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. The processor has a photographing time mode and a non-photographing time mode. In an imaging mode, the displacer is continuously operated at a constant frequency regardless of the pressure in the container of the superconducting magnet.

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; liquid helium disposed within the container; a refrigerator installed within the container; a compressor supplying compressed refrigerant gas to the refrigerator; 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 refrigerator includes: a cylinder supplied with refrigerant gas compressed by the compressor; a displacement device disposed within the cylinder; a displacement device drive unit that periodically moves the displacement device within the cylinder; and a refrigerator inverter that adjusts the drive frequency of the displacement device drive unit. The processor controls the pressure within the container of the superconducting magnet by controlling the compressor inverter and the refrigerator inverter. The processor has an imaging mode and a non-imaging mode. In the imaging mode, the displacement device operates continuously at a constant frequency regardless of the pressure within the container of the superconducting magnet.

[0010] -Invention Effects-

[0011] According to the present invention, in the case of imaging mode, regardless of the pressure inside the container of the superconducting magnet, by continuously operating the displacer at a constant frequency, the replacement life of the refrigerator is extended, and by reducing the replacement frequency of the refrigerator, the operating rate of the MRI device can be improved. 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 of 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 chamber, 128-Sequencer, 131-Mechanism unit, 132-Compressor drive Part, 133-Inverter for compressor, 201-Vacuum container, 201a-Outer container, 201b-Inner container, 203-Superconducting coil, 204-Liquid helium, 205-Liquid level sensor, 206-Temperature sensor, 209-Exhaust pipe, 212-Exhaust valve, 213-Pressure sensor, 216-Radiative heat shield, 217-Super insulator, 219-First cooling platform, 220-Second cooling platform, 225-Heat-conducting component, 301-GM cycle control unit, 302-Displacement drive unit, 303-Displacement, 303a, 303b-Displacement, 304-Cylinder block, 304a, 304b-Cylinder block, 305-Intake valve, 306-Exhaust valve, 307-Pressure gas hose, 308-Pressure 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 102; 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 102, 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 102. 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 examinee 102.

[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 This 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] Liquid helium 204 exists in the space within the inner container 201b of the vacuum container 201, where a superconducting coil 203 is configured.

[0044] An exhaust pipe 209 extends through the vacuum container 201, reaching into the inner container 201b. An exhaust valve 212 is installed on the exhaust pipe 209, which opens when the pressure inside the inner container 201b reaches a predetermined level (e.g., 20 kPa). Thus, in cases where a large amount of helium needs to be released, such as during quenching, the exhaust valve 212 is opened, allowing helium to be released from the exhaust pipe 209. Furthermore, a pressure sensor 213 is provided in the exhaust pipe 209 to measure the pressure of the helium vaporized from liquid helium 204. A heater 207 is disposed inside the inner container 201b to heat the liquid helium 204 as needed to vaporize it, maintaining a constant pressure inside the inner container 201b.

[0045] 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.

[0046] 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.

[0047] 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. The front end of the cold head 107 cools the space inside the inner container 201b, condensing the liquid helium gas inside the inner container 201b back into liquid helium. Thus, the superconducting magnet 101 is cooled by liquid helium.

[0048] 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.

[0049] 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.

[0050] Furthermore, multiple pressure sensors 213 or temperature sensors 206 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.

[0051] The magnet control unit 110 monitors the operating status of the superconducting magnet 101 and controls the cold head 107 and the compressor 108.

[0052] 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.

[0053] <Shim-plate 111>

[0054] 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).

[0055] <Inclined Magnetic Field Coil 112>

[0056] 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.

[0057] 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.

[0058] <RF Transmit Coil 115>

[0059] 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.

[0060] 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.

[0061] <RF receiving coil 117>

[0062] 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.

[0063] <Processor 20>

[0064] 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.

[0065] 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.

[0066] 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.

[0067] <Bedside Device 122>

[0068] 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.

[0069] 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.

