Magnetic resonance imaging apparatus and control method thereof

Abstract

To suppress an occurrence of artifacts attributed to an FID signal even when parallel imaging is applied to imaging using a spin echo-based pulse sequence.SOLUTION: A high-frequency transmission unit of an MRI device changes a phase of an inversion RF pulse according to a phase encode granted to each echo signal and the number of phase encodes when executing a spin echo-based pulse sequence using an excitation RF pulse for exciting a nuclear spin and the inversion RF pulse for inverting the excited nuclear spin as high-frequency magnetic field pulses. Specifically, control is executed so as to change the phase of the inversion RF pulse to a quadratic function of the phase encode of the echo signal.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a magnetic resonance imaging apparatus (hereinafter abbreviated as an MRI apparatus), and more particularly to a technique for acquiring an image in which artifacts caused by FID (free induction decay) signals are reduced. [Background technology]

[0002] A typical imaging method for MRI devices is a spin-echo pulse sequence. In a spin-echo pulse sequence, an excitation RF pulse (90-degree pulse) is applied, followed by an inversion RF pulse (180-degree pulse) to diffuse the spins, and the NMR signals from the refocused spins are collected as echo signals. In such a spin-echo pulse sequence, in addition to the echo signals from the spins excited by the 90-degree pulse, the spins are also excited by the 180-degree pulse, and a signal (FID signal) is generated by the free induction decay. The spin-echo signal is encoded by the phase encoding gradient magnetic field applied after the 90-degree pulse is applied, but the FID signal is not encoded, so it is collected as a zero-encoded signal superimposed on the spin echo. For this reason, in an image reconstructed from k-space data obtained by a spin-echo sequence, a zipper-shaped artifact (an artifact caused by the FID signal: hereinafter referred to as the FID artifact) appears in the center of the image, parallel to the frequency encoding direction.

[0003] In imaging using spin echo pulse sequences, the phase of a 180-degree pulse is usually inverted for each repetition of the sequence in order to remove the FID artifacts, which allows the FID artifacts to be moved to both sides of the image (e.g., Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Michael N. Hoff et al. “Artifacts in Magnetic Resonance Imaging”, Capter 9, pp165-190, Image Principles, Neck, and the Brain, ResearchGate (2016) Summary of the Invention [Problem to be solved by the invention]

[0005] Spin-echo pulse sequences are less susceptible to static magnetic field inhomogeneity and are an excellent imaging method for obtaining T1-weighted and T2-weighted images, but there is a problem that conventional FID artifact avoidance techniques do not work when parallel imaging is applied to spin-echo pulse sequences. This is because when parallel imaging is applied to imaging using spin-echo pulse sequences, even if FID artifacts are shifted to both sides of the image before folding, in the image after folding, FID artifacts appear not at the edge of the image but at the position where they overlap with the subject image. Moreover, the higher the speed factor, the more FID artifacts there are, so it was difficult to shorten the measurement time by increasing the speed factor.

[0006] An object of the present invention is to provide an MRI apparatus capable of acquiring images from which artifacts are removed even when parallel imaging is applied to imaging using a spin echo pulse sequence. [Means for solving the problem]

[0007] In order to solve the above problem, the MRI apparatus of the present invention controls the phase of the inversion RF pulse so that it becomes a quadratic function of the phase encoding of the echo signal. This makes the absolute value of the FID signal substantially constant (for example, zero), and zipper-shaped artifacts do not appear on the image. Appearance do not.

[0008] That is, the MRI apparatus of the present invention includes a static magnetic field generating magnet that generates a static magnetic field, a radio frequency transmitting unit that irradiates a radio frequency magnetic field pulse to a subject placed in a static magnetic field space, a receiving unit that receives an echo signal generated from the subject, a gradient magnetic field generating unit that generates a gradient magnetic field that encodes the echo signal, a control unit that controls the radio frequency transmitting unit, the receiving unit, and the gradient magnetic field generating unit according to a predetermined pulse sequence, and a calculation unit that reconstructs an image using the echo signal. When executing a spin echo system pulse sequence that uses an excitation RF pulse that excites nuclear spins and an inversion RF pulse that inverts the excited nuclear spins as radio frequency magnetic field pulses, the radio frequency transmitting unit changes the phase of the inversion RF pulse according to the phase encoding and the number of phase encodings given to each echo signal.

