JP2016002107A - Magnetic resonance imaging apparatus and magnetic resonance imaging imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus and a magnetic resonance imaging method capable of evaluating the stability of a subject (fluid) by evaluating a variation in the signal ratio between an image signal at a measurement position and a reference signal.SOLUTION: A magnetic resonance imaging apparatus comprises: a measurement position setting unit 210 which sets a measurement position to one or more of a measurement area, a measurement line, and a measurement position, for a magnetic resonance image; a signal ratio calculation unit 211 which calculates the signal ratio between an image signal at the measurement position and a reference signal; and a fluidity evaluation unit 212 which evaluates the stability of a fluid in the magnetic resonance image on the variation in the signal ratio.

Description

  The present invention relates to a magnetic resonance imaging apparatus and a magnetic resonance imaging method, and more particularly to a magnetic resonance imaging apparatus and a magnetic resonance imaging method for evaluating a stable state of a fluid.

  An MRI apparatus (magnetic resonance imaging apparatus) is a high-frequency excitation pulse having a specific fundamental frequency along with application of a uniaxial slice selective gradient magnetic field that specifies an imaging region in a state where a uniform static magnetic field is applied to a subject. (Excitation RF pulse) is irradiated, gradient magnetic fields in two axial directions (phase direction and frequency direction) orthogonal to the slice direction are applied, and the magnetic resonance signal (echo signal) generated by excitation is two-dimensional The tomographic image data of the subject is acquired by reconstructing the obtained echo signal by giving position information and measuring. The gradient magnetic fields in the biaxial directions (phase direction and frequency direction) used for giving two-dimensional position information are generally referred to as a phase encoding gradient magnetic field and a frequency encoding gradient magnetic field, respectively. A pulse train in which RF pulses and a gradient magnetic field are arranged in time series according to a certain rule is generally called a sequence (pulse sequence).

  In MR image (magnetic resonance image) imaging, a sequence arranged in chronological order is input, so that the state of the subject (imaging target) changes during imaging, which may cause image quality defects and artifacts. For example, when an MR image is picked up using a medical image phantom, the solution (fluid) in the phantom flows immediately after the phantom is set in the MRI apparatus. And distortion may occur.

  In addition, when an MR image is captured in synchronization with a patient's pulse wave or heartbeat, the patient's state may change between when imaging is started and during imaging. For example, the patient's state transitions from an unstable state (tensed state) to a stable state. In this way, when the pulse wave or heartbeat changes due to a change in the state of the subject (patient or diagnosis site), even if an MR image is captured in synchronization with the pulse wave or heartbeat of the subject under a preset condition, An appropriate MR image may not be acquired. In particular, in non-contrast-enhanced MRA in which blood flow is observed based on the difference between MR images using electrocardiogram and pulse wave data, it is desirable that an MR image be captured when the subject is in a stable state. If an MR image is taken before the subject is in a stable state, adjustment for obtaining an appropriate MR image becomes difficult, or misdiagnosis is caused by a difference in MR image difference when using non-contrast-enhanced MRA. There is a risk of

  In addition, a magnetic resonance imaging apparatus that acquires a stable MR image by reducing noise associated with vibration of the gradient coil has been proposed (see, for example, Patent Document 1).

JP 2006-334050 A

  However, the magnetic resonance imaging apparatus described in Patent Document 1 is a magnetic resonance imaging apparatus that acquires a stable MR image by reducing noise associated with the vibration of the gradient magnetic field coil. ) Does not evaluate the stable state of the subject (fluid) when the state changes from an unstable state (tensile state) to a stable state.

  The present invention provides a magnetic resonance imaging apparatus and a magnetic resonance imaging method capable of grasping the state transition of a subject (fluid) and evaluating the stable state of the subject (fluid).

  The magnetic resonance imaging apparatus of the present invention includes a measurement position setting unit that sets at least one of a measurement region, a measurement line, and a measurement point as a measurement position in a magnetic resonance image, and a signal between an image signal and a reference signal at the measurement position. A signal ratio calculation unit that calculates a ratio; and a fluidity evaluation unit that evaluates a stable state of the fluid in the magnetic resonance image based on a change in the signal ratio.

  According to the present invention, the stable state of the subject (fluid) can be evaluated by evaluating the change in the signal ratio between the image signal and the reference signal at the measurement position.

