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EP-4741862-A1 - MAGNETIC RESONANCE IMAGING APPARATUS AND METHOD OF CONTROLLING CRYOCOOLER

EP4741862A1EP 4741862 A1EP4741862 A1EP 4741862A1EP-4741862-A1

Abstract

An object is to extend a replacement lifetime of a cryocooler and reduce a replacement frequency of the cryocooler, thereby improving an operating rate of an MRI apparatus. A cold head lifetime extension mode is executed. In the cold head lifetime extension mode, a displacer of a cryocooler is driven at a constant frequency that is lower than a predetermined upper limit frequency regardless of a temperature of a superconducting coil, and a drive frequency of a compressor drive unit adjusted by an inverter for a compressor is controlled in accordance with the temperature of the superconducting coil.

Inventors

  • YATSUO, TAKESHI

Assignees

  • FUJIFILM Corporation

Dates

Publication Date
20260513
Application Date
20251103

Claims (11)

  1. A magnetic resonance imaging apparatus comprising: a superconducting magnet that generates a static magnetic field in an imaging space, wherein the superconducting magnet includes a superconducting coil, a vessel that houses the superconducting coil, a cold head that is attached to the vessel, a compressor that supplies compressed refrigerant gas to the cold head, and a processor, the compressor includes a mechanism unit, a compressor drive unit that periodically drives the mechanism unit to compress the refrigerant gas, and an inverter for a compressor that adjusts a drive frequency of the compressor drive unit, the cold head includes a cylinder into which the refrigerant gas compressed by the compressor is supplied, a displacer that is disposed in the cylinder, and a displacer drive unit that periodically drives the displacer in the cylinder, the cylinder of the cold head is connected to the superconducting coil by a heat conduction member made of metal and cools the superconducting coil, and the processor has a cold head lifetime extension mode, and in the cold head lifetime extension mode, the processor drives the displacer at a constant frequency that is lower than a predetermined upper limit frequency regardless of a temperature of the superconducting coil, and controls the drive frequency of the compressor drive unit adjusted by the inverter for a compressor in accordance with the temperature of the superconducting coil.
  2. The magnetic resonance imaging apparatus according to claim 1, wherein the displacer drive unit and the inverter for a compressor are supplied with power at a constant frequency from a commercial alternating-current power supply.
  3. The magnetic resonance imaging apparatus according to claim 1, wherein the cold head further includes an inverter for a cold head that adjusts a drive frequency of the displacer drive unit, the processor controls the inverter for a cold head in addition to the inverter for a compressor, the cold head lifetime extension mode of the processor includes an imaging mode and a non-imaging mode, and in the imaging mode, the processor causes the displacer to operate continuously at the constant frequency regardless of the temperature of the superconducting coil.
  4. The magnetic resonance imaging apparatus according to claim 3, wherein in the non-imaging mode, the processor causes the displacer to operate at a frequency that is lower than the constant frequency of the imaging mode.
  5. The magnetic resonance imaging apparatus according to claim 3, wherein in the non-imaging mode, the processor stops the displacer in accordance with the temperature of the superconducting coil.
  6. The magnetic resonance imaging apparatus according to claim 3, wherein the processor determines the constant frequency at which the displacer is driven, based on a repetition frequency used as a parameter of an imaging sequence executed by the magnetic resonance imaging apparatus for imaging.
  7. The magnetic resonance imaging apparatus according to claim 1, wherein the processor controls the drive frequency of the compressor drive unit in accordance with the temperature of the superconducting coil, and stops the compressor and the displacer in a case in which the drive frequency of the compressor drive unit reaches a predetermined lower limit frequency.
  8. The magnetic resonance imaging apparatus according to claim 1, wherein the processor controls the drive frequency of the compressor drive unit in accordance with the temperature of the superconducting coil, and stops the compressor and the displacer in a case in which the temperature of the superconducting coil reaches a predetermined lower limit temperature.
  9. The magnetic resonance imaging apparatus according to claim 7, wherein the processor restarts the compressor and the displacer in a case in which a predetermined time elapses after the compressor and the displacer are stopped, in a case in which the temperature of the superconducting coil reaches a predetermined upper limit temperature, or in a case in which a pressure in the vessel reaches a predetermined upper limit pressure.
  10. The magnetic resonance imaging apparatus according to claim 1, wherein the processor executes the cold head lifetime extension mode in a case in which the magnetic resonance imaging apparatus is performing imaging or is in an imaging standby state.
