Static magnetic field magnet and magnetic resonance imaging apparatus
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- CANON KK
- Filing Date
- 2022-09-05
- Publication Date
- 2026-08-03
Smart Images
Figure 0007899015000001 
Figure 0007899015000002 
Figure 0007899015000003
Abstract
Description
Technical Field
[0001] The embodiments disclosed in this specification and the drawings relate to a static magnetic field magnet and a magnetic resonance imaging apparatus.
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 a magnetic resonance signal (MR (Magnetic Resonance) signal) generated from the subject upon excitation to generate an image.
[0003] The static magnetic field magnet includes a vacuum vessel, a radiation shield, a helium vessel, a superconducting coil, and a winding frame. The winding frame that supports the superconducting coil of the static magnetic field magnet also serves as the helium vessel. Therefore, there is only about several millimeters between the outer frame of the helium vessel and the superconducting coil, and heat due to eddy currents caused by the induced heating (GCIH) of the gradient magnetic field coil directly propagates to the superconducting coil, making quenching likely to occur.
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 to be solved by the embodiments disclosed in this specification and the drawings is to suppress heat generation in the superconducting coil. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. It is also possible to identify the problems corresponding to the respective effects of the respective configurations shown in the following embodiments as other problems. [Means for solving the problem]
[0006] One embodiment of the static magnetic field magnet includes a vacuum vessel, a radiation shield, a superconducting coil, and a winding frame. The radiation shield is provided inside the vacuum vessel. The superconducting coil is provided inside the radiation shield and generates a static magnetic field. The winding frame holds the superconducting coil. The winding frame is provided with a heat-suppressing shield section having a skin portion and a dermis portion that are structurally or functionally separated. The skin portion is the part through which eddy currents generated in the winding frame on the gradient magnetic field coil side flow. The dermis portion is the part on the superconducting coil side through which eddy currents do not flow. [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) is a diagram showing a helium container provided in an MRI apparatus according to a comparative example, and (B) is a diagram showing a helium container provided in an MRI apparatus according to the first embodiment. [Figure 7] A diagram showing a heat-suppressing shield provided in an MRI apparatus according to the first embodiment. [Figure 8] A block diagram showing an example configuration of an MRI apparatus according to the second embodiment. [Figure 9] A cross-sectional view showing the configuration of a magnet base provided in an MRI apparatus according to the second embodiment. [Modes for carrying out the invention]
[0008] Hereinafter, embodiments of the present invention will be described based on the attached 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] Hereinafter, 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 in 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 of both bottom surfaces of the substantially cylindrical shape, is parallel to the Y-axis. Further, 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 composed of a superconducting coil, a static magnetic field is generated by applying a current supplied from a static magnetic field power source in an excitation mode to the superconducting coil. 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 configured as a permanent magnet.
[0017] FIG. 2 is a diagram showing an arrangement example of a 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 main body 31. This MRI apparatus 1 includes a bed 30, unlike FIG. 1.
[0018] The bed 30 includes a bed main body 31 and a bed top plate 32. The bed main 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 in the horizontal direction 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 perpendicular 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 housed, for example, 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 114 and 115.
[0022] Adjacent to the vacuum vessel 111 of the static magnetic field magnet 11, a gradient magnetic field coil 12 that generates a gradient magnetic field superimposed on the static magnetic field and a transmission coil 13 that applies a high-frequency pulse, that is, an RF (Radio Frequency) pulse, to the patient U are arranged. The gradient magnetic field coil 12 is configured, for example, as a flat coil. Also, the transmission coil 13 is configured, for example, as a flat coil.
[0023] 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 comprises a vacuum vessel 111, a radiation shield 112 provided inside the vacuum vessel 111, a helium vessel 113 housing superconducting coils 114, 115 and reel frames 116, 117, superconducting coils 114, 115 provided inside the radiation shield 112, a reel frame 116 holding the superconducting coil 114, and a reel frame 117 holding the superconducting coil 115. The static magnetic field magnet 11 incorporates the superconducting coils 114, 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, 115. Subsequently, when it transitions to persistent current mode, the static magnetic field power source is disconnected. Once it transitions to persistent current mode, the static magnetic field magnet 11 continues to generate a static magnetic field for a long time, for example, for more than one year.