It is a block diagram which shows the magnetic resonance imaging device which concerns on this Embodiment. It is the block diagram which showed an example of the control processing system. It is a flowchart explaining the operation | movement of the magnetic resonance imaging device which concerns on this Embodiment, and a magnetic resonance imaging method. It is the figure which showed that a measurement position setting part sets a measurement area | region as a measurement position in a magnetic resonance image. It is the figure which showed that a fluidity | liquidity evaluation part evaluates the stable state of a fluid based on the difference of the maximum value and minimum value of a signal ratio. It is a flowchart explaining the operation | movement of the magnetic resonance imaging device which concerns on the modification of this Embodiment, and the magnetic resonance imaging method. (A) It is the figure which showed that a measurement position setting part sets a measurement line as a measurement position in a magnetic resonance image. (B) It is the figure which showed that the signal ratio calculation part calculates the signal ratio of a measurement line. It is the figure which showed that a fluidity | liquidity evaluation part calculates the difference of the maximum value and minimum value of the signal ratio in a measurement line. It is the figure which showed the difference of the signal ratio for every measurement line. (A) It is the figure which showed including the measurement line of a parallel line and an orthogonal line. (B) It is the figure which showed including the measurement line of the straight line and concentric circle which have a predetermined angle.

  Hereinafter, a magnetic resonance imaging apparatus according to an embodiment of the present invention will be described with reference to the drawings. A magnetic resonance imaging apparatus according to an embodiment of the present invention evaluates a stable state of a subject (a living body or a medical image phantom), and includes at least one of a measurement region, a measurement line, and a measurement point on the magnetic resonance image. A measurement position setting unit for setting one as a measurement position, a signal ratio calculation unit for calculating a signal ratio between the image signal and the reference signal at the measurement position, and a stable state of the fluid in the magnetic resonance image based on the change in the signal ratio A fluidity evaluation unit for evaluating

  FIG. 1 is a block diagram showing a magnetic resonance imaging apparatus (MRI apparatus) according to the present embodiment. As shown in FIG. 1, the MRI apparatus 10 acquires a tomographic image of the subject 11 using a magnetic resonance phenomenon, and generates a static magnetic field generation system 20, a gradient magnetic field generation system 30, a transmission system 50, a reception system 60, and a control. A processing system 70 and a sequencer 40 are provided.

  The static magnetic field generation system 20 generates a uniform static magnetic field in a direction perpendicular to the body axis in the space around the subject 11 if the vertical magnetic field method is used, and is uniform in the body axis direction if the horizontal magnetic field method is used. A static magnetic field is generated. The static magnetic field generation system 20 includes at least one static magnetic field generation source of a permanent magnet system, a normal conduction system, and a superconductivity system disposed around the subject 11.

  The gradient magnetic field generation system 30 drives the gradient magnetic field coils 31 wound in the three axis directions of the X axis, the Y axis, and the Z axis, which are the coordinate system (stationary coordinate system) of the MRI apparatus 10, and the respective gradient magnetic field coils. And a gradient magnetic field power source 32. The gradient magnetic field generation system 30 drives gradient magnetic field power sources 32 of the respective gradient magnetic field coils 31 in accordance with instructions from the sequencer 40, whereby gradient magnetic fields Gx, Gy are arranged in three axial directions (X axis, Y axis, Z axis). , Gz.

  The transmission system 50 irradiates the subject 11 with a high-frequency magnetic field pulse (RF pulse) in order to cause nuclear magnetic resonance to occur in the nuclear spins of the atoms constituting the living tissue of the subject 11. The transmission system 50 includes a high-frequency oscillator (synthesizer) 52, a modulator 53, a high-frequency amplifier 54, and a transmission-side high-frequency coil (transmission coil) 51. The high frequency oscillator 52 generates an RF pulse, and outputs the RF pulse at a timing according to a command from the sequencer 40. The modulator 53 amplitude-modulates the output RF pulse. The high-frequency amplifier 54 amplifies the amplitude-modulated RF pulse and supplies the amplified RF pulse to the transmission coil 51 disposed close to the subject 11. The transmission coil 51 irradiates the subject 11 with the supplied RF pulse.

  The receiving system 60 detects a nuclear magnetic resonance signal (echo signal or NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the biological tissue of the subject 11. The reception system 60 includes a reception-side high-frequency coil (reception coil) 61, a signal amplifier 62, a quadrature detector 63, and an A / D converter 64. The receiving coil 61 is disposed in the vicinity of the subject 11 and detects an NMR signal emitted from the subject 11 induced by the electromagnetic wave irradiated from the transmitting coil 51. The signal amplifier 62 amplifies the detected NMR signal. The quadrature detector 63 divides the amplified NMR signal into two orthogonal signals at a timing according to a command from the sequencer 40. The A / D converter 64 converts each of the two systems of signals into digital quantities and outputs them to the control processing system 70.

