JP2008148806A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus improving an examination efficiency by adjusting a displacement of an imaging area due to respiratory movement within a prescribed range, improving an acquisition efficiency of MRI signals and shortening an imaging time, and providing high image-quality MRI images by reducing the artifact due to the respiratory movement. <P>SOLUTION: This MRI apparatus has a respiratory movement adjusting device 115 to adjust the displacement of the imaging area due to the respiratory movement of a subject 101 within the prescribed range. The respiratory movement adjusting device 115 consists of a respiratory movement adjusting belt 115a having an air layer for taking air in/out, closely sticking to the imaging area of the subject 101 and adjusting the displacement of the imaging area, a pump 115b for taking a necessary amount of air into/out from the respiratory movement adjusting belt 115a, and an air diffusion tube 115c diffusing the air between the pump 115b and the respiratory movement adjusting belt 115a. This MRI apparatus adjusts the displacement of the imaging area due to the respiratory movement of the subject 101 by the respiratory movement adjusting belt 115a, monitors the adjusted displacement with navigator echoes and, when the displacement of the imaging area becomes a preset displacement, starts the imaging. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic resonance imaging apparatus, and more particularly, to a magnetic resonance imaging apparatus suitable for improving examination efficiency and reducing body movement artifacts due to a means for adjusting the respiratory motion of a subject to a predetermined range. .

  A magnetic resonance imaging system that uses the nuclear magnetic resonance (NMR) phenomenon to obtain tomographic images of the human body from the density distribution in the body of the main substance protons that make up the subject and the spatial distribution of the relaxation time of nuclear spins in the subject ( Hereinafter, it may be referred to as an MRI apparatus) is widely used in medical institutions.

  This MRI device has excellent contrast resolution, is considered non-invasive because it does not use ionizing radiation, the images obtained are less susceptible to bone and air, and is sensitive to fluid behavior, so it is vascular It has features such as being effective for diagnosis of diseases and spinal cord regions.

The MRI apparatus having the above features has been developed with the development of high-speed imaging methods along with recent advances in hardware, and diagnosis using the MRI in the heart region, that is, cardiac MRI has begun to spread in clinical settings, cardiac function analysis, Viability testing, coronary angiography, etc. are performed.
In this cardiac MRI, there is a problem of body motion artifacts due to respiratory motion in addition to heartbeat, and the influence of respiratory motion is significant particularly in coronary angiography that requires high spatial resolution.

The body motion artifact is caused by a change between when the position of an area to be imaged is excited and when a signal is measured, and reduces the body motion artifact due to the respiratory motion. As a method, there is a synchronous imaging method (respiration gating imaging method) in accordance with the time phase of respiration.
In this method, respiratory motion is monitored by a respiratory sensor attached to the abdominal wall or chest wall of a subject, and data is collected by setting an imaging trigger at a specific respiratory phase. As a result, data is collected in a time phase where the displacement of respiratory motion is small, and body motion artifacts are reduced.

  As described above, although the respiratory motion is monitored using the external respiratory sensor, the deviation between the position of the region to be imaged and the position of the excited region is further reduced to reduce artifacts caused by heartbeat and respiratory motion. Non-Patent Document 1 discloses a method for monitoring respiratory motion using navigator echo, which is an additional echo, as a method for reducing the above.

  This is a breathing gating method using navigator echo in combination with electrocardiogram synchronization. After detecting the electrocardiogram, a delay time of a predetermined time is set from the predetermined phase of the electrocardiogram, and the navigator sequence is determined by this delay time. Is to execute. This navigator sequence excites a region of interest (e.g., the diaphragm) to be monitored locally, acquires an echo signal from the local excitation region without adding a phase encoding gradient magnetic field, i.e., a navigator echo, and performs respiratory gating imaging. Is a sequence for executing

A displacement due to respiratory motion of the region of interest is acquired by the navigator echo, and a main measurement sequence for measuring MRI image data is executed.
In this case, only the MRI signal when the displacement due to the acquired respiratory motion is within a preset narrow window width is acquired, and the MRI signal outside the window is discarded. Such acquisition control of the main measurement data is repeated, and the process ends when data acquisition necessary for image reconstruction is completed.

  By this method, by acquiring data at substantially the same displacement, an image in which the influence of body motion due to respiratory motion is greatly reduced can be obtained. However, since there is a lot of data to be discarded, the shooting time is extended.

  This is because the preset window width is narrow, and if the window width is widened, data to be discarded is reduced and the imaging time can be shortened. For this purpose, the respiratory motion of the subject is minimized. It is necessary to suppress.

Non-patent document 2 discloses a technique for fixing the chest and abdomen with a belt-like cloth as a method for suppressing the subject's respiratory movement.
This is a technique for physically suppressing respiratory movement by wrapping and compressing an abdominal band called a belt around the abdomen or chest of a subject.
Navigator Echoes in Cardiac Magnetic Resonance; David Firmin and Jenny Keegan, Journal of Cardiovascular Magnetic Resonance, 3 (3), 183-193 (2001) Initial study of 4D Whole Heart Imaging: Yoshinori Ota and 6 others, Proceedings of the 62nd Annual Conference of the Radiological Society of Japan 375, p.188

  If the means of Non-Patent Document 2 can suppress respiratory motion to an appropriate level by the belt, the MRI signal acquisition efficiency is increased, the imaging time is shortened, and the examination efficiency is also improved.

However, it is difficult to wind while confirming the degree of suppression of respiratory motion, and it is unclear how much respiratory motion is suppressed by the belt.
In addition, because the belt is wrapped around the subject manually, the range of respiratory motion varies depending on the strength of the belt, and the image quality also varies. Cannot be suppressed at the same level.

As described above, the means according to Non-Patent Document 2 cannot stabilize the displacement due to the respiratory motion, so that it is difficult to photograph in the optimum state.
If it becomes clear that respiratory motion cannot be suppressed and the suppression state is adjusted, it is necessary for the operator to rewind the belt while the imaging is stopped, and the inspection efficiency is poor.

  Therefore, the method of physically suppressing fluctuation due to breathing of the subject using the belt disclosed in Non-Patent Document 2 is a quantitative determination of the strength of compression, the actual degree of respiratory movement suppression due to compression, and the like. Therefore, it is difficult to always take an image in the state of optimal respiratory motion suppression, and the imaging results vary.

