Superconducting magnet

Abstract

To efficiently cool a heat shield using a refrigerator.SOLUTION: A superconducting magnet includes a liquid reservoir, a heat shield, a refrigerator and a thermal conductor. The liquid reservoir stores liquid helium and a superconducting coil. The heat shield is installed around the liquid reservoir. The refrigerator cools the heat shield. The thermal conductor extends between the refrigerator and the heat shield and transfers heat of the heat shield to the refrigerator. Alternatively, the thermal conductor includes a first block body to be attached to the refrigerator, a second block body to be attached to the heat shield, and a body part extends between the first block body and the second block body. The body part extends horizontally from the first block body and the second block body. A position where the body extends from the first block body and a position where the body part extends from the second block body are located at the same height.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The embodiments disclosed in this specification and the drawings relate to superconducting magnets. [Background technology]

[0002] A superconducting magnet installed in a magnetic resonance imaging (MRI) device includes a vacuum vessel that forms the exterior of the superconducting magnet, a superconducting coil and a liquid reservoir tank that contains liquid helium, a heat shield that provides insulation between the vacuum vessel and the liquid reservoir tank, and a refrigerator that cools the heat shield and the liquid reservoir tank. The refrigerator and the thermal shield are connected via a thermal conductor with high thermal conductivity. To efficiently cool the thermal shield with the refrigerator, it is necessary to reduce the thermal resistance of the thermal conductor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-267183 A Summary of the Invention [Problem to be solved by the invention]

[0004] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to efficiently cool the heat shield using a refrigerator. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described below can also be positioned as other problems. [Means for solving the problem]

[0005] The superconducting magnet according to the embodiment includes a liquid reservoir, a heat shield, a refrigerator, and a heat conductor. The liquid reservoir contains liquid helium and a superconducting coil. The heat shield is installed around the liquid reservoir. The refrigerator cools the heat shield. The heat conductor extends between the refrigerator and the heat shield, and transfers heat from the heat shield to the refrigerator. The heat conductor includes a first block body attached to the refrigerator, a second block body attached to the heat shield, and a main body extending between the first block body and the second block body. The main body extends horizontally from the first block body and the second block body. The position where the main body extends from the first block body and the position where the main body extends from the second block body are located at the same height. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a magnetic resonance imaging apparatus according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of the structure of a superconducting magnet according to an embodiment. [Diagram 3] FIG. 3 is a diagram showing a cross section of a thermal conductor according to the embodiment. [Figure 4] FIG. 4 is a diagram showing the measurement results of a vibration measurement test simulating the superconducting magnet according to the embodiment. [Diagram 5] FIG. 5 is a diagram showing a simplified model used in Comparative Example 1 of FIG. [Figure 6] FIG. 6 is a diagram showing a simplified model used in Comparative Example 2 of FIG. [Figure 7] FIG. 7 is a diagram showing a simplified model used in the embodiment of FIG. [Figure 8] FIG. 8 is a diagram showing an example of a cross section of a thermal conductor according to the second modified example. [Figure 9] FIG. 9 is a diagram showing an example of the structure of a superconducting magnet according to the third modified example. [Figure 10] FIG. 10 is a diagram showing an example of the structure of a superconducting magnet according to the fourth modified example. [Figure 11] FIG. 11 is a bottom view of the thermal conductor connection structure of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, an embodiment of a superconducting magnet will be described in detail with reference to the drawings. In the following description, components having substantially the same functions and configurations are given the same reference numerals, and repeated description will be given only when necessary.

[0008] (Embodiment) Fig. 1 is a diagram showing a control configuration of a magnetic resonance imaging (MRI) apparatus 1 having a superconducting magnet of this embodiment. As shown in Fig. 1, the magnetic resonance imaging apparatus 1 has a gantry 11, a bed 13, a gradient magnetic field power supply 21, a transmission circuit 23, a reception circuit 25, a bed driving device 27, a sequence control circuit 29, and a host computer 50. The host computer is an example of a data processing device.

[0009] As shown in Fig. 1, the gantry 11 has a static magnetic field magnet 41, which is a superconducting magnet of this embodiment, and a gradient magnetic field coil 43. The static magnetic field magnet 41 and the gradient magnetic field coil 43 are housed in a housing 111 of the gantry 11. A bore 112 having a hollow shape is formed in the housing 111 of the gantry 11. A transmitting coil 45 and a receiving coil 47 are arranged in the bore 112 of the gantry 11. The gantry 11 may be called a "gantry."

[0010] The static magnetic field magnet 41 has a hollow, approximately cylindrical shape, and generates a static magnetic field inside the approximately cylinder. For example, a superconducting magnet is used as the static magnetic field magnet 41. Here, the central axis of the static magnetic field magnet 41 is defined as the Z axis, the axis perpendicular to the Z axis is defined as the Y axis, and the axis horizontally perpendicular to the Z axis is defined as the X axis. The X axis, Y axis, and Z axis form an orthogonal three-dimensional coordinate system.

[0011] The gradient coil 43 is a coil unit attached to the inside of the static magnetic field magnet 41 and formed in a hollow, approximately cylindrical shape. For example, an ASGC (Active Shield Gradient Coil) is used as the gradient coil 43. The gradient coil 43 generates a gradient magnetic field by receiving a current from the gradient magnetic field power supply 21. More specifically, the gradient coil 43 has three coils corresponding to the X-axis, Y-axis, and Z-axis that are orthogonal to each other. The three coils form a gradient magnetic field whose magnetic field strength changes along each of the X-axis, Y-axis, and Z-axis. The gradient magnetic fields along each of the X-axis, Y-axis, and Z-axis are synthesized to form a slice selection gradient magnetic field Gs, a phase encoding gradient magnetic field Gp, and a frequency encoding gradient magnetic field Gr that are orthogonal to each other in a desired direction. The slice selection gradient magnetic field Gs is used to arbitrarily determine an imaging section (slice). The phase encoding gradient magnetic field Gp is ​​used to change the phase of a magnetic resonance signal (hereinafter referred to as an MR signal) according to a spatial position. The frequency encoding gradient magnetic field Gr is used to change the frequency of the MR signal depending on the spatial position. In the following description, the gradient direction of the slice selection gradient magnetic field Gs is the Z axis, the gradient direction of the phase encoding gradient magnetic field Gp is ​​the Y axis, and the gradient direction of the frequency encoding gradient magnetic field Gr is the X axis.

