Magnetic resonance imaging apparatus and image processing apparatus

Abstract

The present invention provides a magnetic resonance imaging (MRI) system that, when imaging the same subject multiple times with a time interval between images, accurately matches a specific position of the subject, which should be depicted at the center of the current image, to a specific position depicted at the center of past images. [Solution] When the same subject is imaged multiple times with a time interval between each image, the acquisition unit acquires a first image, which is a past image in which the subject's anatomical feature points are depicted, and a locator image, which is the current image (second image), in which the anatomical feature points are depicted. The calculation unit calculates the amount of tabletop movement required to move the tabletop on which the subject is placed, based on the difference between the position of the anatomical feature points depicted in the first image and the position of the anatomical feature points depicted in the locator image, so that a specific position of the subject depicted at the center of the first image is depicted at the center of the locator image. The bed control device controls the movement of the tabletop based on the amount of tabletop movement.

Description

Technical Field

[0001] The embodiments disclosed in this specification and the drawings relate to a magnetic resonance imaging (MRI) device and an image processing device.

Background Art

[0002] An MRI device performs a scan that excites the nuclear spins of a subject placed in a static magnetic field with a high-frequency (RF: Radio Frequency) pulse at the Larmor frequency and collects the magnetic resonance (MR: Magnetic Resonance) signal generated from the subject along with the excitation, and generates an MR image based on the MR signal collected by the scan.

[0003] In an examination using an MRI device, for example, in follow-up examinations such as before and after administration of a contrast agent, periodic medical check-ups, and after surgery, the same subject may be imaged multiple times at intervals. In this case, it is preferable to perform a scan that can acquire a current image at the same imaging position as the imaging position of a past image. For example, as a method for simplifying or improving the efficiency of setting this imaging position, a method using a marker attached to a predetermined part of the subject or a pressure sensor that acquires a pressure distribution representing the body structure of the subject is known.

[0004] Also, due to circumstances such as the transfer of a patient who is the subject or the allocation of examinations within a hospital facility, examinations that image the same subject multiple times at intervals are not necessarily performed on the same MRI device. Therefore, it is difficult for an engineer who is a user to finely adjust the imaging position manually while referring to past images, and thus it is difficult to acquire an image at the same imaging position as the imaging position of a past image with high accuracy.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] One of the problems that the embodiments disclosed herein and in the drawings aim to solve is to accurately match a specific position of a subject, which should be depicted at the center of the current image, with a specific position of the subject depicted at the center of past images, when imaging the same subject multiple times with a time interval between images. However, the problems that the embodiments disclosed herein and in the drawings aim to solve are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0007] An MRI apparatus according to one embodiment comprises a static magnetic field magnet, a tabletop, an image processing device, and a patient control device. The static magnetic field magnet generates a static magnetic field. The tabletop places a subject being brought into the static magnetic field. When the same subject is imaged multiple times with a time interval between images, the acquisition unit acquires a first image, which is a past image in which the anatomical feature points of the subject are depicted, and a locator image, which is a locator image for positioning the current image (second image), in which the anatomical feature points are depicted. The calculation unit calculates the amount of tabletop movement to move the tabletop on which the subject is placed, based on the difference between the position of the anatomical feature points depicted in the first image and the position of the anatomical feature points depicted in the locator image, so that a specific position of the subject depicted at the center of the first image is depicted at the center of the locator image. The patient control device controls the movement of the tabletop based on the amount of tabletop movement. [Brief explanation of the drawing]

[0008] [Figure 1] A block diagram showing an example of the overall configuration of an MRI apparatus according to the first embodiment. [Figure 2] A flowchart showing an example of operation of an MRI device according to the first embodiment. [Figure 3] An explanatory diagram of (A) the first image, (B) the locator image, and (C) the image that should be acquired after the top plate is moved from the state in (B), according to the first embodiment, where the cross-section plane is the YZ plane. [Figure 4] An explanatory diagram on how to move the tabletop. [Figure 5] A block diagram showing an example of the overall configuration of an MRI apparatus according to the second embodiment. [Figure 6] A diagram showing an example of the mechanism for moving the top plate along the Y-axis according to the embodiment, (A) before lift-up and (B) after lift-up. [Figure 7] A block diagram showing an example of the overall configuration of an MRI apparatus according to the third embodiment. [Figure 8] An explanatory diagram illustrating (A) a locator image with the cross-section plane being the XY plane, (B) a locator image with the cross-section plane being the XZ plane, (C) an image that should be acquired after the top plate is moved from the state in (A), and (D) an image that should be acquired after the top plate is moved from the state in (C) according to the third embodiment. [Figure 9] A flowchart showing an example of the operation of an MRI device according to the third embodiment. [Figure 10] A flowchart showing an example of the operation of an MRI device according to the fourth embodiment. [Figure 11] A block diagram showing an example of the overall configuration of an MRI apparatus according to the fifth embodiment. [Figure 12] A flowchart showing an example of the operation of an MRI device according to the fifth embodiment. [Modes for carrying out the invention]

[0009] The embodiments of the MRI apparatus and image processing apparatus will be described below with reference to the drawings. In each figure, the same elements are denoted by the same reference numerals, and redundant explanations are omitted.

