Superconducting magnet and magnetic resonance imaging apparatus

Abstract

To reduce a difference in current in a plurality of superconducting coils which are different in inductance at the time of the generation of a quench in a quench back system.SOLUTION: A superconducting magnet includes: a plurality of superconducting coils; and a plurality of quench back parts. The plurality of superconducting coils are used for the generation of a static magnetic field, and different in inductance. The plurality of quench back parts include: a plurality of insulation layers; and a plurality of conductive plates. The plurality of insulation layers are provided in the plurality of superconducting coils. The plurality of conductive plates can supply heat to the plurality of superconducting coils via the plurality of insulation layers, respectively. The plurality of quench back parts make the plurality of superconducting coils to generate the quench. The plurality of quench back parts are a different in specification in accordance with the plurality of superconducting coils.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Conventionally, a circuit in which multiple superconducting coils with different inductances are electrically connected is divided into two systems: a group of superconducting coils with low inductance (hereinafter referred to as the small coil system) and a group of superconducting coils with high inductance (hereinafter referred to as the large coil system). In this case, a mechanism (quench back method) is sometimes installed in a superconducting magnet to disperse the magnetic energy consumed by a superconducting coil that has experienced a quench by intentionally causing a quench in other superconducting coils, thereby suppressing the temperature and voltage rise of the superconducting coil that has experienced a quench.

[0003] The principle of the quench-back method is that when a quench occurs and the current path transfers to a protection circuit via a diode, a quench is generated in any superconducting coil by the heat of a heating conductor (also called a quench-back plate) connected to the protection circuit.

[0004] During a quench, a deviation occurs in the current difference and current decay rate between the circuits of the small coil system and the large coil system in the quench-back method. The deviation in the current difference and current decay rate is caused by mutual induction in the large coil system and the small coil system. The deviation in the current difference and current decay rate during a quench may cause the leakage magnetic field leaking from the superconducting magnet to temporarily expand, or eddy currents generated in the conductors near the superconducting coil may affect the mechanical strength and image adjustment of the superconducting magnet. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-67516 Summary of the Invention [Problem to be solved by the invention]

[0006] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to reduce the difference in current in multiple superconducting coils with different inductances when a quench occurs in the quench-back method. 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 later can also be positioned as other problems. [Means for solving the problem]

[0007] A superconducting magnet according to an embodiment has a plurality of superconducting coils and a plurality of quench-back sections. The plurality of superconducting coils are used to generate a static magnetic field and have different inductances. The plurality of quench-back sections have a plurality of insulating layers and a plurality of conductive plates. The plurality of insulating layers are provided on the plurality of superconducting coils. The plurality of conductive plates are capable of supplying heat to the plurality of superconducting coils via the plurality of insulating layers, respectively. The plurality of quench-back sections generate quenches in the plurality of superconducting coils. The plurality of quench-back sections have different specifications depending on the plurality of superconducting coils. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an example of a magnetic resonance imaging apparatus according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of a circuit configuration of a superconducting magnet according to an embodiment. [Diagram 3] FIG. 3 is a diagram showing an example of a quench-back portion in one superconducting coil according to the embodiment. [Figure 4] FIG. 4 is a diagram showing an example in which the installation area of ​​a quench back plate is changed in the embodiment. [Diagram 5] FIG. 5 is a schematic diagram showing an example of a temperature margin on a side surface of a superconducting coil in the embodiment. [Figure 6] FIG. 6 is a diagram showing an example of attenuation of the first current and the second current when a quench occurs in a pair of shield coils in a comparative example in which the specifications of multiple quench-back sections are the same regardless of the number of superconducting coils. [Figure 7] FIG. 7 is a diagram showing an example of attenuation of a first current and a second current when a quench occurs in a pair of shield coils in the present embodiment, in which the specifications of a plurality of quench-back sections differ according to a plurality of superconducting coils. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of a superconducting magnet and a magnetic resonance imaging apparatus will be described with reference to the drawings. The magnetic resonance imaging apparatus according to the embodiment will be described as having a superconducting magnet according to the embodiment. In the following embodiments, parts with the same reference numerals perform the same operation, and duplicated descriptions will be omitted as appropriate.

[0010] The superconducting magnet and the magnetic resonance imaging device in the embodiments are not limited to a single magnetic resonance imaging (MRI) device. The superconducting magnet and the magnetic resonance imaging device in the embodiments may be realized by a composite device having an MRI device such as a PET (Positron Emission Tomography)-MRI device or a SPECT (single photon emission computed tomography)-MRI device.

[0011] (Embodiment) Fig. 1 is a diagram showing an example of an MRI apparatus 100 according to the present embodiment. As shown in Fig. 1, the MRI apparatus 100 includes a superconducting magnet 101, a gradient magnetic field coil 103, a gradient magnetic field power supply 105, a bed 107, a bed control circuit (bed control unit) 109, a transmission circuit 113, a transmission coil 115, a reception coil 117, a reception circuit 119, an imaging control circuit (acquisition unit) 121, a storage device 125, a system control circuit 12, a console 70, a static magnetic field power supply (also called an external power supply) 130, a heater power supply 131, and a resistance detector 132.

[0012] The heater power supply 131 may be integrated into the external power supply 130. In this case, the external power supply 130 functions as the heater power supply 131 in addition to supplying a current to the superconducting magnet 101. The static magnetic field power supply 130, the heater power supply 131, and the resistance detector 132 may be mounted on a current control device provided separately from the MRI apparatus 100.

