WO2021052760A1 - Magnet pre-cooling device for magnetic resonance imaging system - Google Patents

Magnet pre-cooling device for magnetic resonance imaging system Download PDF

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Publication number
WO2021052760A1
WO2021052760A1 PCT/EP2020/074480 EP2020074480W WO2021052760A1 WO 2021052760 A1 WO2021052760 A1 WO 2021052760A1 EP 2020074480 W EP2020074480 W EP 2020074480W WO 2021052760 A1 WO2021052760 A1 WO 2021052760A1
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WIPO (PCT)
Prior art keywords
refrigerant
magnet
flow path
gas
cooling device
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Application number
PCT/EP2020/074480
Other languages
French (fr)
Inventor
Bi Hui LAI
Jun Zhao WU
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Siemens Healthcare Limited
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Publication of WO2021052760A1 publication Critical patent/WO2021052760A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/3804—Additional hardware for cooling or heating of the magnet assembly, for housing a cooled or heated part of the magnet assembly or for temperature control of the magnet assembly
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F6/00—Superconducting magnets; Superconducting coils
    • H01F6/04—Cooling
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/381—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets
    • G01R33/3815—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets with superconducting coils, e.g. power supply therefor
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]

Definitions

  • the present invention relates to a magnet pre-cooling device for a magnetic resonance imaging (MRI) system.
  • MRI magnetic resonance imaging
  • a superconducting coil used to generate a magnetic field must be immersed in liquid helium stored in a liquid helium tank, and the superconducting coil can be changed to a superconducting state by cooling the coil to -269°C.
  • liquid helium is poured directly into a liquid helium tank that is in a room temperature state, a large amount of liquid helium will change to a gaseous state and overflow from the liquid helium tank.
  • the price of liquid helium is relatively high; thus, to avoid the loss of a large amount of liquid helium, the liquid helium tank must be pre cooled, e.g.
  • liquid nitrogen can be used to fill the liquid helium tank and held therein for a period of time, until the liquid helium tank and the superconducting coil therein reach -196°C.
  • Helium gas is then used to blow out the liquid nitrogen; at this time, the liquid helium tank is filled with pure helium gas and the temperature is held at -196°C.
  • liquid nitrogen when liquid nitrogen is used for pre-cooling for example, liquid nitrogen accumulates at the bottom of the liquid helium tank; thus, from the perspective of the coil immersed in the liquid helium tank, a relatively large gradient temperature difference will arise between the bottom and the top, and this gradient temperature difference will subject the coil to high thermal stress, and in turn might affect the normal operation of the coil.
  • a large amount of helium gas must be used to blow out the liquid nitrogen, and since helium gas is very expensive, the cost of using such a method is still relatively high.
  • helium gas may also be used directly to pre-cool the liquid helium tank; the helium gas will become high-temperature through heat exchange with the liquid helium tank and thus a high-priced, high-power refrigerating machine must be used to cool the helium gas with the raised temperature .
  • the object of the present invention is to propose a magnet pre-cooling device for an MRI system, which can reduce thermal stress in a superconducting coil during magnet pre-cooling and reduce helium loss, without any need for a large refrigerating machine.
  • An embodiment of the present invention provides a magnet pre-cooling device for an MRI system, comprising: a first refrigerant flow path, for supplying a first refrigerant to a first magnet; a second refrigerant flow path, for supplying a second refrigerant to a second magnet; the first refrigerant flow path undergoes heat exchange with the second refrigerant flow path by means of a heat exchanger; the second refrigerant is used to cool the first refrigerant that has passed through the first magnet and enable the first refrigerant to be used for cooling the first magnet again, and the second refrigerant that has undergone heat exchange is used to cool the second magnet.
  • the first refrigerant flow path comprises a first refrigerant supply path for supplying a low- temperature first refrigerant supply gas to the first magnet, and a first refrigerant return path for returning a high- temperature first refrigerant return gas from the first magnet;
  • the heat exchanger cools the first refrigerant return gas to be re-used as the first refrigerant supply gas by causing the first refrigerant return gas in the first refrigerant return path to undergo heat exchange with the second refrigerant, which is in a liquid state, from a second refrigerant source, and the liquid-state second refrigerant changes to a gaseous second refrigerant gas that can be used to cool the second magnet.
