Magnetic resonance imaging apparatus

Abstract

To provide means capable of more detailed analysis of a body movement occurring during an MRI examination, thereby providing an MR image in which body movement correction with high accuracy is performed.SOLUTION: An MRI apparatus includes a processor configured to perform body movement processing. The processor is configured to set, in a video of an imaging device that monitors a body movement, a region (target region) for monitoring a body movement with respect to an examination target, monitor a movement of a subject between the target region and a region outside the target region along with a retention time in each region, and accurately specify a part of measurement data to be a target of body movement correction.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus), and more particularly to a processing technique for body movement of a subject during an examination using an MRI apparatus. [Background technology]

[0002] In an MRI device, a subject is placed in an examination space where a static magnetic field is generated, a gradient is applied to the static magnetic field, position information is assigned to nuclear magnetic resonance signals (hereinafter referred to as NMR signals or echo signals), and k-space data necessary for image reconstruction is collected.

[0003] If the subject moves during this examination, the gradient magnetic field will not properly assign positional information, resulting in problems such as misalignment and artifacts in the reconstructed image. Body motion can be divided into periodic body motions with relatively small displacements, such as the subject's breathing and pulsation, and irregular body motions, such as sudden movements of the subject. The latter, irregular body motion, is particularly problematic. To address such subject motion during an examination, the device corrects it by removing a portion of the k-space data collected during the motion and zero-filling or estimating the missing data (see, for example, Patent Document 1). This correction for body motion is called body motion correction. Patent Document 2 also describes an X-ray CT device that sets the imaging range based on the subject's body motion data and stops the scan if the body motion range deviates from the imaging range during the scan.

[0004] On the other hand, various methods are known for detecting body movements during an examination, such as a method using images from a camera (monitoring camera) for monitoring the subject installed in or near the examination space, a method collecting NMR signals (called navigator echoes) for detecting body movements separately from the NMR signals for generating images collected from the subject, and detecting body movements from the navigator echoes. For body movement correction, information from these body movement detection means is processed within the device to determine whether any body movements that affect imaging have occurred, and then the above-mentioned body movement correction is performed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 09-028689 [Patent Document 2] Japanese Patent Application Publication No. 2018-050668 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology described in Patent Document 1 determines whether the magnitude of body motion is above an allowable range and determines whether body motion correction is necessary, but it is unable to analyze details such as the magnitude, direction, and duration of body motion. As a result, problems arise, such as excessive body motion correction (over-correction) resulting in blurred images, or conversely, insufficient body motion correction making it impossible to completely eliminate artifacts caused by body motion. Patent Document 2 is a technology targeted at X-ray CT devices, and when the body motion range falls outside the allowable range, it issues a warning or stops the scan, without even considering the relationship between body motion and body motion correction.

[0007] An object of the present invention is to provide a means for more precisely analyzing body movements that occur during an examination, thereby providing images that have been subjected to highly accurate body movement correction. [Means for solving the problem]

[0008] In order to solve the above problems, the MRI apparatus of the present invention is equipped with a processor that performs body motion processing. The processor sets an area (target area) for monitoring body motion of the subject in an image captured by an imaging device that monitors body motion, monitors the subject's movement between the target area and outside the target area, along with the residence time in each area, and accurately identifies the portion of the measurement data that should be subject to body motion correction.

[0009] That is, the MRI apparatus of the present invention comprises an imaging unit that collects nuclear magnetic resonance signals generated from a subject, an image generation unit that generates an image using the nuclear magnetic resonance signals, and a processor that acquires video from an imaging device that detects the subject's body movement and processes information about the subject's body movement. The processor sets a first imaging area for monitoring the subject's examination region in the video from the imaging device, and determines at least one of the presence or absence of body movement, the duration of the body movement, the direction and magnitude of the body movement based on whether the examination region has shifted from the first imaging area to outside the first imaging area, and controls body movement correction by the image generation unit.

