JP2024053665A - Superconducting magnet and magnetic resonance imaging device - Google Patents

Abstract

[Problem] To provide a superconducting magnet capable of reducing consumption of refrigerant during demagnetization and excitation. [Solution] The present invention comprises a superconducting coil according to an embodiment, a plurality of persistent current switches, a heater, and a thermal conductor. The superconducting coil generates a static magnetic field. The plurality of persistent current switches are electrically connected to the superconducting coil. The heater is provided inside at least one of the plurality of persistent current switches. The thermal conductor is provided between two adjacent persistent current switches in the plurality of persistent current switches, and is capable of thermally conducting self-heating by one of the plurality of persistent current switches that has been made normal conductive by the heater to the other persistent current switch. [Selected Figure] Figure 2

Description

The embodiments disclosed in this specification and the drawings relate to a superconducting magnet and a magnetic resonance imaging device.

Conventionally, when a superconducting magnet is excited or demagnetized, a current is swept into the superconducting magnet from an external power source. At this time, a persistent current switch (hereafter referred to as PCS), which is connected in parallel to the superconducting coil in a superconducting circuit, is temporarily made normal conductive. A relatively common thermal PCS employs a method in which a heater built into the PCS is energized to generate heat, thereby making the PCS normal conductive and maintaining it.

The superconducting magnet is immersed in a coolant such as liquid helium. The PCS is also immersed in the coolant. When excitation and demagnetization are performed, current also flows through the normally conductive PCS. This causes the PCS to self-heat. As a result, the liquid helium is vaporized due to the self-heating of the PCS and the heat generated by the heater, and is discharged outside the superconducting magnet. In order to suppress the self-heating of the PCS, measures can be taken to increase the combined resistance by connecting multiple PCSs in series. On the other hand, the more PCSs there are, the more heaters are built into the PCS. This causes the total amount of heat generated by the heaters to increase, which can lead to increased consumption of liquid helium.

JP 2015-167827 A

One of the problems that the embodiments disclosed in this specification and the drawings aim to solve is to provide a superconducting magnet that can reduce the consumption of refrigerant during demagnetization and excitation. However, the problems that the embodiments disclosed in this specification and the drawings aim to solve are not limited to the above problem. Problems that correspond to the effects of each configuration shown in the embodiments described below can also be positioned as other problems.

The superconducting magnet according to the embodiment includes a superconducting coil, a plurality of PCSs, a heater, and a thermal conductor. The superconducting coil generates a static magnetic field. The plurality of PCSs are electrically connected to the superconducting coil. The heater is provided inside at least one of the plurality of PCSs. The thermal conductor is provided between two adjacent PCSs in the plurality of PCSs, and is capable of thermally conducting the self-heating of one of the plurality of PCSs that has been made normal conductive by the heater to the other PCS.

FIG. 1 is a diagram showing an example of a magnetic resonance imaging apparatus according to an embodiment. FIG. 2 is a diagram showing an example of a cross section of a PCS unit (or a PCS module) according to an embodiment. FIG. 3 is a flowchart illustrating an example of a procedure of a current supply control process according to the embodiment. FIG. 4 is a diagram showing an example of a closed circuit and components related to the closed circuit when performing excitation and demagnetization of a superconducting magnet having two PCSs, one in parallel and two in series, according to an embodiment. FIG. 5 is a diagram showing an example of a cross section of a PCS unit (or a PCS module) according to a modified example of the embodiment. FIG. 6 is a diagram showing an example of a closed circuit and components related to the closed circuit when excitation and demagnetization are performed for a superconducting magnet having six PCSs, two in parallel and three in series, according to a modified example of the embodiment. FIG. 7 is a diagram showing an example of a current control device together with an MRI apparatus according to an application example of the embodiment.

Below, embodiments of a superconducting magnet and a magnetic resonance imaging device will be described with reference to the drawings. In the following embodiments, parts with the same reference numbers perform similar operations, and duplicated descriptions will be omitted as appropriate. The functions in the embodiments are not limited to magnetic resonance imaging (MRI) devices, and may be realized, for example, by a PET (Positron Emission Tomography)-MRI device, a SPECT (single photon emission computed tomography)-MRI device, etc.