  • the magnet pre-cooling device for an MRI system described above preferably further comprises: a first refrigerant source, for supplying the first refrigerant, which is gaseous, to the first refrigerant flow path; and a second refrigerant source, for supplying the second refrigerant, which is in a liquid state, to the second refrigerant flow path.
  • a driving device is provided at the first refrigerant return path, the driving device being used to cause the first refrigerant to flow in the first refrigerant flow path.
  • the first refrigerant source is disposed at the first refrigerant return path.
  • the gaseous first refrigerant is helium gas
  • the liquid-state second refrigerant is liquid nitrogen.
  • a magnet pre-cooling device for an MRI system, comprising: a refrigerant source storing a liquid-state refrigerant; a refrigerant flow path for supplying the refrigerant to a magnet; and a heat exchanger storing a heat exchange liquid at a temperature higher than the vaporization temperature of the refrigerant; the refrigerant flow path passes through the heat exchanger, the heat exchange liquid is used to change the liquid-state refrigerant to a refrigerant gas, and the refrigerant gas is supplied to the magnet.
  • a temperature sensor for detecting the temperature of the refrigerant gas is provided at a downstream side of the heat exchanger.
  • a heater is provided at the heat exchanger, and when the temperature of the refrigerant gas detected by the temperature sensor is lower than a preset value, the heater is used to heat the heat exchange liquid.
  • the heat exchange liquid is water
  • the liquid-state refrigerant is liquid nitrogen.
  • the superconducting coil can be cooled uniformly in the magnet, and no excessive gradient temperature difference will arise between the bottom and top of the superconducting coil, thereby reducing thermal stress.
  • helium gas is supplied to the first magnet
  • nitrogen gas is supplied to the second magnet.
  • the helium gas supplied to the first magnet will be re-cooled using the liquid nitrogen supplied by the second refrigerant source; thus, there is no need for a large refrigerating machine to re-cool the high-temperature helium gas, as was the case previously.
  • the liquid nitrogen supplied by the second refrigerant source after cooling the helium gas supplied to the first magnet and thus becoming high-temperature and changing to nitrogen gas, will be used to cool the second magnet; thus, from the perspective of the second magnet, compared with the previous scenario in which liquid nitrogen was used for pre-cooling, there is no need to use a large amount of helium gas to blow out liquid nitrogen; only a small amount of helium gas needs to be used to blow out the nitrogen gas and thus the amount of high- priced helium gas used is correspondingly reduced.
  • Fig. 1 is an explanatory drawing of a magnet pre-cooling device for an MRI system according to a first embodiment of the present invention.
  • FIG. 2 is an explanatory drawing of a magnet pre-cooling device for an MRI system according to a second embodiment of the present invention. Key to the drawings:
  • Fig. 1 shows a schematic drawing of a pre-cooling device for an MRI system according to a first embodiment of the present invention.
  • the pre-cooling device 10 can separately pre-cool a first magnet 20 and a second magnet 30 used for an MRI apparatus.
  • the pre-cooling device 10 comprises: a first refrigerant flow path 11 for supplying a first refrigerant to the first magnet 20 to perform pre cooling, and a second refrigerant flow path 12 for supplying a second refrigerant to the second magnet 30.
  • the first refrigerant flow path 11 and second refrigerant flow path 12 can undergo heat exchange in a heat exchanger 13.
  • a first refrigerant source 14 for supplying the first refrigerant is connected at the first refrigerant flow path 11, and a second refrigerant source 15 for supplying the second refrigerant is connected in the second refrigerant flow path 12.
  • the first refrigerant source supplies helium gas for example
  • the second refrigerant source supplies liquid nitrogen for example.
  • the first refrigerant flow path 11 comprises a first refrigerant supply path 111 for supplying low-temperature first refrigerant such as helium gas to the first magnet 20, and a first refrigerant return path 112 for returning high-temperature first refrigerant from the first magnet 20.