[0070] <Detailed Structure of Vacuum Container 201 for Superconducting Magnets>

[0071] use Figure 3 The detailed structure of the vacuum container 201 of the superconducting magnet 101 described above will be further explained.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] A temperature sensor 206 for measuring the temperature of the inner container 201b is provided inside the container. 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.

[0076] 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.

[0077] The inner container 201b is filled with a specified amount (approximately 30% to 90% of the container volume) of liquid helium-204, and the superconducting coil 203 is immersed in the liquid helium-204. Thus, the superconducting coil 203 is cooled to the boiling point of liquid helium-204, i.e., 4.2 Kelvin (-268.8℃), and can maintain its superconducting state.

[0078] Pressure sensor 213 detects the pressure in the space within the inner container 201b that is not filled with liquid helium 204. Furthermore, a liquid level sensor 205 is disposed inside the inner container 201b to measure the level of the liquid helium 204. The output signal line of the liquid level sensor 205 is led out from the sensor connection terminal 109 to the outside of the superconducting magnet 101.

[0079] <Detailed information on the vacuum container 201 for superconducting magnets>

[0080] 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℃).

[0081] 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.

[0082] The front end of the second cooling stage 220 directly cools the helium gas inside the inner container 201b, cooling it to its boiling point of 4.2 Kelvin for condensation and liquefaction. Liquid helium then cools the superconducting coil 203.

[0083] <Detailed information about Refrigeration unit 70>

[0084] Next, use Figure 4 The detailed structure of the refrigeration unit 70 is described below.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] The cooling head 107 generates a cooling effect by performing the following steps (1) to (3) in sequence.

[0090] (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.

[0091] (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.

[0092] (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.

[0093] 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.

[0094] <First Embodiment>

[0095] In the first embodiment, the processor 20 has a photography mode and a non-photography mode. In the photography mode, regardless of the pressure inside the inner container 201b of the superconducting magnet 101, the displacement devices 303a and 303b operate continuously at a constant frequency. The frequency at which the displacement devices 303a and 303b operate is preferably set to a frequency lower than the driving frequency of the compressor drive unit 132.

[0096] use Figure 5 The process will provide a detailed explanation of the action.

[0097] (Step S501)

[0098] First, the magnet control unit 110 proceeds to step S502, where it reads the pressure from the pressure sensor 213 inside the inner container 201b.

[0099] (Step S502)

[0100] The magnet control unit 110 determines whether to execute the mode for photography or the mode for non-photography.

[0101] For example, when the imaging control unit 21 of the MRI apparatus 1 executes an imaging protocol (an imaging sequence for achieving the desired imaging method) or various sequences under that protocol, the magnet control unit 110 executes an imaging mode.

[0102] Furthermore, for example, if the operator sets a predetermined specific mode (e.g., when the operator presses the start button in the input device 121), the magnet control unit 110 can be configured to perform a photography mode during a specified period (from pressing the start button until the end of a series of photographs).

[0103] Furthermore, for example, the magnet control unit 110 can be configured to perform a photography mode when the bed device 122 is in a predetermined action or position (for example, when the operator presses the start button and begins to send the top plate of the subject 102 equipped with the bed device 122 toward the magnetic field space 103 in the frame, until the end of a series of photographs and the top plate returns to its original position).

[0104] Furthermore, for example, when an operator or service personnel operates the input device 121 of the UI unit 30 or via the communication control device provided with the MRI device 1 ( Figure 1 , Figure 2 (Not shown in the image) When remote operation is performed and the magnet control unit 110 is set to the mode for performing photography, the mode for performing photography is performed regardless of whether photography is being performed.

[0105] On the other hand, the magnet control unit 110 executes a non-photography mode when it is not executing a photography mode. For example, when the photography control unit 21 does not execute a photography protocol, or when the operator sets a predetermined specific mode (for example, when the operator sets a standby mode, sleep mode, or low power consumption mode in standby mode in the input device 121), the magnet control unit 110 executes a non-photography mode.

