JP2013240537A - Mri apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an MRI (Magnetic Resonance Imaging) apparatus suppressing artifacts generated by local phase change of echo signals.SOLUTION: An MRI apparatus 10 includes: a high frequency pulse irradiation part 140 for irradiating a subject with high frequency pulses; a gradient magnetic field application part 150 for applying gradient magnetic field pulses in a frequency direction and a phase encoding direction to the subject; a reception part 160 for receiving echo signals generated from the subject; an image reconstruction part 174 for reconstructing images on the basis of the echo signals; and a display part 180 for displaying the images. After the high frequency pulse is irradiated once by the high frequency pulse irradiation part, the gradient magnetic field application part inverts positive and negative gradient magnetic field pulses in the frequency direction, and the reception part acquires the plurality of echo signals. The image reconstruction part reconstructs a plurality of images including artifacts, that appear at different positions, and averages the plurality of images.

Description

  The present invention relates to a magnetic resonance imaging (MRI) apparatus that measures nuclear magnetic resonance signals (hereinafter referred to as echo signals) from hydrogen or the like in a subject and visualizes nuclear density distribution, relaxation time distribution, and the like. In particular, the present invention relates to an MRI apparatus that suppresses artifacts caused by local phase changes of echo signals.

  As an imaging method using an MRI apparatus, there is a multi-echo imaging method such as a multi-shot echo planar imaging (EPI) method that acquires an echo signal necessary for image reconstruction by one or several RF irradiations. In multi-echo imaging, multiple echo signals are acquired in time series while inverting the frequency encoding gradient magnetic field, so in the measurement space (k space), even-numbered echoes (hereinafter referred to as even-numbered echoes) and odd-numbered ones are acquired. The direction of the frequency direction is arranged opposite to the echo acquired in (1) (hereinafter referred to as odd-numbered echo). Normally, when even-numbered echoes and odd-numbered echoes are sampled and used as time-series data, local inhomogeneity of the static magnetic field or imperfection of the gradient magnetic field occurs, and the center of the sampling time and the peak of the echo do not match. It becomes. In that case, the peaks of the even-numbered echo and the odd-numbered echo are positions on the opposite side with respect to the frequency encode 0 axis (ky axis) in the measurement space. Such a peak shift between the even echo and the odd echo causes an artifact called an N / 2 artifact.

  Patent Document 1 discloses a technique in which an echo for reference calculation is acquired in addition to the echo of the main measurement, and the main measurement data and the reference measurement data are complex-added. Patent Document 1 discloses an invention in which N / 2 artifacts are reduced by canceling the phase error between the main measurement data and the reference measurement data.

JP 2003-116815 A

  However, the N / 2 artifact may be caused by the movement of the subject, but the invention of Patent Document 1 cannot eliminate such an artifact.

  Therefore, an object of the present invention is to suppress artifacts with high accuracy regardless of any cause.

  An MRI apparatus according to a first aspect includes a high-frequency pulse irradiation unit that irradiates a subject with a high-frequency pulse, a gradient magnetic field application unit that applies a gradient magnetic field pulse in a frequency direction and a phase encoding direction, and an echo signal generated from the subject. A receiving unit for receiving, an image reconstructing unit for reconstructing an image based on an echo signal, and a display unit for displaying the image are provided. Then, after one high-frequency pulse irradiation by the high-frequency pulse irradiation unit, the gradient magnetic field application unit reverses the gradient magnetic field pulse in the frequency direction, the reception unit acquires a plurality of echo signals, and the image reconstruction unit A plurality of images including artifacts appearing at different positions are reconstructed on the basis of the echo signal, and the plurality of images are averaged. This increases the sharpness and contrast of the real image and reduces artifacts.

  The gradient magnetic field application unit of the MRI apparatus according to the second aspect changes the phase of the gradient magnetic field pulse in the phase encoding direction so as to change the imaging region (FOV). The image reconstruction unit reconstructs images having different shooting areas, and adds and averages a plurality of images having different shooting areas.

