JP2013121437A - MAGNETIC RESONANCE IMAGING APPARATUS AND T1ρ IMAGING METHOD - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus and a T1ρ imaging method which are configured such that even if a magnetic field of RF radiation is temporally varied, spatial inhomogeneity of the magnetic field of RF radiation is compensated, and generation of artifact in a T1ρ-weighted image is prevented.SOLUTION: Based on T1ρ sequence consisting of a spin-lock sequence for locking the spins in a subject around an effective magnetic field in a rotating coordinate system, using a spin-lock RF pulse, and a main measurement sequence for measuring an echo signal from magnetization decayed with a time constant T1ρ during the spin-locking, the echo signal from the subject is measured, and the measured echo signal is used to obtain a T1ρ-weighted image of the subject. At the time, around half (T/2) of a spin-lock time (T) being a time for application of spin-lock RF pulse, the phase of the spin-lock RF pulse is changed by 180°, or a 180 degree pulse is applied.

Description

  The present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as “MRI apparatus”) using a nuclear magnetic resonance phenomenon, and in particular, a longitudinal relaxation time in a rotating coordinate system using a spin-locked RF pulse to which an RF pulse is continuously applied. The present invention relates to a technique for obtaining a T1ρ-weighted image or a T1ρ-value image using T1ρ.

  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.

  In the MRI apparatus, a technique for obtaining a T1ρ-weighted image or a T1ρ value image using T1ρ that is a time constant of T1 relaxation of magnetization (spin) in a rotating coordinate system is known (for example, Patent Document 1). In this technique, weighting is performed by T1ρ relaxation with a spin-lock RF pulse, and then a T1ρ-weighted image is generally obtained by an imaging method such as a gradient echo method. Then, multiple T1ρ-weighted images with different T1ρ-weighted degrees are acquired by changing the application time of the spin-lock RF pulse and imaging multiple times, and T1ρ values are calculated for each pixel using these multiple T1ρ-weighted images. To obtain a T1ρ value image.

  In the spin lock, the spin rotates around the effective magnetic field in the rotating coordinate system, and such spin rotation depends on the static magnetic field and the irradiation RF magnetic field. Therefore, the spatial nonuniformity of the static magnetic field and the spatial nonuniformity or temporal variation of the irradiation RF magnetic field adversely affect the spin rotation. Therefore, it can be said that the T1ρ imaging method is prone to generate artifacts.

  Therefore, in order to compensate for the spatial non-uniformity of the irradiation RF magnetic field, there is a technique (Non-patent Document 1) that reverses the phase of the irradiation RF magnetic field at exactly half the irradiation time of the spin lock RF pulse. Alternatively, a technique for applying a 180 ° pulse at just half the irradiation time of a spin-lock RF pulse has also been proposed (Non-Patent Document 2).

Japanese Unexamined Patent Publication No. 60-231145

Charagundla et. Al. J. Magn. Reson. 162 (2003) 113-121 Witschey et. Al. J. Magn. Reson. 186 (2007) 75-85

  As described above, the technology that reverses the phase of the irradiation RF magnetic field and the technology that applies the 180 ° pulse in just half the irradiation time of the spin-lock RF pulse are technologies that compensate for the spatial nonuniformity of the irradiation RF magnetic field. .

  On the other hand, in the T1ρ imaging method, an irradiation RF magnetic field with a strong intensity must be applied for a long time, but it may be difficult to keep the output of the RF amplifier constant for a long time. That is, the irradiation RF magnetic field may fluctuate with time due to fluctuations in the output of the RF amplifier. Such a temporal variation of the irradiation RF magnetic field cannot be compensated only by a technique of inverting the phase of the irradiation RF magnetic field or a technique of applying a 180 ° pulse in exactly half the irradiation time of the spin lock RF pulse. As a result, the spatial inhomogeneity of the irradiation RF magnetic field cannot be compensated, and an artifact is generated in the T1ρ-weighted image. When the T1ρ value image is calculated from this, the quantitativeness is lowered.

  Therefore, the present invention has been made in view of the above problems, and even if the irradiation RF magnetic field fluctuates with time, spatial nonuniformity of the irradiation RF magnetic field can be compensated for, and artifacts are generated in the T1ρ-weighted image. It is to provide an MRI apparatus and T1ρ imaging method that can be prevented.

In order to solve the above problems, the present invention provides a spin lock sequence unit for spin-locking a spin of an object around an effective magnetic field of a rotating coordinate system using a spin-lock RF pulse, and a time constant T1ρ during spin lock. Based on the T1ρ sequence consisting of this measurement sequence unit that measures the echo signal from the magnetization attenuated in step 1, the echo signal from the subject is measured, and the T1ρ-weighted image of the subject is measured using the measured echo signal get. At that time, the phase of the spin lock RF pulse is changed by 180 ° or a 180 ° pulse is applied before and after half of the spin lock time (T _SL ) which is the application time of the spin lock RF pulse (T _SL / 2). To do.

  According to the MRI apparatus and the T1ρ imaging method of the present invention, even if the irradiation RF magnetic field fluctuates with time, it is possible to compensate for the spatial nonuniformity of the irradiation RF magnetic field and to prevent occurrence of artifacts in the T1ρ-weighted image. It becomes.

