Magnetic resonance imaging equipment

Abstract

To normally generate an image even when a subject moves during imaging, in imaging using a magnetic resonance imaging apparatus of a plane open type.SOLUTION: The magnetic resonance imaging apparatus according to one embodiment comprises a magnet of a current drive type, a detection unit, and a control unit. The magnet of the current drive type generates a magnetic field which dominantly determines a magnetic resonance frequency. The detection unit detects a position of a subject which is imaged in a movable state within the magnetic field. The control unit controls the driving current of the magnet based on the position of the detected subject.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The embodiments disclosed in this specification and in the drawings relate to a magnetic resonance imaging apparatus. [Background technology]

[0002] A magnetic resonance imaging device is an imaging device that excites the nuclear spins of a subject placed in a static magnetic field with a radio frequency (RF) signal at the Larmor frequency, and generates an image by reconstructing the magnetic resonance (MR) signals generated from the subject in response to the excitation.

[0003] Many magnetic resonance imaging (MRI) devices have a configuration called a gantry, in which a cylindrical space (called a bore) is formed. An object (e.g., a patient) lying on a tabletop is carried into the cylindrical space and imaged. A cylindrical static magnetic field magnet, a cylindrical gradient magnetic field coil, and a cylindrical RF coil (i.e., a WB (Whole Body) coil) are housed inside the gantry. In many conventional magnetic resonance imaging devices of this type, the static magnetic field magnet, the gradient magnetic field coil, and the RF coil are cylindrical, and therefore, hereinafter, this type of magnetic resonance imaging device will be referred to as a cylindrical magnetic resonance imaging device.

[0004] In a cylindrical magnetic resonance imaging apparatus, imaging is performed in a closed space inside a bore, which may make imaging difficult for some patients, such as those who suffer from claustrophobia.

[0005] In response to this, a magnetic resonance imaging apparatus has been proposed and developed in which the static magnetic field magnet, gradient magnetic field coil, and RF coil are flat and configured to image a subject such as a patient in an open space sandwiched between two flat static magnetic field magnets. This type of magnetic resonance imaging apparatus will be referred to as a planar open-type magnetic resonance imaging apparatus hereinafter. In the planar open-type magnetic resonance imaging apparatus, imaging is performed in an open space, making it possible to image claustrophobic patients.

[0006] On the other hand, in a cylindrical magnetic resonance imaging device, the patient's movements are restricted because the imaging is performed in a small closed space, whereas in a planar open magnetic resonance imaging device, the patient is imaged in an open space, allowing greater freedom of movement and the patient may move during imaging. In general, imaging using a magnetic resonance imaging device takes a relatively long time, making it difficult to maintain the same posture, which is also a factor in the patient moving during imaging. If the patient moves in a planar open magnetic resonance imaging device, it becomes difficult to generate a normal image. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2002-53212 Summary of the Invention [Problem to be solved by the invention]

[0008] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to enable normal generation of images even if the subject moves during imaging using a planar open-type magnetic resonance imaging apparatus. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in each embodiment described later can also be positioned as other problems. [Means for solving the problem]