[0010] Here, the "duration of body movement" includes not only the time during which the movement of the examination region continues, but also the time during which the movement stops but the region remains in a position different from the initial position. [Effects of the Invention]

[0011] According to the present invention, by monitoring the movement and residence time of the subject outside the target region, detailed information such as the magnitude, direction, and time of the body movement can be obtained, and appropriate body movement correction can be performed based on this information. This makes it possible to prevent image blurring due to overcorrection and artifacts due to inappropriate correction. [Brief explanation of the drawings]

[0012] [Figure 1] Diagram showing the overall outline of an MRI device [Figure 2] FIG. 1 shows an example of the arrangement of a body motion detection means in an MRI apparatus. [Figure 3] Diagram showing the processor configuration of an MRI device [Figure 4] A diagram showing the flow of body movement processing by a processor. [Figure 5] FIG. 1 is a diagram showing the flow of body movement processing in the first embodiment. [Figure 6] 1A to 1D are diagrams for explaining the setting of a target region in the first embodiment, each showing a specific example of a target region. [Figure 7]1A and 1B are diagrams illustrating an example of body movement processing according to the first embodiment, in which (A) shows a case where the signal acquisition order is sequential order, and (B) shows a case where the signal acquisition order is centric order. [Figure 8] FIG. 10 is a diagram showing the flow of body movement processing in the second embodiment. [Figure 9] 10A to 10C are diagrams for explaining the setting of a target region in the second embodiment, each showing a specific example of a target region. [Figure 10] FIG. 10 is a diagram illustrating body movement processing according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0014] 1 is a diagram showing an overall overview of an MRI apparatus to which the present invention is applied. The MRI apparatus mainly comprises an imaging unit 10 that provides an examination space, generates NMR in an examination region of a subject 50 placed in the examination space, and collects NMR signals generated from the examination region, a calculation unit that reconstructs an image using k-space data consisting of the NMR signals collected by the imaging unit 10, and a processor 20 that has the functions of a control unit that controls the entire apparatus including the imaging unit 10.

[0015] The imaging unit 10 has the same functions as those of a known MRI apparatus, and detailed description thereof will be omitted in this specification, but as shown in the figure, it includes a static magnetic field magnet 101 that generates a uniform magnetic field (static magnetic field) in an examination space in which a subject 50 is placed, a gradient magnetic field coil 102 that applies a gradient magnetic field to the static magnetic field, an RF transmission coil 103 that applies a high frequency magnetic field that excites the nuclei of atoms that constitute the tissue of the subject, and an RF reception coil 104 that receives an NMR signal generated by the subject, and the gradient magnetic field coil 102, RF transmission coil 103, and RF reception coil 104 are connected to a gradient magnetic field power supply 105, a transmitter 106, and a receiver 107, respectively. The operations of the gradient magnetic field power supply 105, the transmitter 106, and the receiver 107 are controlled by a sequencer 108. The sequencer 108 determines a pulse sequence for each scan using the set pulse sequence type and imaging conditions (imaging parameters) such as imaging parameters, and controls each part of the imaging unit 10 to operate in accordance with the determined pulse sequence and collect echo signals (k-space data) required for image reconstruction. The functions and operations of each part when the imaging unit 10 collects k-space data are the same as those of a general MRI device, so detailed description will be omitted here.

[0016] The static magnetic field magnet 101, gradient magnetic field coil 102, and RF transmitting coil 103 are housed in the gantry, and the subject 50 has an RF receiving coil 104 attached to the area to be examined and is positioned in the examination space within the gantry while lying on a bed device 40.

[0017] The processor 20 controls imaging via the sequencer 108 and also functions as a control unit that controls the operation of the entire apparatus, and functions as a calculation unit that reconstructs an image of the subject using echo signals collected by the imaging unit 10 and performs calculations such as correction on k-space data before reconstruction or on the reconstructed image. In addition to the functions of the control unit and calculation unit described above, the processor 20 of this embodiment has a function of collecting and processing body movement information occurring in the subject 50 during an examination, such as the magnitude and duration of the body movement, and presenting the body movement information to the user by linking it to the scan (imaging) in progress.

[0018] The processor 20 can be configured with one or more computers 200 equipped with a CPU, a GPU, or both, and memory, and performs various calculations using NMR signals and controls the entire device, as described above. However, some of the functions of the processor 20 can also be realized by a programmable IC such as an ASIC or PGFA, and these are all collectively referred to as the processor 20.

[0019] The processor 20 is connected to a UI unit 30 including a display device 31 and an output device (not shown) for interacting with a user, an external storage device 60, and the like. As shown in Fig. 2, the display device 31 may be provided in a console operated by a user, or in multiple locations, such as near or on the surface of a gantry 100 that provides an examination space. The processor 20 may also be connected to an external database such as a PACS or other image processing device via a known network connection.

