Superconducting magnet and magnetic resonance imaging apparatus

Abstract

To reduce an eddy current generated in a radiation shield.SOLUTION: A superconducting magnet according to the embodiment is a superconducting magnet used in a magnetic resonance imaging apparatus, and includes a superconducting coil and a radiation shield. The superconducting coil is formed of a wound superconducting wire. The radiation shield is formed in a cylindrical shape having an outer cylinder portion and an inner cylinder portion, and covers the superconducting coil with the outer cylinder portion and the inner cylinder portion. In the radiation shield, the outer cylinder portion is made of a metal, and at least a part of the inner cylinder portion is made of an insulator or a high-resistance material.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] Conventionally, as a static magnetic field magnet that generates a static magnetic field in an imaging space where a subject is placed, a magnetic resonance imaging (MRI) apparatus including a superconducting magnet is known.

[0003] Generally, a superconducting magnet provided in an MRI apparatus includes a radiation shield for reducing heat intrusion into the superconducting coil in addition to a vacuum vessel and a superconducting coil.

[0004] In this way, in a configuration where the superconducting magnet provided in the MRI apparatus has a radiation shield, when the gradient magnetic field coil disposed inside the superconducting magnet is excited, eddy currents are generated in the radiation shield by the fluctuating magnetic field generated from the gradient magnetic field coil, and due to these eddy currents, the superconducting coil may generate heat or artifacts may occur in the image.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

[0006] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to reduce the eddy current generated in the radiation shield. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. The problems corresponding to the respective effects of the respective configurations shown in the embodiments described later can also be positioned as other problems. [Means for Solving the Problems]

[0007] The superconducting magnet according to the embodiment is a superconducting magnet used in a magnetic resonance imaging apparatus, and includes a superconducting coil and a radiation shield. The superconducting coil is composed of a wound superconducting wire. The radiation shield is formed in a cylindrical shape having an outer cylindrical portion and an inner cylindrical portion, and covers the superconducting coil with the outer cylindrical portion and the inner cylindrical portion. The radiation shield is configured such that the outer cylindrical portion is made of metal, and at least a part of the inner cylindrical portion is made of an insulator or a high-resistance material. [Brief Description of the Drawings]

[0008]

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[0009] Hereinafter, embodiments of the superconducting magnet and the MRI apparatus according to the present application will be described in detail with reference to the drawings.

[0010] (First Embodiment) FIG. 1 is a diagram showing an example of the configuration of an MRI apparatus according to the first embodiment.

[0011] For example, as shown in FIG. 1, the MRI apparatus 100 includes a static magnetic field magnet 1, a gradient magnetic field coil 2, a gradient magnetic field power supply 3, a whole-body radio frequency (RF) coil 4, a local RF coil 5, a transmission circuit 6, a reception circuit 7, an RF shield 8, a gantry 9, a bed 10, an input interface 11, a display 12, a memory circuit 13, and processing circuits 14 to 17.

[0012] The static magnetic field magnet 1 generates a static magnetic field in the imaging space where the subject S is placed. Specifically, the static magnetic field magnet 1 is formed in a hollow substantially cylindrical shape (including those with an elliptical cross-sectional shape perpendicular to the central axis), and generates a static magnetic field in the imaging space formed on the inner peripheral side thereof.

[0013] The gradient magnetic field coil 2 is disposed inside the static magnetic field magnet 1 and generates a gradient magnetic field in the imaging space where the subject S is placed. Specifically, the gradient magnetic field coil 2 is formed in a hollow substantially cylindrical shape (including those with an elliptical cross-sectional shape perpendicular to the central axis), and has an X coil, a Y coil, and a Z coil corresponding to the X-axis, Y-axis, and Z-axis that are perpendicular to each other. The X coil, Y coil, and Z coil generate a gradient magnetic field that linearly changes along each axial direction in the imaging space based on the current supplied from the gradient magnetic field power supply 3. Here, the Z-axis is set to be along the magnetic flux of the static magnetic field generated by the static magnetic field magnet 1. Also, the X-axis is set to be along the horizontal direction perpendicular to the Z-axis, and the Y-axis is set to be along the vertical direction perpendicular to the Z-axis. Here, the X-axis, Y-axis, and Z-axis constitute a device coordinate system unique to the MRI apparatus 100.

[0014] The gradient magnetic field power supply 3 generates a gradient magnetic field in the imaging space by supplying current to the gradient magnetic field coil 2. Specifically, the gradient magnetic field power supply 3 supplies current to the X coil, Y coil, and Z coil of the gradient magnetic field coil 2 individually, thereby generating a gradient magnetic field that linearly changes along the readout direction, phase encoding direction, and slice direction that are orthogonal to each other in the imaging space. Here, the axis along the readout direction, the axis along the phase encoding direction, and the axis along the slice direction constitute a logical coordinate system for defining the slice region or volume region to be imaged.