(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 coil 103, a gradient 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 system control circuit (system control unit) 12, a storage device 125, 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.

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 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 device 100. The functional configuration in this case will be described in the application example.

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 superconducting coil that generates a static magnetic field, and a PCS (Persistent Current Switch) unit (or PCS module). The PCS unit has a number of PCSs electrically connected to the superconducting coil, and a heater provided inside at least one of the PCSs. In the following, for the sake of concrete explanation, the number of PCS switches will be described as two (a first PCS and a second PCS). Note that the number of PCS switches is not limited to two. As an example, a case in which the number of PCS switches is three will be described in the application example.

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. When the mode subsequently transitions 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 PCS switches 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.

2 is a diagram showing an example of a cross section of a PCS unit (or PCS module) 80. As shown in FIG. 2, the first PCS 10 and the second PCS 20 in the superconducting magnet 101 are arranged adjacent to each other. That is, as shown in FIG. 2, the second PCS 20 is arranged on one side of the first PCS 10. As shown in FIG. 2, the first PCS 10 and the second PCS 20 in the superconducting magnet 101 have a superconducting wire 2 and a heater wire 3 wound around a winding core 1 formed of a heat insulating material. That is, as shown in FIG. 2, the heater wire 3 has a structure in which it is wound together with the superconducting wire 2 and is close to the superconducting wire 2. This allows the heat generated by the heater wire 3 to be efficiently transferred to the superconducting wire 2. The heater wire 3 is an example of a heater. In FIG. 2, the heater 3 is provided in each of the multiple PCSs, but it may be provided in a specific PCS (the first PCS 10).

The side of the first PCS 10 and the side of the second PCS 20 are formed by a heat transfer plate 5 and an outer cylinder 6. In the first PCS 10 and the second PCS 20, the gaps between the winding core 1, the superconducting wire 2, the heater wire 3, the heat transfer plate 5, and the outer cylinder 6 are filled with molding resin material 4, as shown in FIG. 2.

When the first PCS 10 and the second PCS 20 are electrically connected, the first PCS 10 and the second PCS 20 are arranged so that their sides are adjacent to each other. At this time, the gap at the boundary between the first PCS 10 and the second PCS 20 is filled with the thermal conductor 7. That is, the thermal conductor 7 is provided between two adjacent PCSs in the plurality of PCSs. At this time, the thermal conductor 7 can thermally conduct the self-heating of one of the plurality of PCSs that has been made normally conductive by the heater wire (heater) 3 to the other PCS. In other words, the first PCS 10 and the second PCS are thermally connected via the thermal conductor 7.

The thermal conductor 7 is made of, for example, a metal. Note that the thermal conductor 7 is not limited to a metal, and any known thermal conductive material can be used. The metal as the thermal conductor 7 is, for example, solder. Note that the metal is not limited to solder, and may be other metals as long as they have thermal conductivity. When the thermal conductor 7 is solder, the above-mentioned gap is filled with solder as the thermal conductor 7.

As shown in FIG. 2, a heat insulating material 8 is disposed on the other side opposite the boundary surface between the first PCS 10 and the second PCS 20. The heat insulating material 8 is, for example, glass-fiber-reinforced plastics (GFRP). Note that the heat insulating material 8 is not limited to GFRP material, and other known materials may be used.

For the above reasons, in the first PCS 10 and the second PCS 20, at least the side where the two PCSs are adjacent is made of a heat conductor 7 (metal) having high thermal conductivity, and the winding core 1 and the outer frame (e.g., the insulation material 8 and the outer tube 6) are made of an insulating material with low thermal conductivity. This allows the adjacent first PCS 10 and second PCS 20 to transfer heat to each other efficiently.

The gradient coil 103 is a hollow coil formed in a substantially cylindrical shape, and is disposed on the inner surface side of a cylindrical cooling vessel. The gradient coil 103 receives current individually from the gradient power supply 105 to generate gradient magnetic fields whose magnetic field strength changes along 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 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 the MR signal according to a spatial position.

