JP6234214B2 - Magnetic resonance imaging system - Google Patents

Description

  The present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus) that includes means for suppressing artifacts caused by static magnetic field inhomogeneity and gradient magnetic field nonlinearity.

  In order to emphasize the open feeling of the subject in the horizontal magnetic field MRI, a short gantry type MRI in which the Z-axis length of the gantry is shortened has become mainstream. However, the short gantry type MRI has a problem that artifacts due to magnetic field distortion are likely to occur due to a narrow static magnetic field uniform space and a gradient magnetic field linear region. In particular, in Fast Spin Echo imaging of SAG and COR sections with the Z axis set in the phase encoding direction, bright spot artifacts may be folded back in the region of interest in the imaging FOV, which may hinder diagnosis.

  In order to avoid this artifact, several countermeasures have been examined from the viewpoint of hardware, imaging sequence, reconstruction processing, and imaging method.

  From a hardware standpoint, there is a method of limiting the reception of NMR signals from the magnetic field distortion region by optimizing the design of the phased array coil itself and optimizing the selection of receiving elements. However, this also leads to a signal reduction in the region of interest, and there is a limit to optimization.

  From the viewpoint of the imaging sequence, there is a method for suppressing the generation of the Spin Echo signal by preventing the two excitation cross sections of the excitation RF pulse and the refocusing RF pulse from overlapping in the magnetic field distortion region (Patent Document 1). Non-Patent Document 1). However, due to the difference in excitation band between the excitation RF pulse and the refocus RF pulse, the effect cannot be expected for the FID (Free Induction Decay) signal generated by the influence of a single refocus RF pulse. On the contrary, it is conceivable that artifacts due to the FID signal are enhanced.

  From the viewpoint of reconstruction processing, there are methods for suppressing artifacts by using sensitivity distribution data of phased array coils acquired in advance measurement (Patent Documents 2 and 3, Non-Patent Documents 2 and 3). However, when the artifact strength is highly dependent on the image type and measurement conditions, the artifact cannot be completely removed. In addition, when using the parallel imaging technique, there is a limit on the development accuracy to develop fine folding in high-resolution imaging such as joint imaging, which is not a realistic technique.

  From the viewpoint of the imaging method, a method of shielding the RF irradiation by covering the magnetic field distortion region with an RF blanket may be considered, but safety problems such as SAR (Specific Absorption Rate) remain.

US Patent Application Publication No. 2012/0025826 US Pat. No. 7,250,762 US Pat. No. 6,134,465

Novena Rangwala et al. “Reduction of Fast Spin Echo Cusp Artifact Using a Slice-Tilting Gradient”, Magn Reson Med 2010; 64: 220-228 David Atkinson et al. “Coil-Based Artifact Reduction” Magn Reson Med 2004; 52: 825-830 Larkman et al. “Elimination of Magnetic Field Foldover Artifacts in MR Images”, J Magn Reson Imaging 2000; 12: 795-797.

  When the Fast Spin Echo sequence is used, aliasing artifacts may occur due to the influence of the refocus RF pulse in the magnetic field distortion region. If an artifact that is superimposed on the region of interest and interferes with the diagnosis can be moved to the extended FOV, the artifact can be suppressed in appearance.

  In the above-described conventional technology, the problem of safety such as SAR (Specific Absorption Rate) cannot be solved, and the signal degradation of the region of interest, the increase of artifacts due to the FID signal, the high dependency of the image type and measurement conditions, and the like.

  Accordingly, an object of the present invention is to provide a magnetic resonance that does not cause signal degradation in a region of interest, suppresses an increase in artifacts due to an FID signal, has less dependency on image types and measurement conditions, and can perform imaging without causing problems such as SAR. An imaging device is provided.

  In order to solve the above problems, main features of the magnetic resonance imaging apparatus according to the present invention are as follows.

  Based on the echo signal detected by the echo signal detecting means, the detecting means for detecting the echo signal from the subject according to the data acquisition sequence, the static magnetic field generating means, the gradient magnetic field generating means, the high frequency magnetic field generating means, Signal processing means for reconstructing an image of the image, wherein the data acquisition sequence includes an excitation RF pulse and a refocusing RF pulse, and the signal processing means is caused by a pre-measured static magnetic field generation means and a gradient magnetic field generation means. Based on the image distortion position caused by the magnetic field distortion and the imaging conditions including the imaging FOV, a determination reference value for predicting a position generated as a folding artifact in the imaging FOV is calculated, and based on the determination reference value, the refocus RF pulse is calculated. By changing the irradiation phase according to the pulse condition of the data acquisition sequence, artifacts can be detected by the imaging F Wherein the moving outside the range of V.