  • the first refrigerant source 14 supplies low-temperature helium gas as the first refrigerant to the first refrigerant flow path 11; the helium gas is supplied to the first magnet 20 via the first refrigerant supply path 111, and flows in the direction indicated by arrow A to pre-cool the first magnet 20.
  • a first refrigerant gas resulting from pre-cooling of the first magnet 20 has become high-temperature and flows out as a first refrigerant return gas via the first refrigerant return path 112; the first refrigerant return path 112 then passes through the heat exchanger 13 to form a loop with the first refrigerant supply path 111.
  • the second refrigerant flow path 12 is connected to the second refrigerant source 15, passes through the heat exchanger 13 and is connected to the second magnet 30, and flows in the direction indicated by arrow B in the second magnet 30 to pre-cool the second magnet 30, subsequently being discharged into the atmosphere.
  • the second refrigerant source 15 can supply liquid nitrogen as the second refrigerant to the second refrigerant flow path 12.
  • the first refrigerant return gas which has been used to pre-cool the first magnet 20, in the first refrigerant return path 112 undergoes heat exchange with liquid nitrogen, which comes from the second refrigerant source 15 as the second refrigerant, in the second refrigerant flow path 12; thus, the high-temperature first refrigerant return gas is cooled by the relatively low-temperature second refrigerant and is cooled back to a low-temperature first refrigerant supply gas that can be re-used, and is again conveyed to the first magnet 20 via the first refrigerant supply path 111 to continue to pre-cool the first magnet 20.
  • the low- temperature liquid nitrogen used as the second refrigerant in the second refrigerant flow path 12 is heated by the high- temperature first refrigerant return gas in the first refrigerant return path 112 and changes to nitrogen gas, and then flows into the second magnet 30 through the second refrigerant flow path 12, and flows in the direction indicated by arrow B to pre-cool the second magnet 30.
  • a fan 16 serving as a first refrigerant driving apparatus is further provided at the first refrigerant return path 112; the fan 16 can rotate under the driving action of a motor 17 to impel the flow of helium gas as the first refrigerant in the first refrigerant flow path 11.
  • the pre-cooling device for an MRI system since a gaseous refrigerant is supplied separately to the first magnet 20 or second magnet 30 - helium gas is supplied to the first magnet 20, and nitrogen gas is supplied to the second magnet 30 - to perform pre-cooling, the superconducting coil can be pre-cooled uniformly in the magnet, and no gradient temperature difference will arise between the bottom and top of the superconducting coil, thereby reducing thermal stress.
  • the helium gas supplied to the first magnet 20 will be re-cooled using the liquid nitrogen supplied by the second refrigerant source 15; thus, there is no need for a large refrigerating machine to re-cool the high- temperature helium gas, as was the case previously.
  • the liquid nitrogen supplied by the second refrigerant source 15 after cooling the helium gas supplied to the first magnet 20 and thus becoming high-temperature and changing to nitrogen gas, will be used to pre-cool the second magnet 30; thus, from the perspective of the second magnet 30, compared with the previous scenario in which liquid nitrogen was used for pre-cooling, there is no need to use a large amount of helium gas to blow out liquid nitrogen; only a small amount of helium gas needs to be used to blow out the nitrogen gas and thus the amount of high-priced helium gas used is correspondingly reduced.
  • Second embodiment Second embodiment
  • Fig. 2 shows an explanatory drawing of a magnet pre-cooling device in a second embodiment of the present invention.
  • the magnet pre-cooling device of this embodiment comprises: a refrigerant source 15 storing a liquid-state refrigerant, which is for example liquid nitrogen in this embodiment; a refrigerant flow path 12, connected to the refrigerant source 15 and supplying the refrigerant to a magnet 30; a heat exchanger 13' storing a heat exchange liquid at a temperature higher than the vaporization temperature of the refrigerant, wherein the heat exchange liquid is for example water in a room-temperature state in this embodiment.