[0020] Furthermore, in the MRI apparatus of this embodiment, a body motion detection means such as a monitoring camera is installed inside or near the examination space so that the processor 20 can perform a detailed analysis of the body motion of the subject that occurs during the examination and make appropriate body motion correction. Multiple monitoring cameras 80 may be installed, for example, at two or more locations, such as at two openings of the gantry 100, on the entrance side and the opposite side, as shown in Fig. 2, and in this case, the processor 20 processes images from the multiple monitoring cameras. In addition to the monitoring cameras 80, information from NMR signals (navigator echoes) may also be used as body motion detection means.

[0021] 3 shows an example of the configuration of the processor 20 of this embodiment. As shown in the figure, the processor 20 includes an imaging control unit 210 that controls the imaging unit 10 via the sequencer 108 described above, a display control unit 250 that controls the display of images and GUIs on the display device of the UI unit 30, an image generation unit 220 that generates an image of the subject using k-space data consisting of NMR signals, and a body motion processing unit 230. Although not shown in the figure, the processor 20 may also include functional units included in known MRI devices, such as functional units that perform calculations using reconstructed images and image correction.

[0022] The body movement processing unit 230 includes an area setting unit 231 that sets an area (target area) for monitoring the body movement of the subject, a body movement analysis unit 233 that analyzes the movement (magnitude, direction, residence time, etc.) of the subject entering and exiting the target area using information (called body movement information) from the body movement detection means, and a judgment unit 235 that judges subsequent processing by the calculation unit or control unit based on the results of the analysis by the body movement analysis unit 233.

[0023] An outline of the processing of the MRI apparatus of this embodiment with the above configuration is shown in Fig. 4. As shown in the figure, when imaging starts, the body movement analysis unit 233 analyzes the video from the monitoring camera 80 (S1), the determination unit determines whether the examination region of the subject is within a region set in advance based on the initial position of the examination region, and whether the time the subject is within or outside the region is within a predetermined time (S2), and the content of body movement correction is determined based on the determination result (S3).

[0024] The MRI apparatus of this embodiment sets a region (referred to as a target region) for monitoring body movement from the initial position of the examination region of the subject in the camera image at the start of imaging, prior to analysis by the body movement analysis unit 233, monitors the residence time of the examination region inside and outside the target region, and determines the content of body movement correction accordingly. How to set the region and the content of body movement correction according to the determination result will be described in detail in the following embodiments.

[0025] According to this embodiment, instead of estimating the presence or absence and magnitude of body movement from the movement of a feature point of interest as in the past, a target region (two-dimensional extent) is set to include the examination region, and body movement is determined based on whether the examination region remains within the target region, thereby making it possible to accurately determine body movement even for movements in various directions, thereby reducing over-correction and under-correction of body movement correction.

[0026] A specific embodiment of the processing by the processor of this embodiment will be described below.

[0027] <Embodiment 1> In this embodiment, the processor sets one area in the camera image that includes the examination area at the start of the examination as the target area to be monitored, monitors the movement of the examination area from the target area to outside the target area, and the time (residence time) when part of the examination area is outside the target area, and controls the content of subsequent body movement correction depending on the results.

[0028] The processing flow of this embodiment will be described with reference to the flowchart of FIG.

[0029] <s11> First, once the scan task (pulse sequence) and scan parameters to be executed in one imaging are determined according to a preset examination protocol, etc., the imaging control unit 221 controls the imaging unit 10 to start imaging (S11). One imaging may include one or more scans, and the type of imaging executed in each scan (e.g., T1-weighted imaging, T2*-weighted imaging, diffusion-weighted imaging) and imaging technique (sampling technique) are arbitrary and are not particularly limited. Here, as an example, the flow when executing one scan to collect k-space data required to reconstruct one image or one set of images is shown.

[0030] When navigator data is used in combination as a body motion detection means, the imaging unit 10 performs imaging by adding a sequence for acquiring navigator echoes to a pulse sequence for acquiring an image of the subject. As a sequence for acquiring navigator echoes, various methods are known, such as a method of adding a step for generating RF pulses to acquire navigator echoes in the pulse sequence for actual imaging, or a method of executing a navigator sequence separately from the pulse sequence for actual imaging, and any of these methods can be adopted.