[0013] The superconducting magnet 101 is a magnet formed in a hollow, approximately cylindrical shape. The superconducting magnet 101 generates an approximately uniform static magnetic field in the internal space. The superconducting magnet 101 has, for example, a plurality of superconducting coils that generate a static magnetic field, and a PCS (Persistent Current Switch) unit (or PCS module). The PCS unit has a plurality of PCSs electrically connected to the superconducting coils, a heater provided in at least one of the plurality of PCSs, and the like. In the following, for the sake of concrete explanation, the plurality of PCS switches will be explained as being two (a first PCS and a second PCS). Note that the number of the plurality of PCS switches is not limited to two.

[0014] In the excitation mode, the superconducting magnet 101 generates a static magnetic field by applying a current supplied from the static magnetic field power supply 130 to the superconducting coil. After that, when the mode shifts to the persistent current mode, the static magnetic field power supply 130 is disconnected from the superconducting coil. That is, when the superconducting magnet 101 is in a superconducting state, the multiple PCSs and the superconducting coil form a closed circuit. In the superconducting magnet 101, the superconducting coil is cooled to an extremely low temperature by a refrigerant such as liquid helium. That is, the superconducting coil and the multiple PCSs are immersed in a refrigerant related to the superconducting state. The superconducting magnet 101 according to the embodiment will be described in detail later.

[0015] The gradient coil 103 is a coil formed in a hollow, approximately cylindrical shape, and is disposed on the inner surface side of a cylindrical cooling vessel. The gradient coil 103 receives currents individually from a gradient power supply 105 to generate gradient magnetic fields whose magnetic field strength changes along each of the mutually orthogonal X, Y, and Z axes. The gradient magnetic fields of the X, Y, and Z axes generated by the gradient coil 103 form, for example, a slice selection gradient magnetic field, a phase encoding gradient magnetic field, and a frequency encoding gradient magnetic field (also called a readout gradient magnetic field). The slice selection gradient magnetic field is used to arbitrarily determine an imaging cross section. The phase encoding gradient magnetic field is used to change the phase of a magnetic resonance signal (hereinafter referred to as an MR (Magnetic Resonance) signal) according to a spatial position. The frequency encoding gradient magnetic field is used to change the frequency of an MR signal according to a spatial position.

[0016] The gradient magnetic field power supply 105 is a power supply device that supplies a current to the gradient magnetic field coil 103 under the control of the imaging control circuit 121 .

[0017] The bed 107 is a device including a top plate 1071 on which the subject P is placed. The bed 107 inserts the top plate 1071 on which the subject P is placed into the bore 111 under the control of a bed control circuit 109.

[0018] The bed control circuit 109 is a circuit that controls the bed 107. The bed control circuit 109 drives the bed 107 in response to an instruction from an operator via the input / output interface 17, thereby moving the tabletop 1071 in the longitudinal direction, the up-down direction, and in some cases, the left-right direction.

[0019] The transmission circuit 113 supplies a radio frequency pulse modulated at the Larmor frequency to the transmission coil 115 under the control of the imaging control circuit 121. For example, the transmission circuit 113 has an oscillation unit, a phase selection unit, a frequency conversion unit, an amplitude modulation unit, an RF amplifier, and the like. The oscillation unit generates an RF pulse of a resonance frequency specific to a target atomic nucleus in a static magnetic field. The phase selection unit selects the phase of the RF pulse generated by the oscillation unit. The frequency conversion unit converts the frequency of the RF pulse output from the phase selection unit. The amplitude modulation unit modulates the amplitude of the RF pulse output from the frequency conversion unit according to, for example, a sinc function. The RF amplifier amplifies the RF pulse output from the amplitude modulation unit and supplies it to the transmission coil 115.

[0020] The transmission coil 115 is an RF (Radio Frequency) coil disposed inside the gradient magnetic field coil 103. In response to the output from the transmission circuit 113, the transmission coil 115 generates an RF pulse that corresponds to a high frequency magnetic field.

[0021] The receiving coil 117 is an RF coil disposed inside the gradient magnetic field coil 103. The receiving coil 117 receives an MR signal emitted from the subject P by a high frequency magnetic field. The receiving coil 117 outputs the received MR signal to a receiving circuit 119. The receiving coil 117 is, for example, a coil array having one or more, typically a plurality of coil elements. For the sake of concrete explanation, the receiving coil 117 will be described below as a coil array having a plurality of coil elements.

[0022] The receiving coil 117 may be composed of one coil element. Although the transmitting coil 115 and the receiving coil 117 are illustrated as separate RF coils in Fig. 1, the transmitting coil 115 and the receiving coil 117 may be implemented as an integrated transmitting / receiving coil. The transmitting / receiving coil corresponds to an imaging region of the subject P, and is, for example, a local transmitting / receiving RF coil such as a head coil.

[0023] The receiving circuit 119 generates magnetic resonance data (hereinafter referred to as MR data) as digital MR signals based on the MR signals output from the receiving coil 117 under the control of the imaging control circuit 121. Specifically, the receiving circuit 119 performs various signal processing on the MR signals output from the receiving coil 117, and then performs analog / digital (A / D (Analog to Digital)) conversion on the data that has been subjected to various signal processing to generate MR data. The receiving circuit 119 outputs the generated MR data to the imaging control circuit 121. For example, the MR data is generated for each coil element, and is output to the imaging control circuit 121 together with a tag that identifies the coil element.

[0024] The imaging control circuit 121 controls the gradient magnetic field power supply 105, the transmission circuit 113, the reception circuit 119, etc. according to the imaging protocol output from the processing circuit 15, and performs imaging of the subject P. The imaging protocol has a pulse sequence according to the type of examination. The imaging protocol defines the magnitude of the current supplied to the gradient magnetic field coil 103 by the gradient magnetic field power supply 105, the timing at which the current is supplied to the gradient magnetic field coil 103 by the gradient magnetic field power supply 105, the magnitude and time width of the high frequency pulse supplied to the transmission coil 115 by the transmission circuit 113, the timing at which the high frequency pulse is supplied to the transmission coil 115 by the transmission circuit 113, the timing at which the MR signal is received by the reception coil 117, etc. When the imaging control circuit 121 drives the gradient magnetic field power supply 105, the transmission circuit 113, the reception circuit 119, etc. to image the subject P, and receives MR data from the reception circuit 119, the imaging control circuit 121 transfers the received MR data to the image processing device 1, etc.

