Magnetic resonance imaging apparatus, control method thereof, and control program

Abstract

This invention relates to a magnetic resonance imaging (MRI) apparatus, its control method, and control program. It enables MRI imaging that is less affected by body movement without prolonging the imaging time. The control unit acquires images captured by the camera at a given frame rate. The imaging pulse sequence is divided into small sequences with time widths corresponding to the camera's frame rate. Before executing a small sequence, the control unit detects the displacement or velocity of the subject relative to a predetermined reference position from the most recent frame image. If the detection result is within a predetermined allowable range, the control unit executes the small sequence; if the detection result exceeds the allowable range, the control unit does not execute the small sequence and waits until the next frame image is acquired according to the frame rate.

Description

Technical Field

[0001] This invention relates to a magnetic resonance imaging (MRI) device that measures nuclear magnetic resonance (NMR) signals from hydrogen, phosphorus, etc., in a subject and visualizes the density distribution, relaxation time distribution, etc. of the nuclei, and the device has the function of observing the activity of the subject. Background Technology

[0002] An MRI device is an apparatus that measures NMR signals generated by the nuclear spins of atoms constituting a subject, particularly human tissue, to create two-dimensional or three-dimensional images of the morphology and function of the head, abdomen, limbs, etc. During imaging, the NMR signals are assigned different phase codes based on a tilted magnetic field and are also frequency-coded, thus providing time-series data for measurement. The measured NMR signals are then reconstructed into images through two-dimensional or three-dimensional Fourier transforms.

[0003] MRI scans can take anywhere from tens of minutes to an hour, during which time artifacts can occur in the images if the subject moves.

[0004] Therefore, Patent Document 1 discloses an invention that involves acquiring still images of the subject before and during an MRI scan using a video camera, and determining the presence or absence of body movement by calculating the correlation function between the two images. If body movement is detected, the MRI scan is restarted from the beginning.

[0005] Furthermore, in Patent Document 2, during MRI imaging, images of the subject are captured using a TV camera. If the subject's movement exceeds the permissible range, the MR data at the time point of the movement is deleted, or a new image is captured, or corrections are made. Alternatively, the RF pulses and gradient magnetic fields are optimized to counteract the effects of the subject's movement.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: JP Japanese Patent Application Publication No. 2006-346235

[0009] Patent Document 2: JP Japanese Patent Application Publication No. 9-28689

[0010] In the invention of Patent Document 1, if body movement of the subject is detected during MRI imaging, the time required for imaging will be longer if the MRI imaging is repeated from the beginning.

[0011] Furthermore, in Patent Document 2, in order to delete or re-encode MR data acquired during body movement during imaging, it is necessary to determine the MR data acquired during the period of body movement. During MRI imaging, the following action is repeated 256 or 512 times while changing the phase code: acquiring one echo signal (MR data) obtained by applying a given phase code. The time required to acquire one echo signal is very short, as short as 1-2 ms. In order to accurately determine which echo signal was acquired at the moment of body movement for deletion or re-encoding, the TV camera and MRI device need to be synchronized, which is not easy. Summary of the Invention

[0012] The purpose of this invention is to perform MRI imaging that is less affected by body movement without prolonging the imaging time.

[0013] To address the aforementioned issues, the present invention provides an MRI apparatus comprising: a static magnetic field generating device that applies a static magnetic field to an imaging area; an imaging unit that applies high-frequency magnetic field pulses and tilting magnetic field pulses to a subject disposed in the imaging area to acquire an MRI signal generated from the subject; a control unit that, according to a predetermined imaging pulse sequence, repeatedly causes the imaging unit to apply high-frequency magnetic field pulses and tilting magnetic field pulses and acquire MRI signals at a given timing, so that the imaging unit acquires a number of MRI signals required for image reconstruction; and a camera that continuously, optically, images the subject disposed in the imaging area during the operation of the imaging unit.

[0014] The control unit acquires images captured by the camera at a given frame rate. The captured pulse sequence is divided into small sequences with time widths corresponding to the camera's frame rate.

[0015] The control unit executes a small sequence of images sequentially at time intervals corresponding to the frame rate by repeating the following actions: before executing a small sequence of images, the control unit detects the displacement of the subject relative to a predetermined reference position or the speed of the subject's movement from the image of the most recent frame. If the detection result is within a predetermined allowable range, the control unit executes the small sequence of images. If the detection result exceeds the allowable range, the control unit does not execute the small sequence of images and waits until the next frame of images is captured according to the frame rate.

[0016] Invention Effects

[0017] According to the present invention, since the imaging pulse sequence is divided into small sequences with a time width corresponding to the frame rate of the camera, the displacement and movement speed of the subject are detected before the execution of the small sequence. If the detection result exceeds the allowable range, the small sequence is not executed and the system waits until the next timing. Therefore, it is not necessary to delete NMR signal data after imaging or to re-encode the image. MRI imaging that suppresses the influence of the subject's body movement can be performed without prolonging the imaging time. Attached Figure Description

[0018] Figure 1 This is a block diagram showing the overall structure of the MRI device according to the first embodiment of the present invention.

[0019] Figure 2 This is an explanatory diagram showing an example of the camera configuration of the MRI apparatus of the first embodiment.

