Magnetic resonance camera device and method of controlling the same

Abstract

The present application aims to improve the data acquisition efficiency in the imaging using both ECG synchronization and respiratory motion synchronization. During the imaging, the respiratory motion is monitored to detect the start of the respiratory stable period (exhalation). After detecting the R wave, it is confirmed that the respiratory motion immediately before the R wave has transitioned to the respiratory stable period, and the formal measurement is performed at the time when the cardiac phase and the respiratory phase of the subject coincide, and the image data is acquired. The cardiac phase at which the image data is acquired is fixed, and the slice position for the formal measurement is adjusted using the respiratory motion displacement acquired immediately before. Thus, it is possible to acquire image data of two heart rate quantities within the respiratory cycle after entering the stable period while suppressing the influence of motion.

Description

Magnetic resonance imaging device and its control method Technical Field

[0001] This invention relates to a magnetic resonance imaging device (hereinafter referred to as an MRI device), and more particularly to a control method for an MRI device when performing electrocardiogram-synchronized imaging. Background Technology

[0002] When using MRI to diagnose diseases involving the heart or surrounding blood vessels, the images are affected by cardiac and respiratory motion, producing motion artifacts. To suppress these artifacts, image data should be acquired at moments when cardiac and respiratory motions are stable. Typically, MRI signals from the subject are acquired during phases of the cardiac cycle with minimal motion (diastole) and during the expiratory phase (stability phase) with almost no motion, thus obtaining images that minimize the influence of cardiac motion.

[0003] Therefore, conventionally, signals from an electrocardiograph or heart rate monitor are received, and the generation time of the R wave, etc., is used as a trigger to execute a pulse sequence for imaging during the diastolic phase after a predetermined delay time. At this time, a navigation echo (hereinafter referred to as navigation echo) for monitoring respiratory motion and formal imaging are executed in a set, and the signal for image reconstruction (image data) is collected only when the respiratory displacement is within a preset threshold of several millimeters (Patent Document 1).

[0004] Patent Document 1: Japanese Patent Application Publication No. 2011-147560

[0005] In previous dual synchronization methods using simultaneous ECG and respiratory motion synchronization, data collection relied on the subject's respiratory and heart rate cycles, resulting in low data acquisition efficiency and long imaging times. For example, some methods involved capturing two heart rate values ​​during the expiratory stabilization phase and then capturing one data point within those two heart rates. However, in previous controls, formal imaging was not performed if the respiratory displacement deviated from a set threshold after the R wave was detected. Therefore, the two heart rate values ​​were cumulatively prolonged in the imaging process that captured data within the two heart rate intervals. Furthermore, in subjects with short respiratory stabilization phases, it was difficult to perform the imaging process itself, which involved capturing data within the two heart rate intervals. Summary of the Invention

[0006] The objective of this invention is to improve the data acquisition efficiency in dual-synchronous imaging. Furthermore, the objective is to suppress the effects of motion and acquire data across two consecutive heart rates, even when the steady-state period of the subject's respiratory movements is relatively short.

[0007] To address the aforementioned issues, this invention monitors respiratory movements during imaging to detect the onset of the respiratory stabilization phase (exhalation). Upon receiving an electrocardiogram synchronization signal, image data is acquired at the moment when the preceding respiratory movements have transitioned into the respiratory stabilization phase, at which the subject's cardiac and respiratory phases coincide. This allows for the acquisition of image data for two heart rate measurements within each respiratory cycle.

[0008] That is, the MRI device of the present invention comprises: an imaging unit that collects magnetic resonance signals generated from a subject, performs navigation measurements to detect the respiratory movements of the subject, and performs formal measurements to generate images of the subject; a measurement control unit that controls the imaging unit; a respiratory movement monitoring unit that monitors the respiratory movements of the subject using the results of the navigation measurements, and sends acceptance and rejection signals to the measurement control unit based on whether the magnitude of the respiratory movements of the subject is inside or outside a pre-set threshold window; and a cardiac cycle monitoring unit that monitors the cardiac cycle of the subject and generates a threshold signal at the moment when the R wave of the cardiac cycle is generated.

