JP2012095891A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly correct k-space data distortion due to the application of MPG pulses even if remanent magnetization remains in an MRI apparatus.SOLUTION: A degauss sequence for degaussing remanent magnetization remaining in a stationary structure is performed between first and second preliminary measurements for measuring correction echo data while varying the phase encoding direction of a correction echo data measuring unit.

Description

  The present invention measures nuclear magnetic resonance (hereinafter referred to as `` NMR '') signals from hydrogen, phosphorus, etc. in a subject and images nuclear density distribution, relaxation time distribution, etc. In particular, the present invention relates to correcting k-space data distortion in diffusion weighted images.

  The MRI device measures NMR signals generated by the spins of the subject, especially the tissues of the human body, and visualizes the form and function of the head, abdomen, limbs, etc. in two or three dimensions Device. In imaging, the NMR signal is given different phase encoding depending on the gradient magnetic field, frequency-encoded, and measured as time series data. The measured NMR signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.

  A sequence that acquires a diffusion-weighted image (hereinafter referred to as a “DWI pulse sequence”) adds a pair of powerful gradient magnetic field pulses (hereinafter referred to as “MPG pulses”) before and after the π (180 degree) pulse, thereby spreading It is possible to acquire molecules with low motion with high contrast. On the other hand, k-space data distortion is likely to occur due to eddy currents caused by strong gradient magnetic field pulses.

  Therefore, the technique disclosed in Patent Document 1 sets the k-space data distortion amount due to the eddy current caused by the MPG pulse, sets the readout direction and the phase encoding direction to the first set, and sets the first reference data as Then, the readout direction and the phase encoding direction are switched and set to the first set to obtain the second reference data, and the first reference data and the second reference data are used to The distortion in the k-space data measured by photographing (image echo data measurement unit) is corrected.

International Publication WO2010 / 035569 JP 2003-225223 A JP 2005-46587 A

  However, in the technique disclosed in Patent Document 1 described above, the first reference data and the second reference data are different from each other in the magnetic field environment when residual magnetization due to application of a gradient magnetic field such as an MPG pulse remains in the MRI apparatus. Will be measured. Using reference data measured in such a different magnetic field environment, even if k-space data distortion is corrected, there is a possibility that artifacts may remain in the finally reconstructed image without being corrected properly. It is done.

  Therefore, an object of the present invention is to provide an MRI apparatus that can appropriately correct k-space data distortion associated with MPG pulse application even when residual magnetization remains in the MRI apparatus.

  In order to solve the above-described problem, the present invention provides a difference between the first preliminary measurement and the second preliminary measurement in which the correction echo data is measured by changing the phase encoding direction of the correction echo data measurement unit. The degauss sequence for demagnetizing the residual magnetization remaining in the mounting structure is executed.

  Specifically, the MRI apparatus of the present invention uses an imaging sequence including a correction echo data measurement unit and an image echo data measurement unit, respectively, a measurement control unit that controls the measurement of echo data, An arithmetic processing unit that performs distortion correction of the k-space data measured by the image echo data measurement unit using the correction echo data measured by the correction echo data measurement unit. A first preliminary measurement for measuring the first correction echo data with the direction of 1 as the phase encoding direction, and a second preliminary measurement for measuring the second correction echo data with the second direction as the phase encoding direction; Then, the correction echo data measurement unit is executed, and the arithmetic processing unit corrects the distortion of the k-space data using the first correction echo data and the second correction echo data. At this time, the measurement control unit executes a degauss sequence for demagnetizing residual magnetization remaining in the apparatus structure between the first preliminary measurement and the second preliminary measurement.

  According to the MRI apparatus of the present invention, even when residual magnetization remains in the MRI apparatus, k-space data distortion accompanying MPG pulse application can be corrected appropriately. As a result, a high-quality DWI image can be acquired even when residual magnetization remains in the MRI apparatus.

1 is a block diagram showing an overall basic configuration in one embodiment of an MRI apparatus according to the present invention. The flowchart showing the processing flow of one Example of this invention. A sequence chart showing an example of a DWI sequence based on an SE-EPI sequence. The sequence chart which shows an example of the echo data measurement part for correction | amendment for measuring the echo data for correction | amendment. FIG. 5A is a sequence chart illustrating an example of a correction echo data measurement unit in the first preliminary measurement, and FIG. 5B is a sequence chart illustrating an example of a correction echo data measurement unit in the second preliminary measurement. The figure which shows the degaussing pulse series which shows an example of a degauss sequence.

