Magnetic resonance imaging apparatus and method for controlling refrigerator

Abstract

The purpose of the present invention is to provide a magnetic resonance imaging apparatus and a method for controlling a refrigerator. The magnetic resonance imaging apparatus increases the operating rate of an MRI apparatus by prolonging the replacement life of the refrigerator and reducing the replacement frequency of the refrigerator. And executing a cold head life prolonging mode. In the cold head life extension mode, regardless of the temperature of the superconducting coil, the displacer of the refrigerator is moved at a constant frequency lower than a predetermined upper limit frequency, and the drive frequency of the compressor drive unit adjusted by the compressor inverter is controlled in accordance with the temperature of the superconducting coil.

Description

Technical Field

[0001] This invention relates to a magnetic resonance imaging (MRI) device. Background Technology

[0002] There are known MRI devices that use liquid helium to cool superconducting magnets. The superconducting coil is housed within a liquid helium container, which contains a cold head for a refrigerator that cools and reliquefies vaporized helium.

[0003] Patent document 1 discloses a technique for changing the drive frequency of the compressor of a refrigeration machine to make the cooling capacity variable in order to keep the pressure inside the liquid helium container constant.

[0004] On the other hand, MRI devices that do not use liquid helium are also known. For example, Patent Document 2 discloses an MRI device in which the cold heads of two or more refrigerators conduct heat to the spools of superconducting coils arranged in a vacuum container. An inverter is connected to the compressor of the refrigerator and is controlled according to the temperature of the superconducting coil unit. Thus, by changing the capacity of the compressor, the temperature of the superconducting coil unit is controlled to be constant.

[0005] Patent Document 1: Japanese Patent No. 5960152

[0006] Patent Document 2: Japanese Patent Application Publication No. 2013-144099

[0007] MRI devices using superconducting coils require a cooling system to cool the coils. The MRI device must be shut down when the cooling system is replaced. Summary of the Invention

[0008] The purpose of this invention is to improve the operating rate of MRI devices by extending the lifespan of the refrigerator and reducing the frequency of refrigerator replacement.

[0009] According to one aspect of the present invention, a magnetic resonance imaging apparatus using a superconducting magnet is provided, which generates a static magnetic field in the imaging space. The superconducting magnet includes: a superconducting coil; a container housing the superconducting coil; a cold head mounted in the container; a compressor supplying compressed refrigerant gas to the cold head; and a processor. The compressor includes: a mechanism; a compressor drive unit that periodically moves the mechanism and compresses the refrigerant gas; and a compressor inverter that adjusts the drive frequency of the compressor drive unit. The cold head includes: a cylinder in which refrigerant gas compressed by the compressor is supplied; a displacement device disposed within the cylinder; and a displacement device drive unit that periodically moves the displacement device within the cylinder. The cylinder of the cold head is connected to and cools the superconducting coil via a metal heat-conducting component. The processor has a cold head lifespan extension mode, in which the displacement device moves at a constant frequency lower than a predetermined upper limit frequency regardless of the temperature of the superconducting coil, and the processor controls the drive frequency of the compressor drive unit adjusted by the compressor inverter according to the temperature of the superconducting coil.

[0010] Invention Effects

[0011] According to the present invention, by operating the MRI device in a cold head life extension mode, the number of times the replacement device moves is reduced, thereby extending the replacement life of the refrigerator. This reduces the frequency of refrigerator replacement for the MRI device and improves the operating efficiency of the MRI device. Attached Figure Description

[0012] Figure 1 This is a block diagram illustrating the overall structure of an MRI device according to an embodiment of the present invention.

[0013] Figure 2 It means Figure 1 A cross-sectional view of the configuration of superconducting magnets and other components in the MRI device shown.

[0014] Figure 3 It means Figure 1 A diagram showing the cross-sectional structure of the superconducting magnet in an MRI device.

[0015] Figure 4 It means Figure 3 Cross-sectional view of the structure of the superconducting magnet cold head 107 and compressor 108.

[0016] Figure 5 This is a flowchart illustrating the control of the cold head 107 and the compressor 108 by the processor of the superconducting magnet of the first embodiment.

[0017] Figure 6 This is a flowchart illustrating the control of the cold head 107 and the compressor 108 by the processor of the superconducting magnet in a modified embodiment of the first embodiment.

[0018] Figure 7 This is a flowchart illustrating the control of the cold head 107 and the compressor 108 by the processor of the superconducting magnet of the second embodiment.

[0019] Figure 8 (a) is a graph showing the input heat of the superconducting magnet and the operating frequency of the compressor based on photography in the fourth embodiment. Figure 8 (b) is a graph showing the operating frequency of the compressor and the magnet temperature of the superconducting magnet in the fourth embodiment.

[0020] Figure 9 This is a flowchart illustrating the control of the cold head 107 and the compressor 108 by the processor of the superconducting magnet of the fourth embodiment.

[0021] Figure 10 This is a flowchart illustrating the control of the cold head 107 and the compressor 108 by the processor of the superconducting magnet in the modified example of the fourth embodiment.

[0022] Figure 11 This is a graph showing the input heat of the superconducting magnet based on photography and the state of the MRI device in the fifth embodiment.

[0023] Figure 12 This is a flowchart illustrating the control of the cold head 107 and the compressor 108 by the processor of the superconducting magnet in the fifth embodiment.

[0024] Symbol Explanation

[0025] 1-MRI apparatus, 10-Camera unit, 20-Processor, 21-Camera control unit, 22-Image generation unit, 25-Display control unit, 30-UI unit, 60-External storage device, 70-Refrigerator, 101-Superconducting magnet, 102-Subject, 103-Magnetic field space, 107-Cold head, 108-Compressor, 109-Sensor connection terminal, 110-Magnet control unit, 111-Shimming plate, 112-Tilted magnetic field coil, 113-Tilted magnetic field power supply, 114-Shimming power supply, 115-RF transmitting coil, 116-RF transmitting unit, 117-RF receiving coil, 118-RF receiving unit, 120-Display, 121-Input device, 122-Bedside device, 123-Examination room, 128-Sequencer 131-Mechanical Unit, 132-Compressor Drive Unit, 133-Compressor Inverter, 201-Vacuum Container, 201a-Outer Container, 201b-Inner Container, 203-Superconducting Coil, 205-Liquid Level Sensor, 206-Temperature Sensor, 216-Radiative Heat Shielding Plate, 217-Super Insulator, 219-First Cooling Platform, 220-Second Cooling Platform, 225-Heat Conducting Component, 301-GM Circulation Control Unit, 302-Displacement Device Drive Unit, 303-Displacement Device, 303a, 303b-Displacement Device, 304-Cylinder Block, 304a, 304b-Cylinder Block, 305-Intake Valve, 306-Exhaust Valve, 307-Pressurized Gas Hose, 308-Pressurized Gas Hose, 309-Upper Space, 310-Lower Space. Detailed Implementation

[0026] The MRI apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. Furthermore, in all the drawings used to illustrate embodiments of the present invention, components having the same function are labeled with the same symbols, and repeated descriptions are omitted.