[0009] According to one embodiment, a magnetic resonance imaging apparatus includes a current-driven magnet, a detector, and a controller. The current-driven magnet generates a magnetic field that predominantly determines a magnetic resonance frequency. The detector detects a position of a subject to be imaged in a movable state within the magnetic field. The controller controls a drive current for the magnet based on the detected position of the subject. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram showing a first operation concept of a planar open-type magnetic resonance imaging apparatus according to an embodiment. [Diagram 2] FIG. 4 is a diagram showing a second operation concept of the planar open-type magnetic resonance imaging apparatus according to the embodiment. [Diagram 3] FIG. 2 is a diagram showing an example of an internal configuration of a magnet according to an embodiment. [Figure 4] 1 is a block diagram showing an example of the arrangement of a magnetic resonance imaging apparatus according to a first embodiment. [Diagram 5] FIG. 2 is a block diagram showing an example of the configuration of a magnetic resonance imaging apparatus according to a first modified example of the first embodiment. [Figure 6] FIG. 11 is a block diagram showing an example of the configuration of a magnetic resonance imaging apparatus according to a second modified example of the first embodiment. [Figure 7] FIG. 11 is a block diagram showing an example of the arrangement of a magnetic resonance imaging apparatus according to a second embodiment. [Figure 8] FIG. 1 is a first diagram for explaining the arrangement of magnetic field sensors and the estimated magnetic field strength of an imaging area. [Figure 9] FIG. 2 is a second diagram for explaining the arrangement of the magnetic field sensors and the estimated magnetic field strength in the imaging area. [Figure 10] FIG. 13 is a diagram showing an example of the structure of a magnet of a magnetic resonance imaging apparatus according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0012] (First embodiment) Fig. 1 is a diagram showing a first configuration example of a planar open-type magnetic resonance imaging apparatus 1 according to the first embodiment. As illustrated in Fig. 1, the magnetic resonance imaging apparatus 1 has, for example, two magnets 10 each having a circular plate shape (in other words, a thin cylindrical shape).

[0013] Each magnet 10 is arranged so that the central axis of the magnet 10, i.e., the axis passing through the center of the circle at each end face of the cylindrical shape, is parallel to, for example, the floor surface. The two magnets 10 are arranged so as to sandwich the subject. By arranging the magnets 10 in this way, a magnetic field is formed in the open space between the two magnets 10. The subject is imaged in this open space, for example, in an upright position.

[0014] In a conventional cylindrical magnetic resonance imaging apparatus, the magnetic field that predominantly determines the magnetic resonance frequency is called a static magnetic field, and is generated by a static magnetic field magnet. The static magnetic field magnet is configured to generate a magnetic field of constant intensity. For example, when the static magnetic field magnet is configured with a superconducting coil, a static magnetic field is generated by applying a current supplied from a static magnetic field power supply to the superconducting coil in the excitation mode, and then, when the mode is switched to the persistent current mode, the static magnetic field power supply is disconnected, and a magnetic field of constant intensity is generated. The static magnetic field magnet can also be configured as a permanent magnet. In this case, the intensity of the magnetic field generated by the permanent magnet as the static magnetic field magnet is always constant.

[0015] On the other hand, the magnet 10 of the embodiment is the same as a conventional static magnetic field magnet in that it generates a magnetic field that predominantly determines the magnetic resonance frequency. However, as described below, the magnet 10 of the embodiment is significantly different from a conventional static magnetic field magnet in that it is configured as an electromagnet that is driven by a current even during operation (i.e., during imaging). Since the magnet 10 of the embodiment can change the magnetic field strength depending on the magnitude of the driving current, the magnetic field generated by the magnet 10 is not strictly a "static magnetic field". Therefore, hereinafter, the magnetic field generated by the magnet 10 of the embodiment will be referred to as the "main magnetic field" or simply as the "magnetic field".

[0016] Fig. 2 is a diagram showing a second configuration example of the planar open-type magnetic resonance imaging apparatus 1 according to the first embodiment. While Fig. 1 shows a configuration example for imaging a subject in an upright position, Fig. 2 shows a configuration example for imaging a subject in a supine position lying on a top board 80 extending from a bed 81. When imaging a subject in a supine position, the two magnets 10 are arranged so that their central axes are in the vertical direction as shown in Fig. 2, and for example, one magnet 10 is arranged below the top board 80 and the other magnet 10 is arranged above the top board 80.

[0017] 1 and 2, in imaging using the magnet 10 of the embodiment, imaging of the subject in an open magnetic field space is possible, so that even claustrophobic patients can be imaged. On the other hand, imaging in an open space allows for a high degree of freedom of movement, increasing the possibility that the subject will move during imaging.