[0010] (Overall configuration of the MRI system) FIG. 1 is a block diagram showing an example of the overall configuration of an MRI apparatus 1 according to an embodiment. The MRI apparatus 1 includes a gantry device 100, a control cabinet 300, an image processing device 400, and a couch 500. Note that the image processing device 400 may be mounted on a server of a medical image management system (PACS: Picture Archiving and Communication Systems), a server of a hospital information system (HIS: Hospital Information System), or the like, and may be connected to the MRI apparatus 1 via a network.

[0011] Here, the Z-axis direction is defined as the direction along the magnetic flux of the static magnetic field generated by the static magnetic field magnet 10, and is the same as the longitudinal direction of the top plate 51. The Y-axis direction is a vertical direction orthogonal to the Z-axis direction, and is defined as a direction perpendicular to the top plate 51. The X-axis direction is a direction orthogonal to each of the Z-axis and the Y-axis, and is defined as the same as the lateral direction of the top plate 51.

[0012] The XY plane is defined as a plane perpendicular to the Z-axis direction. The XZ plane is defined as a plane perpendicular to the Y-axis direction with respect to the top plate 51. The YZ plane is defined as a plane perpendicular to the X-axis direction. The anatomical cross-section varies depending on how the subject P is placed on the top plate 51. In FIG. 1, the XY plane is an axial cross-section, the YZ plane is a coronal cross-section, and the YZ plane is a sagittal cross-section.

[0013] The gantry device 100 includes a static magnetic field magnet 10, a gradient magnetic field coil 11, and a whole body (WB) coil 12. These components are housed in a cylindrical housing.

[0014] The static magnetic field magnet 10 of the gantry device 100 has a generally cylindrical shape and generates a static magnetic field in a bore into which a patient serving as the subject P is carried. The bore is the inspection space inside the cylinder of the static magnetic field magnet 10. The static magnetic field magnet 10 incorporates a superconducting coil, and the superconducting coil is cooled to an extremely low temperature by liquid helium.

[0015] The static magnetic field magnet 10 generates a static magnetic field by applying a current supplied from a static magnetic field power supply (not shown) to the superconducting coil in the excitation mode. After that, when the static magnetic field magnet 10 shifts to the persistent current mode, the static magnetic field power supply is disconnected. Once the static magnetic field magnet 10 shifts to the persistent current mode, it continues to generate a large static magnetic field for a long time, for example, over one year. Note that the static magnetic field magnet 10 may be constituted by a permanent magnet.

[0016] The gradient magnetic field coil 11 has a substantially cylindrical shape and is fixed inside the static magnetic field magnet 10. The gradient magnetic field coil 11 generates a gradient magnetic field by receiving the supply of current from the gradient magnetic field power supply 31. Specifically, the gradient magnetic field coil 11 has three coils corresponding to the X-axis, Y-axis, and Z-axis that are orthogonal to each other, and the three coils generate a gradient magnetic field in which the magnetic field strength changes along each of the X-axis, Y-axis, and Z-axis.

[0017] The WB coil 12 has a substantially cylindrical shape and is an RF coil fixed so as to surround the subject P inside the gradient magnetic field coil 11. The WB coil 12 transmits an RF pulse transmitted from the transmitter 32 to the subject P and receives an MR signal emitted from the subject P by the excitation of hydrogen nuclei.

[0018] The MRI apparatus 1 may have a local coil 20 in addition to the WB coil 12. The local coil 20 is an RF coil disposed close to the subject P and receives an MR signal emitted from the subject P at a position close to the subject P. The local coil 20 may transmit an RF pulse transmitted from the RF transmitter 32 to the subject P. There are various types of local coils 20 corresponding to imaging regions of the subject P such as the head, chest (for example, FIG. 1), spine, lower limbs, and whole body.

[0019] The control cabinet 300 includes a gradient magnetic field power supply 31, a transmitter 32, a receiver 33, and a sequence controller 34.

[0020] The gradient magnetic field power supply 31, under the control of the sequence controller 34, supplies current to the gradient magnetic field coil 11, generating gradient magnetic fields along the X, Y, and Z axes from the gradient magnetic field coil 11.

[0021] Based on instructions from the sequence controller 34, the transmitter 32 generates an RF pulse train in the Larmor frequency band as an RF transmission wave and outputs it to the RF coil to excite the subject P.

[0022] The receiver 33 converts the MR signal received by the RF coil from analog to digital (AD) and outputs it to the sequence controller 34. The digitized MR signal is called raw data.

[0023] The sequence controller 34 performs a scan of the subject P by driving the gradient magnetic field power supply 31, the transmitter 32, and the receiver 33, respectively, under the control of the image processing device 400. The sequence controller 34 receives raw data from the RF receiver 33 during the scan and transmits this raw data to the image processing device 400.

[0024] The sequence controller 34 includes a processing circuit (not shown). This processing circuit consists of, for example, a processor that executes a predetermined program, or hardware such as an FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit).

[0025] The bed 500 comprises a bed body 50, a top plate 51, and a bed control device 52. The top plate 51 is on which the subject P, which is brought into the static magnetic field, is placed. The bed body 50 moves the top plate 51 into the bore under the control of the bed control device 52. The bed control device 52 moves the top plate 51 in the vertical and horizontal directions under the control of the image processing device 400.

