Static magnetic field magnet and magnetic resonance imaging apparatus

Abstract

To suppress damage to a radiation shield and reduce an evaporation amount of liquid helium in a helium container.SOLUTION: A static magnetic field magnet includes a superconducting coil and a radiation shield. The superconducting coil generates a static magnetic field. The radiation shield surrounds the superconducting coil. A surface at least on a gradient magnetic field coil side of the radiation shield includes a peripheral part for forming a plurality of recesses or concave parts so as to be provided with a plurality of recesses or concave parts linearly. The shape of an orthogonal cross section in a depth direction of the plurality of recesses or concave parts formed by the peripheral part is polygonal or circular respectively.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The embodiments disclosed in this specification and the drawings relate to static magnetic field magnets and magnetic resonance imaging apparatuses.

Background Art

[0002] A magnetic resonance imaging (MRI) apparatus excites the nuclear spins of a subject (e.g., a patient) placed in a static magnetic field generated by a static magnetic field magnet with a high-frequency (RF: Radio Frequency) signal at the Larmor frequency, and reconstructs the magnetic resonance signal (MR (Magnetic Resonance) signal) generated from the subject accompanying the excitation to generate an image.

[0003] A radiation shield is disposed between the vacuum vessel and the helium vessel of the static magnetic field magnet. By being cooled by a refrigerator, the radiation shield functions to reduce the evaporation amount of the liquid helium in the helium vessel due to radiation. Since the metal material of the radiation shield has the characteristic of high electrical conductivity, due to the large eddy current I caused by the gradient magnetic field coil and the electromagnetic force resulting from the induced heating (GCIH) by the gradient magnetic field coil caused by the operation of the gradient magnetic field coil, there is a possibility that the radiation shield may be damaged. On the other hand, even if damage does not occur, deformation may occur when the rigidity is insufficient, and the radiation shield may contact the outer vacuum vessel or the inner helium vessel. In that case, the amount of heat intrusion into the helium vessel increases, and there is a possibility that the evaporation amount of the liquid helium in the helium vessel increases.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] One of the problems that the embodiments disclosed in this specification and drawings aim to solve is to suppress damage to the radiation shield and reduce the evaporation rate of liquid helium in the helium container. However, the problems that the embodiments disclosed in this specification and drawings aim to solve 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]

[0006] One embodiment of the static magnetic field magnet includes a superconducting coil and a radiation shield. The superconducting coil generates a static magnetic field. The radiation shield surrounds the superconducting coil. At least the side of the radiation shield facing the gradient magnetic field coil has a peripheral portion that forms a plurality of depressions or recesses in a linear fashion, and the shape of the cross-sectional area perpendicular to the depth direction of the depressions or recesses formed by the peripheral portion is polygonal or circular. [Brief explanation of the drawing]

[0007] [Figure 1] A diagram showing a first configuration example of an MRI apparatus according to the first embodiment. [Figure 2] A diagram showing a second configuration example of an MRI apparatus according to the first embodiment. [Figure 3] A diagram showing an example of the internal configuration of a static magnetic field magnet provided in an MRI device according to the first embodiment. [Figure 4] A block diagram showing an example configuration of an MRI apparatus according to the first embodiment. [Figure 5] A cross-sectional view showing the configuration of a static magnetic field magnet and a gradient magnetic field coil provided in an MRI apparatus according to the first embodiment. [Figure 6] A diagram showing the side of the radiation shield on the gradient magnetic field coil side of the MRI apparatus provided according to the first embodiment. [Figure 7] A block diagram showing an example configuration of an MRI apparatus according to the second embodiment. [Figure 8] A cross-sectional view showing the configuration of a magnet base provided in an MRI apparatus according to the second embodiment. [Figure 9] A cross-sectional view showing the configuration of a radiation shield provided in an MRI apparatus according to the second embodiment. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the accompanying drawings.