[0018] Therefore, as described above, the magnet 10 of the embodiment is configured as a current-driven magnet (i.e., an electromagnet). The driving current applied to the magnet 10 is controlled in accordance with the movement of the subject or the position of the subject, thereby changing the spatial distribution of the magnetic field that predominantly determines the magnetic resonance frequency. As a result, it is possible to move the region from which a signal of a predetermined magnetic resonance frequency is obtained from the subject, i.e., the imaging region of the subject, in accordance with the movement of the subject or the position of the subject.

[0019] Figure 3 is a diagram showing an example of the internal configuration of magnet 10. Figure 3(a) is a diagram illustrating an internal cross section of magnet 10 as viewed from a direction perpendicular to the central axis. Also, 3(b) is a diagram illustrating an internal cross section of magnet 10 as viewed from the central axis direction, which is a cross section taken along line A-A' in Figure 3(a).

[0020] Magnet 10 is composed of one or more coil units, which are housed, for example, in a flat magnet housing having a predetermined thickness, as shown in Fig. 3. In the example shown in Fig. 3, for example, two circular coil units (coil unit 11 and coil unit 12) with different cross-sectional areas are housed in the magnet housing.

[0021] Each of the coil units 11 and 12 is configured as an electromagnet whose magnetic field strength changes depending on the magnitude of the driving current. The coil units 11 and 12 may be configured as a superconducting electromagnet or a normal electromagnet. The coil units 11 and 12 generate a magnetic field (i.e., a main magnetic field) that predominantly determines the magnetic resonance frequency.

[0022] Adjacent to the magnet housing are a gradient magnetic field coil 60 that generates a gradient magnetic field to be superimposed on the main magnetic field, and an RF coil 62 that applies an RF (Radio Frequency) pulse to the subject and receives a magnetic resonance signal (MR signal) emitted from the subject.

[0023] The gradient coil 60 includes, for example, an X-direction gradient coil, a Y-direction gradient coil, and a Z-direction gradient coil. The gradient coils in each direction are, for example, planar coils. The RF coil 62 is also, for example, planar coil.

[0024] Fig. 4 is a block diagram showing an example of the configuration of a magnetic resonance imaging apparatus 1 according to the first embodiment, which includes the magnet 10 described above. This magnetic resonance imaging apparatus 1 has two magnet units each composed of the magnet 10, the gradient magnetic field coil 60, and the RF coil 62 shown in Fig. 3. The two magnet units are arranged to face each other with a subject in between. In addition to the magnet units, the magnetic resonance imaging apparatus 1 also includes at least a detection device 20, a control circuit 30, and a magnet power supply 40. The detection device 20 detects the position of the subject to be imaged in a movable state within the magnetic field generated by the magnet 10.

[0025] The control circuit 30 calculates the current value of the drive current to be applied to the magnet 10 based on the position of the subject detected by the detection device 20. The magnet 10 illustrated in Fig. 4 has two coil units 11 and 12, and therefore calculates current values ​​(1) and (2) for the coil units 11 and 12, respectively. By controlling the current values ​​(1) and (2), it is possible to set the imaging area of ​​the subject in accordance with the movement of the subject.

[0026] The magnet power supply 40 is a power supply that generates currents (1), (2) corresponding to the current values ​​(1), (2) calculated by the control circuit 30, and applies these currents to the two coil units 11, 12 as drive currents.

[0027] Currents (1), (2) generated by magnet power supply 40 are applied to coil units (1), (2), respectively, and magnet 10 generates a magnetic field having a distribution of magnetic field strength corresponding to currents (1), (2). In the configuration example shown in Fig. 4, currents (1) and (2) are supplied to each of the two magnets 10 on the left and right sides sandwiching the subject, and the currents (1) and (2) are applied to the coil units (1) and (2) of the respective magnets 10, but the magnetic resonance imaging apparatus 1 of the embodiment is not limited to this configuration. For example, the magnetic resonance imaging apparatus 1 may be configured such that only one of the two magnets 10 on the left and right sides sandwiching the subject (for example, only the right magnet 10 in Fig. 4) is supplied with currents (1) and (2) whose current values ​​are controlled to change according to the position of the subject, and the other magnet 10 is supplied with a current whose current value is constant. Alternatively, the other magnet 10 may be configured to generate a predetermined static magnetic field in the excitation mode, and then be disconnected from the power source and operated in the persistent current mode. 4, currents (1) and (2) are applied to coil units (1) and (2), respectively, but the present invention is not limited to this configuration. For example, coil unit (1) and coil unit (2) may be connected in series or in parallel, and one current (for example, current (1)) may be applied to coil unit (1) and coil unit (2).