[0031] <S12、S13> The body movement processing unit 230 captures video from the monitoring camera 80 around the time of the start of imaging (S12). Before the scan (pulse sequence) begins, the region setting unit 231 first uses the image of the subject to set a region of the examination area (hereinafter referred to as the target region) at an initial position (S13). The target region is a region set to monitor the body movement of the examination area, and its size and shape are not particularly limited and can vary depending on the examination area. That is, the target region can have any shape, such as a circle, ellipse, rectangle, or trapezoid, depending on the shape of the examination area. Furthermore, the size of the region is set depending on the size of the examination area, for example, so as to cover the examination area. This setting may be performed, for example, by displaying an image (video) showing the examination area on the display device 31 of the UI unit 30, allowing the user to determine a target area of ​​a predetermined size and shape on the screen of the display device 31 by operating a cursor or the like, and then the area setting unit 231 may set this as the target area in the video (a fixed area in the video of the position displayed by the surveillance camera), or the area setting unit 231 may use image recognition or feature extraction algorithms based on information about the examination area included in the examination protocol to identify the area of ​​the head or the examination area where the receiving coil is attached in the camera image, and set the target area so that it includes the examination area. In this way, the size and shape of the target area may be set by the user or automatically by the device based on the size and direction of allowable body movement depending on the area to be imaged and the type of imaging, as described below.

[0032] An example where the examination region is the head is shown in Figure 6. (A) is an example where a rectangular region whose length and width are the maximum vertical width x maximum horizontal width of the examination region in an area (examination region) 501 on the camera image that has been identified as the head is set as target region 502a, and the region inscribed in region 501 is set as target region 502b. (B) is an example where a region wider than region 502a is set as target region 502b, (C) is an example where a circular target region 502c is set, and (D) is an example where the horizontal width of circular region 502c shown in (C) is widened to form elliptical target region 502d. These are just examples, and the shape of the target region, the clearance in each direction relative to the examination region, etc. can be changed in various ways.

[0033] For example, the clearance of target region 502 (502a to 502d are collectively referred to as 502) from region 501 may be changed depending on the tolerance for body movement, and the presence or absence of the clearance and its size may be changed. When the tolerance for body movement is small, that is, in the case of imaging in which even slight body movement is not allowed, the clearance is made small so that movement of the examination region that extends beyond target region 502 can be detected with high accuracy. In the case of imaging in which the tolerance for body movement is relatively large, target region 502 is set with a clearance (of the order of several mm) between it and region 501, as in the examples shown in (B) and (D).

[0034] The tolerance for body movement may differ depending on the imaging region and type of imaging. For example, the head, where minute structures are an issue, may have a lower tolerance for body movement than the trunk. In addition, the head may be allowed to move to the left and right to a certain extent, but the tolerance for vertical movement may be lowered because it is thought to involve large body movements. In such cases, the amount of clearance or the presence or absence of clearance may be different between the left and right and vertical directions, as in the example shown in (D).

[0035] The types of imaging that may have different tolerances for body motion include the sampling method used to collect data in k-space and the type of scan. For example, sampling methods such as radial sampling, which samples k-space radially from the center, the PROPELLER method, and spiral scan, which samples k-space spirally, are robust sampling methods with high tolerances for body motion. Furthermore, scout imaging scans, which position the subject in the examination space, have a relatively high tolerance for body motion. Alternatively, a GUI for presetting the user's desired motion tolerance may be displayed on the UI unit 30, and the user may set information regarding the motion tolerance in advance, taking into account the type of imaging, etc.

[0036] When the region setting unit 231 sets a region, for example, a rectangle or a circle may be prepared as a basic shape, and the region setting unit 231 may set the region automatically or by accepting a user selection according to the shape characteristics of the examination region. Also, when setting the clearance based on the body movement tolerance, similarly to the shape selection, if information on the body movement tolerance is obtained in advance, the region setting unit 231 may set the region automatically based on that information, or may set the region by accepting a user specification via the UI unit 30.

[0037] <s14> Once the target region is set, the body movement analysis unit 233 analyzes the video sent from the monitoring camera 80 for each frame and determines whether the test region remains within the target region 502 or has protruded outside the target region (i.e., whether a portion of the test region has shifted outside the target region) using known image recognition technology, optical flow, non-rigid transformation, or other technology (S14). If the body movement analysis unit 233 determines that the test region has protruded from the target region, it records the time of the video frame when the protrusion occurred. The body movement analysis unit 233 continues to determine whether the test region is within the target region 502 or has protruded, and if the test region returns to the target region 502 after protruding, it records the time of the frame when it returns, and determines the time that a portion of the test region was outside the target region as the residence time.