[0026] The image processing device 400 includes a processing circuit 41, a storage circuit 42, an input interface 43, a network interface 44, and a display 45. The image processing device 400 is configured, for example, by a computer.

[0027] The processing circuit 41 is, for example, a circuit equipped with a CPU or a dedicated or general-purpose processor. The processor of the processing circuit 41 realizes various functions corresponding to various programs by executing various programs that are pre-stored in the memory circuit 42 or directly incorporated into the processing circuit 41.

[0028] The memory circuit 42 is a storage medium that includes ROM (Read Only Memory), RAM (Random Access Memory), and external storage devices such as HDD (Hard Disk Drive) and optical disc drives. The memory circuit 42 stores various information and data, and stores various programs that the processor of the processing circuit 41 will execute.

[0029] The input interface 43 includes various input devices for the user to input various types of information and data, and an input circuit that processes signals from the input devices. Examples of input devices include a mouse, keyboard, trackball, touch panel, non-contact input device using an optical sensor, and voice input device. When an input device is operated, the input circuit generates an instruction signal corresponding to that operation and outputs it to the processing circuit 41.

[0030] The network interface 44 communicates with various devices connected to the network via wired or wireless means, and exchanges various types of information and data.

[0031] The display 45 is a display device such as a liquid crystal display panel, a plasma display panel, or an organic EL panel. The display 45 may also be a GUI (Graphical User Interface) that displays various information and data under the control of the processing circuit 41 and also functions as an input device.

[0032] These components enable the image processing device 400 to control the entire MRI apparatus 1. Specifically, the processing circuit 41 receives instructions regarding imaging conditions and other various information from a user, such as a medical technologist, via the input interface 43. The processing circuit 41 then instructs the sequence controller 34 to perform a scan based on the input imaging conditions. The processing circuit 41 also reconstructs the MR image based on the raw data transmitted from the sequence controller 34. The reconstructed MR image is displayed on the display 45 and stored in the memory circuit 42.

[0033] In MRI examinations, for example, in pre- and post-contrast agent administration, longitudinal screenings, and post-operative follow-up examinations, the same subject may be imaged multiple times with time intervals between scans. In this case, it is preferable to perform scans that acquire the current image at the same imaging position as the previous images. For example, it is preferable that the posture of the subject P, the position in which the subject P is placed on the rigging device 100 during the scan (i.e., the relative position of the subject P with respect to the magnetic field center in the Z-axis direction of the static magnetic field), and the diagnostic area of ​​the subject P depicted at the center of the image are the same.

[0034] However, due to circumstances such as the transfer of the patient P to another hospital or the allocation of examinations within the hospital facility, when imaging the same subject multiple times with a time gap in between, the examinations are not necessarily performed using the same MRI device, and may be performed using different manufacturers or different models. For example, DICOM (Digital Imaging and Communications in Medicine) images, which are past images stored in the PACS server or memory circuit 42, have different formats and text data handling methods between manufacturers. Therefore, when performing a scan to acquire the current image, it is not always possible to directly refer to non-image information such as the type of pulse sequence, imaging conditions, and imaging position. It is preferable that the type of pulse sequence and imaging conditions are the same between past images and current images.

[0035] In this case, conventionally, the user, the technician, manually fine-tuned the imaging position while referring to past images, making it difficult to acquire images with high accuracy at the same imaging position as past images. Therefore, the MRI apparatus 1 according to this embodiment enables the acquisition of the current image at the same imaging position as past images during follow-up examinations. Specifically, it precisely matches the specific position of the subject that should be depicted at the center of the current image to be acquired with high accuracy to the specific position of the subject depicted at the center of past images.

[0036] In the following description, the first and second images are MR images generated based on MR signals acquired by the main scan for diagnosis or examination. The locator image is an MR image generated based on MR signals acquired by a positioning scan, i.e., a locator scan, used to define the scan area of ​​the main scan.

[0037] (First Embodiment) In the MRI apparatus 1 according to the first embodiment, the processing circuit 41 performs an acquisition function F1 and a calculation function F2. Referring to the flowchart in Figure 2 and Figures 3(A) to 4, an example of operation when the MRI apparatus 1 according to the first embodiment images the same subject multiple times with a time interval in between will be explained.

[0038] In step ST1, the MRI device 1 performs a locator scan to collect MR signals related to the locator image. The imaging position for the locator scan may be set so that one parallel plane is scanned in multislice mode, or it may be set so that two or three mutually orthogonal planes are scanned simultaneously. Note that the processing in step ST1 may be performed after step ST2.

[0039] In step ST2, the acquisition function F1 acquires a first image from past images in which the anatomical feature points of subject P are depicted. In the first embodiment, the first image is an image cut along the YZ plane, which is a plane perpendicular to the X-axis direction (i.e., the sagittal section of subject P in Figure 1). The acquisition function F1 acquires the first image from, for example, a PACS server or a DICOM image stored in the memory circuit 42.

[0040] In step ST3, the acquisition function F1 acquires a locator image for positioning the current image, which is the second image, and which depicts the anatomical feature points of the subject P. Preferably, the locator image is an image with the same anatomical cross-section as the first image (for example, if the first image is a sagittal cross-section, the locator image is also a sagittal cross-section).