[0027] <Overall structure of the MRI device in this embodiment>

[0028] First, the overall structure of the MRI device operating in this embodiment will be described.

[0029] Figure 1 This describes the overall structure of the MRI device of this embodiment when it is installed in a medical facility.

[0030] First, a general overview of the MRI device to which the present invention is applied will be described. For example... Figure 1As shown, the MRI apparatus 1 includes: an imaging unit 10 that generates nuclear magnetic resonance in the atomic nuclei of the atoms constituting the tissue of the subject 102, thereby collecting nuclear magnetic resonance signals generated from the subject; a processor 20 that processes the nuclear magnetic resonance signals collected by the imaging unit 10 and controls the imaging unit 10; and a user interface unit (hereinafter, UI unit) 30 for operators of the MRI apparatus 1, such as doctors or technicians (hereinafter referred to as users), to set imaging conditions, input necessary instructions, and display images obtained by the MRI apparatus 1 or the GUI. Furthermore, the MRI apparatus 1 may have an interface (not shown) for exchanging information with an external storage device 60 or an external device that stores the generated images and other information.

[0031] The imaging unit 10 includes a superconducting magnet 101 that generates a uniform static magnetic field in the examination space where the subject 102 is placed, a tilted magnetic field coil 112 that imparts a magnetic field gradient to the static magnetic field, an RF transmitting coil 115 that applies a predetermined high-frequency magnetic field to the subject, and an RF receiving coil 117 that receives the nuclear magnetic resonance signal (hereinafter also referred to as the echo signal) generated from the subject. The tilted magnetic field coil 112 is connected to a tilted magnetic field power supply 113, the RF transmitting coil 115 is connected to an RF transmitting unit 116 consisting of an RF transmitter and an RF amplifier, and the RF receiving coil 117 is connected to an RF receiving unit 118 equipped with a QD detector and an AD converter. In addition, sometimes a single RF coil serves as both the RF transmitting coil 115 and the RF receiving coil 117, but usually the RF transmitting coil 115, together with the superconducting magnet 101 and the tilted magnetic field coil 112, is housed in a frame (not shown) in a manner that surrounds the examination space, and the RF receiving coil 117 is arranged in the examination space when the subject 102 is installed.

[0032] The imaging unit 10 also includes a sequencer 128 that enables the RF transmitter 116, the tilting magnetic field power supply 113, and the RF receiver 118 to operate according to a predetermined pulse sequence, and performs imaging according to the imaging sequence set in the sequencer 128. The imaging operations are the same as those in a conventional MRI device.

[0033] The imaging department 10 also includes a bed device 122 for placing the subject.

[0034] The processor 20 controls the imaging unit 10 and performs signal processing or various calculations on the nuclear magnetic resonance signals collected by the imaging unit 10.

[0035] To achieve the above processing, the processor 20 includes a photography control unit 21 for controlling photography, a display control unit 25 for controlling the display in the UI unit 30, an image generation unit 22 for performing various operations related to image generation such as image reconstruction, and a magnet control unit 110 for controlling the superconducting magnet 101.

[0036] In this embodiment, the aforementioned processes of processor 20 can be executed by any computer. Furthermore, any computer can execute these processes via a processor as hardware, a program as software, or a combination thereof. In this case, the processor is configured to cooperate with the program in executing the various processes of this embodiment, and can function as units 21, 22, 25, 110, etc., or means in this embodiment. Moreover, the execution order of the processor-based processes is not limited to the order described and can be appropriately varied. Any computer can be a general-purpose computer, a special-purpose computer, a workstation, or other system capable of executing the processes.

[0037] A processor can be composed of one or more hardware components, and the type of hardware is not limited. For example, a processor can be composed of programmable logic devices such as CPUs (Central Processing Units), MPUs (Micro Processing Units), FPGAs (Field Programmable Gate Arrays), dedicated circuits for performing specific processes such as ASICs (Application Specific Integrated Circuits), GPUs (Graphics Processing Units), or NPUs (Neural Processing Units). Furthermore, the type of hardware can be a combination of different types of hardware. When multiple hardware components are configured to execute one or more processes of a certain processor, these multiple hardware components can exist in physically separate devices or in the same device. Moreover, in any embodiment, the order of the processor's processes is not limited to the above order and can be appropriately varied. Additionally, the hardware can be composed of circuits, such as those combining semiconductor elements.

[0038] Furthermore, the program can be software such as firmware or microcode. The program can also be, for example, a group of program modules, each of which can be implemented by a processor configured to execute that function. The program can be program code or multiple code segments stored in one or more non-transitory computer-readable media (e.g., storage media or other storage devices). The program can be divided into multiple non-transitory computer-readable media existing in physically separate devices and stored therein. Program code or code segments can represent any combination of steps, functions, subroutines, routines, subroutines, modules, software packages, classes, or commands, data structures, or program statements. Program code or code segments can be connected to other code segments or hardware circuitry by sending and receiving information, data, arguments, parameters, or the contents of memory.

[0039] use Figures 2-4 The structure of MRI device 1 will be further explained. Figure 2 It is a diagram showing the configuration of superconducting magnets, etc. Figure 3 This is a diagram showing the cross-sectional structure of the superconducting magnet 101. Figure 4 This is a diagram showing the structure of the refrigeration unit 70.

[0040] <Superconducting Magnet 101>

[0041] The MRI device 1 includes a superconducting magnet 101 as a magnet that generates a static magnetic field. The superconducting magnet 101 can generate a static magnetic field in either the vertical or horizontal direction; however, an example of a superconducting magnet 101 generating a static magnetic field in the horizontal direction will be provided for illustration. Figure 3 As shown, the superconducting magnet 101 that generates a static magnetic field in the horizontal direction uses a superconducting coil 203 with a coil wound in a cylindrical shape to generate a static magnetic field in the horizontal direction (the direction of the body axis of the subject 102). The superconducting coil 203 wound in a cylindrical shape is disposed inside a cylindrical vacuum container 201.

[0042] The cylindrical vacuum container 201 has a dual structure consisting of an outer container 201a and an inner container 201b. The space between the outer container 201a and the inner container 201b is evacuated to a specified pressure and is equipped with a radiative heat shield 216. A superconducting coil 203 is disposed inside the inner container 201b.

[0043] The space within the inner container 201b containing the superconducting coil 203 is evacuated to a specified pressure.

[0044] The magnetic field space 103, which contains the subject 102, is formed in the space near the central axis of the cylindrical vacuum container 201.

[0045] The vacuum container 201 includes a cold head 107. The front end of the cold head 107 is inserted into the interior of the inner container 201b of the vacuum container 201. A compressor 108 is connected to the cold head 107, and compressed refrigerant gas is supplied from the compressor 108. The cold head 107 and the compressor 108 constitute a refrigerator (Clio cooler) 70 for cooling the superconducting magnet 101.