[0015] The gradient magnetic fields along the readout direction, phase encoding direction, and slice direction are superimposed on the static magnetic field generated by the static magnetic field magnet 1, thereby imparting spatial position information to the nuclear magnetic resonance (NMR) signal generated from the subject S. Specifically, the gradient magnetic field in the readout direction imparts the position information in the readout direction to the NMR signal by changing the frequency of the NMR signal according to the position in the readout direction. Also, the gradient magnetic field in the phase encoding direction imparts the position information in the phase encoding direction to the NMR signal by changing the phase of the NMR signal according to the position in the phase encoding direction. Also, when two-dimensional MR images (slice images) are acquired, the gradient magnetic field in the slice direction determines the position, thickness, and number of slices to be imaged by changing the frequency of the NMR signal according to the position in the slice direction. Also, when three-dimensional MR images (volume images) are acquired, the gradient magnetic field in the slice direction imparts the position information in the slice direction to the NMR signal by changing the phase of the NMR signal according to the position in the slice direction.

[0016] The whole-body RF coil 4 is arranged on the inner peripheral side of the gradient magnetic field coil 2, applies an RF pulse (excitation pulse, etc.) to the subject S arranged in the imaging space, and receives an NMR signal (echo signal, etc.) generated from the subject S under the influence of the RF pulse. Specifically, the whole-body RF coil 4 is formed in a hollow substantially cylindrical shape (including those with an elliptical cross-sectional shape orthogonal to the central axis), and based on the RF pulse signal supplied from the transmission circuit 6, applies an RF pulse to the subject S arranged in the imaging space located on its inner peripheral side. Then, the whole-body RF coil 4 receives the NMR signal generated from the subject S under the influence of the RF pulse, and outputs the received NMR signal to the reception circuit 7. For example, the whole-body RF coil 4 is a birdcage coil or a TEM (Transverse Electromagnetic) coil.

[0017] The local RF coil 5 is arranged near the subject S during imaging and receives the NMR signal generated from the subject S. Specifically, the local RF coil 5 is prepared for each part of the subject S, is arranged near the part to be imaged when imaging of the subject S is performed, receives the NMR signal generated from the subject S under the influence of the RF pulse applied by the whole-body RF coil 4, and outputs the received NMR signal to the reception circuit 7. For example, the local RF coil 5 is a surface coil or a phased array coil formed by combining a plurality of surface coils as coil elements. Note that the local RF coil 5 may further have a transmission function for applying an RF pulse to the subject.

[0018] The transmission circuit 6 outputs an RF pulse signal corresponding to the resonance frequency (Larmor frequency) specific to the target atomic nucleus placed in the static magnetic field to the whole-body RF coil 4 or the local RF coil 5. Specifically, the transmission circuit 6 includes a pulse generator, an RF generator, a modulator, and an amplifier. The pulse generator generates the waveform of the RF pulse signal. The RF generator generates an RF signal at the resonance frequency. The modulator generates an RF pulse signal by modulating the amplitude of the RF signal generated by the RF generator with the waveform generated by the pulse generator. The amplifier amplifies the RF pulse signal generated by the modulator and outputs it to the whole-body RF coil 4 or the local RF coil 5.

[0019] The reception circuit 7 generates NMR data based on the NMR signal output from the whole-body RF coil 4 or the local RF coil 5, and outputs the generated NMR data to the processing circuit 15. Specifically, the reception circuit 7 includes a selector, a pre-stage amplifier, a phase detector, and an A / D (Analog / Digital) converter. The selector selectively inputs the NMR signal output from the whole-body RF coil 4 or the local RF coil 5. The pre-stage amplifier amplifies the NMR signal output from the selector. The phase detector detects the phase of the NMR signal output from the pre-stage amplifier. The A / D converter generates NMR data by converting the analog signal output from the phase detector into a digital signal, and outputs the generated NMR data to the processing circuit 15. Here, it should be noted that not all of the processes described as being performed by the reception circuit 7 necessarily need to be performed by the reception circuit 7, and some processes (for example, the process by the A / D converter, etc.) may be performed by the whole-body RF coil 4 or the local RF coil 5.

[0020] The RF shield 8 is disposed between the gradient magnetic field coil 2 and the whole-body RF coil 4, and shields the gradient magnetic field coil 2 from the RF pulse generated by the whole-body RF coil 4. Specifically, the RF shield 8 is formed in a hollow substantially cylindrical shape (including those having an elliptical shape in the cross-section perpendicular to the central axis of the cylinder), and is disposed in the space on the inner peripheral side of the gradient magnetic field coil 2 so as to cover the outer peripheral surface of the whole-body RF coil 4.

[0021] The gantry 9 has a hollow bore 9a formed in a substantially cylindrical shape (including those with an elliptical cross-sectional shape perpendicular to the central axis), and houses the static magnetic field magnet 1, the gradient magnetic field coil 2, the whole-body RF coil 4, and the RF shield 8. Specifically, the gantry 9 arranges the whole-body RF coil 4 on the outer peripheral side of the bore 9a, arranges the RF shield 8 on the outer peripheral side of the whole-body RF coil 4, arranges the gradient magnetic field coil 2 on the outer peripheral side of the RF shield 8, and arranges the static magnetic field magnet 1 on the outer peripheral side of the gradient magnetic field coil 2, and houses each of them in this state. Here, the space inside the bore 9a of the gantry 9 becomes the imaging space where the subject S is placed during imaging.