[0106] Furthermore, for example, when the bed table device 122 is in a predetermined position (e.g., when the top plate of the bed table device 122 is in the initial position (the predetermined position before the subject 102 is mounted), the magnet control unit 110 can be configured to perform a non-photographic mode.

[0107] If the photography mode is being performed, proceed to step S503. If the non-photography mode is being performed, proceed to step S507.

[0108] (Step S503)

[0109] 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 that is lower than a predetermined upper limit frequency.

[0110] Therefore, regardless of the pressure inside the inner container 201b of the superconducting magnet 101, the displacement devices 303a and 303b of the cold head 107 operate at a predetermined constant driving frequency.

[0111] The magnet control unit 110 proceeds to step S504.

[0112] (Steps S504 to S506)

[0113] Next, if the pressure read from pressure sensor 213 is higher than the set pressure (step S504), magnet control unit 110 proceeds to step S505, instructing compressor inverter 133 of compressor 108 to increase the drive frequency of compressor drive unit 132. As a result, due to the increase in drive frequency of compressor drive unit 132, the pressure of refrigerant gas delivered from compressor 108 to cold head 107 increases.

[0114] On the other hand, if the pressure read from the pressure sensor 213 is below the set pressure, the magnet control unit 110 proceeds to step S506, instructing 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.

[0115] Thus, the magnet control unit 110 increases or decreases the driving frequency of the compressor drive unit 132 according to the pressure inside the inner container 201b of the superconducting magnet 101, thereby changing the pressure of the refrigerant gas delivered 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 to maintain the pressure inside the inner container 201b of the superconducting magnet 101 constant.

[0116] Furthermore, the set pressure in step S504 can be a specific pressure or a pressure range. When the pressure range is used as the set pressure, the magnet control unit 110 proceeds to step S505 if the pressure read from the pressure sensor 213 is higher than the upper limit of the set pressure range, and proceeds to step S506 if the pressure is lower than the lower limit of the set pressure range. If the pressure read from the pressure sensor 213 is greater than the lower limit but lower than the upper limit, the magnet control unit 110 does not control the compressor 108 and returns to step S501.

[0117] (Steps S507 to S509)

[0118] On the other hand, in step S507, the magnet control unit 110 executes a non-photography mode. Specifically, if the pressure read from the pressure sensor 213 is higher than the set pressure, the process 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.

[0119] On the other hand, in step S507, if the pressure read from the pressure sensor 213 is lower than the set pressure, 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 drive frequency of the displacement devices 303a and 303b is reduced, thereby reducing the cooling capacity of the cold head 107.

[0120] Therefore, in steps S507 to S509, the magnet control unit 110 can adjust the cooling capacity of the cold head 107 by increasing or decreasing the driving frequency of the displacement devices 303a and 303b, and maintain the pressure inside the inner container 201b of the superconducting magnet 101 constant.

[0121] Similar to the setting pressure in step S504, the setting pressure in step S507 can be a specific pressure or within a pressure range.

[0122] As described above, in this embodiment, during the photography mode, the frequency of operation of the displacers 303a and 303b of the cold head 107 in step S503 is set to a constant value less than a predetermined upper limit. Therefore, compared to the case where the driving frequency of the displacers 303a and 303b is increased or decreased according to pressure as in steps S507 to S509, the reciprocating frequency of the displacers 303a and 303b is reduced, which can reduce wear or failure of the displacers 303a and 303b and extend the life of the cold head 107.

[0123] The effects of this implementation method will be explained in further detail.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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 of the refrigerator in a conventional MRI device (1Hz or 1.2Hz in the above example).

[0128] For example, the upper limit of the operating frequency of the displacement devices 303a and 303b is preferably 1 Hz or less, and more preferably 0.8 Hz or less.

[0129] In this embodiment, the displacement drive unit 302 of the cold head 107 can be of any structure as long as it can set the operating frequency of the displacements 303a and 303b to a constant value smaller than a predetermined upper limit. For example, a synchronous motor can be used as in conventional refrigerators, or the operating frequency of the displacements 303a and 303b can be set to a predetermined constant value based on the output frequency of the GM cycle control unit 301.