  According to the present invention, a magnetic resonance imaging apparatus capable of performing imaging without causing a problem such as SAR without causing a signal decrease in a region of interest, suppressing an increase in artifacts due to an FID signal, having less dependency on image types and measurement conditions, and the like. Can provide.

1 is a block diagram showing an overall outline of an MRI apparatus according to the present invention. Fast Spin Echo sequence diagram. (A) is a view showing a shooting FOV and an artifact generation position, (b) is a view showing a shooting FOV, an extended FOV, an artifact generation position, and a folding position, and (c) is a shooting FOV, an extended FOV, and an artifact generation. The figure which shows a position, a return position, and a return movement position. The figure which shows the phase information on k space for moving the folding of a FID signal only by FOV / 2. The figure which shows the echo arrangement | sequence and phase inversion (shading) at the time of Sequential measurement. The figure which shows the echo arrangement | sequence and phase inversion (shading) at the time of Centric measurement. The figure which shows the phase information on k space for making the FID signal at the time of even number addition disappear. The flowchart of RF irradiation phase calculation for artifact avoidance. (a) is a figure which shows the irradiation phase at the time of Sequential measurement in the case of odd Shot number and (b) in the case of even Shot number. (a) is a figure which shows the irradiation phase at the time of Centric measurement when Shot number / 2 is an odd number, and (b) is Shot number / 2.

<Block diagram of MRI system>
Hereinafter, preferred embodiments of the MRI apparatus of the present invention will be described in detail with reference to the accompanying drawings. In all the drawings for explaining the embodiments of the invention, those having the same function are given the same reference numerals, and their repeated explanation is omitted.

  First, an MRI apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the overall configuration of an embodiment of an MRI apparatus according to the present invention.

  This MRI apparatus uses a NMR phenomenon to obtain a tomographic image of a subject 101. As shown in FIG. 1, a static magnetic field generating magnet 102, a gradient magnetic field coil 103, a gradient magnetic field power source 109, and an RF transmission coil 104 and RF transmitter 110, RF receiver coil 105 and signal processor 107, measurement control unit 111, overall control unit 112, display / operation unit 118, and top plate on which the subject 101 is mounted generates a static magnetic field. And a bed 106 to be taken in and out of the magnet 102.

  The static magnetic field generating magnet 102 generates a uniform static magnetic field in the direction perpendicular to the body axis of the subject 101 in the vertical magnetic field method and in the body axis direction in the horizontal magnetic field method. A permanent magnet type, normal conducting type or superconducting type static magnetic field generating source is arranged around the.

  The gradient magnetic field coil 103 is a coil wound in the three-axis directions of X, Y, and Z, which is a real space coordinate system (static coordinate system) of the MRI apparatus, and each gradient magnetic field coil is a gradient magnetic field that drives the coil. A current is supplied to the power source 109. Specifically, the gradient magnetic field power supply 109 of each gradient coil is driven according to a command from the measurement control unit 111 described later, and supplies a current to each gradient coil. Thereby, gradient magnetic fields Gx, Gy, and Gz are generated in the three-axis directions of X, Y, and Z. The gradient magnetic field coil 103 and the gradient magnetic field power supply 109 are included in the gradient magnetic field generator.

  When imaging a two-dimensional slice plane, a slice gradient magnetic field pulse (Gs) is applied in a direction orthogonal to the slice plane (imaging cross section) to set a slice plane for the subject 101, orthogonal to the slice plane and orthogonal to each other. The phase encoding gradient magnetic field pulse (Gp) and the frequency encoding (reading) gradient magnetic field pulse (Gf) are applied in the remaining two directions, and position information in each direction is encoded in the nuclear magnetic resonance signal (echo signal). The

  The RF transmission coil 104 is a coil that irradiates the subject 101 with an RF pulse, and is connected to the RF transmission unit 110 and supplied with a high-frequency pulse current. As a result, an NMR phenomenon is induced in the spins of atoms constituting the living tissue of the subject 101. Specifically, the RF transmission unit 110 is driven in accordance with a command from the measurement control unit 111 (to be described later), amplitude-modulates a high-frequency pulse, and amplifies the RF transmission coil 104 disposed in the vicinity of the subject 101 after amplification. By supplying, the subject 101 is irradiated with the RF pulse. The RF transmitter coil 104 and the RF transmitter 110 are included in the RF pulse generator.

