JPH09299345A - Diffusion intensifying imaging method and mri device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid improper correction and reduce artifact by obtaining the average phase of correction data corresponding to plural rectilinear loci, and re-collecting imaging data and correction data if a difference between the phase of the correction data and the average phase is a designated threshold value or more. SOLUTION: A pre-amplifier 5 amplifies an NMR signal received by a receiving coil of a magnet assembly 1, a phase detector 12 phase-detects an NMR signal taking a carrier wave output signal of a RF oscillating circuit 10 as a reference signal, and an A/D converter 11 converts an analog NMR signal to MR data of digital signal to be output to a calculator 7. The calculator 7 reads MR data from the A/D converter 11 and performs phase correction operation and image re-configuration operation to create an image. The average phase of correction data corresponding to plural rectilinear loci is obtained, and if a difference between the phase of the correction data and the average phase is a designated threshold value or more, imaging data and correction data are re-collected.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a diffusion weighted imaging method and MRI (Magnetic Resonance Imaging).
Related to the device. More specifically, a diffusion weighted imaging method and MR capable of reducing artifacts due to body motion
I device.

[0002]

2. Description of the Related Art As a conventional diffusion-weighted imaging method for removing a body movement component of a phase of imaging data by correction to reduce an artifact due to the body movement, there is disclosed in Japanese Patent Laid-Open No.
The diffusion weighted imaging method described in Japanese Patent No. 314426 and Japanese Patent Application Laid-Open No. 8-10239 is known.

In the diffusion-weighted imaging method disclosed in Japanese Patent Laid-Open No. 4-314426, a plurality of linear loci along the lead axis direction (which are referred to as views) that fill k-space like a raster scan are arranged. A phase encode gradient and a read gradient are applied to collect imaging data including diffusion information, and a phase rewind gradient is applied to collect correction data. Then, for each view, the imaging data and the correction data are Fourier-transformed in the read axis direction to obtain respective intermediate data. Next, for each view, the phase of the intermediate data of the imaging data is corrected with the phase of the intermediate data of the correction data. Next, the intermediate data of the corrected imaging data of all the views is subjected to Fourier transform in the phase encode axis direction to generate image data. Then, a diffusion weighted image is created from this image data. In the diffusion-weighted imaging method, the phase of the imaging data,
It includes both the phase encode component and the body motion component (phase component generated by the body motion). On the other hand, since the correction data is collected after applying the phase rewinding gradient, the phase encode amount is “0”, the phase encode amount is not included, and only the body movement amount is included. Therefore, by correcting the phase of the imaging data with the phase of the correction data,
The body movement can be removed, and the artifact due to the body movement can be reduced.

Further, in the diffusion-weighted imaging method described in Japanese Patent Laid-Open No. 8-10239, a large number of spiral loci extending spirally from the center of the k-space to the end of the k-space ( A phase encode gradient and a read gradient are applied along a (view) to collect imaging data including diffusion information. Next, for each view, the phase of the imaging data other than the central part of the k-space is corrected based on the phase of the imaging data of the central part of the k-space. Next, the corrected imaging data is two-dimensionally Fourier transformed to generate image data.
Then, a diffusion weighted image is created from this image data. In the above diffusion weighted imaging method, the imaging data other than the central portion of the k-space includes both the phase encode component and the body motion component. On the other hand, the imaging data in the central part of the k-space does not include the phase encode amount because the phase encode amount is “0”,
It contains only body movements. Therefore, by correcting the phase of the imaging data other than the central portion of the k-space with the imaging data of the central portion of the k-space, the body movement component can be removed and the artifact due to the body movement can be reduced.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The correction in the diffusion-weighted imaging method described in Japanese Patent No. 426 is appropriate when the body movements included in the correction data and the body movements included in the imaging data are approximately the same, but the body movements included in the correction data are correct. If the amount of body movement included in the imaging data is too large or too small, it becomes inappropriate.
However, in the related art, since such a consideration has not been made, there is a problem in that an inappropriate correction is made and an artifact due to body movement may not be sufficiently reduced.