[0009] Here, the phase encoding number is a value obtained by dividing the phase encoding number of the original image by the thinning rate when thinning measurement (undone sampling) is performed in the phase encoding direction of the k space by parallel imaging. However, it is not essential to perform parallel imaging in the present invention, and the present invention can be applied even when parallel imaging is not performed. Effect of the Invention

[0010] According to the present invention, the phase of the inversion RF pulse is not controlled by switching it between 0-π, but is controlled as a function of the phase encoding, so that the zipper artifact due to the FID signal can be substantially reduced to zero or a uniform signal value, and an image free of zipper artifacts can be obtained. This method differs from the conventional method of simply moving the FID artifact to the edge of the image, and is a novel method that substantially eliminates the FID artifact itself, and by applying it to parallel imaging in particular, it can solve problems that could not be solved by conventional methods. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing an overall overview of an MRI apparatus. [Diagram 2]FIG. 1 shows a typical spin echo sequence. [Diagram 3] FIG. 4 is a diagram showing k-space data measured in the first embodiment. [Figure 4] FIG. 4 is a diagram showing an example of an irradiation phase according to the first embodiment. [Diagram 5] FIG. 5 is a graph showing the signal intensity of an image of an FID signal when the irradiation phase is that of FIG. [Figure 6] FIG. 4 is a flowchart showing the procedure of imaging according to the first embodiment. [Figure 7] FIG. 1 is a diagram for explaining the effect of the embodiment, in which (A) shows an image obtained by a conventional method, and (B) shows an image obtained by the method of the embodiment. [Figure 8] FIG. 11 is a diagram showing k-space data measured in the second embodiment. [Figure 9] FIG. 11 is a diagram showing image reconstruction steps according to the second embodiment. [Figure 10] FIG. 11 is a diagram showing an example of an irradiation phase according to the third embodiment. [Figure 11] FIG. 11 is a graph showing the signal intensity of an image of an FID signal when the irradiation phase is that of FIG. 10. [Figure 12] FIG. 11 is a flowchart showing the procedure of imaging according to the third embodiment.

[0012] Hereinafter, an embodiment of an MRI apparatus of the present invention will be described with reference to the drawings.

[0013] The MRI apparatus 100 mainly comprises an imaging section including a static magnetic field generating magnet, a high frequency transmitting section, a receiving section and a gradient magnetic field generating section, a control section 30 that controls the imaging section according to a predetermined pulse sequence, and a calculation section 20 that reconstructs an image using echo signals collected by the imaging section. As shown in Fig. 1, the imaging section comprises a static magnetic field generating section 11, a gradient magnetic field generating section 12, a transmitting section 13, a receiving section 14, a signal processing section 15 and a sequencer 16.

[0014] The static magnetic field generating unit 11 is composed of a permanent magnet type, normal conducting type, or superconducting type static magnetic field generating magnet (not shown). There are different types, such as a vertical magnetic field type and a horizontal magnetic field type, depending on the direction of the static magnetic field generated by the static magnetic field generating magnet. In the vertical magnetic field type, a uniform static magnetic field is generated in the space around the subject 1 in a direction perpendicular to the body axis, and in the horizontal magnetic field type, a uniform static magnetic field is generated in the direction of the body axis.

[0015] The gradient magnetic field generating unit 12 comprises gradient magnetic field coils 121 wound in the three axial directions of X, Y, and Z, which are the coordinate system (static coordinate system) of the MRI apparatus, and gradient magnetic field power supplies 122 that drive each gradient magnetic field coil. By driving the gradient magnetic field power supplies 122 of each coil in accordance with commands from the sequencer 16, gradient magnetic fields Gx, Gy, and Gz in the three axial directions of X, Y, and Z are applied to the static magnetic field.