The image reconstruction unit of the MRI apparatus according to the third aspect causes the artifacts to appear at different positions by changing the arrangement when the k-space is formed from the echo signal received by the reception unit.
The k-space is formed by arranging odd-numbered echoes and even-numbered echoes alternately obtained by reversing the gradient magnetic field pulse. The odd-numbered echoes are continuous in two or more rows and the even-numbered echoes are continuous in two or more rows. Including how to arrange them.

In the MRI apparatus, the high-frequency pulse irradiation unit applies a 180 ° pulse for obtaining a spin echo signal from the subject, and the gradient magnetic field application unit applies a gradient magnetic field pulse for the diffusion weighted image before and after the 180 ° pulse. It is suitable for the DW-EPI method.
In the MRI apparatus, the gradient magnetic field application unit acquires reference data in a state where no gradient magnetic field pulse is applied, and corrects a plurality of echo signals with the reference data.

  The MRI apparatus of the present invention can increase the sharpness and contrast of an actual image and reduce artifacts.

1 is a block diagram illustrating a configuration of an MRI apparatus 10. It is a flowchart of the image reconstruction of 1st Embodiment. It is a pulse sequence of the DW-EPI method having a phase encoding interval TM1. It is a pulse sequence of the DW-EPI method having a phase encoding interval TM2. It is a flowchart of the image reconstruction of 2nd Embodiment. It is three FOV images by which addition averaging is carried out in 2nd Embodiment. It is three FOV images by which addition averaging is carried out in 3rd Embodiment.

  A magnetic resonance imaging apparatus (hereinafter referred to as “MRI (Magnetic Resonance Imaging) apparatus”) of the first embodiment and the second embodiment will be described.

<Configuration of MRI apparatus>
A configuration of the MRI apparatus 10 according to the present embodiment will be described. FIG. 1 is a block diagram illustrating the configuration of the MRI apparatus according to the embodiment. With reference to FIG. 1, the configuration and basic operation of the MRI apparatus 10 of the present embodiment will be described.

  The MRI apparatus 10 includes a magnet system 100, a gradient coil drive unit 130, an RF coil drive unit 140, a data collection unit 150, a pulse sequence control unit 160, a calculation unit 170, a display unit 180, and an operation unit 190.

  The magnet system 100 includes a main magnetic field coil unit 102, a gradient coil unit 106, and an RF coil unit 108. Each of these coil portions has a substantially cylindrical shape, and is arranged coaxially with each other in a substantially columnar bore. The subject SB is placed on the bed 110 in the bore, and the bed 110 is movable in the bore in the magnet system 100 according to the imaging region.

  The main magnetic field coil unit 102 forms a static magnetic field in the internal space of the magnet system 100. The direction of the static magnetic field is generally parallel to the direction of the body axis of the subject SB and forms a horizontal magnetic field. The main magnetic field coil unit 102 is normally configured using a superconducting coil, but may be configured using a permanent magnet or the like without being limited to the superconducting coil.

  The gradient coil unit 106 has three types of gradients for imparting gradients to the static magnetic field strength formed by the main magnetic field coil unit 102 in the three axes orthogonal to each other, that is, in the direction of the slice axis, the phase axis, and the frequency axis. Generate a magnetic field. In order to make it possible to generate such a gradient magnetic field, the gradient coil unit 106 has three gradient coils (not shown). A gradient coil drive unit 130 is connected to the gradient coil unit 106, and the gradient coil drive unit 130 gives a drive signal to the gradient coil unit 106 to generate a gradient magnetic field. The gradient coil drive unit 130 has three drive circuits (not shown) corresponding to the three gradient coils in the gradient coil unit 106.

  The RF coil unit 108 forms a high-frequency magnetic field for exciting spins in the body of the subject SB in the static magnetic field space. Formation of a high-frequency magnetic field is referred to as transmission of an RF excitation signal (RF pulse). An RF coil drive unit 140 is connected to the RF coil unit 108. The RF coil drive unit 140 provides a drive signal to the RF coil unit 108, and the RF coil unit 108 transmits an RF pulse based on the drive signal. An electromagnetic wave generated by the excited spin, that is, an echo signal is received by the RF coil unit 108. A data collection unit 150 is connected to the RF coil unit 108. The data collection unit 150 collects echo signals received by the RF coil unit 108 as digital data.