[0046] The cold head 107 generates a cooling effect through the adiabatic expansion of the refrigerant gas inside, cooling the front end of the cold head 107. A highly thermally conductive heat-conducting component 225 is disposed between the front end of the cold head 107 and the superconducting coil 203. One end of the heat-conducting component 225 is connected to the cold head 107, and the other end is connected to the superconducting coil 203 (see reference). Figure 3 , Figure 4 Thus, the cold head 107 cools the superconducting coil 203 through the heat conduction of the heat-conducting component 225.

[0047] Furthermore, a portion of the cold head 107 is connected to the radiative heat shield 216 of the vacuum container 201 and the inner container 201b, and cools them.

[0048] In this way, the refrigerator maintains the thermal equilibrium state of the superconducting magnet 101, realizing a closed-type superconducting magnet. That is, the heat entering the vacuum container 201 is controlled to achieve a cooling capacity that is just right for cooling.

[0049] Furthermore, multiple temperature sensors 206 or pressure sensors for monitoring the operating status are assembled in the superconducting magnet 101, and their sensor connection terminals 109 are connected to the magnet control unit 110.

[0050] The magnet control unit 110 monitors the operating status of the superconducting magnet 101 and controls the cold head 107 and the compressor 108.

[0051] Thus, the superconducting coil 203 is cooled to below the critical temperature and becomes superconducting. By allowing a specified constant current to flow through it, a stable static magnetic field with a magnetic field strength of 1.5 Tesla can be generated in the magnetic field space (photographic space) 103.

[0052] <Shim-plate 111>

[0053] like Figure 2 As shown, a shimming plate 111 is installed on one side of the magnetic field space 103 of the vacuum container 201. Multiple screw holes (not shown in the figure) are formed on the shimming plate 111, and small screws containing magnetic materials are embedded in appropriate positions. By altering the magnetic flux distribution generated by the superconducting magnet 101 through the magnetic field generated by the small screws, the magnetic field uniformity of the magnetic field space 103 is adjusted to a target value (e.g., below 3 ppm).

[0054] <Inclined Magnetic Field Coil 112>

[0055] An inclined magnetic field coil 112 for generating an inclined magnetic field is disposed on one side of the magnetic field space 103 of the shimming plate 111. The inclined magnetic field coil 112 consists of three types of coils: x, y, and z, which generate inclined magnetic fields in three mutually orthogonal axes. Figure 1 The structure is composed of stacked layers (not distinguished in the text). Each of the x, y, and z coils is connected to an independently applied tilted magnetic field power supply 113.

[0056] In the tilted magnetic field coil 112, in addition to the x coil, y coil, and z coil, a B0 coil is also assembled to compensate for the magnetic field strength generated by the superconducting magnet 101, as well as higher-order modes such as ZX, ZY, XY, and Z that generate x, y, and z. 2 x 2 +y 2 The magnetic field is shim coils, etc. Current is applied to them by the shim power supply 114.

[0057] <RF Transmit Coil 115>

[0058] An RF transmission coil 115 is mounted on the magnetic field space 103 side of the tilted magnetic field coil 112. An RF transmission unit 116 is connected to the RF transmission coil 115 and is supplied with a high-frequency current. This generates a high-frequency magnetic field required for nuclear spin nuclear magnetic resonance of the imaging site of the subject 102.

[0059] By combining the aforementioned stable and highly uniform static magnetic field, tilted magnetic field, and high-frequency magnetic field, nuclear magnetic resonance (NMR) can be accurately and selectively induced in the hydrogen nuclei of the imaging area of ​​the subject 102. Then, three-dimensional position information is added by applying a tilted magnetic field in a pulsed manner during the subsequent precession of the nuclear spin.

[0060] <RF receiving coil 117>

[0061] An RF receiving coil 117 is positioned approximately at the center of the magnetic field space 103, i.e., at the imaging site of the subject 102. This RF receiving coil 117 detects the minute magnetic field fluctuations caused by the precession of nuclear spins as an electrical signal (NMR signal) based on the induced current in the RF receiving coil 117. The detected NMR signal is transmitted to an RF receiving unit 118 connected to the RF receiving coil 117. After amplifying and detecting the NMR signal, the RF receiving unit 118 converts it into a digital signal.

[0062] <Processor 20>

[0063] The image generation unit 22 of the processor 20 generates MRI images or spectra based on the NMR signals converted into digital signals. The generated images, etc., are stored in the external storage device 60. The display control unit 25 displays the MRI images, etc., on the display 120 of the UI unit 30.

[0064] Furthermore, the imaging control unit 21 of the processor 20 performs the following control to implement a predetermined imaging method: at a time determined by a predetermined imaging sequence, an inclined magnetic field and a high-frequency magnetic field are applied to the subject 102 from the inclined magnetic field coil 112 and the RF transmission coil 115, and the generated NMR signal is detected at a predetermined time. The imaging sequence varies depending on the imaging method and imaging conditions. The imaging control unit 21 generates an imaging sequence that implements the imaging method and imaging conditions input by the operator via the input device 121 of the UI unit 30 by executing a program pre-stored in the built-in storage device. Thus, multiple imaging methods can be implemented under various imaging conditions. In addition, the input device 121 is, for example, a keyboard or a mouse.

[0065] The operating status of the magnet control unit 110, tilting magnetic field power supply 113, shimming power supply 114, RF transmitter 116, RF receiver 118, etc., is recorded in a storage device built into the processor 20. Furthermore, the processor 20 can also output this operating status information to an external device via a communication control device (not shown). This enables remote monitoring of the MRI device.

[0066] <Bedside Device 122>

[0067] The MRI device includes a bedside device 122 that transports the imaging area of ​​the subject 102 to the center of the magnetic field space 103.

[0068] The superconducting magnet 101 and the bed device 122 are installed in the examination chamber 123, which is electromagnetically shielded. This prevents electromagnetic waves generated by external equipment from entering the RF receiving coil 117 as noise and degrading the quality of the diagnostic images.

[0069] <Detailed Structure of Vacuum Container 201 for Superconducting Magnets>

[0070] use Figure 3 The detailed structure of the vacuum container 201 of the superconducting magnet 101 described above will be further explained.

[0071] Load supports (not shown) are installed on the outer container 201a, the radiative heat shield 216, and the inner container 201b of the vacuum container 201 of the superconducting magnet 101 to fix their positions. In order to minimize thermal conductivity, the load supports are made of stainless steel and resin.

[0072] The outer container 201a of the vacuum container 201 is made of stainless steel with a thickness of 10 mm, for example. The inner container 201b is made of stainless steel with a thickness of 15 mm, for example, and has rigidity to withstand the electromagnetic force applied to the superconducting coil 203 and the pressure difference between the inside and outside.

[0073] The superconducting coil 203 inside the inner container 201b is composed of multiple coils. The superconducting coil 203 is fixed to the inner container 201b.