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

The bed 107 is a device equipped with a tabletop 1071 on which the subject P is placed. Under the control of the bed control circuit 109, the bed 107 inserts the tabletop 1071 on which the subject P is placed into the bore 111.

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 instructions from the operator via the input/output interface 17, thereby moving the tabletop 1071 in the longitudinal direction, the vertical direction, and in some cases the horizontal direction.

Under the control of the imaging control circuit 121, the transmission circuit 113 supplies radio frequency pulses modulated at the Larmor frequency to the transmission coil 115. For example, the transmission circuit 113 has an oscillator, a phase selection unit, a frequency conversion unit, an amplitude modulation unit, an RF amplifier, and the like. The oscillator generates an RF pulse with a resonance frequency specific to the target atomic nucleus in a static magnetic field. The phase selection unit selects the phase of the RF pulse generated by the oscillator. 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.

The transmission coil 115 is an RF (Radio Frequency) coil arranged inside the gradient magnetic field coil 103. The transmission coil 115 generates an RF pulse equivalent to a high frequency magnetic field in response to the output from the transmission circuit 113.

The receiving coil 117 is an RF coil arranged 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 multiple coil elements. For the sake of concrete explanation, the receiving coil 117 will be described below as a coil array having multiple coil elements.

The receiving coil 117 may be composed of a single coil element. Also, although the transmitting coil 115 and the receiving coil 117 are shown 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 the imaging site of the subject P, and is, for example, a local transmitting/receiving RF coil such as a head coil.

Under the control of the imaging control circuit 121, the receiving circuit 119 generates magnetic resonance data (hereinafter referred to as MR data) as a digital MR signal based on the MR signal output from the receiving coil 117. Specifically, the receiving circuit 119 performs various signal processing on the MR signal 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 output to the imaging control circuit 121 together with a tag that identifies the coil element.

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 gradient magnetic field power supply 105 supplies the current to the gradient magnetic field coil 103, 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.

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 explanation, an example was explained in which the "processor" reads a program corresponding to each function from the memory 13 and executes it, but the embodiment is not limited to this.

The term "processor" refers to circuits such as a CPU, a GPU (Graphics Processing Unit), 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)).

When the processor is, for example, a CPU, the processor realizes a function by reading and executing a program stored in memory 13. On the other hand, when the processor is an ASIC, instead of storing a program in 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 its 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.

The storage device 125 stores various programs executed in the system control circuit 12, 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 (CD)-ROM drive, a digital versatile disc (DVD) drive, or a flash memory. The data stored in the storage device 125 may also be stored in the memory 13. In this case, the memory 13 functions as a substitute for the storage device 125.

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 the medical institution, such as a HIS and a radiology information system (RIS), so that they can communicate with each other. The console 70 may also include a static magnetic field power supply 130, a heater power supply 131, and a resistance detector 132.

The communication interface 11 performs data communication between, for example, various modalities that image the subject P during an examination of the subject P, a hospital information system (HIS), a picture archiving and communication systems (PACS), and the like. The standard for communication between the communication interface 11 and the various modalities and the hospital information system may be any standard, but examples of such standards include HL7 (Health Level 7), DICOM (Digital Imaging and Communications in Medicine), or both.

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

For example, the system control circuit 12 reads out an imaging protocol from the storage device 125 based on imaging conditions input by the 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.

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 RAM (Random Access Memory) or a flash memory, an optical disk such as a CD (Compact Disc) or a DVD (Digital Versatile Disc), a portable storage medium, or a semiconductor memory element such as a RAM. The memory 13 stores the image generation function 151 and the current control function 153 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 generation function 151.

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 has an image generation function 151, a current control function 153, and the like. The processing circuit 15 that realizes the image generation function 151 and the current control function 153, respectively, corresponds to an image generation unit and a current control unit. Each function, such as the image generation function 151 and the current control function 153, is stored in the memory 13 in the form of a program executable by a computer. For example, the processing circuit 15 realizes the function corresponding to each program by reading and executing the program from the memory 13. In other words, the processing circuit 15 in a state in which each program has been read has each function, such as the image generation function 151 and the current control function 153.