[0022] The bed 10 includes a top plate 10a on which the subject S is placed, and when imaging of the subject S is performed, the top plate 10a on which the subject S is placed is moved into the imaging space. For example, the bed 10 is installed such that the longitudinal direction of the top plate 10a is parallel to the central axis of the static magnetic field magnet 1.

[0023] The input interface 11 receives various instructions and input operations of various information from the operator. Specifically, the input interface 11 is connected to the processing circuit 17, converts the input operation received from the operator into an electrical signal, and outputs it to the processing circuit 17. For example, the input interface 11 is realized by a trackball, a switch button, a mouse, a keyboard, a touch pad for performing an input operation by touching an operation surface, a touch screen in which a display screen and a touch pad are integrated, a non-contact input circuit using an optical sensor, and an audio input circuit for setting imaging conditions and a region of interest (ROI). In this specification, the input interface 11 is not limited to only those having physical operation components such as a mouse and a keyboard. For example, an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the apparatus and outputs this electrical signal to the control circuit is also included in the example of the input interface 11.

[0024] The display 12 displays various types of information. Specifically, the display 12 is connected to the processing circuit 17, and converts the data of various types of information sent from the processing circuit 17 into an electrical signal for display and outputs it. For example, the display 12 is realized by a liquid crystal monitor, a CRT (Cathode Ray Tube) monitor, a touch panel, or the like.

[0025] The memory circuit 13 stores various types of data. Specifically, the memory circuit 13 is connected to the processing circuits 14 to 17, and stores various types of data input and output by each processing circuit. For example, the memory circuit 13 is realized by a semiconductor memory element such as a RAM (Random Access Memory) or a flash memory, a hard disk, an optical disk, or the like.

[0026] The processing circuit 14 has a bed control function 14a. The bed control function 14a controls the operation of the bed 10 by outputting a control electrical signal to the bed 10. For example, the bed control function 14a receives, via the input interface 11, an instruction from the operator to move the top plate 10a in the longitudinal direction, the vertical direction, or the left - right direction, and operates the moving mechanism of the top plate 10a of the bed 10 so as to move the top plate 10a according to the received instruction.

[0027] The processing circuit 15 has a collection function 15a. The collection function 15a collects NMR data of the subject S by executing various pulse sequences. Specifically, the collection function 15a drives the gradient magnetic field power supply 3, the transmission circuit 6, and the reception circuit 7 according to the sequence execution data output from the processing circuit 17 to execute various pulse sequences. Here, the sequence execution data is data representing a pulse sequence, and includes information specifying the timing at which the gradient magnetic field power supply 3 supplies current to the gradient magnetic field coil 2 and the strength of the supplied current, the timing at which the transmission circuit 6 supplies an RF pulse signal to the whole-body RF coil 4 and the strength of the supplied RF pulse signal, the timing at which the reception circuit 7 samples the NMR signal, etc. Then, the collection function 15a receives the NMR data output from the reception circuit 7 as a result of executing the pulse sequence and stores it in the storage circuit 13. At this time, the NMR data stored in the storage circuit 13 is stored as k-space data representing a two-dimensional or three-dimensional k-space by being given position information along the lead-out direction, the phase encoding direction, and the slice direction by the above-described respective gradient magnetic fields.

[0028] The processing circuit 16 has a generation function 16a. The generation function 16a generates an MR image from the NMR data collected by the collection function 15a of the processing circuit 15. Specifically, the generation function 16a reads out the NMR data collected by the collection function 15a of the processing circuit 15 from the storage circuit 13 under the control of the processing circuit 17, and performs reconstruction processing such as Fourier transform on the read-out NMR data to generate a two-dimensional or three-dimensional MR image. Then, the generation function 16a stores the generated MR image in the storage circuit 13.

[0029] The processing circuit 17 has an imaging control function 17a. The imaging control function 17a performs overall control of the MRI apparatus 100 by controlling each component of the MRI apparatus 100. Specifically, the imaging control function 17a displays a GUI (Graphical User Interface) for receiving input operations of various instructions and various information from the operator on the display 12, and controls each component of the MRI apparatus 100 according to the input operation received via the input interface 11. For example, the imaging control function 17a receives an input of imaging conditions from the operator, and sets a pulse sequence for collecting NMR data of the subject S based on the input imaging conditions. Then, the imaging control function 17a generates sequence execution data representing the set pulse sequence and outputs it to the processing circuit 15, thereby causing the collection function 15a of the processing circuit 15 to execute various pulse sequences. Also, for example, the imaging control function 17a controls the generation function 16a of the processing circuit 16 to cause the processing circuit 15 to reconstruct an MR image from the k-space data collected by the processing circuit 15. Also, for example, the imaging control function 17a reads out the MR image stored in the memory circuit 13 according to a request from the operator, and causes the read MR image to be displayed on the display 12.