[0012] The gradient magnetic field power supply 21 supplies a current to the gradient magnetic field coil 43 in accordance with a sequence control signal from the sequence control circuit 29. The gradient magnetic field power supply 21 supplies a current to the gradient magnetic field coil 43, thereby causing the gradient magnetic field coil 43 to generate gradient magnetic fields along the X-axis, Y-axis, and Z-axis. The gradient magnetic field is superimposed on the static magnetic field formed by the static magnetic field magnet 41 and applied to the subject P.

[0013] The transmission coil 45 is disposed, for example, inside the gradient magnetic field coil 43, and receives RF pulses from the transmission circuit 23 to generate a high-frequency magnetic field.

[0014] The transmission circuit 23 supplies an RF pulse for exciting the target protons present in the subject P to the transmission coil 45 so as to apply the RF pulse to the subject P via the transmission coil 45. The RF pulse corresponds to a Larmor frequency determined by the type of the target atomic nucleus and the strength of the magnetic field. The RF pulse vibrates at a resonance frequency specific to the target protons, exciting the target protons. An MR signal is generated from the excited target protons and detected by the reception coil 47.

[0015] The receiving coil 47 is fixed inside the bore 112. The receiving coil 47 receives an MR signal emitted from the target protons present inside the imaging region under the action of an RF pulse. The received MR signal is supplied to the receiving circuit 25 via a wired or wireless connection.

[0016] The receiving circuitry 25 receives MR signals generated from excited target protons via the receiving coil 47. The receiving circuitry 25 processes the received MR signals to generate digital MR signals. The digital MR signals can be expressed in k-space defined by spatial frequencies. Therefore, hereinafter, the digital MR signals will be referred to as k-space data. The k-space data is a type of raw data used for image reconstruction. The k-space data is supplied to a host computer 50 via a wired or wireless connection.

[0017] The bed 13 is installed adjacent to the gantry 11. The bed 13 has a top plate 131 and a base 133. The subject P is placed on the top plate 131. The base 133 supports the top plate 131 so that it can move along the Z-axis direction. The base 133 also supports the top plate 131 so that it can slide along each of the X-axis, Y-axis, and Z-axis. A bed driving device 27 is housed in the base 133. The bed driving device 27 moves the top plate 131 under the control of a sequence control circuit 29. The bed driving device 27 may include any motor, such as a servo motor or a stepping motor.

[0018] The sequence control circuit 29 has, as hardware resources, a processor such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) and memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory). The sequence control circuit 29 synchronously controls the gradient magnetic field power supply 21, the transmission circuit 23, and the reception circuit 25 based on an imaging protocol determined by an imaging protocol setting function 511 of the processing circuit 51, performs magnetic resonance imaging on the subject P according to a pulse sequence corresponding to the imaging protocol, and collects k-space data regarding the subject P.

[0019] As shown in FIG. 1, the host computer 50 is a computer having a processing circuit 51 , a memory 52 , a display 53 , an input interface 54 and a communication interface 55 .

[0020] The processing circuitry 51 has a processor such as a CPU as a hardware resource. The processing circuitry 51 functions as the core of the magnetic resonance imaging apparatus 1. For example, the processing circuitry 51 has an imaging protocol setting function 511, a data acquisition function 512, an image generation function 513, an image processing function 514, a display control function 515, and a sequence control function 516 by executing various programs.

[0021] 1, the imaging protocol setting function 511, the data acquisition function 512, the image generation function 513, the image processing function 514, the display control function 515, and the sequence control function 516 are realized by a single processing circuit 51. However, a processing circuit may be configured by combining a plurality of independent processors, and each processor may execute a program to realize each function. Also, the imaging protocol setting function 511, the data acquisition function 512, the image generation function 513, the image processing function 514, the display control function 515, and the sequence control function 516 may be called an imaging protocol setting circuit, a data acquisition circuit, an image generation circuit, an image processing circuit, a display control circuit, a sequence adjustment circuit, and a sequence control circuit, respectively, and may be implemented as individual hardware circuits. The above description of each function executed by the processing circuit 51 is the same in the following embodiments and modified examples.

[0022] The term "processor" used in the above description means a circuit such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an ASIC, a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)). When the processor is, for example, a CPU, the processor realizes a function by reading and executing a program stored in a memory. On the other hand, when the processor is an ASIC, instead of storing a program in a memory, the function is directly incorporated as a logic circuit in the circuit of the processor. Note that each processor in this embodiment is not limited to being configured as a single circuit for each processor, and may be configured as a single processor by combining multiple independent circuits to realize the function. Furthermore, the multiple components in FIG. 1 may be integrated into a single processor to realize the function. The above description of the "processor" is also applicable to the following embodiments and modified examples.

[0023] The memory 52 is a storage device such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), or an integrated circuit storage device that stores various information. The memory 52 may also be a drive device that reads and writes various information from and to a portable storage medium such as a CD-ROM drive, a DVD drive, or a flash memory. For example, the memory 52 stores a trained model, k-space data, MR image data, a control program, and the like.

[0024] The display 53 displays various information using a display control function 515. For example, the display 53 displays an MR image generated by an image generation function 513, an MR image generated by an image processing function 514, an imaging protocol setting screen, etc. As the display 53, for example, a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display known in the art can be appropriately used.

[0025] The input interface 54 includes an input device that accepts various commands from a user. Examples of the input device that can be used include a keyboard, a mouse, various switches, a touch screen, a touch pad, and the like. Note that the input device is not limited to devices that have physical operation parts such as a mouse and a keyboard. For example, an example of the input interface 54 also includes an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the magnetic resonance imaging apparatus 1 and outputs the received electrical signal to various circuits.