  A pulse sequence control unit 160 is connected to the gradient coil drive unit 130, the RF coil drive unit 140, and the data collection unit 150.

  The pulse sequence control unit 160 drives the gradient coil driving unit 130 and the RF coil driving unit 140 in accordance with the imaging conditions input by the operator, that is, the imaging protocol. More specifically, the pulse sequence control unit 160 generates sequence information for capturing an MRI image. The sequence information is transmitted to the gradient coil driving unit 130 and the RF coil driving unit 140.

  The display unit 180 is configured by a graphic display or the like. The display unit 180 is connected to the calculation unit 170. The display unit 180 can display a GUI operation screen, a magnetic resonance image reconstructed based on an echo signal for MRI image reconstruction, and the like.

  The operation unit 190 includes a keyboard having a pointing device. The operation unit 190 is connected to the calculation unit 170. The operation unit 190 is operated by the operator via the display unit 180. The operation unit 190 may arrange a touch panel on the display unit 180 instead of a keyboard or the like.

The calculation unit 170 includes a control unit 171, a storage unit 172, and an image reconstruction unit 174.
The arithmetic unit 170 executes various data processes and programs. The control unit 171 controls the data collection unit 150, the pulse sequence control unit 160, and the like. The storage unit 172 stores various shooting protocols, various programs, and various data. The storage unit 172 stores the echo signal collected by the data collection unit 150. The image reconstruction unit 174 reconstructs a magnetic resonance image based on the echo signal for MRI image reconstruction.

<< First Embodiment >>
<Generating Image 1 to Reduce Artifacts>
FIG. 2 is a flowchart of image reconstruction according to the first embodiment. FIG. 3 shows a pulse sequence for obtaining the first echo signal EC1. FIG. 4 shows a pulse sequence for obtaining the second echo signal EC2.

  In step S11, based on the control of the pulse sequence control unit 160, the gradient coil drive unit 130 and the RF coil drive unit 140 execute the first pulse sequence PS1 shown in FIG. Then, the data collection unit 150 receives the first echo signal EC1. In the first pulse sequence PS1 shown in FIG. 3, the phase encoding interval is TM1. The pulse sequence in FIG. 3 will be described later.

In step S13, the storage unit 172 of the calculation unit 170 embeds the first echo signal EC1 received by the data collection unit 150 in k-space in the first phase encoding order.
In step S15, the image reconstruction unit 174 of the calculation unit 170 performs a Fourier transform on the first echo signal EC1 stored in the k-space in the X-axis direction and the Y-axis direction, thereby generating a first FOV (Field of View: imaging region). ) Image. The first FOV image 91 is stored in the storage unit 172.

  The first FOV image is an image 91 as depicted on the right side of step S15, for example. The first FOV image 91 includes an actual image RL at the center of the FOV (imaging area), and includes an artifact AF at the end in the vertical direction (phase encoding direction) of the FOV in FIG.

  In step S17, the pulse sequence control unit 160 executes the pulse sequence PS2 with the phase encode interval TM2. Then, the data collection unit 150 receives the second echo signal EC2. In the second pulse sequence PS2 shown in FIG. 4, the phase encode interval TM2 is a short interval unlike the phase encode interval TM1 in FIG. The pulse sequence in FIG. 4 will be described later.

In step S19, the storage unit 172 of the calculation unit 170 embeds the second echo signal EC2 received by the data collection unit 150 in k-space in the first phase encoding order.
In step S <b> 21, the image reconstruction unit 174 of the calculation unit 170 reconstructs the second FOV image 92 by performing a Fourier transform on the second echo signal EC <b> 1 stored in the k-space in the X axis direction and the Y axis direction. The second FOV image 92 is stored in the storage unit 172.

  The second FOV image is an image 92 as depicted on the right side of step S21, for example. The second FOV image 92 includes an actual image RL in the center of the FOV (imaging area), and includes an artifact AF at the end in the vertical direction (phase encoding direction) of the FOV in FIG. The second FOV image 92 is different from the first FOV image 91 in the vertical size of the FOV.