[0030] Here, the above-described processing circuits 14 to 17 are realized by, for example, processors respectively. In this case, the processing functions of each processing circuit are stored in the memory circuit 13 in the form of a program executable by a computer, for example. Then, each processing circuit reads out and executes each program from the memory circuit 13 to realize the processing function corresponding to each program. In other words, each processing circuit has each processing function shown in FIG. 1 in a state where each program is read out.

[0031] Here, it is assumed that the processing circuits 14 to 17 are each realized by a single processor, but the embodiment is not limited to this. For example, each processing circuit may be configured by combining a plurality of independent processors, and each processor may execute a program to realize each processing function. Further, the processing functions of each processing circuit may be appropriately distributed or integrated into a single or a plurality of processing circuits for realization. Further, in the above description, it is assumed that a single storage circuit 13 stores programs corresponding to each processing function, but the embodiment is not limited to this. For example, a plurality of storage circuits may be distributed and arranged for each processing circuit, and each processing circuit may read a corresponding program from an individual storage circuit.

[0032] As described above, the configuration example of the MRI apparatus 100 according to the present embodiment has been described. Under such a configuration, the MRI apparatus 100 according to the present embodiment includes a superconducting magnet as a static magnetic field magnet 1 that generates a static magnetic field in an imaging space where the subject S is placed.

[0033] Generally, a superconducting magnet provided in an MRI apparatus includes a radiation shield for reducing heat intrusion into the superconducting coil in addition to a vacuum vessel and the superconducting coil.

[0034] FIG. 2 is a diagram showing a superconducting magnet 900 according to a comparative example of the first embodiment.

[0035] For example, as shown in FIG. 1, the superconducting magnet 900 provided in the MRI apparatus includes a vacuum vessel 910, a superconducting coil 920, and a radiation shield 930.

[0036] The vacuum vessel 910 is a cylindrically formed vessel that hermetically insulates the superconducting coil 920 from the outside by housing the superconducting coil 920 inside.

[0037] The superconducting coil 920 is composed of a superconducting wire wound around the axis of the superconducting magnet 900, and generates a static magnetic field when energized in a superconducting state.

[0038] The radiation shield 930 is formed in a hollow cylindrical shape having an outer cylindrical portion 931 and an inner cylindrical portion 932, is disposed between the vacuum vessel 910 and the superconducting coil 920, and covers the superconducting coil 920 with the outer cylindrical portion 931 and the inner cylindrical portion 932.

[0039] Specifically, the radiation shield 930 has an outer cylindrical portion 931, an inner cylindrical portion 932, and two annular side plate portions 933 that close both ends of the outer cylindrical portion 931 and the inner cylindrical portion 932, and accommodates the superconducting coil 920 between the outer cylindrical portion 931 and the inner cylindrical portion 932.

[0040] For example, the entire radiation shield 930 including the outer cylindrical portion 931, the inner cylindrical portion 932, and the side plate portion 933 is made of a metal such as aluminum or copper, and by maintaining the intermediate temperature (20 to 77K), heat intrusion from the vacuum vessel at room temperature to the superconducting coil is reduced.

[0041] In this way, in a configuration where the superconducting magnet provided in the MRI apparatus has a radiation shield, when the gradient magnetic field coil disposed inside the superconducting magnet is excited, eddy currents are generated in the radiation shield by the fluctuating magnetic field generated from the gradient magnetic field coil, and due to these eddy currents, the superconducting coil may generate heat or artifacts may occur in the image.

[0042] Specifically, when eddy currents are generated in the radiation shield, a vibration force acts due to the interaction with the static magnetic field generated by the superconducting coil, causing the radiation shield to vibrate. This vibration makes the radiation shield a heat source, and thus the superconducting coil may generate heat. Also, when the radiation shield is made of a metal with a low electrical resistivity such as aluminum or copper, the eddy currents may remain for a long time, and artifacts may occur in the image due to the magnetic field generated by the eddy currents.

[0043] Therefore, in the MRI apparatus 100 according to the present embodiment, the superconducting magnet provided as the static magnetic field magnet 1 is configured to be able to reduce the eddy currents generated in the radiation shield.

[0044] FIG. 3 is a diagram showing an example of the superconducting magnet 200 according to the first embodiment.

[0045] For example, as shown in FIG. 3, the superconducting magnet 200 according to the present embodiment includes a vacuum vessel 210, a superconducting coil 220, and a radiation shield 230.

[0046] The vacuum vessel 210 is a cylindrically formed vessel that vacuum-insulates the superconducting coil 220 from the outside by housing the superconducting coil 220 therein.

[0047] The superconducting coil 220 is composed of superconducting wire wound around the axis of the superconducting magnet 200, and generates a static magnetic field when energized in a superconducting state.

[0048] The radiation shield 230 is formed in a hollow cylindrical shape having an outer cylinder portion 231 and an inner cylinder portion 232, is disposed between the vacuum vessel 210 and the superconducting coil 220, and covers the superconducting coil 220 with the outer cylinder portion 231 and the inner cylinder portion 232.