[0026] The communication interface 55 is an interface that connects the magnetic resonance imaging apparatus 1 to a workstation, a PACS (Picture Archiving and Communication System), a HIS (Hospital Information System), a RIS (Radiology Information System), etc. via a LAN (Local Area Network) etc. The communication interface 55 transmits and receives various information to and from the connected workstation, PACS, HIS, and RIS.

[0027] Next, each function executed by the processing circuit 51 will be described in detail. The processing circuitry 51 sets an imaging protocol for magnetic resonance imaging by an imaging protocol setting function 511 in response to a user instruction via the input interface 54 or automatically. The imaging protocol is a set of various imaging parameters for one magnetic resonance imaging. As the imaging parameters, various parameters that are set directly or indirectly to perform magnetic resonance imaging, such as the type of pulse sequence, the type of k-space filling method, the imaging time, the repetition time (TR), and the echo time (TE), can be applied. As the pulse sequence, for example, EPI (echo planar imaging) is used.

[0028] The processing circuitry 51 acquires MR data related to a processing target such as a subject P by using a data acquisition function 512. MR data is a general term for k-space data, MR image data, and hybrid data. The k-space data may be original k-space data, or may be data obtained by performing any data processing such as data compression processing, resolution decomposition processing, data interpolation processing, and resolution synthesis processing on the original k-space data. The hybrid data is data obtained by performing a Fourier transform or an inverse Fourier transform along at least one axis of the k-space data.

[0029] The processing circuitry 51 reconstructs an MR image of the subject P based on the MR data acquired from the receiving circuitry 25 by using the image generating function 513. The processing circuitry 51 performs, for example, a Fourier transform on the MR data arranged in the k-space or the frequency space to generate an MR image defined in real space. Instead of or in combination with the Fourier transform, an iterative reconstruction method or a reconstruction method using a machine learning model may be performed. The processing circuitry 51 that realizes the image generating function 513 is an example of a reconstruction unit.

[0030] The processing circuitry 51 performs various image processing on the MR image using the image processing function 514. For example, the processing circuitry 51 performs image processing such as volume rendering, surface rendering, pixel value projection processing, MPR (Multi-Planer Reconstruction) processing, and CPR (Curved MPR) processing.

[0031] The processing circuitry 51 displays various information on the display 53 using the display control function 515. For example, the processing circuitry 51 displays on the display 53 an MR image generated by the image generation function 513, an MR image generated by the image processing function 514, an imaging protocol setting screen, and the like.

[0032] The processing circuitry 51 generates imaging sequence information based on imaging conditions input by an operator using a sequence control function 516, and controls imaging by transmitting the generated imaging sequence information to the sequence control circuit 29. In addition, in the sequence control function 516, the processing circuitry 51 receives MR data from the sequence control circuit 29, and stores the received MR data in the memory 52. ​​The processing circuitry 51 that realizes the sequence control function 516 is an example of a sequence control unit.

[0033] Next, the configuration of the static magnetic field magnet 41 will be described in detail.

[0034] Fig. 2 is a diagram showing the internal configuration of the static magnetic field magnet 41. As shown in Fig. 2, the static magnetic field magnet 41 includes a vacuum vessel 411, a heat shield 412, a helium vessel 413, a superconducting coil 414, a refrigerator 415, and a heat conductor 416. The heat shield 412, the helium vessel 413, the superconducting coil 414, and the heat conductor 416 are accommodated inside the vacuum vessel 411.

[0035] The vacuum vessel 411 is a housing that forms the exterior of the static magnetic field magnet 41. The heat shield 412 is installed around the helium vessel 413. The heat shield 412 is attached between the vacuum vessel 411 and the helium vessel 413, and provides shielding between the vacuum vessel 411 and the helium vessel 413. The heat shield 412 is also called a radiation shield.

[0036] The inside of helium container 413 is filled with liquid helium LHe and helium gas GHe formed by vaporizing liquid helium LHe. Furthermore, superconducting coil 414 is housed inside helium container 413. Liquid helium LHe functions as a refrigerant to cool superconducting coil 414. Superconducting coil 414 is cooled to an extremely low temperature by the refrigerant and maintains a superconducting state. Helium container 413 is a liquid reservoir that houses liquid helium and the superconducting coil.

[0037] The refrigerator 415 is attached to the vacuum vessel 411 and cools the superconducting coil 414. The cooling mechanism of the refrigerator 415 may be a water-cooled type, an air-cooled type, or another cooling method. The refrigerator 415 is connected to a refrigerator compressor (not shown). The refrigerator compressor compresses a refrigerant and supplies it to the refrigerator 415. The refrigerator 415 cools the inside of the static magnetic field magnet 41 by the compressed refrigerant. The temperature of each part of the refrigerator 415 is controlled to a predetermined temperature by the control of the host computer 50 and the sequence control circuit 29.

[0038] The refrigerator 415 includes a first stage 4151 for cooling the heat shield 412 and a second stage 4152 for cooling the helium container 413. The temperatures of the first stage 4151 and the second stage 4152 are controlled to different temperatures. For example, the temperature of the first stage 4151 is controlled to any temperature between 40K and 90K. The second stage 4152 cools the helium in the helium container 413. Specifically, the second stage 4152 cools and liquefies the helium gas GHe filled in the helium container 413, and maintains the helium in a liquid state. The temperature of the second stage 4152 is controlled to a temperature that maintains the liquid helium LHe in a liquid state. For example, the temperature of the second stage 4152 is controlled to any temperature between 2K and 30K.

[0039] An outer case 418 is attached to the outside of the refrigerator 415. The outer case 418 is a case that surrounds and holds the refrigerator 415 from the outside, and is provided to fix the refrigerator 415 at a predetermined position in the vacuum vessel 411. The outer case 418 is attached to the vacuum vessel 411 with the refrigerator 415 supported therein. The outer case 418 supports the first stage 4151 of the refrigerator 415, thereby fixing the refrigerator 415. The outer case 418 is inserted into a hole (opening) provided in the upper surface of the heat shield 412. A gap is formed between the outer case 418 and the heat shield 412.