[0041] Furthermore, the acquisition function F1 may acquire multiple past images in step ST2, acquire multiple locator images in step ST3, and then select and acquire a first image and locator image that contain the same anatomical feature points from the multiple past images and multiple locator images. Generally, when a subject P is brought into the bore as shown in Figure 1, the subject P is placed so that the sagittal cross section, which is the left-right center of the subject P, is at the center of the static magnetic field in the X-axis direction. If a first image and locator image that contain the same anatomical feature points are selected from multiple past images and multiple locator images, the amount of top plate movement can be calculated in step ST4, for example, even if the sagittal cross section, which is the left-right center of the subject P, is misaligned.

[0042] In step ST4, the calculation function F2 calculates the amount of tabletop movement required to move the tabletop 51 on which the subject P is placed, based on the difference between the position S1 of the anatomical feature points depicted in the first image and the position S2 of the anatomical feature points depicted in the locator image, so that the specific position of the subject P depicted at the center of the first image is depicted at the center of the locator image.

[0043] Here, the amount of top plate movement will be explained with reference to Figures 3(A) to 3(C). Figure 3(A) is the first image IM1, Figure 3(B) is the locator image IM2, and Figure 3(C) is the image IM3 (i.e., the second image) that should be acquired after the top plate 51 has been moved from the state in Figure 3(B) based on the amount of top plate movement. Here, the intersections O1, O2, and O3 of the dashed lines in each image represent the center positions of each image. The center position of the first image, the center position of the locator image, and the center position of the second image are the positions corresponding to the magnetic field center (i.e., iso center) of the static magnetic field in each image.

[0044] Furthermore, the intersections C1, C2, and C3 of the cross in each image represent specific positions of the subject P where it is desired to be at the center of the static magnetic field in each image. That is, the intersections C1, C2, and C3 represent the same specific position of the same subject. As shown in Figure 3(A), the specific position C1 of the subject P where it is desired to be at the center of the static magnetic field in the first image is at the center position O1 of the first image. In contrast, as shown in Figure 3(B), the specific position C2 of the subject P is different from the center position O2 of the locator image.

[0045] The anatomical feature points depicted in the first image, the locator image, and the second image are the same. Furthermore, the relative positional relationship between the anatomical feature point S1 in the first image and the specific location C1 on the subject is the same as the relative positional relationship between the anatomical feature point S2 in the locator image and the specific location C2 on the subject, and also the same as the relative positional relationship between the anatomical feature point S3 in the second image and the specific location C3 on the subject.

[0046] Therefore, based on the difference between the position S1 of the anatomical feature point depicted in the first image and the position S2 of the anatomical feature point depicted in the locator image, the amount of tabletop movement is calculated so that a specific position of the subject P depicted at the center position O1 of the first image is depicted at the center position O2 of the locator image.

[0047] Furthermore, anatomical feature points only need to be depicted in both the first image and the locator image, and are not limited to a single point; they may be multiple points or even a region. The location of the anatomical feature points may be the center of either the first image or the locator image, or it may not be the center of either image. Additionally, anatomical feature points can be detected using known methods such as machine learning.

[0048] In step ST5, the bed control device 52 controls the movement of the tabletop 51 based on the amount of tabletop movement. Specifically, the tabletop 51 is moved so that the position S1 of the anatomical feature point depicted in the first image matches the position S2 of the anatomical feature point depicted in the locator image. Here, Figure 4 is an explanatory diagram of the movement of the tabletop 51. The bed control device 52 moves the tabletop 51 in both the Z-axis direction (direction D1 in Figure 4) and the Y-axis direction (direction D2 in Figure 4). The bed control device 52 may move the tabletop 51 along the Z-axis direction first and then along the Y-axis direction, or it may move the tabletop 51 along the Y-axis direction first and then along the Z-axis direction.

[0049] As shown in Figure 4, when the top plate 51 is moved based on the amount of top plate movement, as shown in Figure 3(B), a specific position C2 of the subject P, which is desired to be at the center of the static magnetic field in the locator image, moves in directions D1 and D2. As a result, as shown in Figure 3(C), the specific position C3 of the subject P moves to the center position O3 (i.e., the position of the magnetic field center) of the image IM3 (i.e., the second image) that will be acquired in this scan after the top plate 51 has been moved.

[0050] Further details regarding the mechanism for moving the top plate 51 by the bed control device 52 will be described later.

[0051] In step ST6, the MRI device 1 performs the main scan to collect the MR signal related to the second image. That is, a specific position of the subject P, which is depicted at the center of the first image, is depicted at the center of the second image.

[0052] According to the MRI apparatus 1 of the first embodiment, since an image cut in the YZ plane is used as the first image, the amount of tabletop movement in both the Y-axis and Z-axis directions can be automatically calculated using only the first image of apparatus 1. Furthermore, in follow-up examinations, scans are performed at the same imaging position as past images with high accuracy, and the user's workload is reduced through automation. In addition, since the center position of the second image (current image) is positioned at the magnetic field center with high magnetic field uniformity, similar to the center position of the first image (past image), high-quality images can be secured in the region of interest used for diagnosis, etc.