[0020] Figure 3 This is a flowchart illustrating the operation of the central processing unit 110 of the MRI apparatus of the first embodiment.

[0021] Figure 4 This is a timing diagram showing the displacement and movement of the subject in the first embodiment, the timing of the acquisition of camera images by the central processing unit 110 of the MRI apparatus, and the imaging period of the imaging unit 300.

[0022] Figure 5 This is a flowchart illustrating the operation of the central processing unit 110 of the MRI apparatus of the second embodiment.

[0023] Figure 6 This is a timing diagram showing the displacement and movement of the subject in the second embodiment, the timing of the acquisition of camera images by the central processing unit 110 of the MRI apparatus, and the imaging period of the imaging unit 300.

[0024] Figure 7 This is a flowchart illustrating the operation of the central processing unit 110 of the MRI apparatus of the second embodiment.

[0025] Figure 8 This is a timing diagram showing the displacement and movement of the subject in the second embodiment, the timing of the acquisition of camera images by the central processing unit 110 of the MRI apparatus, and the imaging period of the imaging unit 300.

[0026] Explanation of reference numerals in the attached figures

[0027] 10 subjects

[0028] 20 Shooting Areas

[0029] 30 beds

[0030] 100 MRI devices

[0031] 110 Central Processing Unit

[0032] 120 Sequence Generator

[0033] 130 Static Magnetic Field Generating Device

[0034] 132 Inclined Magnetic Field Generating Device

[0035] 134 Inclined Magnetic Field Coil

[0036] 136 Inclined Magnetic Field Power Supply

[0037] 140 RF signal irradiation device

[0038] 142 High-frequency oscillator

[0039] 144 modulator

[0040] 146 High-frequency amplifier

[0041] 148 High-frequency coil

[0042] 150 receiving devices

[0043] 152 High-frequency coil

[0044] 154 signal amplifier

[0045] 156 Quadrature Phase Detector

[0046] 158 converter

[0047] 160 processing unit

[0048] 162 CDs

[0049] 164 disks

[0050] 169 Monitor

[0051] 170 Operating device

[0052] 174 Indicating devices

[0053] 176 Keyboard

[0054] 200 cameras

[0055] 300 Filming Department

[0056] 310 rack Detailed Implementation

[0057] The embodiments of the present invention are illustrated using the accompanying drawings.

[0058] <<<First Implementation Method>>>

[0059] use Figures 1-4 The MRI apparatus of the first embodiment will be described below. In this embodiment, the MRI apparatus includes a camera that continuously captures images of a subject positioned in the imaging area using an optical method. A control unit acquires images captured by the camera at a given frame rate. The imaging pulse sequence is divided into small sequences with time widths corresponding to the frame rate. Before the imaging unit executes a small sequence, the control unit detects the displacement or velocity of the subject relative to a predetermined reference position from the image of the most recent frame. If the detection result is within a predetermined allowable range, the control unit executes the small sequence; if the detection result exceeds the allowable range, the small sequence is not executed, and the unit waits until the next frame is acquired, repeating the above-described operation.

[0060] That is, the control unit is structured as follows: under timing synchronized with the frame rate of the acquired image, it determines whether the subject has positional deviation or body movement that exceeds the allowable range, and decides whether to execute a small sequence during the period until the next frame of the image is acquired.

[0061] Therefore, since no short sequence is executed immediately after the subject deviates from its position or moves beyond the permissible range, and the system remains idle until the next frame is acquired, no NMR signal data is acquired during the period when the subject deviates from its position or moves. Thus, there is no need to delete NMR signal data after imaging or to re-encode the image, allowing for MRI imaging that suppresses the effects of subject movement without prolonging the imaging time.

[0062] (Structure of an MRI device)

[0063] Next, use Figure 1 The structure of the MRI device 100 of this embodiment will be explained.

[0064] The MRI apparatus 100 comprises the following elements: a static magnetic field generating device 130; a tilted magnetic field generating device 132 for applying tilted magnetic field pulses to the subject 10; an RF signal irradiation device 140 for irradiating the subject 10 with high-frequency magnetic field pulses (hereinafter referred to as RF pulses); a receiving device 150 for receiving echo signals as NMR signals from the subject 10; a processing device 160 having a central processing unit (hereinafter referred to as CPU) 110; a sequence generator 120; an operating device 170 for performing various operations related to data input, image capture, etc.; a bed 30; and a camera 200.

[0065] The static magnetic field generating device 130 applies an extremely uniform magnetic field to the shooting area 20.

[0066] The bed table carries the subject 10, and at least the part of the subject being photographed is placed in the imaging area 20.

[0067] The tilting magnetic field generating device 132, the RF signal irradiation device 140, and the receiving device 150 constitute the imaging unit 300. The imaging unit 300 applies RF pulses and tilting magnetic field pulses to the subject 10 disposed in the imaging area 20 to obtain the NMR signal generated from the subject.

[0068] The central processing unit 110 functions as a control unit, controlling the sequence generator 120 according to a predetermined imaging pulse sequence, so that the imaging unit 300 repeatedly applies high-frequency magnetic field pulses and tilting magnetic field pulses and acquires nuclear magnetic resonance signals at a given timing. Furthermore, the central processing unit 110 also functions as an image reconstruction unit, processing the number of NMR signals required for image reconstruction acquired by the imaging unit 300 to generate a tomographic image of the subject 10.

