Magnetic resonance imaging device and control method thereof

Abstract

The present invention provides a magnetic resonance imaging apparatus and a control method thereof. Even when parallel imaging is employed for imaging using a spin-echo pulse sequence, artifacts caused by FID signals are suppressed. When executing a spin-echo pulse sequence using an excitation RF pulse to excite nuclear spins and an inversion RF pulse to invert the excited nuclear spins as high-frequency magnetic field pulses, the high-frequency transmitting unit of the MRI apparatus changes the phase of the inversion RF pulse according to the phase encoding and the number of phase encodings assigned to each echo signal. Specifically, the phase of the inversion RF pulse is controlled to be a quadratic function of the phase encoding of the echo signal.

Description

Technical Field

[0001] The present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus), and more particularly to a technique for obtaining an image with reduced artifacts caused by a FID (free induction decay) signal. Background Art

[0002] A typical imaging method used in MRI systems is a spin-echo pulse sequence. In a spin-echo pulse sequence, after applying an excitation RF pulse (90-degree pulse), an inversion RF pulse (180-degree pulse) is applied to diffuse the spins, and the NMR signals from the converged spins are collected again as echo signals. In this spin-echo pulse sequence, separate from the echo signals from the spins excited by the 90-degree pulse, the 180-degree pulse also excites the spins, generating a signal (FID signal) due to their free induction decay. The spin echo signals are encoded by a phase-encoding gradient magnetic field applied after the 90-degree pulse. However, since the FID signal is unencoded, it is superimposed on the spin echo and collected as a zero-encoded signal. Consequently, in images reconstructed from the k-space data obtained in the spin-echo sequence, a zipper-like artifact parallel to the frequency encoding direction appears at the center of the image (artifacts caused by the FID signal: hereinafter referred to as FID artifacts).

[0003] In imaging using a spin echo pulse sequence, to remove FID artifacts, the pulse phase is typically inverted 180 degrees each time the sequence is repeated. This allows the FID artifacts to be moved to both sides of the image (e.g., Non-Patent Document 1).

[0004] Prior art literature

[0005]

Non-patent literature

[0006] Non-Patent Document 1: Michael N. Hoff et al., “Artifacts in Magnetic Resonance Imaging”, Capter 9, pp. 165-190, Image Principles, Neck, and the Brain, Research Gate (2016)

[0007] Spin echo pulse sequences are less susceptible to static magnetic field inhomogeneities and are an excellent imaging method for acquiring T1- and T2-weighted images. However, using parallel imaging with spin echo pulse sequences presents a problem in that existing FID artifact avoidance techniques are ineffective. This is because, when parallel imaging is used for imaging using spin echo pulse sequences, even if FID artifacts are moved to the sides of the image before folding and unfolding, they will appear in the unfolded image not at the image ends but at locations where they overlap with the subject image. Furthermore, since FID artifacts increase with increasing the magnification rate, shortening measurement time by increasing the magnification rate is difficult. Summary of the Invention

[0008] An object of the present invention is to provide an MRI apparatus capable of acquiring an image with artifacts removed even when parallel imaging is applied to imaging using a spin echo pulse sequence.

[0009] To address the above issues, the MRI apparatus of the present invention controls the phase of the inversion RF pulse to a quadratic function of the phase encoding of the echo signal. This ensures that the absolute value of the FID signal remains essentially constant (e.g., zero), eliminating zipper-like artifacts on the image.

[0010] Specifically, the MRI apparatus of the present invention includes: a static magnetic field generating magnet for generating a static magnetic field; a high-frequency transmitting unit for irradiating a subject placed in a static magnetic field space with high-frequency magnetic field pulses; a receiving unit for receiving echo signals generated from the subject; a gradient magnetic field generating unit for generating a gradient magnetic field for encoding the echo signals; a control unit for controlling the high-frequency transmitting unit, the receiving unit, and the gradient magnetic field generating unit according to a predetermined pulse sequence; and a computing unit for reconstructing an image using the echo signals. When the high-frequency transmitting unit executes a spin echo pulse sequence using an excitation RF pulse for exciting nuclear spins and an inversion RF pulse for inverting the excited nuclear spins as high-frequency magnetic field pulses, the high-frequency transmitting unit changes the phase of the inversion RF pulse according to the phase encoding and the number of phase encodings assigned to each echo signal.