[0025] The imaging control circuit 121 is realized by, for example, a processor. The imaging control circuit 121 realizes each function related to the processing content by reading a program that realizes the above processing content from the memory 13 and executing the program. The imaging control circuit 121 corresponds to the imaging control unit. In the above description, an example has been described in which the "processor" reads a program corresponding to each function from the memory 13 and executes the program, but the embodiment is not limited to this.

[0026] The term "processor" refers to circuits such as a CPU, a graphics processing unit (GPU), an application specific integrated circuit (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)).

[0027] For example, if the processor is a CPU, the processor realizes the function by reading and executing a program stored in the memory 13. On the other hand, if the processor is an ASIC, instead of storing a program in the memory 13, 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, but may be configured as a single processor by combining multiple independent circuits to realize the function. Also, although a single storage circuit has been described as storing a program corresponding to each processing function, multiple storage circuits may be distributed and arranged, and the processing circuit may read the corresponding program from each storage circuit.

[0028] The storage device 125 stores various programs executed in the system control circuit 123, various imaging protocols, imaging conditions including a plurality of imaging parameters that define the imaging protocols, and the like. The storage device 125 is, for example, a semiconductor memory element such as a RAM or a flash memory, a hard disk drive (HDD), a solid state drive (SSD), an optical disk, and the like. The storage device 125 may also be a drive device that reads and writes various information between a portable storage medium such as a compact disc (ROM) drive, a digital versatile disc (DVD) drive, or a flash memory. The data stored in the storage device 125 may be stored in the memory 13. In this case, the memory 13 functions as a substitute for the storage device 125.

[0029] The console 70 has a communication interface 11, a system control circuit 12, a memory 13, a processing circuit 15, and an input / output interface 17. As shown in Fig. 1, in the console 70, the communication interface 11, the system control circuit 12, the memory 13, and the processing circuit 15 are electrically connected by a bus. As shown in Fig. 1, the console 70 is connected to a network via the communication interface 11. The network is connected to, for example, various modalities and information processing systems in a medical institution, such as an HIS and a Radiology Information System (RIS), so as to be able to communicate with each other.

[0030] The communication interface 11 performs data communication with, for example, various modalities that capture images of the subject P in an examination on the subject P, a hospital information system (HIS), a picture archiving and communication system (PACS), etc. Any standard may be used for communication between the communication interface 11 and the various modalities and the hospital information system, and examples of such standards include HL7 (Health Level 7), DICOM (Digital Imaging and Communications in Medicine), or both.

[0031] The system control circuit 12 has a processor, memories such as a ROM (Read-Only Memory) and a RAM (Random Access Memory), etc., which are not shown as hardware resources, and uses a system control function to control the MRI apparatus 100. Specifically, the system control circuit 12 reads out a system control program stored in the storage device 125, expands it on the memory, and controls each circuit of the MRI apparatus 100 according to the expanded system control program.

[0032] For example, the system control circuit 12 reads out an imaging protocol from the storage device 125 based on imaging conditions input by an operator via the input / output interface 17. The system control circuit 12 transmits the imaging protocol to the imaging control circuit 121 and controls imaging of the subject P. The system control circuit 12 is realized by, for example, a processor. The system control circuit 12 may be incorporated in the processing circuit 15. In this case, the system control function is executed by the processing circuit 15, and the processing circuit 15 functions as a substitute for the system control circuit 12. The system control circuit 12 corresponds to a system control unit.

[0033] The memory 13 is realized by a storage circuit that stores various information. For example, the memory 13 is a storage device such as an HDD, SSD, or integrated circuit storage device. The memory 13 corresponds to a storage unit. In addition to an HDD or SSD, the memory 13 may be a drive device that reads and writes various information between a semiconductor memory element such as a random access memory (RAM) or a flash memory, an optical disk such as a compact disc (CD) or a digital versatile disc (DVD), a portable storage medium, or a semiconductor memory element such as a RAM. The memory 13 stores an image generating function 151 realized by the processing circuit 15 in the form of a program executable by a computer. The memory 13 stores image data generated by the image generating function 151.

[0034] The processing circuit 15 performs overall control of the console 70. The processing circuit 15 is realized by the above-mentioned processor or the like. The processing circuit 15 includes an image generating function 151 and a current control function 153. The processing circuit 15 that realizes the image generating function 151 corresponds to an image generating unit. The image generating function 151 is stored in the memory 13 in the form of a program executable by a computer. For example, the processing circuit 15 reads out the program from the memory 13 and executes it to realize a function corresponding to the program. In other words, the processing circuit 15 in a state in which the program has been read out has the image generating function 151.

[0035] The processing circuitry 15 generates an MR image based on the MR data by the image generation function 151. For example, the image generation function 151 generates an MR image by performing a Fourier transform on the MR data arranged in the k-space. Since a known process can be applied to generate the MR image, a description thereof will be omitted. The image generation function 159 stores the generated MR image in the memory 13.

[0036] The processing circuit 15 controls the supply of current to the multiple heaters built in the superconducting magnet 101 and the stop of the supply of the current by the current control function 153. The control of the current supply by the current control function 153 is performed, for example, when the superconducting magnet 101 is excited and when the superconducting magnet 101 is demagnetized. Specifically, before the superconducting magnet 101 is excited and demagnetized, the current control function 153 supplies current to the multiple heaters in the superconducting magnet 101. In addition, the current control function 153 compares the value of resistance (hereinafter referred to as resistance value) detected by the resistance detector 132 with a predetermined threshold value before and / or during the excitation and demagnetization. Next, if the resistance value is greater than the predetermined threshold value, the current control function 153 supplies current to the multiple heaters in the superconducting magnet 101.