[0038] The capture (S12) and analysis (S13) of the camera image by the body movement analysis unit 233 is continued until one scan is completed, i.e., until all planned k-space data is collected, unless a situation arises in which the scan should be stopped.

[0039] <S15~S18> The determination unit 235 determines subsequent processing in consideration of the residence time and the arrangement in k-space of the k-space data collected during that time. Regarding the body movement of the examination region, after the examination region leaves the target region, there are cases where the examination region returns to the target region during the scan and cases where the examination region does not return to the target region. If the examination region returns to the target region, it is first determined whether the examination region has returned to the target region within a predetermined time (S15).

[0040] The predetermined time is determined by whether the amount of data that can be corrected has been collected, and also varies depending on the TR (repetition time) of the imaging mode and the motion correction method that can be used in subsequent image processing, and can be set in advance accordingly. By appropriately setting the predetermined time depending on the type of scan, the motion correction method, etc., over-correction or under-correction can be avoided.

[0041] For example, if the TR is long, the interval between data acquisition of one line of k-space and data acquisition of the next line will be long, so even if the dwell time is set relatively long, the number of lines acquired during that time will be smaller than in a scan with a short TR. Therefore, the predetermined time may be set long.

[0042] For example, when zero-filling is used for motion correction or when iterative reconstruction is used, where data estimation is performed by repeated calculation, image reconstruction using zero-filling is possible if at least approximately 80% of the phase encode number of k-space data has been acquired, i.e., if the dwell time is less than the time required to acquire data equivalent to 20% of the phase encode number, then this time is set as the predetermined time. Furthermore, as a motion correction method, in the case of half-scanning, image reconstruction is possible if one of the two high-frequency data sets flanking the low-frequency k-space has been acquired. Therefore, the predetermined time can be set to the time required to acquire 60% to 70% of the data, provided that one of the high-frequency data sets has been acquired. It is also possible to set an even shorter time (50% or more) as the predetermined time. However, since image reconstruction using a small number of data sets results in a poor signal-to-noise ratio, it is preferable to set the predetermined time short for imaging aimed at a high signal-to-noise ratio. In this case, the target signal-to-noise ratio may be taken into consideration when setting the predetermined time.

[0043] If the examination region does not return to the target region within a predetermined time (S15), the determination unit 235 determines that meaningful image reconstruction is difficult even with body motion correction and that remeasurement is necessary (S17), and passes the result to the imaging control unit 210 and / or the display control unit 250. The imaging control unit 210 may automatically execute remeasurement based on the determination result of the determination unit 235 that remeasurement is necessary, or the display control unit 250 may notify the user by displaying, on the display device 31, a message such as "The subject has moved, so remeasurement is necessary" or a mark indicating that body motion has occurred. In response to this notification, the user may send a command to the imaging control unit 210 via the UI unit 30 to execute remeasurement or to specify the remeasurement range.

[0044] On the other hand, if the dwell time is within a predetermined time (S15), the determination unit 235 further determines whether the k-space data collected during that time is in the low frequency range of k-space (S16). For example, even if the dwell time is the time to collect 20% of the data, if the k-space data collected during that time is low frequency data, an image with diagnostic value cannot be reconstructed, and remeasurement of the low frequency data is required. In this case, the determination result indicating the need for remeasurement is sent to the imaging control unit 210 and the display control unit 250, as described above.

[0045] If the result of the above judgment (S15, S16) is that the dwell time is within a predetermined time and the necessary low-frequency data has been collected, the processor 20 (judgment unit 235) controls the image reconstruction unit to reconstruct the image using a body motion correction method corresponding to the set predetermined time, such as zero fill.

[0046] The motion correction method may be selected taking into consideration the order of data acquisition (ordering) in k-space, in addition to the set predetermined time and the ratio of data acquired during that time to k-space data. While there are no particular limitations on the data acquisition order that can be employed in this embodiment, two typical examples of data acquisition orders are shown in Fig. 7. Fig. 7(A) is an example of a sequential order in which high-frequency data from one side of k-space is acquired, via zero encoding, before high-frequency data from the other side. Fig. 7(B) is an example of a centric order in which data is acquired alternately from the center of k-space toward the high frequencies on both sides.

