JP2011110328A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus capable of collecting data while a body movement by breathing is little. <P>SOLUTION: The magnetic resonance imaging apparatus outputs an inhalation direction A and an exhalation direction B in order, synchronized with a peak P1 of a PG signal. A subject 14 inhales in response to the inhalation direction A and exhales in response to the exhalation direction B. Then the magnetic resonance imaging apparatus is synchronized with a peak P2 of the PG signal, which appears second after the exhalation direction B, and the a pulse sequence PS is executed. The pulse sequence PS is executed just a delay time TD1 later after the peak P2 of the PG signal. Therefore, a data collection sequence DAQ can be executed while the body movement by breathing is little as well as during a diastole period DP. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a magnetic resonance imaging apparatus that collects data from a subject.

  When photographing the chest and abdomen, a pulse sequence may be executed using both heartbeat synchronization and respiratory synchronization (see Patent Document 1).

JP 2009-160378 A

  However, the method of Patent Document 1 has a problem that if the breathing of the subject is disturbed, it is difficult to collect data while the body movement due to the breathing is small.

  In view of the above circumstances, an object of the present invention is to provide a magnetic resonance imaging apparatus capable of collecting data while body movement due to respiration is small.

The magnetic resonance imaging apparatus of the present invention that solves the above problems
A magnetic resonance imaging apparatus that executes a pulse sequence in synchronization with a heartbeat of a subject,
Instruction output means for outputting an instruction related to respiration to the subject in synchronization with the heartbeat of the subject.

  In the present invention, a breathing instruction is output to the subject in synchronization with the heartbeat of the subject. Therefore, the inspiration timing and the expiration timing of the subject can be matched with the heartbeat of the subject. For this reason, when the movement of the subject due to respiration is small, the pulse sequence can be executed by the heartbeat synchronization method, and a high-quality image can be obtained.

1 is a schematic diagram of a magnetic resonance imaging apparatus according to an embodiment of the present invention. FIG. 3 is a diagram schematically showing an imaging region of a subject 14. It is a figure which shows an example of pulse sequence PS used when image | photographing the test subject 14. FIG. It is explanatory drawing of the heart rate synchronization method. It is a figure which shows the processing flow of the MRI apparatus. It is a figure which shows the output timing (d) of the instruction | indication regarding a respiration waveform (a), PG signal (b), pulse sequence PS (c), and respiration when the processing flow of FIG. 5 is performed. It is a figure which shows the example which performs pulse sequence PS synchronizing with the peak P3. It is a figure which shows the example which performs pulse sequence PS synchronizing with the peak P5.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following embodiments.

FIG. 1 is a schematic view of a magnetic resonance imaging apparatus according to an embodiment of the present invention.
A magnetic resonance imaging (MRI) apparatus 1 includes a magnetic field generator 2, a table 3, a pulse wave sensor 4, a receiving coil 5, and the like.

  The magnetic field generator 2 includes a bore 21 in which the subject 14 is accommodated, a superconducting coil 22, a gradient coil 23, and a transmission coil 24. The superconducting coil 22 applies a static magnetic field B0, the gradient coil 23 applies a gradient pulse, and the transmission coil 24 transmits an RF pulse.

  The magnetic field generator 2 has a built-in speaker 25. The speaker 25 is controlled by the central processing unit 11 to be described later, and outputs a breathing instruction.

  The table 3 has a cradle 31 for transporting the subject 14. The subject 14 is transported to the bore 21 by the cradle 31.

  The pulse wave sensor 4 detects the pulse wave of the subject 14.

  The receiving coil 5 is attached to the abdomen 14a of the subject 14 and receives a magnetic resonance signal from the abdomen 14a.

  The MRI apparatus 1 further includes a sequencer 6, a transmitter 7, a gradient magnetic field power supply 8, a PG unit 9, a receiver 10, a central processing unit 11, an input device 12, and a display device 13.