[0074] A temperature sensor 206 for measuring the temperature of the superconducting coil 203 is provided on the superconducting coil 203. The output signal line of the temperature sensor 206 is led out from the sensor connection terminal 109 to the outside of the superconducting magnet 101.

[0075] The radiant heat shield 216 is made of 5 mm thick aluminum. Its surface is mirror-polished to suppress radiant heat. Furthermore, a super insulator (not shown) is laid in the gap between the vacuum container 201 and the radiant heat shield 216. The super insulator 217 is composed of multiple layers of polyethylene sheets coated with aluminum films, further reducing radiant heat.

[0076] The inner container 201b is evacuated to a specified vacuum level.

[0077] <Detailed information on the vacuum container 201 for superconducting magnets>

[0078] A cold head 107 is configured in the vacuum container 201. For example... Figure 4 As shown, the cold head 107 has a two-stage cooling platform. The first cooling platform 219 of the first stage has a temperature of 43 Kelvin (-230℃), and the second cooling platform 220 of the second stage has a temperature of 4 Kelvin (-269℃).

[0079] The first cooling platform 219 of the cold head 107 is in thermal contact with the radiant heat shield 216 and cools the radiant heat shield 216. The front end of the second cooling platform 220 of the cold head 107 is inserted into the inner container 201b.

[0080] The front end of the second cooling stage 220 is connected to the superconducting coil 203 by a heat-conducting component 225. This cools the superconducting coil 203 to 4 Kelvin.

[0081] <Detailed information about Refrigeration Unit 70>

[0082] Next, use Figure 4 The detailed structure of the refrigeration unit 70 is described below.

[0083] The cold head 107 includes a cylinder block 304a, 304b with a two-stage structure consisting of a first cooling platform 219 and a second cooling platform 220, two-stage displacement devices 303a, 303b, and a displacement device drive unit 302 that reciprocates the displacement devices 303a, 303b within the cylinder block 304a, 304b. Within the displacement device 303, a first stage is filled with lead balls and a second stage is filled with copper holobium balls, forming a heat exchange structure that occurs as refrigerant gas passes through them.

[0084] The displacement drive unit 302 includes an intake valve 305 for drawing in refrigerant gas compressed by the compressor 108 and an exhaust valve 306 for discharging the refrigerant gas. These valves open and close synchronously with the reciprocating motion of the displacement unit 303. The intake valve 305 and the exhaust valve 306 are connected to the compressor 108 via pressurized gas hoses 307 and 308, respectively.

[0085] like Figure 4 As shown, the refrigeration unit 70 has a GM circulation control unit 301 between the cold head 107 and the magnet control unit 110. Figure 2 (Illustrations omitted). The GM cycle control unit 301 causes the motor of the displacement drive unit 302 of the cold head 107 to operate at a frequency indicated by the magnet control unit 110. Specifically, the GM cycle control unit 301 controls the frequency of the drive power output to the displacement drive unit 302 of the cold head 107. Therefore, for example, the GM cycle control unit 301 has the function of a variable inverter, converting power input from an external source such as a commercial power supply into multiple frequencies including frequencies lower than the frequency of the input power supply (and, further, voltage conversion as needed), and supplying it to the displacement drive unit 302.

[0086] The compressor 108 includes a mechanism 131 such as a cylinder and piston, a compressor drive 132 that causes the piston of the mechanism 131 to move periodically and compress refrigerant gas in the cylinder, and a compressor inverter 133 that adjusts the drive frequency of the compressor drive 132.

[0087] The cooling head 107 generates a cooling effect by performing the following steps (1) to (3) in sequence.

[0088] (1) If the displacement devices 303a and 303b are moved toward the front end (below) of the cold head 107, the compressed refrigerant gas drawn in from the compressor 108 will fill the upper space 309 in the cylinder 304a.

[0089] (2) Next, if the displacementrs 303a and 303b are moved upward, the compressed refrigerant gas moves downward into the space 310 while passing through the refrigerant in the displacementrs 303a and 303b.

[0090] (3) Simultaneously with the displacement devices 303a and 303b reaching their uppermost positions, the exhaust valve 306 opens. The refrigerant gas in the cylinders 304a and 304b undergoes adiabatic expansion due to the pressure reduction, resulting in a decrease in temperature. Then, it returns from the exhaust valve 306 to the compressor 108 through the pressurized gas hose 308.

[0091] By repeating the cycles (1) to (3), the refrigerant gas continuously absorbs heat from the lower space 310 of the cylinder 304. This thermal cycle is called the Gifford-MacMahon cycle (GM), and a cooling device using the GM cycle is called a GM-type refrigerator.

[0092] <First Embodiment>

[0093] In the first embodiment, the processor 20 has a cold head life extension mode. In the cold head life extension mode, regardless of the temperature of the superconducting coil 203, the magnet control unit 110 of the processor 20 causes the displacement devices 303a and 303b to move at a constant frequency lower than a predetermined upper limit frequency, and controls the drive frequency of the compressor drive unit 132 adjusted by the compressor inverter 133 according to the temperature of the superconducting coil 203. The frequency at which the displacement devices 303a and 303b operate is preferably set to a frequency lower than the drive frequency of the compressor drive unit 132.

[0094] The extended lifespan mode for the cooling head can be set by the user or service personnel through the input device 121 of the UI unit 30, which is located in the magnet control unit 110 of the processor 20. Furthermore, it can also be set by the user or service personnel through the communication control device provided with the MRI device 1. Figure 1 , Figure 2 (Not shown in the image) The magnet control unit 110 of the remote operation processor 20 is used to set the cold head life extension mode.

[0095] use Figure 5 The process will be explained in detail for the operation of the magnet control unit 110 of the processor 20.

[0096] (Step S501)

[0097] First, the magnet control unit 110 proceeds to step S502, where it reads the temperature of the superconducting coil 203 from the temperature sensor 206 inside the inner container 201b.

[0098] (Step S502)

[0099] The magnet control unit 110 determines whether the "cold head life extension mode" has been set by the user or service personnel. If the "cold head life extension mode" has been set by the user, the process proceeds to step S503; otherwise, it proceeds to step S507.

[0100] (Step S503)

[0101] The magnet control unit 110 instructs the GM cycle control unit 301 to set the frequency at which the displacers 303a and 303b of the cold head 107 operate to a constant drive frequency lower than a predetermined upper limit frequency. Therefore, for example, the GM cycle control unit 301 converts power with a constant frequency input from an external power source such as a commercial power supply to a lower frequency (and, further, the voltage, if necessary), and supplies it to the displacer drive unit 302.

[0102] Therefore, regardless of the temperature of the superconducting coil 203, the displacement devices 303a and 303b of the cold head 107 operate at a predetermined constant frequency.

[0103] The magnet control unit 110 proceeds to step S504.