[0016] The transmitting unit 13 irradiates the subject 1 with a radio frequency magnetic field pulse (RF pulse) in order to cause nuclear magnetic resonance in the nuclear spins of atoms constituting the biological tissue of the subject 1, and includes a radio frequency oscillator 131, a modulator 132, a radio frequency amplifier 133, and a transmitting radio frequency coil (transmitting coil) 134. The RF pulse output from the radio frequency oscillator 131 is amplitude-modulated by the modulator 132 at a timing according to a command from the sequencer 16, and the amplitude-modulated radio frequency pulse is amplified by the radio frequency amplifier 133 and then supplied to a transmitting coil 134 arranged close to the subject 1, whereby the RF pulse is irradiated to the subject 1.

[0017] The intensity and phase of the RF pulse are controlled by a modulator 132, and it is possible to output 90-degree pulses and 180-degree pulses with different intensities, and also to control their phases. In this embodiment, a spin echo system pulse sequence, which will be described later, is executed, and at that time, the phases of the excitation pulse (90-degree pulse) and inversion pulse (180 degrees) that are applied are controlled. The details of the control will be described later.

[0018] The receiver 14 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of atomic spins constituting the biological tissue of the subject 1, and includes a receiver-side high-frequency coil (receiving coil) 141, a signal amplifier 142, a quadrature phase detector 143, and an A / D converter 144. The NMR signal of the response of the subject 1 induced by the electromagnetic wave irradiated from the transmitting coil 134 is detected by the receiving coil 141 arranged close to the subject 1, amplified by the signal amplifier 142, and then divided into two orthogonal signals by the quadrature phase detector 143 at a timing according to a command from the sequencer 16, each of which is converted into a digital quantity by the A / D converter 144 and sent to the signal processor 15. When a coil combining a plurality of sub-coils is used as the receiving coil 141, each of the sub-coils is connected to the signal amplifier 142, the quadrature phase detector 143, and the A / D converter 144, and the signal processor 15 collects signals for each sub-coil.

[0019] The signal processing unit 15 includes an external storage device 151 such as an optical disk or a magnetic disk, a display 152, and an operation unit 153 including input devices such as a trackball, a mouse, a keyboard, etc. The signal processing unit 15 executes signal processing, image reconstruction, and other processes, and displays the resulting tomographic images of the subject 1 on the display 152 and records them on a magnetic disk or the like of the external storage device 151. The operation unit 153 is disposed close to the display 152, and an operator interactively controls various processes of the MRI apparatus through the operation unit 153 while looking at the display 152.

[0020] 1, the MRI apparatus further includes a computer 50 having a CPU and a memory, and the computer 50 realizes part of the functions of the signal processing unit 15 described above, and the functions of the calculation unit 20 and the control unit 30. Note that part or all of the functions of the calculation unit 20 are included in the signal processing unit 15, and are executed by the CPU reading a predetermined program stored in a storage device. Some of the functions performed by the computer 50 can also be realized by hardware such as ASIC or FPGA.

[0021] The sequencer 16 is a control means that repeatedly applies the above-mentioned RF pulses and gradient magnetic field pulses in a predetermined pulse sequence, and operates under the control of the control unit 30, and sends various commands required for collecting tomographic image data of the subject 1 to the transmitting unit 13, the gradient magnetic field generating unit 12, and the receiving unit 14.

[0022] There are various pulse sequences depending on the imaging method, which are stored in advance in a storage device, and the imaging sequence is determined by the user selecting a desired pulse sequence via the operation unit 153 and setting imaging parameters such as echo time (TE), repetition time (TR), imaging field of view (FOV), and speed ratio in parallel imaging. In this embodiment, the sequencer 16 executes a spin echo type pulse sequence.