[0053] (Second Embodiment) Figure 5 is a block diagram showing an example of the overall configuration of the MRI apparatus 1 according to the second embodiment. The MRI apparatus 1 according to the second embodiment differs from the first embodiment in that it further includes a sensor 2.

[0054] As described above in step ST5 of the first embodiment, the bed control device 52 controls the movement of the tabletop 51 based on the amount of tabletop movement. The bed control device 52 moves the tabletop 51 in both the Z-axis direction and the Y-axis direction. Figures 6(A) and 6(B) show an example of the tabletop movement mechanism along the Y-axis direction according to the embodiment. Conventionally, the position of the subject P in the Y-axis direction is adjusted by placing one or more pads of a predetermined thickness between the tabletop 51 and the subject P, whereas in the MRI apparatus 1 according to the embodiment, it is adjusted by the tabletop 51 movement mechanism along the Y-axis direction.

[0055] As the mechanism for moving the top plate 51, an air suspension system that does not require a pump and utilizes a compressible fluid (e.g., compressed air) is preferred. The mechanism for moving the top plate 51 may also be a hydraulic pump installed in a position unaffected by the static magnetic field. The use of an electric motor inside the bore is undesirable.

[0056] The air suspension mechanism for moving the bedtop 51 consists of the bedtop 51, an air spring (i.e., an airbag) 53, and wheels 54. The wheels 54 travel on rails 55 provided on the frame device 100. The bed control device 52 moves the bedtop 51 along the Z-axis direction by making the wheels travel on the rails 55.

[0057] The air spring 53 is installed beneath the top plate 51. The bed control device 52 moves (i.e., lifts up) the top plate 51 along the Y-axis by injecting gas into the air spring 53. Figure 6(A) shows the state before gas is injected into the air spring 53, and Figure 6(B) shows the state after gas is injected into the air spring 53. A compressor (not shown) that discharges compressed air is connected to the air spring 53, and the flow rate of gas injected into the air spring 53 may be adjusted, for example, by adjusting the air pressure. By adjusting the amount of gas injected into the air spring 53, the height of the top plate 51 moving along the Y-axis is controlled.

[0058] In the case of a mechanism for moving the top plate 51 using air suspension, where the top plate 51 is lifted up using compressed air, the relationship between the flow rate of the injected gas and the amount of movement of the lifted top plate 51 may not be constant. Therefore, in the second embodiment, feedback control by the sensor 2 is performed to match the amount of top plate movement calculated in step ST4 with the effective amount of movement of the top plate 51 that is actually moved.

[0059] Sensor 2 detects the effective amount of movement of the tabletop 51 along the Y-axis. Preferably, the effective amount of movement of the tabletop 51 is detected in real time. Based on the effective amount of movement of the tabletop 51 detected by Sensor 2, the bed control device 52 provides feedback control to the amount of movement of the tabletop 51 along the Y-axis.

[0060] It is preferable for the bed control device 52 to move the bed plate 51 along the Z-axis direction, and then move the bed plate 51 along the Y-axis direction. When using the rails 55 and wheels 54 of the existing frame device, the air suspension mechanism for moving the bed plate 51 requires returning the bed plate 51 to the lower limit of its movable range when moving the bed plate 51 in the Z-axis direction. Therefore, if the bed plate 51 is moved in the Y-axis direction after being moved in the Z-axis direction, the number of times the bed plate 51 is moved along the Y-axis direction can be reduced.

[0061] Furthermore, since the top plate 51 in the Y-axis direction can only move upward relative to the rail 55 of the mounting device 100, the starting position of the top plate 51's movement in the Y-axis direction is the lower limit of the range in which the top plate 51 can move.

[0062] The mechanism for moving the top plate 51 along the Y-axis direction according to the second embodiment can also be applied when the user manually sets the amount of top plate movement in both the Y-axis direction and the Z-axis direction.

[0063] According to the MRI apparatus 1 of the second embodiment, the calculated amount of tabletop movement and the effective amount of movement of the tabletop 51 are matched by feedback control by the sensor 2. Therefore, the specific position of the subject depicted at the center of the first image (past image) is depicted with higher precision than the center of the second image (current image).

[0064] (Third embodiment) Figure 7 is a block diagram showing an example of the overall configuration of the MRI apparatus 1 according to the third embodiment. The MRI apparatus 1 according to the third embodiment differs from the first embodiment in that the processing circuit 41 further performs the display control function F3. Also, in the third embodiment, the cross-section of the first image differs from that of the first embodiment.

[0065] An example of operation of the MRI apparatus 1 according to the third embodiment will be described with reference to the flowchart in Figure 9 and Figures 8(A) to 8(D). Here, steps ST11, ST13, and ST18 in the flowchart of Figure 9 are substantially the same as steps ST1, ST2, and ST6 in the flowchart of Figure 2 which describes an example of operation of the MRI apparatus 1 according to the first embodiment, so redundant explanations will be omitted.

[0066] In step ST12, the acquisition function F1 acquires a first image from the past in which the anatomical feature points of subject P are depicted in the image. In the third embodiment, the first image is an image cut in the XY plane, which is a plane perpendicular to the Z axis (i.e., the axial section of subject P in Figure 1), or an image cut in the XZ plane, which is a plane perpendicular to the Y axis (i.e., the coronal section of subject P in Figure 1).