The processing circuitry 15 generates an MR image based on the MR data using the image generation function 159. For example, the image generation function 151 generates an MR image by performing a Fourier transform on the MR data arranged in k-space. Since known processes 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.

The processing circuit 15 uses the current control function 153 to control the supply of current to the first heater built into the first PCS 10 and the second heater built into the second PCS 20 and to stop the supply of the current. The control of the current supply by the current control function 153 is performed, for example, when the superconducting magnet 101 is excited and demagnetized.

Specifically, before the superconducting magnet 101 is excited and demagnetized, the current control function 153 supplies a current to the first heater in the first PCS 10. That is, the current control function 153 supplies a current to the heater in one of the multiple PCSs. Also, before and/or during the excitation and demagnetization, the current control function 153 compares the resistance value (hereinafter referred to as the resistance value) detected by the resistance detector 132 with a predetermined threshold. Then, if the resistance value is smaller than the predetermined threshold, the current control function 153 supplies a current to the second heater in the second PCS 20. That is, the current control function 153 controls the supply of a current to the heater in the other PCS according to the resistance value. Also, when a current is being supplied to the second heater, if the resistance value is larger than the predetermined threshold, the current control function 153 stops the supply of a current to the second heater. The procedure of the process of controlling the supply of a current from the heater power source 131 to the multiple heaters (hereinafter referred to as the current supply control process) will be described later.

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 touchscreen that integrates a display screen and a touchpad, a non-contact input circuit that uses 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.

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

The output interface is realized, for example, by a display. Under the control of the processing circuitry 15 or the system control circuitry 12, the display displays various GUIs (Graphical User Interfaces) and MR images generated by the processing circuitry 15. The display also displays imaging parameters related to the scan and various information related to image processing. The display is realized, for example, by a display device such as a CRT display, liquid crystal display, organic EL display, LED display, plasma display, or any other display or monitor known in the art.

The static magnetic field power supply 130 is electrically connected to a closed circuit in the superconducting magnet 101 during excitation and demagnetization of the superconducting magnet 101. The static magnetic field power supply 130 may be referred to as an external power supply, for example, since it is provided outside the gantry of the MRI apparatus 100. When exciting the superconducting magnet 101, the static magnetic field power supply 130 supplies a current to the superconducting magnet 101 until the value of the current flowing through the superconducting magnet 101 reaches a specified value. The specified value is, for example, a current value corresponding to the strength of the static magnetic field. The specified value is set in advance and stored in the memory 13 or the storage device 125. When demagnetizing the superconducting magnet 101, the static magnetic field power supply 130 reduces the current flowing through the superconducting magnet 101 until the current flowing through the superconducting magnet 101 becomes zero.

The heater power supply 131 is electrically connected to the heater wire 3 during excitation and demagnetization of the superconducting magnet 101. The heater power supply 131 supplies current to the heater 3 under the control of the current control function 153. Note that the functions realized by the heater power supply 131 may be integrated into the static magnetic field power supply 130.

The resistance detector 132 is electrically connected to the closed circuit of the superconducting magnet 101 in parallel with the static magnetic field power supply 130 when the superconducting magnet 101 is excited and demagnetized. The resistance detector 132 detects the resistance in the closed circuit. The resistance detector 132 outputs the detected resistance value (resistance value) to the processing circuit 15. In this way, the resistance detector 132 monitors the resistance of the closed circuit in the superconducting magnet 101 when the superconducting magnet 101 is excited and demagnetized. The resistance detector 132 corresponds to a resistance detection unit.

The current supply control process executed by the MRI apparatus 100 of this embodiment configured as described above will be described with reference to Figs. 3 and 4. The current supply control process is executed during excitation and demagnetization of the superconducting magnet 101. To make the explanation more specific, the procedure for the current supply control process will be described below using the excitation of the superconducting magnet 101 as an example.