[0011] Here, when performing thinning measurement (undersampling) of the phase encoding direction in k-space using parallel imaging, the phase encoding number is the value obtained by dividing the phase encoding number of the original image by the thinning rate. However, the present invention does not necessarily require parallel imaging and can be applied even without parallel imaging.

[0012] Effects of the Invention

[0013] According to the present invention, rather than controlling the phase of the inversion RF pulse by switching it between 0 and π, it controls it as a function of phase encoding. This effectively reduces the zipper artifact associated with the FID signal to zero or a uniform signal value, resulting in an image free of zipper artifacts. Unlike conventional methods that simply shift FID artifacts to the edges of the image, this novel approach virtually eliminates the FID artifact itself. Particularly by applying it to parallel imaging, it can address issues that have remained unresolved with conventional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a block diagram showing the overall outline of an MRI apparatus.

[0015] Figure 2 is a diagram showing a typical spin echo sequence.

[0016] Figure 3 This is a diagram showing k-space data measured in the first embodiment.

[0017] Figure 4 This is a diagram showing an example of the irradiation phase in the first embodiment.

[0018] Figure 5 Is the representation set to Figure 4 A graph showing the signal intensity of an FID signal image under the illumination phase.

[0019] Figure 6 This is a diagram showing the imaging process in the first embodiment.

[0020] Figure 7 These are diagrams for explaining the effects of the embodiment. (A) shows an image obtained by a conventional method, and (B) shows an image obtained by the method of the embodiment.

[0021] Figure 8 This is a diagram showing k-space data measured in the second embodiment.

[0022] Figure 9 This is a diagram showing the image reconstruction steps in the second embodiment.

[0023] Figure 10 This is a diagram showing an example of the irradiation phase in the third embodiment.

[0024] Figure 11 Is the representation set to Figure 10 A graph showing the signal intensity of an FID signal image under the illumination phase.

[0025] Figure 12 This is a diagram showing the imaging process of the third embodiment.

[0026] Description of Reference Numerals

[0027] 11: Static magnetic field generator, 12: Gradient magnetic field generator, 13: Transmitter (high-frequency transmitter), 14: Receiver, 15: Signal processor, 16: Sequencer, 20: Calculator, 30: Control unit, 50: Computer DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the MRI apparatus according to the present invention will be described with reference to the accompanying drawings.

[0029] The MRI apparatus 100 mainly comprises: an imaging unit including a static magnetic field generating magnet, a high frequency transmitting unit, a receiving unit, and a gradient magnetic field generating unit; a control unit 30 for controlling the imaging unit according to a predetermined pulse sequence; and a computing unit 20 for reconstructing an image using echo signals collected by the imaging unit. Figure 1 As shown, the apparatus includes a static magnetic field generator 11 , a gradient magnetic field generator 12 , a transmitter 13 , a receiver 14 , a signal processor 15 , and a sequencer 16 .

[0030] The static magnetic field generating unit 11 includes a static magnetic field generating magnet (not shown) of a permanent magnet type, a normal conductivity type, or a superconducting type. Depending on the direction of the static magnetic field generated by the static magnetic field generating magnet, there are different types of static magnetic field generating magnets, such as a vertical magnetic field type and a horizontal magnetic field type. 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 subject's body axis. In the horizontal magnetic field type, a uniform static magnetic field is generated in the space around the subject 1 in the direction of the subject's body axis.