[0009] The measurement control unit controls the camera unit as follows: it continuously performs navigation measurements before and after the generation of a threshold signal. If a threshold signal is received from the cardiac cycle monitoring unit, and the most recent transition in the transition of the signal from the respiratory motion monitoring unit generated during the navigation measurement before receiving the threshold signal is a transition from a rejection signal to an acceptance signal, the formal measurement is performed after a preset delay time.

[0010] Even if the signal from the respiratory motion monitoring unit is a receiving signal more than twice consecutively at the closest threshold signal, a formal measurement is performed after the delay time.

[0011] Invention Effects

[0012] According to the present invention, the start of the formal measurement is controlled by using respiratory motion monitoring results immediately preceding the threshold signal used for the formal measurement, thereby ensuring data acquisition during a period of minimal respiratory motion and within a fixed cardiac phase. This suppresses motion artifacts. Furthermore, data can be efficiently acquired at the moment when the cardiac phase and respiratory displacement coincide, thus minimizing the extension of imaging time. Moreover, since the displacement based on respiratory motion can be detected from the navigation echo during the delay period, the position of the image slice corresponding to the detected displacement can be corrected, enabling the acquisition of an image with suppressed positional deviations. Attached Figure Description

[0013] Figure 1 is a block diagram showing a structural example of the MRI device of the present invention.

[0014] Figure 2 is a block diagram showing details of the imaging section of an MRI device.

[0015] Figure 3 is a diagram illustrating the processing of the MRI device of the present invention.

[0016] Figure 4 is a diagram illustrating the processing of pre-set information.

[0017] Figure 5 is a diagram showing the control flow of Implementation Method 1.

[0018] Figure 6 is a diagram illustrating the control of Implementation Method 1.

[0019] Figure 7 is a diagram illustrating the control in Implementation Method 2.

[0020] Symbol Explanation

[0021] 1-MRI device, 10-Camera unit, 20-Computer, 21-Measurement and control unit, 211-Prior information acquisition unit, 213-Respiratory motion monitoring unit, 215-Cardiocardiogram monitoring unit, 30-UI unit, 40-Storage device, 50-Electrocardiograph. Detailed Implementation

[0022] The embodiments of the MRI device and its control method of the present invention will be described below.

[0023] First, referring to Figures 1 and 2, the overall structure of the MRI device will be explained.

[0024] As shown in Figure 1, the MRI device 1 includes: an imaging unit 10 for collecting magnetic resonance signals generated from a subject; a computer 20 for controlling the imaging unit 10 and performing operations such as image reconstruction using the magnetic resonance signals collected by the imaging unit; a user interface unit 30 for displaying a device and an input device; and a storage device 40.

[0025] This invention relates to a technique for simultaneous electrocardiogram (ECG) imaging using an MRI device. Its key feature is the structure and function of the control unit of the MRI device used for controlling simultaneous imaging. The computer 20, which functions as the control unit, includes a measurement control unit 21 that performs the control measurement. This unit comprises: a respiratory motion monitoring unit 213 that monitors respiratory motion using navigation echoes and sends signals required for measurement control; a cardiac cycle monitoring unit 215 that inputs signals from an ECG machine 50 or similar device installed on the subject to monitor the cardiac cycle; and a pre-setting information unit 211 for setting parameters required for simultaneous imaging.

[0026] Apart from the measurement control unit 21, the computer 20 is similar to a conventional MRI device, including an image processing unit 22 that performs image reconstruction and other image processing using MRI signals collected from the subject, and a display control unit 23 that controls the display of the UI unit 30.

[0027] The functions of the aforementioned computer 20 can be implemented in a general-purpose computer or workstation by reading programs that can perform various functions, but some functions can also be implemented through hardware such as programmable ICs. Moreover, sometimes some functions are implemented by processing devices different from those of the MRI device.