[0049] Specifically, the radiation shield 230 has an outer cylinder portion 231, an inner cylinder portion 232, and two annular side plate portions 233 that close both ends of the outer cylinder portion 231 and the inner cylinder portion 232, and houses the superconducting coil 220 between the outer cylinder portion 231 and the inner cylinder portion 232.

[0050] And in the present embodiment, the outer cylinder portion 231 and the side plate portions 233 of the radiation shield 230 are made of a metal such as aluminum or copper, and by being maintained at an intermediate temperature (20 to 77K), heat intrusion from the room-temperature vacuum vessel to the superconducting coil is reduced. For example, the outer cylinder portion 231 and the side plate portions 233 are made of pure aluminum (A1050, A1070, etc.), oxygen-free copper (C1020), etc.

[0051] In addition, in the present embodiment, at least a part of the inner cylinder portion 232 of the radiation shield 230 is made of fiber reinforced plastics (FRP). Here, FRP is an example of an insulator or a high-resistance material. For example, the inner cylinder portion 232 is made of glass fiber reinforced plastics (GFRP), carbon fiber reinforced plastics (CFRP), or the like.

[0052] Thus, the radiation shield 230 according to the present embodiment is not entirely made of metal like the radiation shield 930 according to the comparative example shown in FIG. 2. Instead, while the outer cylinder portion 231 and the side plate portion 233 are made of metal, at least a part of the inner cylinder portion 232 is made of FRP.

[0053] Normally, in a configuration where an inclined magnetic field coil is disposed inside a superconducting magnet as in the present embodiment, the inner cylinder portion is dominant in the location where eddy currents are generated in the radiation shield. Therefore, by configuring at least a part of the inner cylinder portion 232 of the radiation shield 230 according to the present embodiment with FRP, it becomes possible to significantly reduce the eddy currents generated in the radiation shield 230.

[0054] Therefore, according to the first embodiment, it is possible to reduce the generation of eddy currents in the radiation shield 230 while maintaining the cooling performance, which is the role of the radiation shield 230. In addition, by reducing the generation of eddy currents in the radiation shield 230, it is possible to suppress the vibration and magnetic field of the radiation shield 230 caused by the eddy currents, and reduce the heat generation of the superconducting coil and the artifacts generated in the image.

[0055] As described above, the first embodiment has been explained. However, in the superconducting magnet 200 described above, since the radiation shield 230 is disposed in an extremely narrow space, there are shape constraints, and a design considering the assembly procedure is required.

[0056] FIGS. 4 to 6 are diagrams showing the constraints regarding the radiation shield 230 according to the first embodiment.

[0057] For example, as shown in FIG. 4, since the radiation shield 230 generally has a thickness of about several millimeters, it is difficult to secure a joint surface 934 with a sufficient area between the inner cylinder portion 232 and the side plate portion 233. Also, as shown in FIG. 4, when fastening the inner cylinder portion 232 and the side plate portion 233 with bolts 935, it is necessary to provide threaded holes near the end of the inner cylinder portion 232. However, if such holes are drilled in the FRP, the ends may crack.

[0058] In addition, in the superconducting magnet 200 provided in the MRI apparatus 100, in order to increase the bore diameter and shorten the bore length, it is required that the radiation shield 230 has no unnecessary irregularities. However, for example, as shown in FIG. 5, when a fastening portion 936 is provided at the end of the inner cylinder portion 232 and the inner cylinder portion 232 and the side plate portion 233 are fastened via the fastening portion 936, the inner cylinder portion 232 has a shape protruding in the axial direction.

[0059] Also, for example, as shown in FIG. 6, when ribs 937 for fastening to the side plate portion 233 are integrally provided at the end of the inner cylinder portion 232, the ribs 937 may interfere with the superconducting coil 220 and it may become impossible to assemble.

[0060] Therefore, hereinafter, examples of the radiation shield 230 considering such constraints related to the shape and the assembly procedure will be described as the second to eighth embodiments. In the following embodiments, the description will focus on the points different from the above-described first embodiment, and detailed description of the content common to the previously described embodiment will be omitted.

[0061] (Second Embodiment) FIG. 7 is a diagram showing an example of the radiation shield 230 according to the second embodiment.

[0062] For example, as shown in FIG. 7, in the present embodiment, the radiation shield 230 further has two annular coupling rings 240 disposed at both ends of the inner cylindrical portion 232, and the inner cylindrical portion 232 is fixed to the side plate portion 233 via the coupling rings 240.

[0063] Here, in the present embodiment, the coupling ring 240 is made of metal. For example, the coupling ring 240 is made of any of aluminum alloy, stainless steel, and copper. For example, the coupling ring 240 is made of an aluminum alloy (such as A5083), stainless steel (such as SUS304, SUS316), etc.

[0064] According to such a configuration, a bonding surface 251 with a sufficient area can be ensured between the coupling ring 240 and the inner cylindrical portion 232. Further, by making the coupling ring 240 made of metal, a screw hole can be provided near the end of the coupling ring 240.

[0065] For example, in the present embodiment, the coupling ring 240 and the inner cylindrical portion 232 are adhered to each other at the bonding surface 251. Note that the method of fixing the coupling ring 240 and the inner cylindrical portion 232 is not limited to adhesion, and for example, they may be fixed by press-fitting or shrink fitting.