Figure 3 is a flowchart showing an example of a procedure for current supply control processing. Figure 4 is a diagram showing an example of a closed circuit and components related to the closed circuit when performing excitation and demagnetization of a superconducting magnet 101 having two PCSs (first PCS 10 and second PCS 20) with one in parallel and two in series.

(Current supply control process)
(Step S301)
An external power supply 130 is electrically connected to the closed circuit, thereby forming a circuit for supplying a current to the superconducting coil SCC.

(Step S302)
The resistance detector 132 starts monitoring the resistance value of the closed circuit. Through this monitoring, the resistance detector 132 detects the resistance in the closed circuit. Through the detection of the resistance, the resistance detector 132 outputs data related to the resistance value to the processing circuit 15.

(Step S303)
The processing circuit 15 supplies current from the heater power supply HPS to the first heater H1 by the current control function 153. As a result, the first heater H1 generates heat, and the first PCS 10 becomes a normal conductive state as shown in Fig. 4. Next, the Joule heat generated by the current flowing through the first PCS 10 is transferred to the second PCS 20 via the heat transfer plate 5 in the first PCS 10 and the thermal conductor 7 between the first PCS 10 and the second PCS 20. As a result, the temperature of the second PCS rises.

(Step S304)
The processing circuit 15 compares the resistance value with the threshold value by the current control function 153. If the resistance value is less than the threshold value (NO in step S304), the process of step S305 is executed. The state in which the resistance value is less than the threshold value corresponds to, for example, the second PCS not reaching a normal conductive state due to the heat transferred from the first PCS 10 to the second PCS 20. If the resistance value is equal to or greater than the threshold value (YES in step S304), the process of step S306 is executed. The state in which the resistance value is equal to or greater than the threshold value corresponds to, for example, the second PCS reaching a normal conductive state due to the heat transferred from the first PCS 10 to the second PCS 20.

(Step S305)
The processing circuit 15 supplies current from the heater power supply HPS to the second heater H2 by the current control function 153. This causes the second heater H2 to generate heat and the second PCS 20 to enter a normal conducting state. After this step, the processing of step S304 is repeated.

(Step S306)
A current is supplied to the closed circuit from the external power source 130. At this time, the external power source 130 gradually increases the current supplied from the external power source 130 to the closed circuit until it reaches a predetermined value. The arrow shown in Fig. 4 indicates the direction CD of the current flowing through the closed circuit.

(Step S307)
The processing circuit 15 compares the current value with the specified value by the current control function 153. If the current value reaches the specified value (YES in step S307), the process proceeds to step S308. If the current value does not reach the specified value (NO in step S307), the process proceeds to step S304.

(Step S308)
The processing circuit 15 stops the supply of current to all the heaters by the current control function 153. Also, the resistance detector 132 stops monitoring the resistance value in the closed circuit.

(Step S309)
The current supply from the external power supply 130 to the closed circuit is reduced to zero. When the current supply to the closed circuit reaches zero, the external power supply 130 is electrically disconnected from the closed circuit, i.e., from the superconducting magnet 101. With this, the current supply control process ends.

The superconducting magnet 101 according to the embodiment described above has a heater provided inside at least one of the multiple PCSs electrically connected to the superconducting coil SCC, and a thermal conductor 7 capable of thermally conducting the self-heating of one of the multiple PCSs that has been made normal conductive by the heater to the other PCS. In the superconducting magnet 101 according to the embodiment, the thermal conductor 7 is made of, for example, a metal, and the metal is, for example, solder. Also, in the superconducting magnet 101 according to the embodiment, the superconducting coil SCC and the multiple PCSs are immersed in a refrigerant related to the superconducting state, and in the superconducting state, the multiple PCSs and the superconducting coil SCC form a closed circuit.

For these reasons, according to the superconducting magnet 101 and MRI apparatus 100 of the embodiment, when the superconducting magnet 101 is excited and demagnetized, the first heater H1 included in a specific PCS (first PCS10 in Figures 2 to 4) among the multiple connected PCSs (self-heating conductive type PPCS) is heated and put into a normal conductive state. Thereafter, with a current sweep from the external power supply 130 to the superconducting magnet SCC, only the specific PCS (for example, first PCS10) self-heats. As a result, the heat generated in the first PCS10 can be conducted to the other PCS (second PCS20), making all the PCSs normal conductive.