[0009] MRI devices equipped with static magnetic field magnets according to the embodiment can be broadly classified into two types: open-plan and cylindrical. In an open-plan MRI device, the static magnetic field magnet and gradient magnetic field coil are in the shape of flat plates, and the device is configured to image a subject (e.g., a patient) in an open space sandwiched between, for example, two flat-plate static magnetic field magnets.

[0010] On the other hand, cylindrical MRI devices have a configuration called a magnet gantry, which forms a cylindrical space (this space is called a bore) within the gantry. Patients lying on the tabletop are brought into this cylindrical space and imaged. Inside the gantry are a cylindrical static magnetic field magnet, a cylindrical gradient magnetic field coil, and a cylindrical transmitting coil (for example, a WB (Whole Body) coil). In other words, in a cylindrical MRI device, the static magnetic field magnet, gradient magnetic field coil, and transmitting coil all have a roughly cylindrical shape.

[0011] Cylindrical MRI machines expose patients to noise for extended periods in a confined space within the bore during imaging, and require them to remain motionless. If a patient moves during imaging with a cylindrical MRI machine, artifacts can appear in the image, potentially hindering diagnosis. Furthermore, cylindrical MRI machines make it difficult to image patients in various positions, such as those with curved spines. Open-plan MRI machines can overcome these challenges associated with cylindrical machines.

[0012] In the following, the open-plan MRI apparatus according to the embodiment will be described in the first embodiment, and the cylindrical type will be described in the second embodiment.

[0013] (First embodiment) FIG. 1 is a diagram showing an arrangement example of a static magnetic field magnet 11, in particular, in a first configuration example (standing position) of a flat-open type MRI apparatus 1 according to the first embodiment. As shown in FIG. 1, the MRI apparatus 1 has, for example, two static magnetic field magnets 11 having a circular flat plate shape (that is, a substantially thin cylindrical shape).

[0014] The static magnetic field magnet 11 is arranged such that the central axis of the static magnetic field magnet 11, that is, the axis passing through the centers of the circles on both bottom surfaces of the substantially cylindrical shape, is parallel to the Y-axis. Also, the two static magnetic field magnets 11 are arranged so as to sandwich a subject (for example, patient U). Here, the left-right direction of the patient U is defined as the X-axis direction, the thickness direction of the patient U is defined as the Y-axis direction, and the head-foot direction of the patient U is defined as the Z-axis direction.

[0015] With such an arrangement of the static magnetic field magnets 11, a magnetic field is formed in the released space between the two static magnetic field magnets 11. The patient U is imaged, for example, in a standing position in this open space.

[0016] When the static magnetic field magnet 11 is constituted by a superconducting coil, a static magnetic field is generated by applying a current supplied from a static magnetic field power source to the superconducting coil in the excitation mode. Then, when shifting to the permanent current mode, the static magnetic field power source is disconnected and a magnetic field of a constant intensity is always generated. The static magnetic field magnet can also be constituted by a permanent magnet.

[0017] FIG. 2 is a diagram showing an arrangement example of the static magnetic field magnet 11, in particular, in a second configuration example (lying position) of the MRI apparatus 1. While FIG. 1 shows a configuration example for imaging a standing patient U, FIG. 2 shows a configuration example for imaging a patient U in a lying position lying on a bed top plate 32 extending from a bed body 31. This MRI apparatus 1 includes a bed 30, unlike FIG. 1.

[0018] The bed 30 includes a bed body 31 and a bed top plate 32. The bed body 31 is movable in the vertical and horizontal directions with respect to the bed top plate 32, and moves a patient U placed on the bed top plate 32 to a predetermined height before imaging. Then, at the time of imaging, the bed top plate 32 is moved horizontally to move the patient U to the imaging region.

[0019] When imaging the patient U in the lying position, as shown in FIG. 2, the static magnetic field magnet 11 is arranged such that its central axis is in the vertical direction. For example, one static magnetic field magnet 11 is arranged below the bed top plate 32, and the other static magnetic field magnet 11 is arranged above the bed top plate 32.