  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 supply 109, and an RF transmission coil 104, an RF transmitter 110, an RF receiver coil 105, a signal detector 106, a signal processor 107, a measurement controller 111, an overall controller 108, a display / operation unit 113, and a subject 101 are mounted. And a bed 112 for taking the top plate into and out of the static magnetic field generating 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 [m1] is a coil wound in the three-axis directions of X, Y, and Z, which is the real space coordinate system (stationary coordinate system) of the MRI apparatus, and each gradient magnetic field coil drives it A gradient magnetic field power supply 109 is connected to supply current. 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.

  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. Phase encoding gradient magnetic field pulse (Gp) and frequency encoding (leadout) gradient magnetic field pulse (Gf) are applied in the remaining two directions, and position information in each direction is encoded in the NMR signal (echo signal). .

  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 described later, and the RF transmission coil 104 is disposed in the vicinity of the subject 101 after the high frequency pulse is amplitude-modulated and amplified. , The subject 101 is irradiated with an RF pulse.

  The RF receiving coil 105 is a coil that receives an echo signal emitted by the NMR phenomenon of spin that constitutes the living tissue of the subject 101. The received echo signal is connected to the signal detecting unit 106 and is received by the signal detecting unit 106. Sent.

  The signal detection unit 106 performs processing for detecting an 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 detection unit 106 amplifies the received echo signal, divides the signal 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 and sent to a signal processing unit 107 described later. 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.

  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 detection unit 106. And a control unit for controlling them. Specifically, the measurement control unit 111 operates under the control of the overall control unit 108 described later, and controls the gradient magnetic field power source 109, the RF transmission unit 110, and the signal detection unit 106 based on a predetermined sequence, Echo data necessary for reconstructing the image of the imaging region of the subject 101 by repeatedly performing 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 Control the collection. 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 108.

  The overall control unit 108 controls the measurement control unit 111 and controls various data processing and processing result display and storage, and includes an arithmetic processing unit 114 having a CPU and a memory, an optical disc, And a storage unit 115 such as a magnetic disk. Specifically, the measurement control unit 111 is controlled to execute the collection of echo data, and when 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. Hereinafter, the description 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 [m2] in the memory. A group of echo data stored in an area corresponding to the k space in the memory 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 113 described later. And is recorded in the storage unit 115.

  The display / operation unit 113 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 108. Etc., and an operation unit. The operation unit is disposed in the vicinity of the display unit, and an operator interactively controls various processes of the MRI apparatus 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 being widely used clinically. By imaging the information on the spatial distribution of proton density and the spatial distribution of the relaxation time of the excited state, the form or function of the human head, abdomen, limbs, etc. is imaged in two or three dimensions.

  Next, an embodiment of the MRI apparatus of the present invention will be described. This embodiment uses the correction data measured by the correction echo data measurement unit when performing DWI measurement using the imaging sequence including the correction echo data measurement unit and the image echo data measurement unit. Then, the distortion of the k-space data measured by the image echo data measuring unit is corrected. In the measurement of the echo data for correction, in the same phase encoding direction as the first preliminary measurement in which the echo data for correction is measured by the correction echo data measurement unit set in a phase encoding direction different from that of the image echo data measurement unit. The second preliminary measurement of measuring the correction echo data by the set correction echo data measurement unit is performed. Then, the distortion of the k-space data measured by the image echo data measurement unit is corrected using both of the correction echo data.

  At that time, a degauss sequence for demagnetizing the residual magnetic field remaining in the MRI apparatus structure is executed between the two preliminary measurements. This prevents the error magnetic field due to residual magnetization remaining in the MRI apparatus after the first preliminary measurement from affecting the second preliminary measurement and the subsequent measurement of image echo data. In addition, the phase encoding direction of the correction echo data measurement unit in the first preliminary measurement performed first is different from the phase encoding direction in the image echo data measurement unit, and the correction is performed in the second preliminary measurement performed later. The phase encoding direction of the echo data measuring unit is the same as the phase encoding direction in the image echo data measuring unit. Thereby, the influence on the image echo data measured by the image echo data measurement unit can be minimized, and the image quality of the image is improved.

  Hereinafter, the outline of the processing flow of this embodiment will be described with reference to the flowchart shown in FIG. This processing flow is stored in advance in the storage unit as a program, and is executed by the arithmetic processing unit 114 reading and executing the program from the storage unit.