[0066] Also, in the present embodiment, the coupling ring 240 and the side plate portion 233 are fixed by bolt fastening using bolts 252 or welding 253 at the end of the coupling ring 240. Note that the method of fixing the coupling ring 240 and the side plate portion 233 is not limited to bolt fastening or welding, and for example, they may be fixed by adhesion using an adhesive such as an epoxy resin or rivet fastening using rivets.

[0067] (Third Embodiment) FIGS. 8 and 9 are diagrams showing an example of the radiation shield 230 according to the third embodiment.

[0068] For example, as shown in FIGS. 8 and 9, in the present embodiment, the coupling ring 240 and the inner cylinder portion 232 are each formed in a stepped shape having a radial step, and the stepped portion 254 of the coupling ring 240 and the stepped portion 255 of the inner cylinder portion 232 are fitted together so that no step is formed at the joint portion and they are fixed.

[0069] Here, FIG. 8 shows an example of the case where the stepped shape of the inner cylinder portion 232 is formed by cutting the inside of the inner cylinder portion 232. In this case, the coupling ring 240 is formed in a shape in which the inner side protrudes toward the inner cylinder portion 232 so as to fit into the cut portion inside the inner cylinder portion 232.

[0070] Further, FIG. 9 shows an example of the case where the stepped shape of the inner cylinder portion 232 is formed by cutting the outside of the inner cylinder portion 232. In this case, the coupling ring 240 is formed in a shape in which the outer side protrudes toward the inner cylinder portion 232 so as to fit into the cut portion outside the inner cylinder portion 232.

[0071] According to such a configuration, an increase in the thickness at the joint portion between the coupling ring 240 and the inner cylinder portion 232 can be suppressed.

[0072] (Fourth Embodiment) FIG. 10 is a diagram showing an example of the radiation shield 230 according to the fourth embodiment.

[0073] For example, as shown in FIG. 10, in the present embodiment, the coupling ring 240 has an annular rib 256 protruding outward in the radial direction at the end, and the rib 256 and the side plate portion 233 are fixed by bolt fastening using bolts 252. Note that the method of fixing the rib 256 of the coupling ring 240 and the side plate portion 233 is not limited to bolt fastening, and for example, they may be fixed by adhesion using an adhesive such as epoxy resin, welding, or rivet fastening using rivets.

[0074] According to such a configuration, by providing the rib 256 on the coupling ring 240, even when the thickness of the side plate portion 233 is thin, the coupling ring 240 and the side plate portion 233 can be easily fixed by adhesion, welding, bolt fastening, rivet fastening, or the like.

[0075] (The fifth embodiment) FIG. 11 is a diagram showing an example of the radiation shield 230 according to the fifth embodiment.

[0076] For example, as shown in FIG. 11, in the present embodiment, similar to the fourth embodiment, the coupling ring 240 has an annular rib 256 protruding radially outward at its end, and the rib 256 and the side plate portion 233 are fixed by any one of adhesion, bolt fastening, and rivet fastening.

[0077] And in the present embodiment, the coupling ring 240 and the rib 256 are made of FRP.

[0078] According to such a configuration, a part of the side surface of the radiation shield 230 is formed by the FRP rib 256, and the eddy current generated by the fluctuating magnetic field M reaching from the side plate portion 233 side can be reduced.

[0079] (The sixth embodiment) FIG. 12 is a diagram showing an example of the radiation shield 230 according to the sixth embodiment.

[0080] For example, as shown in FIG. 12, in the present embodiment, the side plate portion 233 is omitted, and the inner cylinder portion 232 of the radiation shield 230 is fixed to the outer cylinder portion 231 via the coupling ring 240.

[0081] Here, in the present embodiment, the coupling ring 240 has, at its end, an annular rib 257 that protrudes radially outward and extends to the outer cylinder portion 231, and the rib 257 and the outer cylinder portion 231 are fixed by bolt fastening using bolts 252. Note that the method of fixing the rib 257 of the coupling ring 240 and the outer cylinder portion 231 is not limited to bolt fastening, and for example, they may be fixed by adhesion using an adhesive such as epoxy resin or by rivet fastening using rivets.

[0082] And, in the present embodiment, the coupling ring 240 and the rib 257 are made of FRP.

[0083] According to such a configuration, the entire side surface of the radiation shield 230 is composed of the FRP rib 257, and the eddy current generated by the fluctuating magnetic field M reaching from the side plate portion 233 side can be further reduced.

[0084] (Seventh Embodiment) FIGS. 13 and 14 are diagrams showing an example of the radiation shield 230 according to the seventh embodiment.

[0085] For example, as shown in FIGS. 13 and 14, in the present embodiment, a plurality of strip-shaped metal thin plates 258 are attached in parallel to the axial direction of the inner cylinder portion 232 to the portion of the inner cylinder portion 232 made of FRP. For example, the metal thin plate 258 is made of high-purity aluminum foil.