Further, the correction in the diffusion weighted imaging method described in the above-mentioned Japanese Patent Laid-Open No. 8-10239 is performed by k-
The body movement and k included in the imaging data of the center of the space
-It is appropriate when the body movements included in the imaging data other than the central portion of the space are similar, but the body movements other than the central portion of the k-space are larger than the body movements included in the imaging data in the central portion of the k-space. If the amount of body movement included in the imaging data is too large or too small, it will be inappropriate. However, in the related art, since such a consideration has not been made, there is a problem in that an inappropriate correction is made and an artifact due to body movement may not be sufficiently reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a diffusion weighted imaging method and an MRI apparatus that can avoid improper correction and can sufficiently reduce the artifacts due to body movement.

[0008]

SUMMARY OF THE INVENTION In a first aspect, the present invention provides a phase encoding gradient and lead along each of a number of lead axial linear trajectories that fill k-space like a raster scan. A gradient is applied to collect imaging data including diffusion information and a phase rewind gradient is applied to collect correction data, and the phase of the correction data is determined for each data corresponding to each linear locus. In the diffusion-weighted imaging method that corrects the phase of the imaging data and creates an image that reflects the diffusion information based on the corrected imaging data, obtains the average phase of the correction data corresponding to a plurality of linear loci. However, if the difference between the phase of the correction data corresponding to each linear locus and the average phase is equal to or greater than a predetermined threshold value, the linear locus is imaged. To provide a diffusion weighted imaging method comprising the the use data re collecting the correction data. In the diffusion-weighted imaging method according to the first aspect, when the phase of a certain correction data greatly deviates from the average of the phases of a plurality of correction data, the data is retaken. The reason is that there was a non-average body movement at that time, so there is a high probability that the body movement included in the imaging data is too large or too small as compared to the body movement included in the correction data, and that data is used. It is better not to. As a result, it is possible to avoid using the imaging data that has been improperly corrected for creating an image, and it is possible to sufficiently reduce the artifacts due to body movement. Since the appropriate value of the threshold differs depending on the MRI apparatus, the subject, the diagnosis site, etc., it is preferable to empirically determine the value.

In a second aspect, the present invention provides a phase encode gradient and a read gradient along each of a number of spiral trajectories that spiral out from the center of k-space to the ends of k-space. Collect imaging data including diffusion information by applying, for each data corresponding to each spiral trajectory,
The phase of the imaging data other than the central part of the k-space is corrected based on the phase of the imaging data of the central part of the k-space, and the image in which the diffusion information is reflected is created based on the corrected imaging data. In the diffusion-weighted imaging method, the k-corresponding to a plurality of spiral trajectories is used.
If the average phase of the imaging data of the central part of the space is obtained and the difference between the phase of the imaging data of the central part of the k-space corresponding to each spiral locus and the average phase is a predetermined threshold value or more, the spiral Provided is a diffusion-weighted imaging method characterized by recollecting imaging data for a trajectory. In the diffusion-weighted imaging method according to the second aspect, when the phase of the imaging data at the center of a certain k-space deviates significantly from the average of the phases of the imaging data at the center of a plurality of k-spaces, Retake the data. The reason is that there was a non-average body movement at that time, so the body movement included in the imaging data other than the central portion of k-space is more than the body movement included in the imaging data of the central portion of k-space. This is because there is a high probability that the minutes will be too large or too small, and it is better not to use that data. As a result, it is possible to avoid using the imaging data that has been improperly corrected for creating an image, and it is possible to sufficiently reduce the artifacts due to body movement. Since the appropriate value of the threshold differs depending on the MRI apparatus, the subject, the diagnosis site, etc., it is preferable to empirically determine the value.

In a third aspect, the present invention applies a phase encode gradient and a read gradient along each of a number of lead-axis linear trajectories that fill k-space like a raster scan and diffuse. Raster scanning means for collecting imaging data including information and for applying correction data by applying a phase rewinding gradient, and average phase acquisition for acquiring average phase of correction data corresponding to a plurality of linear loci Means and data re-acquisition means for controlling the raster scanning means so as to recollect the imaging data and the correction data for a linear locus in which the difference between the phase of the correction data and the average phase is a predetermined threshold value or more. , Phase correction means for correcting the phase of the imaging data based on the phase of the correction data, and the phase correction means based on the corrected imaging data It was equipped with an image generating means for generating an image reflecting the spread information Te provides an MRI apparatus wherein. In the MRI apparatus according to the third aspect,
The diffusion weighted imaging method according to the first aspect can be suitably implemented. Therefore, as described above, it becomes possible to sufficiently reduce the artifact due to the body movement.

