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EP-4741861-A1 - MAGNETIC RESONANCE IMAGING APPARATUS AND METHOD OF CONTROLLING CRYOCOOLER

EP4741861A1EP 4741861 A1EP4741861 A1EP 4741861A1EP-4741861-A1

Abstract

An object is to extend a replacement lifetime of a cryocooler (70) and reduce a replacement frequency of the cryocooler, thereby improving an operating rate of an MRI apparatus (1). A processor (20) has an imaging mode and a non-imaging mode. In the imaging mode, a displacer is caused to operate continuously at a constant frequency regardless of a pressure in a vessel of a superconducting magnet (101).

Inventors

  • TAKESHI, Yatsuo

Assignees

  • FUJIFILM Corporation

Dates

Publication Date
20260513
Application Date
20251030

Claims (10)

  1. A magnetic resonance imaging apparatus (1) comprising: a superconducting magnet (101) that generates a static magnetic field in an imaging space, wherein the superconducting magnet includes a superconducting coil (203), a vessel that houses the superconducting coil, liquid helium (204) that is disposed in the vessel, a cryocooler (70) that is attached to the vessel, a compressor (108) that supplies compressed refrigerant gas to the cryocooler, and a processor (20), the compressor (108) includes a mechanism unit (131), a compressor drive unit (132) 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 cryocooler includes a cylinder into which the refrigerant gas compressed by the compressor is supplied, a displacer (303) that is disposed in the cylinder, a displacer drive unit (302) that periodically drives the displacer in the cylinder, and an inverter for a cryocooler that adjusts a drive frequency of the displacer drive unit, the processor controls the inverter for a compressor and the inverter for a cryocooler to control a pressure in the vessel, and the processor has an imaging mode and a non-imaging mode and causes, in the imaging mode, the displacer to operate continuously at a constant frequency regardless of the pressure in the vessel.
  2. The magnetic resonance imaging apparatus according to claim 1, wherein the processor (20) sets the constant frequency at which the displacer is caused to operate in the imaging mode to a frequency that is lower than the drive frequency of the compressor drive unit.
  3. The magnetic resonance imaging apparatus according to claim 1, wherein in the non-imaging mode, the processor (20) causes the displacer to operate at a frequency that is lower than the constant frequency of the imaging mode.
  4. The magnetic resonance imaging apparatus according to claim 3, wherein in the non-imaging mode, the processor (20) stops the displacer in accordance with the pressure in the vessel.
  5. The magnetic resonance imaging apparatus according to claim 1, wherein the processor (20) 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.
  6. The magnetic resonance imaging apparatus according to claim 1, wherein the processor (20) controls the drive frequency of the compressor drive unit in accordance with the pressure in the vessel, 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.
  7. The magnetic resonance imaging apparatus according to claim 1, wherein the processor (20) controls the drive frequency of the compressor drive unit in accordance with the pressure in the vessel, and stops the compressor and the displacer in a case in which the pressure in the vessel reaches a predetermined lower limit pressure.
  8. The magnetic resonance imaging apparatus according to claim 6, wherein the processor (20) 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 pressure in the vessel reaches a predetermined upper limit pressure, or in a case in which the pressure in the vessel reaches a predetermined upper limit pressure.
  9. The magnetic resonance imaging apparatus according to claim 1, wherein the processor (20) executes the imaging mode in a case in which the magnetic resonance imaging apparatus is performing imaging or is in an imaging standby state.
  10. A method of controlling a cryocooler (70) provided in a superconducting magnet of a magnetic resonance imaging apparatus (1), wherein the cryocooler includes a cold head provided in the superconducting magnet and a compressor (108) that supplies compressed refrigerant gas to the cold head, an imaging mode and a non-imaging mode are provided, and in the imaging mode, a displacer of the cold head is caused to operate continuously at a constant frequency regardless of a pressure in a vessel 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. 2024-196767, 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, liquid helium that is disposed in the vessel, a cryocooler that is attached to the vessel, a compressor that supplies compressed refrigerant gas to the cryocooler, 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 cryocooler includes a cylinder into which the refrigerant gas compressed by the compressor is supplied, a displacer that is disposed in the cylinder, a displacer drive unit that periodically drives the displacer in the cylinder, and an inverter for a cryocooler that adjusts a drive frequency of the displacer drive unit. The processor controls the inverter for a compressor and the inverter for a cryocooler to control a pressure in the vessel of the superconducting magnet. The processor has an imaging mode and a non-imaging mode. The processor causes, in the imaging mode, the displacer to operate continuously at a constant frequency regardless of the pressure in the vessel of the superconducting magnet. According to the aspect of the present invention, in a case of the imaging mode, the operating rate of the MRI apparatus can be improved by extending the replacement lifetime of the cryocooler and reducing the replacement frequency of the cryocooler by causing the displacer to operate continuously at the constant frequency regardless of the pressure in the vessel of the superconducting magnet. 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 magnet of a fourth embodiment and an operation frequency of