JPH11164819A - Magnetic resonance image device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an artifact by periodic movement possible to be positioned in the end part of a view field and to enable an image with high diagnostic value to be produced, by equipping a function to control phase encode so that projection data neighboring in k-space are shifted about half a cycle of periodic movement such as respiratory movement. SOLUTION: Various parameters are set for phase encode control at a control part 11 and the cycle Tp of respiratory movement of a subject is inputted. Next, the cycle Tp and a projection number Pr are related each other to control the phase encode quantity. That is, the projection number n collected in a cycle is calculated from repeating time TR and an addition time number k of an imaging sequence, and projection data required for 1 slice of image are divided into segments of every n projections. The phase encode is controlled so as to shift the projection data neighboring on k space by about half a cycle to make the imaging pulse sequence performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging (hereinafter abbreviated as "MRI") for obtaining a tomographic image of a desired portion of a subject by utilizing a nuclear magnetic resonance (hereinafter abbreviated as "NMR") phenomenon. The present invention relates to an MRI apparatus suitable for capturing an image of an object that fluctuates at a constant cycle.

[0002]

2. Description of the Related Art As is generally known, MRI is susceptible to movement and flow of a subject during measurement, and it is known that such influences cause artifacts. The causes of such artifacts include periodic movements such as heart beats and breathing. Artifacts due to the periodic movement appear as artifacts 111 flowing in the phase encoding direction as shown in FIG. 11 and overlap with the true image 112, thereby hindering diagnosis.

[0003] As a method of suppressing artifacts due to periodic motion, there is a synchronous measurement method for controlling the photographing timing in accordance with the periodic motion. For example, when the movement is a respiratory movement, the following respiratory synchronization measurement method is generally used. (1) Detect abdominal wall movement due to breathing. (2) A trigger signal is generated when the detected motion of the abdominal wall reaches a predetermined value. (3) A pulse sequence is started after a certain period of time has elapsed from the generation of the trigger signal, and necessary signal measurement is performed while the movement of the abdominal wall is stable (there is little work). (4) In the case of multi-slice measurement in which a plurality of slices are sequentially measured, the number of slices to be measured is selected so that measurement of all slices is completed during a period in which the movement of the imaging region due to respiration is stable.

According to this respiratory synchronization measurement method, the signals of all slices are measured during a period in which the movement of the imaging region due to respiration is stable, so that the influence of the movement on the signal can be minimized. As a result, in the reconstructed image, artifacts due to respiration were small, and an image having no problem in diagnosis could be obtained.

[0005]

However, in the above-mentioned conventional synchronous measurement method, a signal is measured only during a period in which the respiratory movement is stable, and no signal measurement is performed in other periods. There was a problem of inviting. Prolonging the examination time increases the burden on the patient during the examination and decreases the examination efficiency.

[0006] Therefore, the present invention eliminates artifacts due to periodic motion (respiratory motion) without prolonging the photographing time.
MR that can be well excluded from images required for diagnosis
It is intended to provide an I device.

[0007]

In order to achieve the above object, in the MRI apparatus of the present invention, a control system for controlling the gradient magnetic field generating means assigns a different phase encoding to the echo signal to convert k-space data. At the time of collection, phase encoding amount control during signal measurement is performed such that data of adjacent projections in the k-space are measured at a timing shifted by substantially a half cycle of the period (Tp) of the periodic motion.

That is, the MRI apparatus of the present invention comprises a static magnetic field generating means for applying a static magnetic field to a subject, a gradient magnetic field generating means for applying a gradient magnetic field to the subject, and a nucleus of an atom constituting a living tissue of the subject. A transmission system that irradiates a high-frequency magnetic field that causes nuclear magnetic resonance, and a reception system that detects an echo signal emitted by nuclear magnetic resonance as projection data,
These gradient magnetic field generating means, a control system for controlling the transmission system and the reception system according to a predetermined pulse sequence, a signal processing system for performing an image reconstruction operation using the projection data detected by the reception system, and displaying the obtained image. The control system controls the gradient magnetic field generating means to control the phase encoding amount of the echo signals sequentially acquired based on the period (Tp) of the periodic movement of the subject. Then, the acquisition timings of the projection data adjacent to each other in the k space are shifted from each other by approximately 1/2 cycle of the periodic motion. Note that the k space is an arrangement of projection data in the phase encoding direction.