[0023] FIG. 2 shows an example of a typical spin echo pulse sequence 200. In this pulse sequence, as shown in the figure, a 90-degree pulse 211 is applied together with a slice gradient magnetic field 221 for selecting a predetermined slice of the subject 1 to excite spins in the predetermined slice. Next, a phase encoding gradient magnetic field 231 is applied, and a 180-degree pulse 212 is applied together with a slice gradient magnetic field 222 at 1 / 2 (TE / 2) of the echo time. This generates an echo signal (NMR signal) 251 that peaks at the echo time. This echo signal is collected for a predetermined sampling time while applying a frequency encoding gradient magnetic field 241. After a predetermined repetition time TR has elapsed, the above-mentioned process from the excitation of the spins to the collection of the echo signal is repeated while changing the strength of the phase encoding gradient magnetic field 231, and a set number of echo signals are collected. In the figure, a signal 261 indicated by a dotted line is an FID signal generated by the 180-degree pulse 212.

[0024] 2 shows a two-dimensional imaging sequence in which the phase encoding gradient magnetic field 231 is applied in one axial direction (Gp), but a three-dimensional imaging sequence in which it is applied in two axial directions may be used. Also, in FIG. 2, a case in which one echo signal 251 is generated and collected after one excitation is shown, but a multi-echo sequence in which multiple echo signals are generated using multiple 180-degree pulses may be used.

[0025] The MRI apparatus of this embodiment is characterized in that it controls the phase of the 180-degree pulse when executing the spin echo pulse sequence described above. Hereinafter, an embodiment of the control according to the k-space data acquisition method will be described.

[0026] <Embodiment 1> In this embodiment, in the repetition of the sequence shown in FIG. 2, the phase encoding step is thinned out and changed according to a set speed ratio, and parallel imaging is performed. As shown in FIG. 3, parallel imaging is an imaging method in which k-space data is thinned out in the phase direction according to a predetermined speed ratio, and data of phase encoding that has not been measured is inferred by calculation to obtain an image without aliasing. Several parallel imaging reconstruction methods for reconstructing an image without aliasing (SENSE method, GRAPPA method, CAIPIRINHA method, etc.) have been established, but these methods cannot separate only the FID signal that is not phase encoded from the original image signal. For this reason, artifacts caused by the FID signal occur, but the conventional phase control (0-π control) of the inversion pulse cannot control the appearance position of the artifact in the parallel imaging image.

[0027] The MRI apparatus of this embodiment eliminates FID artifacts by making the irradiation phase of the inversion RF pulse a quadratic function of the phase encoding and applying it while changing the effective phase encoding number as a coefficient in the range of 0 to 360 degrees.

[0028] Specifically, the irradiation phase θ of the inversion RF pulse is controlled by the formula (1) for each echo signal to be measured.

number

[0029] The phase of equation (1) is shown in Fig. 4. In the figure, the horizontal axis is the phase encode, and the vertical axis is the irradiation phase of the 180-degree pulse. In the conventional method, the phase θ between adjacent phase encodes is either 0 or π, but in the phase control of this embodiment, the phase is a quadratic function of the phase encode and is folded over by a coefficient (2l+1), but when it is continuous without folding over, it becomes a graph of a continuous quadratic function.

[0030] Next, it will be explained how the FID artifacts disappear by the above-mentioned phase control. The FID signal when RF irradiation is performed with the phase expressed by equation (1) is expressed by equation (2).

number

[0031] The FID signal is the Fourier transform of equation (2) in the image space, and can be expressed by equation (3).

number

number

[0032] Figure 5 shows equation (4) plotted against pixel position. In Figure 5, the horizontal axis represents position in the phase encoding direction (y), and the vertical axis represents signal intensity. As can be seen from Figure 5, the absolute value of signal intensity is constant regardless of position in the phase encoding direction, and the FID signal is uniformly distributed. Therefore, the FID signal does not appear as an artifact at a specific position on the image.