[0037] The input / output interface 17 includes, for example, an input interface that accepts various instructions and information input from an operator, and an output interface that outputs various information. The input interface is realized by, for example, a trackball, a switch button, a mouse, a keyboard, a touchpad that performs input operations by touching the operation surface, a touch screen in which a display screen and a touchpad are integrated, a non-contact input circuit using an optical sensor, and a voice input circuit. The input interface is connected to the processing circuit 15, and converts input operations received from the operator into electrical signals and outputs them to the processing circuit 15.

[0038] In this specification, the input interface is not limited to an interface having physical operation parts such as a mouse, a keyboard, etc. For example, an example of the input interface 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 MRI apparatus 100 and outputs the electrical signal to a control circuit.

[0039] The output interface is realized by, for example, a display. The display displays various GUIs (Graphical User Interfaces) and MR images generated by the processing circuitry 15 under the control of the processing circuitry 15 or the system control circuitry 123. The display also displays imaging parameters related to the scan and various information related to image processing. The display is realized by, for example, a display device such as a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display or monitor known in the art.

[0040] The configuration of the MRI apparatus 100 according to this embodiment has been described above. The superconducting magnet 101 according to this embodiment will be described in detail below with reference to FIG.

[0041] Fig. 2 is a diagram showing an example of a circuit configuration of the superconducting magnet 101. As shown in Fig. 2, the superconducting magnet 101 has a PCS unit (or a PCS module) PM, a plurality of superconducting coils, a first protection circuit PRC1, a second protection circuit PRC2, and a quench-back unit QBU. The circuit configuration shown in Fig. 2 is an example, and can be changed as desired as long as the quench-back method can be implemented. Note that the superconducting magnet 101 may further have, for example, various circuits and heaters related to an ERDU (Emergency Ramp Down Unit).

[0042] The PCS unit (or PCS module) PM includes a first PCS, a second PCS, a first heater H1 provided adjacent to the first PCS, and a second heater H2 provided adjacent to the second PCS. As shown in FIG. 2, the first PCS and the second PCS are electrically connected in parallel at a first node N1 and a second node N2 by superconducting connection. The superconducting connection is realized, for example, by twisting filaments in a superconducting wire and then soldering, crimping, solid-state connection, or the like. Since other known methods can be applied to the superconducting connection, a description thereof will be omitted. One end of the first heater H1 and one end of the second heater H2 are electrically connected in series. The other end of the first heater H1 and the other end of the second heater H2 are electrically connected to a heater power source 131. The operation of the PCS unit (or PCS module) PM in excitation and demagnetization is not described here because known techniques can be applied to the operation. Note that the nodes may be referred to as taps.

[0043] The multiple superconducting coils are used to generate a static magnetic field and have different inductances. For example, as shown in FIG. 2, the multiple superconducting coils include a pair of middle coils, a center coil, a pair of side coils, and a pair of shield coils. The pair of middle coils, the center coil, the pair of side coils, and the pair of shield coils are electrically connected in series by superconducting connection. The pair of middle coils, the center coil, and the pair of side coils correspond to a main coil that forms a static magnetic field. The configuration of the main coil shown in FIG. 2 is an example, and may be realized by any known configuration.

[0044] The pair of shield coils is used to reduce leakage of the main magnetic field generated by the main coil to the outside of the bore 111. For example, the pair of shield coils generates a magnetic field in a direction opposite to that of the main magnetic field. This suppresses the leakage magnetic field to a value equal to or less than a specified value in the MRI apparatus 100.

[0045] The pair of middle coils and center coil have a smaller inductance and a smaller volume than the pair of side coils and the pair of shield coils. For ease of explanation, the pair of middle coils and center coil will be described below as a first superconducting coil having a first inductance and a first volume. The pair of middle coils and center coil may be collectively referred to as a small coil system.

[0046] The pair of side coils and the pair of shield coils have a larger inductance and a larger volume than the pair of middle coils and the center coil. For ease of explanation, the pair of side coils and the pair of shield coils will be described below as a second superconducting coil having a second inductance and a second volume. The superconducting coils in the superconducting magnet 101 according to the embodiment include a first superconducting coil having a first inductance and a first volume, and a second superconducting coil having a second inductance larger than the first inductance and a second volume larger than the first volume. The pair of side coils and the pair of shield coils may be collectively referred to as a large coil system.

[0047] As shown in Fig. 2, a third node N3 is provided by soldering to the superconducting wire (which may be referred to as a superconducting wire) between the second node N2 and the large coil system LCS. This electrically connects the superconducting wire to the third node N3. The third node N3 is electrically connected to the static magnetic field power supply 130, the resistance detector 132, the first protection circuit PRC1, and the ground (earth). The circuit configuration of the first protection circuit PRC1 is realized, for example, by connecting a plurality of diodes in parallel. The circuit configuration of the first protection circuit PRC1 is not limited to the above, and a known method can be applied, so a detailed description will be omitted.

[0048] As shown in Fig. 2, a fourth node N4 is provided by soldering to the superconducting wire between the first node N1 and the small coil system SCS. This electrically connects the superconducting wire to the fourth node N4. The static magnetic field power supply 130, the resistance detector 132, and the second protection circuit PRC2 are electrically connected to the fourth node N4. The circuit configuration of the second protection circuit PRC2 is similar to that of the first protection circuit PRC1, and a known method can be applied, so a detailed description will be omitted.