[0020] FIG. 3 is a diagram showing an example of the internal structure of the static magnetic field magnet 11. FIG. 3(A) is a diagram illustrating an internal cross-section viewed from a direction orthogonal to the central axis of the static magnetic field magnet 11. Further, FIG. 3(B) is a diagram illustrating an internal cross-section viewed from the central axis direction of the static magnetic field magnet 11, and is a cross-sectional view taken along the line A-A in FIG. 3(A).

[0021] The static magnetic field magnet 11 is arranged in front of the patient U and is composed of one or more superconducting coils. These one or more superconducting coils are, for example, housed in a flat magnet housing having a predetermined thickness, that is, a vacuum vessel 111 (shown in FIG. 5). In the example shown in FIG. 3, for example, two circular superconducting coils 114 and 115 having different cross-sectional areas are housed in the vacuum vessel 111. A static magnetic field that determines the magnetic resonance frequency is generated by the superconducting coils​​​​​​​Figure 4 is a block diagram showing a second configuration example of MRI apparatus 1. This MRI apparatus 1 comprises a magnet unit 10, a receiving coil 20, a control cabinet 40, and an image processing device (e.g., a console) 50. The magnet unit 10 and the receiving coil 20 are usually located in an examination room, which is a shielded room. The control cabinet 40 is located in a room called, for example, a machine room, and the console 50 is located in an operating room. Note that the second configuration example of MRI apparatus 1 (supine position) is equivalent to the first configuration example (standing position) shown in Figure 4, except for the examination table 30 (shown in Figure 2).

[0024] Each of the two magnet units 10 comprises a static magnetic field magnet 11, a gradient magnetic field coil 12, and a transmitting coil 13. The two magnet units 10 are positioned opposite each other with the patient U in between.

[0025] The static magnetic field magnet 11 incorporates superconducting coils 114 and 115, which are cooled to extremely low temperatures by liquid helium. In excitation mode, the static magnetic field magnet 11 generates a static magnetic field by applying a current supplied from a static magnetic field power source (not shown) to the superconducting coils 114 and 115. Subsequently, when it transitions to persistent current mode, the static magnetic field power source is disconnected. Once in persistent current mode, the static magnetic field magnet 11 continues to generate a static magnetic field for a long period of time, for example, more than one year.

[0026] The configuration of the static magnetic field magnet 11 will be described later using Figures 5 and 6.

[0027] The gradient magnetic field coil 12 is installed inside the static magnetic field magnet 11. The gradient magnetic field coil 12 generates a gradient magnetic field using current (power) supplied from the gradient magnetic field power supply 41, which will be described later, and applies it to the patient U. The gradient magnetic field coil 12 comprises an Xch coil that generates a gradient magnetic field in the X-axis direction, a Ych coil that generates a gradient magnetic field in the Y-axis direction, and a Zch coil that generates a gradient magnetic field in the Z-axis direction.

[0028] Here, since the eddy currents generated by the creation of the gradient magnetic field interfere with imaging, an ASGC (Actively Shielded Gradient Coil), for example, may be used as the gradient magnetic field coil 12, with the aim of reducing eddy currents. An ASGC is a gradient magnetic field coil in which a shield coil is provided outside the main coil for forming the gradient magnetic fields in the orthogonal three-axis directions, the X, Y, and Z axes, respectively, in order to suppress leakage magnetic fields.

[0029] The transmitting coil 13 is installed inside the gradient coil 12. The transmitting coil 13 transmits RF pulses toward patient U according to the RF pulse signal transmitted from the RF transmitter 42, which will be described later. When the excitation pulse transmitted from the transmitting coil 13 is applied to patient U, an MR signal is emitted from patient U in response to the application of this excitation pulse. This MR signal is received by the receiving coil 20. The receiving coil 20 is configured, for example, as a planar receiving antenna with a wide area.