  The sequencer 40 repeatedly applies RF pulses and gradient magnetic field pulses according to a predetermined pulse sequence. The pulse sequence defines (describes) the timing and intensity of a high-frequency magnetic field, a gradient magnetic field, and signal reception, and is held (stored) in the control processing system 70. The sequencer 40 operates in accordance with instructions from the control processing system 70 and transmits various commands necessary for collecting tomographic image data of the subject 11 to the gradient magnetic field generation system 30, the transmission system 50, and the reception system 60.

  The control processing system 70 controls the MRI apparatus 10, processes various data, displays / stores processing results, and the like. The control processing system 70 includes a CPU (processing device) 71, a storage device 72, a display device 73, and an input device 74. The storage device 72 includes an external storage device such as a hard disk, an optical disk, and a magnetic disk. The display device 73 includes a display device such as a CRT and a liquid crystal.

  The input device 74 is an interface for inputting control information (such as instructions and data) necessary for processing performed by the MRI apparatus 10 and the control processing system 70, and includes, for example, a trackball, a mouse, and a keyboard. The input device 74 is disposed in the vicinity of the display device 73. The operator interactively inputs instructions and data necessary for various processes of the MRI apparatus 10 through the input device 74 while looking at the display device 73.

  A CPU (processing device) 71 executes a program stored in advance in the storage device 72 in accordance with an instruction input from the input device 74, thereby controlling the operation of the MRI apparatus 10 and various data processing. Implement each process.

  Next, a configuration and a function for the MRI apparatus 10 to evaluate a stable state of a subject (a living body or a medical image phantom) will be described with reference to the drawings. For example, when evaluating the stable state of the medical image phantom, the MRI apparatus 10 evaluates the stable state of the internal solution (fluid) based on a signal decrease due to the flow of the internal solution (fluid) of the medical image phantom. .

  FIG. 2 is a block diagram showing an example of the control processing system 70. As shown in FIG. 2, the CPU (processing device) 71 includes an imaging unit 201 and an evaluation unit 202. The imaging unit 201 generates a sequence of imaging control data according to the set parameters, notifies the sequencer 40 of the sequence, and causes the sequencer 40 to execute MR image imaging. The evaluation unit 202 receives the data signal of the captured MR image from the reception system 60, reconstructs the MR image, and evaluates the stable state of the fluid.

  The evaluation unit 202 calculates a signal ratio between the image signal and the reference signal at the measurement position, and a measurement position setting unit 210 that sets at least one of a measurement region, a measurement line, and a measurement point as a measurement position in the magnetic resonance image. A signal ratio calculation unit 211 and a fluidity evaluation unit 212 that evaluates a stable state of the fluid in the magnetic resonance image based on a change in the signal ratio are provided. The evaluation unit 202 includes a notification unit 213 that notifies that the fluid is in a stable state or an unstable state.

  The storage device 72 includes an evaluation program storage unit 203 that stores an evaluation program for evaluating the stable state of the fluid. The evaluation unit 202 (control processing system 70) evaluates the stable state of the fluid by executing the evaluation program.

  FIG. 3 is a flowchart for explaining the operation of the MRI apparatus 10 and the magnetic resonance imaging method according to the present embodiment. As shown in FIG. 3, in step S100, the input device 74 inputs a command for starting an evaluation program for evaluating the stable state of the fluid, and the imaging unit 201 executes MR image capturing on the sequencer 40 according to the evaluation program. The evaluation unit 202 receives the captured MR image from the reception system 60.

  In step S101, the measurement position setting unit 210 sets at least one of a measurement region, a measurement line, and a measurement point as a measurement position in the MR image (magnetic resonance image). FIG. 4 is a diagram illustrating that the measurement position setting unit 210 sets a measurement region as a measurement position in the MR image (magnetic resonance image). As illustrated in FIG. 4, the measurement position setting unit 210 sets the measurement regions ROI <b> 1 to n as measurement positions in the portion of the subject 401 in the MR image 400. The measurement position setting unit 210 may set one measurement position or a plurality of measurement positions. Measurement position information such as the position, number, size, and shape of measurement positions (measurement area, measurement line, and measurement point) is stored in the evaluation program storage unit 203. The measurement position setting unit 210 acquires measurement position information from the evaluation program storage unit 203.