[0049] As shown in Fig. 2, a plurality of quench-back units QBU are provided for a plurality of superconducting coils. That is, a plurality of quench-back units QBU are provided corresponding to a plurality of superconducting coils. Specifically, as shown in Fig. 2, a plurality of quench-back units QBU are provided for a pair of middle coils, a pair of side coils, and a pair of shield coils. Note that, although a quench-back unit QBU is not provided for the center coil in Fig. 2, a quench-back unit QBU may be provided for the center coil.

[0050] The multiple quench back units QBU have multiple insulating layers provided on the multiple superconducting coils, and multiple conductive plates (which may be referred to as quench back plates) QBP that can supply heat to the multiple superconducting coils via the multiple insulating layers. The multiple plates QBP are plate-shaped metals that generate heat when electricity is passed through them. That is, the quench back plates QBP are electrically insulated by an insulating layer such as an insulating film, and are attached to the coil surface of the superconducting coil. The multiple quench back units QBU generate quenches in the multiple superconducting coils. The multiple quench back units QBU may be referred to as quench back devices, quench back mechanisms, quench back modules, etc.

[0051] In the example shown in Fig. 2, the multiple insulating layers and the multiple plates QBP are provided on a pair of middle coils, a pair of side coils, and a pair of shield coils. Specifically, the multiple insulating layers are provided on the exterior of the pair of middle coils, the pair of side coils, and the pair of shield coils. Each of the multiple plates QBP is provided on the surface of each of the multiple insulating layers opposite to the contact surface between the superconducting coil and each of the multiple insulating layers. In other words, an insulating layer is provided between the plate QBP and the superconducting coil.

[0052] A fifth node N5 is provided by soldering to the superconducting wire that electrically connects the small coil system SCS and the large coil system LCS. The fifth node N5 is electrically connected to a resistance detector 132. The resistance detector 132 detects the resistance of the small coil system SCS between the fourth node N4 and the sixth node N6 (hereinafter referred to as the small coil system resistance value). The resistance detector 132 also detects the resistance of the large coil system LCS between the third node N3 and the sixth node N6 (hereinafter referred to as the large coil system resistance value). If the small coil system resistance value or the large coil system resistance value is greater than a predetermined threshold, the current control function 153 supplies a current to one end of the first heater H1 and the second heater H2. The predetermined threshold corresponds to, for example, a resistance value in a quench occurrence state. Therefore, the resistance detector 132 corresponds to a detector that detects a quench in the small coil system SCS and / or the large coil system LCS.

[0053] As shown in Fig. 2, the first protection circuit PRC1, a plurality of plates (hereinafter referred to as first plates) QBP provided in the first superconducting coil in the small coil system SCS, and the sixth node N6 are electrically connected. As a result, the first plates (a plurality of plates included in the small coil system, two plates provided in a pair of middle coils in Fig. 2) provided in the first superconducting coil among the plurality of plates via an insulating layer, the second superconducting coil (a plurality of superconducting coils in the large coil system (a pair of shield coils and a pair of side coils)), the first protection circuit PRC1, and the third node N3 are electrically connected in series via the fifth node N5 and the sixth node N6 to form a first circuit.

[0054] As shown in Fig. 2, the second protection circuit PRC2, a plurality of plates (hereinafter referred to as second plates) QBP provided in the second superconducting coil in the large coil system LCS, and the sixth node N6 are electrically connected. As a result, the second plates (a plurality of plates included in the large coil system, in Fig. 2, four plates provided in a pair of side coils and a pair of shield coils) provided in the second superconducting coil through an insulating layer among the plurality of plates, the first superconducting coil (a plurality of superconducting coils in the small coil system (a pair of middle coils and a center coil)), the second protection circuit PRC2, and the fourth node N4 are electrically connected in series through the fifth node N5 and the sixth node N6 to form a second circuit. When a quench occurs in any one of the plurality of superconducting coils, a first current flows in the first circuit, and a second current smaller than the first current flows in the second circuit.

[0055] The specifications of the multiple quench back parts QBU are different depending on the multiple superconducting coils. The specifications of the multiple quench back parts QBU are, for example, at least one of the structure of the multiple insulating layers and the multiple plates QBP and the material of the multiple insulating layers and the multiple plates QBP. The structure of the multiple insulating layers and the multiple plates QBP specifically corresponds to at least one of the thickness of each of the multiple insulating layers, the area of ​​each of the multiple plates QBP, and the relative installation position of each of the multiple plates QBP with respect to the multiple superconducting coils. In addition, the material of the multiple insulating layers and the multiple plates corresponds to at least one of the thermal property of each of the multiple insulating layers and the thermal property of each of the multiple plates QBP. The thermal property is, for example, specific heat, thermal conductivity, etc.

[0056] Fig. 3 is a diagram showing an example of a quench back part QBU in one superconducting coil. As shown in Fig. 3, the thickness ILT of the insulating layer between the quench back plate QBP and the superconducting coil surface can be adjusted in advance depending on the purpose. For example, when manufacturing the superconducting magnet 101, the thickness ILT of the insulating layer can be set depending on the inductance, volume, etc. of the superconducting coil included in the small coil system SCS or the large coil system LCS.

[0057] 3, the thermal material of the quench back plate QBP can be adjusted in advance depending on the purpose. For example, when manufacturing the superconducting magnet 101, a metal having desired thermal properties can be selected and used as the thermal material of the quench back plate QBP depending on the inductance, volume, etc. of the superconducting coil included in the small coil system SCS or the large coil system LCS.

[0058] In addition, the thermal material of the insulating layer between the quench back plate QBP and the superconducting coil surface can be adjusted in advance according to the purpose, as shown in Fig. 3. For example, when manufacturing the superconducting magnet 101, an insulator having desired thermal properties can be selected and used as the thermal material of the insulating layer according to the inductance, volume, etc. of the superconducting coil included in the small coil system SCS or the large coil system LCS.