[0030] The receiving coil 20 is positioned slightly away from the magnet unit 10 on the left side of the page, with the patient U in between. An imaging space (or FOV (Field of View)) is formed between the magnet unit 10 and the receiving coil 20. The receiving coil 20 may have multiple coil elements. A coil in which these multiple coil elements are arranged in an array is sometimes called a PAC (Phased Array Coil).

[0031] Next, we will move on to the explanation of the control cabinet 40. The control cabinet 40 comprises gradient magnetic field power supplies 41 (for the X axis, Y axis, and Z axis), an RF transmitter 42, an RF receiver 43, and a sequence controller 44.

[0032] The gradient power supply 41 includes a gradient power supply for each channel that drives the coils that generate gradient magnetic fields in the X-axis, Y-axis, and Z-axis directions. The gradient power supply 41 outputs the required current independently for each channel according to the command of the sequence controller 44. As a result, the gradient coils 12 can apply gradient magnetic fields (also called "gradient magnetic fields") in the X-axis, Y-axis, and Z-axis directions to the patient U.

[0033] The RF transmitter 42 generates an RF pulse signal based on instructions from the sequence controller 44. The RF transmitter 42 transmits the generated RF pulse signal to the transmitting coil 13.

[0034] The MR signal received by the receiving coil 20, or more specifically, the MR signal received by each coil element within the receiving coil 20, is transmitted to the RF receiver 43. The output line of each coil element is called a channel. For this reason, the MR signal output from each coil element is sometimes called a channel signal.

[0035] The RF receiver 43 converts the channel signal from the receiving coil 20, i.e., the MR signal, using an analog-to-digital (AD) conversion and outputs it to the sequence controller 44. The MR signal converted to digital is sometimes called raw data.

[0036] The sequence controller 44 performs imaging of patient U by driving the gradient power supply 41, the RF transmitter 42, and the RF receiver 43, respectively, under control from the console 50. When raw data is received from the RF receiver 43 during imaging, the sequence controller 44 transmits that raw data to the console 50.

[0037] Next, we will move on to the explanation of the console 50. The console 50 comprises a processing circuit 51, a memory 52, an input interface 53, and a display 54.

[0038] The processing circuit 51 refers to a processor such as a dedicated or general-purpose CPU (Central Processing Unit) or MPU (Micro Processor Unit), as well as application-specific integrated circuits (ASICs) and programmable logic devices. Examples of programmable logic devices include simple programmable logic devices (SPLDs), complex programmable logic devices (CPLDs), and field-programmable gate arrays (FPGAs). The processing circuit 51 controls the operation of the sequence controller 44 by reading and executing a program stored in the memory 52 or directly embedded within the processing circuit 51, thereby realizing the function of generating MR images by performing imaging according to the pulse sequence. Note that the processing circuit 51 is an example of a processing unit.

[0039] Furthermore, the processing circuit 51 may be composed of a single processing circuit, or it may be composed of a combination of multiple independent processing circuit elements. In the latter case, multiple memories 52 may each store a program corresponding to the function of multiple processing circuit elements, or one memory 52 may store a program corresponding to the function of multiple processing circuit elements.

[0040] Memory 52 includes semiconductor memory elements such as RAM (Random Access Memory) and flash memory, a hard disk, and an optical disc. Memory 52 may also include portable media such as USB (Universal Serial Bus) memory and DVD (Digital Video Disk). Memory 52 stores various processing programs used in the processing circuit 51 (including application programs and the OS (Operating System)), data necessary for program execution, and medical images. The OS may also include a GUI (Graphical User Interface) that makes extensive use of graphics to display information on the display 54 for the operator and allows basic operations to be performed via the input interface 53. Note that memory 52 is just one example of a storage unit.

[0041] The input interface 53 includes an input device that can be operated by the user and an input circuit that receives signals from the input device. The input device can be a trackball, a switch, a mouse, a keyboard, a touchpad that allows input by touching the operating surface, a touchscreen that integrates a display screen and a touchpad, a non-contact input device using an optical sensor, or an audio input device. When the user operates the input device, the input circuit generates a signal corresponding to that operation and outputs it to the processing circuit 51. Note that the input interface 53 is just one example of an input section.