  • the refrigerant flow path 12 passes through the heat exchanger 13', and low-temperature liquid nitrogen from the refrigerant source 15 undergoes heat exchange with the heat exchange liquid in the heat exchanger 13', such that the liquid nitrogen as the liquid-state refrigerant absorbs heat from the heat exchange liquid and changes to nitrogen gas in a gaseous state; the nitrogen gas is then supplied to the magnet 30 via the refrigerant flow path 12, passes through a cavity of superconducting magnet 30 along a path indicated by arrow C, and is then discharged into the air through a gas discharge channel.
  • a heat sensor 121 is provided at a downstream side of the heat exchanger 13'.
  • the heat sensor 121 is used to detect the temperature of gaseous refrigerant in the refrigerant flow path 12; when the temperature of the gaseous refrigerant is lower than a predetermined value, a heater 18 disposed at the heat exchanger 13' is switched on to heat the heat exchange liquid. This may be employed to avoid the formation of liquid nitrogen within the superconducting magnet 30.
  • the superconducting coil can be cooled uniformly in the magnet, and no gradient temperature difference will arise between the bottom and top of the superconducting coil, thereby reducing thermal stress.
  • the perspective of the magnet 30, compared with the prior art in which liquid nitrogen was used for pre-cooling there is no need to use a large amount of helium gas to blow out liquid nitrogen; only a small amount of helium gas needs to be used to blow out the nitrogen gas used for pre-cooling and thus the amount of high- priced helium gas used is correspondingly reduced.

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Abstract

The invention provides a magnet pre-cooling device of magnetic resonance imaging system, including: a first refrigerant flow path to supply first refrigerant to a first magnet; a second refrigerant flow path to supply second magnet to a second refrigerant; the first refrigerant flow path exchanges heat with the second refrigerant flow path via a heat exchanger, and cools the first refrigerant flowing through the first magnet with the second refrigerant and enables the first refrigerant to be used again for cooling the first magnet, and the second refrigerant after heat exchange is used for cooling the second magnet.

Description

Magnet pre-cooling device for magnetic resonance imaging system
Technical field
The present invention relates to a magnet pre-cooling device for a magnetic resonance imaging (MRI) system.
Background art
In a superconducting MRI apparatus, a superconducting coil used to generate a magnetic field must be immersed in liquid helium stored in a liquid helium tank, and the superconducting coil can be changed to a superconducting state by cooling the coil to -269°C. However, if liquid helium is poured directly into a liquid helium tank that is in a room temperature state, a large amount of liquid helium will change to a gaseous state and overflow from the liquid helium tank. The price of liquid helium is relatively high; thus, to avoid the loss of a large amount of liquid helium, the liquid helium tank must be pre cooled, e.g. pre-cooled to -196°C using a refrigerant, and the liquid helium is then poured into the pre-cooled liquid helium tank. At present, when pre-cooling the magnet, liquid nitrogen can be used to fill the liquid helium tank and held therein for a period of time, until the liquid helium tank and the superconducting coil therein reach -196°C. Helium gas is then used to blow out the liquid nitrogen; at this time, the liquid helium tank is filled with pure helium gas and the temperature is held at -196°C. However, in this method, when liquid nitrogen is used for pre-cooling for example, liquid nitrogen accumulates at the bottom of the liquid helium tank; thus, from the perspective of the coil immersed in the liquid helium tank, a relatively large gradient temperature difference will arise between the bottom and the top, and this gradient temperature difference will subject the coil to high thermal stress, and in turn might affect the normal operation of the coil. In addition, a large amount of helium gas must be used to blow out the liquid nitrogen, and since helium gas is very expensive, the cost of using such a method is still relatively high. Alternatively, helium gas may also be used directly to pre-cool the liquid helium tank; the helium gas will become high-temperature through heat exchange with the liquid helium tank and thus a high-priced, high-power refrigerating machine must be used to cool the helium gas with the raised temperature .