According to a preferred embodiment of the MRI apparatus of the present invention, the control system divides all the projection data in the k space into a group of projection data measured within the cycle (Tp), and sets each group in the phase encoding direction. A group of projection data is measured. At this time, if the number (n) of projection data of different phase encoding amounts measured in a cycle is odd, odd-numbered projection data or even-numbered projection data is provided in the first half of the cycle. One of the projection data is collected in numerical order, then the other is collected in numerical order, and so on.The measurement is repeated until the projection data of all the phase encoding amounts is collected in the same manner. When the number (n) of data is even, in the first cycle (Tp), the number of In the first half, one of the odd-numbered projection data or the even-numbered projection data is collected in numerical order, then the other is collected in numerical order, and in the next cycle (Tp), the other is collected in the first half in numerical order, and then the other is numbered. The gradient magnetic field generation means is controlled so that the measurement is repeated until the projection data is collected in order and the projection data of all the phase encoding amounts is collected while changing the order of the projection data collected in each cycle.

The fact that adjacent projection data on the k-space is out of phase by about 1/2 cycle with respect to the periodic movement means that a signal change due to a periodic movement in which the projection data is alternately shifted by 1/2 a cycle. Means to do. This periodic signal change corresponds to the highest frequency that can be displayed on the reconstructed image. Normal MR
In the I image, the center of the image is a frequency 0 (DC) component, and the end of the image is displayed at the highest frequency. Therefore, when an image is reconstructed by FFT (Fast Fourier Transform) using this k-space data, a signal change due to a periodic motion corresponding to the highest frequency appears at an end of the image due to the nature of FFT.
As a result, the influence (artifact) of a periodic motion such as respiratory motion appears only at the end of the image, and does not overlap with the center of the image that is important for diagnosis.

In the MRI apparatus of the present invention, the field of view (FO)
V) in the phase encoding direction. The technique of measuring the field of view in the phase encoding direction wider than the required field of view and cutting out and displaying the required field of view in post-processing is known as the aliasing artifact removal function (called the anti-wrap function, wrap-around removal function, etc.). ing. By using the anti-wrap function together, the respiratory motion artifact can be further moved away from the main part of the image and can be driven out of the required visual field.

In the MRI apparatus according to the present invention, artifacts can be satisfactorily excluded from images required for diagnosis, and imaging is performed continuously during a periodic movement, so that it is not necessary to extend the imaging time. . As a result, the burden on the patient undergoing the examination can be reduced, and the throughput of the apparatus can be increased.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 10 is a diagram schematically showing an MRI apparatus according to the present invention. This MRI apparatus includes a static magnetic field generating magnet 402 for generating a uniform static magnetic field in a space around a subject 401 and a gradient magnetic field in this space. The gradient coil 403 to be generated and the subject 401
Coil 404 for irradiating the subject with a high-frequency magnetic field, and RF probe 4 for receiving an NMR signal generated from subject 401
05 and. The subject 401 is laid on the bed 412 and sent to the static magnetic field space.

The gradient magnetic field coils 403 are composed of gradient magnetic field coils of three orthogonal axes, and generate gradient magnetic fields in accordance with signals from a gradient magnetic field power supply 409. With these three-axis gradient magnetic field coils, gradient magnetic fields in the slice direction, the phase encoding direction, and the readout direction can be applied to the space where the subject is placed.