[0086] Here, the plurality of metal thin plates 258 are arranged at intervals in the circumferential direction of the inner cylinder portion 232 so that eddy currents are interrupted and are not connected to the coupling ring 240 and the side plate portion 233 made of metal. Also, as shown in FIG. 13, the plurality of metal thin plates 258 may be attached to the inner peripheral surface of the inner cylinder portion 232, or as shown in FIG. 14, they may be attached to the outer peripheral surface of the inner cylinder portion 232.

[0087] According to such a configuration, by attaching the metal thin plate 258 to the inner cylinder portion 232 made of FRP, the cooling performance of the radiation shield 230 can be improved.

[0088] (Eighth Embodiment) FIGS. 15 and 16 are diagrams showing an example of the radiation shield 230 according to the eighth embodiment.

[0089] For example, as shown in FIGS. 15 and 16, in the present embodiment, similar to the fifth embodiment, the coupling ring 240 has an annular rib 256 protruding radially outward at its end, and the coupling ring 240 and the rib 256 are made of FRP.

[0090] And in the present embodiment, a plurality of strip-shaped metal thin plates 259 are attached to the surface of the rib 256 of the coupling ring 240 so as to extend in the radial direction of the rib 256. For example, the metal thin plate 259 is made of high-purity aluminum foil.

[0091] Here, the plurality of metal thin plates 259 are arranged so as to be spaced apart from each other in the circumferential direction of the rib 256 and not to be connected to the side plate portion 233 made of metal so that eddy currents are interrupted. Note that the plurality of metal thin plates 259 may be attached to the outer surface of the rib 256 or the inner surface of the rib 256 as shown in FIG. 15.

[0092] According to such a configuration, by attaching the metal thin plate 259 to the rib 256 of the coupling ring 240 made of FRP, the cooling performance of the radiation shield 230 can be improved.

[0093] According to the second to eighth embodiments described above, by using the coupling ring 240, the inner cylinder portion 232 made of FRP and the outer cylinder portion 231 or the side plate portion 233 made of metal can be coupled with each other in a minimum space.

[0094] Further, according to the second to eighth embodiments described above, since the coupling ring 240 and the inner cylinder portion 232 have a separated structure, they do not interfere with the superconducting coil 220 during assembly.

[0095] Further, according to the above-described seventh and eighth embodiments, the outer cylinder portion 231 made of metal and the inner cylinder portion 232 made of FRP or the metal thin plates 258 or 259 attached to the coupling ring 240 can uniformly cool the radiation shield 230 and maintain the original function as the radiation shield.

[0096] Note that the superconducting magnet 200 according to the above-described embodiment is a so-called high-temperature superconducting magnet in which the radiation shield 230 is maintained at an intermediate temperature (20 to 77K). Since the high-temperature superconducting magnet can maintain the superconducting state at a higher temperature compared to a superconducting magnet using liquid helium, even the radiation shield 230 with the inner cylinder portion 232 made of FRP as in the above-described embodiment can maintain sufficient coolability.

[0097] On the other hand, the above-described radiation shield 230 is not limited to high-temperature superconducting magnets and can maintain coolability even when applied to low-temperature superconducting magnets using liquid helium. In particular, the radiation shield 230 described in the seventh and eighth embodiments can uniformly cool the radiation shield 230 by the outer cylinder portion 231 and the metal thin plates 258 or 259 attached to the inner cylinder portion 232 or the coupling ring 240, so that sufficient coolability can be maintained even in low-temperature superconducting magnets.

[0098] Also, in the above-described embodiment, an example in which at least a part of the inner cylinder portion 232 of the radiation shield 230 is made of FRP has been described, but the embodiment is not limited thereto. For example, at least a part of the inner cylinder portion 232 of the radiation shield 230 may be made of an insulator or a high-resistance material other than FRP.

[0099] Note that in this specification, the high-resistance material means a material having a resistivity of 20 times or more the resistivity of stainless steel (SUS304) (about 6 × 10 -7 [Ωm]). For example, an example of the high-resistance material in this specification is the aforementioned CFRP. CFRP has the property that its resistivity changes depending on the fiber direction, and the direction in which the resistivity is the smallest is 1 × 10 -5[Ωm], and the direction with the highest resistivity is 1×10 -1 [Ωm]. Normally, eddy currents flow in a loop, but in CFRP, due to such anisotropy of resistivity, compared to a homogeneous material with a resistivity of about 1×10 -5 [Ωm], it has the characteristic that eddy currents are much less likely to occur. Therefore, when at least a part of the inner cylinder portion 232 of the radiation shield 230 is made of CFRP, the eddy currents generated in the radiation shield can be more effectively reduced.

[0100] Also, in the above description, an example where the "processor" reads and executes a program corresponding to each processing function from the storage circuit has been described, but the embodiment is not limited to this. The term "processor" means, for example, a circuit such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an application specific integrated circuit (ASIC), a programmable logic device (for example, a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA)). When the processor is, for example, a CPU, the processor realizes each processing function by reading and executing a program stored in the storage circuit. On the other hand, when the processor is an ASIC, instead of storing a program in the storage circuit, the processing function is directly incorporated as a logic circuit in the circuit of the processor. Each processor of the present embodiment is not limited to being configured as a single circuit for each processor, and may be configured as one processor by combining a plurality of independent circuits to realize its processing function. Further, a plurality of components in FIG. 1 may be integrated into one processor to realize its processing function.