[0130] In this embodiment, the magnet control unit 110 reduces the frequency of the operation of the displacement devices 303a and 303b to a constant value (step S503), but in order to variably control the drive frequency of the compressor 108 (steps S505 and S506), the overall cooling performance of the refrigerator 70 is not reduced.

[0131] 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.

[0132] Furthermore, as control methods for steps S504 to S506 and S507 to S509, examples of increasing or decreasing the drive frequency of compressor 108 or the operating frequency of displacement devices 303a and 303b based on whether the pressure is higher or lower than the set pressure have been described. However, since various known control methods exist, the desired method can be used. For example, PID control, as a type of feedback control, can be used.

[0133] As described above, in the cold head life extension mode of the MRI apparatus 1 of this embodiment, regardless of the pressure inside the inner container 201b of the superconducting magnet 101, by moving the displacement devices 303a and 303b at a constant frequency lower than a predetermined upper limit frequency, the number of reciprocating movements can be reduced compared to conventional displacement devices, and the replacement life of the cold head 107 can be extended. Furthermore, by controlling the drive frequency of the displacement device drive unit 302, the overall cooling capacity of the refrigerator 70 can be maintained.

[0134] Furthermore, in the imaging mode of the MRI apparatus 1 in this embodiment, regardless of the pressure inside the inner container 201b of the superconducting magnet 101, the displacement devices 303a and 303b move at a constant frequency lower than the predetermined upper limit frequency. Therefore, even 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.

[0135] If, during the imaging sequence, the displacement devices 303a and 303b stop operating, or conversely begin operating, or their operating frequency changes, the vibration state of the superconducting magnet 101 changes, which may cause degradation of the image being photographed. However, in this embodiment, during the imaging process, the displacement devices 303a and 303b always operate at a constant frequency, thus also having the advantage of preventing degradation of the image being photographed.

[0136] In addition, such as Figure 6As shown, it can also be configured so that users or staff can set a cold head life extension mode via input device 121 or remote operation. In this case, after the magnet control unit 110 obtains pressure from the pressure sensor 213 inside the inner container 201b in step S501, it proceeds to step S611. The magnet control unit 110 in Figure 6 In step S611, it is determined whether a cold head life extension mode is set. If a cold head life extension mode is not set, the magnet control unit 110 executes steps S507 to S509. On the other hand, in step S611, if a cold head life extension mode is set, the magnet control unit 110 proceeds to step S502, where it determines whether to execute a photography mode or a non-photography mode.

[0137] In step S502, the magnet control unit 110 enters step S503 when it determines that it is in the mode of performing photography, and causes the displacement devices 303a and 303b to operate continuously at a constant first frequency, regardless of the temperature of the superconducting coil.

[0138] On the other hand, in step S502, the magnet control unit 110 enters step S613 when it is determined that a non-photography mode is being executed, and causes the displacement devices 303a and 303b to operate continuously at a constant second frequency.

[0139] Considering that the heat input to the superconducting magnet 101 is small when not photographing, the second frequency is set to be lower than the first frequency of the photographing mode. The second frequency can be set by the magnet control unit 110 based on the temperature obtained in step S501.

[0140] Therefore, when the cold head life extension mode is set, the number of actions is further reduced in the non-photography mode compared to the photography mode, thus extending the life of the cold head 107.

[0141] <Second Implementation>

[0142] Next, use Figure 7 The process of the second implementation method will be described.

[0143] 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 pressure obtained from the pressure sensor 213 (step S501), the magnet control unit 110 determines whether it is a situation requiring accelerated cooling (step S601). If it is a situation requiring accelerated cooling, it proceeds to step S602.

[0144] 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.

[0145] Therefore, the superconducting coil 203 is cooled as quickly as possible.

[0146] In addition, Figure 7 In step S601, if the magnet control unit 110 determines that accelerated cooling is not required, the process after step S502 is performed in the same manner as in the first embodiment.