The RF coil 404 generates a high-frequency magnetic field as a pulse in response to a signal from the RF transmitting unit 410. RF probe
The signal of 405 is detected by the signal detection unit 406, and the signal processing unit 40
The signal is processed in 7 and converted into an image signal by calculation. The image is displayed on the display unit 408. Gradient magnetic field power supply 409,
The RF transmission unit 410 and the signal detection unit 406 are controlled by the control unit 411 according to a predetermined pulse sequence.

In the MRI apparatus of the present invention, the control unit 411
Controls the amount of phase encoding of each projection data based on the periodic movement of the subject when executing a predetermined imaging sequence. In this embodiment, a respiratory motion will be described as an example of the periodic motion. The phase encoding control in the control unit 411 is performed in accordance with a control program (pulse sequence) incorporated in advance, and a gradient magnetic field coil in a phase encoding direction (in some cases, a combination of gradient magnetic field coils in three axial directions).
This is performed by sequentially controlling the current value applied to the power supply.

Hereinafter, the phase encoding control in the control unit 411 will be described with reference to the flowchart of FIG. First, prior to the start of MRI imaging, the type of imaging sequence,
Repetition time TR, echo time TE, number of slices s,
Number of additions k, number of projections Pr, field of view FOV
Are set (101). As the imaging sequence, a sequence for collecting projection data of one phase encoding by one excitation, such as a spin echo method and a gradient echo method, is selected. The number Pr of projections is the number of projection data necessary to reconstruct an image for one slice, and is the number of data in the phase encoding direction of k-space data (the number of phase encodings).
Is the same as The setting of these parameters is performed by an operator using an input device such as an operator console (not shown).

Further, in the present invention, the period Tp of the respiratory movement of the subject is
Enter The period Tp of the respiratory movement is, for example, the respiratory movement of the subject (up and down movement of the abdominal wall: FIG.
Is measured, and the average value of each cycle can be used.

Next, the period Tp and the number of projections P
r, thereby controlling the amount of phase encoding. Therefore, first, the control unit 411 obtains 1 from the set repetition time TR of the imaging sequence and the number of additions k.
The number of projections n collected in a cycle is expressed by the following equation (1).
(102).

[0021]

## EQU1 ## n = Tp / (TR × k) (1) The value of n is set as an integer by an appropriate method such as rounding.

Next, projection data necessary to form an image of one slice is divided into segments (groups) for every n projections (103). Number of segments m
Is

[0023]

M = Pr / n (2), which is determined as an integer by rounding up the first decimal place. As a result, the k space is divided into m segments from first to m-th. The first to (m-1) th segments each have n pieces of projection data in the segment, and the mth segment may be less than n pieces depending on the number of measurement projections.

Usually, the projection number Pr is 128,
In this embodiment, the number of projections is 32 and the number of additions is 1 in order to simplify the description.
The following is an example of the case. 2 and 3 are diagrams for explaining division of k-space data in the phase encoding direction. FIG. 2 shows that the number n of projection data collected in one cycle of respiratory movement is 5, and 32 projections are 7 Divided into segments. Each segment is
Except for the seventh segment, each has five projection data. FIG. 3 shows that the number n of projection data collected in one cycle of respiratory movement is 6,
Thirty-two projections are divided into six segments. Each segment has six projection data except for the sixth segment. In the drawing, each projection data is represented by a data identification number ab (b-th projection data in the a-th segment).

The measurement is performed for each segment corresponding to one cycle of the movement, for example, the first segment, the second segment,.
Are performed in the order of numbers, etc., but at this time, phase encoding control is performed so that adjacent projection data is collected at a timing shifted from each other by approximately 略 phase with respect to the cycle of movement.