1 is a block diagram showing the overall configuration of an embodiment of an MRI apparatus according to the present invention. It is an example of the pulse sequence for implement | achieving T1 (rho) imaging method, Comprising: The sequence chart which showed the application order of the RF pulse in it in detail. (a) is a diagram for explaining a technique for inverting the phase of the spin lock pulse by 180 ° with exactly half the spin lock time (T _SL ) (T _SL / 2). (b) is a diagram for explaining a technique for applying a 180 ° pulse at half the irradiation time of a spin-lock RF pulse. The figure which shows a mode that the amplitude of a spin lock RF pulse reduces gradually by the output of RF amplifier falling gradually during application of a spin lock RF pulse. (a) The figure which shows the example which increased / decreased the timing which changes the phase of the spin lock RF pulse 203 180 degree | times from the center ( _TSL / 2) of the application time of this spin lock RF pulse 203. FIG. FIG. 6B is a diagram showing an example in which a 180 ° pulse is applied at a timing increased or decreased by Δt from the center (T _SL / 2) of the application time of the spin lock RF pulse 203. FIG. 4A is a functional block diagram illustrating functions of an arithmetic processing unit 114 for realizing the T1ρ imaging method according to the first embodiment. (b) is a flowchart showing a processing flow of the first embodiment. (a) is a functional block diagram showing each function of the arithmetic processing unit 114 for realizing the T1ρ imaging method of the second embodiment. (b) is a flowchart showing a processing flow of the second embodiment. A sequence chart in which an echo signal or an FID signal is obtained by changing the shift time Δt a plurality of times with the unit time τ as a unit before and after the center of the spin lock time (T _SL / 2). FIG. 9 is a graph showing the relationship between the signal strength of each FID signal or gradient echo signal measured in the sequence of FIG. 8 and the shift time Δt. (a) is a functional block diagram showing each function of the arithmetic processing unit 114 for realizing the T1ρ imaging method of the third embodiment. (b) is a flowchart showing the processing flow of the third embodiment. (a) is a functional block diagram showing each function of the arithmetic processing unit 114 for realizing the T1ρ imaging method of the fourth embodiment. (b) is a flowchart showing the processing flow of the fourth embodiment.

  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 and RF transmitter 110, RF receiver coil 105 and signal processor 107, measurement control unit 111, overall control unit 112, display / operation unit 113, and top plate on which the subject 101 is mounted generates a static magnetic field. And a bed 106 to be taken in and out of the magnet 102.

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

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

  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 irradiation RF magnetic field pulse (hereinafter abbreviated as an RF pulse), and is connected to the RF transmission unit 110 and supplied with a high-frequency pulse current. As a result, an NMR phenomenon is induced in the spins of atoms constituting the living tissue of the subject 101. Specifically, the RF transmission unit 110 is driven in accordance with a command from the measurement control unit 111 (to be described later), amplitude-modulates and amplifies the high-frequency pulse, and then the RF transmission unit 104 is placed near the subject 101 after being amplified. By supplying, the subject 101 is irradiated with the 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, and is connected to the signal processing unit 107 so that the received echo signal is sent to the signal processing unit 107. Sent.

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

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

  The overall control unit 112 controls the measurement control unit 111 and controls various data processing and processing result display and storage, and includes an arithmetic processing unit (CPU) 114, a memory 113, and a magnetic disk. And the like, and a network IF 116 that interfaces with an external network.

  Further, an external storage unit 117 such as an optical disk may be connected to the overall control unit 112. Specifically, 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 113. Hereinafter, the statement that the echo data is arranged in the k space means that the echo data is stored in an area corresponding to the k space in the memory 113.

  A group of echo data stored in an area corresponding to the k space in the memory 113 is also referred to as k space data. The arithmetic processing unit 114 performs processing such as signal processing and image reconstruction by Fourier transform on the k-space data, and displays the resulting image of the subject 101 on the display / operation unit 113 described later. The data is recorded in the internal storage unit 115 or the external storage unit 117, or transferred to an external device via the network IF 116.

  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 112. 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 information on the spatial distribution of proton density and the spatial distribution of relaxation time in the excited state, the form or function of the human head, abdomen, limbs, etc. is imaged two-dimensionally or three-dimensionally.

(About T1ρ imaging method)
First, the T1ρ imaging method will be described. FIG. 2 is an example of a pulse sequence for realizing the T1ρ imaging method, and is a sequence chart showing in detail the application order of RF pulses therein.

  The T1ρ imaging method uses a spin lock sequence unit 201 to lock the spin around the effective magnetic field of the rotating coordinate system (spin lock), and this measurement to measure echo signals from magnetization attenuated by the time constant T1ρ during spin lock A T1ρ sequence composed of the sequence unit 211 is repeated every repetition time (TR) to acquire a T1ρ-weighted image.

  The spin lock sequence unit 201 includes a pair of 90 ° pulses (202, 204) having a phase difference of 180 ° and a spin lock RF pulse 203 sandwiched between the pair of 90 ° pulses.

  A pair of 90 ° pulses, for example, as shown in FIG. 2, excites magnetization in a rotating coordinate system by 90 ° + x pulse 202 that excites + 90 ° around the x axis and −90 ° around the x axis. 90 ° -x pulse 204. That is, the magnetization excited by the 90 ° + x pulse 202 and the magnetization excited by the 90 ° -x pulse 204 are directed in opposite directions. Therefore, the phase of the pair of 90 ° pulses (202, 204) is They will be 180 ° different from each other.

The spin lock RF pulse 203 is an RF pulse whose application time (spin lock time (T _SL )) is several ms to several tens of ms or more (about the T1ρ value of the subject, for example, a value of 50 msec or less). In (T _SL ), the magnetization is attenuated by the time constant T1ρ of T1 relaxation in the rotating coordinate system, and the magnetization is weighted. In the conventional T1ρ imaging method, the irradiation intensity of the spin lock RF pulse is constant.

  Then, since the echo signal from the magnetization weighted as described above is measured by the measurement sequence unit 211, the intensity of the measured echo signal is also weighted by the time constant T1ρ. Therefore, an image reconstructed from this echo signal is enhanced with the time constant T1ρ, and a T1ρ-weighted image can be obtained.

In addition, by changing the spin lock time (T _SL ), acquiring a plurality of images with different degrees of T1ρ enhancement, and calculating the T1ρ value for each pixel using the plurality of T1ρ enhanced images, A T1ρ value image representing the distribution of T1ρ values for each pixel can also be acquired.