  The RF receiving coil 105 is a coil that receives an echo signal emitted by the NMR phenomenon of the spin constituting the living tissue of the subject 101. The received echo signal is connected to the signal processing unit 107 and is received by the signal processing unit 107. Sent.

  The signal processing unit 107 performs detection processing of the echo signal received by the RF receiving coil 105. Specifically, in accordance with a command from the measurement control unit 111 described later, the signal processing unit 107 amplifies the received echo signal and divides it into two orthogonal signals by quadrature detection, For example, 128, 256, 512, etc.) are sampled, and each sampling signal is A / D converted into a digital quantity. Therefore, the echo signal is obtained as time-series digital data (hereinafter referred to as echo data) composed of a predetermined number of sampling data. Then, the signal processing unit 107 performs various processes on the echo data, and sends the processed echo data to the measurement control unit 111.

  The measurement control unit 111 mainly transmits various commands for collecting echo data necessary for reconstruction of the tomographic image of the subject 101 to the gradient magnetic field power source 109, the RF transmission unit 110, and the signal processing unit 107. And a control unit for controlling them. Specifically, the measurement control unit 111 operates under the control of the overall control unit 112 described later, and the gradient magnetic field power source 109, the RF transmission unit 110, and the signal processing unit 107 are controlled based on control data of a predetermined pulse sequence. The control 101 repeatedly executes the irradiation of the RF pulse and the application of the gradient magnetic field pulse to the subject 101 and the detection of the echo signal from the subject 101 to reconstruct the image of the imaging region of the subject 101. Control the collection of required echo data. In the repetition, the application amount of the phase encoding gradient magnetic field is changed in the case of two-dimensional imaging, and the application amount of the slice encoding gradient magnetic field is further changed in the case of three-dimensional imaging. Values such as 128, 256, and 512 are normally selected as the number of phase encodings, and values such as 16, 32, and 64 are normally selected as the number of slice encodings. With these controls, echo data from the signal processing unit 107 is output to the overall control unit 112.

  The overall control unit 112 controls the measurement control unit 111 and controls various data processing and display and storage of processing results, and includes an arithmetic processing unit (CPU) 114, a memory 113, and a magnetic disk. And the like, and a network IF 116 that interfaces with an external network. Further, an external storage unit 117 such as an optical disk may be connected to the overall control unit 112.

  Specifically, when the measurement control unit 111 collects echo data by executing an imaging sequence and the echo data is input from the measurement control unit 111, the arithmetic processing unit 114 converts the encoded information applied to the echo data. Based on this, it is stored in an area corresponding to the k space in the memory 113. Hereinafter, the statement that the echo data is arranged in the k space means that the echo data is stored in an area corresponding to the k space in the memory 113. A group of echo data stored in an area corresponding to the k space in the memory 113 is also referred to as k space data.

  The arithmetic processing unit 114 performs processing such as signal processing and image reconstruction by Fourier transform on the k-space data, and displays the resulting image of the subject 101 on the display / operation unit 118 described later. The data is recorded in the internal storage unit 115 and the external storage unit 117, or transferred to an external device via the network IF 116.

  The display / operation unit 118 includes a display unit for displaying the reconstructed image of the subject 101, a trackball or a mouse and a keyboard for inputting various control information of the MRI apparatus and control information for processing performed by the overall control unit 112. Etc., and an operation unit. The operation unit is disposed in the vicinity of the display unit, and the operator controls various processes of the MRI apparatus interactively through the operation unit while looking at the display unit.

  At present, the radionuclide to be imaged by the MRI apparatus is a hydrogen nucleus (proton) which is a main constituent material of the subject as widely used clinically. Information on the spatial distribution of the proton density and the spatial distribution of the relaxation time of the excited state is imaged, thereby imaging the form or function of the human head, abdomen, limbs, etc. two-dimensionally or three-dimensionally.

FIG. 2 shows a pulse sequence of an FSE (Fast Spin Echo) method for acquiring a plurality of echo signals as a subject of the present invention.
In this figure, RF, Gs, Gp, Gr, and Signal respectively apply RF pulse, slice selective gradient magnetic field pulse, phase encode gradient magnetic field pulse, frequency encode gradient magnetic field pulse, and echo signal acquisition. Represents the axis shown. In addition, here, as an example, an FSE sequence for acquiring the echo signals 322 for one 90 ° excitation RF pulse 308 is shown.