[0031] The gradient magnetic field generating unit 12 includes: a gradient magnetic field coil 121 wound in the coordinate system (stationary coordinate system) of the MRI apparatus, i.e., in the three-axis directions of X, Y, and Z; and a gradient magnetic field power supply 122 for driving each gradient magnetic field coil. By driving the gradient magnetic field power supply 122 of each coil in accordance with commands from the sequencer 16, gradient magnetic fields Gx, Gy, and Gz in the three-axis directions of X, Y, and Z are applied to the static magnetic field.

[0032] The transmitter 13 is a unit that irradiates the subject 1 with high-frequency magnetic field pulses (RF pulses) in order to induce nuclear magnetic resonance in the nuclear spins of atoms constituting the biological tissue of the subject 1. The transmitter 13 includes a high-frequency oscillator 131, a modulator 132, a high-frequency amplifier 133, and a high-frequency coil (transmitting coil) 134 on the transmitting side. The modulator 132 amplitude-modulates the RF pulses output from the high-frequency oscillator 131 at a timing based on instructions from the sequencer 16. The amplitude-modulated high-frequency pulses are amplified by the high-frequency amplifier 133 and then supplied to the transmitting coil 134, which is positioned close to the subject 1, thereby irradiating the subject 1 with RF pulses.

[0033] The intensity and phase of the RF pulses are controlled by the modulator 132, enabling the output of 90-degree and 180-degree pulses of varying intensities, and their phases to be controlled. In this embodiment, a spin-echo pulse sequence, described later, is executed. In this case, the phases of the applied excitation pulses (90-degree pulses) and inversion pulses (180-degree pulses) are controlled. Details of this control are described later.

[0034] The receiving unit 14 detects echo signals (NMR signals) emitted by nuclear magnetic resonance of the atomic nuclear spins constituting the biological tissue of the subject 1. It comprises a receiving-side high-frequency coil (receiving coil) 141, a signal amplifier 142, a quadrature phase detector 143, and an A / D converter 144. The NMR signals of the subject 1, which are a response to the electromagnetic waves radiated from the transmitting coil 134, are detected by the receiving coil 141, which is positioned close to the subject 1. After being amplified by the signal amplifier 142, they are split into two orthogonal signals by the quadrature phase detector 143 at a timing based on instructions from the sequencer 16. These signals are then converted into digital quantities by the A / D converter 144 and sent to the signal processing unit 15. When a coil composed of a plurality of sub-coils is used as the receiving coil 141 , each sub-coil is connected to a signal amplifier 142 , a quadrature phase detector 143 , and an A / D converter 144 , and the signal processing unit 15 collects signals for each sub-coil.

[0035] The signal processing unit 15 includes an external storage device 151 such as an optical disk or magnetic disk, a display 152, and an operation unit 153 including input devices such as a trackball, mouse, and keyboard. The signal processing unit 15 performs signal processing, image reconstruction, and other processes, and displays the results, namely, tomographic images of the subject 1, on the display 152 and stores them on a magnetic disk or other device in the external storage device 151. The operation unit 153 is located near the display 152, and the operator interactively controls various processes of the MRI apparatus through the operation unit 153 while viewing the display 152.

[0036] exist Figure 1 In the illustrated example, the MRI apparatus further includes a computer 50 having a CPU and memory. Computer 50 implements some of the functions of the aforementioned signal processing unit 15, as well as the functions of the computing unit 20 and the control unit 30. Furthermore, some or all of the functions of the computing unit 20 are included in the signal processing unit 15 and are executed by the CPU by reading a predetermined program stored in a storage device. Some of the functions performed by computer 50 can also be implemented using hardware such as an ASIC or FPGA.

[0037] The sequencer 16 is a control unit that repeatedly applies the above-mentioned RF pulses and gradient magnetic field pulses in a given pulse sequence. It 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 transmission unit 13, the gradient magnetic field generation unit 12, and the reception unit 14.

[0038] Pulse sequences vary depending on the imaging method and are pre-stored in a storage device. The user determines the imaging sequence by selecting a desired pulse sequence through the operation unit 153 and setting imaging parameters such as the echo time (TE), repetition time (TR), imaging field of view (FOV), and magnification rate for parallel imaging. In this embodiment, the sequencer 16 executes a spin echo pulse sequence.