(Effect of spatial nonuniformity of irradiation RF magnetic field)
In spin lock, since the spin rotates around the effective magnetic field when viewed in the rotating system, the behavior of magnetization varies spatially due to the spatial inhomogeneity of both the static magnetic field and the irradiation RF magnetic field that affect the direction of the effective magnetic field. To do. As a result, when the spatial uniformity of both the static magnetic field and the irradiated RF magnetic field is not sufficient and non-uniform, striped artifacts appear in the T1ρ-weighted image depending on these spatial non-uniformities. May end up.

Therefore, among these effects, as a first method for compensating the spatial non-uniformity of the irradiation RF magnetic field, as shown in FIG. 3 (a), the irradiation RF magnetic field in the spin lock (spin lock RF pulse) There is a technique that reverses the phase of 180 ° by exactly half the spin lock time (T _SL ) (T _SL / 2). In FIG. 3 (a), + y and -y indicate the phases of the irradiation RF magnetic field, indicating that the 90 ° phase is different for the 90 ° pulse and that the 180 ° phase is different from each other. . Specifically, the spin lock time was divided into two, and the + y pulse 203-1 that rotates the magnetization around the y axis in the rotating coordinate system was applied to the first half of the spin lock time (T _SL / 2). Later, a -y pulse 203-2 that counter-rotates around the y-axis is applied for the second half of the spin lock time (T _SL / 2). As a result, even if there is a spatial non-uniformity of the irradiation RF magnetic field, the spatial non-uniformity of the rotation amount (phase) generated during the application of the + y pulse 203-1 in the first half is changed to the -y pulse 203-2 in the second half. The amount of anti-rotation (anti-polarity phase) generated during the application of is canceled by the spatial nonuniformity. As a result, immediately after the end of the spin lock time (T _SL ) and immediately before the 90 ° -x pulse 203, the influence of spatial nonuniformity of the irradiation RF magnetic field is eliminated.

As a second method for compensating for the spatial nonuniformity of the irradiation RF magnetic field, as shown in FIG. 3 (b), there is a technique in which a 180 ° pulse is applied at half the irradiation time of the spin lock RF pulse. is there. In the second method, the phase of the spin lock RF pulse 203 is not changed during the spin lock time (T _SL ), and in the example of FIG. 3B, a + y pulse is used. Instead, a 180 ° pulse is applied at half the time (T _SL / 2) of the spin lock time (T _SL ). By applying a 180 ° pulse in the spin lock time (T _SL) in half the time (T _SL / 2), during the application of + y pulse 203-1 of the first half of half the spin lock time (T _SL / 2) The spatial non-uniformity of the rotation amount (phase) generated in Fig. 2 is reversed in polarity by the 180 ° pulse, and the rotation amount generated during the application of the second half (T _SL / 2) + y pulse 203-2 ( Canceled by spatial non-uniformity in phase). As a result, as in the first method, immediately after the end of the spin lock time (T _SL ) and immediately before the 90 ° -x pulse 203, the influence of spatial nonuniformity of the irradiation RF magnetic field is eliminated.

(Outline of the subject of the present invention and its solution)
The spin lock RF pulse is generally an RF pulse having a high intensity and a long application time. On the other hand, due to its characteristics, it is difficult for RF amplifiers to keep high output constant for a long time. When high output is continued for a long time, it is generally called droop due to the influence of heat generation etc. The output may decrease. FIG. 4 shows an example in which the output reduction of the RF amplifier occurs during application of the spin lock RF pulse. FIG. 4 shows how the amplitude of the spin-lock RF pulses 203-1 and 203-2 gradually decreases as the output of the RF amplifier gradually decreases during application of the spin-lock RF pulse.

From this, the uniformity of the irradiation RF magnetic field must consider not only spatial nonuniformity but also temporal nonuniformity. If there is instability in the temporal intensity of such a spin-lock RF pulse, the irradiation RF will be applied even if the phase is changed by 180 ° or a 180 ° pulse is applied at just half the spin-lock time (T _SL ). The spatial inhomogeneity of the magnetic field cannot be sufficiently compensated.

Therefore, in the present invention, the timing for changing the phase of the spin lock RF pulse by 180 ° or applying the 180 ° pulse is not half of the spin lock time (T _SL / 2), but before and after T _SL / 2. Basically, the spatial nonuniformity of the irradiation RF magnetic field is compensated more accurately by adjusting (time shift) to. Since the output of the RF amplifier generally decreases with time, the application intensity of the spin lock RF pulse also decreases with time. In that case, 180 ° phase change or 180 ° pulse application occurs before half of the spin lock time (T _SL / 2). Hereinafter, each embodiment of the present invention in which the 180 ° phase change of the spin lock RF pulse and the 180 ° pulse application are performed before and after half of the spin lock time (T _SL / 2) will be described in detail.

(Example 1)
First, a first embodiment of the MRI apparatus and T1ρ imaging method of the present invention will be described. In the first embodiment, the phase of the spin lock RF pulse is changed by 180 ° at a timing increased or decreased by Δt from the center (half) of the application time of the spin lock RF pulse. Hereinafter, the first embodiment will be described in detail based on FIG. 5 (a) and FIG.

First, the outline of the first embodiment will be described with reference to FIG. FIG. 5 (a) is a diagram showing an example in which the timing for changing the phase of the spin lock RF pulse 203 by 180 ° is increased or decreased by Δt from the center (T _SL / 2) of the application time of the spin lock RF pulse 203. . Specifically, under the condition that the entire spin lock time (T _SL ) is the same, the application time of the first half + y pulse 203-1 is T _SL / 2-Δt, and the second half -y pulse 203- The application time of 2 is T _SL / 2 + Δt.

This shift time Δt needs to be adjusted according to the measurement conditions, but is a value mainly depending on the spin lock time (T _SL ) and the characteristics of the RF amplifier.