  The present invention has been made in view of the above problems, and by adjusting the displacement of the imaging region due to respiratory motion to a predetermined range, the MRI signal acquisition efficiency is increased, the imaging time is shortened, and the examination efficiency is improved. The purpose is to obtain high-quality MRI images by reducing artifacts due to imaging and respiratory motion.

  In order to achieve the above object, the magnetic resonance imaging apparatus of the present invention is configured as follows. That is, a static magnetic field generating means for generating a substantially uniform static magnetic field, a gradient magnetic field generating means for generating a gradient magnetic field in the static magnetic field region, and a high frequency magnetic field for causing nuclear magnetic resonance in the subject are generated. High-frequency magnetic field generating means, receiving means for receiving a nuclear magnetic resonance signal from the subject, signal processing means for processing the nuclear magnetic resonance signal to generate an image, and an image obtained by the signal processing means Display means for displaying the bed, a bed on which the subject is placed, bed movement control means for controlling movement of the bed, operation means for performing an operation for taking the image, and an operation signal of the operation means The control means for controlling each of the means corresponding to the above and the respiratory motion suppression means for suppressing the respiratory motion of the subject, and taking an image while suppressing the respiratory motion of the subject by the respiratory motion suppression means Magnetic resonance imaging equipment A is, the respiratory motion suppression device is configured with a respiratory motion adjusting means for adjusting the displacement of the imaging region by respiratory motion of the subject in a predetermined range.

  The breathing motion adjusting means has an air layer for taking in and out air, a pressing means for pressing the imaging area in close contact with the imaging area of the subject, and an air pressure adjusting means for adjusting the air pressure of the air layer of the pressing means The displacement of the imaging region due to the respiratory motion of the subject is adjusted to a predetermined range.

  First displacement determination means for determining that the displacement of the imaging region of the subject adjusted by the respiratory motion adjustment means has become a preset displacement, and imaging is started by the first displacement determination means The first photographing start means is further included in the control means, and photographing is started by the photographing start means.

  Furthermore, navigator echo acquisition means for locally exciting an imaging region by the high-frequency magnetic field generation means to acquire navigator echo, and imaging by respiratory motion adjusted by the respiratory motion adjustment means based on the acquired navigator echo Displacement calculating means for calculating the displacement of the region, and the displacement calculated by the displacement calculating means is used as the first displacement determining means.

  The displacement calculating means is means for calculating a respiratory motion displacement characteristic that is a relationship between time and displacement of the imaging region due to respiratory motion, and the first displacement determining means is the respiratory motion calculated by the displacement calculating means. First respiratory motion amplitude ratio calculating means for calculating a ratio between the amplitude of the displacement due to the respiratory motion before putting air into the air layer and the amplitude of the displacement due to the respiratory motion after putting air using the displacement characteristics; A first respiratory motion amplitude ratio setting means for setting a predetermined value of the amplitude ratio; an amplitude ratio calculated by the respiratory motion amplitude ratio calculation means; and a predetermined value of the amplitude ratio set by the respiratory motion amplitude ratio setting means; A first respiratory motion amplitude ratio comparing means for comparing the first respiratory motion amplitude ratio comparing means, and a first air injection determination for determining whether or not to continue air injection into the air layer based on a comparison result of the first respiratory motion amplitude ratio comparing means Means.

  A first gate window width setting unit configured to set a gate window width at which a displacement of the respiratory motion displacement characteristic that is an acquisition range of the nuclear magnetic resonance signal by the reception unit is substantially constant; and the first respiratory motion amplitude Respiration gating imaging is performed in synchronization with the navigator echo signal by detecting that the amplitude ratio calculated by the ratio calculation means has become the predetermined amplitude ratio that has been set.

  In the respiratory gating imaging, means for detecting that the displacement due to the respiratory motion has reached a predetermined value in synchronization with the navigator echo signal, and automatically adjusting the first gate window width based on the detection signal Further provided.

  The respiratory motion adjusting means includes a plurality of respiratory motion adjusting means corresponding to a plurality of imaging regions, and the multi-station imaging or moving bed is used for imaging by moving the bed to the plurality of spatially different imaging regions. Take a picture.

The multi-station shooting or moving bed shooting is configured to include the following means.
(1) The plurality of respiratory motion adjusting means includes a plurality of compression means having an air layer through which air is taken in and out, in close contact with the plurality of imaging areas of the subject, and compressing the imaging areas, and these compression means Air pressure adjusting means for adjusting the air pressure of the air layer.

  (2) The displacement due to the respiratory motion of the subject adjusted by the respiratory motion adjustment unit corresponding to the imaging region to be imaged first among the plurality of respiratory motion adjustment units is a preset displacement. The control means further includes a second displacement determining means for determining and a second imaging start means for starting imaging by the second displacement determining means.

  (3) A plurality of navigator echo acquisition means for locally exciting the plurality of imaging regions by the high-frequency magnetic field generating means to acquire a plurality of navigator echoes, and the plurality of imaging based on the acquired plurality of navigator echoes A plurality of displacement calculating means for calculating the displacement of the area is further provided, and the displacement of the imaging area in which imaging is first performed among the plurality of displacements calculated by the multiple displacement calculating means is used as the second displacement determining means.

  (4) The plurality of displacement calculating means is means for calculating a respiratory motion displacement characteristic of the plurality of imaging regions, which is a relationship between time and displacement of the imaging region due to respiratory motion, and the second displacement determining means is The ratio of the displacement amplitude due to the respiratory motion before the air is introduced into the air layer and the amplitude of the displacement due to the respiratory motion after the air is introduced is calculated using the respiratory motion displacement characteristics calculated by the multiple displacement calculating means. Second respiratory motion amplitude ratio calculating means, second respiratory motion amplitude ratio setting means for setting a predetermined value of the amplitude ratio, amplitude ratio calculated by the second respiratory motion amplitude ratio calculating means, and the first The second respiratory motion amplitude ratio comparison means for comparing the predetermined value of the amplitude ratio set by the second respiratory motion amplitude ratio setting means and the comparison result of the second respiratory motion amplitude ratio comparison means to the air layer And second air injection determination means for determining whether or not to continue the air injection.

  (5) further comprising a second gate window width setting means for setting a gate window width in which the displacement of the respiratory motion displacement characteristic that is an acquisition range of nuclear magnetic resonance signals by the plurality of receiving means is substantially constant; And means for detecting that the amplitude ratio calculated by the respiratory motion amplitude ratio calculating means is equal to the predetermined amplitude ratio set and starting respiratory gating imaging in synchronization with the navigator echo signal.