If n = 2 (two repetitions of the pulse sequence in one cycle of the respiratory movement), the projection data is in the phase encoding order (1-1, 1-2, 2-1, 2-2,...).・
), Adjacent data are shifted in phase by half the period. However, even in the simplest example described above, n = 5, and when the periodic motion is a respiratory motion, usually several tens or more projections are collected in one cycle (about 3 seconds). Therefore, in order to cause adjacent projection data to be shifted from the movement cycle by approximately 1/2 phase, it is necessary to change the collection timing of the projection data in the segment. For this reason, in this embodiment, the projections within one cycle (one segment) are divided into odd-numbered projections and even-numbered projections, and either one of the data is collected in the first half of one cycle, and the other data is collected in one cycle. Collect in the second half.

In this case, the projection number n is set so that the above condition is satisfied for the last projection of the segment (for example, data number 1-n) and the first projection of the next segment (data number 2-1). The phase encoding control is changed depending on whether is odd or even (103).

In the embodiment shown in FIG. 2, since n = 5,
The phase encoding control I as shown in FIG. 4 is performed. That is,
For example, odd-numbered projection data 1-1, 1-3, 1-
5 are collected in ascending order, and then the even-numbered projection data 1-2 and 1-4 are collected in ascending order. This is because while the conventional phase encoding amount was incremented by one, the data number is incremented by two from data number 1-1 to data number 1-n, and then the data number is incremented by one.
Control returns to the phase encoding amount of 2 and increments by 2 until the data number becomes 1- (n−2). In the next period, the same phase encoding control as in the first period is performed by changing the offset amount of the phase encoding. That is, odd-numbered projection data is collected first, and then even-numbered projection data is collected. Although FIG. 4 shows only the respiratory cycle up to the third cycle, the measurement is repeated in the same manner until the last projection data 7-2 is collected.

By performing such phase encoding control, the intervals between adjacent projection data are all {(n ± 1) / 2} × TR. In the example shown in the figure, the interval T (1-2) for collecting the data numbers 1-1 and 1-2 is 3
× TR, and the collection interval T (2-3) of the data numbers 1-2 and 1-3 is 2 × TR, and the collection interval T (of the data numbers 1-5 and 2-1 5-1) is 3 × TR. As described above, since the value of n is usually about several tens, this interval is substantially nTR / 2 (= Tp / 2).

An imaging pulse sequence is performed according to the phase encoding control, and an image reconstruction is performed after the signal measurement is completed. Image reconstruction is performed in the same manner as in the normal case.
T (fast Fourier transform) and the like are performed (106). As described above, due to the nature of the FFT, a signal change due to a periodic motion such that the phase is shifted by 周期 cycle for each adjacent projection data can be displayed on the reconstructed image in the image. Corresponds to the highest frequency. Therefore, when the image is displayed such that the center of the image has a frequency of 0 (DC) component and the end of the image has the highest frequency, the effect (artifact) 111 of the periodic motion is as shown in FIG. At the end of the image, and does not overlap the central part of the image which is important for diagnosis (108).

Although the case where the number of additions k is 1 has been described above, even when the number of additions is two or more, data of the same phase encoding amount (a plurality of projection data to be added) is continuously collected. Similarly, it is possible to perform phase encoding control so that projection data adjacent on the k-space is collected at a timing shifted from each other by approximately 1/2 phase with respect to the cycle of motion.

FIG. 6 shows a case where the number of additions is two. For simplicity of explanation, the case where the number of projections n measured in one cycle of movement is set to 5 as in FIG. 4 and TR is １ ／ of that in FIG. 4 is exemplified. Here, data of the same projection is indicated by ab or ab ′. Also in this case, the k-space data is divided into segments for each cycle Tp,
Perform the measurement in numerical order. Within each segment,
In the first half of the cycle, odd-numbered projection data is collected in numerical order, and in the second half, even-numbered projection data is collected.