[0104] (Steps S504 to S506)

[0105] Next, when the temperature read from the temperature sensor 206 is higher than the set temperature (step S504), the magnet control unit 110 proceeds to step S505, instructing the compressor inverter 133 of the compressor 108 to increase the drive frequency of the compressor drive unit 132. As a result, due to the increase in the drive frequency of the compressor drive unit 132, the pressure of the refrigerant gas delivered from the compressor 108 to the cold head 107 increases.

[0106] On the other hand, when the temperature read from the temperature sensor 206 is below the set temperature, the magnet control unit 110 proceeds to step S506 and instructs the compressor inverter 133 of the compressor 108 to reduce the drive frequency of the compressor drive unit 132. As a result, since the drive frequency of the compressor drive unit 132 is reduced, the pressure of the refrigerant gas delivered from the compressor 108 to the cold head 107 decreases.

[0107] Thus, the magnet control unit 110 increases or decreases the driving frequency of the compressor drive unit 132 according to the temperature of the superconducting coil 203, thereby changing the pressure of the refrigerant gas sent to the cold head 107. Therefore, even if the driving frequency of the displacement devices 303a and 303b of the cold head 107 is constant, the cooling capacity of the cold head 107 can be adjusted and the temperature of the superconducting coil 203 can be kept constant.

[0108] Furthermore, the set temperature in step S504 can be a specific temperature such as 5 Kelvin or 4 Kelvin, or a temperature range such as above 4 Kelvin and below 5 Kelvin. When using a temperature range (4 to 5 Kelvin) as the set temperature, the magnet control unit 110 proceeds to step S505 if the temperature read from the temperature sensor 206 is higher than the upper limit of the set temperature range (5 Kelvin), and proceeds to step S506 if the temperature is below the lower limit of the set temperature range (4 Kelvin). If the temperature read from the temperature sensor 206 is greater than 4 Kelvin and less than 5 Kelvin, the magnet control unit 110 does not control the compressor 108 and returns to step S501.

[0109] (Steps S507 to S509)

[0110] On the other hand, in step S502, if the magnet control unit 110 determines that it is not in the cold head life extension mode, it proceeds to step S507; if the temperature read from the temperature sensor 206 is higher than the set temperature, it proceeds to step S508. In step S508, the magnet control unit 110 instructs the GM cycle control unit 301 to increase the frequency at which the displacement drive unit 302 of the cold head 107 operates. As a result, the drive frequency of the displacement devices 303a and 303b increases, thereby increasing the cooling capacity of the cold head 107.

[0111] On the other hand, if the temperature read from the temperature sensor 206 in step S507 is lower than the set temperature, the magnet control unit 110 proceeds to step S509. In step S509, the magnet control unit 110 instructs the GM cycle control unit 301 to reduce the frequency of operation of the displacement drive unit 302 of the cold head 107. As a result, the driving frequency of the displacement devices 303a and 303b is reduced, thereby reducing the cooling capacity of the cold head 107.

[0112] Therefore, in steps S507 to S509, the magnet control unit 110 can adjust the cooling capacity of the cold head 107 and maintain the temperature of the superconducting coil 203 at a constant level by increasing or decreasing the driving frequency of the displacement devices 303a and 303b.

[0113] Similar to the set temperature in step S504, the set temperature in step S507 can be a specific temperature or a temperature range.

[0114] As described above, in the cold head life extension mode, in step S503, the operating frequency of the displacers 303a and 303b of the cold head 107 is set to a constant value less than a predetermined upper limit. Therefore, compared with the case where the driving frequency of the displacers 303a and 303b is increased or decreased according to temperature as in steps S507 to S509, the reciprocating frequency of the displacers 303a and 303b is reduced, which can reduce the wear or failure of the displacers 303a and 303b and extend the life of the cold head 107.

[0115] The effects of this implementation method will be explained in further detail.

[0116] In conventional MRI scanners, the motor of the displacement drive unit 302, which serves as the cold head 107, is a synchronous motor that rotates at a constant speed (synchronous speed) if the power supply frequency is constant. The displacement units 303a and 303b are driven at a frequency corresponding to the frequency of commercial AC power. For example, a synchronous motor that operates the displacement units 303a and 303b at 1Hz relative to a 50Hz power supply frequency is used as the displacement drive unit 302. In this MRI scanner, where the commercial AC power supply is 60Hz, the displacement units 303a and 303b are driven at 1.2Hz.

[0117] In contrast, in this embodiment, the GM cycle control unit 301 controls the displacement devices 303a and 303b to operate at a frequency of 0.8Hz, which is lower than 1Hz or 1.2Hz, in step S503. Therefore, for example, the GM cycle control unit 301 has the function of a variable inverter and can convert 50Hz power, which is a commercial power source, not only to 50Hz but also to 40Hz and other frequencies. By converting the frequency to 40Hz and supplying it to the displacement device drive unit 302, the displacement devices 303a and 303b can operate at a frequency of 0.8Hz, which is lower than 1Hz or 1.2Hz.

[0118] Because the frequency of the displacement devices 303a and 303b is reduced, the frequency of reciprocating motion is reduced, thereby extending the lifespan of the cold head 107.

[0119] Therefore, in step S503, the magnet control unit 110 instructs the GM cycle control unit 301 to set the upper limit of the frequency at which the displacement devices 303a and 303b operate to be lower than the operating frequency of the displacement devices in the refrigerator of a conventional MRI device (1 Hz or 1.2 Hz in the above example). Thus, for example, the GM cycle control unit 301 has the function of reducing the frequency of the input power supply and supplying it to the displacement device drive unit 302.

[0120] The upper limit frequency for the operation of the displacement devices 303a and 303b is preferably a value obtained by dividing the frequency of the input power of the commercial power supply, etc., by the inherent value of the displacement device drive unit 302. Specifically, for example, if the commercial power supply is 50Hz and the inherent value of the displacement device drive unit 302 with a synchronous motor is 50, the upper limit is preferably 1Hz or less, and more preferably 0.8Hz or less.

[0121] The structure of the displacement drive unit 302 and the GM cycle control unit 301 of the cold head 107 in this embodiment is not limited to the above example. As long as the frequency of operation of the displacement units 303a and 303b can be set to a constant value smaller than a predetermined upper limit, it can be any structure.

[0122] In this embodiment, the magnet control unit 110 reduces the frequency of operation of the displacement devices 303a and 303b to a constant value by instructing the GM cycle control unit 301 (step S503). On the other hand, the drive frequency of the compressor 108 is variablely controlled (steps S505 and S506), so the overall cooling performance of the refrigerator 70 is not reduced.

[0123] Furthermore, the driving frequency of the displacement drive unit 302 of the cold head 107 and the operating frequency of the displacement units 303a and 303b are preferably set to avoid the natural vibration frequency of the superconducting magnet 101. This is because if the displacement drive unit 302 or the displacement units 303a and 303b operate near the natural frequency of the superconducting magnet 101, the vibration will propagate into the superconducting magnet 101, causing unexpected structural vibration, which may lead to image quality degradation in the MRI image. For example, when using a synchronous motor that operates the displacement units 303a and 303b at a frequency of 1 / 50th of the input power frequency as the displacement drive unit 302, the power frequency input to the displacement drive unit 302 is preferably set to avoid being more than 50 times the natural frequency of the superconducting magnet 101.