[0067] In step ST14, the calculation function F2 calculates the amount of tabletop movement required to move the tabletop 51 on which the subject P is placed, based on the difference between the positions of the anatomical feature points depicted in the first image and the positions of the anatomical feature points depicted in the locator image, so that a specific position of the subject depicted at the center of the first image is depicted at the center of the locator image.

[0068] In step ST15, the bed control device 52 controls the movement of the bedtop 51 based on the amount of bedtop movement.

[0069] Here, Figure 8(A) illustrates locator image IM2A, where the cross-section plane is the XY plane, and Figure 8(B) illustrates image IM3A, which should be acquired after the top plate 51 has been moved from the state in Figure 8(A) based on the amount of top plate movement. Furthermore, Figure 8(C) illustrates locator image IM2B, where the cross-section plane is the XZ plane, and Figure 8(D) illustrates image IM3B, which should be acquired after the top plate 51 has been moved from the state in Figure 8(C) based on the amount of top plate movement. Here, the intersections O4, O5, O6, and O7 of the dashed lines in each image represent the center position of each image. Also, the intersections C4, C5, C6, and C7 of the cross marks in each image represent the same specific position of the same subject where it is desired to be at the center of the static magnetic field in each image.

[0070] Figures 8(A) and 8(C), similar to Figure 3(B), show that the specific position of subject P, which is desired to be at the center of the static magnetic field in the locator image, is different from the center position of the locator image. Therefore, based on the difference between the position of the anatomical feature points depicted in the first image and the position of the anatomical feature points depicted in the locator image, the amount of tabletop movement is calculated so that the specific position of subject P depicted in the first image is depicted at the center position of the locator image.

[0071] Figures 8(B) and 8(D), similar to Figure 3(C), show how a specific position of the subject P is depicted at the center of the image (i.e., the position of the magnetic field center) that will be acquired in this scan after the tabletop 51 has been moved (i.e., the second image). However, in Figure 8(A), since the cross-section plane is the XY plane, position C4 is moved only in direction D2 (i.e., the Y-axis direction), and in Figure 8(C), since the cross-section plane is the XZ plane, position C6 is moved only in direction D1 (i.e., the Z-axis direction). Thus, in step ST15, in the third embodiment, the bed control device 52 moves the tabletop 51 with respect to either the Y-axis direction or the Z-axis direction.

[0072] In step ST16, the display control function F3 displays a prompt (i.e., an alert) to manually move the tabletop 51 along an axis other than the Y-axis or Z-axis axis along which the bed control device 52 moved the tabletop 51 in step ST15. For example, the prompt is displayed on the display 45, and the user performs an operation to set the amount of tabletop movement via the input interface 43 in accordance with the prompt.

[0073] In step ST17, the bed control device 52 controls the movement of the bedtop 51 based on the amount of bedtop movement set by the user.

[0074] According to the MRI apparatus 1 of the third embodiment, even when only the amount of tabletop movement for one of the Y-axis and Z-axis directions is automatically calculated from the first image, the user can set the amount of tabletop movement for the other axis that is not automatically calculated. Compared to the conventional case where the user had to manually set the amount of tabletop movement for both the Y-axis and Z-axis directions, the user's effort is reduced because they only need to manually set the amount of tabletop movement for either the Y-axis or Z-axis direction.

[0075] (Fourth Embodiment) The fourth embodiment differs from the first embodiment in that at least two mutually orthogonal first images and locator images are used to calculate the amount of tabletop movement. An example of the operation of the MRI apparatus 1 according to the fourth embodiment will be described with reference to the flowchart in Figure 10. Here, steps ST21 and ST29 in the flowchart of Figure 10 are substantially the same as steps ST1 and ST6 in the flowchart of Figure 2 which describes an example of the operation of the MRI apparatus 1 according to the first embodiment, so redundant explanations will be omitted.

[0076] In step ST22, the acquisition function F1 acquires a first image from the past in which the anatomical feature points of subject P are depicted. Here, the first image is either an image cut in the XY plane, which is perpendicular to the Z axis (i.e., the axial section of subject P in Figure 1), or an image cut in the XZ plane, which is perpendicular to the Y axis (i.e., the coronal section of subject P in Figure 1).

[0077] In step ST23, the acquisition function F1 acquires a locator image for positioning the current image, which is the second image, and the locator image depicts the anatomical feature points of the subject P. Here, it is preferable that the locator image is an image with the same anatomical cross-section as the first image acquired in step ST22 (for example, if the first image is an axial cross-section, the locator image is also an axial cross-section).

[0078] In step ST24, the calculation function F2 calculates a first amount of tabletop movement for moving the tabletop 51 on which the subject P is placed, based on the difference between the positions of the anatomical feature points depicted in the first image in step ST22 and the positions of the anatomical feature points depicted in the locator image in step ST23, so that a specific position of the subject P depicted at the center of the first image is depicted at the center of the locator image.

[0079] In step ST25, the acquisition function F1 acquires a first image from the past in which the anatomical features of subject P are depicted. The first image acquired in step ST25 is an image cut by a plane that is orthogonal to the first image acquired in step ST22. In other words, in the fourth embodiment, at least two first images are acquired.