(6) Detecting that the displacement due to the respiratory motion has reached a predetermined value in synchronization with the plurality of navigator echo signals, and having means for automatically adjusting the second gate window width based on the detection signal .
(7) The plurality of respiratory motion adjustment means includes a respiratory motion adjustment selection unit that selects a respiratory motion adjustment unit corresponding to the imaging region only at the time of imaging in the imaging region where the respiratory motion needs to be adjusted. The respiratory motion of the subject is adjusted by the selected respiratory motion adjusting means.

According to the present invention, the displacement of the imaging region due to the breathing motion of the subject is adjusted by the air pressure compression means, and the adjusted displacement is monitored by the navigator echo, so that the displacement of the imaging region becomes a preset displacement. Occasionally, since the imaging is started, the acquisition efficiency of the MRI signal is increased, thereby shortening the imaging time and improving the inspection efficiency. In addition, since the displacement of the imaging region due to the respiratory motion is small and the respiratory motion can be stably suppressed, a high-quality image with reduced body motion artifacts due to the respiratory motion can be acquired.
Furthermore, the present invention can be applied to breathing gating imaging using navigator echo, multi-station imaging for capturing a wide imaging area, moving bed imaging, and the like, thereby obtaining the same effects as described above.

Preferred embodiments of a magnetic resonance imaging apparatus (MRI apparatus) according to the present invention will be described below in detail with reference to the accompanying drawings.
Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments of the present invention, and the repetitive description thereof will be omitted.

  FIG. 1 is a diagram showing an overall configuration of an MRI apparatus including means for suppressing respiratory movement of a subject with air pressure while monitoring the respiratory movement of the subject using navigator echo.

  In FIG. 1, an MRI apparatus includes a static magnetic field magnet 102 that generates a uniform static magnetic field in a body axis direction around a subject 101, a gradient magnetic field coil 103 that applies a gradient magnetic field to the subject 101, and this gradient A gradient magnetic field power source 104 for supplying a gradient magnetic field current to the magnetic field coil 103 and a high frequency magnetic field for causing an NMR (nuclear magnetic resonance) phenomenon in the atomic nucleus constituting the biological tissue of the subject 101 are generated. An RF irradiation coil 105, a transmission unit 106 that transmits a high-frequency pulse for generating the high-frequency magnetic field in the RF irradiation coil 105, an RF probe 107 and a signal detection unit 108 that detect an echo signal emitted by the NMR phenomenon And an image processing such as image reconstruction calculation using the echo signal detected by the signal detection unit 108 and a signal processing unit 109 for processing various signals, and a reconstructed image processed by the signal processing unit 109. Display unit 110 for displaying, and A bed 112 on which the examiner 101 is placed and can be moved in the body axis direction (arrow 111 in the figure) of the examinee, a bed control unit 113 for controlling the movement of the bed 112, a photographing sequence, and necessary for photographing An operation console (not shown) for performing an imaging operation by setting various parameters, an imaging section, and the like, a control unit 114 for controlling the entire system based on an operation signal set by the operation console, and breathing of the subject by air pressure And a respiratory motion adjustment device 115 for adjusting the amount of displacement of the imaging region due to motion.

  The respiratory motion adjusting device 115 (respiratory motion adjusting means) includes a respiratory motion adjusting belt 115a (compression means) attached to a subject, and a pump for taking in and out necessary air to and from the respiratory motion adjusting belt 115a. 115b (air pressure adjusting means) and an air supply / discharge tube 115c for supplying or discharging the air between the pump 115b and the breathing motion adjusting belt 115a.

  The gradient magnetic field coil 103 is composed of gradient magnetic field coils in three directions of X, Y, and Z, supplied with a gradient magnetic field current from the gradient magnetic field power supply 104, and a slice selection gradient magnetic field, a phase encoding gradient magnetic field, and a readout gradient. Generate a magnetic field.

  Air pressures of the gradient magnetic field power source 104, the transmission unit 106, the signal detection unit 108, and the respiratory motion adjustment device 115 are controlled by the control unit 114.

  The bed 112 is movable in the direction of the head and feet of the subject 101, and moves the subject 101 to the position of the imaging region while matching the execution of the imaging sequence by the bed control unit 113.

In the MRI apparatus configured as described above, the imaging object that is currently widely used in clinical practice is proton, which is the main constituent material of the subject.
By imaging the spatial distribution of the proton density and the relaxation state of the excited state, the shape of the human head, abdomen, limbs, etc., or the functions of blood vessels (blood, blood flow), etc. Take a dimensional shot.

Using the MRI apparatus configured as described above, different phase encodings are given by the phase encoding gradient magnetic field, and echo signals obtained by the respective phase encodings are detected.
As the number of phase encodings, values such as 128, 256, and 512 are usually selected per image. Each echo signal is usually obtained as a time-series signal composed of 128, 256, 512, and 1024 sampling data, and one MR image is created by two-dimensional Fourier transform of these data.

  Next, in the MRI apparatus having the above-described configuration, a description will be given of a method for reducing respiratory motion artifacts using navigator echoes in cardiac imaging when the respiratory motion adjustment device 115 does not adjust the displacement of the imaging region due to the respiratory motion of the subject. To do.

FIG. 2 is a sequence diagram of respiratory gating imaging using navigator echo in combination with electrocardiogram synchronization.
In the imaging by this sequence, when the amount of displacement of the imaging region (target region) due to the respiratory motion of the subject is not adjusted by the respiratory motion adjustment device 115, the target site of the subject is displaced as 202 by the respiratory motion. In order to reduce artifacts due to this respiratory motion, a predetermined displacement width 203 is set in the respiratory motion signal 202, and only the NMR signal within this displacement width is acquired. The image is reconstructed.

  Specifically, a navigator sequence 208 is executed after a set delay time 207 after detecting a specific time phase of the heart radio wave of the subject 101, for example, an R wave 201, with a biological monitor device (not shown). The navigator sequence is a sequence for locally exciting a region of interest (for example, a diaphragm) to be monitored and acquiring an echo signal from the local excitation region, that is, a navigator echo without applying a phase encoding gradient magnetic field.

  A displacement 204 due to respiratory motion of the region of interest is obtained by the navigator echo acquired by the navigator sequence, and the main measurement sequence 209 for images is executed following the navigator sequence 208.