[0040] A thermal conductor 416 is provided between the refrigerator 415 and the heat shield 412. The thermal conductor 416 is made of a material having high thermal conductivity. Specifically, the thermal conductor 416 is provided between an outer case 418 holding the refrigerator 415 and the heat shield 412, and connects the outer case 418 holding the refrigerator 415 and the heat shield 412. The thermal conductor 416 has a function of transferring heat from the heat shield 412 to the refrigerator 415 via the outer case 418, thereby cooling the heat shield 412 with the refrigerator 415.

[0041] The number of the thermal conductors 416 is set to an appropriate number depending on the required thermal conduction performance, design conditions such as the size of the gap between the outer case 418 and the heat shield 412, and costs. The number of the thermal conductors 416 may be one or more. When a plurality of the thermal conductors 416 are used, the thermal conductors 416 are preferably arranged in a dispersed manner at positions spaced apart in the circumferential direction of the outer case 418. In this embodiment, a total of four thermal conductors 416 are arranged, and two thermal conductors 416 are arranged at each of two positions spaced apart in the circumferential direction of the first stage 4151.

[0042] The thermal conductor 416 includes a first block body 4161 attached to the refrigerator 415 via an outer case 418, a second block body 4162 attached to the heat shield 412, and a main body 4163 extending between the first block body 4161 and the second block body 4162. For example, the thermal conductor 416 is formed in a structure in which both ends of the main body 4163 are compressed with the first block body 4161 and the second block body 4162. The first block body 4161 and the second block body 4162 are formed of a material in which pure copper, such as oxygen-free copper or tough pitch copper, is plated with tin or silver. The first block body 4161 and the second block body 4162 may be a crimp terminal.

[0043] The outer case 418 includes a connection part 4181, a high temperature side housing part 4183, and a low temperature side housing part 4184. The connection part 4181 supports the first stage 4151 of the refrigerator 415, and is connected to the refrigerator 415 and the heat shield 412. The high temperature side housing part 4183 surrounds the first stage 4151 of the refrigerator 415 from the outside. The low temperature side housing part 4184 surrounds the second stage 4152 of the refrigerator 415 from the outside. The connection part 4181 is made of a material with high thermal conductivity such as aluminum or copper in order to efficiently cool the heat shield 412 by the refrigerator 415. On the other hand, the high temperature side housing part 4183 and the low temperature side housing part 4184 are made of a material with low thermal conductivity such as SUS in order to suppress the intrusion of heat from the outside. The connection part 4181 is located at approximately the same height as the upper surface of the heat shield 412 when the outer case 418 is attached to the vacuum container 411. The connection part 4181 supports the first stage 4151 of the refrigerator 415. The connection part 4181 includes a first connection surface 4182 to which the first block body 4161 is fixed. In this embodiment, the first connection surface 4182 is provided on the bottom surface of the connection part 4181, and is a horizontal flat surface facing downward.

[0044] The thermal conductor 416 is fastened to the connection portion 4181 by using a bolt 417. In the following description, when a bolt is used to fasten the thermal conductor 416, another fastening member such as a screw may be used instead of the bolt. The first block body 4161 is provided with an insertion hole into which the bolt 417 is inserted. The first connection surface 4182 of the connection portion 4181 is also provided with an insertion hole into which the bolt 417 is inserted. The thermal conductor 416 is fixed to the connection portion 4181 of the outer case 418 from below by inserting the bolt 417 into the insertion hole of the first block body 4161 and the insertion hole of the connection portion 4181. The bolt 417 is inserted vertically.

[0045] The heat shield 412 has a second connection surface 4121 to which the second block body 4162 is fixed. In this embodiment, the second connection surface 4121 is provided on the back side of the portion forming the upper surface of the heat shield 412, and is a horizontal plane facing downward inside the heat shield 412.

[0046] The second block body 4162 is fastened to the heat shield 412 by using a bolt 417. The second block body 4162 has an insertion hole into which the bolt 417 is inserted. In addition, a second connection surface 4121 of the heat shield 412 also has an insertion hole into which the bolt 417 is inserted. The thermal conductor 416 is fixed to the heat shield 412 from below by inserting the bolt 417 into the insertion hole of the second block body 4162 and the insertion hole of the heat shield 412. The bolt 417 is inserted vertically.

[0047] FIG. 3 is a diagram showing a cross section of the main body 4163. FIG. 3 shows a cross section perpendicular to the extending direction of the main body 4163. The main body 4163 is formed by bundling metal wires 4164. The metal wires 4164 are formed of a metal material having high thermal conductivity. For example, copper wires can be used as the metal wires 4164. In this embodiment, a bundle of metal wires 4164 having a diameter of 0.12 mm is used. The main body 4163 is formed so that its cross section is rectangular. That is, in order to provide both high thermal conductivity and high flexibility, the main body 4163 is formed by bundling thin metal wires having high thermal conductivity in a net shape to form a rectangle.

[0048] One end of the main body 4163 is connected to the inside of the first block body 4161, and the other end is connected to the inside of the second block body 4162. A portion of the main body 4163 extending from the inside of the first block body 4161 extends horizontally toward the second block body 4162. A portion of the main body 4163 extending from the inside of the second block body 4162 extends horizontally toward the first block body 4161.

[0049] Moreover, the first connection surface 4182 of the outer case 418 is provided at the same height as the second connection surface 4121 of the heat shield 412. Moreover, the first connection surface 4182 is formed so as to be located on the same plane as the second connection surface 4121. Therefore, the first block body 4161 and the second block body 4162 are fixed at the same height. Moreover, the position where the main body portion 4163 extends from the first block body 4161 and the position where the main body portion 4163 extends from the second block body 4162 are located at the same height.

[0050] The first stage 4151 of the refrigerator 415 cools the heat shield 412 via the connection part 4181 of the outer case 418, the first block body 4161, the main body part 4163, and the second block body 4162. At this time, thermal contraction occurs in the outer case 418, the thermal conductor 416, and the heat shield 412. In addition, since the helium container 413 and other components are in contact with the outer case 418 and the heat shield 412, when the heat shield 412 is cooled by the refrigerator 415, thermal contraction also occurs in these structures. For this reason, when the heat shield 412 is cooled by the refrigerator 415, the distance between the heat shield 412 and the outer case 418 may increase.