[0059] Fig. 4 is a diagram showing an example in which the installation area of ​​the quench-back plate QBP is changed. As shown in Fig. 4, the installation area of ​​the quench-back plate QBP can be adjusted in advance depending on the purpose. For example, when manufacturing the superconducting magnet 101, the installation area of ​​the quench-back plate QBP with respect to the superconducting coil can be set depending on the inductance, volume, etc. of the superconducting coil included in the small coil system SCS or the large coil system LCS. If the installation area of ​​the quench-back plate QBP is made larger, heat can be transferred to a larger number of turns (windings), and if it is made smaller, heat can be transferred to a smaller number of turns (windings).

[0060] On the side surface of the cylindrical shape formed by the superconducting coil, the magnetic flux density in the superconducting coil is high in the portion adjacent to the opening 111 of the cylindrical shape and is low in the central portion of the side surface of the cylinder. Meanwhile, the superconducting state depends on the magnetic flux and temperature, and the higher the magnetic flux, the lower the temperature required to maintain the superconducting state. In other words, the temperature margin required to maintain the superconducting state (the margin above the critical temperature of the superconducting state) is smaller the higher the magnetic flux density, and is larger the lower the magnetic flux density. In other words, the higher the magnetic flux density, the easier quenching occurs, and the lower the magnetic flux density, the harder quenching occurs.

[0061] FIG. 5 is a schematic diagram showing an example of a temperature margin on the side of a superconducting coil. Arrows CD in FIG. 5 indicate the circumferential direction of the cylindrical superconducting coil. As shown in FIG. 5, on the surface of the cylindrical superconducting coil, the ends of the cylinder are regions TML where the temperature margin is low. Also, as shown in FIG. 5, on the surface of the cylindrical superconducting coil, the central part of the cylinder is a region TMH where the temperature margin is high. That is, a region with a low temperature margin is distributed on the end face side of the superconducting coil, and a region with a high coil temperature margin is distributed on the central side of the superconducting coil.

[0062] When the quench back plate QBP is placed in the region TML where the temperature margin is low, the quench is accelerated. On the other hand, when the quench back plate QBP is placed in the region TMH where the temperature margin is high, the onset of the quench is delayed.

[0063] The thickness of each of the multiple insulating layers, the area of ​​each of the multiple plates QBP, the relative installation position of each of the multiple plates QBP with respect to the multiple superconducting coils, the thermal properties of each of the multiple insulating layers, and the thermal properties of each of the multiple plates are set to reduce the difference between the second current and the first current.

[0064] For example, the thickness of each of the insulating layers, the area of ​​each of the plates QBP, the relative installation positions of each of the plates QBP with respect to the superconducting coils, the thermal properties of each of the insulating layers, and the thermal properties of each of the plates QBP are set so as to bring the value of the first current closer to the value of the second current. At this time, the settings of the thickness of each of the insulating layers, the area of ​​each of the plates QBP, the relative installation positions of each of the plates QBP with respect to the superconducting coils, the thermal properties of each of the insulating layers, and the thermal properties of each of the plates QBP have at least one of the following four settings:

[0065] (1) The thickness of a second insulating layer among the plurality of insulating layers located between the second superconducting coil and the second plate is thicker than the thickness of a first insulating layer among the plurality of insulating layers located between the first superconducting coil and the first plate. (2) The specific heat and / or thermal conductivity of the second plate is lower than the specific heat and / or thermal conductivity of the first plate. (3) The specific heat and / or thermal conductivity of the second insulating layer is lower than the specific heat and / or thermal conductivity of the first insulating layer. (4) The relative installation position of the second plate with respect to the second superconducting coil is set to a central portion of the superconducting coil as compared with the relative installation position of the first plate with respect to the first superconducting coil.

[0066] The thickness of each of the insulating layers, the area of ​​each of the plates QBP, the relative installation position of each of the plates QBP with respect to the superconducting coils, the thermal property of each of the insulating layers, and the thermal property of each of the plates QBP may be set so as to bring the value of the second current closer to the value of the first current. In this case, the thickness of each of the insulating layers, the area of ​​each of the plates QBP, the relative installation position of each of the plates QBP with respect to the superconducting coils, the thermal property of each of the insulating layers, and the thermal property of each of the plates QBP are set to at least one of the following four settings:

[0067] (1) The thickness of a first insulating layer among the plurality of insulating layers located between the first superconducting coil and the first plate is thinner than the thickness of a second insulating layer among the plurality of insulating layers located between the second superconducting coil and the second plate. (2) The specific heat and / or thermal conductivity of the first plate is higher than the specific heat and / or thermal conductivity of the second plate. (3) The specific heat and / or thermal conductivity of the first insulating layer is higher than the specific heat and / or thermal conductivity of the second insulating layer. (4) The relative installation position of the first plate with respect to the first superconducting coil is set to an end of the superconducting coil as compared with the relative installation position of the second plate with respect to the second superconducting coil.

[0068] The superconducting magnet 101 according to the embodiment described above includes a plurality of superconducting coils having different inductances used for generating a static magnetic field, a plurality of insulating layers provided on the plurality of superconducting coils, and a plurality of conductive plates QBP capable of supplying heat to the plurality of superconducting coils via the plurality of insulating layers, and includes a plurality of quench back units QBU that generate a quench for the plurality of superconducting coils, and the specifications of the plurality of quench back units QBU differ according to the plurality of superconducting coils. The specifications of the plurality of quench back units QBU in the superconducting magnet 101 according to the embodiment are at least one of the structure of the plurality of insulating layers and the plurality of plates QBP and the material of the plurality of insulating layers and the plurality of plates QBP. In the superconducting magnet 101 according to the embodiment, the structure of the plurality of insulating layers and the plurality of plates corresponds to at least one of the thickness of each of the plurality of insulating layers, the area of ​​each of the plurality of plates QBP, and the relative installation position of each of the plurality of plates QBP with respect to the plurality of superconducting coils. In the superconducting magnet 101 according to the embodiment, the materials of the insulating layers and the plates QBP correspond to at least one of the thermal properties of each of the insulating layers and the thermal properties of each of the plates QBP.