Summary of the invention In view of the above, the object of the present invention is to propose a magnet pre-cooling device for an MRI system, which can reduce thermal stress in a superconducting coil during magnet pre-cooling and reduce helium loss, without any need for a large refrigerating machine. An embodiment of the present invention provides a magnet pre-cooling device for an MRI system, comprising: a first refrigerant flow path, for supplying a first refrigerant to a first magnet; a second refrigerant flow path, for supplying a second refrigerant to a second magnet; the first refrigerant flow path undergoes heat exchange with the second refrigerant flow path by means of a heat exchanger; the second refrigerant is used to cool the first refrigerant that has passed through the first magnet and enable the first refrigerant to be used for cooling the first magnet again, and the second refrigerant that has undergone heat exchange is used to cool the second magnet. In the magnet pre-cooling device for an MRI system described above, preferably, the first refrigerant flow path comprises a first refrigerant supply path for supplying a low- temperature first refrigerant supply gas to the first magnet, and a first refrigerant return path for returning a high- temperature first refrigerant return gas from the first magnet; the heat exchanger cools the first refrigerant return gas to be re-used as the first refrigerant supply gas by causing the first refrigerant return gas in the first refrigerant return path to undergo heat exchange with the second refrigerant, which is in a liquid state, from a second refrigerant source, and the liquid-state second refrigerant changes to a gaseous second refrigerant gas that can be used to cool the second magnet.
The magnet pre-cooling device for an MRI system described above preferably further comprises: a first refrigerant source, for supplying the first refrigerant, which is gaseous, to the first refrigerant flow path; and a second refrigerant source, for supplying the second refrigerant, which is in a liquid state, to the second refrigerant flow path.
In the magnet pre-cooling device for an MRI system described above, preferably, a driving device is provided at the first refrigerant return path, the driving device being used to cause the first refrigerant to flow in the first refrigerant flow path.
In the magnet pre-cooling device for an MRI system described above, preferably, the first refrigerant source is disposed at the first refrigerant return path. In the magnet pre-cooling device for an MRI system described above, preferably, the gaseous first refrigerant is helium gas, and the liquid-state second refrigerant is liquid nitrogen.
Another embodiment of the present invention provides a magnet pre-cooling device for an MRI system, comprising: a refrigerant source storing a liquid-state refrigerant; a refrigerant flow path for supplying the refrigerant to a magnet; and a heat exchanger storing a heat exchange liquid at a temperature higher than the vaporization temperature of the refrigerant; the refrigerant flow path passes through the heat exchanger, the heat exchange liquid is used to change the liquid-state refrigerant to a refrigerant gas, and the refrigerant gas is supplied to the magnet.
In the magnet pre-cooling device for an MRI system described above, preferably, in the refrigerant flow path, a temperature sensor for detecting the temperature of the refrigerant gas is provided at a downstream side of the heat exchanger.
In the magnet pre-cooling device for an MRI system described above, preferably, a heater is provided at the heat exchanger, and when the temperature of the refrigerant gas detected by the temperature sensor is lower than a preset value, the heater is used to heat the heat exchange liquid.
In the magnet pre-cooling device for an MRI system described above, preferably, the heat exchange liquid is water, and the liquid-state refrigerant is liquid nitrogen. According to the magnetic resonance magnet pre-cooling system in embodiments of the present invention, since a gaseous refrigerant is supplied separately to the first magnet or second magnet to perform pre-cooling, the superconducting coil can be cooled uniformly in the magnet, and no excessive gradient temperature difference will arise between the bottom and top of the superconducting coil, thereby reducing thermal stress. In the described example, helium gas is supplied to the first magnet, and nitrogen gas is supplied to the second magnet. In addition, after being heated through the heat exchanger, the helium gas supplied to the first magnet will be re-cooled using the liquid nitrogen supplied by the second refrigerant source; thus, there is no need for a large refrigerating machine to re-cool the high-temperature helium gas, as was the case previously. At the same time, the liquid nitrogen supplied by the second refrigerant source, after cooling the helium gas supplied to the first magnet and thus becoming high-temperature and changing to nitrogen gas, will be used to cool the second magnet; thus, from the perspective of the second magnet, compared with the previous scenario in which liquid nitrogen was used for pre-cooling, there is no need to use a large amount of helium gas to blow out liquid nitrogen; only a small amount of helium gas needs to be used to blow out the nitrogen gas and thus the amount of high- priced helium gas used is correspondingly reduced.