[0028] The structure and function of the imaging unit 10 are the same as those of a conventional MRI device. To simplify, as shown in Figure 2, it includes a magnet 101 that generates a static magnetic field, a tilted magnetic field coil 102 that generates tilted magnetic fields in three mutually orthogonal axes, an RF transmitting coil 103 that irradiates a high-frequency magnetic field, an RF receiving coil 104 that detects the MRI signal generated from the subject 105, a transmitter 113 that sends a predetermined high-frequency current to the RF transmitting coil 103, a receiver 114 connected to the RF receiving coil 104, a tilted magnetic field power supply 112 that drives the tilted magnetic field coil 102, and a sequencer 115. Sometimes, one RF coil serves as both the RF transmitting coil 103 and the RF receiving coil 104. In this case, a switch (not shown) is added between the transmitter 113 and the receiver 114. Under the control of the control unit, the sequencer 115 drives the transmitter 113, the receiver 114, and the tilted magnetic field power supply 112 according to a pulse sequence.

[0029] The subject 105 is typically moved into the static magnetic field space (camera space) generated by the magnet 101 while lying on the bed 106, and is then positioned so that the examination area is the center of the static magnetic field space before being photographed.

[0030] Next, based on the above structure, a dual-synchronization imaging method using an MRI device for both electrocardiographic and respiratory motion synchronization will be described. A summary of the process is shown in Figure 3.

[0031] First, as preliminary measurements, positioning photography (S1) is performed to position the subject within the imaging space, or scanning images (hereinafter referred to as scans) of three cross-sections of the imaging site taken at the center of the imaging space. Based on these preliminary measurements, synchronization parameters required for controlling the actual imaging are set (S2). These synchronization parameters include a threshold window for monitoring the stable period of respiratory movement, a delay time from a specific phase of the cardiac cycle (R wave) to the actual measurement, and the location for acquiring the navigation echo. The synchronization parameters vary depending on the subject and are therefore determined based on the images and data obtained from the preliminary measurements using the subject as the subject.

[0032] Then, navigation measurement begins, and monitoring of respiratory movements begins (S3). Simultaneously, or before or after the navigation measurement, electrocardiogram waveforms from electrocardiograph 50 are read to monitor the cardiac cycle (S4).

[0033] Formal measurements are performed at the moment when respiratory movement is in a prescribed stable period and the cardiac phase becomes a specific phase, and image data is collected (S5). Therefore, the transition of the cardiac cycle obtained from the moment before the detection of the specific phase (R wave) is confirmed (the transition from outside the threshold window to inside the threshold window), and the execution of formal measurements is determined based on the results.

[0034] Formal measurements, such as cardiac imaging, involve executing known 2D or 3D pulse sequences. At this time, the cardiac phase at the time of image data acquisition is fixed, and the slice position for formal measurement is corrected as needed based on the displacement of respiratory motion obtained from the navigation echo acquired before image data acquisition. If the image data required for image reconstruction is collected, image reconstruction and display are performed (S6).

[0035] Through the above processing, the moment when cardiac phase and respiratory displacement coincide can be utilized to the maximum extent to perform imaging, thereby improving data acquisition efficiency and suppressing the extension of imaging time. Furthermore, imaging can be performed without missing the moment when cardiac phase and respiratory displacement coincide, thus enabling imaging to perform two formal measurements in each respiratory cycle.

[0036] The following describes the specific implementation methods of each process and its control, using the heart as an example. The process in Figure 3 is common in the following implementation methods, and will be explained with appropriate reference.

[0037] <Implementation Method 1>

[0038] This embodiment is an example of a subject with relatively stable respiratory movements, and the respiratory movement monitoring window is set in a way that includes the entire exhalation period (exhalation period) of respiratory movements that lasts for a relatively long time.

[0039] First, referring to Figure 4, the details of the prior measurement (S1) and synchronization parameter setting (S2) involved in the prior information setting unit 211 will be explained.