In a fourth aspect, the present invention provides a phase encode gradient and a read gradient along each of a number of spiral loci that spirally extend from the center of k-space to the ends of k-space. Spiral scan means for applying and collecting imaging data including diffusion information; average phase acquisition means for acquiring an average phase of imaging data at the center of k-space corresponding to a plurality of spiral trajectories;
-Data re-acquisition means for controlling the spiral scanning means so as to re-collect the imaging data for a spiral locus in which the difference between the phase of the imaging data in the center of the space and the average phase is a predetermined threshold value or more, k-
K- based on the phase of imaging data at the center of the space
Provided is an MRI apparatus including a phase correction unit that corrects the phase of imaging data other than the central portion of a space, and an image creating unit that creates an image in which diffusion information is reflected based on the corrected imaging data. The MRI apparatus according to the fourth aspect can suitably implement the diffusion weighted imaging method according to the second aspect. Therefore, as described above, it becomes possible to sufficiently reduce the artifact due to the body movement.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited by this.

First Embodiment FIG. 1 is a block diagram of an MRI apparatus according to the first embodiment of the present invention. In this MRI apparatus 100, the magnet assembly 1 has a space portion (hole) for inserting a subject therein, and a main magnetic field for applying a constant main magnetic field to the subject by surrounding this space portion. A coil,
A gradient magnetic field coil for generating a gradient magnetic field (the gradient magnetic field coil includes x-axis, y-axis, and z-axis coils.
A lead coil is determined), a transmission coil that transmits an RF pulse for exciting spins of atomic nuclei in the subject, a reception coil that receives an NMR signal from the subject, and the like are arranged. The main magnetic field coil, gradient magnetic field coil, transmitting coil and receiving coil are connected to a main magnetic field power supply 2, a gradient magnetic field driving circuit 3, an RF power amplifier 4 and a preamplifier 5, respectively.

The computer 7 creates a pulse sequence,
It is passed to the sequence storage circuit 8. Sequence storage circuit 8
Stores a pulse sequence, operates the gradient magnetic field drive circuit 3 based on the pulse sequence, generates a gradient magnetic field from the gradient magnetic field coil of the magnet assembly 1, operates the gate modulation circuit 9, and operates the RF oscillation circuit 10
Is modulated into a pulse signal having a predetermined timing and a predetermined envelope shape, which is applied as an RF pulse to the RF power amplifier 4 and power-amplified by the RF power amplifier 4 and then transmitted to the transmission coil of the magnet assembly 1. Apply.

The preamplifier 5 includes a magnet assembly 1
, And amplifies the NMR signal received by the receiving coil, and inputs the amplified signal to the phase detector 12. The phase detector 12 is an RF oscillation circuit 1
The carrier signal of 0 is used as a reference signal, the NMR signal is subjected to phase detection, and given to the A / D converter 11. A / D converter 1
1 is a method for converting an analog NMR signal into a digital signal M signal.
The data is converted into R data and input to the computer 7.

The computer 7 reads MR data from the A / D converter 11 and performs phase correction calculation and image reconstruction calculation to create an image. This image is displayed on the display device 6. Further, the computer 7 is responsible for overall control such as receiving information input from the console 13.

FIG. 2 is a flowchart of the average phase acquisition process in the MRI apparatus 100. Step V1
Then, the view number counter m is initialized to "1".
In step V2, the correction data e2 (m) is collected by the pulse sequence QR shown in FIG. That is, in this pulse sequence QR, the 90 ° RF pulse R1
And the slice gradient S1 is applied to the slice axis. Next, the phase encode gradient P on the phase encode axis
Apply E (m). Next, a powerful MP for diffusion enhancement
(Motion Probing) Gradient MPG1 is applied to an arbitrary gradient axis. Next, a 180 ° RF pulse R2 is applied and a slice gradient S2 is applied to the slice axis. Next, the MP gradient MPG2 for diffusion enhancement is applied to an arbitrary gradient axis. Next, the echo echo1 is sampled while applying the read gradient RD1 to the read axis, and the imaging data e1 (m) is collected. Next, a phase rewinding encode gradient PR (m) having the same magnitude as the phase encode gradient PE (m) is applied to the phase encode axis. Next, echo echo2 is applied while applying the read gradient RD2 to the read axis.
Is sampled to collect the correction data e2 (m). In FIG. 4A, the imaging data e1 (1) and the correction data e2 (1) of the first view (m = 1) are shown.
3 illustrates an example of a linear trajectory (raster trajectory).
Further, in FIG. 4B, the imaging data e1 (2) and the correction data e2 of the second view (m = 2) are shown.
The linear locus of (2) is shown. In the mean phase acquisition process, the collection of the imaging data e1 (m) may be omitted.

