible to appropriately measure the BOLD signal of the whole region of the human brain, including the brain activity site that was difficult to detect in the conventional magnetic resonance technology, and to apply it to the high-resonance magnetic resonance technology with high sensitivity. to enable. For this reason, the visualization of such magnetic resonance images can be expected to lead to the development of functional research of the human brain, and thus breakthrough advances in diagnostic technology in brain medicine.

  In the magnetic resonance imaging method of the present invention, the imaging scan may be performed using an echo planar imaging method (EPI).

  By such an EPI method, high-speed single imaging when measuring brain activation by the BOLD effect can be performed.

  According to the present invention, magnetic resonance imaging capable of appropriately suppressing the influence of local gradient magnetic fields existing in the X and Y directions in the slice plane, and magnetic resonance imaging using such magnetic resonance imaging A magnetic resonance imaging device that can be displayed is obtained.

It is the block diagram which showed the structural example of the magnetic resonance imaging device of embodiment of this invention. It is the figure which showed an example of the pulse sequence used for the magnetic resonance imaging method of embodiment of this invention. It is the figure which showed an example of the K-space obtained by the magnetic resonance imaging method of embodiment of this invention, and an example of the fMRI image in a slice surface obtained by performing a Fourier transform to K-space. It is the figure which illustrated typically the problem of the image analysis of the fMRI technique by EPI method in case a local gradient magnetic field exists in a X direction and a Y direction. It is a figure used for description of the magnetic resonance imaging method (XY-shimming method) of embodiment of this invention. It is a figure used for description of the magnetic resonance imaging method (XY-shimming method) of embodiment of this invention. It is a figure showing the result of carrying out experiment verification of the validity of the magnetic resonance imaging method (XY-shimming method) of embodiment of this invention. It is a figure showing the result of carrying out experiment verification of the validity of the magnetic resonance imaging method (XY-shimming method) of embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

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

  As shown in FIG. 1, a functional magnetic resonance imaging apparatus 1 (hereinafter sometimes abbreviated as “fMRI apparatus 1”) is a static magnetic field generating magnet capable of generating a uniform static magnetic field in a space where a subject X is placed. 2 (static magnetic field generating means) and gradient magnetic field coils 5 and 5 (gradient magnetic field generating means) capable of generating a gradient magnetic field in three orthogonal directions in the space. The gradient magnetic field coils 5 and 5 are supplied with driving power by the gradient magnetic field generator 11.

  A high-frequency signal output from the high-frequency generator 8 (high-frequency pulse generator) of the fMRI apparatus 1 is modulated into an appropriate signal by the modulator 9, amplified by the amplifier 10, and supplied to the high-frequency transmission coil 3. Thereby, the high frequency transmission coil 3 can irradiate the high frequency pulse which can cause nuclear magnetic resonance to the nucleus (proton) in the static magnetic field which comprises the biological tissue of the subject X.

  A magnetic resonance signal such as an echo signal radiated using proton nuclear magnetic resonance is received by the high frequency receiving coil 4 of the fMRI apparatus 1 and amplified by the amplifier 12, and then the phase detector 13 ( Signal detection means) detects an analog signal. The analog signal is converted into measurement data of a digital signal by the AD converter 14 and sent to the computer 6.

  The computer 6 of the fMRI apparatus 1 includes a storage device 15 (RAM, ROM, etc.), a display device 16 (liquid crystal monitor, etc.), an operation input unit (not shown), a CPU, etc. (not shown), and will be described later. It functions as an image processing apparatus that can execute image construction and display. That is, the CPU reads out the image processing program stored in the storage device 15, processes the measurement data of the digital signal received from the AD converter 14 according to the processing procedure by the image processing program, and outputs the processing result to the display device 16. Display as a magnetic resonance image.

  The sequencer 7 of the fMRI apparatus 1 is constituted by, for example, a microprocessor and is connected to the computer 6. The sequencer 7 sends a command necessary for performing magnetic resonance imaging in accordance with a pulse sequence (imaging sequence) to be described later, a magnetic field generation system (such as the gradient magnetic field coils 5 and 5 and the gradient magnetic field generation device 11) of the fMRI apparatus 1 and a high frequency. Send to transmission / reception system (high frequency generator 8, modulator 9, amplifiers 10, 12, high frequency transmission coil 3, high frequency reception coil 4, phase detector 13, AD converter 14, etc.) and control these operations Yes.

  Next, a pulse sequence for capturing a tomographic image of the subject X using the fMRI apparatus 1 will be described with reference to FIG.