[0080] In step ST26, the acquisition function F1 acquires a locator image for positioning the current image, which is the second image, and which depicts the anatomical feature points of the subject P. Here, it is preferable that the locator image is an image with the same anatomical cross-section as the first image acquired in step ST25 (for example, if the first image is a coronal cross-section, the locator image is also a coronal cross-section). The locator image acquired in step ST25 is an image cut by a plane that is orthogonal to the locator image acquired in step ST23. In other words, in the fourth embodiment, at least two locator images are acquired.

[0081] In step ST27, the calculation function F2 calculates a second amount of tabletop movement for moving the tabletop 51 on which the subject P is placed, based on the difference between the positions of the anatomical feature points depicted in the first image in step ST25 and the positions of the anatomical feature points depicted in the locator image in step ST26, so that a specific position of the subject P depicted at the center of the first image is depicted at the center of the locator image.

[0082] In other words, the calculation function F2 calculates a tabletop movement amount which is the sum of a first tabletop movement amount calculated in step ST24 and a second tabletop movement amount calculated in step ST27, based on at least two first images acquired in steps ST22 and ST25 and at least two locator images acquired in steps ST23 and ST26.

[0083] In step ST28, the bed control device 52 controls the movement of the bedtop 51 based on the amount of bedtop movement. In the fourth embodiment, the bed control device 52 moves the bedtop 51 in both the Y-axis direction and the Z-axis direction.

[0084] According to the MRI apparatus 1 of the fourth embodiment, at least two mutually orthogonal first images and locator images are used to calculate the amount of tabletop movement. In this case, the amount of tabletop movement for one of the Y-axis and Z-axis directions is automatically calculated from the one first image, and the amount of tabletop movement for the other of the Y-axis and Z-axis directions is automatically calculated from the other first image. Therefore, the amount of tabletop movement for both the Y-axis and Z-axis directions is automatically calculated.

[0085] (Fifth embodiment) Figure 11 is a block diagram showing an example of the overall configuration of the MRI apparatus 1 according to the fifth embodiment. The MRI apparatus 1 according to the fifth embodiment differs from the first embodiment in that it includes a camera 3 for photographing the subject P.

[0086] Camera 3 is composed of, for example, a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor, and captures images of the subject P placed on the top plate 51. Camera 3 generates an optical image of the subject P and transmits it to the processing circuit 41. The optical image of the subject P may be a still image or a moving image captured sequentially at a predetermined frame rate.

[0087] It is preferable that camera 3 is positioned to image the upper surface of the top plate 51 before it is inserted into the bore. Camera 3 is installed, for example, on the ceiling, wall, or outer wall of the rigging device 100 of the examination room where the MRI apparatus 1 is installed.

[0088] Furthermore, the MRI apparatus 1 according to the fifth embodiment differs from the first embodiment in that the processing circuit 41 further performs an adjustment function F4. An example of the operation of the MRI apparatus 1 according to the fifth embodiment will be described with reference to the flowchart in Figure 12. In the fifth embodiment, after steps ST31 and ST32 in the flowchart of Figure 12, the same processing as in the first embodiment shown in steps ST1 to ST6 in the flowchart of Figure 2 is performed.

[0089] In step ST31, the adjustment function F4 acquires an optical image using camera 3.

[0090] In step ST32, the adjustment function F4 adjusts the feed rate of the subject P based on the acquired optical image. Here, the feed rate of the subject is the amount by which the subject P is fed into the stand device 100, that is, relative to the magnetic field center in the Z-axis direction of the static magnetic field. The adjustment function F4 may also adjust the feed rate of the subject relative to the magnetic field center in the X-axis direction or the magnetic field center in the Y-axis direction of the static magnetic field.

[0091] In the fifth embodiment, in step ST4, the calculation function F2 calculates the top plate movement amount such that the specific position of the subject P depicted at the center position of the first image is depicted at the center position of the locator image of the subject P that was brought in by the feed amount.

[0092] According to the MRI apparatus 1 of the fifth embodiment, the amount of subject P being fed into the cradle device 100 is adjusted based on the optical image from the camera 3. As a result, the top plate 51 can be moved in axial directions not included in the first image, and the specific position of subject P depicted at the center of the first image (past image) is depicted with higher precision than the center of the second image (current image).

[0093] According to the MRI apparatus and image processing apparatus of at least one embodiment described above, when imaging the same subject multiple times with a time interval between images, it is possible to accurately match the specific position of the subject that should be depicted at the center position of the current image to be acquired with the specific position of the subject depicted at the center position of past images.

[0094] In the above embodiment, the term "processor" refers to circuits such as a dedicated or general-purpose CPU (Central Processing Unit), GPU (Graphics Processing Unit), or Application Specific Integrated Circuit (ASIC), or a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)).

[0095] If the processor is, for example, a CPU, it implements various functions by reading and executing programs stored in memory circuits. Alternatively, if the processor is, for example, an ASIC, instead of storing programs in memory circuits, functions equivalent to those programs are directly incorporated as logic circuits within the processor's circuitry. In this case, the processor implements various functions through hardware processing that reads and executes the programs incorporated within the circuitry. Furthermore, a processor can also implement various functions by combining software and hardware processing.