[0069] During the operation of the imaging unit 300, the camera 200 continuously captures images of the subject 10 disposed in the imaging area 20 in an optical manner. The central processing unit 110 sequentially acquires the images captured by the camera at a given frame rate.

[0070] Furthermore, the details of each part will be explained. The specific structure of the static magnetic field generating device 130 is omitted, but in the case of a vertical magnetic field, it generates an extremely uniform static magnetic field in the space surrounding the subject 10 in a direction orthogonal to its body axis; in the case of a horizontal magnetic field, it generates an extremely uniform static magnetic field in the direction of the body axis. The static magnetic field generating device 130 is arranged around the subject 10 to generate the aforementioned static magnetic field and has a permanent magnet, a normally conductive magnet, or a superconducting magnet as the static magnetic field source.

[0071] The tilting magnetic field generating device 132 includes: tilting magnetic field coils 134 wound along three axes—X-axis, Y-axis, and Z-axis—which serve as the coordinate system of the MRI device 100, such as a stationary coordinate system; and a tilting magnetic field power supply 136 that supplies drive current to generate tilting magnetic fields in each tilting magnetic field coil. The tilting magnetic field power supply 136 operates according to commands from the sequence generator 120, supplying drive current to the tilting magnetic field coils 134 along the three axes. As a result, the tilting magnetic field coils 134 generate tilting magnetic fields Gx, Gy, and Gz along the three axes. The generated tilting magnetic fields Gx, Gy, and Gz are applied to the subject 10 within the imaging area 20. For example, during imaging, according to the imaging pulse sequence, a slice-direction tilting magnetic field pulse (Gs) is applied in a direction orthogonal to the imaging section, i.e., the slice plane, and the slice plane is set for the subject 10. Phase-coded directional tilt magnetic field pulses (Gp) and frequency-coded directional tilt magnetic field pulses (Gf) are applied in the remaining two directions that are orthogonal to and mutually orthogonal to the slice plane, and the position information of each direction is encoded in the NMR signal as the echo signal.

[0072] An RF signal irradiation device 140 irradiates a subject 10 with an RF pulse, causing the nuclear spins of the atoms constituting the biological tissue of the subject 10 to generate nuclear magnetic resonance (NMR). For example, the RF signal irradiation device 140 includes a high-frequency oscillator 142, a modulator 144, a high-frequency amplifier 146, and a high-frequency coil 148 operating as a transmitting coil. The high-frequency pulse output from the high-frequency oscillator 142 is amplitude-modulated by the modulator 144 at a timing indicated by a sequence generator 120, and the amplitude-modulated high-frequency pulse is amplified in the high-frequency amplifier 146. The amplified high-frequency pulse is supplied to the high-frequency coil 148 positioned close to the subject 10. Thus, the high-frequency coil 148 irradiates the subject 10 with an RF pulse. In the biological tissue of the subject 10 irradiated with the RF pulse, the nuclear spins of the atoms constituting the biological tissue generate NMR, emitting an echo signal.

[0073] The receiving device 150 detects and processes the emitted NMR signal. The receiving device 150 includes: a high-frequency coil 152 operating as a receiving coil on the receiving side; a signal amplifier 154 amplifying the received NMR signal; a quadrature phase detector 156; and an A / D converter 158 converting the analog signal into a digital signal. The high-frequency coil 152 detects the NMR signal emitted by the sample, and the signal amplifier 154 amplifies the detected NMR signal. The quadrature phase detector 156, under timing instructions from the sequence generator 120, splits the NMR signal into two orthogonal systems. The two split system signals are converted into digital quantities in the A / D converter 158 and sent to the central processing unit 110.

[0074] The high-frequency coil 148 and the tilting magnetic field coil 134 on the transmitting side are disposed within the static magnetic field space of the static magnetic field generating device 130 on which the subject 10 is to be disposed. Regarding their orientation, in the case of a vertical magnetic field, they are positioned opposite the subject 10; in the case of a horizontal magnetic field, they are positioned to surround the subject 10. Furthermore, the high-frequency coil 152 on the receiving side is positioned opposite or surrounding the subject 10.

[0075] Under the control of the central processing unit 110, the sequence generator 120 outputs control signals (commands) to the RF signal irradiation device 140, the tilting magnetic field generating device 132, and the receiving device 150 at a given timing. Thus, at the timing of a predetermined imaging pulse sequence, RF pulses and tilting magnetic field pulses are applied to the subject, causing the imaging unit 300 to repeatedly acquire NMR signals while changing the phase encoding amount.

[0076] In addition to the central processing unit 110, the processing device 160 also includes: external storage devices such as optical disc 162 and magnetic disk 164 for storing information; ROM 166 for storing required data and processing programs; RAM 168 for temporary storage of processing data; and a display 169 such as a CRT. Thus, the processing device 160 performs various data processing, displays processing results, and saves them. For example, if the processing result received and processed by the receiving device 150 is input to the processing device 160, the central processing unit 110 of the processing device 160 performs signal processing, image reconstruction, and other processing. The resulting tomographic image of the subject 10 is displayed on the display 169 and, as needed, recorded to external storage devices such as optical disc 162 and magnetic disk 164. Furthermore, although not shown, it can also be printed or sent to other systems.