  11. A method of controlling a cryocooler provided in a superconducting magnet of a magnetic resonance imaging apparatus, wherein the cryocooler includes a cold head that is provided in the superconducting magnet and a compressor that supplies compressed refrigerant gas to the cold head, and a displacer of the cold head is driven at a constant frequency that is lower than a predetermined upper limit frequency regardless of a temperature of the superconducting magnet, and a drive frequency of a compressor drive unit of the compressor is controlled in accordance with the temperature of the superconducting magnet.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2024-196758, filed November 11, 2024. Each of the above application(s) is hereby expressly incorporated by reference, in its entirety, into the present application. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging (hereinafter, referred to as MRI) apparatus. 2. Description of the Related Art An MRI apparatus that cools a superconducting magnet using liquid helium is known. A superconducting coil is disposed in a liquid helium vessel, and the liquid helium vessel comprises a cold head of a cryocooler that cools vaporized helium to re-liquefy the helium. JP5960152B discloses a technology of changing a drive frequency of a compressor of a cryocooler to vary the cooling capacity in order to maintain a pressure in a liquid helium vessel constant. Meanwhile, an MRI apparatus that does not use liquid helium is also known. For example, JP2013-144099A discloses an MRI apparatus that conduction-cools a bobbin of a superconducting coil disposed within a vacuum vessel by cold heads of two or more cryocoolers. An inverter is connected to the compressor of the cryocooler, and the inverter is controlled based on a temperature of a superconducting coil unit. As a result, the capacity of the compressor is changed to control the temperature of the superconducting coil unit to a constant value. SUMMARY OF THE INVENTION The MRI apparatus that uses the superconducting coil requires the cryocooler to cool the superconducting coil. In a case of replacing the cryocooler, the MRI apparatus should be shut down. An object of the present invention is to extend a replacement lifetime of a cryocooler and reduce a replacement frequency of the cryocooler, thereby improving an operating rate of an MRI apparatus. An aspect of the present invention provides a magnetic resonance imaging apparatus including: a superconducting magnet that generates a static magnetic field in an imaging space. The superconducting magnet includes a superconducting coil, a vessel that houses the superconducting coil, a cold head that is attached to the vessel, a compressor that supplies compressed refrigerant gas to the cold head, and a processor. The compressor includes a mechanism unit, a compressor drive unit that periodically drives the mechanism unit to compress the refrigerant gas, and an inverter for a compressor that adjusts a drive frequency of the compressor drive unit. The cold head includes a cylinder into which the refrigerant gas compressed by the compressor is supplied, a displacer that is disposed in the cylinder, and a displacer drive unit that periodically drives the displacer in the cylinder. The cylinder of the cold head is connected to the superconducting coil by a heat conduction member made of metal and cools the superconducting coil. The processor has a cold head lifetime extension mode, and in the cold head lifetime extension mode, the processor drives the displacer at a constant frequency that is lower than a predetermined upper limit frequency regardless of a temperature of the superconducting coil, and controls the drive frequency of the compressor drive unit adjusted by the inverter for a compressor in accordance with the temperature of the superconducting coil. According to the aspect of the present invention, by operating the MRI apparatus in the cold head lifetime extension mode, the number of displacer strokes is reduced, whereby the replacement lifetime of the cryocooler can be extended. As a result, the replacement frequency of the cryocooler of the MRI apparatus can be reduced, and the operating rate of the MRI apparatus can be improved. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating an overall configuration of an MRI apparatus according to an embodiment of the present invention.FIG. 2 is a cross-sectional view illustrating the arrangement of a superconducting magnet and the like of the MRI apparatus illustrated in FIG. 1.FIG. 3 is a diagram illustrating a cross-sectional structure of the superconducting magnet of the MRI apparatus illustrated in FIG. 1.FIG. 4 is a cross-sectional view illustrating a configuration of a cold head 107 and a compressor 108 of the superconducting magnet illustrated in FIG. 3.FIG. 5 is a flowchart illustrating control of the cold head 107 and the compressor 108 by a processor of a superconducting magnet according to a first embodiment.FIG. 6 is a flowchart illustrating control of the cold head 107 and the compressor 108 by a processor of a superconducting magnet according to a modification example of the first embodiment.FIG. 7 is a flowchart illustrating control of the cold head 107 and the compressor 108 by a processor of a superconducting magnet according to a second embodiment.FIG. 8A is a graph illustrating an amount of heat input during imaging of a superconducting mag