  In step S102, the signal ratio calculation unit 211 calculates the signal ratio between the image signal and the reference signal at the measurement position. When a plurality of measurement positions are set in the MR image (magnetic resonance image) 400, the signal ratio calculation unit 211 calculates a signal ratio for each of the plurality of measurement positions (for example, ROI1 to n). As illustrated in FIG. 4, the signal ratio calculation unit 211 acquires image signals at measurement positions (measurement regions ROI <b> 1 to n) among the image signals that constitute the MR image 400. In addition, the signal ratio calculation unit 211 acquires, as a reference signal, at least one of an image signal of a part other than the subject 401 and a preset signal value in the MR image 400. In FIG. 4, the signal ratio calculation unit 211 acquires, as a reference signal, the image signal N of the measurement region ROIref of the part other than the subject 401 among the image signals constituting the MR image 400. The signal ratio calculation unit 211 calculates a signal ratio between the image signal and the reference signal at the measurement position (measurement regions ROI1 to ROI1). An SN ratio (SNR) is used as the signal ratio. For example, a value obtained by dividing the variance of the image signal by the variance of the reference signal is used as the SN ratio. Further, as the signal ratio, a value obtained by dividing the average of the image signal by the average of the reference signal may be used, or in addition, a value obtained by dividing the statistical value of the image signal by the statistical value of the reference signal may be used. Good.

  In step S103, the fluidity evaluation unit 212 evaluates the stable state of the fluid in the MR image (magnetic resonance image) 400 based on the change in the signal ratio. For example, the fluidity evaluation unit 212 evaluates the stable state of the fluid based on the difference between the maximum value and the minimum value of the signal ratio. FIG. 5 is a diagram showing that the fluidity evaluation unit 212 evaluates the stable state of the fluid based on the difference between the maximum value and the minimum value of the signal ratio. As illustrated in FIG. 5, the fluidity evaluation unit 212 calculates a signal ratio (for example, SNR) at the measurement position (measurement regions ROI1 to ROI1), and calculates a difference between the maximum value and the minimum value of the SNR. In FIG. 5, since the SNR in the measurement region ROI5 is the maximum value and the SNR in the measurement region ROI2 is the minimum value, the fluidity evaluation unit 212 calculates the difference D1 between the SNR in the measurement region ROI5 and the SNR in the measurement region ROI2. calculate.

  In step S103, the fluidity evaluation unit 212 evaluates the stable state of the fluid based on a predetermined threshold. For example, when a predetermined threshold value T1 is set, the fluidity evaluation unit 212 compares the SNR difference D1 with the threshold value T1, and when the SNR difference D1 is smaller than the threshold value T1, the fluid is in a stable state. And evaluate.

  Due to the flow of the fluid in the subject 401, a signal decrease region A is generated in the MR image 400. Therefore, a difference D1 between a portion where the signal decrease occurs (measurement region ROI2) and a portion where the signal decrease does not occur (measurement region ROI5). Is compared with the threshold value T1, it is possible to evaluate the stable state of the portion (measurement region ROI2) where the signal drop is caused by the flow of the fluid.

  The fluidity evaluation unit 212 also includes a spatial change in the signal ratio (for example, SNR), a temporal change in the signal ratio, and statistical values (average, median, variance, standard deviation, etc.) of these changes. The stable state of the fluid may be evaluated based on at least one of the following.

  When evaluating the stable state of the fluid based on the spatial change in the signal ratio (for example, SNR), the fluidity evaluation unit 212 determines the maximum value of SNR (SNR of the measurement region ROI5) and each measurement position (measurement). The difference D2 from the SNR in the regions ROI1 to 12) is calculated, the SNR difference D2 is compared with the threshold T2, and when the SNR difference D2 is smaller than the threshold T2, it is evaluated that the fluid is in a stable state. On the other hand, when the SNR difference D2 is larger than the threshold value T2, it is evaluated that the fluid is in an unstable state. Thereby, the position of signal fall field A (for example, measurement field ROI2, ROI3, ROI4) can be specified.