  In step S <b> 23, the image reconstruction unit 174 adds and averages the first FOV image and the second FOV image stored in the storage unit 172. Then, the weighted average image is displayed on the display unit 180. The averaged image is drawn on the right side of step S23. The actual image RL of the first FOV image 91 and the actual image RL of the second FOV image 92 overlap, and the artifact AF of the first FOV image 91 and the artifact AF of the second FOV image 92 are shifted.

  Since the real image RL is overlapped and averaged, the definition and contrast of the real image RL are maintained. On the other hand, since the artifact AF is shifted and averaged, the artifact AF becomes difficult to see. In the flowchart of FIG. 2, an example in which the first FOV image 91 and the second FOV image 92 are averaged is shown. However, in the first embodiment, three or more different FOVs (imaging regions) may be averaged. If many different FOVs are averaged, the artifact AF becomes less visible.

  Prior to this step S11, reference data for correction is acquired in a state where no phase encoding gradient magnetic field is applied. The correction reference data, the first echo signal EC1 and the second echo signal EC2 are each subjected to a one-dimensional Fourier transform in the reading direction, and the phase of the correction reference data is calculated from the first echo signal EC1 and the second echo signal EC2. To correct the first echo signal EC1 and the second echo signal EC2.

  Next, a pulse sequence for obtaining the first echo signal EC1 and the second echo signal EC2 will be described with reference to FIGS. The pulse sequence control unit 160 controls the gradient coil driving unit 130 and the RF coil driving unit 140 and applies them to the gradient coil unit 106 and the RF coil unit 108.

  FIG. 3 shows a pulse sequence called a diffusion weighted-echo planar imaging (DW-EPI) method. Both FIG. 3 and FIG. 4 show the high-frequency magnetic field pulse RF, the slice selection gradient magnetic field Gz, the phase encode gradient magnetic field Gx, the frequency encode (lead-out) gradient magnetic field Gy, and the echo signal SGN in order from the top, and the vertical axis represents their intensities. The horizontal axis indicates time. By repeating this pulse sequence once or a plurality of times, echo signals necessary for image reconstruction are collected in k-space.

  First, the RF coil driving unit 140 irradiates the subject with an RF pulse RF01 that excites the portion of the subject. The RF pulse RF01 is, for example, a 90 ° pulse. A gradient magnetic field pulse CG01 for selecting a slice is applied simultaneously with the RF pulse RF01, and a slice to be imaged is selected. Next, the gradient coil driver 130 applies gradient magnetic field pulses CG11 and CG21 for positioning to the phase encode gradient magnetic field Gx and the frequency encode gradient magnetic field Gy.

  After a predetermined time has elapsed, the RF coil driver 140 applies a 180 ° pulse RF02 to obtain a spin echo signal. Before and after the 180 ° pulse RF02, the gradient coil driver 130 applies a gradient magnetic field MPG for the diffusion weighted image. 3 and 4, the gradient magnetic field MPG is applied to the frequency encoding gradient magnetic field Gy. However, as indicated by a dotted line in FIGS. 3 and 4, in another imaging, the gradient magnetic field MPG is also applied to the slice selection gradient magnetic field Gz and the phase encoding gradient magnetic field Gx.

  Thereafter, as illustrated in FIGS. 3 and 4, the gradient coil driving unit 130 applies the phase encoding gradient magnetic field pulse CG12 and the frequency encoding gradient magnetic field pulses CG22 (CG22 +, CG22−) that are continuously inverted. . Since the first echo signal EC1 (EC11 to EC19) and the second echo signal EC2 (EC21 to EC29) are generated in time series within each cycle of the frequency encoding gradient magnetic field CG22 to be inverted, the data collection unit 150 A time-series first echo signal EC1 and second echo signal EC2 are received. The first echo signals EC11, EC13, EC15,... Are odd-numbered odd-numbered echoes, and the first echo signals EC12, EC14, EC16,. Similarly, the second echo signals EC21, EC23, EC25... Are odd-numbered odd echoes, and the second echo signals EC22, EC24, EC26... Are even-numbered even echoes.