  Under the control of the central processing unit 11, the sequencer 6 sends RF pulse information (center frequency, bandwidth, etc.) to the transmitter 7, and gradient magnetic field information (gradient magnetic field strength, etc.) to the gradient magnetic field power supply 8. send.

  The transmitter 7 drives the transmission coil 24 based on the information sent from the sequencer 6.

  The gradient magnetic field power supply 8 drives the gradient coil 23 based on the information sent from the sequencer 6.

  The PG unit 9 performs various processes including a digitization process on a PG (Peripheral Gating) signal from the pulse wave sensor 4 and transmits the signal to the central processing unit 11.

  The receiver 10 performs various processes including a digitization process on the magnetic resonance signal received by the receiving coil 5 and transmits the processed signal to the central processing unit 11.

  The central processing unit 11 implements various operations of the MRI apparatus 1 such as transmitting necessary information to the sequencer 6 and the display device 13 and reconstructing an image based on a signal received from the receiver 10. The operation of each part of the MRI apparatus 1 will be summarized. Further, the central processing unit 11 determines a delay time TD1 (see FIG. 4 described later) when executing the pulse sequence based on the signal from the PG unit 9. Further, the central processing unit 11 controls the speaker 25 so that an instruction regarding breathing is output from the speaker 25. The central processing unit 11 is configured by, for example, a computer. A combination of the central processing unit 11 and the speaker 25 corresponds to an example of an instruction output unit of the present invention.

  The input device 12 inputs various commands to the central processing unit 11 according to the operation of the operator 15. The display device 13 displays various information.

  The subject 14 is imaged using the MRI apparatus 1 configured as described above.

  FIG. 2 is a diagram schematically illustrating an imaging region of the subject 14, and FIG. 3 is a diagram illustrating an example of a pulse sequence PS used when imaging the subject 14.

  In this embodiment, the abdomen 14a of the subject 14 is imaged. The MRI apparatus 1 executes a pulse sequence PS for rendering the arterial blood 14c in the imaging region R using the inflow effect of the arterial blood 14c from the heart 14b.

The pulse sequence PS is a selective inversion pulse SIR (Selective
Inversion Recovery) and data collection sequence DAQ.

The selective inversion pulse SIR is a pulse for inverting the longitudinal magnetization of blood (arterial blood and venous blood) in the imaging region R (see FIG. 2) of the subject 14. The inversion time TI of the selective inversion pulse SIR is set to a time from when the longitudinal magnetization of the blood is inverted by the selective inversion pulse SIR until the inverted longitudinal magnetization of the blood reaches the null point. The inversion time TI is a value of about 1 (sec) to 1.5 (sec), for example. Since the arterial blood 14c from the heart 14b flows into the imaging region R during the inversion time TI, by executing the data collection sequence DAQ when the inversion time TI has elapsed, the arterial blood is emphasized and depicted in the vein MR images in which blood is suppressed can be obtained. The data collection sequence DAQ is, for example, FSE (Fast Spin Echo) or SSFP (Steady State Free).
Precession).

  When the arterial blood 14c is drawn using the inflow effect of the arterial blood 14c, if data is collected during the systole of the heart 14e, the arterial blood 14c cannot be drawn with high contrast by a flow void. Therefore, it is desirable that the data acquisition sequence DAQ is executed in the diastole as much as possible. Therefore, in this embodiment, the pulse sequence PS is executed by the heartbeat synchronization method. Hereinafter, the heartbeat synchronization method will be described.

FIG. 4 is an explanatory diagram of the heartbeat synchronization method.
FIG. 4A shows a PG signal, and FIG. 4B shows a pulse sequence PS.

As described above, it is desirable that the data collection sequence DAQ is executed in the diastole DP. In order to execute the data acquisition sequence DAQ during the diastole DP, the data acquisition sequence DAQ may be executed with a delay time TD2 from the peak P _{n + 1} of the PG signal. The delay time TD2 is a fixed value and can be determined empirically. For example, when the time length of the data collection sequence DAQ is 400 ms, the delay time TD2 can be set to 200 ms. Generally, since the peak interval PPint of the PG signal is about 1 second, if the delay time TD2 is set to 200 ms, the data acquisition sequence DAQ can be executed in the diastole DP.