[0028] As shown in FIG. 4, the magnetic resonance imaging apparatus 1 of the embodiment includes a gradient magnetic field power supply 51, a transmitting / receiving circuitry 52, a sequence controller 53, an imaging condition setting circuitry 54, and a reconstruction processing circuitry 55 in addition to the above-mentioned components.

[0029] The imaging condition setting circuit 54 sets imaging conditions, such as the type of pulse sequence and the values ​​of various parameters, inputted via a user interface (not shown), in the sequence controller 53 .

[0030] The sequence controller 53 scans the subject based on the set imaging conditions by driving the gradient magnetic field power supply 51 and the transmission / reception circuit 52. The gradient magnetic field power supply 51 applies a gradient magnetic field current to the gradient magnetic field coil 60 based on a drive signal from the sequence controller 53.

[0031] The transmission / reception circuitry 52 generates an RF pulse based on a drive signal from the sequence controller 53, and applies the RF pulse to the RF coil 62. The RF coil 62 applies the RF pulse to the subject, while receiving an MR signal emitted from the subject in response to the application of the RF pulse. The MR signal received by the RF coil 62 is converted from an analog signal to a digital signal by the transmission / reception circuitry 52. ​​The MR signal converted to a digital signal is supplied to the reconstruction processing circuitry 55 as k-space data. The reconstruction processing circuitry 55 performs reconstruction processing such as inverse Fourier transform processing on the k-space data to generate a magnetic resonance image.

[0032] The imaging condition setting circuit 54, the sequence controller 53, and the reconstruction processing circuit 55 are configured with hardware such as a processor that executes a predetermined program, an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or the like.

[0033] In the magnetic resonance imaging apparatus 1 according to the first embodiment, the detection device 20 includes a camera 21 and a position detection circuit 22. The camera 21 captures an image of a subject or a marker 25 attached to a receiving surface coil attached to the subject. The position detection circuit 22 detects the position of the marker 25 from the image of the marker 25 captured by the camera 21, and further detects the imaging target position of the subject, for example, the positions of organs such as the heart and lungs, and the positions of organs such as the shoulders and knees, based on the position of the marker 25.

[0034] When detecting the position of the subject three-dimensionally along the X-axis, Y-axis, and Z-axis, one or more cameras 21 may be provided and the position of the subject may be detected from images of the marker 25 captured from one or more directions. On the other hand, when the position of the subject is limited to only one axial direction, for example, the Z-axis direction, by limiting the movement of the subject with a jig or the like, it is possible to detect the position of the subject with one camera 21.

[0035] The detection device 20 continues to operate even during imaging, and even when the subject moves within the imaging space, it continues to detect not only the positions of the imaging target before and after the movement, but also the position of the imaging target during the movement.

[0036] Based on the position of the imaging subject detected by the detection device 20, the control circuit 30 and the magnet power supply 40 control the currents (1), (2) applied to the coil units 11, 12 so that the magnetic field strength generated by the magnet 10 (in the example of Figure 4, the coil units 11, 12) becomes the desired magnetic field strength at the detected position of the imaging subject.

[0037] By having two or more coil units in magnet 10, and by independently setting the value and direction of the current applied to each coil unit, it becomes possible to form the magnetic field distribution in a shape with a high degree of freedom. However, it is also possible for magnet 10 to have only one coil unit.