[0042] The display 54 is composed of a general display output device such as a liquid crystal display or an OLED (Organic Light Emitting Diode) display. The display 54 displays various information according to the control of the processing circuit 51. Note that the display 54 is just one example of a display unit.

[0043] The console 50, under the control of the processing circuit 51, places the raw data transmitted from the sequence controller 44 into k-space and stores it in memory 52. ​​The console 50, under the control of the processing circuit 51, generates desired MR images of patient U by performing reconstruction processing such as inverse Fourier transform on the k-space data stored in memory 52. ​​Then, under the control of the processing circuit 51, the console 50 stores the generated MR images in memory 52.

[0044] Next, the configuration of the static magnetic field magnet 11 will be explained using Figures 5 and 6.

[0045] Figure 5 is a cross-sectional view showing the configuration of the static magnetic field magnet 11 and the gradient magnetic field coil 12. As shown in Figure 5, the static magnetic field magnet 11 is housed in a vacuum vessel 111 which has a roughly cylindrical shape in which the axis passing between the centers of the circles on both bottom surfaces is parallel to the Y-axis. The static magnetic field magnet 11 comprises a radiation shield 112, a helium container 113, superconducting coils 114, 115, and winding frames 116, 117.

[0046] The radiation shield 112, like the vacuum vessel 111, has a roughly cylindrical shape in which the axis passing between the centers of the circles on both bottom surfaces is parallel to the Y-axis, and is installed inside the vacuum vessel 111 so as to surround the helium vessel 113 (i.e., the superconducting coils 114, 115). Here, the roughly cylindrical shape includes not only a strictly cylindrical shape but also shapes that have been deformed during the manufacturing of the cylindrical radiation shield 112. For example, shapes that have been deformed include polygonal indentations, uneven surfaces, or distortions that occur on the surface of the radiation shield 112 during press working.

[0047] The helium container 113, like the vacuum container 111, has a roughly cylindrical shape with an axis passing between the centers of the circles on both bottom surfaces parallel to the Y-axis, and is housed inside the radiation shield 112 to hold liquid helium. The superconducting coils 114 and 115 are housed inside the helium container 113 to generate a static magnetic field. The reel frames 116 and 117 respectively hold the superconducting coils 114 and 115 by wiring, arranging, and fixing them. The static magnetic field magnet 11 is equipped with a refrigerator (not shown) for cooling the liquid helium to an extremely low temperature. The static magnetic field magnet 11 may also be composed of permanent magnets. The following description will focus on the case where the static magnetic field magnet 11 has the superconducting coils 114 and 115.

[0048] Here, the radiation shield 112 is placed between the vacuum vessel 111 and the helium vessel 113 and is cooled by a refrigerator (not shown), thereby reducing the amount of liquid helium evaporated from the helium vessel 113 by radiation. To give the radiation shield 112 this function, a metal material with high heat transfer performance and non-magnetic properties is generally used for the radiation shield 112. Such metal materials have the characteristic of high electrical conductivity (i.e., conductivity).

[0049] Therefore, due to induction heating (GCIH) caused by the operation of the gradient coil 12, a large eddy current I and the sum of the Lorentz forces acting radially and axially due to the eddy current I (i.e., electromagnetic force) are generated at the bottom surface 112' of the radiation shield 112. Therefore, if the strength of the radiation shield 112 is insufficient, damage to the radiation shield 112 may occur. On the other hand, even if the radiation shield 112 is not damaged, if the rigidity of the radiation shield 112 is insufficient, the radiation shield 112 may vibrate due to the electromagnetic force caused by the eddy current I, causing deformation of the radiation shield 112. Then, the deformed radiation shield 112 may come into contact with the outer vacuum vessel 111 or the inner helium vessel 113, and the amount of heat entering the helium vessel 113 may increase. In that case, the amount of evaporation of liquid helium in the helium vessel 113 may increase. Furthermore, if the rigidity of the radiation shield 112 is low, it may vibrate due to ambient influences, potentially affecting the adjustment of eddy currents and other related processes.