However, as described above, data of the same projection is continuously measured. Thereby, for example, the first projection data of the first segment (1-1 and 1-
1 ') are 1-1 and 1-1' in the figure as phases for respiratory movement.
Can be regarded as a phase corresponding to the average value of. Similarly, the phase of each projection data of each segment with respect to the respiratory motion is determined. The measurement timing of each projection data of each segment is shifted by (n ± 1) × TR from the projection data adjacent on the k space. From equation (1), Tp = 2 (the number of additions) × TR ×
In this case, as in the case of FIG. 3, the data is shifted from the adjacent data by about 1/2 cycle of the respiration cycle.

Next, phase encoding control II (FIG. 1: step 109) in the case where the number of projections n measured in one cycle of movement is an even number will be described with reference to FIGS. FIG. 3 shows the total number of projections Pr = 32 in k-space.
FIG. 9 is a diagram showing an embodiment in the case of n = 6, where k-space is divided into six segments.

When n is an even number, the six projections included in one segment are divided into odd-numbered projections (1-1, 1-3, 1-5) and even-numbered projections (1-2, 1). -4, 1-6), and phase encoding control is performed so that the group measured in the first half and the group measured in the second half are different for each segment.

For example, as shown in FIG. 7, in the first segment, odd-numbered projection data (1-1, 1-
3, 1-5) are sequentially measured, and then even-numbered projection data (1-2, 1-4, 1-6) are sequentially measured. Then the second
The segments are measured. Here, even-numbered projection data (2-2, 2-4, 2-6) is measured sequentially, and then odd-numbered projection data (2-1, 2-3, 2-5)
Are sequentially measured. Hereinafter, similarly, measurement is performed in the order of odd-numbered projection data and even-numbered projection data in the odd-numbered segment, and in the order of even-numbered projection data and odd-numbered projection data in the even-numbered segment. By changing the order of measurement between the odd-numbered segment and the even-numbered segment in this way, the interval between the last projection of the segment and the first projection of the next segment can also be set to approximately の of the period Tp. it can.

In this case, in the first segment, adjacent projections on the k-space are (n / 2)
× TR or {(n / 2) -1} × TR, and the last projection (1-
6) to the first projection of the third segment (3
Until -1), the adjacent projections on the k space are (n / 2) × TR or {(n / 2) +1} × TR
It is measured at intervals. The same applies to the third and subsequent segments, and the intervals between adjacent projections are all n.
TR / 2 (= Tp / 2) or {(n / 2) ± 1} × TR
Becomes If the value of n is large enough, this interval will be approximately nT
R / 2 (= Tp / 2).

Therefore, even when data measured by photographing according to such phase encoding control is reconstructed, the phase of each adjacent projection data is reduced by half.
Signal changes due to periodic movements that are shifted by the period
Appears as an artifact 111 at the end of the image (Fig. 5
(A)), it does not overlap the image central part 112 important for diagnosis.

Next, the number of projections n measured within one cycle of movement is an even number (n = 6) and the number of additions k =
8 is shown in FIG. Also in this case, the measurement of the same projection is continuously performed when n = odd number (FIG. 6).
Is the same as As a result, the phase with respect to the movement of one projection data becomes the average value of the projection data to be added, and the cycle deviation between adjacent projections obtained from this is all nkTR / 2 or ｛as in the case of the number of additions of 1 (FIG. 7). (N / 2) ± 1｝ × k
It becomes TR. That is, the adjacent data is approximately 1 / the respiration cycle.
It is shifted by two cycles. As a result, as in the case where the number of additions is one (FIG. 7), artifacts due to periodic movement can be set at the end of the image. The same applies to the case where the number of additions is three or more.

In FIGS. 7 and 8, assuming that n is an even number, the odd-numbered segment has an odd projection number.
The case where measurement is performed in the order of even projection and even-numbered segment in the order of even-numbered projection-odd-numbered projection has been described. -Even if the measurement is performed in the order of the even projections, similarly, adjacent data on the k space can be shifted by about １ ／ cycle of the respiratory cycle.