Returning to FIG. 2, in step V3, the correction data e2 (m) is Fourier-transformed in the direction of the lead axis to obtain intermediate data E2 (m), and its phase φ
Calculate 2 (m). In steps V4 and V5, m = 2
Step V2 for N (N is, for example, 8 to 12)
And step V3 is repeated. In step V6, the average phase φ2av of the phases φ2 (1) to φ2 (N) is calculated.

FIG. 5 is a flowchart of the diffusion weighted imaging process in the MRI apparatus 100. In step B1, the operator sets a threshold value δ (δ is, for example, 10 °).
Set. At step B2, the view number counter m is initialized to "1". At step B3, the imaging data e is obtained by the pulse sequence QR shown in FIG.
1 (m) and correction data e2 (m) are collected. That is, in this pulse sequence QR, the RF pulse R1 of 90 ° is applied and the slice gradient S1 is applied to the slice axis.
Is applied. Next, the phase encode gradient PE (m) is applied to the phase encode axis. Next, the MP gradient MPG1 for diffusion enhancement is applied to an arbitrary gradient axis. Next, 180 °
The RF pulse R2 is applied and the slice gradient S2 is applied to the slice axis. Next, the MP gradient M for diffusion enhancement
Apply PG2 to any gradient axis. Next, the echo echo1 is sampled while applying the read gradient RD1 to the read axis, and the imaging data e1 (m) is collected. Next, a phase rewinding encode gradient PR (m) having the same magnitude as the phase encode gradient PE (m) is applied to the phase encode axis. Next, the lead gradient R on the lead shaft
Sampling echo echo2 while applying D2,
The correction data e2 (m) is collected.

Returning to FIG. 5, in step B4, the correction data e2 (m) is Fourier transformed in the lead axis direction to obtain intermediate data E2 (m), and the intermediate data E2 is obtained.
The phase φ2 (m) of (m) is obtained. In step B5,
It is determined whether | φ2 (m) −φ2av | <δ. │φ2
If (m) -φ2av | <δ, proceed to step B6. │φ2
If (m) −φ2av | <δ is not satisfied, the process returns to step B3, and the imaging data e1 (m) and the correction data e2 (m) of the m-th view are retaken.

In step B6, the imaging data e1 (m) is Fourier-transformed in the lead axis direction to obtain intermediate data E1 (m), which is multiplied by exp {-iφ2 (m)}, Intermediate data E1 'after phase correction of m view
(M) is obtained. In steps B7 and B8, m = 2 to M
(M is, for example, 126), the above steps B3 to B6 are repeatedly executed. In step B9, the obtained phase-corrected intermediate data E1 ′ (1) to E1 ′ (M)
Is Fourier-transformed in the phase encode axis direction to generate image data. In step B10, a diffusion weighted image is created from the image data.

FIG. 6 is an explanatory diagram of the progression of m in the diffusion weighted imaging process (FIG. 5). m = 6,8
Then, the data is re-acquired twice until the difference between φ2 (m) and the average phase φ2av falls within the threshold δ.

According to the MRI apparatus 100 of the first embodiment described above, the data that the probability that the body movement included in the imaging data e1 is too large or too small is not used as the body movement included in the correction data e2 is not used. Therefore, only properly corrected imaging data can be used for image creation at any time, and the artifact due to body movement can be sufficiently reduced.

In the diffusion weighted imaging process of FIG. 5, the data is reacquired without incrementing m until | φ2 (m) −φ2av | <δ, but m is incremented without reacquiring the data. However, the data may be collected, and then the data may be recollected for m where | φ2 (m) −φ2av | <δ. Further, as an extension of this method, in the average phase acquisition processing of FIG. 2, the imaging data e1 (m) and the correction data e2 (m) are collected with N = M, and the correction data e2 (m) is collected. Obtain the average phase φ2av from all or part, use the data for m that is | φ2 (m) -φ2av | <δ for image creation, and recollect the data for m that is not | φ2 (m) -φ2av | <δ You may do it.