  In the FSE sequence, first, a slice selective gradient magnetic field pulse 309 is applied together with a 90 ° excitation RF pulse 308 that applies a high-frequency magnetic field to spins in the imaging plane. Thereafter, a 180 ° inversion RF pulse 314 for reversing the spin in the slice plane is repeatedly applied. As described above, in order to acquire the echo signals 322 for one 90 ° excitation RF pulse 308, the 180 ° inversion RF pulse 314 is applied a plurality of times. Therefore, by reversing the irradiation phase of the refocus RF pulse for each shot, phase information inverted by 180 degrees can be given to the FID signal generated from each refocus RF pulse.

  The FSE sequence is a sequence in which a plurality of echo data is measured after excitation by one RF pulse and the echo data is arranged in one k space. The measured echo data is arranged and filled in the k space in the same order as the measured echo order for each echo number.

<Identify the position where artifacts are generated due to magnetic field distortion and the folding position based on the FOV>
The short gantry type MRI has a problem that artifacts due to magnetic field distortion are likely to occur due to a narrow static magnetic field uniform space and a gradient magnetic field linear region.

  Assuming that there is a region where image distortion due to magnetic field distortion occurs at a position 250 mm from the center of the FOV in the Z-axis direction (the body axis direction of the subject), it is 150 for Spine imaging using an FOV size of about 400 mm. Since the magnetic field distortion region can be sufficiently accommodated in the expanded FOV with the aliasing removal function that internally expands the FOV by about%, the artefact that becomes a problem does not become a problem.

  However, in joint imaging such as Knee and Ankle, the FOV size is often 200 mm or less, and if the expanded FOV is expanded to include the magnetic field distortion region, it is necessary to greatly expand it to 300 to 400 times. It's not a realistic way.

  FIG. 3A shows an example in which an artifact that becomes a bright spot due to an increase in brightness due to image distortion occurs at a position of Body = Z = 250 mm in Knee SAG imaging with an FOV of 150 mm.

  Assuming the use of alias removal that expands to 200% internally, the FOV is 300 mm and the image distortion is at the position of Z = 250 mm, so this bright spot artifact is shown in FIG. Thus, folding occurs at a position of −50 mm from the center of the FOV.

Since it is necessary to determine whether or not the return position is displayed in the display FOV, the determination method will be described next.
The artifact generation position [mm] in the shooting FOV is Z _alias , the internally expanded FOV size [mm] is FOV, Z _alias is divided by FOV, the remainder after the decimal point is R _alias , and the Z coordinate of the FOV center Let [mm] be Z _FOV , (Z _FOV + FOV / 2) divided by FOV, the remainder after the decimal point is R _FOV , and the judgment value d is defined as (Formula 1).
d = R _alias -R _FOV (Equation 1)
Although the expansion rate is fixed to 200%, it can be determined from the following determination formula whether the occurrence position of the artifact in photographing is in the expanded FOV or the display FOV.
Within the extended FOV: 0 <d <0.25, or 0.75 <d <1.0 (Equation 2)
In the display FOV: 0.25 ≤ d ≤ 0.75 ... (Formula 3)

In the example of FIG. 3A, since Z _alias = 250, Z _FOV = 0, and FOV = 300, R _alias = 0.833, R _FOV = 0.5, and d = 0.333, so that this occurs in the display FOV. become. In the case of shooting with the _FOV off-centered at a position of 75 mm in the Z direction, Z _FOV = 75, R _alias = 0.833, R _FOV = 0.75, d = 0.083, so artifacts will occur in the expanded FOV Become.

When artifacts occur in the display FOV, artifacts may be superimposed on the region of interest and may interfere with diagnosis. To avoid this situation, the artifact position is moved by FOV / 2 and expanded. FIG. 3C shows an explanatory diagram of the state in the FOV.
From this figure, it can be seen that the artifact appearing at the turn-back position in FIG. 3 (b) moves upward as shown by the arrow in FIG. 3 (c) and comes into the expanded FOV.