  FIG. 2 is a diagram showing an example of a pulse sequence used in the magnetic resonance imaging method of the embodiment of the present invention. Several methods have been proposed for a pulse sequence for obtaining a magnetic resonance signal. Here, a pulse sequence based on the EPI method, which is frequently used as a high-speed imaging method when measuring brain activation by the BOLD effect, is shown. ing.

  The fMRI apparatus 1 according to the present embodiment uses a known EPI method, and is characterized by a post process (image processing) called “XY-shimming method” of measurement data measured by the EPI method. Therefore, here, the EPI method of FIG. 2 will be schematically described focusing on the portion related to the “XY-shimming method”.

  As shown in FIG. 2, simultaneously with the application of the slice gradient magnetic field pulse Gz, by applying an α-degree high frequency pulse α (RF excitation pulse), protons on the slice plane of the subject X are selectively excited. This releases a free induction decay signal (not shown) during the recovery process from the proton excited state. In this way, the slice plane in the slice selection direction, which is a two-dimensional image of the subject X, can be specified.

  Next, when measuring the echo signal, the gradient magnetic field Gx in the readout direction (X direction) and the gradient magnetic field Gy in the phase encoding direction (Y direction) are switched at high speed, and the K space is imaged and scanned like a single stroke. Here, the integrated values of the applied gradient magnetic fields Gx and Gy become the position coordinates of the frequency information in the X direction and the Y direction in the K space.

  That is, when the echo signal is measured, plus and minus gradient magnetic fields Gx are alternately applied in the lead-out direction (X direction), thereby, as shown in FIG. An imaging scan is performed so as to reciprocate the coordinate position (Kx) of the frequency information in the X direction in the K space. In addition, by applying the gradient magnetic field Gy in the phase encoding direction (Y direction) for a short time in accordance with the switching between the plus and minus of the gradient magnetic field Gx, the frequency coordinate position (Ky) in the Y direction of the K space can be set a little. Shifted in the positive direction. In this way, when both are combined, as shown in FIG. 2, the K-space can be imaged and scanned in a single stroke.

  The K space as the two-dimensional frequency information is obtained by the one imaging scan described above. When this K space is subjected to Fourier transform, a magnetic resonance function image (fMRI image; hereinafter, simply “MRI”) as shown in FIG. Abbreviated as “image”).

  The K space itself is well known in the MRI technique. Therefore, detailed description of the K space is omitted.

  Next, problems when local gradient magnetic fields ΔGx and ΔGy exist in the X direction and the Y direction will be described.

  FIG. 4 is a diagram schematically illustrating a problem of image analysis of the fMRI technique by the EPI method when local gradient magnetic fields exist in the X direction and the Y direction.

  FIG. 4A schematically illustrates the influence of the imaging scan when the local gradient magnetic field ΔGx exists uniformly in the X direction. FIG. 4B schematically illustrates the influence of the imaging scan when the local gradient magnetic field ΔGy is uniformly present in the Y direction. FIG. 4C schematically illustrates the influence of the imaging scan when local gradient magnetic fields ΔGx and ΔGy exist uniformly in the X and Y directions.

  As described above, the integrated value of the applied gradient magnetic field Gx becomes the position coordinate (Kx) of the frequency information in the X direction in the K space. Therefore, if the local gradient magnetic field ΔGx in the X direction exists uniformly, the trajectory in the K space shifts to the positive side of Kx as shown in FIG. Then, the echo center P of the locus of the K space is also shifted to the plus side of Kx. Therefore, a shift occurs in the slice plane between the sampling window 20 (acquisition window) and the locus of the K space. Then, since only the frequency information of the sampling window 20 is Fourier transformed, the MRI signal is attenuated and adversely affects the sensitivity of the BOLD signal. In the worst case, the dropout of the MRI signal may be caused.

  As shown in FIG. 4B, even when the local gradient magnetic field ΔGy in the Y direction exists uniformly, as shown in FIG. 4C, the local gradient magnetic fields ΔGx, ΔGy in the X direction and the Y direction are obtained. However, the same kind of problem occurs, but a detailed description thereof will be omitted here.

  Next, a shift adjustment method (XY-shimming method) of the echo center P in the slice plane at the post process (image processing) stage, which is a characteristic part of the fMRI apparatus 1 of the present embodiment, will be described with reference to the drawings.

  First, the present inventor applies a prepulse for compensation in the X direction and / or the Y direction in the same kind of method as the existing “Z-shimming method”, that is, in the shift adjustment of the echo center P in the slice plane. The possibility of this method was examined. As a result, it has been concluded that such a pre-pulse application method for compensation causes an increase in imaging time and is unusable. In particular, since it is considered that the intensity of the local gradient magnetic field is different for each pixel, it is necessary to apply different prepulses for each pixel. Judging from the actual situation of brain function research intended to know in a short time).