[0040] After locating the imaging area of ​​the subject, a scan is performed to capture images of the subject's imaging target area (S101-S104). During the scan, for example, three cross-sections (Ax, COR, SAG) are first captured with the heart as the magnetic field center (S101). Then, an Ax cross-section near the center of the left ventricle, determined from the three cross-sections, is captured (S102). A long-axis cross-section of the left ventricle, determined from the Ax cross-section in S102, is captured (S103). Finally, a short-axis cross-section of the left ventricle, determined from the Ax cross-section in S102 and the long-axis cross-section in S103, is captured (S104).

[0041] Next, an animated image is captured of the cross-section determined in S102 or S104 (S105), and displayed on the display device of the UI unit 30. The animated image can be understood as a low-resolution continuous image of the heart moving along the time axis. The user can observe the animated image displayed on the display device, confirm the start time of the period with smaller beats (diastole), and set this start time as the delay time for subsequent images (S106).

[0042] Next, the user sets the location of the navigation echo at a predetermined distance from the heart as the location for obtaining the navigation echo (S107). The location of the navigation echo is not limited, but is usually set to the diaphragm. The location of the diaphragm can be set, for example, based on the SAG image via the UI unit 30.

[0043] Next, a threshold window for navigation measurements is determined (S108). For example, the threshold window position is aligned with the upper end of the diaphragm on the SAG image obtained in S101. This allows data to be collected during the stable expiratory phase of respiratory movement. The threshold window width is preset to a predetermined value, for example, approximately 3 mm, as a scanning parameter.

[0044] After the above processing, the pre-measurement and synchronization parameter settings are completed, and the recording begins (S109). As shown in Figure 3, the recording includes respiratory motion monitoring (navigation measurement) S3, cardiac cycle monitoring S4, and formal measurement S5. Hereinafter, the control flow will be explained with reference to Figures 5 and 6. Figure 5 shows the control flow, and Figure 6 shows the progress of cardiac cycle, respiratory cycle, and measurement along the time axis. In Figure 6, as an example, the ECG waveform, respiratory motion, and measurement time elapsed are shown when two formal measurements are performed and one data point is acquired in two cardiac cycles. In Figure 6, “●” indicates the acceptance signal generated by the respiratory motion monitoring unit 213, and “○” indicates the rejection signal.

[0045] If imaging begins, the measurement control unit 21 begins navigation measurement, detecting the displacement of the diaphragm based on respiratory motion (S201). Specifically, the imaging unit 10 acquires MRI signals (data) from an elongated region containing the diaphragm along approximately the body axis, and the respiratory motion monitoring unit 213 detects the diaphragm position from an image obtained by performing a one-dimensional Fourier transform on the data of the elongated region along a direction parallel to the body axis, and displays it on the UI unit 30 (display device). After imaging begins, the user observes the subject's respiratory status and adjusts the position of the threshold window set in S106 as needed. Typically, the upper end of the window is aligned with the upper end of the diaphragm, which moves up and down with breathing.

[0046] Before and after respiratory motion monitoring, the cardiac cycle monitoring unit 215 reads signals from the electrocardiograph 50. If an R wave is detected, a threshold signal is sent to the measurement control unit 21 (S203). If the measurement control unit 21 receives the threshold signal, it confirms, based on the previously received signals from the respiratory motion monitoring unit 213, whether the most recent signal transition was a transition from a rejection signal to an acceptance signal (rejection / acceptance transition) or a transition from an acceptance signal to a rejection signal (acceptance / rejection transition) (S204). As a result, as shown in FIG6, if a rejection / acceptance transition is confirmed at the time shown in (A), the camera unit 10 is controlled to start the formal measurement (Main1) after a predetermined delay time from the R wave (S205). The delay time from the R wave to the start of the formal measurement is the time set in the synchronization parameter setting step (FIG. 3: S2, FIG. 4: S106). In addition, unlike the example shown in FIG. 6, the same processing is performed even if it is confirmed at the time shown in FIG. 6 that it is not a rejection / acceptance transition but more than two consecutive acceptances.