[0051] The main body 4163 includes a flexible portion 4165 that is flexible upward or downward. In this embodiment, the flexible portion 4165 is formed in a shape that is flexible downward. In other words, the main body 4163 is formed in a shape that is convex downward. The flexible portion 4165 may be formed in a shape that is flexible upward. When the distance between the heat shield 412 and the outer case 418 is expanded due to thermal contraction, the flexible portion 4165 is expanded, and the entire heat conductor 416 is expanded, thereby maintaining the connection between the heat shield 412 and the outer case 418 by the heat conductor 416. Therefore, even when the distance between the heat shield 412 and the outer case 418 is expanded due to thermal contraction, the heat shield 412 can be effectively cooled by the refrigerator 415 via the heat conductor 416. The shape of the flexible portion 4165 is preferably designed according to the amount of thermal contraction. It is preferable that the flexible portion 4165 is formed in a shape such that the flexible portion 4165 remains even when the distance between the heat shield 412 and the outer case 418 becomes the largest due to thermal contraction, and the overall length of the thermal conductor 416 becomes the smallest. The flexible portion 4165 may be called a protrusion or a convex portion. The flexible portion 4165 is provided, for example, in the center of the main body portion 4163.

[0052] The effects of the superconducting magnet according to this embodiment will be described below.

[0053] The static magnetic field magnet 41, which is a superconducting magnet according to this embodiment, includes a helium container 413, a heat shield 412, a refrigerator 415, and a heat conductor 416. The helium container 413 contains liquid helium, helium gas, and a superconducting coil. The heat shield 412 is installed around the helium container 413. The refrigerator 415 cools the heat shield 412. The heat conductor 416 extends between an outer case 418 that holds the refrigerator 415 and the heat shield 412, and transmits heat from the heat shield 412 to the refrigerator 415 via the outer case 418. The heat conductor 416 also includes a first block body 4161 attached to the refrigerator 415, a second block body 4162 attached to the heat shield 412, and a main body 4163 extended between the first block body 4161 and the second block body 4162. The main body 4163 extends horizontally from the first block body 4161 and the second block body 4162. The position where the main body 4163 extends from the first block body 4161 and the position where the main body 4163 extends from the second block body 4162 are located at the same height.

[0054] As described above, in this embodiment, the main body 4163 of the thermal conductor 416 extends from the first block body 4161 and the second block body 4162 at the same height, and also extends horizontally from the first block body 4161 and the second block body 4162. With this configuration, the main body 4163 can be made into a shape closer to a straight line, compared to when the main body 4163 extends upward or downward from the first block body 4161 or the second block body 4162, or when the main body 4163 is formed into an S-shape or a semicircular shape. By making the main body 4163 into a shape closer to a straight line, the entire length of the thermal conductor 416 can be shortened, and the manufacturing cost of the thermal conductor 416 can be reduced. Furthermore, by shortening the entire length of the thermal conductor 416, the thermal resistance of the thermal conductor 416 can be reduced. By reducing the thermal resistance of the thermal conductor 416, the heat of the refrigerator 415 can be effectively transferred to the heat shield 412. Furthermore, by using a thermal conductor 416 with low thermal resistance, the number of thermal conductors 416 required for heat transfer and the cross-sectional area of ​​each thermal conductor 416 can be reduced, and the manufacturing cost of the thermal conductor 416 can be reduced. Furthermore, by reducing the number of thermal conductors 416 required, the static magnetic field magnet 41 can be made smaller. Furthermore, when the main body 4163 is formed in an S-shape or semicircular shape, it is necessary to use a material with excellent flexibility for the main body 4163. On the other hand, in this embodiment, by forming the main body 4163 in a shape close to a straight line, the options for usable materials can be expanded, and costs can be reduced.

[0055] The thermal conductor 416 transfers heat from the heat shield 412 to the refrigerator 415 via the outer case 418, while transferring vibrations caused during operation of the refrigerator 415 to the heat shield 412 via the outer case 418. When the heat shield 412 vibrates, eddy currents are generated in the heat shield 412, causing the heat shield 412 to generate heat, or the magnetic field around the heat shield 412 to become distorted, which may result in degradation of captured images.

[0056] In this embodiment, the first block body 4161 is fixed to the first connection surface 4181 of the outer case 418 from below, and the second block body 4162 is fixed to the second connection surface 4121 of the heat shield 412 from below. Therefore, the heat conductor 416 is fixed to the outer case 418 and the heat shield 412 from below. If the heat conductor 416 is fixed to the outer case 418 and the heat shield 412 from above, the transmission rate of vibration from the outer case 418 to the heat shield 412 via the heat conductor 416 increases due to the influence of the weight of the heat conductor 416. On the other hand, in this embodiment, by attaching the heat conductor 416 to the outer case 418 and the heat shield 412 from below, the transmission of vibration from the outer case 418 to the heat shield 412 via the heat conductor 416 can be suppressed compared to the case where the heat conductor 416 is attached to the outer case 418 and the heat shield 412 from above.

[0057] In this embodiment, the outer case 418 has a first connection surface 4182 to which the first block body 4161 is fixed, and the heat shield 412 has a second connection surface 4121 to which the second block body 4162 is fixed, and the first connection surface 4182 and the second connection surface 4121 are located at the same height.

[0058] By providing the first connection surface 4182 of the outer case 418 and the second connection surface 4121 of the heat shield 412 at the same height, there is no step between the first connection surface 4182 and the second connection surface 4121, compared to when the first connection surface 4182 and the second connection surface 4121 are at different heights, and the length of the heat conductor 416 can be further shortened.