[0039] exist Figure 2 An example of a typical spin echo pulse sequence 200 is shown in FIG. In this pulse sequence, as shown, a 90-degree pulse 211 is applied along with a slice gradient magnetic field 221 for selecting a given cross section of the subject 1 to excite spins within the given cross section. Next, a phase encoding gradient magnetic field 231 is applied, and a 180-degree pulse 212 is applied along with a slice gradient magnetic field 222 at half the echo time (TE / 2). This generates an echo signal (NMR signal) 251 with a peak value within the echo time. This echo signal is collected for a given sampling time while applying a frequency encoding gradient magnetic field 241. After a given repetition time TR, the above-described process from spin excitation to echo signal collection is repeated while varying the intensity of the phase encoding gradient magnetic field 231, collecting echo signals for the set phase encoding number. Signal 261, shown as a dotted line in the figure, is the FID signal generated by the 180-degree pulse 212.

[0040] in addition, Figure 2 The two-dimensional imaging sequence in which the phase encoding gradient magnetic field 231 is applied in one axis direction (Gp) is shown, but a three-dimensional imaging sequence in which the phase encoding gradient magnetic field 231 is applied in two axis directions may also be used. Figure 2 , a case is shown in which one echo signal 251 is generated after one excitation and collected, but a multi-echo sequence may be used in which a plurality of echo signals are generated using a plurality of 180-degree pulses.

[0041] The MRI apparatus of this embodiment is characterized by controlling the phase of the 180-degree pulse when executing the above-mentioned spin echo pulse sequence. An embodiment of the control according to the k-space data acquisition method will be described below.

[0042] <Implementation Method 1>

[0043] In this embodiment, Figure 2In the repetition of the sequence shown, the phase encoding step is varied by thinning out at a set rate to perform parallel imaging. Figure 3 The imaging method shown here involves thinning out k-space data in the phase direction at a predetermined rate and using calculations to infer unmeasured phase-encoded data, thereby obtaining an image without foldback. Several parallel imaging reconstruction methods (such as the SENSE method, the GRAPPA method, and the CAIPIRINHA method) have been established to reconstruct an image without foldback. However, these methods cannot simply separate the non-phase-encoded FID signal from the original image signal. Therefore, artifacts caused by the FID signal occur, and conventional inversion pulse phase control (0-π control) cannot control the location of these artifacts in the parallel imaging image.

[0044] The MRI apparatus of this embodiment eliminates FID artifacts by setting the irradiation phase of the inversion RF pulse to a quadratic function of phase encoding and applying the phase encoding while changing it within the range of 0 to 360 degrees using the actual phase encoding number as a coefficient.

[0045] Specifically, for each measured echo signal, the irradiation phase θ of the inversion RF pulse is controlled by equation (1).

[0046]

Mathematical formula 1

[0047]

[0048] Here, k is the phase encoding applied to the echo signal, and N is the actual phase encoding number, expressed as N = #ph / R, when the number of encodings in the original image is #ph and the thinning-out rate is R. Furthermore, since the numerator on the right side only needs to be an odd multiple of π, the coefficient (2l+1) (where 1 is an integer greater than or equal to 0) is provided for generality (the definitions of the symbols in the formula apply similarly below).

[0049] exist Figure 4 The phase of equation (1) is shown. In the figure, the horizontal axis represents the phase encoding, and the vertical axis represents the irradiation phase of the 180-degree pulse. In conventional methods, the phase θ between adjacent phase encodings is either 0 or π. However, in the phase control of this embodiment, the phase becomes a quadratic function of the phase encoding, folding back through the coefficient (2l+1). However, when it does not fold back and is continuous, it becomes a continuous quadratic function curve.

[0050] Next, a description will be given of how the FID artifact is eliminated by the above-described phase control.