[0038] The spatial distribution of the magnetic field is a three-dimensional distribution in the X, Y, and Z directions. Here, the Z direction corresponds to the central axis direction of the magnet 10, and corresponds to, for example, a direction parallel to the floor surface. The Y direction is a direction perpendicular to the central axis, and corresponds to, for example, the vertical direction. The X direction is perpendicular to both the Z and Y directions, and corresponds to, for example, the depth direction of the paper.

[0039] When the current applied to the coil units 11 and 12 is changed, the magnetic field distribution changes, and the position of the same magnetic field strength also changes.

[0040] As is well known, the magnetic resonance frequency is determined by the magnetic field strength. In order to generate a normal image, the magnetic resonance frequency of the region corresponding to the imaging target part of the subject, i.e., the imaging region, must be maintained at the same value during imaging. Meanwhile, the magnetic field strength generated by the magnet 10 does not necessarily have a uniform spatial distribution, but shows different values ​​depending on the position. For this reason, if the subject moves, for example, in the open space between the two magnets 10 during imaging, the magnetic resonance frequency of the region corresponding to the imaging target part will change according to the subject's movement, making it difficult to form a normal image.

[0041] Therefore, in the magnetic resonance imaging apparatus 1 of the embodiment, even if the subject moves during imaging, the position of the subject is successively detected by the detection device 20. Then, based on the detected position of the subject, the current applied to the coil units 11 and 12 is controlled to dynamically set the imaging region (i.e., a region where the magnetic field strength is constant, in other words, a region where the magnetic resonance frequency is constant) so as to follow the movement of the subject. There are various possible methods for determining the currents applied to the coil units 11 and 12 from the detected position of the subject.

[0042] For example, the spatial distribution of the magnetic field generated by the coil units 11 and 12 is calculated in advance for a number of different drive currents, and the magnetic field distribution associated with the drive current is stored as a database in an appropriate storage circuit of the magnetic resonance imaging apparatus 1. On the other hand, as an initial condition for imaging, a desired magnetic resonance frequency fr , or magnetic resonance frequency f r A desired magnetic field strength B0 corresponding to the above is preset.

[0043] Then, the magnetic field distribution that gives the magnetic field strength B0 at the detected position (x, y, z) of the subject is extracted from the database, and the applied current associated with the extracted magnetic field distribution can be determined as the current to be applied to coil units 11 and 12.

[0044] In this case, the position (x, y, z) of the subject may be detected as an absolute value in a predetermined device coordinate system, and the applied current may be calculated as an absolute value of the current. Here, the method of taking the device coordinate system is not particularly limited, but for example, the device coordinate system may be set to a coordinate system in which the center of gravity of the coil surface of the coil units 11 and 12 is the origin, the direction perpendicular to the coil surface (i.e., the central axis direction of the magnet 10) is the Z direction, the direction perpendicular to the Z direction and extending vertically from the floor surface is the Y direction, and the direction perpendicular to both the Z direction and the Y direction is the X direction.

[0045] Alternatively, for example, the position (x, y, z) of the subject at the start of imaging may be set as the reference position, and the value of the applied current at the start of imaging may be set as the reference current I0. Then, the amount of increase or decrease ΔI of the applied current with respect to the reference current may be calculated from the amount of movement (Δx, Δy, Δz) of the subject after the start of imaging.

[0046] Instead of using a database to calculate the current value, the current value can be calculated in real time using a predetermined formula. For example, a formula based on Biot-Savart's law can be used to calculate in real time the current value of the coil units 11 and 12 to obtain a desired magnetic field strength B0 at the position (x, y, z) of the subject.