[0147] In step S601, the situation in which the magnet control unit 110 determines that accelerated cooling is required refers to the following situation.

[0148] For example, when quenching occurs in the superconducting coil 203 immediately after the MRI device 1 is introduced, or when the refrigerator 70 is replaced. In these situations, a stable static magnetic field cannot be generated, so the MRI device cannot perform imaging, requiring the superconducting coil 203 to be cooled as quickly as possible.

[0149] 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. Furthermore, liquid helium is added to the inner container 201b as needed.

[0150] As a result, power consumption increases, and vibrations in the static magnetic field may also increase, but the most important thing is to prioritize cooling the superconducting coil 203.

[0151] 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 pressure detected by the pressure sensor 213 exceeds a predetermined pressure that cannot be a stable state, the process proceeds to step S602 to perform accelerated cooling.

[0152] 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.

[0153] Additionally, in step S501, pressure can also be obtained from a pressure sensor of the superconducting magnet 101 other than pressure sensor 213. Furthermore, the determination in step S601 can be made using detection results other than the pressure within the inner container 201b 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.

[0154] 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.

[0155] <Third Implementation>

[0156] Next, the third embodiment will be described.

[0157] 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).

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] <Fourth Implementation>

[0166] Next, use Figures 8-10 The fourth embodiment will be described.

[0167] The MRI device 1 of the fourth embodiment has the same structure and operation as that of the first embodiment, but consumes less energy compared to the first embodiment.

[0168] When the user sets a photography mode and continues to operate in the photography mode after photography ends, the pressure inside the inner container 201b of the superconducting magnet 101 decreases, especially at night, and the driving frequency of the compressor drive unit 132 of the compressor 108 may sometimes reach a predetermined lower limit. In this case, in the fourth embodiment, the operation of the compressor drive unit 132 of the compressor 108 and the displacement devices 303a and 303b of the cold head 107 is stopped. A detailed explanation will follow.

[0169] In the first embodiment Figure 5 In the process, when the photography mode is set, steps S503 to S506 are executed. As a result, 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 pressure inside the inner container 201b of the superconducting magnet 101, the pressure of the cold head 107 is controlled to be constant.

[0170] By performing this control, during daytime imaging sequences in MRI device 1, and with input heat in superconducting magnet 101, the pressure can be controlled to a constant level via steps S503-S506. Figure 8 (a)).

[0171] However, during nighttime hours when the input heat is low, the drive frequency of the compressor drive unit 132 of the compressor 108 sometimes... Figure 8 As shown in (a), the lower limit frequency is reached. 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 pressure inside the inner container 201b of the superconducting magnet 101 may be excessively lower than the specified pressure.

[0172] 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.

[0173] use Figure 9 The process of controlling the magnet control unit 110 in the fourth embodiment will be explained.

[0174] (Steps S501 to S506)

[0175] exist Figure 9 In the process, steps S501 to S506 are the same actions as in the first embodiment.

[0176] (Step S701)

[0177] In step S504, the pressure inside the inner container 201b of the superconducting magnet 101 is below the set pressure P1. 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 this moment as a1 (step S701).

[0178] (Steps S702, S703)

[0179] 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 pressure inside the inner container 201b of the superconducting magnet 101 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 pressure inside the inner container 201b of the superconducting magnet 101 decreases to pressure P2.

[0180] (Steps S704 and S705)

[0181] 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 pressure increases.

[0182] Therefore, if the time a3 is elapsed after the compressor 108 and the cold head 107 are stopped in step S703, the magnet control unit 110 restarts the compressor 108 and the cold head 107 and returns to step S501.

[0183] At this time, since the pressure rises to pressure P3, in steps S501 to S505, by controlling the drive frequency of the compressor drive unit 132 of the compressor 108 again, the pressure in the inner container 201b of the superconducting magnet 101 is controlled to move towards the set pressure P1.