  5 and 6 are diagrams used for explaining magnetic resonance imaging (XY-shimming method) according to the embodiment of the present invention.

  First, as shown in FIG. 5, a full K-space 30 (raw data) in the slice plane having a higher resolution than that of a normal MRI image is acquired by one EPI imaging scan. The full K space 30 is stored in the storage device 15 (see FIG. 1) of the computer 6. For example, when it is desired to acquire the MRI image 40 by the EPI imaging scan having a spatial resolution of 64 × 64, which is often used in the normal fMRI technique, the full K The space 30 may be acquired.

  In this manner, the full K space 30 larger than the target resolution (64 × 64) is obtained by the EPI imaging scan.

  Next, a high-resolution (here 96 × 96) full K space 30 is read from the storage device 15 to the internal memory of the computer 6 and displayed on the operation screen of the computer 6 (display device 16 in FIG. 1). As shown in FIG. 5, the position setting of the sampling window 20 (moving window) having a size corresponding to the target resolution (low resolution; here, 64 × 64) is performed an appropriate number of times. Each time such position setting is performed, a plurality of pieces of frequency information (KS-1, KS-2,...) That are part of the full K space 30 corresponding to the sampling window 20 are acquired. Frequency information (KS-1, KS-2...) Is stored in the storage device 15 of the computer 6. Note that the sampling window 20 may be set in the full K space 30 in a well-balanced manner.

  Thereafter, each of the plurality of frequency information (KS-1, KS-2,...) Is Fourier-transformed, so that the MRI corresponding to each of these frequency information (KS-1, KS-2,...). A plurality of images 40 (image-1, image-2,...) Are acquired, and these MRI images 40 (image-1, image-2,...) Are stored in the storage device 15 of the computer 6. The

  According to the above construction operation of the MRI image, Fourier transform is performed using frequency information at various set positions in the full K space 30, and many MRI images 40 (image-1, image-2,...・) Is obtained.

  Therefore, as shown in FIG. 6A, when the echo center P is shifted in the Kx direction, the sampling position is shifted by the same amount as the shift amount of the echo center P to the frequency information of the sampling window 20A shifted in the Kx direction. It is good to apply conversion.

  Thereby, an MRI image with little influence of the local gradient magnetic field ΔGx can be obtained.

  The MRI image reconstructed using the frequency information corresponding to a part of the full K space 30 was captured by applying a compensation prepulse (gradient magnetic field) in the lead-out direction (X direction). Can be identified with the image.

  Further, as shown in FIG. 6B, when the echo center P is shifted in the Ky direction, the sampling position is shifted by the same amount as the shift amount of the echo center P to the frequency information of the sampling window 20B shifted in the Ky direction. It is good to apply conversion.

  Thereby, an MRI image with little influence of the local gradient magnetic field ΔGy can be obtained.

  The MRI image reconstructed using the frequency information corresponding to a part of the full K space 30 was picked up by applying a compensation prepulse (gradient magnetic field) in the phase encoding direction (Y direction). Can be identified with the image.

  Further, as shown in FIG. 6C, when the echo center P is shifted in the Kx direction and the Ky direction, the sampling position is shifted in the Kx direction and the Ky direction by the same amount as the shift amount of the echo center P. A Fourier transform may be applied to the 20C frequency information.

  Thereby, an MRI image with little influence of local gradient magnetic fields ΔGx, ΔGy can be obtained.

  The MRI image reconstructed using the frequency information corresponding to a part of the full K space 30 is compensated in the lead-out direction (X direction) and the phase encoding direction (Y direction). It can be identified with an image captured by applying a gradient magnetic field.

  As described above, according to the magnetic resonance imaging method of the present embodiment, only the full K space 30 is acquired by one EPI imaging scan, and the X direction and the Y direction are obtained at the post-process (image processing) stage by the computer 6. A large number of MRI images 40 (image-1, image-2,...) In which various direction shift adjustment effects (shimming effects) are exhibited are obtained.

  Therefore, the magnetic resonance imaging method of the present embodiment has an advantageous effect compared with the conventional compensation pre-pulse application method in which the time of the EPI imaging scan is hardly sacrificed.