[0047] Furthermore, as shown in Figure 6, navigation measurements (B1) continue during the delay time to monitor the respiratory motion position. Then, using the respiratory motion position detected in the navigation echo C acquired just before the delay time expires, it is determined whether the slice position needs to be corrected for the subsequent formal measurement. For example, the slice position is changed by the deviation of the respiratory motion position detected in the navigation echo C from a predetermined position (reference position) within a threshold window, ΔD, or ΔD × a coefficient, for the formal measurement. The coefficient can be empirically calculated, for example, using the ratio of the heart's displacement width to the diaphragm's displacement width, and is typically set to around 60%. When the difference ΔD between the respiratory motion position and the reference position is zero, the formal measurement begins without adjusting the slice position.

[0048] The slice position is adjusted by changing the frequency of the excitation RF. This slice position correction prevents position deviation.

[0049] The formal measurement is not particularly limited, but in the case of cardiac imaging, the blood signal within the heart is suppressed, and a coronary artery examination called "Black Blood" or WHCA (Whole Heart Coronary Angiography) is performed to acquire diagnostic images of the heart wall shape. In these cardiac imaging procedures, a pulse sequence for the formal measurement is performed after a pre-pulse is applied. In Figure 6, such a pre-pulse is shown before the formal measurement (Main 1, Main 2). Specifically, in "Black Blood," as a pre-pulse, two inverted pulses (IR) are applied in a non-selective-selective sequence, followed by a sequence using the 2D-FSE (Fast Spin Echo) method, to image the entire left ventricle in the short-axis section determined in S104 of Figure 4. Furthermore, in “WHCA”, a fat suppression pulse (FatSat) is applied as a pre-pulse, for example using a 3D-BASG (Balanced SARGE: steady-state acquisition with rewinded gradient echo) sequence, to image the entire heart in the Ax profile.

[0050] After the formal measurement is completed, further navigation measurements are performed to monitor respiratory movements. Additionally, in Figure 6, the navigation echo generated after the formal measurement is completed is a virtual echo that is not used for detecting respiratory movement displacement until the signal stabilizes. The respiratory movement monitoring unit 213 continues respiratory movement monitoring using the navigation echo (B2) after the signal stabilizes. By setting a virtual echo, the accuracy of respiratory movement monitoring can be improved.

[0051] In the example shown in Figure 6, at the time point when the second R wave is detected, respiratory motion is in a stable phase and in a state of receiving a signal. Therefore, the transition of the respiratory motion signal closest to the detection of this R wave is the same as when the first R wave is detected—a rejection / acceptance transition. Therefore, a formal measurement (Main 2) is performed after a predetermined delay following the detection of the second R wave. Regarding this formal measurement, the slice position is also adjusted based on the respiratory motion displacement information obtained in the navigation echo C immediately preceding it, which is the same as in the first formal measurement (Main 1).

[0052] On the other hand, if the transition of respiratory motion before the detection of the R wave is not a rejection / acceptance transition (S204), no formal measurement is performed, and the system returns to the respiratory motion monitoring state (S201). The formal measurement becomes standby until the next rejection / acceptance transition. In the example shown in Figure 6, when the third R wave is detected, the transition of the signal immediately preceding it is an acceptance / rejection transition and is in a state of issuing a rejection signal. Therefore, no formal measurement is performed, and only navigation measurement continues (from S204 to S201).

[0053] After repeating the above process and collecting the image data that should be collected in the formal measurement, the image reconstruction process begins (S206, S207). Furthermore, as mentioned above, there are various imaging methods, and measurements based on more than one imaging method can be performed in a single shot; the "formal measurement" in this embodiment includes such a case.

[0054] Thus, in this embodiment, navigation monitoring of respiratory movements is continuously executed to detect the onset of a stable respiratory phase. If an electrocardiogram (ECG) wave is detected, navigation continues until the desired cardiac phase is achieved, ensuring that respiratory movements have entered a stable phase, and then formal measurements are taken. This allows data acquisition without missing moments when the cardiac and respiratory phases (displacement) coincide. Furthermore, since data can be continuously acquired even when the respiratory stable phase continues into the next cardiac cycle, imaging efficiency is improved.