Here, when the displacement 204 deviates from the preset narrow displacement width 203 like the displacement 204 obtained by the navigator sequence 208, the data 214 obtained by the main measurement sequence 209 is discarded.
Similarly, since the displacement 205 due to the respiratory motion in the case of the next navigator sequence 210 is also out of the displacement width 203, the detection data 211 by this is also discarded.
Then, since the displacement 206 due to the respiratory motion in the next navigator sequence 212 is within the displacement width 203, the data 216 is acquired by this measurement sequence 213.
Such acquisition control of the main measurement data is repeated, and the measurement ends when the data acquisition necessary for image reconstruction is completed.

By this method, data is acquired at substantially the same displacement to obtain an image in which the influence of body motion due to respiratory motion is greatly reduced. However, since much data is discarded, it takes a lot of time for imaging.
This is due to the fact that the displacement due to the acquired respiratory motion is narrow in advance, and if the displacement width is widened, the data to be discarded is reduced and the imaging time can be shortened. It is necessary to reduce the amount of displacement caused by the subject's respiratory motion.

  The present invention is provided with the respiratory motion adjustment device 115 in order to reduce the amount of displacement due to respiratory motion and shorten the imaging time. Hereinafter, the displacement amount due to respiratory motion is measured by the respiratory motion adjustment device 115. The first embodiment for photographing with a small size, the second embodiment in which the respiratory gating imaging method using navigator echo is applied to the first embodiment, the multi-station in the first embodiment or the second embodiment A third embodiment and a fourth embodiment will be specifically described in the case where the whole body photographing by photographing or moving bed photographing is applied.

First Embodiment
The first embodiment is an example of performing imaging under free breathing or breath holding imaging in a state in which the displacement of the imaging part due to the respiratory motion of the subject is reduced by the respiratory motion adjustment device 115.

  FIG. 3 is an overall view of the respiratory motion adjusting device 115 (respiratory motion adjusting means). In FIG. 3 (a), the respiratory motion adjusting device 115 is a cylindrical respiratory motion adjusting belt (compression means) capable of adjusting the inner diameter with air pressure as the respiratory motion adjusting belt 115a attached to the subject. A pump 115b (air pressure adjusting means) for taking in and out required air to and from the belt, and an air supply / discharge tube 115c for supplying and discharging the air between the pump 115b and the breathing motion adjusting belt 115a. Is done.

  The respiratory motion adjusting belt 115a has a required thickness for taking in and out air between the outer wall 301 and the inner wall 302, and a layer 303 (hereinafter referred to as an air layer) whose thickness is variable. A subject is inserted into the cylindrical portion and attached to the imaging portion of the subject.

  The air supply / discharge tube 115c is connected to the air layer 303, and when air is sent from the pump 115b to the breathing motion adjustment belt 115a, the air layer in the belt that is thin as shown in FIG. 303 becomes thick like 304 in FIG.

  Since the subject is inserted into the cylindrical portion of the breathing motion adjustment belt 115a capable of adjusting the inner diameter of the cylindrical shape by air pressure, the pump 115b is positioned at the imaging portion of the subject. When the air is introduced into the air layer, the imaging unit of the subject is pressed and the displacement due to the respiratory motion of the subject can be reduced. That is, by selecting the chest or abdomen as the imaging unit of the subject as a part where the respiratory motion adjustment belt 115a is set, fluctuations in the displacement of the imaging unit due to respiratory motion are forcibly suppressed and reduced.

The shape of the respiratory motion adjusting belt 115a shown in FIG. 3 is an example, and may be a shape as shown in FIG. 4, for example. This is a shape like a shirt, waistcoat or life jacket, and is worn by a subject with a slit 402, which will be described later, opened, and the arm of the subject is put out from the circular portion of the figure.
Air is sent from the pump 115b to the air layer 401 of the belt having such a structure to compress the chest and abdomen of the subject.
In addition, in order to make it easy for the subject to wear, it is also possible to divide a part of the air layer and insert the slit 402 and fix only the slit portion 402 with a surface fastener 403 or the like.

  The respiratory motion adjusting belt 115a of the respiratory motion adjusting device 115 shown in FIGS. 3 and 4 is useful when the receiving coil is integrated with the inner wall of the gantry remote from the subject and the whole body is photographed.

  When the MR signal receiving coil is directly attached to the imaging region of the subject, the respiratory motion adjustment belt 115a can be integrated with the receiving coil in close contact with the subject. For example, in photographing the chest and abdomen, the respiratory motion adjustment belt of FIG. 5 integrated with the receiving coils 501 and 502 is composed of two belts 503 and 504, and the subject is sandwiched from above and below by these belts. By providing a layer that allows air to enter the belt inside each coil, it is possible to accurately press the imaging region.

  Next, an example in which imaging is performed by attaching a respiratory motion adjustment belt to a subject will be described with reference to FIGS. In this example, the belt shown in FIG. 3 is used as the respiratory motion adjustment belt 115a.

  Fig. 6 shows an example of taking a coronal image 603 near the heart by attaching the respiratory motion adjustment belt 115a to the region extending from the chest to the abdomen of the subject 101. Fig. 6 (a) shows the respiratory motion adjustment. (B) shows the case where the displacement due to the respiratory motion in the region extending from the chest to the abdomen is reduced by introducing air before the air is put into the working belt 115a.

  In FIG. 6 (a), the respiratory motion adjustment belt 115a is attached to the subject's imaging region (region extending from the chest to the abdomen), and after setting the imaging region to the center of the static magnetic field, the respiratory motion adjustment When air is introduced into the air layer of the belt 115a, as shown in FIG. 6 (b), the chest and abdomen of the subject are compressed by the amount of the swell of the respiratory motion adjustment belt 115a, and the chest and abdomen are displaced by breathing. The amount is smaller.

  In this way, the displacement of the imaging region due to respiratory motion is reduced, and imaging starts (first imaging start means) when the displacement reaches a predetermined value (first displacement determination means) However, in order to do so, the subject's respiratory motion monitor is required. Although it is possible to use a mechanical respiration sensor for this monitor, the navigator echo that can directly monitor the movement of the subject can more accurately monitor the respiration.