[0059] In this embodiment, the main body 4163 of the thermal conductor 416 includes a bending portion 4165 that bends downward. As described above, when the heat shield 412 is cooled by the refrigerator 415, thermal contraction occurs in the connection portion 4181 of the outer case 418, the thermal conductor 416, and the heat shield 412. Since the helium container 413 and other components are in contact with the outer case 418 and the heat shield 412, when the heat shield 412 is cooled by the refrigerator 415, these structures also thermally contract. Therefore, when the heat shield 412 is cooled by the refrigerator 415, the distance between the heat shield 412 and the connection portion 4181 of the outer case 418 may increase. In this case, the bending portion 4165 is stretched from both sides, and the main body 4163 is extended. Therefore, by providing the flexible portion 4165, even when the heat shield 412 thermally contracts, the heat conductor 416 is maintained in a state in which it is appropriately fixed to each of the heat shield 412 and the outer case 418, and the heat conduction performance of the heat conductor 416 is maintained. Furthermore, by forming the flexible portion 4165 in a shape such that the flexible portion 4165 remains even when the distance between the heat shield 412 and the outer case 418 becomes the largest due to thermal contraction and the overall length of the heat conductor 416 is minimized, the heat conductor 416 can be maintained in a state in which it is appropriately fixed to each of the heat shield 412 and the refrigerator 415, and the thermal resistance of the heat conductor 416 can be reduced.

[0060] In this embodiment, the main body 4163 is formed by bundling metal wires 4164. The metal wires 4164 are made of a metal material having high thermal conductivity. By using the thermal conductor 416 formed by bundling the metal wires 4164 in the main body 4163, the flexibility of the main body 4163 can be improved compared to a case where a single metal plate or a laminate of metal plates is used as a thermal conductor. By improving the flexibility of the main body 4163, the transmission of vibrations of the refrigerator 415 to the heat shield 412 can be further suppressed.

[0061] As described above, according to this embodiment, it is possible to suppress the propagation of vibration from the refrigerator 415 to the heat shield 412 via the thermal conductor 416, and also to reduce the thermal resistance of the thermal conductor 416 by shortening the length of the thermal conductor 416.

[0062] Here, the vibration suppression performance in the configuration of this embodiment will be described using experimental results. A vibration measurement test was performed on an example using a simple model in which the thermal conductor 416 is arranged under the same conditions as in this embodiment, and comparative examples 1 and 2 using simple models in which the thermal conductor 416 is arranged under conditions different from those in this embodiment. At this time, vibrations during hammering were measured using each simple model. FIG. 4 shows the vibration measurement results of the example and comparative examples 1 and 2. FIG. 5 is a diagram showing the configuration of the simple model used in comparative example 1. FIG. 6 is a diagram showing the configuration of the simple model used in comparative example 2. FIG. 7 is a diagram showing the configuration of the simple model used in the example.

[0063] The simplified models used in the embodiment, comparative examples 1 and 2 commonly used a dummy body 61, a dummy body 62 and a cushion material 63. The dummy body 61 simulates a connection part 4181 of an outer case 418 attached to a first stage 4151 of a refrigerator 415, and the same heat conductive material as the connection part 4181 was used. The dummy body 62 simulates a part of the heat shield 412 to which the heat conductor 416 is connected, and the same heat conductive material as the heat shield 412 was used. Although not shown in Figs. 5 to 7, the dummy body 62 is also arranged on the back side of the dummy body 61 in the depth direction of the paper. The cushion material 63 is installed between the dummy bodies 61 and 62 and the ground, and supports the dummy bodies 61 and 62. In addition, the embodiment, comparative examples 1 and 2 commonly used four heat conductors 416 having the same thermal conductivity, cross-sectional area and length are connected to the dummy body 61 and the dummy body 62.

[0064] 5, in the simple model of Comparative Example 1, two thermal conductors 416 were fixed to the simulation bodies 61 and 62 from above, and two thermal conductors 416 were fixed to the simulation bodies 61 and 62 from below. The thermal conductors 416 arranged on the upper side of the simulation bodies 61 and 62 were arranged so that the flexible parts 4165 faced upward, and the thermal conductors 416 had an upwardly convex shape. The thermal conductors 416 arranged on the lower side of the simulation bodies 61 and 62 were arranged so that the flexible parts 4165 faced downward, and the thermal conductors 416 had a downwardly convex shape.

[0065] As shown in FIG. 6, in the simple model of Comparative Example 2, four thermal conductors 416 were fixed to the dummy bodies 61 and 62 from above. At this time, two thermal conductors 416 were arranged at the positions shown in FIG. 6. The remaining two thermal conductors 416, which are not shown in FIG. 6, were arranged at positions away from the two thermal conductors 416 shown in FIG. 6, in the depth direction of the paper at positions connecting the dummy body 61 and the dummy body 62, which is not shown and is arranged at the back side of the dummy body 61. In addition, the thermal conductors 416 were arranged so that the bending portion 4165 faces upward, and the thermal conductors 416 were arranged so that they had an upward convex shape.

[0066] As shown in FIG. 7, in the simple model of the embodiment, four thermal conductors 416 were fixed to the dummy bodies 61 and 62 from below. At this time, two thermal conductors 416 were arranged at the positions shown in FIG. 7. The remaining two thermal conductors 416, which are not shown in FIG. 7, were arranged in the depth direction of the paper at positions away from the thermal conductors 416 shown in FIG. 7, at positions connecting the dummy body 61 and the dummy body 62, which is not shown and is arranged at the back side of the dummy body 61. In addition, the thermal conductors 416 were arranged so that the bending parts 4165 faced downward, and the thermal conductors 416 were arranged so that they had a downward convex shape.

[0067] Other conditions were the same for the Example and Comparative Examples 1 and 2. Fig. 4 shows the ratios of the vibration measurement results of Comparative Example 2 and the Example when the vibration measurement result of Comparative Example 1 is set to "1". As shown in Fig. 4, when the vibration measurement result of Comparative Example 1 is set to "1", the vibration measurement result of Comparative Example 2 was "0.53" and the vibration measurement result of the Example was "0.31".

[0068] Comparing the vibration measurement results of Comparative Example 2 and the Example, it is found that the Example suppresses vibration more effectively than the Comparative Example 2. From this, it is found that fixing the thermal conductor 416 from below as in the Example can suppress vibration transmission between the dummy bodies 61 and 62 more effectively than fixing the thermal conductor 416 from above as in Comparative Example 2. Therefore, it is found that by fixing the thermal conductor 416 to the outer case 418 and the heat shield 412 from below as in this embodiment, it is possible to suppress transmission of vibration of the refrigerator 415 to the heat shield 412 more effectively than when the thermal conductor 416 is fixed to the outer case 418 and the heat shield 412 from above.