[0047] (First Modification of the First Embodiment) FIG. 5 is a block diagram showing an example of the configuration of a magnetic resonance imaging apparatus 1 according to a first modified example of the first embodiment. The difference between the first embodiment (FIG. 4) and the first modified example lies in the configuration of a detection device 20. The detection device 20 of the first modified example includes a weight sensor 23 and a position detection circuit 22. The weight sensor 23 is installed, for example, on the floor surface, and detects the position (for example, the position of the center of gravity) of the subject. Alternatively, the weight sensor 23 may be installed, for example, on the top board 80 of a bed 81, and the position of the center of gravity of the subject may be calculated based on the height and weight of the subject. In addition to the weight sensor 23, various sensors such as an infrared sensor or a pressure sensor can also be used to detect the position of the subject.

[0048] (Second Modification of the First Embodiment) Fig. 6 is a block diagram showing an example of the configuration of a magnetic resonance imaging apparatus 1 according to a second modified example of the first embodiment. The difference from the first embodiment (Fig. 4) is in the configuration of the detection device 20, as in the first modified example. The detection device 20 of the second modified example is configured to input a magnetic resonance signal of a subject before and during imaging, and to detect the position of the subject using the input magnetic resonance signal.

[0049] The position detection circuit 22 of the second modified example may detect the position of the subject by reconstructing an image of the subject in real time using the magnetic resonance signal. Alternatively, when the position of the subject is limited to one specific direction (e.g., the Z direction), it may perform a one-dimensional Fourier transform in the specific direction on the input magnetic resonance signal in real time, and detect the position of the subject from the peak position of the signal after the Fourier transform.

[0050] Second embodiment 7 is a block diagram showing a configuration example of a magnetic resonance imaging apparatus 1 according to a second embodiment. The magnetic resonance imaging apparatus 1 of the second embodiment has a configuration in which a magnetic field sensor 70 and a magnetic field measurement / determination circuit 72 are added to the configuration of the first embodiment or each modified example thereof.

[0051] The magnetic field sensor 70 is a sensor that measures the strength of the magnetic field generated by the magnet 10, and an NMR (Nuclear Magnetic Resonance) probe, a gaussmeter, or the like can be used as the magnetic field sensor 70. The position of the magnetic field sensor 70 is not particularly limited, and it may be disposed in the magnetic field space away from the magnet housing that houses the magnet 10, or may be disposed in a position close to the magnet housing, for example, in a partial area of ​​the gradient magnetic field coil 60 or the RF coil 62, as shown in FIG.

[0052] The magnet 10 may require time to reach a desired magnetic field strength after the application of current is started. In this case, the magnetic field measurement / determination circuit 72 determines whether the magnetic field strength generated by the magnet 10 is within a predetermined range based on the magnetic field strength detected by the magnetic field sensor 70. When it is determined that the magnetic field strength is within the predetermined range, the magnetic field measurement / determination circuit 72 issues a command to the sequence controller 53 to start imaging. The sequence controller 53 automatically starts imaging based on this command. Alternatively, after it is determined that the magnetic field strength is within the predetermined range, imaging may be started by, for example, ANDing with a synchronization signal of ECG synchronization imaging. Alternatively, when it is determined that the magnetic field strength is within the predetermined range, a user such as an examiner may be notified of this fact using an appropriate display device or display device provided in the magnetic resonance imaging apparatus 1, and imaging may be started at the discretion of the user.

[0053] The magnetic field measurement / determination circuit 72 may also have a function of calibrating the magnetic field generated by the drive current. Calibration may be performed before starting imaging each time imaging is performed, or when the magnetic resonance imaging apparatus 1 is installed in a medical institution such as a hospital. 8 and 9 are diagrams for explaining the arrangement of the magnetic field sensor 70, for example, the arrangement of the magnetic field sensor 70 when performing calibration, and the estimated magnetic field strength in the imaging region.

[0054] 8 is a diagram illustrating the behavior of the magnetic field strength in a case where the coil planes of multiple coil units included in the magnet 10, for example, two coil units 11 and 12, are arranged parallel to each other and perpendicular to the central axis 90 of the magnet 10, that is, the two coil units 11 and 12 are arranged symmetrically with respect to the central axis 90. Here, the coil plane refers to a plane that includes the entire circumference of the loop-shaped conductor that constitutes each of the coil units 11 and 12. FIG. 8 also illustrates the behavior of the magnetic field strength when a variable current is applied only to the coil units 11 and 12 of one of the two magnets 10 (the magnet 10 on the right side of the page) between which the subject is sandwiched, and a constant current is applied to the coil units 11 and 12 of the other magnet 10.