  In general, the T1ρ imaging method is such that the applied intensity (Hz) of the spin lock RF pulse is fixed so that the rotation speed (Hz) of magnetization around the irradiation RF magnetic field is about several hundred Hz. The echo signal from the spin-locked magnetization is measured. Even when the measurement target such as the subject or the measurement conditions such as the receiving coil is changed, the gain of the RF amplifier is changed to keep the applied intensity (Hz) of the spin lock RF pulse the same. This is common. When the gain (gain) of the RF amplifier is changed, the degree of temporal variation of the application intensity of the spin lock RF pulse changes. Therefore, it is better to obtain the optimum value of the shift time Δt according to the measurement conditions.

On the other hand, if the gain of the RF amplifier and the spin lock time (T _SL ) are determined, a certain degree of reproducibility is expected for the temporal variation of the output of the RF amplifier and the resulting temporal variation of the applied intensity of the spin lock RF pulse. it can. Therefore, using the gain of the RF amplifier and the spin lock time (T _SL ) as parameters, a suitable value or optimum value of the shift time Δt with respect to the values of these two parameters (hereinafter referred to as an optimum value collectively including preferred values) It will be sufficient to set.

The spin lock time (T _SL ) is a value that is set and input as a measurement condition by the operator in order to obtain an image with a desired T1ρ enhancement degree, and a value of several ms to several tens of ms is input and set. On the other hand, the gain characteristic of the RF amplifier differs for each RF amplifier, and also depends on the output value of the RF amplifier (that is, the applied intensity of the spin lock RF pulse) determined based on the measurement conditions. From the above, it is desirable to obtain the optimum value of the shift time Δt each time the measurement conditions are changed such that the spin lock time (T _SL ) or the output value of the RF amplifier changes.

  Hereinafter, the first embodiment will be described assuming that a preset value, for example, a value stored in the internal storage unit 115 or the external storage unit 117, is used as the optimum value of the shift time Δt.

  Next, each function of the arithmetic processing unit 114 for realizing the T1ρ imaging method of the first embodiment will be described based on the functional block diagram shown in FIG. The arithmetic processing unit 114 according to the first embodiment includes an imaging condition setting unit 601, a spin lock time setting unit 602, an RF amplifier gain setting unit 603, a phase change timing setting unit 604, a T1ρ sequence setting unit 605, It has.

The imaging condition setting unit 601 displays an imaging condition setting GUI on the display unit of the display / operation unit 113, and accepts setting input by the operator for the values of various imaging parameters regarding the imaging conditions. In particular, the display of a spin lock time (T _SL ) setting GUI and its setting input are accepted.

The spin lock time setting unit 602 sets the value of the spin lock time (T _SL ) based on the value of the imaging parameter related to the imaging condition input and set via the imaging condition setting unit 601.

  Based on the imaging conditions set by the imaging condition setting unit 601, the RF amplifier gain setting unit 603 sets an RF amplifier gain for irradiating the subject with the spin lock RF pulse 203 with a desired applied intensity. For example, based on the RF amplifier gain for outputting a reference RF pulse (for example, 90 ° pulse), a predetermined coefficient is multiplied to obtain an RF amplifier gain for making the spin lock RF pulse 203 have a desired applied intensity. Also good.

The phase change timing setting unit 604 is based on the spin lock time (T _SL ) set by the spin lock time setting unit 602 and the RF amplifier gain set by the RF amplifier gain setting unit 603. A shift time Δt to be increased / decreased from the center (T _SL / 2) of the spin lock time, which is a shift time for changing the phase of 203 by 180 °, is set. In the first embodiment, a value set in advance according to the spin lock time (T _SL ) and the RF amplifier gain, for example, a value stored in the internal storage unit 115 or the external storage unit 117 is used as the shift time Δt.

The T1ρ sequence setting unit 605 includes the imaging conditions set by the imaging condition setting unit 601, the spin lock time (T _SL ) set by the spin lock time setting unit 602, and the RF set by the RF amplifier gain setting unit 603. Based on the amplifier gain and the shift time Δt set by the phase change timing setting unit 604, various control values of the T1ρ sequence shown in FIG. 5 (a) are specifically generated and notified to the measurement control unit 111. To execute the T1ρ sequence.

  Next, the processing flow of the first embodiment performed in cooperation with each of the functional units will be described based on the flowchart shown in FIG. 6 (b). This processing flow is stored in advance in the internal storage device 115 as a program, and is executed by the arithmetic processing unit 114 reading the program from the internal storage device 115 and executing it. Hereinafter, the processing contents of each processing step will be described in detail.

In step 651, the imaging condition setting unit 601 displays an imaging condition setting GUI on the display unit of the display / operation unit 113, and accepts setting input by the operator for the values of various imaging parameters regarding the imaging conditions. In particular, the imaging condition setting unit 601 displays a spin lock time (T _SL ) setting GUI and accepts the setting input.

In step 652, the spin lock time setting unit 602 sets the spin lock time (T _SL ) based on the imaging condition set in step 651.

  In step 653, the RF amplifier gain setting unit 603 sets an RF amplifier gain for irradiating the subject with the spin lock RF pulse 203 with a desired application intensity based on the imaging conditions set in step 651. The specific setting method is as described above.

In step 654, the phase change timing setting unit 604 changes the phase of the spin lock RF pulse 203 by 180 based on the spin lock time (T _SL ) set in step 652 and the RF amplifier gain set in step 653. ° Set shift time Δt for changing timing. The specific setting method is as described above.

In step 655, the imaging condition setting unit 605 sets the imaging condition set in step 651, the spin lock time (T _SL ) set in step 652, the RF amplifier gain set in step 653, and the step 654. Based on the set shift time Δt, various control values of the T1ρ sequence shown in FIG. 5 are specifically generated and notified to the measurement control unit 111 to execute the T1ρ sequence.

In step 656, the measurement control unit 111 executes the T1ρ sequence generated in step 655, and performs measurement control of the echo signal for acquiring the above-described T1ρ-weighted image.
The above is the description of the processing flow of the first embodiment.