As described above, the navigator echo is a signal obtained from the local excitation region by locally exciting a target region to be monitored without applying a phase encoding gradient magnetic field (navigator echo acquisition means).
In the example of FIG. 6, the local excitation region corresponds to the rod-shaped region indicated by 601. The major axis direction of this rod-shaped region is the echo signal readout direction (frequency encoding direction), and only the region 601 is excited. A navigator echo signal can be acquired.

  FIG. 6 shows an example in which the navigator echo acquisition position 601 is set in the abdomen and the respiratory motion in the AP (Anterior-Posterior) direction is monitored. The navigator is filled with air in the air layer of the respiratory motion adjustment belt 115a. Echo is acquired at regular intervals to calculate the displacement of the imaging area due to respiratory motion (displacement calculation means), and the relationship between time and the displacement of the imaging area due to respiratory motion based on this calculated displacement (hereinafter referred to as respiratory 602) (denoted as dynamic displacement characteristics).

  This respiratory motion displacement characteristic is obtained by performing one-dimensional Fourier transform on the navigator echo signal detected by the RF probe 107 and the signal detection unit 108 by the signal processing unit 109 and performing a process of arranging the converted values in time series. And the position where the navigator echo is acquired (abdomen, AP direction) and the displacement due to respiratory motion can be created (means for calculating respiratory motion displacement characteristics).

  If the respiratory motion displacement characteristic created in this way is displayed on the user interface of the display unit 110 in FIG. 1, as shown in the respiratory motion displacement characteristic 604 in FIG. 6 (b), the compression of the respiratory motion adjustment belt 115a is compressed. The decrease in respiratory motion displacement due to can be confirmed visually.

The time resolution of the respiratory motion monitor for monitoring the respiratory motion displacement characteristic is that the acquisition time of the navigator echo is generally about 20 to 30 ms, including the calculation time until the respiratory motion displacement is calculated from the acquired navigator echo. Is also possible in 100ms.
Therefore, by monitoring the respiratory movement displacement with the navigator echo for several tens of seconds, the respiratory movement displacement characteristic as shown at 701 in FIG. 7 can be obtained.

  As shown in FIG. 7, when the air pressure of the air layer of the respiratory motion adjusting belt 115a is gradually increased by the pump 115b, the air pressure increases as indicated by 706, and the displacement due to the respiratory motion is 702 → 703 → 704. → It becomes small like 705.

  Here, the signal processing unit 109 calculates the ratio between the amplitude 702 of displacement due to breathing motion before the air is introduced and the amplitude 703, 704, 705 of displacement due to the breathing motion after the air is introduced (first breathing). Dynamic amplitude ratio calculating means), and when the value set in advance (first respiratory motion amplitude ratio setting means) becomes 1/2, for example (first respiratory motion amplitude ratio comparison means), the pump 115b automatically Is controlled by the control unit 114 to stop (first air injection determining means) and start photographing.

That is, it is determined whether to continue or stop the injection of air into the air layer of the breathing motion adjustment belt 115a by calculating the ratio every predetermined time interval τ _{0. In} the example of FIG. As a result of calculating (707) the ratio between the amplitudes 702 and 703 at the point a, the ratio is greater than or equal to a predetermined half, so the pump 115b is continuously operated, and the ratio between the amplitudes 702 and 704 is determined at the next point b. As a result of the calculation (708), the ratio is equal to or more than a predetermined ½, so that the pump 115b is continuously operated, and the ratio between the amplitudes 702 and 705 is calculated (709) at the point c. Therefore, the pump 115b is stopped (710) and photographing is automatically started (711).

The imaging start time can be arbitrarily set by the ratio of the amplitude of displacement due to respiratory motion before and after the air injection, and the setting of this ratio is the same as the setting of other imaging parameters on the user interface of the display unit 110. Do. It is also possible that the subject feels pain during the air injection, so the operator can stop the pump 115b at any time before starting the set value, or start imaging. It is also possible to start shooting after the pressure is reduced later.
Note that the internal pressure of the breathing adjustment belt can be reduced by providing a manual valve or an electromagnetic valve in the air supply / discharge tube.

Thus, according to the first embodiment, the displacement of the imaging region due to the respiratory motion is reduced by the respiratory motion adjustment belt by adjusting the air pressure, and this displacement is monitored by the navigator echo, and the imaging region due to the respiratory motion is monitored. Since the imaging is started when the displacement becomes a predetermined value set in advance, the MRI signal acquisition efficiency is improved, thereby shortening the imaging time and improving the inspection efficiency.
In addition, since the imaging area due to respiratory motion is small and the respiratory motion can be stably suppressed, body motion artifacts due to respiratory motion can be reduced, and a high-quality MRI image can be obtained.

<< Second Embodiment >>
In the second embodiment, the respiratory gating imaging method using navigator echo is applied to the first embodiment in which the respiratory motion adjustment device 115 performs imaging while reducing the displacement due to respiratory motion, as shown in FIG. The procedure is the same as in the first embodiment until the imaging is automatically started. However, after the imaging is started, the imaging method for performing respiratory gating by navigator echo (the acceptance / rejection determination of the data by the respiratory movement displacement is performed and the imaging is performed). Shooting).

  In FIG. 8, (a) is a respiratory motion displacement characteristic 801 (relationship between time and displacement due to respiratory motion), (b) is the air pressure of the air layer of the respiratory motion adjustment belt 115a is gradually increased by the pump 115b. FIG. 8 is a diagram showing an increase in the air pressure 809 in the case, and these operating characteristics are the same as those in FIG.

  The second embodiment of the present invention performs respiration gating by analyzing respiration movement displacement characteristics that change as shown in FIG. 8 (a), which will be described in detail.

In FIG. 8 (a), the width 803 of the gate window 802, 804, which is the data acquisition range for acquiring image data, is normally about 5 mm, and this window width setting is set on the user interface of the display unit 110. This is performed in the same manner as other imaging parameter settings (first gate window width setting means).
Then, similarly to the first embodiment, it is detected that the amplitude ratio calculated by the first respiratory motion amplitude ratio calculating means becomes the set predetermined amplitude ratio, and is synchronized with the navigator echo signal. To perform respiratory gating imaging (respiratory gating imaging means).

  Here, when the respiratory motion displacement 806 after the introduction of air (after compression) is 1/2 of the respiratory motion displacement 805 before the introduction of air (before the compression), the rest time 807 of the respiratory motion displacement before the compression is applied. On the other hand, since the stationary time 808 of the respiratory movement displacement after the compression is about twice, in the case of the same gate window width 803, the image data acquisition efficiency is improved about twice.