  Further, when evaluating the stable state of the fluid based on the temporal change in the signal ratio (for example, SNR), the fluidity evaluation unit 212 determines the maximum value of SNR (the SNR of the measurement region ROI5) and the measurement position (for example, , The difference D3 from the SNR in the measurement region ROI2) is calculated, the time change of the SNR difference D3 (for example, the time derivative of the difference D3) is calculated, the time change of the difference D3 is compared with the threshold T3, and the difference D3 When the time change of is smaller than the threshold value T3, it is evaluated that the fluid is in a stable state. In this case, the fluidity evaluation unit 212 may estimate the time until the fluid becomes stable based on the temporal change in the signal ratio (for example, SNR) and the characteristics of the fluid. For example, the fluidity evaluation unit 212 estimates the time until the time change of the difference D3 becomes smaller than the threshold T3 based on the time change rate of the difference D3 and the viscosity coefficient of the fluid.

  The fluidity evaluation unit 212 uses the statistical values (average, median, variance, and standard) of the measurement positions (measurement regions ROI1 to 12) instead of using the difference from the maximum value of SNR (SNR of measurement region ROI5). Deviation or the like) may be used to calculate a spatial / temporal change in the SNR, and the stable state of the fluid may be evaluated based on the change. In addition, the fluidity evaluation unit 212 uses the difference from the predetermined value or the statistical value of the measurement position (measurement regions ROI1 to 12) instead of using the difference from the maximum value of SNR (SNR of measurement region ROI5). May be used to calculate a spatial / temporal change in SNR and evaluate the stable state of the fluid based on the change.

  When it is evaluated that the fluid is in a stable state, in step S104, the notification unit 213 notifies that the fluid is in a stable state using an image, sound, light, and the like. When it is evaluated that the fluid is in an unstable state, in step S105, the notification unit 213 notifies that the fluid is in an unstable state using an image, sound, light, and the like.

  When it is evaluated that the fluid is in an unstable state, in step S106, after a predetermined time (waiting time), the process returns to step S100, and the MR image is re-imaged. In this case, the time until the stable state estimated by the fluidity evaluation unit 212 may be set as a waiting time, or the waiting time may be displayed on the display device 73 by a timer. The scan may be automatically started after the fluid transitions from the unstable state to the stable state.

  Thus, according to the present embodiment, the stable state of the subject (fluid) can be evaluated by evaluating the change in the signal ratio between the image signal and the reference signal at the measurement position.

  As mentioned above, although embodiment concerning this invention was described, this invention is not limited to these, It can change and deform | transform within the range described in the claim.

  For example, as a modification of the present embodiment, the measurement position setting unit 210 sets the first measurement line and the second measurement line as the measurement positions, and the signal ratio calculation unit 211 includes a plurality of measurement points in the first measurement line. The signal ratio is calculated for each of the measurement points, the signal ratio is calculated for each of the plurality of measurement points on the second measurement line, and the fluidity evaluation unit 212 determines the maximum and minimum values of the signal ratio on the first measurement line. Is calculated as the first difference, the difference between the maximum value and the minimum value of the signal ratio in the second measurement line is calculated as the second difference, and based on the difference between the first difference and the second difference The stable state of the fluid may be evaluated.

  FIG. 6 is a flowchart for explaining the operation of the MRI apparatus 10 and the magnetic resonance imaging method according to a modification of the present embodiment. In the modification, parts different from the present embodiment will be mainly described, and parts common to the present embodiment will be denoted by the same reference numerals and description thereof will be omitted. As shown in FIG. 6, in step S201, the measurement position setting unit 210 sets measurement lines (first measurement line and second measurement line) as measurement positions in the MR image (magnetic resonance image). FIG. 7A is a diagram illustrating that the measurement position setting unit 210 sets the measurement lines L1 to L10 as measurement positions in the MR image (magnetic resonance image). As illustrated in FIG. 7A, the measurement position setting unit 210 sets measurement lines (line profiles) L <b> 1 to L <b> 10 as measurement positions in the portion of the subject 401 in the MR image 400. The measurement position setting unit 210 sets a plurality of measurement lines (first measurement line and second measurement line) in the MR image (magnetic resonance image) 400. Measurement position information such as the position, number, length, and shape of the measurement lines is stored in the evaluation program storage unit 203. The measurement position setting unit 210 acquires measurement position information from the evaluation program storage unit 203.

  In step S202, the signal ratio calculation unit 211 calculates the signal ratio between the image signal and the reference signal at the measurement position. The signal ratio calculation unit 211 calculates a signal ratio for each of the plurality of measurement points on the first measurement line (for example, the measurement line L1), and for each of the plurality of measurement points on the second measurement line (for example, the measurement line L2). The signal ratio is calculated.