Brief description of the drawings
Preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, to give those skilled in the art a clearer understanding of the abovementioned and other features and advantages of the present invention.
Fig. 1 is an explanatory drawing of a magnet pre-cooling device for an MRI system according to a first embodiment of the present invention.
Fig. 2 is an explanatory drawing of a magnet pre-cooling device for an MRI system according to a second embodiment of the present invention. Key to the drawings:
10 - pre-cooling device;
11 - first refrigerant flow path;
111 - first refrigerant supply path;
112 - first refrigerant return path;
12 - second refrigerant flow path;
13, 13' - heat exchanger;
14 - first refrigerant source;
15 - second refrigerant source;
16 - fan;
17 - motor;
20 - first magnet; 30 - second magnet.
Detailed description of the invention
To enable those skilled in the art to better understand the solution of the present invention, the technical solution in the embodiments of the present invention is described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art on the basis of the embodiments in the present invention without any creative effort should fall within the scope of protection of the present invention.
It should be noted that the terms "first", "second", etc. in the description, claims and abovementioned drawings of the present invention are used to distinguish between similar objects, but not necessarily used to describe a specific order or sequence. It should be understood that data used in this way can be interchanged as appropriate so that the embodiments of the present invention described here can be implemented in an order other than those shown or described here. In addition, the terms "comprise" and "have" and any variants thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or piece of equipment comprising a series of steps or modules or units is not necessarily limited to those steps or modules or units which are clearly listed, but may comprise other steps or modules or units which are not clearly listed or are intrinsic to such processes, methods, products or equipment.
Fig. 1 shows a schematic drawing of a pre-cooling device for an MRI system according to a first embodiment of the present invention. As shown in Fig. 1, the pre-cooling device 10 can separately pre-cool a first magnet 20 and a second magnet 30 used for an MRI apparatus. The pre-cooling device 10 comprises: a first refrigerant flow path 11 for supplying a first refrigerant to the first magnet 20 to perform pre cooling, and a second refrigerant flow path 12 for supplying a second refrigerant to the second magnet 30. The first refrigerant flow path 11 and second refrigerant flow path 12 can undergo heat exchange in a heat exchanger 13.
In addition, a first refrigerant source 14 for supplying the first refrigerant is connected at the first refrigerant flow path 11, and a second refrigerant source 15 for supplying the second refrigerant is connected in the second refrigerant flow path 12. In this embodiment, the first refrigerant source supplies helium gas for example, and the second refrigerant source supplies liquid nitrogen for example.
In this embodiment, the first refrigerant flow path 11 comprises a first refrigerant supply path 111 for supplying low-temperature first refrigerant such as helium gas to the first magnet 20, and a first refrigerant return path 112 for returning high-temperature first refrigerant from the first magnet 20. In this embodiment, the first refrigerant source 14 supplies low-temperature helium gas as the first refrigerant to the first refrigerant flow path 11; the helium gas is supplied to the first magnet 20 via the first refrigerant supply path 111, and flows in the direction indicated by arrow A to pre-cool the first magnet 20. A first refrigerant gas resulting from pre-cooling of the first magnet 20 has become high-temperature and flows out as a first refrigerant return gas via the first refrigerant return path 112; the first refrigerant return path 112 then passes through the heat exchanger 13 to form a loop with the first refrigerant supply path 111.
The second refrigerant flow path 12 is connected to the second refrigerant source 15, passes through the heat exchanger 13 and is connected to the second magnet 30, and flows in the direction indicated by arrow B in the second magnet 30 to pre-cool the second magnet 30, subsequently being discharged into the atmosphere. In this embodiment, the second refrigerant source 15 can supply liquid nitrogen as the second refrigerant to the second refrigerant flow path 12. In the heat exchanger 13, the first refrigerant return gas, which has been used to pre-cool the first magnet 20, in the first refrigerant return path 112 undergoes heat exchange with liquid nitrogen, which comes from the second refrigerant source 15 as the second refrigerant, in the second refrigerant flow path 12; thus, the high-temperature first refrigerant return gas is cooled by the relatively low-temperature second refrigerant and is cooled back to a low-temperature first refrigerant supply gas that can be re-used, and is again conveyed to the first magnet 20 via the first refrigerant supply path 111 to continue to pre-cool the first magnet 20.