[0047] 7A, for example, when data is collected outside the target region when collecting data from low-frequency data toward other high-frequency data, if the data collection outside the target region is within a predetermined time, and the data collected during that time is not low-frequency data including the center of k-space and is within 20% of k-space, then the data collected outside the target region can be subjected to motion correction, and image reconstruction can be performed using zero-fill or half-scan. With this ordering, half-scan reconstruction is possible because one high-frequency data has been collected.

[0048] In the case of a centric order shown in Figure 7(B), where data is acquired from the center of k-space toward the high frequencies, low-frequency data is acquired first, so there is a high possibility that motion will occur during the acquisition of high-frequency data, making the high-frequency data subject to motion correction. In such cases, image reconstruction using a half scan is not possible, so motion correction is employed, in which high-frequency data on both sides is reconstructed using zero-filling. Also, although not shown, depending on the ordering, discontinuous lines in the phase encoding direction of the k-space data (e.g., the nth, n+3th, and n+6th lines) may be subject to motion correction. In such cases, iterative reconstruction, in which data is estimated by repeated calculations, is also possible.

[0049] As described above, according to this embodiment, a target area in which body movement is permitted for the examination site is set for the image from the surveillance camera, and the protrusion of the examination site outside the target area and the time spent outside the target area are analyzed. Based on the analysis results, it is determined whether body movement correction is necessary, the method of body movement correction to be selected, whether re-measurement is necessary, and other processing is decided. Therefore, compared to body movement correction that is performed simply based on the magnitude of body movement, it is possible to grasp body movement in two dimensions, the accuracy of body movement correction can be improved, and the possibility of over-correction or under-correction can be reduced.

[0050] In particular, the above effect can be enhanced by appropriately setting the clearance between the examination site and the target region according to the examination site and the type of imaging.

[0051] <Embodiment 2> This embodiment is characterized by setting a second region for monitoring body movement outside the target region. The processing of this embodiment will be described below with reference to the flowchart in Fig. 8. In Fig. 8, the same processes as in Fig. 5 are designated by the same reference numerals, and redundant explanations will be omitted.

[0052] In this embodiment, when imaging begins (S11), video is captured from the monitoring camera 80 prior to scanning (S12), and the position of the examination region at that time is used as the initial position to set a region including the examination region (S13). In the first embodiment, a single region of a predetermined shape was set as the target region 502 surrounding the region 501 of the examination region. In this embodiment, the region setting unit 231 sets a second region outside the first region (e.g., region 502 shown in FIG. 6). The first region is a region of any shape that includes the examination region of the subject and can be set in the same manner as region 502 in the first embodiment. The second region is located outside the first region and may surround the entire periphery of the first region, or may be located adjacent to a portion of the periphery, for example, both or one side in the vertical direction, or both or one side in the horizontal direction. A third region may also be set outside the second region.

[0053] Furthermore, it is also possible to provide a gap between the first region and the second region. The width of the gap can be adjusted depending on the tolerance for body movement, similar to the clearance between the examination region 501 and the target region 502 in the first embodiment. That is, the presence or absence of a gap and the width of the gap can be adjusted depending on whether a sampling method (radial sampling, etc.) with a relatively high tolerance for body movement is used or the type of scan is used.

[0054] 9 shows examples of setting the second region. (A) in FIG. 9 shows an example in which a second region 602 is set so as to be in contact with a rectangular first region 601, and (B) shows an example in which a gap 605 is set between the first region 601 and second region 602 in (A). In this example, the gap 605 is provided only on both sides of the first region 601 in the horizontal direction, and the second region 602 is in contact with the first region 601 in the vertical direction. This is applied when the tolerance for body movement in the horizontal direction is relatively large.

[0055] 1C shows an example in which multiple second regions 602 are set outside a first region 601, and a third region 603 is set further outside of those. In the example shown, relatively narrow second regions 602-1, 602-2, and 602-3 are set on both the left and right sides and above the first region 601, and third regions 603-1, 603-2, and 603-2 are set further outside of those. The widths of the second and third regions, as well as the gaps between regions, may be adjusted according to the tolerance for body movement. In this way, by setting second regions 602-1, 602-2, and 602-3 in multiple directions, information on the direction of body movement can be obtained, and by setting multiple regions (second and third regions) toward the outside, information on the magnitude of body movement can be obtained.