As described above, in the MRI apparatus and the T1ρ imaging method of the first embodiment, the timing for changing the phase of the spinlock RF pulse by 180 ° is the spinlock time (T _SL ) that is the application time of the spinlock RF pulse. And a timing setting unit that sets a shift time for shifting to about half (T _SL / 2), and the measurement control unit changes the phase of the spin lock RF pulse by 180 ° at the timing set by the shift time. That is, the phase of the spin lock RF pulse 203 is changed by 180 ° at a timing that is increased or decreased by Δt from the center (T _SL / 2) of the application time of the spin lock RF pulse 203.

  As a result, even if the application intensity of the spin lock RF pulse 203 fluctuates over time, it is possible to compensate for the spatial nonuniformity of the application intensity of the spin lock RF pulse 203 and to prevent occurrence of artifacts in the T1ρ-weighted image. become.

  Specifically, in order to achieve spin lock, a long RF pulse output exceeding several tens of ms is required, so depending on the output characteristics of the RF amplifier, it is difficult to maintain a constant output for a long time. Even if there is a slight fluctuation, the fluctuation of the T1ρ value due to this influence can be compensated, and as a result, high reproducibility can be maintained in the T1ρ-weighted image, and quantitativeness can be improved in the T1ρ value image.

(Example 2)
Next, a second embodiment of the MRI apparatus and T1ρ imaging method of the present invention will be described. In Example 2, a 180 ° pulse is applied at a timing that is increased or decreased by Δt from the center (T _SL / 2) of the application time of the spin lock RF pulse 203 without changing the phase of the spin lock RF pulse 203 in the middle. To do. Hereinafter, the second embodiment will be described in detail based on FIG. 5 (b) and FIG.

First, the outline of the second embodiment will be described with reference to FIG. FIG. 5 (b) is a diagram showing an example in which a 180 ° pulse is applied at a timing increased or decreased by Δt from the center (T _SL / 2) of the application time of the spin lock RF pulse 203. Specifically, under the condition that the application time T _SL of the entire spin lock RF pulse (+ y pulse) is the same, the timing of applying the 180 ° pulse is advanced by Δt from (T _SL / 2), The time from the start of + y pulse 203-1 application to the center of the 180 ° pulse in the first half is T _SL / 2-Δt, and the time from the center of the latter 180 ° pulse to the end of application of the + y pulse 203-2 T _SL / 2 + Δt.

The shift time Δt needs to be adjusted according to the measurement conditions, as in the first embodiment, but is a value mainly depending on the spin lock time (T _SL ) and the characteristics of the RF amplifier.

  Next, each function of the arithmetic processing unit 114 for realizing the T1ρ imaging method of the second embodiment will be described based on a functional block diagram shown in FIG. Each function of the arithmetic processing unit 114 of the second embodiment includes a 180 ° pulse application timing setting unit 614 instead of the phase change timing setting unit 604 illustrated in FIG. 6A described in the first embodiment. . Other functions are the same as those of the first embodiment. Hereinafter, only functions different from those of the first embodiment will be described, and description of the same functions will be omitted.

The 180 ° pulse application timing setting unit 614 is based on the spin lock time (T _SL ) set by the spin lock time setting unit 602 and the RF amplifier gain set by the RF amplifier gain setting unit 603. a shift time for the timing of applying the 180 ° pulses before and after the center of the time (T _SL / 2), setting the time Δt is increased or decreased from the center of the spin lock time (T _SL / 2). A specific setting method is the same as the setting method in the phase change timing setting unit 604 of the first embodiment.

  Next, the processing flow of the second embodiment performed in cooperation with the above functional units will be described based on the flowchart shown in FIG. This processing flow is stored in advance in the internal storage device 115 as a program, and is executed by the arithmetic processing unit 114 reading the program from the internal storage device 115 and executing it. The processing flow of the second embodiment includes a step 664 instead of the step 654 shown in FIG. 6B described in the first embodiment. Other steps are the same as those in the first embodiment. Hereinafter, only steps different from those of the first embodiment will be described, and description of the same steps will be omitted.

In step 664, the 180 ° pulse application timing setting unit 614 applies a 180 ° pulse based on the spin lock time (T _SL ) set in step 652 and the RF amplifier gain set in step 653. Set the shift time Δt for. The specific setting method is as described above.
The above is the description of the processing flow of the second embodiment.

As described above, in the MRI apparatus and the T1ρ imaging method of the second embodiment, the timing of applying the 180 ° pulse is half the spin lock time (T _SL ) that is the spin lock RF pulse application time (T _SL / A timing setting unit for setting a shift time for shifting before and after 2) is provided, and the measurement control unit applies the 180 ° pulse at a timing set by the shift time during application of the spin lock RF pulse. That is, the 180 ° pulse is applied at a timing that is increased or decreased by Δt from the center (half) (T _SL / 2) of the application time of the spin lock RF pulse.

  As a result, as in the case of changing the 180 ° phase of the spin-lock RF pulse in Example 1 described above, even if the application intensity of the spin-lock RF pulse fluctuates with time, the space of the application intensity of the spin-lock RF pulse can be changed. Nonuniformity can be compensated, and artifacts can be prevented from occurring in the T1ρ-weighted image.

(Example 3)
Next, a third embodiment of the MRI apparatus and T1ρ imaging method of the present invention will be described. In the third embodiment, the preparation measurement for obtaining the optimum value of the shift time Δt is executed before the execution of the T1ρ sequence. In this preparatory measurement, the shift time Δt is changed multiple times before and after the center of the application time of the spin lock RF pulse 203 (T _SL / 2), and the echo signal or the FID signal is acquired respectively, and the intensity is maximized. Let Δt be the value of the shift time Δt. Hereinafter, the third embodiment will be described in detail by taking the case where the phase of the spin lock RF pulse described in the first embodiment is changed by 180 ° as an example. The 180 ° pulse described in the second embodiment is applied. The same applies to the case.