[0077] The operating device 170 includes a pointing device 174 such as a trackball or mouse and a keyboard 176. The operator inputs various control information for the MRI apparatus 100 and control information processed by the processing unit 160 via the operating device 170. The operating device 170 is positioned close to the display 169, allowing the operator to interactively operate the device while viewing the display on the MRI apparatus 169. Furthermore, the operating device 170 is not limited to this; for example, it may include a touch panel on the display surface of the display 169. The operating device 170 is located in the operating room, away from the main body of the MRI apparatus 100. A portion of the operating device 170 is further integrated into the main body of the MRI apparatus 100 and the bed 30. This configuration allows the operator to perform the required operations near the patient 10.

[0078] The nuclear species to be imaged in the subject 10 of the MRI apparatus 100 are, for example, clinically common nuclear species, such as the proton, a hydrogen nucleus that is the main constituent of the subject. The MRI apparatus 100 images information related to the spatial distribution of proton density and the spatial distribution of relaxation time of excited states. Thus, the MRI apparatus 100 can image the morphology or function of the subject 10 in two or three dimensions, such as the head, abdomen, or limbs, and display the reconstructed images on the display 169. The reconstructed images are stored as needed on an optical disc 162 or a magnetic disk 164. Furthermore, the images can be printed based on the operation or sent to other systems as required.

[0079] (Structure of camera 200)

[0080] exist Figure 2 The diagram illustrates the configuration of the camera 200 in the MRI apparatus 100. The camera 200 is mounted on the bed 30 and positioned to capture images of the subject 10 positioned in the imaging area 20.

[0081] The camera 200 can be configured as part of the frame 310 in which the imaging unit 300 of the MRI device 100 is built, or it can be configured to capture images of the subject 10 from outside the frame 310.

[0082] Camera 200 is a camera that optically captures continuous images at a frame rate higher than a predetermined frame rate. For example, it is desirable to capture images at 30 frames per second or higher. Central processing unit 110 acquires images from camera 200 at a predetermined frame rate. The frame rate at which camera 200 captures images can be synchronized with the frame rate at which central processing unit 110 acquires images; however, it can also be asynchronous if the camera's frame rate is higher than the frame rate at which central processing unit 110 acquires images. The operator sets the frame rate at which central processing unit 110 acquires images via operation device 170. When the frame rate at which camera 200 captures images is synchronized with the frame rate at which central processing unit 110 acquires images, central processing unit 110 sets the frame rate at which the operator sets it for camera 200.

[0083] Furthermore, the camera 200 has a structure for shielding electromagnetic noise, so that the imaging unit 300 will not generate noise due to the electromagnetic noise generated by the camera 200.

[0084] Furthermore, in order to function as a camera 200 even when subjected to a strong magnetic field generated by the static magnetic field generating device 130, a magnetic field with large time variation applied by the tilted magnetic field coil 134, and RF pulses irradiated by the high-frequency coil 148, the camera 200 is equipped with a structure that shields against large external magnetic fields, magnetic fields with large time variation, and high frequencies.

[0085] Furthermore, the camera 200 configured on the MRI device 100 is not limited to one. In order to capture the position and movement of the subject 10 in all configurations, it is desirable to configure two cameras 200 in front of and behind the subject 10.

[0086] Furthermore, because the MRI apparatus gantry 310 is made in a cylindrical or parallel plate shape, light has difficulty penetrating the imaging area 20. Therefore, in order to improve the image signal-to-noise ratio (SN ratio) of the optical camera 200, it is desirable to configure an illumination device to irradiate the imaging area 20.

[0087] Digital images captured by camera 200 are input into central processing unit 110 at a given frame rate. Central processing unit 110 controls imaging unit 300 using the images captured by camera 200 as described below, causing imaging unit 300 to execute a shooting pulse sequence that implements the shooting method selected by the operator. Imaging unit 300 acquires 256 or 512 echo signals required for image reconstruction while changing the phase coding amount according to the shooting pulse sequence.

[0088] The imaging pulse sequence is pre-stored in a memory or disk 164, ROM 166, etc., built into the central processing unit 110, according to each of multiple imaging methods. The operator selects the imaging method via the operation device 170 and then inputs the imaging conditions (repetition time TR, etc.). As a result, the central processing unit 110 generates an imaging pulse sequence corresponding to the set imaging conditions.

[0089] Here, the central processing unit 110 is a processor (computer) such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), and is implemented by software by reading and executing a program pre-stored in ROM 166. Figure 3 The process is illustrated in the flowchart. Additionally, it can also... Figure 3 Some or all of the processing is implemented in hardware. For example, custom ICs such as ASICs (Application Specific Integrated Circuits) and programmable ICs such as FPGAs (Field-Programmable Gate Arrays) are used to form part or all of the central processing unit 110, and the programmable ICs are designed to perform circuitry. Figure 3 That should suffice.

[0090] The following details Figure 3 The process.

[0091] Subject 10 is mounted on bed 30 and pre-positioned in imaging area 20.