[0101] Here, the program executed by the processor is provided by being pre-installed in a ROM (Read Only Memory), a storage circuit, or the like. This program may be provided by being recorded on a computer-readable storage medium such as a CD (Compact Disk)-ROM, an FD (Flexible Disk), a CD-R (Recordable), or a DVD (Digital Versatile Disk) in a file in a form installable or executable on these devices. Further, this program may be stored on a computer connected to a network such as the Internet and provided or distributed by being downloaded via the network. For example, this program is composed of modules including the above-described respective functional units. As actual hardware, the CPU reads the program from a storage medium such as a ROM and executes it, whereby each module is loaded onto the main storage device and generated on the main storage device.

[0102] Also, in the above-described embodiments, each component of each illustrated device is functionally conceptual and does not necessarily have to be physically configured as illustrated. That is, the specific form of the dispersion or integration of each device is not limited to that illustrated, and all or a part of it can be functionally or physically dispersed or integrated in any unit according to various loads, usage situations, and the like. Further, each processing function performed by each device can be realized in whole or in any part by a CPU and a program analyzed and executed by the CPU, or can be realized as hardware by wired logic.

[0103] Also, among the respective processes described in the above-described embodiments, all or a part of the processes described as being automatically performed can be manually performed, or all or a part of the processes described as being manually performed can be automatically performed by a known method. In addition, regarding the processing procedures, control procedures, specific names, and information including various data and parameters shown in the above document and drawings, they can be arbitrarily changed unless otherwise specified.

[0104] According to at least one embodiment described above, eddy currents generated in the radiation shield can be reduced.

[0105] Although several embodiments have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations of embodiments can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, as well as in the invention described in the claims and the equivalent scope thereof.

Description of Reference Numerals

[0106] 100 Magnetic Resonance Imaging (MRI) apparatus 200 Superconducting magnet 220 Superconducting coil 230 Radiation shield 231 Outer cylinder part 232 Inner cylinder part 233 Side plate part 240 Coupling ring 256, 257 Rib 258, 259 Thin metal plate

Claims

1. A superconducting magnet used in a magnetic resonance imaging apparatus, comprising a superconducting coil formed of wound superconducting wire, and a radiation shield formed in a cylindrical shape having an outer cylinder portion and an inner cylinder portion, the superconducting coil being covered by the outer cylinder portion and the inner cylinder portion, wherein the radiation shield has the outer cylinder portion made of metal and at least a part of the inner cylinder portion made of an insulator or a high-resistance material. Superconducting magnet.

2. The radiation shield further has an annular coupling ring disposed at both ends of the inner cylinder portion, and the inner cylinder portion is an annular side plate portion that closes both ends of the outer cylinder portion and the inner cylinder portion via the coupling ring or is fixed to the outer cylinder portion. The superconducting magnet according to claim 1.

3. The coupling ring and the inner cylinder portion are fixed by any one of adhesion, press-fitting, and shrink fitting. The superconducting magnet according to claim 2.

4. The coupling ring and the side plate portion are fixed by any one of adhesion, welding, bolt fastening, and rivet fastening. The superconducting magnet according to claim 2.

5. The coupling ring and the inner cylinder portion are each formed in a stepped shape having a radial step at each end, and the stepped portion of the coupling ring and the stepped portion of the inner cylinder portion are fitted to each other so that no step is generated at the joint portion. The superconducting magnet according to claim 2.

6. The coupling ring has an annular rib at the end, and the rib and the side plate portion are fixed by any one of adhesion, welding, bolt fastening, and rivet fastening. The superconducting magnet according to any one of claims 2 to 5.

7. The coupling ring has an annular rib at the end, and the rib and the outer cylinder portion are fixed by any one of adhesion, welding, bolt fastening, and rivet fastening. The superconducting magnet according to any one of claims 2, 3, and 5.

8. The coupling ring is made of any one of aluminum alloy, stainless steel, and copper. The superconducting magnet according to any one of claims 2 to 5.

9. The coupling ring and the rib are made of fiber-reinforced plastic. The superconducting magnet according to claim 6.

10. The coupling ring and the rib are made of fiber-reinforced plastic. The superconducting magnet according to claim 7.

11. A plurality of strip-shaped metal thin plates are attached to the surface of the rib of the bonding ring so as to extend in the radial direction of the rib. The superconducting magnet according to claim 9.

12. A plurality of strip-shaped metal thin plates are attached to the portion of the inner cylinder made of the insulator or high-resistance material in parallel with the axial direction of the inner cylinder. The superconducting magnet according to any one of claims 2 to 5.

13. A magnetic resonance imaging apparatus comprising the superconducting magnet according to any one of claims 1 to 5 as a static magnetic field magnet that generates a static magnetic field in an imaging space where a subject is disposed.

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