First, preparation measurement will be described with reference to FIG. FIG. 8 shows a sequence chart in which the shift time Δt is changed a plurality of times with the unit time τ as a unit before and after the center of the spin lock time (T _SL / 2), and the echo signal or the FID signal is respectively acquired. FIG. 8 (a) shows the case where the shift time Δt = 3τ, that is, the application time of the first + y pulse 203-1 is T _SL / 2-3τ, and the application time of the second half -y pulse 203-2 is T An example of _SL / 2 + 3τ is shown. FIG. 8 (b) shows the case where the shift time Δt = 2τ, that is, the application time of the first + y pulse 203-1 is T _SL / 2-2τ, and the application time of the second -y pulse 203-2 is T An example of _SL / 2 + 2τ is shown. FIG. 8 (c) shows the case where the shift time Δt = τ, that is, the application time of the first + y pulse 203-1 is T _SL / 2-τ and the application time of the second -y pulse 203-2 is T An example of _SL / 2 + τ is shown. In any case, after the spin lock sequence unit 201 in which the shift time Δt is set in this way, the measurement sequence unit 211 applies the readout gradient magnetic field 801 and measures the FID signal or the gradient echo signal 802.

  FIG. 9 shows an example in which the relationship between the signal strength of each FID signal or gradient echo signal measured as described above and the shift time Δt is shown in a graph. A curve 901 is a curve that approximates the plot points of each measured value, and Δt (1.5τ in the example of FIG. 9) 903 corresponding to the maximum value 902 of the approximate curve 901 is set as the optimum value of the shift time Δt.

  Next, each function of the arithmetic processing unit 114 for realizing the T1ρ imaging method of the third embodiment will be described based on the functional block diagram shown in FIG. Each function of the arithmetic processing unit 114 of the third embodiment is the same as that of the first embodiment, and is the same as the functional block diagram shown in FIG. 6 (a), but the phase change timing setting unit 604 and the T1ρ sequence setting. The function of the part 605 is different. As a result, the data flow among the phase change timing setting unit 604, the T1ρ sequence setting unit 605, and the measurement control unit 111 is bidirectional. Hereinafter, only functions different from those of the first embodiment will be described, and description of the same functions will be omitted.

  The phase change timing setting unit 604 performs the following processing in order to obtain the optimum value of the shift time Δt.

1) A value that is an integer multiple of unit time τ (m = 0, ± 1, ± 2,...) Is temporarily set as shift time Δt = mτ, and T1ρ sequence setting unit 605 performs preliminary measurement at this shift time mτ. Let it run.
2) Obtain the signal strength from the measured FID signal or echo signal data.
3) Repeat steps 1) and 2) above, changing the integer m.
4) A curve 901 that approximates the change in signal intensity obtained for each integer (m) value is obtained, and the time 903 corresponding to the value 902 at which the obtained curve is maximum is set as the optimum value of the shift time Δt.

Here, as the unit time τ, a time previously stored in the internal storage unit 115 or the external storage unit 117 may be used as τ. Alternatively, the shift time obtained by the same method as the method for setting the shift time Δt in the phase change timing setting unit 604 of the first embodiment is set as the candidate value Δt _cnd and the unit time τ is a natural number of the shift time candidate value Δt _cnd It may be 1 / n. That is, τ = Δt _cnd / n may be set.

  The T1ρ sequence setting unit 605 is a temporary setting value of the shift time Δt set by the phase change timing setting unit 604, and specifically generates various control values of the T1ρ sequence shown in FIG. Notify 111 to execute the preparation measurement sequence. Then, the phase change timing setting unit 604 is notified of the data of the FID signal or echo signal obtained by the measurement. Also, various control values of the T1ρ sequence shown in FIG. 5 (a) are specifically generated with the optimum value of the shift time Δt set by the phase change timing setting unit 604, and notified to the measurement control unit 111 to be Run the measurement sequence.

  Next, the processing flow of the third embodiment performed in cooperation with the above functional units will be described based on the flowchart shown in FIG. This processing flow is stored in advance in the internal storage device 115 as a program, and is executed by the arithmetic processing unit 114 reading the program from the internal storage device 115 and executing it. The processing flow of the third embodiment includes step 674 instead of step 654 shown in FIG. 6B described in the first embodiment, and further includes steps 676, 677, and 678. Other steps are the same as those in the first embodiment. Hereinafter, only steps different from those of the first embodiment will be described, and description of the same steps will be omitted.

In step 674, the phase change timing setting unit 604 performs spin lock RF for preparatory measurement based on the spin lock time (T _SL ) set in step 652 and the RF amplifier gain set in step 653. A unit time τ is set for the timing of changing the phase of the pulse 203 by 180 °. The specific setting method is as described above. Then, the phase change timing setting unit 604 temporarily sets a value that is an integer (m) times the unit time τ as the shift time Δt = mτ, notifies the T1ρ sequence setting unit 605, and notifies the T1ρ sequence setting unit 605 Preparation measurement is executed at the shift time mτ.

In step 675, the imaging condition setting unit 605, the imaging condition set in step 651, the spin lock time (T _SL ) set in step 652, the RF amplifier gain set in step 653, and the step 674 Based on the temporarily set shift time Δt = mτ, the T1ρ sequence shown in FIG. 5 (a) is used as a preparation measurement sequence, and various control values are specifically generated and notified to the measurement control unit 111. Run the preparatory measurement sequence.

  In step 676, the measurement control unit 111 executes the preparation measurement sequence set in step 675, and notifies the phase change timing setting unit 604 of the measured FID signal or echo signal data via the T1ρ sequence setting unit 605. To do.

  In Step 677, the phase change timing setting unit 604 determines whether or not the number of times of repeating the preparation measurement by changing m of the shift time Δt = mτ is finished, and if not finished (No), m is changed. To step 674. If completed (Yes), the process proceeds to step 656.