[0051] The FID signal when RF irradiation is performed at the phase represented by equation (1) is represented by equation (2).

[0052]

Mathematical formula 2

[0053]

[0054] The FID signal becomes a signal obtained by Fourier transforming equation (2) in the image space and can be expressed by equation (3).

[0055]

Mathematical formula 3

[0056]

[0057] At this time, the absolute value of the image of the FID signal becomes equation (4).

[0058]

Mathematical formula 4

[0059]

[0060] exist Figure 5 The results of plotting Equation (4) relative to pixel positions are shown. Figure 5 In the figure, the horizontal axis is the position (y) in the phase encoding direction, and the vertical axis is the signal strength. Figure 5 As is known, the absolute value of the signal intensity is constant regardless of the position in the phase encoding direction, and the FID signal is uniformly dispersed. Therefore, the FID signal does not appear as an artifact at a specific position on the image.

[0061] exist Figure 6 The imaging process of the MRI apparatus of this embodiment is shown in FIG. As shown in the figure, the imaging conditions including the rate are initially set by user specification or inspection protocol (S61). The control unit 30 uses the set rate and measurement matrix size (phase encoding number) to determine the irradiation phase of the 180-degree pulse by formula (1) and sets the transmitter 13 (S62). The sequencer 16 uses the set imaging conditions to calculate the spin echo pulse sequence and starts imaging. During imaging, the transmitter 13 controls the 180-degree pulse with the set irradiation phase (S63).

[0062] After imaging is performed by controlling the irradiation phase of the inverted RF pulses in this manner, image reconstruction is performed according to a parallel imaging algorithm using the echo signals collected by the computing unit 20 (S64). The image reconstruction technique is the same as that of a conventional MRI apparatus, and thus, a high-quality image can be obtained without the FID signal appearing as an artifact.

[0063] According to this embodiment, artifacts caused by FID signals can be substantially eliminated in imaging using a spin echo sequence, thereby enabling the parallel imaging magnification rate to be set high and achieving faster imaging speed.

[0064] exist Figure 7 The following figure shows the results of comparing images acquired using the MRI apparatus of this embodiment with images acquired using conventional phase control of inverted RF pulses. (A) shows the conventional method, and (B) shows the conventional method. Both figures illustrate imaging with a magnification rate R set to 2. While the conventional method shows FID signals as artifacts at the locations indicated by arrows, these artifacts are no longer visible in the images acquired using this embodiment.

[0065] The above describes the embodiment for parallel imaging. However, this embodiment can also be applied to the case where measurement is performed without demarcating the k-space (when R in equation (1) is 1), and the same effect of eliminating artifacts of the FID signal is achieved.

[0066] <Implementation Method 2>

[0067] In this embodiment, when an imaging method (asymmetric measurement method) in which a portion of k-space is left unmeasured is used, phase control of the inversion RF pulse is performed. The pulse sequence is a spin echo pulse sequence, which is the same as in the first embodiment. However, in this embodiment, Figure 8 As shown, a portion 820 of the high-frequency region in the phase encoding direction of the k-space data 800 is not measured to achieve high speed. The measurement region 810 is not essential, but may be thinned out at a predetermined thinning rate.

[0068] In this embodiment, the flow of actions is similar to Figure 6 Similarly, imaging is performed by controlling the inverted RF pulse irradiation phase. Phase control uses equation (1), where N is the phase encoding number #ph for the image, including the unmeasured region 810. When parallel imaging is performed, N = #ph / R, as in the embodiment.

[0069] The computing unit 20 uses the echo signals collected by controlling the phase of the inverted RF pulses as described above to reconstruct the image. However, prior to this, processing is performed to virtually generate FID signals for the unmeasured region. Specifically, in the asymmetric measurement method, image reconstruction is performed by, for example, zero-filling the unmeasured region 820. However, in this case, the FID signal that would have been generated if measurement had been performed is not reflected. Therefore, the influence of the FID signal differs between the measured region 810 and the unmeasured region 820.