[0033] The flow of imaging by the MRI apparatus of this embodiment is shown in Fig. 6. As shown in the figure, first, imaging conditions including a speed ratio are set by user specification or examination protocol, etc. (S61). Using the set speed ratio and measurement matrix size (phase encoding number), the control unit 30 determines the irradiation phase of the 180-degree pulse by equation (1) and sets it to the transmission unit 13 (S62). The sequencer 16 calculates a spin echo system pulse sequence using the set imaging conditions, and starts imaging. During imaging, the transmission unit 13 controls the 180-degree pulse at the set irradiation phase (S63).

[0034] After imaging is performed by controlling the irradiation phase of the inversion RF pulse in this manner, the image is reconstructed in accordance with the parallel imaging calculation method using the echo signals collected by the calculation unit 20 (S64). The image reconstruction method is the same as that of a normal MRI device, and this makes it possible to obtain an image of good quality in which the FID signal does not appear as an artifact.

[0035] According to this embodiment, in imaging using a spin echo sequence, artifacts caused by FID signals can be substantially eliminated. This allows the speed ratio of parallel imaging to be set high, thereby enabling faster imaging.

[0036] A comparison of an image acquired by the MRI apparatus of this embodiment with an image acquired by conventional phase control of an inversion RF pulse is shown in Fig. 7. In the figure, (A) is an example of control by the conventional method, and (B) is an example of control by this embodiment, both of which were taken with a speed factor R of 2. In the conventional method, an FID signal is imaged as an artifact at the position indicated by the arrow, but in the image captured by this embodiment, no FID signal artifact can be confirmed.

[0037] Although an embodiment for performing parallel imaging has been described above, this embodiment can also be applied to a case where measurement is performed without thinning out the k-space (when R in equation (1) is 1), and similarly has the effect of making artifacts in the FID signal invisible.

[0038] <Embodiment 2> In this embodiment, when an imaging method (asymmetric measurement method) in which a part of the k-space is left unmeasured is used, the phase of the inversion RF pulse is controlled. The pulse sequence is the same as in the first embodiment, but in this embodiment, as shown in Fig. 8, a part 820 of the high frequency region in the phase encoding direction of the k-space data 800 is left unmeasured to increase the speed. Although not essential, the measurement region 810 may be thinned out at a predetermined thinning rate.

[0039] In this embodiment, the operation flow is the same as in Fig. 6, and imaging is performed by controlling the irradiation phase of the inversion RF pulse. The phase control uses equation (1), where N is the phase encoding number #ph of the image including the unmeasured region 810. When parallel imaging is performed, N = #ph / R, as in the embodiment.

[0040] The calculation unit 20 performs image reconstruction using echo signals collected by controlling the phase of the inversion RF pulse as described above, but prior to that, it performs processing to artificially create FID signals in unmeasured regions. That is, in the asymmetric measurement method, for example, zero-filling is performed for the unmeasured region 820, and image reconstruction is performed. In that case, however, the FID signal that would be generated if the region had been measured is not reflected, and so the influence of the FID signal differs between the measured region 810 and the unmeasured region 820.

[0041] Therefore, the calculation unit 20 first estimates the FID signal of the unmeasured region 820 using data of the region 810A that is symmetrical to the unmeasured region 820 with respect to the axis (phase encoding 0) in the ky direction of the k-space. Details of the image reconstruction step (FIG. 6: S64) in this embodiment are shown in FIG. 9. In this embodiment, as shown in FIG. 9, specifically, the absolute value is calculated from the complex signal of the region 810A (S641), and the phase of the phase encoding corresponding to the region 820 is calculated by the formula (1) (S642). The calculated absolute value and phase of the region 820 are used to artificially create a complex signal of the FID signal of the region 820. In the case of parallel imaging, the signal of the region 820 is created with the same thinning rate as the region 810. As a result, k-space data that evenly fills the entire k-space is obtained (S643).

[0042] The computing unit 20 uses this k-space data to perform normal image reconstruction or image reconstruction including parallel imaging calculation (S644). In the image obtained in this way, the echo signals are reconstructed as they are, and the FID signal components to which no phase encoding is applied are uniform throughout the phase encoding direction as shown in Fig. 5, so they do not appear as artifacts on the image.