  In step 201, the arithmetic processing unit 114 sets the phase encoding direction to the first direction, and causes the measurement control unit 111 to execute the correction echo data measuring unit to perform the first preliminary measurement. The first direction is a direction different from the second direction which is the phase encoding direction in the correction echo data measurement unit executed in the second preliminary measurement described later and the subsequent image echo data measurement unit, and the slice direction The direction is also orthogonal to. That is, in the first preliminary measurement, the phase encoding direction is the first direction and the frequency encoding direction is the second direction. Upon receiving this instruction, the measurement control unit 111 executes the correction echo data measurement unit with the phase encoding direction as the first direction, measures the correction echo data, and measures the measured correction echo data (hereinafter referred to as the first correction data). 1 (referred to as correction echo data 1) is sent to the arithmetic processing unit 114. The details of the correction echo data measurement unit in which the phase encoding direction is set to the first direction will be described later.

  In step 202, the arithmetic processing unit 114 causes the measurement control unit 111 to execute a Degauss sequence. In response to the instruction, the measurement control unit 111 executes a degauss sequence to demagnetize the residual magnetic field remaining in the MRI apparatus main body. Details of the degauss sequence will be described later.

  In step 203, the arithmetic processing unit 114 sets the phase encoding direction to the second direction, and causes the measurement control unit 111 to execute the correction echo data measuring unit to perform the second preliminary measurement. The second direction is a direction different from the first direction which is the phase encoding direction in the correction echo data measurement unit executed in the first preliminary measurement described above, and is also a direction orthogonal to the slice direction. . That is, in the second preliminary measurement, the phase encoding direction is the second direction and the frequency encoding direction is the first direction. In response to this instruction, the measurement control unit 111 executes the correction echo data measurement unit with the phase encoding direction as the second direction, measures the correction echo data, and measures the corrected echo data (hereinafter referred to as the first correction echo data). 2 (referred to as correction echo data 2)). Note that the phase encoding direction in the correction echo data measurement unit executed in the second preliminary measurement is preferably the same as the phase encoding direction in the image echo data measurement unit executed thereafter, and therefore this step And the phase encoding direction of the image echo data measurement unit are the same second direction. The details of the correction echo data measurement unit in which the phase encoding direction is set to the second direction will be described later.

  In step 204a, the arithmetic processing unit 114 sets the phase encoding direction to the second direction, and causes the measurement control unit 111 to execute the image echo data measurement unit. Upon receiving the instruction, the measurement control unit 111 executes the image echo data measurement unit with the phase encoding direction as the second direction, measures the image echo data, and calculates the measured image echo data. Notify 114. The arithmetic processing unit 114 arranges the measured image echo data in a predetermined k space in the memory to obtain k space data.

  In step 204b, the arithmetic processing unit 114 uses the first correction echo data acquired in step 201 and the second correction echo data acquired in step 203, and is acquired in step 204a. Create correction data to correct distortion of k-space data. Note that the arithmetic processing in step 204b may be performed by the arithmetic processing unit 114, and may be performed in parallel with the measurement processing in step 204a.

  In step 205, the arithmetic processing unit 111 performs k-space data distortion correction on the k-space data acquired in step 204a using the correction data created in step 204b. Details of the k-space data distortion correction are described in Patent Document 1, and since this method is also used in the present embodiment, detailed description thereof is omitted.

  In step 206, the arithmetic processing unit 111 reconstructs an image using the k-space data whose distortion has been corrected in step 205.

In step 207, the arithmetic processing unit 111 causes the display unit to display the image reconstructed in step 206.
The above is the outline of the processing flow of the present embodiment.

  Next, details of each process in the process flow will be described. First, details of the correction echo data measurement unit and the image echo data measurement unit will be described.

  Since the image echo data measurement unit acquires a diffusion weighted image (DWI), the pulse sequence is based on the DWI pulse sequence. As an example of the DWI pulse sequence, a pulse sequence in which an MPG pulse is applied to an SE-EPI pulse sequence is known (Patent Document 2), and the echo data measuring unit for images of this embodiment is based on this SE-EPI pulse sequence. And Further, the correction echo data measurement unit measures echo data for correcting the phase distortion latent in the echo data measured by the image echo data measurement unit, and therefore has substantially the same shape as the image echo data measurement unit. A pulse sequence is used, but no phase encoding gradient magnetic field is applied. Therefore, the correction echo data measurement unit other than the phase encoding gradient magnetic field is also based on the SE-EPI pulse sequence. It should be noted that the basic pulse sequence of the image echo data measurement unit and the correction echo data measurement unit may be other types of DWI pulse sequences.