In the diffusion-weighted imaging process of FIG. 5, the number of times of data reacquisition is not limited, but the number of times of reacquisition in the same view is limited (for example, 10 times), and the data is reacquired by that number of times. Also | φ2 (m)-
If φ2av | <δ does not hold, the data obtained last may be used for image creation.

-Second Embodiment- The configuration of the MRI apparatus according to the second embodiment of the present invention is the same as that shown in FIG. 7 and 8 are flowcharts of diffusion weighted imaging processing in the MRI apparatus according to the second embodiment of the present invention. In step C1, the operator sets the threshold value δ.
(Δ is set to 10 °, for example). At step C2, the view number counter m is initialized to "1". At step C3, the imaging data e1 (m) and the correction data e2 are obtained by the pulse sequence QR shown in FIG.
Collect (m). That is, this pulse sequence Q
At R, the RF pulse R1 of 90 ° is applied and the slice gradient S1 is applied to the slice axis. Next, the phase encode gradient PE (m) is applied to the phase encode axis.
Next, the MP gradient MPG1 for diffusion enhancement is applied to an arbitrary gradient axis. Next, a 180 ° RF pulse R2 is applied and a slice gradient S2 is applied to the slice axis. Next, the MP gradient MPG2 for diffusion enhancement is applied to an arbitrary gradient axis. Next, the echo echo1 is sampled while applying the read gradient RD1 to the read axis, and the imaging data e1 (m) is collected. Next, a phase rewinding encode gradient PR (m) having the same magnitude as the phase encode gradient PE (m) is applied to the phase encode axis. Next, echo is applied while applying the read gradient RD2 to the read axis.
Echo 2 is sampled to collect correction data e2 (m).

Returning to FIG. 7, in step C4, the imaging data e1 (m) is Fourier-transformed in the direction of the lead axis to obtain intermediate data E1 (m), and exp {-iφ2 (m)} And the intermediate data E1 ′ after the phase correction of the m-th view
(M) is obtained. In steps C5 and C6, m = 2 to N
(N is, for example, 8 to 12), the above step C3 is repeatedly executed.

At step C7, the correction data e2
Fourier transform of (1) to e2 (N) in the lead axis direction is performed to obtain intermediate data E2 (1) to E2 (N), and the phase φ2 (1) of the intermediate data E2 (1) to E2 (N) is obtained. ~ Φ
2 (N), and further the phases φ2 (1) to φ2
The average phase φ2av of (N) is calculated.

Proceeding to FIG. 8, in step C8, the imaging data e is obtained by the pulse sequence QR shown in FIG.
1 (m) and correction data e2 (m) are collected. Here, N <m. In step C9, the correction data e2 (m) is Fourier-transformed in the lead axis direction to obtain intermediate data E2 (m), and the phase φ2 (m) of the intermediate data E2 (m) is obtained. In step C10, | φ2
(M) -φ2av | <δ is determined. | Φ2 (m) -φ
If 2av | <δ, the process proceeds to step C11. │φ2 (m)-
If φ2av | <δ is not satisfied, the process returns to step C8, and the m-th
The view imaging data e1 (m) and the correction data e2 (m) are retaken.

In step C11, the imaging data e1 (m) is Fourier-transformed in the lead axis direction to obtain intermediate data E1 (m), which is multiplied by exp {-iφ2 (m)}, Intermediate data E1 'after phase correction of m view
(M) is obtained. In steps C12 and C13, m = N +
2 to M (M is, for example, 126), the above step C
8 to Step C11 is repeatedly executed. At Step C14, the obtained intermediate E1 ′ (1) to E1 ′ after the phase correction are obtained.
Fourier transform is performed on (M) in the phase encode axis direction to generate image data. In step C15, a diffusion weighted image is created from the image data.

Also in the MRI apparatus of the second embodiment described above, it becomes possible to sufficiently reduce the artifact due to the body movement. Further, the prescan of the average phase acquisition processing shown in FIG. 2 can be omitted.