[0069] Furthermore, when comparing the vibration measurement results of Comparative Example 1 and Comparative Example 2, it is found that Comparative Example 2 is able to suppress vibrations, even though some of the thermal conductors 416 are fixed from below in Comparative Example 1. From this, it is found that arranging the thermal conductors 416 at multiple locations as in Comparative Example 2 can suppress vibration transmission between the simulants 61 and 62 more effectively than arranging all of the thermal conductors 416 together in one location as in Comparative Example 1. Therefore, it is found that by fixing multiple thermal conductors 416 at multiple locations as in this embodiment, it is possible to suppress transmission of vibrations of the refrigerator 415 to the heat shield 412 more effectively than arranging the thermal conductors 416 together in one location.

[0070] (First Modification) In the embodiment, the metal wire 4164 having a diameter of 0.12 mm is used, but the diameter of the metal wire 4164 may be made smaller. By using the metal wire 4164 having a smaller diameter, the vibration of the refrigerator 415 can be further suppressed from being transmitted to the heat shield 412. The heat conductor 416 having the main body 4163 having the same cross-sectional area as that of the embodiment is formed by bundling the metal wires 4164 having a diameter of 0.05 mm, and a vibration measurement test is performed using the formed heat conductor 416 in the same manner as the embodiment of FIG. 7. In this case, the vibration measurement result is "0.01" when the vibration measurement result of the comparative example 1 is set to "1". This shows that the vibration of the refrigerator 415 can be further suppressed from being transmitted to the heat shield 412 by using the metal wire 4164 having a smaller diameter.

[0071] (Second Modification) In the embodiment, the cross-sectional shape of the main body 4163 is formed to be rectangular, but this is not limited thereto. For example, as shown in FIG. 8, the cross-sectional shape of the main body 4163 may be formed to be substantially circular. In this case, by forming the thermal conductor 416 by bundling metal wires 4164 into a circular shape, the main body 4163 can be formed to have flexibility in all directions perpendicular to the extension direction. By using the thermal conductor 416 that has flexibility in all directions, it is possible to further suppress the transmission of vibrations of the refrigerator 415 to the heat shield 412.

[0072] (Third Modification) FIG. 9 is a diagram showing an internal configuration of the static magnetic field magnet 41 according to the third modified example. As shown in FIG. 9, the first block body 4161 of the thermal conductor 416 has a groove portion 4166 recessed inward from an end surface facing outward. The groove portion 4166 is formed in a shape that allows an end of the connection portion 4181 of the outer case 418 to be fitted therein. The first block body 4161 is provided with an insertion hole into which the bolt 417 is inserted. In addition, an insertion hole into which the bolt 417 is inserted is also provided at an end of the connection portion 4181 of the outer case 418. The thermal conductor 416 is fastened to the outer case 418 by inserting the bolt 417 into the insertion hole of the first block body 4161 and the insertion hole of the connection portion 4181 with the end of the connection portion 4181 fitted in the groove portion 4166 of the first block body 4161. The bolt 417 is inserted along the vertical direction. When the thermal conductor 416 is fixed to the connection portion 4181 of the outer case 418, the groove portion 4166 contacts the upper, lower and lateral sides of the end portion of the connection portion 4181. Therefore, the first connection surface 4182 of this modification is formed by a part of the top surface, bottom surface and side surface of the end portion of the connection portion 4181, and includes flat surfaces facing the upper, lower and lateral sides.

[0073] Like the first block body 4161, the second block body 4162 has a groove portion 4167 recessed inward from an end surface facing outward. The groove portion 4167 is formed in a shape that allows the end of the heat shield 412 to be fitted therein. The second block body 4162 has an insertion hole into which the bolt 417 is inserted. The heat shield 412 also has an insertion hole into which the bolt 417 is inserted. The heat conductor 416 is fastened to the heat shield 412 by inserting the bolt 417 into the insertion hole of the second block body 4162 and the insertion hole of the heat shield 412 with the end of the heat shield 412 fitted in the groove portion 4167. The bolt 417 is inserted along the vertical direction. When the heat conductor 416 is fixed to the heat shield 412, the groove portion 4167 comes into contact with the end of the heat shield 412 from the upper side, the lower side, and the side. Therefore, the second connecting surface 4121 of this modified example is formed by a part of the top surface, bottom surface and side surface of the end portion of the heat shield 412, and includes flat surfaces facing upward, downward and laterally.

[0074] In this modification, similarly to the embodiment, the main body 4163 extends horizontally from the first block body 4161 and the second block body 4162, and the position where the main body 4163 extends from the first block body 4161 and the position where the main body 4163 extends from the second block body 4162 are located at the same height. Therefore, similarly to the embodiment, the main body 4163 can be made to have a shape close to a straight line, and therefore the length of the thermal conductor 416 can be shortened, and the thermal resistance of the thermal conductor 416 can be reduced.

[0075] In addition, in this modified example, the thermal conductor 416 is fixed to the outer case 418 and the heat shield 412 from the top, bottom, and sides, so that the contact area between the thermal conductor 416 and the outer case 418 and the heat shield 412 is increased, improving the thermal conductivity.

[0076] (Fourth Modification) In the embodiment, the thermal conductor 416 is disposed below the heat shield 412, and is fixed to the outer case 418 and the heat shield 412 from below. In this modification, the thermal conductor 416 is disposed between the outer case 418 and the heat shield 412, and is fixed to the outer case 418 and the heat shield 412 from the side.

[0077] Fig. 10 is a diagram showing the internal configuration of a static magnetic field magnet 41 according to a fourth modified example. Fig. 11 is a diagram showing the connection structure of an outer case 418 and a heat shield 412 with a heat conductor 416, as viewed from below.