[0092] (Step 301)

[0093] The central processing unit 110 receives the frame rate of images captured from the camera 200 and the shooting conditions (shooting method, repetition time TR, TE, etc.) of the shooting pulse sequence from the operator via the operating device 170. The frame rate for image capture here should be within the maximum frame rate that the camera 200 can capture. As an example, the central processing unit 110 captures images from the camera 200 at a frame rate of 33 frames per second, or a time interval of 30 ms. Alternatively, the frame rate for images captured from the camera 200 may not be received from the operator, but rather a predetermined value may be used.

[0094] (Step 302)

[0095] The central processing unit 110 uses the shooting conditions received from the operator in step 301 to adjust the shooting pulse sequence of the reference for each shooting method pre-stored in ROM 166, etc., to generate a shooting pulse sequence of 256 or 512 NMR signals (echo signals) required for image reconstruction under the shooting conditions.

[0096] The central processing unit 110 divides the generated imaging pulse sequence into small sequences with time widths corresponding to the frame rate set in step 301. Here, since the set frame rate is 33 frames per second, the central processing unit 110 divides the imaging pulse sequence every 30 ms. Generally, since the time (TR) required to acquire one NMR signal is 1 to 2 ms, one small sequence (30 ms) becomes a sequence for acquiring 15 to 30 echo signals.

[0097] (Step 303)

[0098] When the operator instructs the central processing unit 110 to start shooting via the operating device 170, the central processing unit 110 proceeds to step 304.

[0099] (Step 304)

[0100] The central processing unit 110 instructs the camera 200 to start filming the subject 10, and captures the image of frame n (n=1) at the frame rate set in step 301.

[0101] (Step 305)

[0102] The central processing unit 110 detects the position of the subject from the image of frame n (n=1) acquired in step 304.

[0103] Alternatively, the difference between the image of frame n and the image of the previous frame (n-1) can be calculated, and the velocity (displacement vector) can be calculated. From this, the activity of the object 10 can be determined.

[0104] Alternatively, the central processing unit 110 may select an image of a frame (n=0) set as a reference, and calculate the difference between the image of the reference frame (n=0) and the image of frame n taken in step 304 as the displacement relative to the reference position.

[0105] Alternatively, calculate the cumulative velocity (displacement vector) from the start of filming to the present, and use that as the displacement.

[0106] The reference frame (n=0) can be any timed image, such as a frame with a predetermined timing earlier than step 304, or the image of frame n (n=1) obtained in the initial step 304. Specifically, the frame with a predetermined timing earlier than step 304 can be the frame at the time when the subject 10 is positioned in the imaging area 20, or the frame at the time when the door of the imaging chamber is closed after the subject 10 has been positioned in the imaging area 20. Alternatively, it can be the frame at the time when the imaging begins, as indicated by the operating device 170.

[0107] To improve the detection accuracy of position, displacement relative to a reference position, and movement (velocity), markers can be installed on the test object 10 and the high-frequency coil (receiving coil) 152. For example, non-magnetic objects arranged in a grid pattern can be attached as markers to the clothing, receiving coil, etc. of the test object 10. Preferably, the non-magnetic object has upright corners.

[0108] (Steps 306, 307, 308)

[0109] The central processing unit 110 determines whether the position (displacement) or movement (velocity) calculated in step 305 is within the predetermined allowable range of each.

[0110] If the position (displacement) or movement (speed) is within the permissible range, the central processing unit 110 determines that it can capture images, proceeds to step 308, and hands over the initial small sequence m (m=1) of the capture pulse sequence to the sequence generator 120, and instructs it to execute. Thus, the sequence generator 120 causes each part of the capturing unit 300 to execute the small sequence m (m=1) and obtain the echo signal m (m=1). Alternatively, the handover of the small sequences to the sequence generator 120 may not be performed one by one, but rather several small sequences may be combined and handed over.

[0111] On the other hand, in step 306, if the position (displacement) or movement (speed) exceeds the allowable range, the central processing unit 110 determines that it cannot take pictures, does not allow the shooting unit 300 to execute the small sequence, and returns to step 304, waiting until the next frame (n+1) of the image is taken from the camera 200 according to the frame rate.

[0112] The central processing unit 110 repeats steps 304 to 306 for the image obtained in frame (n+1). Specifically, the central processing unit 110 detects the position of the subject 10 in the image of frame (n+1), or calculates the movement (velocity) by calculating the difference with frame n, or calculates the displacement by calculating the difference with the image of the reference frame (n=0). If the calculated position (displacement) or movement (velocity) is within an acceptable range, the central processing unit 110 causes the sequence generator 120 to execute the small sequence m.

[0113] (Step 308)

[0114] (Steps 309 and 310)

[0115] After obtaining the echo signal m (m=1) in step 307, the central processing unit 110 proceeds to step 309 to determine whether all the predetermined number (m=256 or 512) of echo signals m required for image reconstruction have been obtained. If not all echo signals m have been obtained, the central processing unit 110 returns to step 304 and repeats steps 304 to 307.

[0116] Thus, the MRI apparatus of this embodiment can repeatedly perform the following operations: acquiring images from the camera 200 at a given frame rate, determining the position (displacement) or movement (velocity) of the subject 10 from the images, executing a small sequence m and acquiring echo signals m when the position (displacement) or movement (velocity) is within an acceptable range, and not executing the small sequence m when the position (displacement) or movement (velocity) exceeds the acceptable range, and waiting until the next image is acquired. Therefore, small sequences m (m = 1 to 256 or 512) can be executed sequentially to acquire all echo signals m (m = 1 to 256 or 512).