However, the pulse sequence PS has a selective inversion pulse SIR before the data acquisition sequence DAQ. Therefore, the peak P _{n + 1} of the PG signal generated immediately before the data acquisition sequence DAQ cannot be set as the trigger point, and the peak P _n of the PG signal generated immediately before the data acquisition sequence DAQ must be set as the trigger point. Therefore, in order to execute the data acquisition sequence DAQ in the diastole DP, the delay time TD1 of the pulse sequence PS is set so that the data acquisition sequence DAQ is executed with a delay time TD2 from the peak P _{n + 1} of the PG signal. It is necessary to decide. Hereinafter, a method for determining the delay time TD1 of the pulse sequence PS will be described.

From FIG. 4, the following relational expression holds among the delay time TD1, the inversion time TI, the peak interval PPint, and the delay time TD2.
TD1 = PPint + TD2-TI (1)

The peak interval PPint is expressed by the following equation using the heart rate HR.
PPint = 60 / HR (2)

Therefore, when the formula (2) is substituted into the formula (1), the following formula is obtained.
TD1 = (60 / HR) + TD2-TI (3)

  In Expression (3), the inversion time TI is a fixed value determined by the pulse sequence PS, and the heart rate HR is a value obtained from the PG signal. Further, the delay time TD2 is a value that is empirically determined in advance as described above. Therefore, the delay time TD1 can be determined using Equation (3). The central processing unit 11 calculates the heart rate HR based on the PG signal, and calculates the delay time TD1 by substituting the calculated heart rate HR into Equation (3). Therefore, even if the heart rate HR of the subject 14 changes during imaging, the delay time TD1 suitable for the changed heart rate HR can be calculated.

  Depending on the value of the heart rate HR, the data acquisition sequence DAQ may be shifted from the diastole DP. However, as long as the heart rate HR does not become extremely small or large, the data acquisition sequence DAQ can be executed during the diastole DP by determining the delay time TD1 according to the equation (3). it can.

  However, even if the data acquisition sequence DAQ can be executed in the diastole DP, if the data acquisition sequence DAQ is executed while the body movement due to respiration is large, the body movement artifact cannot be suppressed. High-quality MR images cannot be obtained. Therefore, in this embodiment, the subject 14 is imaged using both heartbeat synchronization and respiratory synchronization. Hereinafter, a processing flow when imaging the subject 14 in the present embodiment will be described.

  Hereinafter, a processing flow of the MRI apparatus 1 for executing the pulse sequence PS will be described with reference to FIGS. 5 and 6.

  FIG. 5 is a diagram showing a processing flow of the MRI apparatus 1, and FIG. 6 is a diagram illustrating a respiratory waveform (a), a PG signal (b), a pulse sequence PS (c) when the processing flow of FIG. It is a figure which shows the output timing (d) of the instruction | indication regarding breathing.

  The processing flow in FIG. 5 will be described with reference to FIG. 6 as necessary.

  First, in step S1, the heart rate HR of the subject 14 is calculated. Here, the heart rate HR of the subject 14 at time t1 is calculated (see FIG. 6). After calculating the heart rate HR, the process proceeds to step S2.

  In step S2, the central processing unit 11 outputs, in synchronization with the peak P1 of the PG signal, an inspiration instruction A that prompts the subject 14 to inhale and an expiration instruction B that prompts the subject 14 to exhale. The speaker 25 is controlled. In the present embodiment, first, when the delay time TD3 has elapsed from the peak P1 of the PG signal, an inspiration instruction A (for example, “breath in”) is output from the speaker 25. The value of the delay time TD3 is, for example, 100 ms. The subject 14 inhales in response to the inspiration instruction A. In addition, at the time t3 after the elapse of the predetermined time Δt from the output of the inspiration instruction A, the expiration instruction B (for example, “vomit”) is output. The subject 14 exhales in response to the exhalation instruction B. After the inspiration instruction A and the expiration instruction B are output, the process proceeds to step S3.