  FIG. 7B is a diagram illustrating that the signal ratio calculation unit 211 calculates the signal ratio of the measurement lines L1 to L10. As shown in FIG. 7B, the signal ratio calculation unit 211 calculates signal ratios SNR (L1) to SNR (L10) for each measurement point in the X-axis direction on the plurality of measurement lines L1 to L10. Due to the flow of the fluid in the subject 401, the signal reduction region A is generated in the MR image 400, so that the signal is reduced at the measurement point corresponding to the signal reduction region A.

  The signal ratio calculation unit 211 acquires image signals of the measurement lines L <b> 1 to L <b> 10 among the image signals constituting the MR image 400. In addition, the signal ratio calculation unit 211 acquires, as a reference signal, at least one of an image signal of a part other than the subject 401 and a preset signal value in the MR image 400. The signal ratio calculation unit 211 calculates the signal ratio between the image signal and the reference signal on the measurement lines L1 to L10.

  In step S203, the fluidity evaluation unit 212 calculates the difference between the maximum value and the minimum value of the signal ratio in the first measurement line (for example, the measurement line L1) as the first difference D (L1), and the second A difference between the maximum value and the minimum value of the signal ratio in the measurement line (for example, the measurement line L2) is calculated as the second difference D (L2). FIG. 8 is a diagram illustrating that the fluidity evaluation unit 212 calculates the difference between the maximum value and the minimum value of the signal ratio on the measurement line L2. As shown in FIG. 8, the fluidity evaluation unit 212 determines the difference D () between the maximum value (measurement point P1) and the minimum value (measurement point P2) of the signal ratio based on the signal ratio SNR (L2) of the measurement line L2. L2) is calculated. Thus, the fluidity evaluation unit 212 calculates the difference D (L1) to D (L10) between the maximum value and the minimum value of the signal ratio for each of the measurement lines L1 to L10.

  In step S204, the fluidity evaluation unit 212 evaluates the stable state of the fluid in the MR image (magnetic resonance image) 400 based on the change in the signal ratio. For example, the fluidity evaluation unit 212 evaluates the stable state of the fluid based on the difference between the first difference D (L1) and the second difference D (L2). FIG. 9 is a diagram illustrating signal ratio differences D (L1) to D (L10) for the measurement lines L1 to L10. As illustrated in FIG. 9, the fluidity evaluation unit 212 calculates signal ratios (for example, SNR) differences D (L1) to D (L10) in the measurement lines L1 to L10, and the differences D (L1) to D ( The difference between the maximum value and the minimum value of L10) is calculated. In FIG. 9, since the difference D (L2) in the measurement line L2 is the maximum value and the difference D (L1) in the measurement line L1 is the minimum value, the fluidity evaluation unit 212 determines the difference D (L2 in the measurement line L2). ) And a difference D (L1) in the measurement line L1 is calculated.

  In step S204, the fluidity evaluation unit 212 evaluates the stable state of the fluid based on a predetermined threshold. For example, when the predetermined threshold value T4 is set, the fluidity evaluation unit 212 compares the difference D4 with the threshold value T4, and evaluates that the fluid is in a stable state when the difference D4 is smaller than the threshold value T4.

  Since the signal drop region A is generated in the MR image 400 due to the flow of the fluid in the subject 401, the maximum and minimum values of the signal ratio in the measurement line (for example, the measurement line L2) passing through the portion where the signal drop occurs. The difference (for example, D (L1)) becomes large, and the difference between the maximum value and the minimum value of the signal ratio (for example, D (L1)) in the measurement line (for example, the measurement line L1) that passes through the portion where no signal decrease occurs ) Becomes smaller. Therefore, by comparing the difference D4 between the signal ratios D (L1) to D (L10) for each of the measurement lines L1 to L10 with the threshold value T4, the portion where the signal decrease occurs due to the fluid flow (signal decrease region A ) Can be evaluated.

  In addition, the fluidity evaluation unit 212 performs the spatial change of the signal ratio difference D (L1) to D (L10) or the signal ratio difference D (L1) to D (L10), and the signal ratio over time. The steady state of the fluid may be evaluated based on at least one of the changes and statistics of these changes (such as mean, median, variance, and standard deviation).