The MRI device 100 having the superconducting magnet 101 according to the embodiment also controls the supply and stop of current to the heater in order to control the current supplied to the superconducting coil SCC from the static magnetic field power supply 130 electrically connected to the closed circuit in the superconducting magnet SCC during excitation and demagnetization of the static magnetic field. For example, the MRI device 100 having the superconducting magnet 101 according to the embodiment detects the resistance in the closed circuit by a resistance detector 132 electrically connected to the closed circuit in parallel with the static magnetic field power supply 130 during excitation and demagnetization, and controls the supply of current to the heater in the other PCS according to the detected resistance value.

As a result, the MRI apparatus 100 according to the embodiment can monitor the resistance of the closed circuit in the superconducting magnet 101 to control ON/OFF of the heaters other than a specific heater among the multiple heaters. Therefore, the superconducting magnet 101 according to the embodiment can adaptively reduce the amount of heat applied to the multiple PCSs by the multiple heaters when the multiple PCSs are made normal conductive.

From the above, according to the superconducting magnet 101 and MRI device 100 of the embodiment, the combined resistance can be increased by making all of the multiple serially connected PCSs in a normal conductive state, while the consumption of the refrigerant (liquid helium) can be reduced by minimizing the heater heat generated to achieve and maintain normal conductivity. Therefore, according to the superconducting magnet 101 and MRI device 100 of the embodiment, the costs of exciting and demagnetizing the superconducting magnet 101 can be reduced.

(Modification)
This modification is to arrange multiple PCSs in a PCS unit (or PCS module) in two parallel and three series configurations. Note that, in this modification, multiple PCSs are described in two parallel and three series configurations, but the arrangement of the PCSs is not limited to this, and the arrangement of multiple PCSs can be set arbitrarily as long as heat can be transferred via the thermal conductor 7 to heat the adjacent PCSs to make them normal conductive.

Figure 5 is a diagram showing an example of a cross section of a PCS unit (or PCS module) 90 according to this modified example. As shown in Figure 5, in a plurality of PCSs (first PCS 10, second PCS 20, third PCS 30, fourth PCS 40, fifth PCS 50, sixth PCS 60), the second PCS 20 and the third PCS 30 are arranged adjacent to each other on both sides of the first PCS 10. Also, as shown in Figure 5, the fifth PCS 50 and the sixth PCS 60 are arranged adjacent to each other on both sides of the fourth PCS 40. In addition, as shown in Figure 5, the third PCS 30 and the fifth PCS 50 are arranged adjacent to each other.

The structure of each of the multiple PCSs is the same as in the embodiment, so a description is omitted. In addition, as in the embodiment, a thermal conductor 7 made of a metal material such as solder is provided between two adjacent PCSs among the multiple PCSs.

Figure 6 is a diagram showing an example of a closed circuit and components related to the closed circuit when performing excitation and demagnetization of a superconducting magnet 101 having six PCSs (first PCS10, second PCS20, third PCS30, fourth PCS40, fifth PCS50, sixth PCS60) with two in parallel and three in series. As shown in Figure 6, the three PCSs are electrically connected in series in the order of the second PCS20, the first PCS10, and the third PCS30. Also, as shown in Figure 6, the three PCSs are electrically connected in series in the order of the fifth PCS50, the fourth PCS40, and the sixth PCS60. Furthermore, the first PCS10, the second PCS20, and the third PCS30, which are electrically connected in series, and the fourth PCS40, the fifth PCS50, and the sixth PCS60, which are electrically connected in series, are electrically connected in parallel in the closed circuit in the superconducting magnet 101.

In the current supply control process in this modified example, in step S303, the processing circuit 15 uses the current control function 153 to supply current from the heater power supply HPS to the first heater in the first PCS 10 and the fourth heater in the fourth PCS 40. In step S305, the processing circuit 15 uses the current control function 153 to supply current from the heater power supply HPS to the second heater in the second PCS 20, the third heater in the third PCS 30, the fifth heater in the fifth PCS 50, and the sixth heater in the sixth PCS 60.