As described above, it has been described that by performing the above-described phase encoding control by the control unit, the artifact due to the respiratory movement can be located at the end of the image.
When the subject is relatively large with respect to the set field of view (FOV), as shown in FIG. 5B, the artifact 111 located at the end of the image overlaps with the true image 112 required for diagnosis, which may hinder the diagnosis. Could be.

In such a case, the known anti-wrap function can be used to drive out artifacts out of the required field of view. The anti-wrap function is generally known as a technique for removing aliasing artifacts. As shown in FIG. 9A, a wide area is photographed in a phase encoding direction with respect to a required field of view, and the necessary image is reconstructed after image reconstruction. Area outside the field of view (anti-wrap area) 113
Is truncated, and only the image of the necessary field of view is displayed.

When the anti-wrap function is employed, parameters relating to the function are first set in step 101 of the flow shown in FIG. Specifically, the field of view (FO
V) is set longer in the phase encoding direction. in this case,
The number Pr of projections may be increased in accordance with the magnification of the visual field, or may be the same as in normal shooting. In the former case, the required spatial resolution of the visual field is the same as when the anti-wrap function is not used, but the photographing time is long. In the latter case, the spatial resolution of the field of view is reduced, but the photographing time is not extended. FIG. 9A shows an enlargement ratio of 15 in the phase encoding direction of the visual field.
At 0%, the case where the number Pr of projections is the same as when the anti-wrap function is not used is shown. In this case, the required spatial resolution of the visual field is 170/256 (about 2/3), but the photographing time does not change. As a method of using the anti-wrap function without extending the photographing time, there are other methods such as reducing the number of additions, and these methods may be used.

After the anti-wrap function is selected, the parameters (TR, the number of projections Pr when the anti-wrap function is used together) set in step 101 are selected.
Etc.), the steps 102 to 106 (or 10
Execute 9). This is exactly the same as when the anti-wrap function is not selected. That is, the number of projections Pr
The phase encoding control is performed in accordance with whether the number of projections n per cycle Tp obtained from the above is odd or even, and the projection data adjacent on the k-space is shifted by approximately 1/2 the phase of the motion cycle Tp.

An image obtained by photographing by performing such phase encoding control and reconstructing the obtained data by FFT becomes an image long in the phase encoding direction as shown in FIG. 9B. Also in this case, the artifact 111 due to respiratory movement is located at the end of the visual field in the phase encoding direction. By setting the region including the respiratory motion artifact 111 as the anti-wrap region 113, it is possible to set the image region so that the respiratory motion artifact is not included in the desired visual field.

The magnification of the field of view and the number of projections when the anti-wrap function is selected are not limited to those in the above-described embodiment, but may vary depending on the degree of overlap between the artifact and the true image, the resolution required for the image, and the SN. Any setting can be made accordingly.

[0047]

As described above, in the MRI apparatus of the present invention, phase encoding during signal measurement is controlled such that adjacent projection data on the k-space is shifted by about a half cycle of a periodic motion such as a respiratory motion. By providing the function, the artifacts due to these periodic movements can be located at the ends of the visual field. As a result, an image having a high diagnostic value can be obtained. Furthermore, by using the anti-wrap function together and expanding the imaging region in the phase encoding direction, even when the subject is large relative to the visual field, it is possible to reliably remove the artifacts due to the periodic movement out of the required visual field. .

In the MRI apparatus of the present invention, unlike a general respiratory synchronization measurement method, there is no method of selecting only a period in which the action of the target periodic motion is stable and measuring the signal during the period. Therefore, there is an effect that the burden on the patient during the examination is reduced without extending the imaging time. Similarly, since the photographing time is not extended, the efficiency of the inspection is not reduced.

[Brief description of the drawings]

FIG. 1 is a flowchart showing phase encoding control of a control unit in an MRI apparatus of the present invention.

FIG. 2 is a diagram illustrating k-space segmentation according to an embodiment of the phase encoding control of the present invention.