[0117] (Step 311)

[0118] The central processing unit 110 reconstructs the tomographic image of the subject 10 by using all the obtained echo signals m (m = 1 to 256 or 512) to perform predetermined image reconstruction processing, and displays it on the display 169. In addition, the reconstructed image is stored in the disk 164 or the like as needed.

[0119] As described above, in this embodiment, since the small sequence of events is performed and echo signals are acquired only when the position (displacement) or movement (velocity) of the subject 10 is within an acceptable range, the acquired echo signals are less susceptible to the influence of the movement or displacement of the subject 10. Therefore, sudden human movement is avoided, meaning that a tomographic image of the subject 10 in a stable state can be generated.

[0120] Therefore, even if the subject moves during MRI imaging, it is not necessary to start the MRI imaging process again from the beginning, delete the echo signals acquired during the movement, or start the imaging process again, allowing the imaging to be completed without being prolonged. Thus, the MRI apparatus of this embodiment can perform MRI imaging that is less affected by body movement without prolonging the imaging time.

[0121] <<<Second Implementation Method>>>

[0122] The MRI apparatus of the second embodiment will be described.

[0123] The activities of subject 10 were classified into the following three types: a) constant random activities captured as background noise; b) periodic activities synchronized with human breathing and heart rhythm; and c) sudden human activities.

[0124] In the first embodiment, the structure for executing the small pulse sequence avoids sudden human activity (c). In the second embodiment, the periodic activity (b) is used to control the imaging. For example, the small pulse sequence is executed synchronously with the displacement caused by the respiratory activity of the subject 10 to acquire NMR data. Thus, the same effect as the previous scheme of equipping the subject 10 with a respiratory activity sensor for synchronized respiratory imaging can be achieved without a respiratory activity sensor.

[0125] use Figure 5 The process and Figure 6 The MRI apparatus of the second embodiment will be described in detail. Since the hardware structure of the MRI apparatus of the second embodiment is the same as that of the first embodiment, its description will be omitted.

[0126] (Steps 301-306)

[0127] The central processing unit 110 of the MRI device in the second embodiment performs steps 301 to 305 in the same way as in the first embodiment, dividing the imaging pulse sequence into small sequences corresponding to the frame rate, and calculating the activity and displacement of the subject from the image of the camera 200.

[0128] The difference from the first embodiment is that, in step 305, the central processing unit 110 calculates both the displacement and movement of the subject 10, and in step 306, it determines whether the subject 10 has any sudden movement based on the movement calculated in step 305. If the movement is within the acceptable range, it proceeds to step 501. If the movement exceeds the acceptable range, it returns to step 304 in the same manner as in the first embodiment.

[0129] (Steps 501, 307)

[0130] The central processing unit 110 determines whether the displacement of the subject 10 calculated in step 305 has reached the given position of the respiratory cycle in advance.

[0131] Specifically, when the given synchronization position of the respiratory activity is, for example, a given displacement position midway through inhalation, and the activity calculated by the central processing unit 110 in step 305 is positive and the displacement reaches the predetermined synchronization position, the process proceeds to step 307 to instruct the sequence generator 120 to execute a small sequence.

[0132] (Steps 307-311)

[0133] The central processing unit 110 performs steps 307 to 311 in the same manner as in the first embodiment to sequentially execute small sequences m (m = 1 to 256 or 512) to obtain all echo signals m (m = 1 to 256 or 512). The central processing unit 110 uses all the obtained echo signals to perform image reconstruction processing, such as reconstructing tomographic images.

[0134] In the second embodiment, as from Figure 6 As explicitly stated, a short sequence of echo signals is executed immediately following the subject 10 only when the subject's activity is within permissible limits and the displacement caused by the subject's respiratory activity reaches a given synchronous position. Thus, the acquired echo signals can generate a tomographic image of the subject 10 in a state unaffected by sudden movements of the subject 10 and where the displacement caused by respiratory activity is at a given synchronous position.

[0135] Furthermore, in the second embodiment described above, the central processing unit 110 determines whether the subject has sudden activity based on the subject's activity (speed). As also described in the first embodiment, the determination can also be based on the subject's displacement.

[0136] Furthermore, in the second embodiment, both determining whether there is a sudden activity and synchronizing respiratory activity are performed, but of course, it is also possible to perform filming by only synchronizing respiratory activity. In this case, by not implementing... Figure 5 Step 306, by performing only the other steps, can achieve synchronized recording of breathing activities.

[0137] In the second embodiment described above, it is determined whether the displacement caused by respiratory activity is located at a given synchronous position. However, this is not limited to respiratory activity; as long as it is a periodic displacement of the subject, this embodiment can be applied in the same way. For example, it can be photographed synchronously with periodic displacements of the chest caused by heart rhythm, periodic displacements of the neck caused by pulsation, etc.

[0138] <<<Third Implementation Method>>>

[0139] The MRI apparatus of the third embodiment will be described.

[0140] The third embodiment, like the second embodiment, involves imaging based on the respiratory cycle when the subject 10 reaches a given respiratory position. In the second embodiment, a small sequence of structures is imaged within one respiratory cycle. However, in the third embodiment, the respiratory cycle of the subject 10 can be detected, and a medium sequence summarizing several small sequences can be set corresponding to that cycle. Alternatively, the operator can be advised to image the medium sequence every one respiratory cycle. Thus, a quantity of NMR data for the medium sequence can be obtained within one cycle.