[0026] The configuration of the static magnetic field magnet 11 will be described later using Figures 5 to 7.
[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 unit.
[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 to 7.
[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 bases is parallel to the Y-axis. The static magnetic field magnet 11 comprises a radiation shield 112, a coolant container (for example, a helium container 113), superconducting coils 114, 115, and winding frames 116, 117. Note that the helium container 113 is not an essential component of the static magnetic field magnet 11.
[0046] The radiation shield 112, like the vacuum vessel 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 installed inside the vacuum vessel 111 so as to surround the helium vessel 113 (i.e., the superconducting coils 114 and 115). The helium vessel 113, like the vacuum vessel 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 installed inside the radiation shield 112 to hold liquid helium. The superconducting coils 114 and 115 are installed inside the helium vessel 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 made of permanent magnets.
[0047] 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 conductivity.
[0048] Therefore, due to induction heating (GCIH) caused by the operation of the gradient magnetic field coil 12, a large eddy current I is generated in the radiation shield 112, and as shown in Figure 6(A), eddy currents (dashed arrows) are also generated in the helium container 113. On the other hand, as shown in Figure 6(A), the helium container 113 also serves as part of the winding frame Q of the comparative example that supports the superconducting coil of the static magnetic field magnet. In other words, the winding frame Q is fixed to the outer frame of the helium container 113. Therefore, there is only a few mm between the outer frame of the helium container 113 and the superconducting coil P, and the heat from the eddy currents generated in the helium container 113 is directly transferred to the superconducting coil P via the winding frame Q, and because heat dissipation is poor, quenching is likely to occur.
[0049] Therefore, as shown in Figures 5 and 6(B), the reel 116 is not fixed to the outer frame of the helium container 113, and comprises a reel body 116a for holding the superconducting coil 114 and a heat-suppressing shield 116b. The heat-suppressing shield 116b is positioned between the gradient magnetic field coil 12 and the superconducting coil 114, on the magnetic field coil 12 side, to suppress the heat generated in the helium container 113.
[0050] The heat-suppressing shield 116b is made of a metal material such as stainless steel or aluminum. However, eddy currents (dashed arrows in Figure 6(B)) are generated in the heat-suppressing shield 116b itself due to the leakage magnetic field of the gradient magnetic field coil 12. Therefore, the heat-suppressing shield 116b has a two-layer structure consisting of a skin portion R1 through which eddy currents generated in the winding frame 116 on the gradient magnetic field coil 12 side flow, and a dermis portion R2 through which eddy currents do not flow on the superconducting coil 114 side, and it is preferable that the thickness of the skin portion R1 through which eddy currents flow is greater than or equal to the thickness of the skin portion R1 through which eddy currents flow (hereinafter referred to as "skin thickness"). Note that the heat-suppressing shield 116b is not limited to a two-layer structure that is structurally separated, and the skin portion R1 and the dermis portion R2 may be configured not to be structurally separated as long as the effects obtained from the skin portion R1 and the dermis portion R2 can be functionally separated. In other words, the skin portion R1 and the dermis portion R2 only need to be structurally separated or functionally separated.
[0051] The eddy current skin thickness is determined based on the electrical conductivity (i.e., conductivity) of the metal material constituting the heat-suppressing shield 116b, the frequency of the imaging conditions (e.g., 100-3000 Hz), or a combination thereof. For example, if the metal material constituting the heat-suppressing shield 116b is stainless steel or aluminum, and the frequency of the imaging conditions is 100-3000 Hz, considering the eddy current skin thickness, the thickness (Y-axis direction) of the heat-suppressing shield 116b can be set to 23-26 mm or more.