[0184] Instead of the above Figure 9 The process can be controlled according to time, just like that. Figure 10 The process can be controlled according to the pressure inside the inner container 201b of the superconducting magnet 101.

[0185] (Steps S501 to S506)

[0186] exist Figure 10 In the process, steps S501 to S506 are the same actions as in the first embodiment.

[0187] (Steps S801, S802)

[0188] 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 pressure inside the inner container 201b of the superconducting magnet 101, 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 pressure P2 is reached.

[0189] (Steps S803, S804)

[0190] The magnet control unit 110 continuously monitors the pressure inside the inner container 201b of the superconducting magnet 101. When the pressure rises to the upper limit pressure P3, 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.

[0191] exist Figure 9 In the process, appropriate times X1 and X2 need to be preset to prevent the re-run of step S705 from occurring too frequently. Similarly, in Figure 10 In the process, appropriate P2 and P3 need to be set in advance so that the restart of step S804 does not occur frequently and P3 does not exceed P1 excessively.

[0192] 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.

[0193] <Fifth Implementation>

[0194] use Figures 11-12 The fifth embodiment will be described.

[0195] In the fifth embodiment, the photography mode is executed according to the state of the device.

[0196] 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.

[0197] 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)).

[0198] In the fifth embodiment, such as Figure 12As shown in the flowchart, during step S1101, it is determined whether the camera is in standby mode (2) or camera mode (3). In the case of mode (2) or (3), the camera mode is executed through steps S503 to S506. As a result, the frequency of operation of the displacement devices 303a and 303b is set to a constant value, and the pressure control in the inner container 201b of the superconducting magnet 101 is kept constant by changing the drive frequency of the compressor drive unit 132 of the compressor 108.

[0199] 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.

[0200] 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; liquid helium disposed within the container; a refrigerator installed within the container; a compressor supplying compressed refrigerant gas to the refrigerator; 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 refrigeration unit includes: a cylinder body supplied with refrigerant gas compressed by the compressor; a displacement device disposed within the cylinder body; a displacement device drive unit for periodically moving the displacement device within the cylinder body; and an inverter for the refrigeration unit for adjusting the drive frequency of the displacement device drive unit. The processor controls the pressure inside the container by controlling the inverter for the compressor and the inverter for the refrigeration unit. The processor has a photography mode and a non-photography mode. In the photography mode, the displacement device operates continuously at a constant frequency regardless of the pressure inside the container.

2. The magnetic resonance imaging device according to claim 1, characterized in that, The processor sets the constant frequency at which the displacement device operates during the photography mode to a frequency lower than the drive frequency of the compressor drive unit.

3. The magnetic resonance imaging device according to claim 1, 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.

4. The magnetic resonance imaging device according to claim 3, characterized in that, In the non-photography mode, the processor stops the displacer based on the pressure inside the container.

5. The magnetic resonance imaging device according to claim 1, 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.

6. The magnetic resonance imaging device according to claim 1, characterized in that, The processor controls the driving frequency of the compressor drive unit according to the pressure inside the container, and stops the compressor and the displacement device when the driving frequency of the compressor drive unit reaches a predetermined lower limit frequency.

7. The magnetic resonance imaging device according to claim 1, characterized in that, The processor controls the drive frequency of the compressor drive unit according to the pressure inside the container, and stops the compressor and the displacement device when the pressure inside the container reaches a predetermined lower limit pressure.

8. The magnetic resonance imaging apparatus according to claim 6, 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 pressure inside the container reaches a predetermined upper limit pressure, or when the pressure inside the container reaches a predetermined upper limit pressure.

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

10. A control method for a refrigerator, which is a control method for a refrigerator incorporated in a superconducting magnet of a magnetic resonance imaging device, characterized in that... The refrigeration unit includes: The cold head is used in superconducting magnets; And the compressor, which supplies compressed refrigerant gas to the cold head. It has a shooting mode and an off-shooting mode. In the photographic mode, regardless of the pressure inside the container of the superconducting magnet, the displacement device of the cold head operates continuously at a constant frequency.

Images