[0069] In the superconducting magnet 101 according to the embodiment, the thickness of each of the insulating layers, the area of ​​each of the plates QBP, the relative installation positions of each of the plates QBP with respect to the superconducting coils, the thermal properties of each of the insulating layers, and the thermal properties of each of the plates QBP are set so as to reduce the difference between the second current and the first current. For example, in the superconducting magnet 101 according to the embodiment, the thickness of each of the insulating layers, the area of ​​each of the plates QBP, the relative installation positions of each of the plates QBP with respect to the superconducting coils, the thermal properties of each of the insulating layers, and the thermal properties of each of the plates MB are set so as to bring the value of the first current closer to the value of the second current.

[0070] Specifically, in the superconducting magnet 101 according to the embodiment, at least one of the following is realized: the thickness of the second insulating layer among the plurality of insulating layers, which is located between the second superconducting coil and the second plate, is thicker than the thickness of the first insulating layer among the plurality of insulating layers, which is located between the first superconducting coil and the first plate; the specific heat and / or thermal conductivity of the second plate is lower than the specific heat and / or thermal conductivity of the first plate; the specific heat and / or thermal conductivity of the second insulating layer is lower than the specific heat and / or thermal conductivity of the first insulating layer; and the relative installation position of the second plate with respect to the second superconducting coil is set to a central portion of the superconducting coil compared to the relative installation position of the first plate with respect to the first superconducting coil.

[0071] Fig. 6 is a diagram showing an example of the decay of the first current and the second current when a quench occurs in a pair of shield coils, with the same specifications for the multiple quench-back units regardless of the multiple superconducting coils, as a comparative example. As shown in Fig. 6, the decay of the second current flowing through the small coil system is slower than the decay of the first current flowing through the large coil system. The difference between the first current and the second current at the same elapsed time shown in Fig. 6 causes the generation of a leakage magnetic field.

[0072] FIG. 7 is a diagram showing an example of attenuation of the first current and the second current when the specifications of the multiple quench back parts are different according to the multiple superconducting coils and a quench occurs in a pair of shield coils according to this embodiment. In FIG. 7, the thickness of each of the multiple insulating layers, the area of ​​each of the multiple plates QBP, the relative installation position of each of the multiple plates QBP with respect to the multiple superconducting coils, the thermal property of each of the multiple insulating layers, and the thermal property of each of the multiple plates QBP are set so that the value of the first current approaches the value of the second current. As shown in FIG. 7, the attenuation of the second current flowing through the small coil system is the same as in FIG. 6, but the attenuation of the first current flowing through the large coil system approaches the attenuation of the second current. Therefore, as shown in FIG. 6 and FIG. 7, according to the superconducting magnet 101 according to this embodiment, it is possible to reduce the leakage magnetic field compared to the comparative example.

[0073] The time required for quenching back is determined by the heat transfer time according to the distance (thickness) of the insulating layer between the quenching back plate QBP and the coil surface of the superconducting coil, the thermal properties of the insulating layer and the quenching back plate QBP, and the temperature margin on the coil surface of the superconducting coil. Therefore, according to the superconducting magnet 101 of this embodiment, the time required for quenching back (the heat transfer time from the quenching back plate QBP to the superconducting coil) can be arbitrarily determined by adjusting the material of the insulating layer, the material of the quenching back plate QBP, the distance (thickness) of the insulating layer, and the arrangement (installation position) of the quenching back plate QBP according to the distribution of the temperature margin. From these facts, according to the superconducting magnet 101 of this embodiment, the specifications of the multiple quenching back parts can be set differently according to the multiple superconducting coils so as to reduce the current difference (the difference between the first current and the second current) between the first circuit related to the small coil system and the second circuit related to the large coil system.

[0074] From the above, the superconducting magnet 101 according to this embodiment can reduce the primary expansion of the leakage magnetic field distribution due to the deviation in the current decay rate, and the effects on the mechanical strength and image adjustment due to eddy currents generated in the conductor near the superconducting coil.

[0075] When the technical ideas in the embodiments are realized in a magnetic resonance imaging apparatus 100, the magnetic resonance imaging apparatus 100 includes a superconducting magnet 101 having superconducting coils with different inductances used to generate a static magnetic field, a plurality of insulating layers provided on the superconducting coils, a plurality of conductive plates QBP capable of supplying heat to the superconducting coils via the insulating layers, and a plurality of quench back units QBU that generate a quench in the superconducting coils, and the specifications of the quench back units QBU differ according to the superconducting coils. The configuration and effects of the superconducting magnet 101 in the magnetic resonance imaging apparatus 100 are similar to those in the embodiments, and therefore will not be described.

[0076] According to at least one of the embodiments described above, when a quench occurs in the quench-back system, the difference in current between a plurality of superconducting coils having different inductances can be reduced.