[0055] In this case, the magnetic field strength changes along the direction of the central axis 90 according to the magnitude of the applied current, and the position of the imaging region corresponding to the same magnetic field strength moves along the direction of the central axis 90. In this case, the magnetic field strength of the imaging region can be estimated by one magnetic field sensor 70. Therefore, the magnetic field of the imaging region generated by the drive current can be calibrated by one magnetic field sensor 70.

[0056] 9 is a diagram illustrating the behavior of the magnetic field strength in a case where the coil surfaces of a plurality of coil units, for example, two coil units 11 and 12, are inclined relative to each other and at least one coil surface is arranged so as to be inclined relative to the central axis 90 of the magnet 10, that is, the two coil units 11 and 12 are arranged asymmetrically relative to the central axis 90. Note that Fig. 9 also illustrates the behavior of the magnetic field strength when a variable current is applied only to the coil units 11 and 12 of one magnet 10 (the magnet 10 on the right side as you face the page) of the two magnets 10 that sandwich the subject, and the current applied to the coil units 11 and 12 of the other magnet 10 is constant.

[0057] In this case, the shape of the distribution of the magnetic field strength can be changed in the X-axis, Y-axis, and Z-axis directions according to the magnitude and direction of the applied current of each coil unit, and the position of the imaging area corresponding to the same magnetic field strength can also be moved in three dimensions in the X-axis, Y-axis, and Z-axis directions. In this case, the magnetic field generated by the driving current is estimated in three dimensions by measuring the spatial distribution of the magnetic field strength using two or more magnetic field sensors 70. This makes it possible to calibrate the spatial distribution of the magnetic field strength of the imaging area generated by the driving current.

[0058] (Other embodiments) Fig. 10 is a diagram showing a structural example of the magnet 10 of the magnetic resonance imaging apparatus 1 according to another embodiment. Although the flat magnet 10 as shown in Fig. 3 and the like has been described so far, the magnet 10 of the magnetic resonance imaging apparatus 1 is not limited to a flat shape. In this case, the gradient magnetic field coil 60 and the RF coil 62 are also not limited to a flat shape.

[0059] For example, as shown in Fig. 10(a), each of the two magnets 10 may be cylindrical with one end open and the other end closed.Alternatively, as shown in Fig. 10(b), the number of magnets 10 may be one, and the magnet may be cylindrical with both end faces open, as provided in a conventional cylindrical magnetic resonance imaging device.

[0060] The diagram shown in the upper part of Fig. 10(a) is a cross section taken along line A-A' of the diagram shown in the lower part of Fig. 10(a). The magnet shown in Fig. 10(a) is configured with a plurality of coil units, for example, coil units 11, 12, and 13. In such a magnet 10, the imaging space may be a closed space 100 inside the cylinder of the magnet 10, or an open space 102 between two magnets 10.

[0061] On the other hand, the diagram shown in the upper part of Fig. 10(b) is a cross section taken along line B-B' of the diagram shown in the lower part of Fig. 10(b). The magnet shown in Fig. 10(b) is configured with a plurality of coil units, for example, coil units 11, 12, 13, and 14. In such a magnet 10, the imaging space may be a closed space 100 inside the cylinder of magnet 10, or an open space 102 away from the cylinder of magnet 10. Up to this point, the magnetic resonance imaging apparatus 1 of the embodiment has been described as having two magnets 10 sandwiching a subject, as exemplified in Figures 1, 2, and 4 to 9, but the magnetic resonance imaging apparatus 1 of the embodiment is not limited to such a configuration. For example, it is also possible to have a configuration in which only one of the two magnets 10 sandwiching a subject is included. Even with this configuration, it is possible to obtain the above-mentioned technical effects.