-Third Embodiment- The configuration of the MRI apparatus according to the third embodiment of the present invention is the same as that shown in FIG. FIG. 9 is a flowchart of the average phase acquisition process in the MRI apparatus of the third embodiment of the present invention.
In step F1, the view number counter m is initialized to "1". At step F2, the imaging data D (m, k) is obtained by the pulse sequence QS shown in FIG.
x, ky) is collected. In this pulse sequence QS, a 90 ° RF pulse R1 is applied and a slice gradient S1 is applied to the slice axis. Next, the MP gradient MPG1 for diffusion enhancement is applied to an arbitrary gradient axis. Then, 1
The RF pulse R2 of 80 ° is applied and the slice gradient S2 is applied to the slice axis. Next, MP for diffusion enhancement
Gradient MPG2 is applied to any gradient axis. Next, FIG.
, The phase encode gradient RD3 and the lead gradient R are formed so as to form a spiral trajectory (spiral trajectory) that spirals from the center to the end of the k-space S.
While applying D4, sample the echo echo,
Imaging data D (m, kx, ky) is collected. FIG. 11A shows the spiral trajectory of the imaging data D (1, kx, ky) of the first view (m = 1). D (1,0,0) is the k-space S
Is data for imaging the central part of the. FIG. 11B shows the spiral trajectory of the imaging data D (2, kx, ky) of the second view (m = 2). It should be noted that D (2,0,0) is imaging data of the central portion of the k-space S.

Returning to FIG. 9, in step F3, the phase φ (m) of the imaging data D (m, 0,0) at the center of the k-space is obtained by the following equation. φ (m) = arg {D (m, 0,0)} In steps F4 and F5, m = 2 to N (N is, for example, 4
0), the above steps F2 and F3 are repeatedly executed. In step F6, the phases φ (1) to φ
The average phase φ2av of (N) is obtained.

FIG. 12 is a flow chart of diffusion weighted imaging processing in the MRI apparatus of the third embodiment. In step H1, the operator sets a threshold value δ (δ is, for example, 10 °). At step H2, the view number counter m is initialized to "1". In step H3,
Imaging data D (m, kx, ky) is collected by the pulse sequence QS shown in FIG. Step H
4, the imaging data D at the center of k-space
The phase φ (m) of (m, 0,0) is calculated by the following equation. φ (m) = arg {D (m, 0,0)} In step H5, it is determined whether or not | φ (m) −φ2av | <δ. If | φ (m) −φ2av | <δ, step H6
Proceed to. If | φ (m) −φ2av | <δ is not satisfied, the procedure returns to step H3, and the imaging data D of the m-th view is obtained.
Retake (m, kx, ky).

In step H6, the imaging data D (m, kx, ky) is multiplied by exp {-iφ (m)}, and this is multiplied by the phase-corrected imaging data D '(m-th view). m, kx, ky). Step H
7 and H8, the above steps H3 to H6 are repeatedly executed for m = 2 to M (M is, for example, 16). In step H9, the obtained phase-corrected imaging data D ′ (1, kx, ky) to D ′ (M, kx, k
y) is two-dimensionally Fourier transformed to generate image data. In step H10, a diffusion weighted image is created from the image data.

According to the MRI apparatus of the third embodiment, the body movement component included in the imaging data other than the center portion of the k-space is larger than the body movement component included in the imaging data of the center portion of the k-space. Since data with a high probability of being too small or too small is not used, only properly corrected imaging data can be used for image creation at any time, and artifacts due to body movement can be sufficiently reduced.

In the diffusion weighted imaging process of FIG. 12, the data is reacquired without incrementing m until | φ (m) −φav | <δ, but m is incremented without reacquiring the data. While collecting data,
Then, the data may be retaken for m for which | φ (m) −φav | <δ does not hold. Further, as an extension of this method, in the average phase acquisition process of FIG. 9, N = M
And collect the imaging data D (m) as
The average phase φav is calculated from all or part of the imaging data D (m), and the data for m where | φ (m) −φav | <δ is used for image creation, and | φ (m) −φav |
Data may be re-acquired for m that is not δ.

In the diffusion-weighted imaging process of FIG. 12, the number of times of data reacquisition is not limited, but the number of times of reacquisition in the same view is limited (for example, 10 times),
Φ (m) -φav
If | <δ does not hold, the last obtained data may be used for image creation.

Further, as in the second embodiment, m
= 1 to N imaging data D (m) is collected, an average phase φav is obtained from them, and | φ (m) −φav | for imaging data D (m) of m = N + 1 to M
The data may be re-acquired when <δ does not hold.