[0124] Furthermore, examples of increasing or decreasing the drive frequency of the compressor 108 or the operating frequency of the displacement devices 303a and 303b based on whether the temperature is higher or lower than the set temperature in steps S504 to S506 and S507 to S509 have been described, but this embodiment is not limited to this control method. Various known control methods exist for controlling the cooling capacity (front-end temperature of the cold head 107), so the desired method can be used. For example, PID control, as a type of feedback control, can be used.

[0125] As described above, in the cold head life extension mode of the MRI apparatus 1 of this embodiment, regardless of the temperature of the superconducting coil 203, the displacement devices 303a and 303b move at a constant frequency lower than a predetermined upper limit frequency. This reduces the number of reciprocating movements compared to conventional displacement devices, thereby extending the replacement life of the cold head 107. Furthermore, by controlling the drive frequency of the displacement device drive unit 302, the overall cooling capacity of the refrigerator 70 can be maintained.

[0126] Furthermore, in the cold head life extension mode of the MRI device 1 in this embodiment, regardless of the temperature of the superconducting coil 203, the displacement devices 303a and 303b move at a constant frequency lower than the predetermined upper limit frequency. Therefore, when an imaging sequence is executed, the frequency of the displacement devices 303a and 303b will not change in the middle of the imaging sequence.

[0127] If, during the middle of the photographic sequence, the displacement devices 303a and 303b stop operating, or conversely begin operating, or the frequency of their operation changes, the vibration state of the superconducting magnet 101 changes, which may be the cause of image degradation.

[0128] In this embodiment, in the cold head life extension mode, the displacement devices 303a and 303b always operate at a constant frequency, thus also having the advantage of preventing image degradation.

[0129] In addition, such as Figure 6 As shown, the cold head life extension mode can include a mode for use during photography and a mode for use during photography. That is, in step S502, when the user sets the cold head life extension mode, the magnet control unit 110 proceeds to step S611 to determine whether current photography is in progress.

[0130] When photography is in progress, the magnet control unit 110 enters step S612, which is a photography mode, as described in step S503 above, in which the displacement devices 303a and 303b operate continuously at a constant first frequency regardless of the temperature of the superconducting coil.

[0131] On the other hand, in step S611, when no photography is being taken, the magnet control unit 110 enters step S613, and in non-photography mode, the displacement devices 303a and 303b operate continuously at a constant second frequency.

[0132] The second frequency is set to be lower than the first frequency used in the photography mode, taking into account the low heat input to the superconducting magnet 101 during non-photography periods. The second frequency can be set by the magnet control unit 110 based on the temperature obtained in step S501.

[0133] Therefore, in non-photography mode, the number of actions is further reduced compared to photography mode, thus extending the lifespan of the 107 cooling head.

[0134] <Second Implementation>

[0135] Next, use Figure 7 The process of the second implementation method will be described.

[0136] The MRI device 1 in the second embodiment has the same structure as that in the first embodiment, but as... Figure 7 As shown, based on the temperature obtained from the temperature sensor 206 (step S501), the magnet control unit 110 determines whether it is a situation that requires accelerated cooling (step S601). If it is a situation that requires accelerated cooling, it proceeds to step S602.

[0137] In step S602, the magnet control unit 110 controls the compressor inverter 133 to set the drive frequency of the mechanism 131 of the compressor 108 to a settable maximum value. At the same time, the magnet control unit 110 instructs the GM cycle control unit 301 to also set the operating frequency of the displacers 303a and 303b of the cold head 107 to a settable maximum value.

[0138] Therefore, the superconducting coil 203 is cooled as quickly as possible.

[0139] In addition, in step S601, if the magnet control unit 110 determines that accelerated cooling is not required, the steps after step S503 are performed in the same manner as in the first embodiment.

[0140] In step S601, the situation in which the magnet control unit 110 determines that accelerated cooling is required refers to the following situation.

[0141] When using an MRI device, unstable cooling is sometimes required. In particular, the superconducting magnet 101, which is not cooled by liquid helium through conduction, cannot dissipate its heat through the latent heat of vaporization of the liquid helium, thus requiring accelerated cooling in many situations. Examples include immediately after the MRI device 1 is connected, during quenching of the superconducting coil 203, during power outages, and when the cooler 70 is being replaced. In these situations, a stable static magnetic field cannot be generated, preventing the MRI device from performing imaging, necessitating the fastest possible cooling of the superconducting coil 203.

[0142] Therefore, in the second embodiment, in step S602, the magnet control unit 110 controls the drive frequency of the mechanism unit 131 of the compressor 108 to a settable maximum value, and the operating frequency of the displacers 303a and 303b of the cold head 107 is also set to a settable maximum value.

[0143] As a result, power consumption increases, and vibrations in the static magnetic field may also increase, but cooling of the superconducting coil 203 is the top priority.

[0144] The aforementioned state requiring unstable cooling capacity may also occur at night, so it is desirable for the magnet control unit 110 to automatically determine this. Therefore, in step S601, if it is determined that the temperature of the superconducting coil 203 detected by the temperature sensor 206 exceeds a predetermined temperature (critical temperature) that is unlikely to be a stable state, the process proceeds to step S602 and accelerated cooling is performed.

[0145] The critical point for superconductivity is determined by three factors: temperature, applied magnetic field, and current. If this critical point is exceeded, the superconducting state cannot be maintained. The applied magnetic field and current values ​​are known at the design time, so the critical temperature is predetermined based on these factors.

[0146] If the temperature of the superconducting coil 203 obtained by the magnet control unit 110 in step S501 is above the predetermined critical temperature in step S601, then since the superconducting coil 203 is no longer in a superconducting state, the process proceeds to step S602 to perform accelerated cooling.

[0147] Additionally, in step S501, the temperature can also be obtained from a temperature sensor of the superconducting magnet 101 other than the temperature sensor 206. Furthermore, the determination in step S601 can be made using detection results other than the temperature of the superconducting magnet 101. For example, a magnetic field sensor for detecting the magnetic field of the superconducting magnet 101 can be pre-configured, and in step S601, if no magnetic field is detected, the process proceeds to step S602 to set the cooling capacity to maximum.

[0148] The MRI device 1 of the second embodiment has the same structure and operation as the first embodiment, except as described above, so the description is omitted.

[0149] <Third Implementation>

[0150] Next, the third embodiment will be described.