  In step S3, the pulse sequence PS is executed. In the present embodiment, the pulse sequence PS is executed in synchronization with the peak P4 of the PG signal that appears immediately after the expiration instruction B. The pulse sequence PS is executed after a delay time TD1 from the peak P4 of the PG signal. The delay time TD1 is a value determined using Equation (5) in Step S1. Therefore, the data collection sequence DAQ can be executed during the diastole DP.

  Further, in the present embodiment, before executing the pulse sequence PS, the inspiration instruction A and the expiration instruction B are sequentially output in synchronization with the peak P1 of the PG signal. Therefore, the data collection sequence DAQ is executed when a predetermined time has elapsed since the subject 14 started to exhale according to the exhalation instruction B. For this reason, the data collection sequence DAQ can be executed while the body movement due to respiration of the subject 14 is small.

After executing the pulse sequence PS, the process proceeds to step S4.
In step S4, it is determined whether or not all data necessary for filling the k space has been collected. Here, it is determined that all data has not been collected, and the process returns to step S1.

  When returning to step S1, steps S1 to S4 are repeatedly executed according to the procedure described above. When it is determined in step S4 that all data necessary for filling the k space has been collected, the flow ends.

  In this embodiment, before executing the pulse sequence PS, the inspiration instruction A and the expiration instruction B are output in synchronization with the peak P1 of the PG signal. Therefore, if the heart rate HR of the subject 14 does not change abruptly, the output period Tout (see FIG. 6D) of the inspiration instruction A and the expiration instruction B can be regarded as substantially constant. Since the subject 14 breathes in response to the inspiration instruction A and the expiration instruction B, if the output period Tout of the inspiration instruction A and the expiration instruction B can be regarded as constant, the respiratory cycle Tresp of the subject 14 (FIG. 6). (See (a)) can also be considered constant. Therefore, by executing the pulse sequence PS in synchronization with the peak P4 appearing immediately after the exhalation instruction B, the data acquisition sequence DAQ can be executed while the body movement due to the respiration of the subject 14 is small. An MR image with reduced artifacts can be obtained.

  In the present embodiment, the delay time TD1 of the pulse sequence PS is a value determined by using Equation (5) in step S1. Therefore, the data acquisition sequence DAQ can be executed in the diastole DP, and arterial blood can be rendered with high contrast.

  In the present embodiment, the pulse sequence PS is executed in synchronization with the peak P4 of the PG signal that appears immediately after the exhalation instruction B. However, the pulse sequence PS is not necessarily executed in synchronization with the peak P4 appearing immediately after the exhalation instruction B, and may be executed in synchronization with another peak other than the peak P4 (see FIGS. 7 and 8). ).

  7 and 8 are diagrams illustrating an example in which the pulse sequence PS is executed in synchronization with a peak other than the peak P4.

  For example, when the pulse sequence PS has another RF pulse before the selective inversion pulse SIR (see FIG. 7), the time length of the pulse sequence PS becomes longer, so the pulse sequence is synchronized with the peak P3. It is desirable to execute PS. Further, when the pulse sequence PS has only the data acquisition sequence DAQ (see FIG. 8), the time length of the pulse sequence PS is shortened, so it is desirable to execute the pulse sequence PS in synchronization with the peak P5. As described above, the timing for executing the pulse sequence PS may be changed as appropriate according to the type of the pulse sequence PS.

  In the present embodiment, the delay time TD3 (see FIG. 6) between the peak P1 of the PG signal and the intake command A is a predetermined fixed value. However, the delay time TD3 may be calculated according to the heart rate HR. For example, when the heart rate HR is larger than a predetermined value, the delay time TD3 is shortened (for example, 50 ms), and when the heart rate HR is smaller than the predetermined value, the delay time TD3 may be increased. Good (eg 150 ms). In this manner, by changing the delay time TD3 according to the heart rate HR, a breathing instruction can be output in accordance with the heartbeat rhythm of the subject, so that a higher quality MR image can be obtained. Become.