[0056] For example, information such as whether the examination region moved to the right or left, whether there was a large body movement exceeding the width of the second region, or whether the body movement was small enough to remain within the second region can be obtained. Furthermore, by using the width information and the region residence time, more detailed information about the body movement can be obtained, such as whether the movement was relatively gradual or instantaneous, and whether the movement will return to normal quickly or not. Based on such information, the determination unit 235 can make appropriate decisions regarding subsequent processing. Information regarding the magnitude and direction of the body movement obtained by the body movement processing unit 230 can also be presented to the user or fed back to the subject during the examination, allowing for intervention to restore the subject's posture or for the subject to be aware of the need to return to normal posture.

[0057] The method of presenting the information is not limited, but various methods can be used, such as displaying an image mark at a reference position that resembles the subject and an image mark in a state where the position has shifted in a distinguishable manner on the screen, or issuing an audio warning such as "It has moved to the right, so please move it back."

[0058] As described above, after the region setting unit 231 sets multiple monitoring regions, the body movement processing unit 230 (body movement analysis unit 233) analyzes the video from the monitoring camera during imaging, and records whether the examination area is within the first region or extends into the second region, the time it remains in the first region or remains there after returning, and the time it remains in the second region (S14).

[0059] If the subject moves and the examination region moves out of the first region and into the second region, the determination unit 235 compares the time the examination region was within the first region, i.e., the measurement time in the first region, with the time the examination region remained in the second region, i.e., the measurement time in the second region (S21). As a result, as shown in FIG. 10(A), if the measurement time in the first region is longer than the measurement time in the second region, the data collected when the examination region moved out of the second region is treated as data to be corrected for body motion (S22), and image reconstruction with body motion correction is performed (S18). On the other hand, as shown in FIG. 10(B), if the measurement time in the first region is shorter than the measurement time in the second region, the data collected when the examination region moved out of the first region is treated as data to be corrected for body motion (S23), and image reconstruction with body motion correction is performed (S18).

[0060] As with the first embodiment, an appropriate method for correcting body motion is adopted, taking into consideration the proportion of the data to be corrected for body motion occupying the k-space and the arrangement in the k-space.

[0061] Although not shown in Fig. 8, when a third region is set outside the second region as shown in Fig. 9(C), the measurement times in each region may be compared, and data other than that measured in the region with the longest measurement time may be subject to body motion correction. Furthermore, when the measurement times in each region are all less than a predetermined time, it may be determined that effective body motion correction is difficult, and a notification urging remeasurement may be issued or remeasurement may be automatically performed, as in the case of remeasurement in embodiment 1 (Fig. 5: S17).

[0062] According to this embodiment, by setting multiple regions around the examination region, the direction of the subject's body movement can be determined, appropriate feedback can be provided to the subject, the examination technician, etc., and the initial position can be quickly restored. This reduces the amount of data that needs to be corrected for body movement, allowing for effective body movement correction. Furthermore, by setting double or triple regions around the examination region, it is possible to grasp the direction and extent of body movement, and it is possible to ensure data that can be effectively used even if the examination region moves, i.e., data that can be used without body movement correction, thereby reducing the need to retest due to body movement.

[0063] <Other embodiments> In the above embodiments, image recognition and feature extraction algorithms have been exemplified as methods for recognizing an examination region when setting a region on a camera image. However, known skeletal detection technology can also be used instead of or in addition to these. Skeletal detection technology is a technology for detecting the skeleton of a human body based on body feature points, such as the ears and jaw for the head, and the shoulders, elbows, wrists, knees, and ankles for the trunk. For example, if the examination region is the chest or abdomen, it is possible to set the target region in the area corresponding to the chest or abdomen based on the skeleton detected from both shoulders and hip joints. Skeletal detection technology can also be used when a body movement analysis unit analyzes body movement, and can detect and analyze movement of the examination region beyond the region from changes in the position of the skeleton.

[0064] In the above embodiment, the target area is set and body movement is analyzed using images from a surveillance camera 80 mounted on a gantry. However, multiple optical imaging devices, such as a stereo camera, can be used instead of or in addition to the surveillance camera. Analysis using surveillance camera images can capture movement within the plane of the image, but it is difficult to capture movement in the depth direction of the image. On the other hand, a stereo camera calculates the angular difference (parallax) from the camera to the target based on the pixel misalignment between the two images, and then uses the inter-camera distance and the parallax to obtain the distance to the target, i.e., depth information. Therefore, by using the surveillance camera 80 and the stereo camera together, three-dimensional information about the magnitude and direction of body movement can be obtained, enabling more accurate body movement detection.