[0151] The MRI apparatus 1 in the third embodiment has the same structure as that in the first embodiment, but the processor 20 makes the frequency determined according to the parameters of the imaging sequence executed by the imaging unit 10 for imaging consistent with the constant frequency at which the displacement devices 303a and 303b move. Specifically, the frequency of the operation of the displacement devices 303a and 303b and the driving frequency of the displacement device drive unit 302 are set to n times the reciprocal of the repetition time (TR) of the imaging sequence (1 / (TR)) (n is an integer).

[0152] The cold head 107 of the refrigerator 70 is inserted into the interior of the superconducting magnet 101. Therefore, the vibrations generated by the operation of the displacement devices 303a and 303b and the operation of the displacement device drive unit 302 cause minute vibrations in the superconducting magnet 101. Therefore, as explained in the first embodiment, the frequencies of the operation of the displacement devices 303a and 303b and the operation of the displacement device drive unit 302 are preferably set to be inconsistent with the natural vibration frequency of the superconducting magnet 101.

[0153] In the third embodiment, the frequency of the operation of the displacement devices 303a and 303b of the cold head 107 and the frequency of the operation of the displacement device drive unit 302 are set to n times the reciprocal of the repetition time (TR) of the imaging sequence (1 / (TR)) (where n is an integer). As a result, the changes in the magnetic field generated by the vibration of the superconducting magnet 101 can be synchronized with the imaging sequence, thereby reducing the impact of the vibration of the cold head 107 on the imaging.

[0154] Variations in the magnetic field that are out of sync with the photographic sequence's TR cannot be corrected even by post-processing the NMR signal acquired during the photograph. However, if the variation in the magnetic field is synchronized with the photographic sequence, its impact can be mitigated.

[0155] The specific vibration frequency will be explained. Conventional MRI devices use a synchronous motor in the cold head's displacement drive section, which is supplied with 50Hz or 60Hz commercial AC power to enable the displacement device to operate at 1Hz or 1.2Hz. Therefore, vibration at 1Hz or 1.2Hz generates a magnetic field variation of 1Hz or 1.2Hz in the superconducting magnet 101.

[0156] In the third embodiment, the driving frequency of the displacement drive unit 302 of the cold head 107 is varied, for example, within the range of 40Hz to 70Hz, according to the photographic sequence. As the displacement drive unit 302, when using the same synchronous motor as before, and with a 50Hz commercial AC power supply, the operating frequency of the displacement units 303a and 303b is 1Hz. Therefore, when the driving frequency of the displacement drive unit 302 is set within, for example, the range of 40Hz to 70Hz, the operating frequency of the displacement units 303a and 303b becomes 0.8Hz to 1.4Hz. This means that, if set to one cycle, it corresponds to 1250ms to 714ms.

[0157] For example, in the case of a photographic sequence with a repetition time (TR) of 800ms, the frequency is 1 / 0.8 = 1.25Hz. Therefore, if 1.25 * 50 = 62.5Hz is selected as the driving frequency of the displacement driver 302, the repetition time (TR) of the photographic sequence can be synchronized with the operating frequency of the displacement drivers 303a and 303b of the cold head 107.

[0158] Thus, according to the third embodiment, the variation of the magnetic field generated by the vibration of the superconducting magnet 101 can be synchronized with the imaging sequence, thereby reducing the impact of the vibration of the cold head 107 on the imaging.

[0159] <Fourth Implementation>

[0160] Next, use Figures 8-10 The fourth embodiment will be described.

[0161] The MRI apparatus 1 of the fourth embodiment has the same structure and operation as that of the first embodiment, but reduces energy consumption compared to the first embodiment. Therefore, when operating in the extended lifespan mode, if the temperature of the superconducting coil 203 decreases at night or other times, and the drive frequency of the compressor drive unit 132 of the compressor 108 reaches a predetermined lower limit, the operation of the compressor drive unit 132 of the compressor 108 and the displacement devices 303a and 303b of the cold head 107 will be stopped. A detailed description will follow.

[0162] In the first embodiment Figure 5 In the process, when the life extension mode is set, steps S503 to S506 are executed, and the displacement devices 303a and 303b operate at a constant frequency. By increasing or decreasing the drive frequency of the compressor drive unit 132 of the compressor 108 according to the temperature of the superconducting coil 203, the temperature of the cold head 107 is controlled to be constant.

[0163] By performing this control, during daytime imaging sequences in MRI device 1, when there is input heat in superconducting magnet 101, the temperature can be kept constant through steps S503 to S506. Figure 8 (a)).

[0164] On the other hand, during nighttime when the input heat is low, the drive frequency of the compressor drive unit 132 of the compressor 108 may sometimes be as low as... Figure 8 The lower limit frequency is reached as shown in (a). If the compressor drive unit 132 continues to reach the lower limit frequency, then as shown in (a), the lower limit frequency is reached. Figure 8 As shown in (b), the temperature of the superconducting coil 203 will be excessively lower than the specified temperature.

[0165] Therefore, in the fourth embodiment, control is performed to temporarily stop the operation of the compressor drive unit 132 of the compressor 108 and the displacement devices 303a and 303b of the cold head 107.

[0166] use Figure 9 The process of controlling the magnet control unit 110 in the fourth embodiment will be explained.

[0167] (Steps S501 to S506)

[0168] exist Figure 9 In the process, steps S501 to S506 are the same actions as in the first embodiment.

[0169] (Step S701)

[0170] In step S504, the temperature of the superconducting coil 203 is below the set temperature. In step S506, the magnet control unit 110 controls the reduction of the drive frequency of the compressor drive unit 132. As a result, when the drive frequency of the compressor drive unit 132 reaches the lower limit, the magnet control unit 110 sets that moment as a1 (step S701).

[0171] (Steps S702, S703)

[0172] In the cold head 107, even if the drive frequency of the compressor drive unit 132 reaches the lower limit, it still has a cooling capacity exceeding the input heat, therefore... Figure 8 As shown in (b), the temperature of the superconducting coil 203 begins to decrease. If time a1 elapses for a predetermined period of X1 to become time a2 (step S702), the magnet control unit 110 proceeds to step S703, stopping the operation of the compressor drive unit 132 of the compressor 108 and the displacement devices 303a and 303b of the cold head 107. At this time, the temperature of the superconducting coil 203 decreases to T2.

[0173] (Steps S704 and S705)

[0174] Since the magnet control unit 110 stops the operation of the compressor 108 and the cold head 107, cooling does not occur thereafter. Therefore, as... Figure 8 As shown in (b), the temperature rises.

[0175] Therefore, if the time a3 is elapsed after stopping the compressor 108 and the cold head 107 in step S703, the magnet control unit 110 restarts the compressor 108 and the cold head 107 and returns to step S501.

[0176] At this time, due to the temperature rise, in steps S501 to S505, by controlling the drive frequency of the compressor drive unit 132 of the compressor 108 again, the temperature of the superconducting coil 203 is controlled to move towards the set temperature.

[0177] Instead of the above Figure 9 The process is controlled based on time, such as... Figure 10 The process is similar, and the temperature of the superconducting magnet 101 can also be controlled.