[0078] As shown in FIG. 10 and FIG. 11, the first block body 4161 of the thermal conductor 416 includes a connection portion 4168. The connection portion 4168 is formed at an end of the first block body 4161 and protrudes outward on both sides in the width direction along the X-axis. The width direction is parallel to the horizontal and perpendicular to the extension direction of the thermal conductor 416. The connection portion 4168 is provided with an insertion hole into which the bolt 417 is inserted. In addition, an insertion hole into which the bolt 417 is inserted is also provided on a side surface of the end of the connection portion 4181 of the outer case 418. The thermal conductor 416 is fastened to the outer case 418 by inserting the bolt 417 into the insertion hole of the connection portion 4168 and the insertion hole of the connection portion 4181. The bolt 417 is inserted horizontally parallel to the extension direction of the thermal conductor 416. In a state where the thermal conductor 416 is fixed to the connection portion 4181, the first block body 4161 is fixed to a first connection surface 4182 of the connection portion 4181, the first connection surface 4182 facing the side where the heat shield 412 is located, from the side where the heat shield 412 is located. Note that the first connection surface 4182 is a part of a side surface of an end portion of the connection portion 4181 in the outer case 418.

[0079] Like the first block body 4161, the second block body 4162 includes a connection portion 4169. The connection portion 4169 is formed at an end of the second block body 4162 and protrudes outward on both sides in the width direction along the X-axis. The connection portion 4169 is provided with an insertion hole into which the bolt 417 is inserted. In addition, an insertion hole into which the bolt 417 is inserted is also provided in a side surface of the end of the heat shield 412. The thermal conductor 416 is fastened to the heat shield 412 by inserting the bolt 417 into the insertion hole of the connection portion 4169 and the insertion hole of the heat shield 412. The bolt 417 is inserted horizontally in parallel to the extension direction of the heat conductor 416. In a state where the thermal conductor 416 is fixed to the heat shield 412, a second block body 4162 is fixed to a second connection surface 4121 of the heat shield 412 facing the side where the refrigerator 415 and the outer case 418 are located, from the side where the refrigerator 415 and the outer case 418 are located. Note that the second connection surface 4121 is a part of a side surface of the end portion of the heat shield 412.

[0080] In this modification, similarly to the embodiment, the main body 4163 extends horizontally from the first block body 4161 and the second block body 4162, and the position where the main body 4163 extends from the first block body 4161 and the position where the main body 4163 extends from the second block body 4162 are located at the same height. Therefore, similarly to the embodiment, the main body 4163 can be made to have a shape close to a straight line, and therefore the length of the thermal conductor 416 can be shortened, and the thermal resistance of the thermal conductor 416 can be reduced.

[0081] In this modification, the first block body 4161 is fixed laterally to the first connection surface 4182 facing the side where the heat shield 412 is located, and the second block body 4162 is fixed laterally to the second connection surface 4121 facing the side where the refrigerator 415 is located. That is, the thermal conductor 416 is fastened laterally to the surface of the outer case 418 facing the heat shield 412 by using the bolts 417, and is fastened laterally to the surface of the heat shield 412 facing the outer case 418 by using the bolts 417. In this case, the thermal conductor 416 is disposed between the outer case 418 that holds the refrigerator 415 and the heat shield 412, so that the length of the main body 4163 can be further shortened.

[0082] According to at least one of the embodiments described above, the heat shield can be efficiently cooled by the refrigerator.

[0083] Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0084] 1...Magnetic resonance imaging device 11... Stand 111…Housing 112…Boa 13. Bed 131…Tabletop 133…Foundation 21...Gradient magnetic field power supply 23...Transmitting circuit 25…Receiver circuit 27...Bed drive unit 29...Sequence control circuit 41...Static magnetic field magnet 411...Vacuum container 412…Heat shield 4121…Connection surface 413…Helium container 414…Superconducting coil 415…Refrigeration machine 4151…First Stage 4152…Second stage 416…Heat conductor 4161, 4162...block letters 4163…Main body 4164…Metal wire 4165…Flexure 4166, 4167...Groove 4168, 4169…Connections 417…Bolt 418…Outer case 4181…Connection 4182…Connection surface 4183, 4184…Housing section 43...Gradient magnetic field coil 45…Transmitting coil 47…Receiver coil 50...Host computer 51... Processing circuit 511... Imaging protocol setting function 512…Data acquisition function 513…Image generation function 514…Image processing function 515…Display control function 516...Sequence control function 52…Memory 53…Display 54...Input interface 55...Communication interface 61, 62...simulation 63…Cushioning material

Claims

1. a liquid reservoir for storing liquid helium and a superconducting coil; a heat shield disposed around the liquid reservoir; a refrigerator for cooling the thermal shield; a thermal conductor extending between the refrigerator and the thermal shield and configured to transfer heat of the thermal shield to the refrigerator; Equipped with the thermal conductor includes a first block body attached to the refrigerator, a second block body attached to the thermal shield, and a main body extending between the first block body and the second block body, the main body portion extends horizontally from the first block body and the second block body, a position where the main body portion extends from the first block body and a position where the main body portion extends from the second block body are located at the same height; Superconducting magnet.

2. Further comprising an outer case for holding the refrigerator, the thermal conductor extends between the outer case and the thermal shield and transmits heat of the thermal shield to the refrigerator via the outer case.

2. The superconducting magnet according to claim 1.

3. the first block body is fixed to the outer case from below, The second block body is fixed to the heat shield from below.

3. The superconducting magnet according to claim 2.

4. the outer case includes a first connection surface to which the first block body is fixed, the heat shield includes a second connection surface to which the second block body is fixed; The first connection surface and the second connection surface are located at the same height.

3. The superconducting magnet according to claim 2.

5. The main body portion has a flexible portion that is flexible upward or downward.

2. The superconducting magnet according to claim 1.

6. The main body is formed by bundling metal wires.

2. The superconducting magnet according to claim 1.

7. The cross-sectional shape of the main body is substantially circular.

2. The superconducting magnet according to claim 1.

8. the outer case includes a first connecting surface facing a side where the heat shield is located; the heat shield has a second connecting surface facing the outer case; the first block body is fixed to the first connecting surface from a side where the heat shield is located, The second block body is fixed to the second connection surface from a side where the outer case is located.

3. The superconducting magnet according to claim 2.

Images