  Therefore, since the rest time of the displacement due to breathing motion is extended by the compression, the ratio of the acquired image data is increased compared to the case where the same gate window width 803 is taken without compression, so the data acquisition efficiency is improved. The shooting time can be shortened.

  For example, as shown in FIG. 8 (c), if there is no compression and 50% of the data is in a non-stationary state (the ratio of the total of 822 and 823 to 821), The ratio of stationary data is about 25% (the total ratio of 825 and 826 to 824), which makes it possible to extend the stationary time by about 25%.

  Note that, as described above, the amplitude of displacement due to respiratory motion is not always half of that before compression during imaging. Therefore, the expansion ratio of the gate window width according to the ratio of the amplitude of displacement due to respiratory movement before and after compression (the ratio is 0.5 if the amplitude becomes 1/2 after compression) is shown in FIG. It is also possible to tabulate the relationship between the expansion ratio and the ratio of respiratory motion displacement before and after compression, and to automatically adjust the gate window width during imaging (first gate window width adjusting means).

  For this purpose, it is necessary to detect that the displacement due to the respiratory motion has reached a predetermined value in synchronization with the navigator echo signal, and to automatically adjust the gate window width based on this detection signal. What is necessary is just to comprise so that it may be performed by the signal processing part 407.

As described above, according to the second embodiment, also in the breathing gating imaging by navigator echo, the acquisition efficiency of the MRI signal is increased similarly to the first embodiment, thereby reducing the imaging time and the inspection. Efficiency is improved.
In addition, since the imaging area due to respiratory motion is small and the respiratory motion can be stably suppressed, body motion artifacts due to respiratory motion can be reduced, and a high-quality MRI image can be obtained.
Furthermore, since the gate window width can be automatically adjusted at the time of photographing, even if the ratio of displacement amplitude due to respiratory motion before and after compression changes, it is possible to easily perform respiration gating photographing corresponding to this, and the amplitude Respiratory gating imaging with a sufficient ratio can be performed stably.

<< Third Embodiment >>
Known as MRI equipment is a method that takes a wide range of images such as the whole body, a method called multi-station imaging and moving bed imaging, which is performed while moving the bed (112 in Fig. 1) on which the subject is placed. Yes.

The multi-station imaging means that when the first imaging for a predetermined imaging area is performed at a certain bed position, the bed (subject) is moved by a distance corresponding to the imaging area, and then the next imaging area is Take a second shot against.
This is a method of photographing a wide range of photographing areas by repeating this photographing and bed movement in order. The moving bed photography method is a photography method in which bed movement and photography are performed simultaneously.
In the present invention, the respiratory motion adjustment and adjustment device 115 moves a plurality of respiratory motion adjustment devices (a plurality of respiratory motion adjustment means) corresponding to a plurality of imaging regions and the plurality of imaging regions spatially different from each other. Multi-station photography or moving bed photography is provided with means for performing multi-station photography or moving bed photography.

  FIG. 10 is an example in which whole body imaging is performed by applying the technique of imaging while reducing the amount of displacement due to respiratory motion by the respiratory motion adjusting device 115 to the multi-station imaging.

In this multi-station radiography, coronal section (CORONAL) imaging is the mainstream, so the imaging slice sections (1003, 1005, 1007) shown in Fig. 10 are also COR sections, and respiratory motion adjustment As the belt 115a, two belts, a chest belt 1001 and an abdominal belt 1002, are used, and these belts are set to match the chest station and the abdominal station.
In other words, the plurality of respiratory motion adjustment devices 115 have a plurality of respiratory motion adjustment belts (a plurality of belts) that have an air layer for taking in and out air and are in close contact with the plurality of imaging regions of the subject and press the imaging regions. Compression means) and a pump 115b (air pressure adjustment means) for adjusting the air pressure of the air layer of these belts.

First, when photographing the station 1003 of the chest, as shown in FIG. 10 (a), air is put into the air layer of the chest belt 1001 to compress the chest, and the displacement due to respiratory motion of the chest becomes a predetermined value. Take a picture at a moment.
The displacement of the chest due to the respiratory motion is monitored in the navigator echo acquisition area 1004 close to the imaging slice position by navigator echo, as in the first and second embodiments. The navigator echo acquisition position 1004 in this example is the chest wall, but of course, it can also be a diaphragm.

  The method of automatically starting imaging when the displacement of the chest due to the respiratory motion is reduced to a set ratio, the method of respiratory gating, and the like are the same as in the first embodiment and the second embodiment.

When imaging of the chest station is completed, the bed 112 is moved, and the bed 112 is positioned so that the next abdominal station 1005 is at the center of the static magnetic field, as shown in FIG. 10 (b).
At this time, air is removed from the chest belt 1001, air is put into the abdomen belt 1002, and the abdomen is compressed (respiratory motion adjustment selection means), and the navigator echo acquisition position 1006 also moves to the abdominal wall along with the movement of the imaging position. Then, when the abdominal displacement due to the respiratory motion is reduced to the set ratio, the photographing is automatically started.

  After the imaging of the abdominal region, the bed 112 is further moved, and the bed 112 is positioned so that the leg-side station 1007 is at the center of the static magnetic field, as shown in FIG. 10 (c).

  Since the station 1007 on the leg side is a station that is not affected by respiratory motion, the chest belt 1001 and the abdominal belt 1002 are evacuated to release the subject from compression (respiratory motion adjustment selection). means).

  In such multi-station shooting, the chest and abdominal displacement due to respiratory movement is reduced to the set ratio and the shooting is automatically started, and the chest is used before shooting at the leg side station where there is no influence of respiratory movement. The control for removing the air from the belt 1001 and the abdomen belt 1002 and automatically starting imaging is performed by the control unit 114 in FIG. 1 recognizing the switching of the station, and the control unit 114 detects the pump 115b when the station is switched. This is done by adopting a configuration that controls the air flow in and out (see FIG. 1).

  That is, the displacement due to the respiratory motion of the subject adjusted by the respiratory motion adjustment device corresponding to the imaging region to be imaged first among the plurality of respiratory motion adjustment devices 115 has become a preset displacement. Determination (second displacement determination means) is performed, and when the displacement becomes a preset displacement, the control unit 114 starts shooting (second shooting start means). Further, the high-frequency magnetic field generation unit locally excites the plurality of imaging regions to acquire a plurality of navigator echoes (a plurality of navigator echo acquisition means), and the plurality of imaging based on the acquired plurality of navigator echoes The displacement of the area is calculated (multiple displacement calculating means), and the displacement of the imaging area where the first imaging is performed among these calculated multiple displacements is used as the second displacement determining means.