[0050] Therefore, the surface 112' of the roughly circular radiation shield 112 on the gradient magnetic field coil 12 side (here, the bottom surface on the gradient magnetic field coil 12 side) is provided with a peripheral portion L (shown in Figure 6) that forms a plurality of linear depressions or recesses (hereinafter simply referred to as "depressions") M, as shown in Figure 6. Here, the depressions M may be non-through holes or through holes. From the viewpoint of the radiation shielding function of the radiation shield 112, non-through holes are preferable to through holes for the depressions M. However, as will be described later, by fitting a metal material of aluminum alloy or copper alloy molded into the shape of the depressions M into the depressions M, the shielding function can be sufficiently ensured even if the depressions M are through holes. Therefore, the case where the depressions M are through holes is not excluded.

[0051] The recesses M are formed by the peripheral portion L, and the cross-sectional shape of each recess M in the depth direction is either polygonal or circular. This improves the strength and rigidity of the radiation shield 112. The radiation shield 112, which has two circular bottom surfaces and sides, can have different structures for each surface. For example, the radiation shield 112 may have a structure in which at least the bottom surface 112' on the gradient magnetic field coil 12 side has a polygonal (or circular) cross-sectional shape of the recesses M, or the entire surface of the radiation shield 112 may have a structure in which the cross-sectional shape of the recesses M is polygonal (or circular).

[0052] If the shape of the orthogonal cross-section in the depth direction is polygonal, the depression M in that orthogonal cross-section will, for example, have an approximately regular polygon (i.e., an approximately regular polygonal prism shape in a three-dimensional system). For example, in the orthogonal cross-section of the base surface 112' shown in Figure 6(A) (i.e., the XZ cross-section), the depression M of the base surface 112' will have an approximately regular hexagon (i.e., an approximately regular hexagonal prism shape in a three-dimensional system). Here, the approximately regular hexagon of the orthogonal cross-section includes not only a strictly regular hexagon (i.e., a honeycomb structure) but also shapes that have undergone deformation during the manufacturing of the radiation shield 112. For example, shapes that have undergone deformation include polygonal depressions, uneven surfaces, or distortions that occur in the peripheral part L during the press working of the radiation shield 112. Note that the orthogonal cross-section of the depression M is not limited to an approximately regular hexagon, but may also be an approximately regular square (i.e., an approximately regular square prism shape in a three-dimensional system), as shown in Figure 6(B). Furthermore, in terms of the strength and rigidity of the radiation shield 112, the orthogonal cross-section of the recess is more preferably a roughly regular hexagon than a roughly regular square.

[0053] Furthermore, if the shape of the orthogonal cross-section in the depth direction is circular (i.e., roughly cylindrical or roughly spherical in a three-dimensional system), then, similar to the case of a polygon, the radiation shield 112 will have polygonal depressions, uneven surfaces, or distortions that occur in the peripheral part L during press working.

[0054] Furthermore, the metal material of the peripheral L forming each recess M is preferably made of an aluminum alloy or copper alloy, which is a non-magnetic material with high heat transfer properties. Because aluminum alloys or copper alloys have high conductivity, they can generate eddy currents with long time constants in the radiation shield 112, and a shielding effect against leakage magnetic fields can be expected. In addition, although the recess M may be hollow, it is preferable that a metal material such as an aluminum alloy or copper alloy molded to the shape of the recess M is fitted (filled) into it. This makes it possible to maintain the radiation shield 112 in a state with high heat transfer properties and non-magnetic properties.