  When evaluating the stable state of the fluid based on the spatial change in the difference between the signal ratio differences D (L1) to D (L10), the fluidity evaluation unit 212 uses the signal ratio difference D (L1) to D A difference D5 between the maximum value of (L10) (signal ratio difference D (L2) in the measurement line L2) and the signal ratio differences D (L1) to D (L10) in the respective measurement lines L1 to L10; The difference D5 is compared with the threshold value T5, and when the difference D5 is smaller than the threshold value T5, it is evaluated that the fluid is in a stable state. On the other hand, when the difference D5 is larger than the threshold value T5, it is evaluated that the fluid is in an unstable state. Thereby, the position of the signal decrease area A can be specified.

  In addition, when evaluating the stable state of the fluid based on the temporal change in the difference between the signal ratios D (L1) to D (L10), the fluidity evaluation unit 212 uses the signal ratio difference D (L1). A difference D6 between a maximum value of ~ D (L10) (a signal ratio difference D (L2) in the measurement line L2) and a signal ratio difference D (L1) ~ D (L10) in the measurement lines L1 to L10 is calculated. The time change of the difference D6 (for example, the time derivative of the difference D6) is calculated, the time change of the difference D6 is compared with the threshold T6, and when the time change of the difference D6 is smaller than the threshold T6, the fluid is in a stable state. Evaluate that there is. In this case, the fluidity evaluation unit 212 may estimate the time until the fluid becomes stable based on the temporal change of the difference D6 and the characteristics of the fluid. For example, the fluidity evaluation unit 212 estimates the time until the time change of the difference D6 becomes smaller than the threshold T6 based on the time change rate of the difference D6 and the viscosity coefficient of the fluid.

  The fluidity evaluation unit 212 uses the statistical values of the signal ratio differences D (L1) to D (L10) instead of using the difference between the signal ratio differences D (L1) to D (L10). Using the average, median, variance, standard deviation, etc.) to calculate the spatial / temporal change of the signal ratio difference D (L1) to D (L10), and based on the change The stable state may be evaluated. In addition, the fluidity evaluation unit 212 uses the difference between the signal ratio difference D (L1) to D (L10) or the difference between the predetermined value or the signal ratio difference D (L1) to D instead of using the difference from the maximum value. Using the difference from the statistical value of (L10), the spatial / temporal change of the difference between the signal ratios D (L1) to D (L10) is calculated, and the stable state of the fluid based on the change May be evaluated.

  Thus, according to the modification of the present embodiment, the stable state of the subject (fluid) can be evaluated by evaluating the change in the signal ratio between the image signal and the reference signal at the measurement position. .

  When setting the first measurement line and the second measurement line, the first measurement line and the second measurement line are at least one part of a parallel line, an orthogonal line, a straight line having a predetermined angle, and a concentric circle. May be included. For example, as shown in FIG. 10A, the first measurement line and the second measurement line may include parallel lines L1 to L10 and orthogonal lines L11 to L13. Further, as shown in FIG. 10B, the first measurement line and the second measurement line may include straight lines L14 to L16 and concentric circles L17 and L18 having a predetermined angle.

  10A, the measurement position setting unit 210 sets the measurement lines L1 to L13, sets a region surrounded by the measurement lines as the measurement region ROI13, and the fluidity evaluation unit 212 The stable state of the fluid may be evaluated based on a signal ratio (for example, SNR) in at least one of the measurement region ROI13 and the measurement lines L1 to L13.

  Further, the measurement position setting unit 210 sets a measurement region (for example, the measurement region ROI13) from a lattice (for example, a lattice formed by the quadrangle in FIG. 10A) formed by polygons, and the boundary line of the lattice From this, the fluidity evaluation unit 212 may evaluate the stable state of the fluid based on the signal ratio in at least one of the measurement region and the measurement line.

  The MR image (magnetic resonance image) is a plurality of tomographic images (multi-slice images) of the subject 11, and the fluidity evaluation unit 212 evaluates the stable state of the fluid for each of the plurality of tomographic images. Good. Thereby, the stable state of the fluid in the three-dimensional space can be evaluated.

  According to the present invention, a magnetic resonance imaging apparatus and a magnetic resonance imaging apparatus capable of evaluating a stable state of a subject (fluid) by evaluating a change in a signal ratio between an image signal and a reference signal at a measurement position. It is useful as a method.