  The plurality of displacement calculating means is means for calculating a respiratory motion displacement characteristic of the plurality of imaging regions, which is a relationship between time and displacement of the imaging region due to respiratory motion, and the second displacement determining means is the plurality of displacement determining means. Using the respiratory motion displacement characteristic calculated by the displacement calculation means, the ratio of the displacement amplitude due to the respiratory motion before the air is introduced into the air layer and the amplitude of the displacement due to the respiratory motion after the air is added is calculated (second (Respiratory motion amplitude ratio calculating means), and comparing the calculated ratio with a predetermined value of the ratio of the preset amplitude (second respiratory motion amplitude ratio setting means) (second respiratory motion amplitude ratio comparing means) Then, based on the comparison result of the second respiratory motion amplitude ratio comparison means, it is determined whether or not the air can be continuously injected into the air layer (second air injection determination means).

  Then, a gate window width is set (second gate window width setting means) in which the displacement of the respiratory motion displacement characteristic, which is the acquisition range of the nuclear magnetic resonance signal by the RF receiving coil 107 (receiving means), becomes substantially constant. Then, it is detected that the amplitude ratio calculated by the second respiratory motion amplitude ratio calculating means has become the predetermined amplitude ratio that has been set, and respiratory gating imaging is started in synchronization with the navigator echo signal (respiration gate). Ting shooting start means).

  Further, it is detected that the displacement due to the respiratory motion has reached a predetermined value in synchronization with the plurality of navigator echo signals, and the second gate window width is automatically adjusted based on the detection signal (second gate). Window width adjusting means).

  In addition, the plurality of respiratory motion adjusting means selects a respiratory motion adjusting device corresponding to the imaging region only during imaging in the imaging region where the respiratory motion needs to be adjusted (respiratory motion adjusting selection unit), and the selected respiratory motion adjusting device. Adjust the respiratory movement of the subject with the adjustment device.

  By controlling as described above, it is possible to acquire a multi-station captured image in which the imaging time is shortened and artifacts due to respiratory motion are reduced. In addition, since the patient's imaging area is pressed with the respiratory motion adjustment belt 115a only at the time of imaging of the station required for respiratory motion adjustment, the burden caused by the subject's pressure is kept to a minimum. be able to.

<< Fourth Embodiment >>
FIG. 11 is an example in which whole body imaging is performed by applying the technique of imaging by reducing the amount of displacement due to respiratory motion by the respiratory motion adjustment device 115 to moving bed imaging.
In this moving bed photography, the AX cross section (AXIAL; the cross section perpendicular to the body axis of the subject) is the mainstream, so the photographing slice cross sections (1103, 1105, 1107) shown in FIG. In this case, the respiratory motion adjustment belt 115a uses two belts, a chest belt 1101 and an abdominal belt 1102, and these belts are set in accordance with the chest imaging region 1103 and the abdominal imaging region 1105 ( A plurality of respiratory motion adjusting means, a plurality of compression means, and an air pressure adjusting means).

First, when imaging the imaging region 1103 of the chest, as shown in FIG. 11 (a), air was put into the chest belt 1101 to compress the chest, and the displacement due to respiratory motion of the chest became a predetermined value. By the way, take a picture.
The displacement of the chest due to the respiratory motion is monitored in the navigator echo acquisition region 1104 close to the imaging slice position by navigator echo as in the first embodiment, the second embodiment, and the third embodiment. Navigator echo acquisition means).

  The method of automatically starting imaging when the displacement of the chest due to the respiratory motion is reduced to a set ratio, the method of respiratory gating, and the like are the same as in the third embodiment (second displacement determination). Means, second photographing start means).

When imaging of the chest imaging region is completed and the bed 112 reaches the abdominal imaging region which is the next imaging region, the abdominal imaging region 1105 becomes the center of the static magnetic field as shown in FIG. Set to position.
At this time, air is evacuated from the chest belt 1101, air is put into the abdominal belt 1102 to compress the abdomen (respiratory motion adjustment selection means), and the navigator echo acquisition position 1106 also moves to the abdominal wall along with the movement of the imaging position. Then, when the abdominal displacement due to the respiratory motion is reduced to the set ratio, the photographing is automatically started.

After the imaging of the abdominal region is completed, the bed 112 further moves and is set at a position where the leg-side imaging region 1107 is the center of the static magnetic field, as shown in FIG. 11 (c).
Since the imaging area 1107 on the leg side is an area that is not affected by respiratory movement, the chest belt 1101 and the abdominal belt 1102 are evacuated to release the subject from compression (respiratory movement adjustment). Selection means).

  In such moving bed photography, the chest and abdominal displacement due to respiratory movements are reduced to the set ratio and the photography starts automatically, and the chest before imaging at the leg side station where there is no influence of respiratory movements As in the case of the third embodiment, the control unit 114 in FIG. 1 recognizes the switching of the imaging area, and controls to automatically start imaging by removing air from the belt 1001 and the abdominal belt 1002 The control unit 114 is configured to control the air flow in and out of the pump 115b (see FIG. 1) at the time of switching (multiple displacement calculating means, respiratory motion displacement characteristic calculating means for a plurality of imaging regions, Second respiratory motion amplitude ratio calculation means, second respiratory motion amplitude ratio setting means, second respiratory motion amplitude ratio comparison means, second air injection determination means, second gate window width setting means, respiratory gating Shooting start means, second game Window width adjusting means).

By controlling as described above, in the moving bed imaging as well as the multi-station imaging, it is possible to acquire an MRI image in which the imaging time is shortened and artifacts due to respiratory motion are reduced.
In addition, since the patient's imaging area is compressed with the respiratory movement adjustment belt 115a only when imaging in the imaging area necessary for adjusting the respiratory movement, the burden caused by the compression of the patient is minimized. Can be stopped.

  As described above, the first embodiment, the second embodiment, the third embodiment, and the fourth embodiment have been described. However, the present invention is not limited to these embodiments. Respiratory motion suppression means using air pressure that can stably reduce the displacement of motion improves the acquisition efficiency of MRI signals, shortens imaging time, improves examination efficiency, and reduces the artifacts due to respiratory motion The present invention can be applied to various MRI imaging methods without departing from the gist of the present invention “to obtain an MRI image”.