[0077] 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]

[0078] 11 Communication Interface 12 System Control Circuit 13. Memory 15 Processing circuit 17 Input / Output Interface 100 Magnetic resonance imaging device 101 Superconducting magnet 103 Gradient magnetic field coil 105 Gradient magnetic field power supply 107 Bed 109 Bed Control Circuit 111 Bore (opening) 113 Transmitting circuit 115 Transmitting Coil 117 Receiving coil 119 Receiving circuit 121 Imaging control circuit 125 Storage device 130 Static magnetic field power supply (external power supply) 131 Heater power supply 132 Resistance detector 151 Image generation function 153 Current control function

Claims

1. A plurality of superconducting coils having different inductances are used to generate a static magnetic field; a plurality of quench-back sections each having a plurality of insulating layers provided on the plurality of superconducting coils and a plurality of conductive plates capable of supplying heat to the plurality of superconducting coils via the plurality of insulating layers, and each quenching the plurality of superconducting coils; Equipped with The multiple quench back units have different specifications depending on the multiple superconducting coils. Superconducting magnet.

2. The specification is at least one of a structure of the insulating layers and the plates and a material of the insulating layers and the plates.

2. The superconducting magnet according to claim 1.

3. a structure relating to the plurality of insulating layers and the plurality of plates corresponds to at least one of a thickness of each of the plurality of insulating layers, an area of ​​each of the plurality of plates, and a relative installation position of each of the plurality of plates with respect to the plurality of superconducting coils; 3. The superconducting magnet according to claim 2.

4. Materials of the plurality of insulating layers and the plurality of plates correspond to at least one of the thermal properties of each of the plurality of insulating layers and the thermal properties of each of the plurality of plates.

3. The superconducting magnet according to claim 2.

5. the plurality of superconducting coils include a first superconducting coil having a first inductance and a first volume, and a second superconducting coil having a second inductance larger than the first inductance and a second volume larger than the first volume; a first circuit electrically connecting in series a first plate, which is provided on the first superconducting coil through the insulating layer, the second superconducting coil, and a first protection circuit; a second circuit electrically connecting in series a second plate among the plurality of plates electrically connected to the second superconducting coil, the first superconducting coil, and a second protection circuit; having When a quench occurs in any one of the plurality of superconducting coils, a first current flows in the first circuit, and a second current smaller than the first current flows in the second circuit.

5. A superconducting magnet according to claim 1.

6. The specification is at least one of a structure related to the plurality of insulating layers and the plurality of plates and a material related to the plurality of insulating layers and the plurality of plates, a structure relating to the plurality of insulating layers and the plurality of plates corresponds to at least one of a thickness of each of the plurality of insulating layers, an area of ​​each of the plurality of plates, and a relative installation position of each of the plurality of plates with respect to the plurality of superconducting coils; Materials of the plurality of insulating layers and the plurality of plates correspond to at least one of a thermal property of each of the plurality of insulating layers and a thermal property of each of the plurality of plates; a thickness of each of the plurality of insulating layers, an area of ​​each of the plurality of plates, a relative installation position of each of the plurality of plates with respect to the plurality of superconducting coils, a thermal property of each of the plurality of insulating layers, and a thermal property of each of the plurality of plates are set so as to reduce a difference between the second current and the first current.

6. The superconducting magnet according to claim 5.

7. a thickness of each of the plurality of insulating layers, an area of ​​each of the plurality of plates, a relative installation position of each of the plurality of plates with respect to the plurality of superconducting coils, a thermal property of each of the plurality of insulating layers, and a thermal property of each of the plurality of plates are set so as to make a value of the first current close to a value of the second current; 7. The superconducting magnet according to claim 6.

8. The thickness of each of the insulating layers, the area of ​​each of the plates, the relative installation positions of each of the plates with respect to the superconducting coils, the thermal properties of each of the insulating layers, and the thermal properties of each of the plates are set as follows: A thickness of a second insulating layer located between the second superconducting coil and the second plate among the plurality of insulating layers is thicker than a thickness of a first insulating layer located between the first superconducting coil and the first plate among the plurality of insulating layers; the specific heat and / or thermal conductivity of the second plate is lower than the specific heat and / or thermal conductivity of the first plate; The specific heat and / or thermal conductivity of the second insulating layer is lower than the specific heat and / or thermal conductivity of the first insulating layer; a relative installation position of the second plate with respect to the second superconducting coil is set to a central portion of the superconducting coil as compared with a relative installation position of the first plate with respect to the first superconducting coil; and having at least one of the following: The superconducting magnet according to claim 7.

9. a thickness of each of the plurality of insulating layers, an area of ​​each of the plurality of plates, a relative installation position of each of the plurality of plates with respect to the plurality of superconducting coils, a thermal property of each of the plurality of insulating layers, and a thermal property of each of the plurality of plates are set so as to make a value of the second current close to a value of the first current.

7. The superconducting magnet according to claim 6.

10. The thickness of each of the insulating layers, the area of ​​each of the plates, the relative installation positions of each of the plates with respect to the superconducting coils, the thermal properties of each of the insulating layers, and the thermal properties of each of the plates are set as follows: a thickness of a first insulating layer located between the first superconducting coil and the first plate among the plurality of insulating layers is thinner than a thickness of a second insulating layer located between the second superconducting coil and the second plate among the plurality of insulating layers; the specific heat and / or thermal conductivity of the first plate is higher than the specific heat and / or thermal conductivity of the second plate; The specific heat and / or thermal conductivity of the first insulating layer is higher than the specific heat and / or thermal conductivity of the second insulating layer; a relative installation position of the first plate with respect to the first superconducting coil is set to an end of the superconducting coil as compared with a relative installation position of the second plate with respect to the second superconducting coil; and having at least one of the following:

10. The superconducting magnet according to claim 9.

11. A plurality of superconducting coils having different inductances are used to generate a static magnetic field; a plurality of quench-back sections each including a plurality of insulating layers provided on the plurality of superconducting coils and a plurality of conductive plates capable of supplying heat to the plurality of superconducting coils via the plurality of insulating layers, the quench-back sections generating quenches in the plurality of superconducting coils; A superconducting magnet having The specifications of the plurality of quench-back units differ depending on the plurality of superconducting coils. Magnetic resonance imaging device.

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