[0070] Therefore, the calculation unit 20 first estimates the FID signal of the region using the data of the region 810A symmetrical to the unmeasured region 820 with respect to the axis in the ky direction of the k-space (phase encoding 0). Figure 9The image reconstruction steps in this embodiment are shown ( Figure 6 : S64) details. In this embodiment, as Figure 9 As shown, specifically, the absolute value of the complex signal of region 810A is calculated (S641), and the phase of the phase encoding corresponding to region 820 is calculated using equation (1) (S642). The calculated absolute value and phase of region 820 are used to virtually create a complex signal of the FID signal of region 820. In the case of parallel imaging, the signal of region 820 is created at the same thinning-out rate as that of region 810. This results in k-space data that evenly fills the entire k-space (S643).

[0071] The operation unit 20 uses the k-space data to perform normal image reconstruction or image reconstruction including parallel imaging operation (S644). In the image thus obtained, the echo signal is reconstructed as it is, and the FID signal component without phase encoding is not reconstructed as it is. Figure 5 As shown, the phase encoding direction is uniform overall and therefore does not appear as an artifact in the image.

[0072] In this embodiment, as in the first embodiment, when parallel imaging is used, its magnification rate can be increased, and further speed-up can be achieved by combining it with asymmetric measurement.

[0073] <Implementation Method 3>

[0074] While the first and second embodiments perform irradiation phase control to make the FID signal uniform over the entire phase encoding direction, the present embodiment performs irradiation phase control to confine the FID artifact to only a predetermined region of the image.

[0075] As described using equations (1) to (4), in order to make the FID signal uniform, in the first embodiment, π is used as a reference and k is multiplied thereto. 2 / N, the irradiation phase θ is calculated. However, in this embodiment, φ (≠π) is used as a reference phase. That is, the irradiation phase is calculated by the following formula (5).

[0076]

Mathematical formula 5

[0077]

[0078] Where φ satisfies φ>π or φ<π. Figure 10 The phase of equation (5) is shown in the case of φ=64π / 18. Figure 4As can be seen from the comparison, when π is used as the reference phase, the phase change becomes symmetrical about the center of the phase encoding direction. In contrast, when φ is not π, the phase change becomes asymmetrical about the k space.

[0079] The absolute value of the phase FID signal in the image space is as follows: Figure 11 As shown, the area indicated by the arrow in (A) increases, but the area indicated by the arrow in (B) is almost zero. Therefore, by making the area required for diagnosis (region of interest) within the image where the signal intensity of the FID signal is zero, a good image free of artifacts can be obtained for the region of interest.

[0080] exist Figure 12 An example of the operation of this embodiment is shown. Figure 12 In, with Figure 6 The same steps are denoted by the same reference numerals, and repeated descriptions are omitted.

[0081] As imaging conditions, the control unit 30 accepts not only the settings of the magnification rate and imaging parameters, but also the settings of the desired region of interest (S611). Next, it determines the φ that does not cause the FID artifact to appear in the region (S612), and determines the irradiation phase of the 180-degree pulse (S62) by formula (5). As for the region where the signal intensity in the image space of the FID signal is zero (FID zero region), it is possible to predict the region based on the deviation of φ from π, so it is determined that the region of interest is included in the predicted region. Alternatively, it is also possible to pre-calculate multiple φs. Figure 10 The FID zero area shown in the figure is registered together with φ, and φ in which the area including the area set as the target area is set as the absolute value zero area can be selected from the pre-registered φ.

[0082] In addition, when there is no FID zero region including the set target region, it is also possible to use equation (1) instead of equation (5).

[0083] Thereafter, imaging is performed and normal image reconstruction or image reconstruction including parallel imaging calculation is performed, which is similar to the first embodiment (S63, S64).

[0084] According to this embodiment, the FID signal can be made substantially zero with respect to the target region. In addition, this embodiment can also be implemented in combination with the above-mentioned embodiment 2.