[0052] Specifically, if the metal material constituting the heat-suppressing shield 116b is stainless steel and the imaging frequency is 600 Hz, the eddy current skin thickness is less than 13 mm, so by providing the dermis R2, the heat-suppressing shield 116b can be made to be approximately 13 mm or thicker. Also, if the metal material constituting the heat-suppressing shield 116b is aluminum (e.g., A5083) and the imaging frequency is 600 Hz, the eddy current skin thickness is less than 3.7 mm, so by providing the dermis R2, the heat-suppressing shield 116b can be made to be approximately 3.7 mm or thicker. Furthermore, not only the thickness of the heat-suppressing shield 116b, but also the material of the heat-suppressing shield 116b (e.g., conductivity) may be set based on the imaging frequency.
[0053] By providing a winding frame 116 equipped with a heat-suppressing shield 116b that takes into account the skin thickness of such eddy currents, it is possible to create a structure in which heat from eddy currents generated in the helium container 113 and winding frame 116 is not directly transmitted to the superconducting coil 114, and eddy currents generated within the winding frame 116 are not transmitted.
[0054] Furthermore, Figure 7 illustrates a case where the dermis portion R2 of the heat-suppressing shield 116b is sufficiently thicker than the epidermis portion R1, and also sufficiently thicker than the portion M of the winding frame body 116a that faces the heat-suppressing shield 116b with the superconducting coil 114 in between. In this case, compared to the case where the dermis portion R2 is thin as shown in Figure 6(B), the transmission of heat and eddy currents due to eddy currents can be suppressed more effectively. Note that while Figure 7 (and similarly Figure 6) describes the case where the static magnetic field magnet is equipped only with the superconducting coil 114, the operation is similar when the static magnetic field magnet 11 has superconducting coils 114 and 115 (as shown in Figure 5).
[0055] Furthermore, if the thickness of the heat-suppressing shield 116b can be sufficiently secured even considering the skin thickness of the eddy currents, the heat-suppressing shield 116b may be directly fixed to the outer frame of the helium container 113.
[0056] Furthermore, as shown in Figure 6(A), when the liquid helium surrounding the superconducting coil P is vaporized by the heat of the eddy currents (dashed arrows) generated in the helium container 113, the helium gas remains in a bubble-like state, surrounding the superconducting coil P and providing insulation. Therefore, it is necessary to circulate the helium container 113 to separate the bubble-like helium gas from the superconducting coil P.
[0057] Therefore, as shown in Figure 6(B), it is preferable that the heat-suppressing shield 116b is positioned on the reel 116 with a gap that allows bubbles to diffuse from the outer frame of the helium container 113, so that bubbles generated in the helium container 113 do not form around the superconducting coil 114. The reel 116 has been described so far, but the same applies to the reel 117. As shown in Figure 5, the reel 117 comprises a reel body 117a corresponding to the reel body 116a and a heat-suppressing shield 117b corresponding to the heat-suppressing shield 116b. The heat-suppressing shield 117b comprises an epidermis portion R1 and a dermis portion R2, similar to the heat-suppressing shield 116b.
[0058] The MRI device 1 described in Figures 1 to 7 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 includes a heat-suppressing shield 116b in which winding frame 116 (similarly winding frame 117) has a skin portion R1 through which eddy currents generated within the winding frame 116 on the gradient coil 12 side flow, and a dermis portion R2 through which eddy currents do not flow on the superconducting coil 114 side.
[0059] As described above, with the static magnetic field magnet 11 and the MRI device 1, the structure of the winding frame 116 (and similarly the winding frame 117) that takes into account the skin thickness of the overcurrent can suppress the heat generation of the superconducting coil 114 caused by eddy currents.
[0060] (Second embodiment) Figure 8 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 8, components that share the same reference numerals as those shown in Figure 4 are denoted by the same numerals and their descriptions are omitted.
[0061] 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 generally cylindrical in shape. A cross-sectional view of the BB of the magnet mount 10A is shown in Figure 9.
[0062] As shown in Figure 9, 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 (not shown), a helium container (not shown), a superconducting coil 114, and a winding frame 116.