DESCRIPTION OF SYMBOLS 10 MRI apparatus 20 Static magnetic field generation system 30 Gradient magnetic field generation system 31 Gradient magnetic field coil 32 Gradient magnetic field power supply 40 Sequencer 50 Transmission system 51 Transmission coil 52 High frequency oscillator 53 Modulator 54 High frequency amplifier 60 Reception system 61 Reception coil 62 Signal amplifier 63 Quadrature phase Detector 64 A / D converter 70 Control processing system 72 Storage device 73 Display device 74 Input device 201 Imaging unit 202 Evaluation unit 203 Evaluation program storage unit 210 Measurement position setting unit 211 Signal ratio calculation unit 212 Fluidity evaluation unit 213 Notification unit

Claims (13)

A measurement position setting unit that sets at least one of a measurement region, a measurement line, and a measurement point as a measurement position in the magnetic resonance image;
A signal ratio calculation unit for calculating a signal ratio between the image signal and the reference signal at the measurement position;
A magnetic resonance imaging apparatus comprising: a fluidity evaluation unit that evaluates a stable state of a fluid in the magnetic resonance image based on a change in the signal ratio. The measurement position setting unit sets a plurality of measurement positions in the magnetic resonance image,
The signal ratio calculation unit calculates the signal ratio for each of the plurality of measurement positions,
The magnetic resonance imaging apparatus according to claim 1, wherein the fluidity evaluation unit evaluates a stable state of the fluid based on a difference between a maximum value and a minimum value of the signal ratio. The measurement position setting unit sets a measurement line as the measurement position,
The signal ratio calculation unit calculates the signal ratio for each of a plurality of measurement points on the measurement line,
The magnetic resonance imaging apparatus according to claim 1, wherein the fluidity evaluation unit evaluates a stable state of the fluid based on a difference between a maximum value and a minimum value of the signal ratio. The measurement position setting unit sets the first measurement line and the second measurement line as the measurement position,
The signal ratio calculation unit calculates the signal ratio for each of a plurality of measurement points on the first measurement line, calculates the signal ratio for each of a plurality of measurement points on the second measurement line,
The fluidity evaluation unit calculates a difference between the maximum value and the minimum value of the signal ratio in the first measurement line as a first difference, and the maximum value and the minimum value of the signal ratio in the second measurement line. 2. The magnetic resonance image according to claim 1, wherein the difference between the first and second differences is calculated as a second difference, and a stable state of the fluid is evaluated based on the difference between the first difference and the second difference. apparatus.   5. The magnetism according to claim 4, wherein the first measurement line and the second measurement line include at least one part of a parallel line, an orthogonal line, a straight line having a predetermined angle, and a concentric circle. Resonance imaging device. The measurement position setting unit sets the measurement line, sets an area surrounded by the measurement line as the measurement area,
The magnetic resonance imaging apparatus according to claim 1, wherein the fluidity evaluation unit evaluates a stable state of the fluid based on the signal ratio in at least one of the measurement region and the measurement line. The measurement position setting unit sets the measurement region from a grid constituted by polygons, sets the measurement line from a boundary line of the grid,
The magnetic resonance imaging apparatus according to claim 1, wherein the fluidity evaluation unit evaluates a stable state of the fluid based on the signal ratio in at least one of the measurement region and the measurement line.   The magnetic resonance imaging apparatus according to claim 1, wherein the fluidity evaluation unit evaluates a stable state of the fluid based on a predetermined threshold.   The fluidity evaluation unit evaluates a stable state of the fluid based on at least one of a spatial change in the signal ratio, a temporal change in the signal ratio, and a statistical value of the change. The magnetic resonance imaging apparatus according to claim 1.   The fluidity evaluation unit estimates a time until the fluid is in a stable state based on a temporal change in the signal ratio and characteristics of the fluid. Magnetic resonance imaging device. The magnetic resonance image is a plurality of tomographic images of a subject,
The magnetic resonance imaging apparatus according to claim 1, wherein the fluidity evaluation unit evaluates a stable state of the fluid for each of the plurality of tomographic images.   2. The magnetic resonance imaging apparatus according to claim 1, wherein the reference signal is at least one of an image signal of a portion other than the subject in the magnetic resonance image and a preset signal value. At least one of a measurement region, a measurement line, and a measurement point is set as a measurement position in the magnetic resonance image,
Calculating a signal ratio between the image signal and the reference signal at the measurement position;
A magnetic resonance imaging method, comprising: evaluating a stable state of a fluid in the magnetic resonance image based on a change in the signal ratio.

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