The figure which shows the whole structure of the MRI apparatus of this invention provided with the means which suppresses a subject's respiratory motion with air pressure, monitoring a subject's respiratory motion with a navigator echo. A sequence diagram of respiratory gating imaging using navigator echo in combination with electrocardiogram synchronization. The figure which shows an example of the shape of the whole figure of a respiratory motion adjustment apparatus, and the respiratory motion adjustment belt used for this. The figure which shows the other example of the belt for respiratory motion adjustment. The figure which shows the other example of the belt for respiratory motion adjustment. An example in which a respiratory motion adjustment belt is attached to an area extending from the chest to the abdomen and a cross section of the coronal image near the heart is photographed. The figure which shows the relationship between time and the air pressure of the air layer of a respiratory motion adjustment belt, and the relationship between time and the displacement of the imaging | photography area | region by respiratory motion. The example which applied the respiratory gating imaging | photography method by a navigator echo to the respiratory motion suppression means by a respiratory motion adjustment apparatus. The figure which shows the relationship between the expansion ratio of a gate window width, and the ratio of the respiratory motion displacement before and behind compression. The example which applied the respiratory motion suppression means by the respiratory motion adjustment apparatus to multi-station imaging. The example which applied the respiratory motion suppression means by a respiratory motion adjustment apparatus to moving bed imaging | photography.

Explanation of symbols

  101 Subject, 102 Static magnetic field magnet, 103 Gradient magnetic field coil, 105 RF irradiation coil, 107 RF reception coil, 106 High-frequency pulse transmission unit, 108 Signal detection unit, 109 Signal processing unit, 110 Display unit, 112 Bed, 113 Bed Control unit, 114 Control unit, 115 Respiratory motion adjustment device, 115a Respiratory motion adjustment belt, 115b Pump, 115c Air supply / discharge tube, 303, 304 Air layer, 601 Navigator echo acquisition position, 602, 604 Respiratory motion displacement characteristics , 603 CORONAL cross section, 701 Respiratory displacement characteristics, 702 to 705 Displacement height of respiratory motion displacement characteristics, 706 hours and air pressure relationship, 801 Respiratory motion displacement characteristics, 805, 806 Displacement height of respiratory motion displacement characteristics, 809 hours 1001 Thoracic belt, 1002 Abdominal belt, 1003, 1005, 1007 Photographed slice cross section, 1004, 1006 Navigator echo acquisition area, 1101 Thoracic belt, 1102 Abdominal belt, 1103, 1105, 1107 , 1104, 1106, navigator echo acquisition area

Claims (7)

A static magnetic field generating means for generating a substantially uniform static magnetic field, a gradient magnetic field generating means for generating a gradient magnetic field in the static magnetic field region, and a high frequency magnetic field for generating a high frequency magnetic field for causing nuclear magnetic resonance in a subject Generating means; receiving means for receiving a nuclear magnetic resonance signal from the subject; signal processing means for processing the nuclear magnetic resonance signal to generate an image; and displaying an image obtained by the signal processing means Corresponding to the operation signal of the display means, the bed on which the subject is placed, the bed movement control means for moving and controlling the bed, the operation means for performing the operation for taking the image Magnetic resonance that includes control means for controlling each of the above means and respiratory movement suppression means for suppressing the respiratory movement of the subject, and controls the respiratory movement of the subject with the respiratory movement suppression means for imaging. An imaging device
The magnetic resonance imaging apparatus, wherein the respiratory motion suppression means includes respiratory motion adjustment means that adjusts a displacement of an imaging region due to respiratory motion of the subject to a predetermined range.   The breathing motion adjusting means has an air layer for taking in and out air, a pressing means for pressing the imaging area in close contact with the imaging area of the subject, and an air pressure adjusting means for adjusting the air pressure of the air layer of the pressing means 2. The magnetic resonance imaging apparatus according to claim 1, further comprising:   First displacement determining means for determining that the displacement of the imaging region of the subject adjusted by the respiratory motion adjusting means has become a preset displacement, and imaging is started by the first displacement determining means. 3. The magnetic resonance imaging apparatus according to claim 1, further comprising a first imaging start unit provided in the control unit.   Navigator echo acquisition means for locally acquiring a navigator echo by exciting the imaging area with the high-frequency magnetic field generating means; and displacement calculating means for calculating a displacement of the imaging area based on the acquired navigator echo. 4. The magnetic resonance imaging apparatus according to claim 3, wherein the displacement calculated by the displacement calculating means is used for the first displacement determining means.   The displacement calculating means is a means for calculating a respiratory motion displacement characteristic that is a relationship between time and a displacement of the imaging region due to respiratory motion, and the first displacement determining means is the respiratory motion calculated by the displacement calculating means. First respiratory motion amplitude ratio calculating means for calculating a ratio between an amplitude of displacement due to respiratory motion before air is introduced into the air layer and an amplitude of displacement due to respiratory motion after the air is introduced using displacement characteristics; A first respiratory motion amplitude ratio setting means for setting a predetermined value of the amplitude ratio; an amplitude ratio calculated by the respiratory motion amplitude ratio calculation means; and a predetermined value of the amplitude ratio set by the respiratory motion amplitude ratio setting means; First respiratory motion amplitude ratio comparison means for comparing the first and second respiratory motion amplitude ratio comparison means, and first air injection determination for determining whether or not to continue air injection into the air layer based on the comparison result of the first respiratory motion amplitude ratio comparison means 5. The magnet according to claim 4, further comprising: means. Resonance imaging apparatus.   A first gate window width setting unit configured to set a gate window width in which a displacement of the respiratory motion displacement characteristic that is an acquisition range of the nuclear magnetic resonance signal by the receiving unit is substantially constant; The apparatus further comprises means for detecting that the amplitude ratio calculated by the ratio calculating means has reached the set predetermined amplitude ratio and performing respiratory gating imaging in synchronization with the navigator echo signal. 5. The magnetic resonance imaging apparatus according to 5.   The apparatus further comprises means for detecting that the displacement due to the respiration movement has reached a predetermined value in synchronization with the navigator echo signal and automatically adjusting the first gate window width based on the detection signal. The magnetic resonance imaging apparatus according to claim 6.

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