At the same time, using the heat exchanger 13, the low- temperature liquid nitrogen used as the second refrigerant in the second refrigerant flow path 12 is heated by the high- temperature first refrigerant return gas in the first refrigerant return path 112 and changes to nitrogen gas, and then flows into the second magnet 30 through the second refrigerant flow path 12, and flows in the direction indicated by arrow B to pre-cool the second magnet 30. In addition, in this embodiment, a fan 16 serving as a first refrigerant driving apparatus is further provided at the first refrigerant return path 112; the fan 16 can rotate under the driving action of a motor 17 to impel the flow of helium gas as the first refrigerant in the first refrigerant flow path 11.
According to the pre-cooling device for an MRI system in this embodiment, since a gaseous refrigerant is supplied separately to the first magnet 20 or second magnet 30 - helium gas is supplied to the first magnet 20, and nitrogen gas is supplied to the second magnet 30 - to perform pre-cooling, the superconducting coil can be pre-cooled uniformly in the magnet, and no gradient temperature difference will arise between the bottom and top of the superconducting coil, thereby reducing thermal stress. In addition, after being heated through heat exchange, the helium gas supplied to the first magnet 20 will be re-cooled using the liquid nitrogen supplied by the second refrigerant source 15; thus, there is no need for a large refrigerating machine to re-cool the high- temperature helium gas, as was the case previously. At the same time, the liquid nitrogen supplied by the second refrigerant source 15, after cooling the helium gas supplied to the first magnet 20 and thus becoming high-temperature and changing to nitrogen gas, will be used to pre-cool the second magnet 30; thus, from the perspective of the second magnet 30, compared with the previous scenario in which liquid nitrogen was used for pre-cooling, there is no need to use a large amount of helium gas to blow out liquid nitrogen; only a small amount of helium gas needs to be used to blow out the nitrogen gas and thus the amount of high-priced helium gas used is correspondingly reduced. Second embodiment
Fig. 2 shows an explanatory drawing of a magnet pre-cooling device in a second embodiment of the present invention. As shown in Fig. 2, the magnet pre-cooling device of this embodiment comprises: a refrigerant source 15 storing a liquid-state refrigerant, which is for example liquid nitrogen in this embodiment; a refrigerant flow path 12, connected to the refrigerant source 15 and supplying the refrigerant to a magnet 30; a heat exchanger 13' storing a heat exchange liquid at a temperature higher than the vaporization temperature of the refrigerant, wherein the heat exchange liquid is for example water in a room-temperature state in this embodiment. In this embodiment, the refrigerant flow path 12 passes through the heat exchanger 13', and low-temperature liquid nitrogen from the refrigerant source 15 undergoes heat exchange with the heat exchange liquid in the heat exchanger 13', such that the liquid nitrogen as the liquid-state refrigerant absorbs heat from the heat exchange liquid and changes to nitrogen gas in a gaseous state; the nitrogen gas is then supplied to the magnet 30 via the refrigerant flow path 12, passes through a cavity of superconducting magnet 30 along a path indicated by arrow C, and is then discharged into the air through a gas discharge channel.
In addition, in the refrigerant flow path 12 of this embodiment, a heat sensor 121 is provided at a downstream side of the heat exchanger 13'. The heat sensor 121 is used to detect the temperature of gaseous refrigerant in the refrigerant flow path 12; when the temperature of the gaseous refrigerant is lower than a predetermined value, a heater 18 disposed at the heat exchanger 13' is switched on to heat the heat exchange liquid. This may be employed to avoid the formation of liquid nitrogen within the superconducting magnet 30.
Since the liquid nitrogen from the refrigerant source 15 is changed to nitrogen gas using the heat exchanger 13' and then supplied to the magnet 30 to perform pre-cooling, the superconducting coil can be cooled uniformly in the magnet, and no gradient temperature difference will arise between the bottom and top of the superconducting coil, thereby reducing thermal stress. In addition, from the perspective of the magnet 30, compared with the prior art in which liquid nitrogen was used for pre-cooling, there is no need to use a large amount of helium gas to blow out liquid nitrogen; only a small amount of helium gas needs to be used to blow out the nitrogen gas used for pre-cooling and thus the amount of high- priced helium gas used is correspondingly reduced.