[0141] The following uses Figure 7 The process and Figure 8 Let me explain. Figure 7 In the process, for the second embodiment Figure 5 The same steps in the process are labeled with the same reference numerals.

[0142] (Steps 301, 302)

[0143] The central processing unit 110 performs steps 301 and 302 to divide the captured pulse sequence into small sequences corresponding to the frame rate.

[0144] (Steps 701, 702)

[0145] Next, the central processing unit 110 acquires the image from the camera 200 and calculates the displacement of the subject relative to the reference position from the image.

[0146] (Step 703)

[0147] The central processing unit 110 detects the periodic activity of the subject 10 based on the calculated displacement, calculates the period, and determines the length t of the appropriate imaging time.

[0148] For example, such as Figure 8 In this way, the given period of inhalation is taken as the period during which shooting can be performed, and the length t is calculated.

[0149] (Step 704)

[0150] The central processing unit 110 aggregates multiple small pulse sequences segmented in step 302 to set a medium pulse sequence, ensuring it falls within the length t. Alternatively, it may suggest a medium pulse sequence to the operator. Furthermore, the central processing unit 110 may also change other imaging parameters or suggest changes to the operator.

[0151] (Steps 303-305, 501)

[0152] Subsequently, if the operator gives an instruction to start filming, the central processing unit 110, in the same manner as in the first and second embodiments, acquires camera images and calculates the displacement of the subject from the acquired frame n (n=1) (steps 303-305). The central processing unit 110 determines whether the displacement of the subject 10 calculated in step 305 has reached a given position of a predetermined breathing cycle (step 501).

[0153] When the calculated displacement reaches a given position within a predetermined respiratory cycle, the central processing unit 110 proceeds to step 705, instructing the sequence generator 120 to execute the intermediate sequence. Since only a series of intermediate sequences are executed in step 705, the processing in steps 304, 305, and 501 can be interrupted. This interruption reduces the load on the central processing unit. Alternatively, steps 304, 305, and 501 can be performed continuously to detect sudden activity in the subject 10 caused by the execution of step 705.

[0154] (Step 309)

[0155] The central processing unit 110 executes the sequence sequentially by repeating steps 304, 305, 501, and 705 to acquire all echo signals. The central processing unit 110 uses all the acquired echo signals to perform image reconstruction processing, reconstructing tomographic images, etc.

[0156] Thus, in the MRI apparatus of the third embodiment, since the structure of the intermediate sequence is set by summarizing the small sequences in accordance with the breathing cycle of the subject 10 and executing the intermediate sequence in sync with breathing, although in the second embodiment, data cannot be acquired unless sequential image processing is performed without interruption, in this third embodiment, the process that requires real-time image processing only extends until the triggering of the execution of the intermediate sequence is acquired. Therefore, sequential image processing can be omitted during the execution of the imaging sequence, and processing can be performed even when the computing power of the computing device is insufficient.

[0157] In addition, in the third embodiment, in step 305, not only the displacement can be calculated, but also the activity of the subject 10 can be calculated. If the activity exceeds the threshold, only the data of the time period in which the activity exceeds the threshold in the NMR data obtained in the intermediate sequence can be discarded, or the data obtained in the intermediate sequence can be discarded as a whole. Then, the intermediate pulse sequence is executed again and the NMR signal is obtained.

Claims

1. A magnetic resonance imaging apparatus, characterized by, have: A static magnetic field generating device applies a static magnetic field to the shooting area; The imaging unit applies high-frequency magnetic field pulses and tilted magnetic field pulses to the subject disposed in the imaging area, and acquires the nuclear magnetic resonance signal generated from the subject; The control unit, according to a predetermined imaging pulse sequence, repeatedly causes the imaging unit to apply the high-frequency magnetic field pulse and the tilting magnetic field pulse and acquire the nuclear magnetic resonance signal at a given timing, so that the imaging unit acquires the number of nuclear magnetic resonance signals required for image reconstruction; and The camera, during the operation of the imaging unit, continuously and optically images the subject positioned within the imaging area. The control unit acquires images captured by the camera at a given frame rate. The captured pulse sequence is divided into small sequences with time widths corresponding to the frame rate. The control unit executes the small sequence sequentially at time intervals corresponding to the frame frequency by repeating the following actions: before executing one of the small sequences, the control unit detects the displacement of the subject relative to a predetermined reference position or the speed of the subject's movement from the image of the most recent frame acquired at the frame frequency; if the detection result is within a predetermined allowable range, the control unit executes the small sequence; if the detection result exceeds the allowable range, the control unit does not execute the small sequence and waits until the next frame is acquired according to the frame frequency.

2. The magnetic resonance imaging device according to claim 1, characterized in that, The magnetic resonance imaging device also has: The operations department receives instructions from the operator. The control unit receives the frame rate from the operator via the operation unit.

3. The magnetic resonance imaging device according to claim 1, characterized in that, The control unit detects at least the displacement from the image of the most recent frame, determines whether the detected displacement reaches a given displacement caused by a predetermined periodic movement of the subject, and if the detection result is within a predetermined allowable range and the displacement of the subject reaches the given displacement caused by the predetermined periodic movement, the imaging unit executes the small sequence.