[0043] In this embodiment, similarly to the first embodiment, when parallel imaging is applied, the speed can be increased, and further speedup can be achieved in combination with asymmetric measurement.

[0044] <Embodiment 3> In the first and second embodiments, irradiation phase control is performed to make the FID signal uniform over the entire phase encoding direction, but in this embodiment, irradiation phase control is performed to limit the FID artifacts to only a predetermined region of the image.

[0045] As described using the formulas (1) to (4), in order to make the FID signal uniform, in the first embodiment, π is used as a reference and k is 2 In the present embodiment, the irradiation phase θ is calculated by multiplying the irradiation phase θ by / N, but φ(≠π) is used as the reference phase. That is, the irradiation phase is calculated by the following equation (5).

[0046]

number

[0047] In the formula, φ is φ>π or φ<π. The phase of formula (5) when φ=64π / 18 is shown in Fig. 10. As can be seen from a comparison with Fig. 4, when π is used as the reference phase, the phase change is symmetrical about the center of the phase encoding direction, whereas when φ is not π, the phase change becomes asymmetric in k-space.

[0048] The absolute value of an FID signal of such a phase in image space is large in the area indicated by the arrow in (A) but is nearly zero in the area indicated by the arrow in (B), as shown in Figure 11. Therefore, by making the area of ​​the image necessary for diagnosis (region of interest) a region where the signal intensity of the FID signal image is zero, it is possible to obtain a good image of the region of interest without artifacts.

[0049] An example of the operation of this embodiment is shown in Fig. 12. In Fig. 12, the same steps as in Fig. 6 are designated by the same reference numerals, and duplicated explanations will be omitted.

[0050] The control unit 30 accepts the setting of a desired region of interest in addition to the speed ratio and imaging parameters as imaging conditions (S611). Next, φ that does not cause FID artifacts in that region is determined (S612), and the irradiation phase of the 180-degree pulse is determined by equation (5) (S62). The region where the signal intensity of the FID signal in the image space is made zero (FID zero region) can be predicted by the deviation amount of φ from π, so φ is determined so that the predicted region includes the region of interest. Alternatively, for multiple φ, FID zero regions as shown in FIG. 10 may be obtained in advance and registered together with φ, or a φ that makes the region including the region set as the region of interest an absolute value zero region may be selected from the previously registered φ.

[0051] In addition, if there is no FID zero region that includes the set region of interest, formula (1) may be used instead of formula (5).

[0052] Thereafter, imaging is performed, and normal image reconstruction or image reconstruction including parallel imaging calculation is performed in the same manner as in the first embodiment (S63, S64).

[0053] According to this embodiment, the FID signal can be made substantially zero in the region of interest. Note that this embodiment can also be implemented in combination with the above-mentioned embodiment 2. [Explanation of symbols]

[0054] 11: static magnetic field generating unit, 12: gradient magnetic field generating unit, 13: transmitting unit (high frequency transmitting unit), 14: receiving unit, 15: signal processing unit, 16: sequencer, 20: calculation unit, 30: control unit, 50: computer

Claims

1. a static magnetic field generating magnet that generates a static magnetic field, a high frequency transmitting unit that irradiates an RF pulse to a subject placed in a static magnetic field space, a receiving unit that receives an echo signal generated from the subject, a gradient magnetic field generating unit that generates a gradient magnetic field that encodes the echo signal, a control unit that controls the high frequency transmitting unit, the receiving unit, and the gradient magnetic field generating unit in accordance with a predetermined pulse sequence, and a calculation unit that reconstructs an image using the echo signal, The magnetic resonance imaging apparatus is characterized in that, in imaging using a spin echo system pulse sequence including irradiation of an excitation RF pulse that excites nuclear spins and irradiation of an inversion RF pulse that inverts the excited nuclear spins as the pulse sequence, the radio frequency transmission unit changes the phase of the inversion RF pulse to be a quadratic function of phase encoding in accordance with the phase encoding and number of phase encodings imparted to each echo signal.