The embodiments above are merely preferred embodiments of the present invention, which are not intended to limit it. Any amendments, equivalent substitutions or improvements etc. made within the spirit and principles of the present invention shall be included in the scope of protection thereof.

Claims

CLAIMS :
1. A magnet pre-cooling device of magnetic resonance imaging system, characterized in that it comprises: a first refrigerant flow path to supply first refrigerant to a first magnet; a second refrigerant flow path to supply second refrigerant to a second magnet; the first refrigerant flow path exchanges heat with the second refrigerant flow path via a heat exchanger, and cools the first refrigerant flowing through the first magnet with the second refrigerant and enables the first refrigerant to be used again for cooling the first magnet, and the second refrigerant after heat exchange is used for cooling the second magnet.
2. The magnet pre-cooling device according to Claim 1, characterized in that: the first refrigerant flow path includes first refrigerant supply path that supplies low-temperature first refrigerant supply gas to the first magnet, and first refrigerant return path that returns high-temperature first refrigerant return gas from the first magnet; and in that the heat exchanger causes the first refrigerant return gas in the first refrigerant return path to exchange heat with the second refrigerant from second refrigerant source, so that the first refrigerant return gas is cooled for re-use as the first refrigerant supply gas, and the liquid refrigerant is converted into second refrigerant gas that can be used for cooling the second magnet.
3. The magnet pre-cooling device according to Claim 1, characterized in that it further comprises: a first refrigerant source for supplying gaseous first refrigerant to the first refrigerant flow path; and a second refrigerant source for supplying gaseous second refrigerant to the second refrigerant flow path.
4. The magnet pre-cooling according to Claim 2, characterized in that, a driving device is provided in the first refrigerant return path which causes the first refrigerant to flow in the first refrigerant flow path.
5. The magnet pre-cooling device according to Claim 2, characterized in that the first refrigerant source is connected at the first refrigerant return path.
6. The magnet pre-cooling device according to Claim 2, characterized in that the gaseous first refrigerant is helium, and the second refrigerant is liquid nitrogen.
7. A magnet pre-cooling device of a magnetic resonance imaging system, characterized in that it comprises: a refrigerant source that stores liquid refrigerant; a refrigerant flow path for supplying refrigerant to a magnet; a heat exchanger storing heat exchange liquid with a temperature higher than the vaporization temperature of the refrigerant, wherein the refrigerant flow path passes through the heat exchanger, wherein the liquid refrigerant is converted into refrigerant gas by heat from the heat exchange liquid, and the refrigerant gas is supplied through the refrigerant flow path to a magnet of a magnetic resonance imaging system.
8. The magnet pre-cooling device according to Claim 7, characterized in that, in the refrigerant flow path, a temperature sensor is provided downstream of heat exchanger to detect temperature of the refrigerant gas.
9. The magnet pre-cooling device according to Claim 8, characterized in that the heat exchanger is provided with a heater, and when the temperature of the refrigerant gas detected by the temperature sensor is lower than a preset value, the heater is used to heat the heat exchange liquid.
10. The magnet pre-cooling device according to Claim 8, characterized in that the heat exchange liquid is water, and the liquid refrigerant is liquid nitrogen.
PCT/EP2020/074480 2019-09-16 2020-09-02 Magnet pre-cooling device for magnetic resonance imaging system WO2021052760A1 (en)

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US5187938A (en) * 1989-05-18 1993-02-23 Spectrospin Ag Method and a device for precooling the helium tank of a cryostat
EP0916890A2 (en) * 1997-11-14 1999-05-19 Air Products And Chemicals, Inc. Method and apparatus for precooling a mass prior to immersion in a cryogenic liquid
US20050016187A1 (en) * 2003-07-03 2005-01-27 Ge Medical Systems Global Technology Company, Llc Pre-cooler for reducing cryogen consumption

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