[0063] The winding frame 116 comprises, as described above, a winding frame body 116a (shown in Figures 5 to 7) and a heat-suppressing shield 116b. The heat-suppressing shield 116b comprises a skin portion R1 (shown in Figures 5 to 7) through which eddy currents generated within the winding frame 116 on the gradient magnetic field coil 12A side flow, and a dermis portion R2 (shown in Figures 5 to 7) through which eddy currents do not flow on the superconducting coil 114 side. By adopting such a structure for the winding frame 116 that takes into account the skin thickness of the overcurrent, it is possible to create a structure in which heat generated in the helium container and winding frame 116 is not directly transmitted to the superconducting coil 114, and eddy currents generated within the winding frame 116 are not transmitted. If the thickness of the heat-suppressing shield 116b can be sufficiently secured, the heat-suppressing shield 116b may be directly fixed to the outer frame of the helium container.
[0064] Furthermore, as described above, in order to circulate the helium inside the helium container and separate the bubble-like helium gas from the superconducting coil 114, it is preferable that the winding frame 116 has a gap that allows bubbles to diffuse from the outer frame of the helium container, so that bubbles generated inside the helium container do not form around the superconducting coil 114, and that the heat-suppressing shield 116b is positioned there.
[0065] As described above, with the static magnetic field magnet 11A and the MRI device 1A, the structure of the winding frame 116, which takes into account the skin thickness of the overcurrent, makes it possible to suppress the heat generation of the superconducting coil 114 caused by eddy currents.
[0066] According to at least one embodiment described above, it is possible to suppress the heat generation of the superconducting coil.
[0067] 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]
[0068] 1…Open-plan MRI device 1A...Cylindrical MRI device 11,11A...Static magnetic field magnet 111...Vacuum container 112... Radiation Shield 112'... The side of the radiation shield facing the gradient magnetic field coil. 113... Helium container 114,115…Superconducting coils 116,117… reel frame 116a, 117a... Winding frame body 116b, 117b... Heat-reducing shields 12,12A…Gradient field coil 13,13A…Transmitting coil R1...epidermis R2…Dermis
Claims
1. Vacuum container and A radiation shield provided inside the vacuum vessel, A superconducting coil is provided inside the aforementioned radiation shield to generate a static magnetic field, A winding frame for holding the superconducting coil, We have established The winding frame is provided with a heat-suppressing shield portion comprising a skin portion and a dermis portion that are structurally or functionally separated, wherein the skin portion is the part through which eddy currents generated within the winding frame on the gradient magnetic field coil side flow, and the dermis portion is the part through which eddy currents do not flow on the superconducting coil side. Static magnetic field magnet.
2. The heat-suppressing shield portion has a thickness greater than or equal to the skin thickness of the eddy current calculated based on the material of the skin portion and the frequency of the imaging conditions under which the static magnetic field magnet is used. A static magnetic field magnet according to claim 1.
3. The epidermis and dermis are structurally separated. The heat-suppressing shield portion is thicker than the skin portion and thicker than the portion of the main body of the winding frame that faces the heat-suppressing shield portion with the superconducting coil in between. A static magnetic field magnet according to claim 1.
4. The refrigerant container further comprises the superconducting coil and the winding frame, The aforementioned winding frame is The refrigerant container is positioned apart from the outer frame of the refrigerant container to prevent bubbles generated within the container from accumulating around the superconducting coil, thereby forming a gap from which the bubbles can diffuse. A static magnetic field magnet according to claim 1.
5. The refrigerant container further comprises the superconducting coil and the winding frame, The heat-suppressing shield portion is directly fixed to the refrigerant container. A static magnetic field magnet according to claim 1.
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, An imaging execution unit controls the operation of the static magnetic field magnet, the gradient magnetic field coil, and the transmitting coil to perform imaging, A magnetic resonance imaging apparatus equipped with a magnetic resonance imaging system.
7. The heat-suppressing shield portion is positioned between the gradient magnetic field coil and the superconducting coil. The magnetic resonance imaging apparatus according to claim 6.
8. 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
9. The material and thickness of the heat-suppressing shield portion are set based on the frequency of the imaging conditions for the imaging. The magnetic resonance imaging apparatus according to claim 6.