[0065] The above has described embodiments of the MRI apparatus of the present invention. However, the present invention is characterized by setting and analyzing regions (two-dimensional regions) for monitoring body movement, and adjusting body movement correction based on movement between regions. However, the present invention is not limited to these embodiments, and also encompasses MRI apparatuses with additional elements and functions, or replaceable elements and functions. [Explanation of symbols]

[0066] 10: imaging unit, 20: processor, 210: imaging control unit, 220: image generation unit, 230: body movement processing unit, 231: region setting unit, 233: body movement analysis unit, 235: determination unit

Claims

1. an imaging unit that collects nuclear magnetic resonance signals generated from the subject; an image generating unit that generates an image using the nuclear magnetic resonance signal; and a processor for acquiring an image from an imaging device that detects body movement of the subject and processing body movement information of the subject; the processor sets a first imaging region for monitoring an examination region of the subject in the image, and determines at least one of the presence or absence of body movement, the duration of the body movement, the direction and magnitude of the body movement based on whether the examination region has shifted from the first imaging region to outside the first imaging region, and controls body movement correction by the image generation unit.

2. 2. The magnetic resonance imaging apparatus according to claim 1, The magnetic resonance imaging apparatus according to claim 1, wherein the processor compares a period during which the examination region remains outside the first imaging region with a predetermined threshold value to determine a duration of the body movement.

3. 3. The magnetic resonance imaging apparatus according to claim 2, The magnetic resonance imaging device is characterized in that, when the period during which the object remains outside the first imaging region is equal to or shorter than a predetermined threshold, the processor designates the nuclear magnetic resonance signals collected by the imaging unit during that period as body motion correction data when the image generation unit generates an image.

4. 3. The magnetic resonance imaging apparatus according to claim 2, The magnetic resonance imaging apparatus, wherein the processor notifies a user when a period during which the object remains outside the first imaging region exceeds a predetermined threshold.

5. 3. The magnetic resonance imaging apparatus according to claim 2, The magnetic resonance imaging apparatus according to claim 1, wherein the predetermined threshold is equal to or less than the time required for the image generating unit to collect nuclear magnetic resonance signals capable of constructing an image.

6. 6. The magnetic resonance imaging apparatus according to claim 5, A magnetic resonance imaging apparatus, wherein the predetermined threshold is equal to or less than the time required for the imaging unit to acquire 20% or more of k-space data consisting of nuclear magnetic resonance signals.

7. 3. The magnetic resonance imaging apparatus according to claim 2, The magnetic resonance imaging apparatus, wherein the processor changes the predetermined threshold value in accordance with a repetition time (TR) in an imaging sequence executed by the imaging unit.

8. 2. The magnetic resonance imaging apparatus according to claim 1, A magnetic resonance imaging apparatus, wherein the first imaging region is a region that includes the region to be examined.

9. 2. The magnetic resonance imaging apparatus according to claim 1, a processor for setting a second imaging region outside the first imaging region, and determining from the image that the examination region has moved outside the first imaging region when the examination region has moved toward the second imaging region.

10. 10. The magnetic resonance imaging apparatus according to claim 9, The magnetic resonance imaging apparatus, wherein the processor sets a gap between the first imaging region and the second imaging region.

11. 10. The magnetic resonance imaging apparatus according to claim 9, The magnetic resonance imaging apparatus according to claim 1, wherein the processor sets the second imaging region to a region obtained by extending the first imaging region in a one-dimensional direction.

12. 10. The magnetic resonance imaging apparatus according to claim 9, The magnetic resonance imaging apparatus according to claim 1, wherein the processor sets the second imaging region to a region obtained by extending the first imaging region in a two-dimensional direction.

13. 10. The magnetic resonance imaging apparatus according to claim 9, The magnetic resonance imaging apparatus according to claim 1, wherein the second imaging region includes an inner region close to the first imaging region and an outer region outside the inner region.

14. 2. The magnetic resonance imaging apparatus according to claim 1, The magnetic resonance imaging apparatus is characterized in that the processor acquires images from a plurality of imaging devices having different image acquisition positions, and determines body movement of the examination region using the plurality of images.

15. 2. The magnetic resonance imaging apparatus according to claim 1, The magnetic resonance imaging apparatus is characterized in that the processor determines the body movement by analyzing feature points or skeletal structure in the image.

Images