Claims

1. A magnetic resonance imaging device, characterized in that have: A static magnetic field generating magnet that produces a static magnetic field; A high-frequency transmitter that irradiates a subject placed in a static magnetic field with RF pulses; a receiving unit for receiving an echo signal generated from the subject; a gradient magnetic field generating unit that generates a gradient magnetic field for encoding the echo signal; a control unit that controls the high-frequency transmitting unit, the receiving unit, and the gradient magnetic field generating unit according to a given pulse sequence; and a computing unit for performing image reconstruction using the echo signal; In imaging using 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 as the pulse sequence, the high-frequency transmitting unit changes the phase of the inversion RF pulse so as to become a quadratic function of the phase encoding in accordance with the phase encoding and the number of phase encodings given to each echo signal.

2. The magnetic resonance imaging apparatus according to claim 1, wherein When the phase encoding is k and the phase encoding number or the actual phase encoding number obtained by dividing the phase encoding number by the thinning rate is N, the phase θ of the inversion RF pulse is represented by the following equation (1): 【Mathematical formula 1】 Wherein, l is an integer greater than 0.

3. The magnetic resonance imaging apparatus according to claim 2, wherein: The control unit is a unit that controls the k-space data to be undersampled at a predetermined thinning-out rate R in the phase encoding direction. The high-frequency transmitting unit controls the phase of the inversion RF pulse using the substantial phase encoding number as N represented by the equation (1).

4. The magnetic resonance imaging apparatus according to claim 2, wherein The control unit is a means for performing control to set a portion of a high-frequency region in the phase encoding direction of k-space data as unmeasured. Regarding the unmeasured high-frequency region, the calculation unit creates data of the unmeasured high-frequency region using the absolute value of the measured signal of another high-frequency region and the phase of the inversion RF pulse calculated for the unmeasured high-frequency region.

5. The magnetic resonance imaging apparatus according to claim 4, wherein The control unit is a unit that controls the k-space data to be measured to be undersampled at a predetermined thinning-out rate R in the phase encoding direction. The high-frequency transmitting unit controls the phase of the inversion RF pulse using the substantial phase encoding number as N represented by the equation (1).

6. The magnetic resonance imaging apparatus according to claim 1, wherein When the phase encoding is k and the phase encoding number or the actual phase encoding number obtained by dividing the phase encoding number by the thinning rate is N, the phase θ of the inversion RF pulse is represented by the following equation (5): 【Mathematical formula 2】 Wherein, φ≠nπ: n is an integer greater than 1, and l is an integer greater than 0.

7. The magnetic resonance imaging apparatus according to claim 6, wherein: The control unit is a unit that controls the k-space data to be measured to be undersampled in the phase encoding direction at a predetermined thinning-out rate R. The high-frequency transmitting unit controls the phase of the inversion RF pulse using the actual phase encoding number obtained by dividing the phase encoding number of the image by the speed multiplication number R as N represented by the equation (5).

8. The magnetic resonance imaging apparatus according to claim 6, wherein The magnetic resonance imaging apparatus further comprises: A receiving unit that receives designation of an area of ​​interest, The high frequency transmitter calculates the phase θ of the inversion RF pulse that sets the pixel value generated by the FID signal to substantially zero or constant in the target region received by the receiver, and controls the phase of the inversion RF pulse to achieve the calculated phase.

9. A method for controlling a magnetic resonance imaging device, characterized in that: 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 is performed. At this time, the irradiation phase of the inversion RF pulse is changed according to the phase encoding and the number of phase encodings given to each echo signal so as to become a quadratic function of the phase encoding.

10. The method for controlling a magnetic resonance imaging apparatus according to claim 9, wherein: Execute the pulse sequence at a given rate, When the phase encoding is k and the actual phase encoding number obtained by dividing the phase encoding number by the multiplication rate is N, the irradiation phase of the inversion RF pulse is set to the phase θ represented by the following formula (1), 【Mathematical formula 1】 Wherein, l is an integer greater than 0.

Images