  The position of the magnetic field distortion (image distortion) is pre-measured with a sufficiently large phantom at the time of installation of the apparatus and a sufficiently large FOV size of 500 mm that does not cause aliasing, and the coordinate information of the magnetic field distortion is stored as system information. deep. It is desirable to use the Fast Spin Echo sequence for the pre-measurement, but this is not the case.

<Movement of folding artifact>
In order to move the position of the folding artifact by FID by FOV / 2, it is necessary to give an inverted phase of 180 degrees for each step of ky (phase encoding direction) in the k space (FIG. 4). FIG. 4 shows the phase of the FID signal in the k space, and shows a state in which the phase is alternately inverted for each step.

  The k-space filling method is classified into two methods: Sequential measurement that fills in order from the top (or from the bottom), and filling from the center to the top, then filling from the center to the bottom (or from the center There is Centric measurement that fills the lower side and then fills the upper side from the center. In each filling method, it is necessary to optimize the irradiation phase of the refocus RF pulse according to the number of segment divisions (Shot number).

  FIG. 5 shows an echo arrangement in the k space at the time of sequential measurement. This figure (a) shows the case where the number of Shots is odd (eg, Shot number 3, Echo number 4), and (b) shows the case where Shot number is even (eg, Shot number 2, Echo number 6). Show. In this figure, the case where the echo arrangement is filled in order from the lower side is illustrated. FIG. 9 shows details of the RF irradiation phase information for giving an inverted phase to the FID signal for each ky 1 step in this echo arrangement.

  In the table shown in FIG. 9, the irradiation phase of the excitation RF pulse indicates the condition of the pulse 308 shown in FIG. 2, and the irradiation phase of the refocus RF pulse shows the condition of the pulse 314 shown in FIG. Further, x and y in the table indicate pulse application in the x direction and pulse application in the y direction, respectively. The same applies to the table shown in FIG.

  When the total number of shots is an even number, the refocus RF pulse of the even-numbered shot always inverts the irradiation phase. On the other hand, when the total number of shots is an odd number, the irradiation phase of the refocus RF pulse is inverted for each pulse, and the even-numbered shot is set to be inverted 180 degrees with respect to the odd-numbered shot.

  Next, FIG. 6 shows an echo arrangement in the k space at the time of Centric measurement. This figure (a) shows the case where Shot number / 2 is an odd number (eg, Shot number 6, Echo number 2), and (b) shows Shot number / 2 is an even number (eg Shot number 4, Echo number 3). ). This figure shows an arrangement in which the k space is halved, the upper half is filled in the first half of the measurement, and then the lower half is filled. In this echo arrangement, RF irradiation phase information for inverting the phase of the FID signal for each ky 1 step is shown in FIG.

  When the quotient obtained by dividing the total number of shots by 2 is an even number, the first half Shot group that fills the upper side of the k space inverts the irradiation phase of the refocus RF pulse in the even-numbered Shot and fills the lower half of the second half In the Shot group, the irradiation phase of the refocus RF pulse in the odd-numbered Shot is reversed.

  On the other hand, when the quotient obtained by dividing the total number of shots by 2 is an odd number, the first half shot group filling the upper side of the k space inverts the irradiation phase of the refocus RF pulse for each pulse, and the odd number The irradiation phase is reversed between Shot and even-numbered Shot. Furthermore, in the Shot group filling the lower half of the second half, the irradiation phase of the first Shot group is completely reversed.

  Thus, by changing the irradiation phase of the refocus RF pulse, the position of the artifact due to the FID signal can be moved by FOV / 2.

<Signal suppression of artifacts by even number of additions>
In addition, when performing addition imaging for an even number of times, the artifact itself is obtained by reversing the RF irradiation phase by 180 degrees with respect to the odd-numbered RF irradiation phase in the imaging of the even-numbered addition, common to all the echo arrays. Can be eliminated. As shown in FIG. 7, in the same ky line in the k space, the phase of the FID is inverted when the odd-numbered addition and even-numbered addition are photographed. You can make it.

  According to the present embodiment, it is possible to determine the position of a bright spot that becomes an artifact caused by a magnetic field distortion that cannot be determined by the prior art. In particular, in Fast Spin Echo that generates multi-echo, the brightness of the bright spot is higher, so that an accurate image can be acquired.

  FIG. 8 shows a flowchart of RF irradiation phase calculation for avoiding artifacts. This flowchart shows the case of processing for automatically determining the occurrence position of an artifact.