  In step 678, the phase change timing setting unit 604 obtains the signal strength from the FID signal or echo signal data measured for each integer (m) value, and the change in signal strength obtained for each integer (m) value. Is obtained, and a time 903 at which the obtained curve 901 is the maximum value 902 is determined as the optimum value of the shift time. Then, the optimum value of the obtained shift time Δt is notified to the T1ρ sequence setting unit 605.

  In step 656, the T1ρ sequence setting unit 605 uses the optimum value of the shift time Δt calculated in step 658 to specifically generate various control values for the T1ρ sequence shown in FIG. The unit 111 is notified to execute the T1ρ sequence.

  The above is the description of the processing flow of the third embodiment.

In order to obtain a T1ρ value image, it is necessary to change the spin lock time (T _SL ), which is the time for applying the spin lock RF pulse, and to capture T1ρ emphasized images having different T1ρ enhancement degrees a plurality of times. When the spin lock time (T _SL ) is changed, the temporal variation of the spin lock RF pulse application intensity also changes, so every time the spin lock time (T _SL ) is changed, the preparation measurement of Example 3 is executed and shifted. By obtaining the optimum value of time Δt, a more optimum T1ρ value image can be obtained.

As described above, the MRI apparatus and the T1ρ imaging method of the third embodiment change the shift time Δt a plurality of times before and after the center of the spin lock time (T _SL / 2), and respectively change the FID signal or the echo signal. Acquired and Δt at which the intensity is maximum is set as the optimum value of the shift time Δt. As a result, the spatial nonuniformity of the irradiation RF magnetic field can be optimally compensated, and artifacts can be prevented from occurring in the T1ρ-weighted image.

(Example 4)
Next, a fourth embodiment of the MRI apparatus and T1ρ imaging method of the present invention will be described. In the fourth embodiment, the relationship between the imaging parameter value of the T1ρ sequence and the actually measured value of the shift time Δt is stored in advance, and based on the relationship, the shift is performed according to the imaging parameter value of the set input T1ρ sequence. Find the time Δt. Hereinafter, the present Example 4 will be described in detail by taking as an example the case where the phase of the spin-lock RF pulse described in Example 1 is changed by 180 °, but the 180 ° pulse described in Example 2 is applied. The same applies to the case.

  First, the relationship between the imaging parameter value of the T1ρ sequence and the actually measured value of the shift time Δt will be described.

  According to the above-described Examples 1 to 3, the relationship between the imaging parameter value of the T1ρ sequence and the actually measured value of the shift time Δt is individually obtained for each imaging. These actually measured values of the shift time Δt obtained for each imaging are stored in the internal storage unit 115 or the external storage unit 117 in association with the imaging parameter values of the T1ρ sequence.

  At the time of another new imaging, the value of the shift time Δt stored in the internal storage unit 115 or the external storage unit 117 is searched based on the imaging parameter value of the T1ρ sequence that has been input and set. The value of the shift time Δt corresponding to the imaging parameter value of the T1ρ sequence or corresponding to the closest imaging parameter value is acquired. A T1ρ sequence is generated and executed using the acquired value of the shift time Δt.

  In the case where the internal storage unit 115 or the external storage unit 117 does not have the value of the shift time Δt corresponding to the imaging parameter value of the input T1ρ sequence, the above-described Examples 1 to 3 are performed, A shift time Δt corresponding to the imaging parameter value of the input T1ρ sequence is newly obtained. Then, the obtained value is stored in the internal storage unit 115 or the external storage unit 117 in association with the imaging parameter value of the T1ρ sequence that has been input and set.

As described above, since the imaging parameters mainly related to the shift time Δt are the spin lock time (T _SL ) and the RF amplifier gain, these values and the measured values of the shift time Δt are stored in association with each other. deep.

  Next, each function of the arithmetic processing unit 114 for realizing the T1ρ imaging method of the fourth embodiment will be described based on the functional block diagram shown in FIG. The arithmetic processing unit 114 according to the fourth embodiment does not include the spin lock time setting unit 602 and the RF amplifier gain setting unit 603 among the functions described in the first embodiment, and includes the phase change timing setting unit 604. Processing contents are different. Hereinafter, only functions different from those of the first embodiment will be described, and description of the same functions will be omitted.

  The phase change timing setting unit 604 searches for the value of the shift time Δt stored in the internal storage unit 115 or the external storage unit 117 based on the imaging parameter value of the input T1ρ sequence, and inputs the set T1ρ sequence. The value of the shift time Δt corresponding to the imaging parameter value is acquired, and the value is set as the shift time Δt.

  When the imaging parameter value that matches the imaging parameter value of the input T1ρ sequence is not stored in the internal storage unit 115 or the external storage unit 117, the imaging parameter close to the imaging parameter value of the input T1ρ sequence The value of the shift time Δt corresponding to the value of is acquired, and the shift time Δt is obtained by interpolation of the imaging conditions. Alternatively, the fourth embodiment is interrupted and the first to fourth embodiments described above are performed to newly determine the shift time Δt, and this calculated value is associated with the imaging parameter value of the input T1ρ sequence. The data is stored in the internal storage unit 115 or the external storage unit 117.

  Next, the processing flow of the fourth embodiment performed in cooperation with the above functional units will be described with reference to the flowchart shown in FIG. This processing flow is stored in advance in the internal storage device 115 as a program, and is executed by the arithmetic processing unit 114 reading the program from the internal storage device 115 and executing it. The processing flow of the fourth embodiment includes step 684 instead of step 654 shown in FIG. 6B described in the first embodiment and does not include steps 652 and 653. Other steps are the same as those in the first embodiment. Hereinafter, only steps different from those of the first embodiment will be described, and description of the same steps will be omitted.

  In step 684, the phase change timing setting unit 604 searches for the value of the shift time Δt stored in the internal storage unit 115 or the external storage unit 117 based on the imaging parameter value of the T1ρ sequence set in step 651, The value of the shift time Δt that corresponds to the imaging parameter value of the T1ρ sequence that has been input or that corresponds to the imaging parameter value obtained by interpolation is acquired, and that value is taken as the shift time Δt.