  Therefore, the details of the SE-EPI pulse sequence will be described based on the sequence chart shown in FIG. This pulse sequence is stored in advance in the storage unit as a program, for example, and is read out by the arithmetic processing unit 114 as necessary and transmitted to the measurement control unit 111 for execution. Then, the measurement control unit 111 performs the following control in the execution of the correction echo data measurement unit. That is, a slice selection 90 ° RF pulse 301 is applied while applying a slice selection gradient magnetic field 311 in the slice direction Gs (Z direction in apparatus coordinates) to excite a desired slice region. Thereafter, the first MPG pulse 331 is applied in the reading direction Gr (X direction in the apparatus coordinates). Next, a gradient magnetic field 312 and a 180 ° inversion RF pulse 302 are applied in the slice direction Gs in order to reverse the magnetization of the excitation region and form an echo signal. Thereafter, the second MPG pulse 332 is applied in the reading direction Gr (the Y direction in the apparatus coordinates). After these RF pulse and gradient magnetic field, a phase encode gradient magnetic field 322 for encoding spatial information in the phase encode direction Gp and a gradient for performing frequency encoding in the signal read direction Gr and simultaneously reading the echo signal It is applied while reversing the polarity of the magnetic field 334 to measure a plurality of echo signals for image reconstruction. Before the application of the phase encoding gradient magnetic field 322 and the signal readout gradient magnetic field 334, the dephase gradient magnetic fields 321 and 333 are applied, respectively, to adjust the initial position of the echo data arranged in the k space.

  Note that the dephasing gradient magnetic field 321 and the phase encoding 322 are not applied to the correction echo data measurement unit. That is, the correction echo data measurement unit does not apply a gradient magnetic field in the phase encoding direction. Since this SE-EPI pulse sequence is described in, for example, (Patent Document 2), further detailed description is omitted.

  In particular, in the correction echo data measurement unit, in the SE-EPI pulse sequence, the first preliminary measurement in which the phase encoding direction is set to the first direction and the second preliminary measurement in which the phase encoding direction is set to the second direction. Perform preliminary measurement. Therefore, the axis in the phase encoding direction Gp shown in FIG. 2 is different between the first preliminary measurement and the second preliminary measurement. For example, regarding the three-axis direction of (X, Y, Z) which is the real space coordinate system (stationary coordinate system) of the MRI apparatus, the phase encoding direction Gp is set in the first preliminary measurement as shown in FIG. In the X-axis direction, as shown in FIG. 4B, in the second preliminary measurement, the phase encoding direction Gp can be set in the Y-axis direction. In the case of oblique imaging, since the slice direction Gs, the phase encoding direction Gp, and the frequency encoding direction Gr rotate in a complicated manner in the stationary coordinate system (X, Y, Z), (Gs, Gp, Gr) and (X , Y, Z) becomes complicated.

  The above is a description of the outline of the correction echo data measurement unit, but the details of the correction echo data measurement unit of the present embodiment and the correction echo data to be measured by this correction echo data measurement unit are as follows: Since the method disclosed in Patent Document 1 is used and the method disclosed in Patent Document 1 is used for details of the present embodiment, detailed description thereof is omitted.

  Next, details of the degauss sequence will be described. Degauss is to make the residual magnetization remaining in the structure of the MRI apparatus based on the application of a gradient magnetic field zero, and the pulse sequence for that purpose is the degauss sequence. FIG. 5 shows a sequence chart of an example of the degauss sequence. The degauss sequence shown in FIG. 5 is composed of a series of degaussing pulse trains in which the amplitude is sequentially attenuated and the polarity is alternately reversed from the gradient magnetic field with the maximum intensity that can be applied by the MRI apparatus. By applying such a demagnetizing pulse train to at least one axis, preferably all three axes, the residual magnetization held by the structure of the MRI apparatus (for example, a ferromagnetic material such as a permanent magnet) can be returned to zero. it can. In FIG. 5, a degaussing pulse train composed of 8 pulses is shown as an example, but the number of gradient magnetic field pulses and the application time can be changed as necessary. Note that details of the degaussing pulse shown in FIG. 3 are described in detail in Patent Document 3, and thus further details are omitted. However, the degauss sequence of the present embodiment is not limited to the degauss sequence shown in FIG. 3, and any pulse sequence having a function of making the residual magnetization zero can be applied.