  Here, in the post-process (image processing) stage by the computer 6, an optimum MRI image (that is, a local gradient magnetic field is most appropriately selected from the MRI images 40 (image-1, image-2,...)). It is necessary to establish a method for evaluating a cancelable image (in other words, a method for selecting such an image). In particular, since the optimum MRI image should be different for each pixel (i, j; i = 1 to 64, j = 1 to 64) of the MRI image in the slice plane (two-dimensional), the above evaluation method It is considered that the creation of (selection method) is indispensable in the practical application of the “XY-shimming method”.

It is convenient for the inventor to use the BOLD sensitivity (BS) as an index correlated with the intensity of the MRI signal formulated by the following formula (1) for such an evaluation method (selection method). I noticed.

BS = TE × I (1)

In Equation (1), “TE” is the effective echo time, and “I” is the intensity (pixel value) of the MRI signal of the MRI image.

  The above formula (1) representing BOLD sensitivity has already been published in a paper (for example, R. Deichmann et al., Compensation of Susceptibility-Induced BOLD Sensitivity Losses in Echo-Planar fMRI Imaging, NeuroImage 15, 120-135 (2002)). Has been. Therefore, detailed description of the above formula (1) is omitted.

  That is, the inventor of the present invention has the MRI that maximizes the BOLD sensitivity (BS) for each pixel (i, j) in the slice plane from the MRI image 40 (image-1, image-2,...). When an image is selected, it is considered that the selected MRI image corresponds to the optimum MRI image for the pixel (i, j) to be selected. And the validity of such an evaluation method (selection method) was supported by experimental verification described later.

  Therefore, in the magnetic resonance imaging method of the present embodiment, for each pixel (i, j) in the slice plane, an MRI image that maximizes the BOLD sensitivity (BS) is represented by a plurality of MRI images 40 (image-1, image-1). -2, ...) Then, the intensity of the MRI signal in the MRI image selected corresponding to the pixel (i, j) is used for the contrast data of the pixel (i, j).

  For example, if the MRI image having the maximum BOLD sensitivity (BS) in the pixel (i = 1, j = 1) is the MRI image 40 (image-1), this pixel (i = 1, j = 1) ), The intensity of the MRI signal of the pixel (i = 1, j = 1) of the MRI image 40 (image-1) is used.

  If the MRI image having the maximum BOLD sensitivity (BS) is the MRI image 40 (image-15) in the pixel (i = 10, j = 10), this pixel (i = 10, j = 10) The intensity of the MRI signal of the pixel (i = 10, j = 10) of the MRI image 40 (image-15) is used for the contrast data of.

  Finally, in the magnetic resonance imaging method of the present embodiment, a magnetic resonance image (contrast image) is reconstructed based on the contrast data of each of the pixels (i, j), and the reconstructed magnetic field is reconstructed. The resonance image is displayed on the display device 16 of the computer 6.

Hereinafter, the results of experimental verification of the validity of the magnetic resonance imaging method (XY-shimming method) of the present embodiment will be described. In the following experiment verification, manganese dioxide (MnO ₂ ) powder in a manganese dry battery is packed in a bag so that a local gradient magnetic field in the slice plane can be artificially (intentionally) created. It was done with this bag on the head.

  7 and 8 are diagrams showing the results of experimental verification of the validity of the magnetic resonance imaging method (XY-shimming method) of the embodiment of the present invention.

  FIG. 7A shows a slice plane (two-dimensional) MRI image (captured photograph) obtained by a conventional EPI imaging scan magnetic resonance functional imaging method (hereinafter abbreviated as “EPI imaging method”). Yes. FIG. 7B shows a slice plane (two-dimensional) MRI image (captured photograph) obtained by the EPI imaging method of the present embodiment. In FIG. 7C, an MRI structure image (captured photograph) obtained by a method slower than the EPI image method, although hardly affected by the gradient magnetic field, is illustrated as a reference for the original MRI image of the entire brain.

  As shown in FIG. 7, in the conventional EPI imaging method, the shadow of the MRI image spreads in the brain region (the arrow portion in FIG. 7A) close to the portion where the bag of manganese dioxide is applied. For this reason, it is considered that the intensity of the MRI signal at the part is lowered due to the influence of the local gradient magnetic field due to manganese dioxide, and as a result, the BOLD sensitivity is attenuated.

  In contrast, as can be easily understood from the comparison between FIG. 7A and FIG. 7B, in the EPI image method of the present embodiment, the shadow portion of the MRI image is compared with the conventional EPI image method. It has recovered significantly.

  In FIG. 8, the subject X is subjected to two-hand tapping, and the time change of the BOLD signal at the three positions where the slice plane positions are “upper”, “middle”, and “lower” is the conventional EPI imaging method ( The profile 100) of FIG. 8 and the EPI imaging method of the present embodiment (profile 200 of FIG. 8) are shown.