In the current supply control process in this modification, the processing circuit 15 may stop the supply of current to the second heater, the third heater, the fifth heater, and the sixth heater by the current control function 153 according to the comparison result (step S307) between the current value and the specified value. This stops the second heater, the third heater, the fifth heater, and the sixth heater from generating heat. If the normal conductive state of the second PCS 20, the third PCS 30, the fifth PCS 50, and the sixth PCS 60 can be maintained by the conduction of self-heating by the first PCS 10 and the fourth PCS 40 without the second heater, the third heater, the fifth heater, and the sixth heater generating heat, the consumption of refrigerant can be reduced. After this process, the process from step S304 onwards is repeated.

Other processes in the current supply control process of this modified example are similar to the current supply control process shown in FIG. 3, so their explanations are omitted. Also, the procedures and effects of other processes in this modified example are similar to those described in the embodiment, so their explanations are omitted.

(Application example)
This application example is to realize a current supply control process by a current control device. Fig. 7 is a diagram showing an example of a current control device 200 together with an MRI device 100. As shown in Fig. 7, the current control device 200 has a static magnetic field power supply 130, a heater power supply 131, a resistance detector 132, and a processing circuit 16 having a current control function 153. The processing procedure and effects of the current supply control process in this application example are the same as those described in the embodiment, so a description will be omitted.

According to at least one of the embodiments described above, it is possible to provide a superconducting magnet 101 that can reduce the consumption of refrigerant during demagnetization and excitation.

Although several 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 within the scope of the invention and its equivalents as set forth in the claims, as well as the scope and spirit of the invention.

1 Winding core 2 Superconducting wire 3 Heater wire (heater)
4 Molding resin material 5 Heat transfer plate 6 Outer cylinder 7 Heat conductor 8 Heat insulating material 10 First persistent current switch 11 Communication interface 12 System control circuit 13 Memory 15 Processing circuit 17 Input/output interface 20 Second PCS
30. Third PCS
40 4th PCS
50 5th PCS
60 6th PCS
70 Console 80 PCS unit (or PCS module)
90 PCS unit (or PCS module)
REFERENCE SIGNS LIST 100 Magnetic resonance imaging apparatus 101 Superconducting magnet 103 Gradient magnetic field coil 105 Gradient magnetic field power supply 107 Bed 109 Bed control circuit 111 Bore 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 generating function 153 current control function 200 current control device

Claims (6)

a superconducting coil for generating a static magnetic field;
a plurality of persistent current switches electrically connected to the superconducting coil;
a heater provided inside at least one of the plurality of persistent current switches;
a thermal conductor provided between two adjacent persistent current switches among the plurality of persistent current switches, capable of thermally conducting self-heat generated by one persistent current switch among the plurality of persistent current switches that has been made normally conductive by the heater to the other persistent current switch;
A superconducting magnet comprising: The thermal conductor is made of metal.
2. The superconducting magnet according to claim 1. The metal is solder.
3. The superconducting magnet according to claim 2. the superconducting coil and the plurality of persistent current switches are immersed in a refrigerant related to a superconducting state;
In the superconducting state, the plurality of persistent current switches and the superconducting coil form a closed circuit.
4. A superconducting magnet according to claim 1. A superconducting magnet according to claim 4;
A static magnetic field power supply electrically connected to the closed circuit during excitation and demagnetization of the static magnetic field;
a current control unit that controls supply of current to the heater and stopping of the supply;
A magnetic resonance imaging apparatus comprising: In the excitation and demagnetization, a resistance detection unit is further provided which is electrically connected to the closed circuit in parallel with the static magnetic field power supply and detects a resistance in the closed circuit;
the heater is provided for each of the plurality of persistent current switches,
the current control unit controls the supply of current to the heater in the other persistent current switch in accordance with a value of the resistance.
6. A magnetic resonance imaging apparatus according to claim 5.

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