[0055] The MRI device 1 described in Figures 1 to 6 is a double-sided device in which static magnetic field magnets 11 are provided on both sides facing the patient U. However, the MRI device 1 is not limited to the double-sided type. For example, the MRI device 1 may be a single-sided device in which static magnetic field magnets 11 are provided on only one of the two sides facing the patient U (for example, only the static magnetic field magnet 11 in front of the patient U in Figure 4). In that case, the static magnetic field magnet 11 provided on only one side has a configuration in which at least the surface 112' of the radiation shield 112 on the gradient coil side has a plurality of recesses arranged without gaps, and the orthogonal cross-sections in the depth direction of the plurality of recesses are each polygonal.

[0056] As described above, the static magnetic field magnet 11 and the MRI device 1 can suppress damage to the radiation shield 112 by improving the strength and rigidity of the radiation shield 112, and can also reduce the amount of liquid helium evaporated. Furthermore, by improving the rigidity of the radiation shield 112, the influence on eddy current regulation can be suppressed.

[0057] (Second embodiment) Figure 7 is a block diagram showing an example configuration of a cylindrical MRI apparatus 1A according to the second embodiment. This MRI apparatus 1A comprises a magnet base 10A, a receiving coil 20, a patient table 30, a control cabinet 40, and a console 50. The magnet base 10A and the receiving coil 20 are typically placed in an examination room that serves as a shielded room. In Figure 7, components that share the same reference numerals as those shown in Figure 4 are denoted by the same numerals and their descriptions are omitted.

[0058] The magnet mount 10A comprises a static magnetic field magnet 11A, a gradient magnetic field coil 12A, and a transmitting coil (e.g., a WB (Whole Body) coil) 13A. The static magnetic field magnet 11A, gradient magnetic field coil 12A, and transmitting coil 13A have the same configuration as the static magnetic field magnet 11, gradient magnetic field coil 12, and transmitting coil 13 shown in Figure 4, except that they are roughly cylindrical in shape. A cross-sectional view of the BB of the magnet mount 10A is shown in Figure 8.

[0059] As shown in Figure 8, the magnet mount 10A comprises a static magnetic field magnet 11A, a gradient magnetic field coil 12A, and a transmitting coil 13A, from its outside. The static magnetic field magnet 11A is housed in a vacuum vessel (not shown) having a roughly cylindrical shape with its axis parallel to the Z-axis. The static magnetic field magnet 11A comprises a radiation shield 112A, a helium container (not shown), a superconducting coil (not shown), and a winding frame (not shown).

[0060] The radiation shield 112A has a generally cylindrical shape with its axis parallel to the Z-axis, similar to the vacuum vessel, and is installed inside the vacuum vessel. The side of the cylindrical radiation shield 112A facing the gradient magnetic field coil 12A (in this case, the inner circumferential surface facing the gradient magnetic field coil 12A) 112A' has a peripheral portion that forms multiple recesses so that multiple recesses can be arranged without gaps, and the shape of the orthogonal cross-section in the depth direction of the multiple recesses formed by the peripheral portion is polygonal. This improves the strength and rigidity of the radiation shield 112A. Because it is generally cylindrical, the radiation shield 112A, which has two ring-shaped bottom surfaces, an inner circumferential surface, and an outer circumferential surface, can have different structures for each surface. For example, the radiation shield 112A may have a structure in which at least the inner circumferential surface 112A' facing the gradient magnetic field coil 12 has a polygonal orthogonal cross-section of the recesses, or the entire surface of the radiation shield 112A may have a structure in which the orthogonal cross-section of the recesses is polygonal.

[0061] Furthermore, for example, in the orthogonal cross-section of the bottom surface 112A', the depression in the bottom surface 112A' has a roughly regular hexagonal shape. That is, the orthogonal cross-section in the depth direction (i.e., the radial direction of the bottom surface 112A') of the depression M in surface 112A' shown in Figure 9 is a roughly regular hexagon as shown in the lower part of Figure 6(A). Note that the orthogonal cross-section of the depression M is not limited to a roughly regular hexagon, and may be a roughly regular square as shown in Figure 6(B). Note that Figure 9 illustrates the case where the depression M is a through hole.