[0055] Furthermore, according to this embodiment, image data is acquired by correcting the position of the camera slice corresponding to the displacement using the respiratory displacement detected during navigation immediately before the desired cardiac phase at the time of data acquisition, thus enabling the acquisition of images without positional deviation.

[0056] <Implementation Method 2>

[0057] In Implementation 1, the subjects were those with relatively stable respiratory movements, but in this implementation, the subjects were those with a relatively short respiratory stability period.

[0058] When the respiratory stabilization period is short, a rejection signal may be received between navigation measurements B2 and B3 as shown in Figure 6, i.e., between the end of one formal measurement and the beginning of the next formal measurement. In this case, a second formal measurement cannot be performed, and the imaging efficiency is reduced. In this embodiment, to avoid a significant reduction in efficiency, the threshold window is set slightly below the peak of the respiratory waveform (exhalation).

[0059] By shifting the threshold window downwards as shown in Figure 7, the transition from rejection to acceptance signals can be generated once before and after the peak of the respiratory waveform. By performing formal measurements after the rejection / acceptance transition, it is possible to achieve two formal measurements (one image data acquisition) within two cardiac cycles.

[0060] In this embodiment, the control flow is the same as that shown in FIG5. Similar to Embodiment 1, respiratory movement monitoring is performed at the start of imaging, and after receiving the acceptance signal, the detected R wave is used as a threshold signal for formal measurement. Referring to FIG7, the control of this embodiment will be described.

[0061] Navigation measurement begins. If respiratory motion enters the threshold window, the signal from the respiratory motion monitoring unit 213 changes from a rejection signal to an acceptance signal. It is set that if an R-wave is detected in this state, formal measurement begins after a predetermined delay (Main 1). Navigation measurement continues until formal measurement begins. The threshold window is set below the peak of respiratory motion; therefore, during formal measurement from B1 in this navigation measurement, there is a shift towards the outside of the threshold window (acceptance / rejection transition), but it remains within a stable period. However, at this time, a slice position correction equivalent to the displacement of respiratory motion detected in the navigation echo C immediately preceding the formal measurement is also performed, and formal measurement is executed.

[0062] In this embodiment, the stabilization period is short and the threshold window is set below the peak, so the signal from the respiratory motion monitoring unit changes from a rejection signal to an acceptance signal again before the next R wave. It is configured that if a second R wave is detected in this state, a formal measurement (Main 2) begins after a predetermined delay. Here, during the delay period and between navigation measurements, the respiratory motion transitions to a state that issues a rejection signal, but by performing slice position correction equivalent to the displacement of the respiratory motion detected in the navigation echo C immediately preceding the formal measurement, and then performing the formal measurement, it is possible to suppress the influence of motion and acquire image data once per two heart rates. Afterwards, navigation measurements are continuously performed until the signal changes from a rejection signal to an acceptance signal; no formal measurement is performed during this period. Furthermore, in the periods shown in examples (A1) and (A2) of Figure 7, the same process is performed even if there is confirmation of two or more consecutive acceptances instead of a rejection / acceptance transition.

[0063] According to this embodiment, even with a short stabilization period, two data points can be acquired within one respiratory cycle, preventing a decrease in imaging efficiency. Furthermore, by using displacement information obtained from the navigation echo immediately preceding the formal measurement to adjust the slice position for the formal measurement, images without positional deviation can be acquired even with a short stabilization period.

[0064] The above description uses cardiac imaging as an example to illustrate the implementation of the MRI device and its control method of the present invention. However, the present invention is not limited to cardiac imaging; it can be applied to imaging any tissue, such as arteries or tissues near the heart, that is easily affected by pulsation and respiratory movements, and the same effect can be obtained. Furthermore, the use of R waves from an electrocardiograph for monitoring the cardiac cycle has been described; however, as long as the cardiac cycle can be monitored, it is not limited to an electrocardiograph, but can also be used with a pulse oximeter, etc.