FIG. 3 is a diagram illustrating k-space segmentation according to another embodiment of the phase encoding control of the present invention.

FIG. 4 is a diagram showing a respiratory movement curve, signal measurement timing, and phase encoding control in the embodiment of FIG. 2, showing a case where the number of additions is one;

FIG. 5 is a diagram schematically showing an example of a reconstructed image by the MRI apparatus of the present invention.

FIG. 6 is a diagram showing a respiratory movement curve, signal measurement timing, and phase encoding control in the embodiment in FIG.

FIG. 7 is a diagram showing a respiratory motion curve, signal measurement timing, and phase encoding control in the embodiment of FIG. 3, showing a case where the number of additions is one;

FIG. 8 is a diagram showing a respiratory movement curve, signal measurement timing, and phase encoding control in the embodiment of FIG. 3, showing a case where the number of additions is two.

FIG. 9 shows an imaging region (a) and an example of a reconstructed image (b) when the anti-wrap function is employed in the MRI apparatus of the present invention.
Figure schematically showing

FIG. 10 is a block diagram showing the whole of an MRI apparatus to which the present invention is applied;

FIG. 11 is a diagram illustrating an artifact that occurs when an image of a subject having a periodic motion such as a respiratory motion is captured.

[Explanation of symbols]

 402: Static magnetic field magnet (static magnetic field generating means) 403: Gradient magnetic field coil (gradient magnetic field generating means) 404: RF coil (transmission system) 405: ..RF probe (reception system) 406... Signal detection unit (reception system) 407... Signal processing unit (signal processing system) 408... Display unit (display means) 409: Gradient magnetic field power supply (gradient magnetic field generating means) 410: RF transmission unit (transmission system) 411: Control unit (control system)

Claims (3)

[Claims] 1. A static magnetic field generating means for applying a static magnetic field to a subject, a gradient magnetic field generating means for applying a gradient magnetic field to the subject,
A transmitting system that irradiates a high-frequency magnetic field that causes nuclear magnetic resonance to the nuclei of atoms constituting the living tissue of the subject, a receiving system that detects an echo signal emitted by the nuclear magnetic resonance as projection data, A control system for controlling the magnetic field generating means, the transmission system and the reception system in accordance with a predetermined pulse sequence, a signal processing system for performing an image reconstruction operation using the projection data detected by the reception system, and displaying the obtained image. The control system controls the gradient magnetic field generating means, and based on the period (Tp) of the periodic movement of the subject, the phase encoding amount of the echo signals sequentially acquired. And the acquisition timing of the projection data adjacent to each other in the k-space is shifted by about 1/2 cycle of the periodic motion. A magnetic resonance imaging apparatus. 2. The control system divides all projection data in k space into a group of projection data measured within the period (Tp), and measures the projection data of each group in a phase encoding direction. When the number (n) of projection data of different phase encoding amounts measured in the cycle is an odd number, one of odd-numbered projection data or even-numbered projection data is collected in the first half of the cycle in numerical order. Thereafter, the other is collected in numerical order, and thereafter, the measurement is repeated until the projection data of all the phase encoding amounts are collected in the same manner, and the number (n) of the projection data of the different phase encoding amounts measured in the cycle is an even number. In the case of the first
In the cycle (Tp), one of odd-numbered projection data or even-numbered projection data is collected in numerical order in the first half of the cycle, and then the other is collected in numerical order. In the next cycle (Tp), the other is numbered in the first half. The gradient magnetic field is collected so that the measurement is repeated until the projection data of all the phase encoding amounts is collected while changing the order of the projection data collected in each cycle in the same manner. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the generation unit is controlled. 3. The control system according to claim 1, wherein the control system has a function of setting an imaging area of the subject, and sets an area wider in a phase encoding direction than a required visual field as the imaging area and performs imaging. Or the magnetic resonance imaging apparatus according to 2.