  In the time change (profile 100) of the BOLD signal in the conventional EPI imaging method shown in FIG. 8, the characteristics of the BOLD signal in the region that is the shadow of the MRI image (see FIG. 7) do not appear.

  On the other hand, in the time change of the BOLD signal (profile 200) in the EPI imaging method of the present embodiment, the time change of the BOLD signal when the original subject X is tapped with both hands (detailed explanation and illustration are omitted). The same tendency is shown.

  It is thought that the validity of the magnetic resonance imaging method (XY-shimming method) of this embodiment was supported by the above experimental verification.

  As described above, the magnetic resonance imaging method of the present embodiment can appropriately suppress the influence of the local gradient magnetic fields ΔGx and ΔGy in the slice plane at the post-process (image processing) stage, so that one EPI imaging scan is performed. By simply acquiring the full K space 30, appropriate contrast data can be obtained with little attenuation of the BOLD sensitivity for each pixel (i, j) in the slice plane. Therefore, the fMRI apparatus 1 of the present embodiment can reconstruct a magnetic resonance image based on such contrast data, and can display the magnetic resonance image (contrast image) on the computer 6.

  Therefore, it is possible to measure the BOLD signal in the entire region of the human brain including the brain activity site that has been difficult to detect in the conventional fMRI technology, and to apply to the highly sensitive high magnetic field fMRI technology. For this reason, by visualizing magnetic resonance images using such an XY-shimming method, it is possible to expect the development of functional research of the human brain, and thus breakthrough advances in diagnostic technology in brain medicine.

  In addition, this invention is not limited to embodiment mentioned above and an Example. In addition, the specific components of each part and each process are not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention.

  For example, in the magnetic resonance imaging method of the present embodiment, the EPI method has been exemplified. However, the present technology is not limited to this, and the present technology can also be applied to magnetic resonance imaging methods using other pulse sequences.

  According to the magnetic resonance imaging method of the present invention, it is possible to appropriately suppress the influence of a local gradient magnetic field existing in the X direction and the Y direction in the slice plane.

  Therefore, the present invention can be used as an imaging method of magnetic resonance imaging using nuclear magnetic resonance of protons, and can be applied to, for example, diagnostic imaging techniques in brain medicine.

DESCRIPTION OF SYMBOLS 1 fMRI apparatus 2 Static magnetic field generating magnet 3 High frequency transmission coil 4 High frequency reception coil 5 Gradient magnetic field coil 6 Computer (image processing apparatus)
7 Sequencer 8 High-frequency generator 9 Modulator 10, 12 Amplifier 11 Gradient magnetic field generator 13 Phase detector 14 AD converter 15 Storage device 16 Display device 20, 20A, 20B, 20C Sampling window 30 Full K space 40 MRI image

Claims (4)

A magnetic resonance imaging method for constructing a magnetic resonance image based on a K space obtained larger than a target resolution by an imaging scan,
The frequency information corresponding to a part of the K space is acquired each time the sampling window having a size corresponding to the target resolution in the K space is set a plurality of times.
By Fourier transforming each of the plurality of frequency information, a plurality of magnetic resonance images corresponding to each of the frequency information is acquired,
For each of the plurality of pixels in the slice plane, from among the plurality of acquired magnetic resonance images, select a magnetic resonance image that maximizes the index correlated with the intensity of the magnetic resonance signal,
Using the intensity of the magnetic resonance signal in the magnetic resonance image selected corresponding to the pixel for the contrast data of each pixel,
Magnetic resonance imaging that reconstructs a magnetic resonance image based on the contrast data.   The magnetic resonance imaging method according to claim 1, wherein the imaging scan is performed using an echo planar imaging method. The magnetic resonance imaging method according to claim 1, wherein the index is BOLD sensitivity (BS) formulated by the following formula (1).
BS = TE × I (1)
However,
TE: Effective echo time, I: Magnetic resonance signal intensity (pixel value) A static magnetic field generating means capable of generating a uniform static magnetic field in a space where the subject is placed;
A gradient magnetic field generating means capable of generating a gradient magnetic field in three orthogonal directions in the space;
High-frequency pulse generating means capable of irradiating a high-frequency pulse causing nuclear magnetic resonance to protons in a static magnetic field constituting the subject's living tissue;
Detecting means for detecting a magnetic resonance signal depending on a magnetic moment state of protons in a slice plane in which the nuclear magnetic resonance has occurred;
A magnetic resonance imaging apparatus comprising: an image processing apparatus that displays the reconstructed magnetic resonance image according to claim 1.