  In the present embodiment, an instruction related to breathing is transmitted to the subject 14 by voice. However, the breathing instruction may be transmitted to the subject 14 using another transmission method other than sound, such as video.

  In the present embodiment, the heart rate HR of the subject 14 is calculated using the pulse wave signal. However, the heart rate HR of the subject 14 may be calculated using an electrocardiogram signal instead of the pulse wave signal.

  In the present embodiment, the pulse sequence PS has a selective inversion pulse SIR before the data acquisition sequence DAQ. However, the pulse sequence PS may have another RF pulse (for example, a non-selective inversion pulse, an RF pulse with a flip angle α of α ≠ 90 °) instead of the selective inversion pulse SIR, if necessary. Good. Further, the pulse sequence PS may include one or more other RF pulses between the selective inversion pulse SIR and the data acquisition sequence DAQ as necessary.

  In the present embodiment, the delay time TD1 of the pulse sequence PS is calculated according to Equation (3). However, the delay time TD1 may be determined according to an equation different from the equation (3).

DESCRIPTION OF SYMBOLS 1 MRI apparatus 2 Magnetic field generator 3 Table 4 Pulse wave sensor 5 Reception coil 6 Sequencer 7 Transmitter 8 Gradient magnetic field power supply 9 PG unit 10 Receiver 11 Central processing unit 12 Input device 13 Display device 14 Subject 15 Operator 21 Bore 22 Over Conductive coil 23 Gradient coil 24 Transmitting coil 25 Speaker 31 Cradle

Claims (13)

A magnetic resonance imaging apparatus that executes a pulse sequence in synchronization with a heartbeat of a subject,
A magnetic resonance imaging apparatus comprising: instruction output means for outputting an instruction related to respiration to the subject in synchronization with the heartbeat of the subject. The instruction output means includes
In synchronization with a first trigger point of a biological signal representing the heartbeat of the subject, an instruction related to respiration is output to the subject,
The pulse sequence is
The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance imaging apparatus is executed in synchronization with a second trigger point of the biological signal.   The magnetic resonance imaging apparatus according to claim 2, wherein the instruction output unit outputs an exhalation instruction for prompting exhalation after outputting an inhalation instruction for prompting inspiration. The instruction output means includes
The magnetic resonance imaging apparatus according to claim 3, wherein the inspiration instruction is output when a first delay time has elapsed from a first trigger point of the biological signal.   The magnetic resonance imaging apparatus according to claim 4, wherein the pulse sequence is executed when a second delay time has elapsed from a second trigger point of the biological signal.   The pulse sequence collects data from the subject after an RF pulse transmitted when the second delay time elapses from the second trigger point of the biological signal and the RF pulse is transmitted. The magnetic resonance imaging apparatus according to claim 5, further comprising:   The magnetic resonance imaging apparatus according to claim 6, wherein the pulse sequence includes one or more other RF pulses between the RF pulse and the data acquisition sequence.   The magnetic resonance imaging apparatus according to claim 7, wherein the RF pulse is an inversion pulse.   The magnetic resonance imaging apparatus according to claim 4, further comprising a delay time determination unit that determines the first delay time of the biological signal based on a heart rate of the subject.   The time interval between the first trigger point and the second trigger point is set such that the data collection sequence is executed during diastole. The magnetic resonance imaging apparatus according to one item.   The magnetic resonance imaging apparatus according to claim 10, wherein the first trigger point is before the second trigger point.   The magnetic resonance imaging apparatus according to claim 1, wherein the instruction output unit outputs an instruction regarding the breathing by voice. The magnetic resonance imaging according to any one of claims 1 to 12, wherein the trigger point of the biological signal is a peak of a pulse wave signal of the subject or an R wave of an electrocardiographic signal of the subject. apparatus.

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