[0062] Furthermore, on the surface 112A' of the radiation shield, similar to the surface 112' of the radiation shield in Figure 6, it is preferable that the peripheral portion L forming each recess M is made of a metal material such as an aluminum alloy or a copper alloy, and that a metal material such as an aluminum alloy or a copper alloy formed into the recess M is fitted into the recess M.

[0063] As described above, the static magnetic field magnet 11A and MRI device 1A improve the strength and rigidity of the radiation shield 112A, thereby suppressing damage to the radiation shield 112A and reducing the amount of liquid helium evaporated. Furthermore, improving the rigidity of the radiation shield 112A also reduces the influence on eddy current regulation.

[0064] According to at least one embodiment described above, damage to the radiation shield can be suppressed, and the amount of evaporation of liquid helium in the helium container can be reduced.

[0065] While several embodiments 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 implemented in a variety of other forms, and various omissions, substitutions, modifications, and combinations of embodiments are possible 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]

[0066] 1…Open-plan MRI device 1A...Cylindrical MRI device 11,11A...Static magnetic field magnet 111...Vacuum container 112,112A…Radiation shielding 112', 112A'... The side of the radiation shield facing the gradient magnetic field coil. 113... Helium container 114,115…Superconducting coils 116,117… reel frame 12,12A…Gradient field coil 13,13A…Transmitting coil 20... Receiving coil

Claims

1. A superconducting coil that generates a static magnetic field, A radiation shield surrounding the superconducting coil, We have established At least the side of the radiation shield facing the gradient magnetic field coil is, It comprises a peripheral portion that forms multiple depressions or recesses, The plurality of recesses or depressions are arranged in at least two directions within the plane, The shape of the cross-sectional area perpendicular to the depth direction of the plurality of depressions or recesses formed by the peripheral portion is a polygon or a circle, respectively. Static magnetic field magnet.

2. The shape of the orthogonal cross-section of the plurality of depressions or recesses formed by the peripheral portion is a polygon. A static magnetic field magnet according to claim 1.

3. A superconducting coil that generates a static magnetic field, A radiation shield surrounding the superconducting coil, We have established At least the side of the radiation shield facing the gradient magnetic field coil is, It comprises a peripheral portion that forms multiple depressions or recesses, The shape of the cross-sectional area perpendicular to the depth direction of the plurality of depressions or recesses formed by the peripheral portion is generally a regular hexagon. Static magnetic field magnet.

4. The metal material of the peripheral part is made of an aluminum alloy or a copper alloy. A static magnetic field magnet according to claim 1.

5. A superconducting coil that generates a static magnetic field, A radiation shield surrounding the superconducting coil, We have established At least the side of the radiation shield facing the gradient magnetic field coil is, It comprises a peripheral portion that forms multiple depressions or recesses, The metal material of the peripheral part is made of an aluminum alloy or a copper alloy. The plurality of recesses or depressions formed by the peripheral portion are fitted with metal materials made of aluminum alloy or copper alloy that are shaped to match the form of the plurality of recesses or depressions. Static magnetic field magnet.

6. A static magnetic field magnet according to any one of claims 1 to 5, A gradient magnetic field coil that generates a gradient magnetic field, A transmitting coil that transmits high-frequency pulses, A magnetic resonance imaging apparatus equipped with a magnetic resonance imaging system.

7. The static magnetic field magnet, the gradient magnetic field coil, and the radiation shield each have a roughly cylindrical shape. At least the side of the radiation shield facing the gradient magnetic field coil is the bottom surface. The magnetic resonance imaging apparatus according to claim 6.

8. The static magnetic field magnet, the gradient magnetic field coil, and the radiation shield each have a generally cylindrical shape. At least the side of the radiation shield facing the gradient magnetic field coil is the inner surface. The magnetic resonance imaging apparatus according to claim 6.

9. The gradient magnetic field coil is Main coils for forming each of the three orthogonal gradient magnetic fields, The outer shield coil of the main coil, The magnetic resonance imaging apparatus according to claim 6, which is provided with

Images