  In the above-described processing flow, the example in which the degauss sequence is executed between the first preliminary measurement and the second preliminary measurement has been described. However, the second preliminary measurement and the execution of the image echo signal measuring unit are described. A degauss sequence execution may be inserted between them. Further, a degauss sequence executed between the first preliminary measurement and the second preliminary measurement and a degauss sequence executed between the second preliminary measurement and the image echo signal measurement unit, and degaussing them. The pulse series may be different. For example, the number of degaussing pulses and the amplitude and polarity of each degaussing pulse may be varied. Since the phase encoding direction is the same in the correction echo data measurement unit and the image echo data measurement unit in the second preliminary measurement, the magnetic field environment between the second preliminary measurement and the image echo data measurement unit The change is considered to be less than between the first preliminary measurement and the second preliminary measurement. Therefore, the degauss sequence executed between the second preliminary measurement and the image echo data measurement unit is more demagnetized than the degauss sequence executed between the first preliminary measurement and the second preliminary measurement. The number and amplitude of the demagnetizing pulse may be reduced.

  As described above, according to the MRI apparatus of the present embodiment, the correction echo data measurement unit and the image echo data measurement unit use substantially the same pulse sequence except for the phase encoding gradient magnetic field. Even so, correction data capable of appropriately correcting k-space data distortion can be acquired. Furthermore, since a degauss sequence for demagnetizing the residual magnetic field remaining in the MRI apparatus structure part is inserted and executed at least between the first preliminary measurement and the second preliminary measurement for measuring the correction echo data, The correction echo data measured in the first preliminary measurement and the second preliminary measurement are measured in the same magnetic field environment, and the distortion of the k-space data acquired by the echo data measurement unit for images is appropriate. It becomes possible to correct to. Furthermore, the echo data measurement unit for image and the correction echo data measurement unit in the second preliminary measurement executed before that are set to the same phase encoding direction, that is, executed in the second preliminary measurement. By using substantially the same pulse sequence for the correction echo data measurement unit and the image echo data measurement unit, the influence on the image echo data measured by the image echo data measurement unit can be minimized. Image quality can be improved.

  101 subject, 102 static magnetic field generation magnet, 103 gradient magnetic field coil, 104 transmission RF coil, 105 reception RF coil, 106 signal detection unit 106, 107 signal processing unit, 108 overall control unit, 109 gradient magnetic field power source, 110 RF transmission unit , 111 Measurement control unit, 112 beds, 113 Display / operation unit, 114 Arithmetic processing unit, 115 Storage unit

Claims (5)

A measurement control unit that controls measurement of echo data using an imaging sequence including a correction echo data measurement unit and an image echo data measurement unit;
An arithmetic processing unit that performs distortion correction of the k-space data measured by the image echo data measurement unit using the correction echo data measured by the correction echo data measurement unit;
With
The measurement control unit measures the first correction echo data for measuring the first correction echo data with the first direction as the phase encoding direction, and measures the second correction echo data with the second direction as the phase encoding direction. In the second preliminary measurement, the correction echo data measurement unit is executed,
The arithmetic processing unit is a magnetic resonance imaging apparatus that performs distortion correction of the k-space data using the first correction echo data and the second correction echo data.
The magnetic resonance imaging apparatus, wherein the measurement control unit executes a degauss sequence for demagnetizing residual magnetization remaining in the apparatus structure between the first preliminary measurement and the second preliminary measurement. The magnetic resonance imaging apparatus according to claim 1,
The measurement control unit performs the second preliminary measurement before the execution of the image echo data measurement unit, and at this time, the phase encoding direction of the correction echo data measurement unit in the second preliminary measurement is A magnetic resonance imaging apparatus characterized in that it is set in the same direction as the phase encoding direction of the echo data measuring unit for images. The magnetic resonance imaging apparatus according to claim 2,
The measurement control unit executes the first preliminary measurement before the second preliminary measurement, and at this time, the phase encoding direction of the correction echo data measuring unit in the first preliminary measurement, and the second The magnetic resonance imaging apparatus is characterized in that the phase encoding direction of the correction echo data measurement unit in the preliminary measurement is different. The magnetic resonance imaging apparatus according to claim 3,
The magnetic resonance imaging apparatus, wherein the measurement control unit executes the degauss sequence between the second preliminary measurement and the image echo data measurement unit. The magnetic resonance imaging apparatus according to claim 4,
The measurement control unit includes a degauss sequence executed between the first preliminary measurement and the second preliminary measurement, and a degauss executed between the second preliminary measurement and the image echo data measurement unit. A magnetic resonance imaging apparatus characterized in that the sequence is different.

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