First, the determination value d is calculated from the position of the magnetic field distortion, the position of the FOV, and the size of the FOV using Equation 1 (801).
Here, the position of the magnetic field distortion is measured in advance, and the measurement result is stored in the memory 113, for example. The position of the FOV and the size of the FOV are set by the user as needed.

  Next, it is determined whether the determination value d is in a range of 0 <d <0.25 or 0.75 <d <1.0 (802). If it is within this range, the process proceeds to step 803, and if it is not within the range, the RF irradiation phase calculation ends.

Next, it is determined whether or not it is sequential measurement (803). If YES, it is determined whether or not the number of shots is an odd number (804), FIG. 9 (a) RF irradiation phase (805a), or FIG. 9 (b). An RF irradiation phase (805b) setting process is performed.
If NO, it is determined whether or not the Shot number / 2 is an odd number (808), and the setting process of FIG. 10 (a) RF irradiation phase (805c) or FIG. 10 (b) RF irradiation phase 805d) is performed.

Next, in any one of steps 805a to 805d, it is determined whether or not the addition is an even number (806). If YES, the RF irradiation phase of the refocus RF is fully inverted (807). If NO, RF is determined. The irradiation phase calculation ends.
The above automatic determination process is executed by the arithmetic processing unit (CPU) 114.

  In the above RF irradiation phase calculation, the case where the occurrence position of the artifact is processed by automatic determination is shown, but it is also possible to make a user determination. For example, when an artifact overlaps the region of interest and hinders diagnosis, it is possible to select a parameter that activates the artifact movement process on the imaging conditions.

  That is, the flowchart of the present RF irradiation phase calculation shows the procedure for automatically setting the determination based on the determination value d in step 802, but it can also be manually set. In that case, a step (not displayed) of displaying the determination value d after the processing of step 802 is provided in the flowchart, and the determination value is displayed on a display unit (for example, 118 in FIG. 1). The user operates a setting button provided on the input unit to set the flow of the flowchart to YES flow or NO flow while referring to the determination value displayed on the display unit and the region of interest on the captured image. It becomes possible to decide.

  According to this embodiment, the occurrence position of the artifact can be automatically determined, and an image can be acquired efficiently. Further, by using the manual mode, it is possible to perform processing according to the situation at the site while determining whether the artifact is in the region of interest.

101: Subject, 102: Static magnetic field generating magnet, 103: Gradient magnetic field coil, 104: RF transmission coil, 105: RF reception coil, 106: Bed, 107: Signal processing unit, 109: Gradient magnetic field power supply, 110: RF transmission 111: Measurement control unit 112: Overall control unit 113: Memory 114: Arithmetic processing unit (CPU) 115: Internal storage unit 116: Network IF 117: External storage unit 118: Display / operation unit .

Claims (4)

Based on the echo signal detected by the echo signal detection means, the static magnetic field generation means, the gradient magnetic field generation means, the high frequency magnetic field generation means, the detection means for detecting an echo signal from the subject according to the data acquisition sequence, Signal processing means for reconstructing an image of the subject,
The data acquisition sequence includes an excitation RF pulse and a refocusing RF pulse;
The signal processing means is within the range of the imaging FOV based on the pre-measured image distortion position caused by the magnetic field distortion caused by the static magnetic field generation means and the gradient magnetic field generation means and the imaging conditions including the imaging FOV. Calculate a criterion value that predicts the position that will occur as a folding artifact,
Based on the determination reference value, the position of the artifact is moved out of the range of the imaging FOV by changing an RF irradiation phase of the refocus RF pulse according to a pulse condition included in the data acquisition sequence. Magnetic resonance imaging apparatus.   2. The magnetic resonance imaging apparatus according to claim 1, wherein the movement of the imaging FOV outside the range is performed by moving the FOV size by a half by adjusting the RF irradiation phase. When the position of the folding artifact appears on the region of interest of the image, the imaging of the subject is performed an even number of times,
For all the echo arrangements in the k-space obtained by acquiring the echo signal, the RF irradiation phase is reversed by 180 degrees with respect to the RF irradiation phase of the odd addition and the RF irradiation phase is inverted by the even addition imaging. The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance imaging apparatus is eliminated. A display unit for displaying an image reconstructed by the signal processing means;
When the user visually recognizes the folded artifact on the region of interest of the image, the position of the artifact is moved outside the region of interest by changing the RF irradiation phase by parameter selection from user parameters on the display unit. The magnetic resonance imaging apparatus according to claim 1.

Images