Note that if the imaging parameter value that matches the imaging parameter value of the input T1ρ sequence is not stored in the internal storage unit 115 or the external storage unit 117, this processing flow is interrupted, and the above-described embodiment You may transfer to any one of 1-3.
The above is the description of the processing flow of the fourth embodiment.

  As described above, the MRI apparatus and the T1ρ imaging method of the fourth embodiment include the storage unit that stores the imaging parameter value of the T1ρ sequence and the shift time in association with each other, and the timing setting unit is input from the storage unit. The shift time corresponding to the imaging parameter value of the T1ρ sequence thus obtained is acquired, and the acquired shift time is set as the shift time. That is, the relationship between the imaging parameter value of the T1ρ sequence and the actually measured value of the shift time Δt is stored in advance, and the shift time Δt is obtained based on the input imaging parameter value of the T1ρ sequence based on the relationship. This eliminates the need for separate calculation and preparatory measurement to determine the shift time Δt, and even if the irradiation RF magnetic field fluctuates over time, it can compensate for the spatial nonuniformity of the irradiation RF magnetic field, resulting in artifacts in the T1ρ-weighted image. Can be prevented from occurring.

While the embodiments of the present invention have been described above, the present invention is not limited to these embodiments. For example, when the RF amplifier gain characteristics increase with time, the timing to change the phase of the spin lock pulse by 180 ° or the timing to apply the 180 ° pulse is after the center of the spin lock time (T _SL / 2) become. That is, the shift time Δt has a negative value.

  101 subject, 102 static magnetic field generating magnet, 103 gradient magnetic field coil, 104 transmitting RF coil, 105 RF receiving coil, 106 bed, 107 signal processing unit, 108 overall control unit, 109 gradient magnetic field power source, 110 RF transmitting unit, 111 measurement Control unit, 113 Display / operation unit, 114 Arithmetic processing unit (CPU), 115 Internal storage unit, 116 Network IF, 117 External storage unit

Claims (8)

An RF amplifier for generating spin-locked RF pulses;
A spin-lock sequence unit for spin-locking the spin of the subject around the effective magnetic field of the rotating coordinate system using the spin-lock RF pulse, and an echo signal from magnetization attenuated by the time constant T1ρ during the spin-lock are measured. A measurement control unit that controls the measurement of an echo signal from the subject by controlling the RF amplifier based on a T1ρ sequence comprising the measurement sequence unit;
An arithmetic processing unit that acquires a T1ρ-weighted image of the subject using the echo signal;
A magnetic resonance imaging apparatus comprising:
A shift time for shifting the timing of changing the phase of the spin lock RF pulse by 180 ° to about half of the spin lock time (T _SL ) that is the application time of the spin lock RF pulse (T _SL / 2) is set. It has a timing setting unit,
The magnetic resonance imaging apparatus, wherein the measurement control unit changes the phase of the spin lock RF pulse by 180 ° at a timing set by the shift time. An RF amplifier for generating spin-locked RF pulses;
A spin-lock sequence unit for spin-locking the spin of the subject around the effective magnetic field of the rotating coordinate system using the spin-lock RF pulse, and an echo signal from magnetization attenuated by the time constant T1ρ during the spin-lock are measured. A measurement control unit that controls the measurement of an echo signal from the subject by controlling the RF amplifier based on a T1ρ sequence comprising the measurement sequence unit;
An arithmetic processing unit that acquires a T1ρ-weighted image of the subject using the echo signal;
A magnetic resonance imaging apparatus comprising:
A timing setting unit for setting a shift time for shifting the timing of applying the 180 ° pulse to about half of the spin lock time (T _SL ) that is the application time of the spin lock RF pulse (T _SL / 2);
The measurement control unit applies the 180 ° pulse at a timing set by the shift time during the application of the spin lock RF pulse. The magnetic resonance imaging apparatus according to claim 1 or 2,
The magnetic resonance imaging apparatus, wherein the timing setting unit obtains an optimum value of the shift time based on signal intensities of a plurality of FID signals or echo signals obtained by changing the shift time. The magnetic resonance imaging apparatus according to claim 3.
The magnetic resonance imaging apparatus, wherein an optimum value of the shift time is obtained each time the execution condition of the T1ρ sequence is changed. The magnetic resonance imaging apparatus according to claim 1 or 2,
A storage unit that stores the imaging parameter value of the T1ρ sequence and the shift time in association with each other;
The timing setting unit acquires a shift time corresponding to the input imaging parameter value of the T1ρ sequence from the storage unit, and uses the acquired shift time as the shift time. apparatus. The magnetic resonance imaging apparatus according to claim 5.
The magnetic resonance imaging apparatus characterized in that the imaging parameter value includes at least one of the spin lock time (T _SL ) and the gain value of the RF amplifier.
A spin lock step for spin-locking the spin of the subject around the effective magnetic field of the rotating coordinate system using a spin-lock RF pulse;
A measurement step for measuring an echo signal from magnetization attenuated by a time constant T1ρ during spin lock;
Obtaining a T1ρ-weighted image of the subject using the echo signal;
With
In the spin lock step, the phase of the spin lock RF pulse is changed by 180 ° before and after half of the spin lock time (T _SL ) that is the application time of the spin lock RF pulse (T _SL / 2). T1ρ imaging method. A spin lock step for spin-locking the spin of the subject around the effective magnetic field of the rotating coordinate system using a spin-lock RF pulse;
A measurement step for measuring an echo signal from magnetization attenuated by a time constant T1ρ during spin lock;
Obtaining a T1ρ-weighted image of the subject using the echo signal;
With
In the spin lock step, a 180 ° pulse is applied before and after half (T _SL / 2) of a spin lock time (T _SL ) that is an application time of a spin lock RF pulse.

Images