[0040]

According to the diffusion weighted imaging method and the MRI apparatus of the present invention, data having a high probability that the body movements contained in the imaging data are too large or too small are discarded and are not used for image creation. An image can be created only from the image-corrected imaging data, and a good diffusion-weighted image with sufficiently reduced artifacts due to body motion can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an MRI apparatus according to a first embodiment of the present invention.

FIG. 2 is a flowchart of an average phase acquisition process according to the first embodiment of the present invention.

FIG. 3 is an exemplary diagram of a pulse sequence according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of a raster trajectory.

FIG. 5 is a flowchart of diffusion weighted imaging processing according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram of data reacquisition.

FIG. 7 is a first half flowchart of a diffusion weighted imaging process according to the second embodiment of the present invention.

FIG. 8 is a second half flow chart of the diffusion weighted imaging process according to the second embodiment of the present invention.

FIG. 9 is a flowchart of an average phase acquisition process according to the third embodiment of the present invention.

FIG. 10 is an exemplary diagram of a pulse sequence according to a third embodiment of the present invention.

FIG. 11 is an explanatory diagram of a spiral trajectory.

FIG. 12 is a flowchart of a diffusion weighted imaging process according to the third embodiment of the present invention.

[Explanation of symbols]

 100 MRI apparatus 1 Magnet assembly 3 Gradient magnetic field drive circuit 7 Computer 8 Sequence storage circuit QR, QS pulse sequence e1, D Imaging data e2 Correction data MPG1, MPG2 MP gradient

Claims (4)

[Claims] 1. Data for imaging including diffusion information is applied by applying a phase encode gradient and a read gradient along each of a number of linear loci along the frequency axis that fills k-space like a raster scan. In addition, the phase rewinding gradient is applied to collect the correction data, and for each data corresponding to each linear locus, the phase of the imaging data is corrected based on the phase of the correction data, and the corrected imaging is performed. In the diffusion-weighted imaging method that creates an image that reflects diffusion information based on the data for correction, the average phase of the correction data for multiple linear trajectories is acquired, and the phase of the correction data for each linear trajectory is acquired. If the difference between the average phase and the average phase is greater than or equal to a predetermined threshold value, recollect imaging data and correction data for the linear trajectory. Diffusion weighted imaging method characterized. 2. Imaging including diffusion information by applying a phase encode gradient and a read gradient along each of a large number of spiral loci that spirally extend from the center of k-space to the end of k-space. Data is collected, and for each data corresponding to each spiral locus, the phase of the imaging data other than the central part of k-space is corrected based on the phase of the imaging data of the central part of k-space, In a diffusion-weighted imaging method for creating an image in which diffusion information is reflected based on the corrected imaging data, an average phase of the imaging data of the central portion of k-space corresponding to a plurality of spiral loci is acquired, and If the difference between the phase of the imaging data at the center of the k-space corresponding to the spiral locus and the average phase is greater than or equal to a predetermined threshold, the spiral locus is imaged. Diffusion weighted imaging method characterized by re-collecting ring data. 3. Data for imaging including diffusion information is applied by applying a phase encode gradient and a read gradient along each of a number of linear loci along the lead axis that fills k-space like a raster scan. And a raster scan means for applying a phase rewinding gradient to collect correction data, and an average phase acquisition means for acquiring an average phase of correction data corresponding to a plurality of linear loci,
For a linear locus in which the difference between the phase of the correction data and the average phase is equal to or more than a predetermined threshold value, data re-acquisition means for controlling the raster scanning means so as to recollect the imaging data and the correction data, An MRI apparatus comprising: a phase correction unit that corrects the phase of the imaging data based on the phase of the data, and an image creating unit that creates an image that reflects diffusion information based on the corrected imaging data. . 4. Imaging including diffusion information by applying a phase encode gradient and a read gradient along each of a large number of spiral loci that spirally extend from the center of k-space to the end of k-space. Scanning means for collecting data for use in scanning, and k- corresponding to a plurality of spiral trajectories
Average phase acquisition means for acquiring the average phase of the imaging data in the center of the space, and imaging for the spiral locus in which the difference between the phase of the imaging data in the center of the k-space and the average phase is a predetermined threshold value or more. Based on the phase of the imaging data at the center of k-space and the data re-acquisition means for controlling the spiral scanning means so as to collect the data for imaging again. An MRI apparatus comprising: a phase correction unit that corrects and an image creating unit that creates an image in which diffusion information is reflected based on the corrected imaging data.