  The phase encode gradient magnetic field pulse CG12 is the phase encode interval TM1 in FIG. 3, but is a phase encode interval TM2 different from the phase encode interval TM1 in FIG. When the phase encoding interval TM is different, the size of the FOV (imaging region) in the vertical direction (phase encoding direction) is different. Therefore, the image reconstruction unit 174 as shown in FIG. 2 can obtain the first FOV image 91 and the second FOV image 92.

<< Second Embodiment >>
<Generation of image 2 for reducing artifacts>
FIG. 5 is a flowchart of image reconstruction according to the second embodiment. The configuration of the MRI apparatus 10 is the same as that of the first embodiment. The pulse sequence for obtaining the echo signal EC may be the same as the pulse sequence shown in FIG. The second embodiment is different from the first embodiment in the collection method in which the image reconstruction unit 174 collects the received echo signal EC in k-space.

  In step S51, based on the control of the pulse sequence control unit 160, the gradient coil driving unit 130 and the RF coil driving unit 140 execute the first pulse sequence PS1 shown in FIG. Then, the data collection unit 150 receives the first echo signal EC1 (EC11 to EC19).

  In step S53, the storage unit 172 of the calculation unit 170 embeds the first echo signal EC1 received by the data collection unit 150 in k-space in the first phase encoding order. In k-space, the vertical axis indicates the phase encoding direction, and the horizontal axis indicates the frequency encoding direction. Thick solid arrows drawn in k-space indicate odd echoes (EC11, EC13...), and thick dotted arrows indicate even echoes (EC12, EC14...). A thin curved arrow indicates a trajectory for collecting echo signals.

  Here, the first phase encoding order refers to the echo signals EC11, EC12, EC13, EC14, EC15, EC16 (see FIG. 3) obtained by the frequency encoding gradient magnetic field pulse CG22 that is continuously inverted, as shown in FIG. In the k-space drawn on the right side of S53, the order is 01, 02, 03, 04, 05, 06. That is, the echo signal EC11 is collected at the bottom of the k-space, the echo signal EC12 is collected from the bottom of the k-space, and the echo signal EC11 is collected at the third of the k-space. For this reason, in the k-space, odd-numbered echoes and even-numbered echoes are alternately arranged one by one.

  In the second embodiment, the echo signal EC11 is set at the lowest side of the k-space. However, the echo signal EC11 may be placed on the uppermost side of the k-space, and the echo signal EC12 may be placed second from the top of the k-space.

  In step S55, the image reconstruction unit 174 performs Fourier transform on the first echo signal EC1 stored in k-space in the X-axis direction and the Y-axis direction to reconstruct the first FOV image. The first FOV image 91 is stored in the storage unit 172.

  The first FOV image is an image 91 as depicted in FIG. The first FOV image 91 forms a real image RL at the center of the FOV (imaging area), and forms an artifact AF at the end of the FOV in the vertical direction (phase encoding direction), that is, at a position 1/2 of the FOV. .

  In step S57, based on the control of the pulse sequence control unit 160, the gradient coil driving unit 130 and the RF coil driving unit 140 execute the first pulse sequence PS1 shown in FIG. Then, the data collection unit 150 receives the first echo signal EC1 (EC11 to EC19).

  In step S59, the storage unit 172 of the calculation unit 170 embeds the first echo signal EC1 received by the data collection unit 150 in k-space in the second phase encoding order. Here, the second phase encoding order refers to the echo signals EC11, EC12, EC13, EC14, EC15, EC16 (see FIG. 3) obtained by the frequency encoding gradient magnetic field pulse CG22 that is continuously inverted, as shown in FIG. In the k-space drawn on the right side of S59, the order is 01, 02, 03, 04, 05, 06. That is, the echo signal EC11 is the lowest side of the k-space, the echo signal EC12 is the third from the bottom of the k-space, the echo signal EC13 is the second from the bottom of the k-space, and the echo signal EC14 is the k-space. The collection order is fourth from the bottom of the space. In the k-space, odd-numbered echoes are arranged in two consecutive rows, and even-numbered echoes are arranged in two consecutive rows. This combination of four rows is repeated.