[0178] (Steps S501 to S506)

[0179] exist Figure 10 In the process, steps S501 to S506 are the same actions as in the first embodiment.

[0180] (Steps S801, S802)

[0181] In step S506, when the driving frequency of the compressor drive unit 132 reaches the lower limit, the magnet control unit 110 continuously monitors the temperature of the superconducting coil 203, and stops the operation of the compressor drive unit 132 of the compressor 108 and the displacement devices 303a and 303b of the cold head 107 when the lower limit temperature T2 is reached.

[0182] (Steps S803, S804)

[0183] The magnet control unit 110 continuously monitors the temperature of the superconducting coil 203. When the temperature rises to the upper limit temperature T3, the compressor drive unit 132 of the compressor 108 and the displacement devices 303a and 303b of the cold head 107 are restarted, and the process returns to step S501.

[0184] exist Figure 9 In the process, appropriate times X1 and X2 need to be preset to ensure that the rerun of step S705 does not occur frequently and that T3 does not excessively exceed T1. Similarly, in Figure 10 In the process, appropriate T2 and T3 need to be set in advance so that the rerun of step S804 does not occur frequently and T3 does not exceed T1 excessively.

[0185] As described above, in the fourth embodiment, when the drive frequency of the compressor drive unit 132 of the compressor 108 reaches a predetermined lower limit, the operation of the compressor 108 and the cold head 107 is stopped, thereby reducing energy consumption.

[0186] <Fifth Implementation>

[0187] use Figures 11-12 The fifth embodiment will be described.

[0188] In the fifth embodiment, a cold head life extension mode is executed according to the state of the device.

[0189] In hospitals where imaging is only performed during the day using MRI device 1, such as Figure 11 As shown, the power supply of the imaging section 10 of the night MRI device 1 is off (state (1)), and only the minimum units such as the cooler 70 of the superconducting magnet 101 or the monitoring device are powered on.

[0190] When the hospital's business hours begin, the power supply to the imaging unit 10 is turned on. With this power supply, all units such as the tilting magnetic field power supply 113 and the RF transmitter 116 are powered on, and the imaging standby state is entered (state (2)). The operator configures the subject 102 and performs imaging after setting the imaging protocol (state (3)).

[0191] In the fifth embodiment, such as Figure 12 As shown in the flowchart, in step S1101, it is determined whether the camera is in standby mode (2) or in camera mode (3). In the case of mode (2) or (3), the cold head life extension mode is executed through steps S503 to S506. As a result, the operating frequency of the displacement devices 303a and 303b is set to a constant value, and the temperature is controlled to be constant by changing the driving frequency of the compressor drive unit 132 of the compressor 108.

[0192] In nighttime mode (1), steps S507 to S509 are performed without taking photographs, thereby increasing or decreasing the frequency of the displacement devices 303a and 303b. Furthermore, although in Figure 12 The process is not described, but in addition to steps S507 to S509, it can also perform... Figure 9 Steps S703, S705 or Figure 10 Steps S802 and S804 are used to stop or restart the compressor 108 and the displacement devices 303a and 303b.

[0193] By controlling the process as described in Embodiment 5, the impact on photography can be minimized while maximizing energy efficiency.

Claims

1. A magnetic resonance imaging device, characterized in that, Superconducting magnets that generate a static magnetic field in the photographic space. The superconducting magnet includes: a superconducting coil; a container housing the superconducting coil; a cold head mounted on the container; a compressor supplying compressed refrigerant gas to the cold head; and a processor. The compressor includes: a mechanism; a compressor drive unit that causes the mechanism to move periodically and compress the refrigerant gas; and a compressor inverter that adjusts the drive frequency of the compressor drive unit. The cold head includes: a cylinder body, into which refrigerant gas compressed by the compressor is supplied; a displacement device disposed within the cylinder body; and a displacement device drive unit that causes the displacement device to move periodically within the cylinder body. The cylinder of the cold head is connected to the superconducting coil via a metal heat-conducting component, and cools the superconducting coil. The processor has a cold head life extension mode, in which the displacement device moves at a constant frequency lower than a predetermined upper limit frequency, regardless of the temperature of the superconducting coil, and the drive frequency of the compressor drive unit adjusted by the compressor inverter is controlled according to the temperature of the superconducting coil.

2. The magnetic resonance imaging device according to claim 1, characterized in that, The displacement drive unit and the compressor inverter are supplied with power at a constant frequency from a commercial AC power source.

3. The magnetic resonance imaging device according to claim 1, characterized in that, The cold head also includes a cold head inverter for adjusting the drive frequency of the displacement drive section. In addition to controlling the inverter for the compressor, the processor also controls the inverter for the cold head. The processor's cold head life extension modes include a mode for use during photography and a mode for use outside of photography. In the photographic mode, the displacement device operates continuously at the constant frequency, regardless of the temperature of the superconducting coil.

4. The magnetic resonance imaging device according to claim 3, characterized in that, In the non-photography mode, the processor causes the displacement device to operate at a frequency lower than the constant frequency in the photography mode.

5. The magnetic resonance imaging device according to claim 3, characterized in that, In the non-photography mode, the processor stops the displacement device based on the temperature of the superconducting coil.

6. The magnetic resonance imaging apparatus according to claim 3, characterized in that, The processor determines the constant frequency at which the displacer moves based on the repetition frequency used in the parameters of the imaging sequence performed by the magnetic resonance imaging device for imaging.

7. The magnetic resonance imaging device according to claim 1, characterized in that, The processor controls the driving frequency of the compressor drive unit based on the temperature of the superconducting coil, and stops the compressor and the displacement device when the driving frequency of the compressor drive unit reaches a predetermined lower limit frequency.

8. The magnetic resonance imaging device according to claim 1, characterized in that, The processor controls the driving frequency of the compressor drive unit based on the temperature of the superconducting coil, and stops the compressor and the displacement device when the temperature of the superconducting coil reaches a predetermined lower limit temperature.

9. The magnetic resonance imaging apparatus according to claim 7, characterized in that, The processor restarts the compressor and the displacer after a predetermined time has elapsed since the compressor and the displacer were stopped, or when the temperature of the superconducting coil reaches a predetermined upper limit temperature, or when the pressure inside the container reaches a predetermined upper limit pressure.

10. The magnetic resonance imaging apparatus according to claim 1, characterized in that, The processor executes the cold head life extension mode when the magnetic resonance imaging device is in the process of taking pictures or in the photography standby state.

11. A control method for controlling the refrigerator of a superconducting magnet in a magnetic resonance imaging device. The refrigeration unit includes: The cold head is used in superconducting magnets; And the compressor, which supplies compressed refrigerant gas to the cold head. The control method is characterized in that... Regardless of the temperature of the superconducting magnet, the displacement device of the cold head moves at a constant frequency lower than a predetermined upper limit frequency, and the drive frequency of the compressor drive unit of the compressor is controlled according to the temperature of the superconducting magnet.

Images