[0096] Furthermore, although the above embodiment shows an example where a single processor in the processing circuit implements each function, a processing circuit may be configured by combining multiple independent processors, with each processor implementing each function. Also, when multiple processors are provided, the memory circuit for storing programs may be provided individually for each processor, or a single memory circuit may store programs corresponding to the functions of all processors together.

[0097] In the description of the embodiment, the acquisition function F1, calculation function F2, display control function F3, and adjustment function F4 are examples of the acquisition unit, calculation unit, display control unit, and adjustment unit, respectively, as defined in the claims.

[0098] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0099] 1…Magnetic Resonance Imaging (MRI) device 2…Sensor 3…Camera 10…Static magnetic field magnet 51…Tabletop 52…Chair control device 400…Image processing device F1…Acquisition function F2…Calculation function F3…Display control function F4…Adjustment function

Claims

1. A static magnetic field magnet that generates a static magnetic field, A top plate on which the subject to be brought into the static magnetic field is placed, When imaging the same subject multiple times with a time interval in between, the acquisition unit acquires a first image, which is a past image in which the anatomical feature points of the subject are depicted, and a locator image for positioning the second image, which is the current image, in which the anatomical feature points are depicted. A calculation unit calculates the amount of tabletop movement required to move the tabletop on which the subject is placed, based on the difference between the position of the anatomical feature point depicted in the first image and the position of the anatomical feature point depicted in the locator image, such that the specific position of the subject depicted at the center of the first image is depicted at the center of the locator image. A bed control device that controls the movement of the top plate based on the amount of top plate movement, A magnetic resonance imaging system equipped with the following features.

2. The specific position depicted at the center of the first image is depicted at the center of the second image. The magnetic resonance imaging apparatus according to claim 1.

3. The center position of the first image, the center position of the locator image, and the center position of the second image are the positions corresponding to the magnetic field center of the static magnetic field in each image. The magnetic resonance imaging apparatus according to claim 1.

4. The acquisition unit selects and acquires the first image and the locator images from a plurality of past images and a plurality of locator images, in which the same anatomical feature points are included in each other. The magnetic resonance imaging apparatus according to claim 1.

5. The first image above is a cross-section of the top plate with a plane perpendicular to the X-axis direction, which is the shorter side of the top plate. The magnetic resonance imaging apparatus according to claim 1.

6. The bed control device moves the top plate along the Z-axis direction, which is the longitudinal direction of the top plate, and then moves the top plate along the Y-axis direction, which is perpendicular to the top plate. The magnetic resonance imaging apparatus according to claim 1.

7. The starting position of the movement of the top plate in the Y-axis direction is the lower limit of the range in which the top plate can move. The magnetic resonance imaging apparatus according to claim 6.

8. An air spring is further provided beneath the aforementioned top plate, The bed control device moves the top plate along the Y-axis direction, which is perpendicular to the top plate, by injecting gas into the air spring. The magnetic resonance imaging apparatus according to claim 1.

9. The system further includes a sensor that detects the effective amount of movement by which the top plate actually moves along the Y-axis, The bed control device provides feedback control of the amount of movement of the bed plate along the Y-axis direction based on the effective amount of movement of the bed plate detected by the sensor. The magnetic resonance imaging apparatus according to claim 8.

10. The first image is an image obtained by cutting the top plate with a plane perpendicular to the Z-axis direction, which is the longitudinal direction of the top plate, or an image obtained by cutting the top plate with a plane perpendicular to the Y-axis direction, which is the direction perpendicular to the top plate. The bed control device moves the top plate with respect to either the Y-axis or the Z-axis, The magnetic resonance imaging apparatus according to claim 1.

11. The display and The bed control device further comprises a display control unit that causes the display to show a prompt to manually move the top plate in the other axis, either the Y-axis or the Z-axis, where the top plate is not moved. The magnetic resonance imaging apparatus according to claim 10.

12. The first image and the locator image are images obtained by cutting each other with at least two planes that are orthogonal to each other. The calculation unit calculates the amount of top plate movement based on the first image cut by the at least two planes and the locator image cut by the at least two planes. The bed control device moves the top plate in both the Y-axis direction, which is perpendicular to the top plate, and the Z-axis direction, which is the longitudinal direction of the top plate. The magnetic resonance imaging apparatus according to claim 1.

13. A camera for photographing the subject, The system further includes an adjustment unit that adjusts the amount of the subject being fed in based on the optical image from the camera, The calculation unit calculates the top plate movement amount such that the specific position depicted at the center of the first image is depicted at the center of the locator image of the subject that was fed in by the feeding amount. The magnetic resonance imaging apparatus according to claim 1.

14. When imaging the same subject multiple times with a time interval in between, the acquisition unit acquires a first image, which is a past image in which the anatomical feature points of the subject are depicted, and a locator image for positioning the second image, which is the current image, in which the anatomical feature points are depicted. A calculation unit calculates the amount of tabletop movement required to move the tabletop on which the subject is placed, based on the difference between the position of the anatomical feature point depicted in the first image and the position of the anatomical feature point depicted in the locator image, such that a specific position of the subject depicted at the center of the first image is depicted at the center of the locator image. An image processing device equipped with the following features.

Images