  In step S61, the image reconstruction unit 174 reconstructs the first FOV image 93 by performing Fourier transform on the first echo signal EC1 stored in k-space in the X-axis direction and the Y-axis direction. The first FOV image 93 is stored in the storage unit 172.

  The first FOV image is an image 93 as depicted in FIG. The first FOV image 93 forms an actual image RL in the center of the FOV (imaging area), and the artifact AF is formed at 1/4 position and 3/4 position obtained by dividing the vertical direction (phase encoding direction) of the FOV into four equal parts. Is forming.

  In step S63, the gradient coil drive unit 130 and the RF coil drive unit 140 execute the first pulse sequence PS1 shown in FIG. Then, the data collection unit 150 receives the first echo signal EC1 (EC11 to EC19).

  In step S65, the storage unit 172 of the calculation unit 170 embeds the first echo signal EC1 received by the data collection unit 150 in k-space in the order of the third phase encoding. Here, the third phase encoding order means the echo signals EC11, EC12, EC13, EC14, EC15, EC16 (see FIG. 3) obtained by the frequency encoding gradient magnetic field pulse CG22 that is continuously inverted, as shown in FIG. In the k-space drawn on the right side of S65, the order is 01, 02, 03, 04, 05, 06. That is, the echo signal EC11 is at the bottom of the k-space, the echo signal EC12 is the fourth from the bottom of the k-space, the echo signal EC13 is the second from the bottom of the k-space, and the echo signal EC14 is the k-space. The collection order is the fifth from the bottom of the space. For this reason, in the k-space, odd-numbered echoes are arranged in three consecutive rows, and even-numbered echoes are arranged in three consecutive rows. These six rows of combinations are repeated.

  In step S67, the image reconstruction unit 174 reconstructs the first FOV image 94 by performing Fourier transform on the first echo signal EC1 stored in k-space in the X-axis direction and the Y-axis direction. The first FOV image 94 is stored in the storage unit 172.

  The first FOV image is an image 94 as depicted in FIG. The first FOV image 94 forms an actual image RL in the center of the FOV (imaging area), and the artifact AF is provided at the 2/6 position and the 4/6 position obtained by dividing the FOV vertical direction (phase encoding direction) into 6 equal parts. Is forming.

  In step S69, the image reconstruction unit 174 averages the first FOV image 91 obtained in step S55, the first FOV image 93 obtained in step S61, and the first FOV image 94 obtained in step S67. Then, the weighted average image is displayed on the display unit 180. The averaged image is drawn on the right side of FIG. The real images RL of the three first FOV images 91, 93, and 94 overlap each other, and are shifted from the artifact AF of the first FOV images 91, 93, and 94.

  Since the actual images RL are overlapped and averaged, the sharpness and contrast of the actual images RL are maintained. On the other hand, since the artifact AF is shifted and averaged, the artifact AF becomes difficult to see. In the flowchart of FIG. 52, an example in which three first FOV images are added and averaged is shown. However, in the second embodiment, two or four or more different k-space arrangement images may be averaged.

<< Third Embodiment >>
<Image Generation 3 to Reduce Artifact>
The third embodiment is a combination of the first embodiment and the second embodiment. Specifically, step S57 and step S63 of the second embodiment described in FIG. 5 may be replaced with step S17 of the first embodiment described in FIG. That is, the pulse sequence of the phase encode interval TM2 is executed in step S57 of FIG. 5, and the pulse sequence of the phase encode interval TM3 different from the phase encode intervals TM1 and TM2 is executed in step S63.

  Then, the image reconstruction unit 174 can obtain the second FOV image 95 and the third FOV image 96 depicted in FIG. The second FOV image 95 is smaller than the first FOV image 91 in the vertical direction of the FOV. Artifact AF is formed at a position of 1/4 and a position of 3/4 obtained by dividing the vertical direction (phase encoding direction) of the FOV into four equal parts. The third FOV image 96 is larger in the vertical size of the FOV than the first FOV image 91. The artifact AF is formed at a position of 2/6 and a position of 4/6, which are obtained by dividing the vertical direction (phase encoding direction) of the FOV into four equal parts.