2. 2. The magnetic resonance imaging apparatus according to claim 1, A magnetic resonance imaging apparatus characterized in that the phase θ of the inversion RF pulse is expressed by the following equation (1), where k is the phase encode and N is the number of phase encodes or the actual number of phase encodes obtained by dividing the number of phase encodes by a thinning rate. [0010] In formula (1), “l” is an integer of 0 or more.

3. 3. The magnetic resonance imaging apparatus according to claim 2, The control unit performs control to undersample the k-space data at a predetermined thinning rate R in a phase encoding direction, The magnetic resonance imaging apparatus according to claim 1, wherein the radio frequency transmission unit uses the effective phase encoding number as N expressed in the formula (1) to control the phase of the inversion RF pulse.

4. 3. The magnetic resonance imaging apparatus according to claim 2, The control unit performs control so that a part of a high frequency region in a phase encoding direction of the k-space data is not measured, The magnetic resonance imaging apparatus is characterized in that the calculation unit creates data for the unmeasured high frequency region using absolute values ​​of signals in other measured high frequency regions and the phase of the inversion RF pulse calculated for the unmeasured high frequency region.

5. 5. The magnetic resonance imaging apparatus according to claim 4, The control unit performs control to undersample the k-space data to be measured at a predetermined thinning rate R in a phase encoding direction, The magnetic resonance imaging apparatus according to claim 1, wherein the radio frequency transmission unit uses the effective phase encoding number as N expressed in the formula (1) to control the phase of the inversion RF pulse.

6. 2. The magnetic resonance imaging apparatus according to claim 1, the high frequency transmission unit controls the phase θ of the inversion RF pulse to be a phase expressed by the following equation (5), where k is the phase encode and N is the number of phase encodes or an actual phase encode number obtained by dividing the number of phase encodes by a thinning rate, and the phase θ is a phase that makes pixel values ​​generated by the FID signal in the region of interest substantially zero or constant. [0025] (In the formula, φ≠nπ: n is an integer of 1 or more, and “l” is an integer of 0 or more.)

7. 7. The magnetic resonance imaging apparatus according to claim 6, The control unit performs control to undersample the k-space data to be measured at a predetermined thinning rate R in a phase encoding direction, The magnetic resonance imaging apparatus is characterized in that the high-frequency transmission unit uses an effective phase encoding number obtained by dividing the phase encoding number of an image by a speed multiplication number R as N expressed in the formula (5) to control the phase of the inversion RF pulse.

8. 7. The magnetic resonance imaging apparatus according to claim 6, A reception unit that receives a designation of a region of interest is further provided, The magnetic resonance imaging apparatus is characterized in that the radio frequency transmission unit calculates a phase θ of the inversion RF pulse that makes the pixel value generated by the FID signal substantially zero or constant in the region of interest accepted by the acceptance unit, and controls the phase of the inversion RF pulse to become the calculated phase.

9. Executing a spin echo pulse sequence including irradiation of an excitation RF pulse for exciting nuclear spins and irradiation of an inversion RF pulse for inverting the excited nuclear spins; In this case, the method for controlling a magnetic resonance imaging apparatus is characterized in that the irradiation phase of the inversion RF pulse is changed so as to become a quadratic function of the phase encoding in accordance with the phase encoding and the number of phase encodings applied to each echo signal.

10. A method for controlling a magnetic resonance imaging apparatus according to claim 9, comprising the steps of: Executing the pulse sequence at a predetermined rate; A method for controlling a magnetic resonance imaging apparatus, characterized in that, when the phase encoding is k and the actual phase encoding number obtained by dividing the phase encoding number by the speed multiplication rate is N, the irradiation phase of the inversion RF pulse is set to a phase θ expressed by the following equation (1). [0010] In formula (1), “l” is an integer of 0 or more.

Images