Claims

1. A magnetic resonance imaging device, characterized in that, It includes: an imaging unit that collects MRI signals generated from a subject, performs navigation measurements to detect respiratory movements of the subject, and performs formal measurements to generate images of the subject; and a measurement control unit that controls the imaging unit. The respiratory motion monitoring unit monitors the respiratory motion of the subject using the results of the navigation measurement. Based on whether the magnitude of the subject's respiratory motion is inside or outside a pre-set threshold window, it sends acceptance and rejection signals to the measurement control unit. The cardiac cycle monitoring unit monitors the cardiac cycle of the subject and generates a threshold signal at the moment the R wave of the cardiac cycle is generated. The measurement control unit controls the camera unit as follows: it continuously performs the navigation measurement before and after the generation of the threshold signal. If a threshold signal is received from the cardiac cycle monitoring unit, and the most recent transition in the signal transition from the respiratory motion monitoring unit generated during the navigation measurement before receiving the threshold signal is from a rejection signal to an acceptance signal, a formal measurement is performed after a pre-set delay time.

2. The magnetic resonance imaging device according to claim 1, characterized in that, The respiratory motion monitoring unit will not use the results of the navigation measurement closest to the formal measurement in the navigation measurement conducted after the formal measurement for respiratory motion monitoring.

3. The magnetic resonance imaging device according to claim 1, characterized in that, The measurement control unit uses the respiratory movement position obtained through the navigation measurement performed within the delay time to adjust the slice position of the subsequent formal measurement following the navigation measurement.

4. The magnetic resonance imaging device according to claim 1, characterized in that, It also includes a pre-set information unit, which sets a threshold window for the respiratory movement, and sets the threshold window at a position that is a stable period of the respiratory movement.

5. The magnetic resonance imaging device according to claim 4, characterized in that, The pre-set information unit sets a threshold window in a manner that includes the maximum value of the steady period of the respiratory movement.

6. The magnetic resonance imaging device according to claim 4, characterized in that, The pre-set information unit sets a threshold window such that a position lower than the maximum value of the steady period of the respiratory movement is set as the upper limit.

7. The magnetic resonance imaging device according to claim 4, characterized in that, The measurement performed by the camera unit includes scanning to determine the camera portion of the subject, and the pre-information setting unit uses the image obtained by the scanning to determine the position of the threshold window.

8. The magnetic resonance imaging device according to claim 4, characterized in that, It also includes a UI unit that accepts user adjustments to the position of the threshold window, and the respiratory motion monitoring unit changes the position of the threshold window set by the pre-set information unit in response to the adjustments accepted by the UI unit.

9. The magnetic resonance imaging device according to claim 1, characterized in that, It also includes a pre-set information unit that sets the delay time for the formal measurement. The pre-set information unit determines the delay time using an animated image obtained by taking an animated camera with the region containing the heart of the subject as the object.

10. A control method for a magnetic resonance imaging (MRI) device, wherein signal collection for generating an image of the subject is performed as a formal measurement when the electrocardiogram (ECG) waveform and respiratory motion waveform of the subject are respectively within a defined range, the control method comprising the following steps: continuously performing navigation measurements to detect respiratory motion waveforms before and after the formal measurement; monitoring the results of the navigation measurements, generating an acceptance signal when the magnitude of the respiratory motion is inside a set threshold window, and generating a rejection signal when the magnitude of the respiratory motion is outside the threshold window; and after detecting the R wave of the ECG waveform, when the most recent transition in the transition of the signals generated in the navigation measurements before the R wave was detected is a transition from a rejection signal to an acceptance signal, starting the formal measurement after a preset delay time.

11. The control method for the magnetic resonance imaging device according to claim 10, characterized in that, It also includes the following step: adjusting the slice position of the formal measurement using the results of the navigation measurement performed immediately prior to the formal measurement.

12. The control method for the magnetic resonance imaging device according to claim 10, characterized in that, It also includes the following steps: performing a scanning video; and obtaining information about the respiratory movements of the subject from the results of the scanning video to set the position of the threshold window.

13. The control method for the magnetic resonance imaging device according to claim 10, characterized in that, It also includes the following steps: acquiring animated images of the heart; and obtaining information about the cardiac cycle from the animated images to determine the delay time.

Images