  The image reconstruction unit 174 averages the first FOV image 91, the second FOV image 95, and the third FOV image 96. The averaged image is depicted on the right side of FIG. The actual images RL of the first FOV image 91, the second FOV image 95, and the third FOV image 96 are overlapped with each other and are shifted from the artifact AF. Therefore, the artifact AF becomes difficult to see.

  The method of collecting the magnitude of the FOV and the echo signal into k-space can be changed as appropriate. As described above, if the artifact AFs are formed so as to be shifted from each other, the addition-averaged artifact AF becomes difficult to see. Therefore, the image reconstruction unit 174 may set the method of collecting the magnitude of the FOV and the echo signal into the k-space so that the artifact AF is formed so as to be shifted from each other.

  As described above, the optimal embodiment of the present invention has been described in detail. However, as will be apparent to those skilled in the art, the present invention can be implemented with various modifications and variations within the technical scope thereof. For example, the first to third embodiments have been described with the diffusion weighted-echo planar imaging (DW-EPI) method, but may be used for echo planar imaging (EPI).

DESCRIPTION OF SYMBOLS 10 ... MRI apparatus 91, 92, 93, 95, 96 ... FOV image 100 ... Magnet system (102 ... Main magnetic field coil part, 106 ... Gradient coil part, 108 ... RF coil part)
DESCRIPTION OF SYMBOLS 110 ... Bed 130 ... Gradient coil drive part 140 ... RF coil drive part 150 ... Data collection part 160 ... Sequence control part 170 ... Calculation part 171 ... Control part 172 ... Memory | storage part 174 ... Image reconstruction part 180 ... Display part 190 ... Operation Part AF ... Artifact EC1 (EC11 to EC19), EC2 (EC21 to EC29) ... Echo signal RL ... Real image

Claims (6)

A high-frequency pulse irradiation unit that irradiates a subject with a high-frequency pulse;
A gradient magnetic field application unit for applying gradient magnetic field pulses in the frequency direction and the phase encoding direction;
A receiver for receiving an echo signal generated from the subject;
An image reconstruction unit for reconstructing an image based on the echo signal;
A display unit for displaying the image,
After one high-frequency pulse irradiation by the high-frequency pulse irradiation unit, the gradient magnetic field application unit reverses the gradient magnetic field pulse in the frequency direction positive and negative, the reception unit obtains a plurality of echo signals,
The image reconstruction unit is an MRI apparatus that reconstructs a plurality of images including artifacts appearing at different positions based on the plurality of echo signals and adds and averages the plurality of images. The gradient magnetic field application unit changes the phase of the gradient magnetic field pulse in the phase encoding direction so as to change the imaging region (FOV),
The MRI apparatus according to claim 1, wherein the image reconstruction unit reconstructs an image having a different imaging area, and averages a plurality of images having different imaging areas.   3. The MRI apparatus according to claim 1, wherein the image reconstruction unit changes the arrangement when k-space is formed from the echo signal received by the reception unit, and causes the artifact to appear at different positions. 4. .   When the k-space is formed, the odd-numbered echoes and even-numbered echoes obtained by reversing the gradient magnetic field pulse are alternately arranged, the odd-numbered echoes are continuous in two or more rows, and the even-numbered echoes are 2 The MRI apparatus according to claim 3, wherein the MRI apparatus includes a method of arranging the columns continuously. The high-frequency pulse irradiation unit applies a 180 ° pulse for obtaining a spin echo signal from the subject,
The MRI apparatus according to any one of claims 1 to 4, wherein the gradient magnetic field application unit applies a gradient magnetic field pulse for a diffusion weighted image before and after the 180 ° pulse. In a state where the gradient magnetic field application unit does not apply the gradient magnetic field pulse, reference data is acquired,
The MRI apparatus according to any one of claims 1 to 5, wherein the plurality of echo signals are corrected with the reference data.