[0062] The detection circuit in each of the above-described embodiments is an example of a detection unit in the claims. Also, the control circuit in each of the embodiments, or a combination of the control circuit and the magnet power supply, is an example of a control unit in the claims.

[0063] According to at least one of the embodiments described above, in imaging using a planar open-type magnetic resonance imaging apparatus, even if a subject moves during imaging, an image can be generated normally.

[0064] Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0065] 1. Magnetic resonance imaging device 10. Magnets 11 Coil unit 1 12 Coil unit 2 20 Detection device 21 Camera 22 Position detection circuit 23 Weight Sensor 30 Control circuit 40 Magnet power supply 70 Magnetic Field Sensor 72 Magnetic field measurement / judgment circuit

Claims

1. A current-driven magnet (excluding a combination of a static magnetic field magnet and a shim coil) that generates a magnetic field that predominantly determines the magnetic resonance frequency; a detection unit that detects a position of a subject to be imaged in a movable state within the magnetic field; a control unit that sets an imaging area of ​​the subject in accordance with a movement of the subject by controlling a drive current of the magnet based on the detected position of the subject; A magnetic resonance imaging apparatus comprising:

2. The magnet is composed of one or more coil units, The one or more coil units are housed in a flat housing, the subject is disposed at a position away from the flat casing in a central axis direction of the magnet during imaging; 2. A magnetic resonance imaging apparatus according to claim 1.

3. The magnet is composed of one or more coil units, The one or more coil units are housed in a cylindrical housing having both end faces or one end face open, The subject is placed in a position in the internal space of the cylindrical casing or in a position away from the cylindrical casing in a central axis direction of the magnet during imaging.

2. A magnetic resonance imaging apparatus according to claim 1.

4. the one or more coil units are arranged such that a coil plane of each of the coil units is perpendicular to a central axis of the magnet; The imaging region is set to be movable along the central axis direction of the magnet.

4. A magnetic resonance imaging apparatus according to claim 2 or 3.

5. The one or more coil units are configured to include a planar coil having two or more coil surfaces; The two or more coil faces are arranged to be inclined relative to each other, The imaging region is set to be independently movable in three directions: a central axis direction of the magnet, a first direction perpendicular to the central axis direction, and a second direction perpendicular to the central axis direction and the first direction.

4. A magnetic resonance imaging apparatus according to claim 2 or 3.

6. The detection unit is configured to include a camera that detects the position of the subject or a marker attached to an RF (radio frequency) coil attached to the subject.

6. A magnetic resonance imaging apparatus according to claim 1.

7. The detection unit is configured to include a sensor that detects the position of the subject.

6. A magnetic resonance imaging apparatus according to claim 1.

8. The detection unit is configured to include a position detection circuit that detects the position of the subject based on a magnetic resonance signal emitted from the subject.

6. A magnetic resonance imaging apparatus according to claim 1.

9. the control unit sets an imaging region of the subject according to a movement of the subject based on a database in which a spatial distribution of the magnetic field and the driving current are associated with each other and which is obtained in advance before imaging the subject.

9. A magnetic resonance imaging apparatus according to claim 1.

10. the control unit calculates the driving current in real time based on a position of the imaging region to be set.

9. A magnetic resonance imaging apparatus according to claim 1.

11. at least one magnetic field sensor for measuring the strength of the magnetic field generated by said magnet; Further comprising:

11. A magnetic resonance imaging apparatus according to claim 1.

12. the control unit starts imaging the subject when the strength of the magnetic field measured by the magnetic field sensor falls within a predetermined range.

12. A magnetic resonance imaging apparatus according to claim 11.

13. The control unit calibrates the magnetic field generated by the drive current by using the strength of the magnetic field measured by the magnetic field sensor.

12. A magnetic resonance imaging apparatus according to claim 11.

Images