4. The magnetic resonance imaging device according to claim 1, characterized in that, The control unit detects the periodic displacement of the subject from the images in multiple frames, calculates the time width for obtaining the nuclear magnetic resonance signal based on the period of the detected displacement, and aggregates multiple small sequences to generate a medium sequence, ensuring that it is within the time width. Subsequently, the control unit acquires the image of the most recent frame and detects displacement, determines whether the periodic displacement of the subject reaches a given displacement, and if the given displacement is reached, causes the imaging unit to execute the intermediate sequence.

5. A magnetic resonance imaging apparatus, characterized by have: A static magnetic field generating device applies a static magnetic field to the shooting area; The imaging unit applies high-frequency magnetic field pulses and tilted magnetic field pulses to the subject disposed in the imaging area, and acquires the nuclear magnetic resonance signal generated from the subject; The control unit, according to a predetermined imaging pulse sequence, repeatedly causes the imaging unit to apply the high-frequency magnetic field pulse and the tilting magnetic field pulse and acquire the nuclear magnetic resonance signal at a given timing, so that the imaging unit acquires the number of nuclear magnetic resonance signals required for image reconstruction; and The camera continuously captures images of the subject positioned in the shooting area using an optical method during the operation of the shooting unit. The control unit acquires images captured by the camera at a given frame rate. The captured pulse sequence is divided into small sequences with time widths corresponding to the frame rate. The control unit sequentially causes the imaging unit to execute the small sequence by repeating the following actions: before the imaging unit executes one of the small sequences, the control unit detects the displacement of the subject from the image of the most recent frame captured at the frame frequency, determines whether the detected displacement reaches a predetermined given displacement caused by the periodic movement of the subject, and if the given displacement is reached, the imaging unit executes the small sequence; if the given displacement is not reached, the control unit does not execute the small sequence and waits until the next frame is captured at the frame frequency.

6. A magnetic resonance imaging device, characterized in that, have: A static magnetic field generating device applies a static magnetic field to the shooting area; The imaging unit applies high-frequency magnetic field pulses and tilted magnetic field pulses to the subject disposed in the imaging area, and acquires the nuclear magnetic resonance signal generated from the subject; and The control unit, according to a predetermined imaging pulse sequence, repeatedly causes the imaging unit to apply the high-frequency magnetic field pulse and the tilting magnetic field pulse, and acquire nuclear magnetic resonance signals at a given timing, so that the imaging unit acquires the number of nuclear magnetic resonance signals required for image reconstruction. During the execution of the imaging pulse sequence, the control unit acquires images of the subject from the connected camera at a given frame rate. The captured pulse sequence is divided into small sequences with time widths corresponding to the frame rate. The control unit executes the small sequence sequentially at time intervals corresponding to the frame frequency by repeating the following actions: before executing one of the small sequences, the control unit detects the displacement of the subject relative to a predetermined reference position or the speed of the subject's movement from the image of the most recent frame acquired at the frame frequency; if the detection result is within a predetermined allowable range, the control unit executes the small sequence; if the detection result exceeds the allowable range, the control unit does not execute the small sequence and waits until the next frame is acquired according to the frame frequency.

7. A control method for a magnetic resonance imaging apparatus, comprising applying high-frequency magnetic field pulses and tilting magnetic field pulses to a subject positioned in the imaging area at timings according to a given imaging pulse sequence, and acquiring nuclear magnetic resonance signals generated from the subject. The control method for the magnetic resonance imaging device is characterized by performing the following actions: The first action involves acquiring images of the subject from the connected camera at a given frame rate during the execution of the imaging pulse sequence. The second action involves detecting, from the image of the most recent frame acquired at the stated frame rate, the displacement of the subject relative to a predetermined reference position or the velocity of the subject's movement. The third action involves, if the detection result is within a predetermined acceptable range, causing the magnetic resonance imaging device to execute a smaller sequence of segments, each segmented with a time width corresponding to the frame frequency. If the detection result exceeds the acceptable range, the smaller sequence is not executed, and the process waits until the next frame is acquired according to the frame frequency. By repeating the first to third actions, the magnetic resonance imaging device is made to execute the small sequence sequentially at time intervals corresponding to the frame rate.

8. A program product comprising a control program for a magnetic resonance imaging apparatus, the magnetic resonance imaging apparatus applying high-frequency magnetic field pulses and tilting magnetic field pulses to a subject positioned in an imaging area at timings according to a given imaging pulse sequence, and acquiring nuclear magnetic resonance signals generated from the subject. The program product is characterized in that the control program of the magnetic resonance imaging device causes the computer to perform the following steps: During the execution of the shooting pulse sequence, images of the subject are captured from the connected camera at a given frame rate; Detect the displacement of the subject relative to a predetermined reference position or the velocity of the subject's movement from the image of the most recent frame acquired at the frame rate; and If the detection result is within a predetermined allowable range, the magnetic resonance imaging device executes a small sequence that divides the imaging pulse sequence into smaller sequences with a time width corresponding to the frame frequency. If the detection result exceeds the allowable range, the small sequence is not executed, and the device waits until the next frame is captured according to the frame frequency.

Images