Patent Publication Number: US-2023141678-A1

Title: Cryostat Structure for Magnetic Resonance Imaging Apparatus, and Magnetic Resonance Imaging Apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a cryostat structure for a magnetic resonance imaging apparatus, and more particularly to a cryostat structure suitable for long-distance transportation and a magnetic resonance imaging apparatus equipped with the cryostat structure. 
     BACKGROUND ART 
     In an existing magnetic resonance imaging apparatus, a superconducting coil used to generate a main magnetic field for imaging is immersed in low-temperature liquid helium with a small latent heat of vaporization, and the liquid helium is kept at 4.2 K by means of a refrigerator, thereby enabling the superconducting coil to remain in a superconducting state. In the cryostat structure of the existing magnetic resonance imaging apparatus, the liquid helium is stored in a liquid helium tank, and a radiation-proof heat shield layer is provided outside the liquid helium tank; the liquid helium tank and the shielding layer are suspended in an outer-layer vacuum chamber by means of a suspension device. The heat shield layer and the liquid helium tank need to be connected to a first stage (temperature of 50 K) and a second stage (temperature of 4.2 K) of the refrigerator respectively. 
     However, in the process of transporting the magnetic resonance apparatus from the factory to the end-of-use (user) site, especially in the process of long-distance transport (e.g. by ship for tens of days), sometimes it is necessary to use air transport, but this method has a very high cost; or the liquid helium tank is filled with liquid helium, but the liquid helium will change to a gaseous state and be completely lost as the temperature rises during transportation, and liquid helium, as an expensive material, will also result in an excessive cost; alternatively, cold chain transportation can also be used, but this method also faces the problem of high cost. 
     SUMMARY OF THE INVENTION 
     In view of the above, the present invention proposes a cryostat structure for a magnetic resonance imaging apparatus that enables long-distance transportation with a simple structure, and a magnetic resonance imaging apparatus equipped with the cryostat structure. 
     An embodiment of the present invention provides a cryostat structure for a magnetic resonance imaging apparatus, comprising: a casing, having an annular chamber formed in the interior thereof; a refrigerant container arranged in the chamber, with a superconducting coil being accommodated in the refrigerant container in such a way that the superconducting coil is immersed in a liquid refrigerant; a heat shield layer, arranged between the casing and the refrigerant container, and configured to block thermal radiation from the casing; the casing having a suction hole, the suction hole being blocked by a sealing cover in a detachable manner, the sealing cover having an adsorption chamber having an opening facing the chamber side, and the adsorption chamber containing an adsorbent capable of adsorbing an overflowing element from the casing or the refrigerant container or the heat shield layer. 
     In the cryostat structure described above, preferably, the opening of the adsorption chamber is covered by a mesh sheet with mesh. 
     In the cryostat structure described above, preferably, the mesh sheet is fixed so as to cover the opening of the adsorption chamber by an annular pressure plate. 
     In the cryostat structure described above, preferably, the overflowing element is hydrogen and the adsorbent is a silver zeolite. 
     Another embodiment of the present invention provides a magnetic resonance imaging apparatus, comprising the cryostat structure described above. 
     According to the structure of the cryostat of the present invention, since the adsorbent provided in the sealing cover is used to adsorb free elements that separate out from the casing or the refrigerant container or the heat shield layer, it is possible to ensure that the cryostat can still keep the vacuum degree of the chamber in a satisfactory state, and reduce the transfer of heat from the casing to the refrigerant container, when the refrigerator is not working for a long period of time (e.g. several tens of days). Therefore, even after long-distance transportation, such as 60 days of sea transportation, the superconducting coil can be kept at a temperature not exceeding a specified temperature, such as 40 degrees. In addition, using the cryostat structure of the present invention, since the vacuum degree of the chamber is maintained effectively and the transfer of heat from the casing to the refrigerant container is reduced, it is not necessary to inject expensive liquid helium into the refrigerant container when long-distance transportation takes place, thus liquid helium loss is reduced and costs are further lowered. 
    
    
     
       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. Drawings: 
         FIG.  1    is an explanatory diagram of the cryostat structure for a magnetic resonance imaging apparatus according to the present invention. 
         FIG.  2    is a schematic explanatory view of the sealing cover according to the present invention. 
     
    
    
     KEY TO THE DRAWINGS 
     
         
           1 . cryostat; 
           10 . casing; 
           12 . chamber; 
           14 . suction hole; 
           16 . sealing cover; 
           161 . adsorption chamber; 
           162 . silver zeolite; 
           163 . pressure plate; 
           164 . screw; 
           20 . refrigerant container; 
           22 . liquid refrigerant; 
           24 . superconducting coil; 
           30 . heat shield layer. 
       
    
     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 that 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 apparatus 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 apparatuses. 
       FIG.  1    shows an explanatory diagram of the structure of a cryostat  1  for a magnetic resonance imaging apparatus according to the present invention. As shown in  FIG.  1   , the cryostat  1  of the present invention comprises: a casing  10 , a refrigerant container  20  and a heat shield layer  30 . In this embodiment, the casing  10  is made of a stainless steel material, an annular chamber  12  is formed inside, and the refrigerant container  20  is arranged in the chamber  12 . The refrigerant container  20  is also made of a stainless steel material; a liquid refrigerant  22 , such as liquid helium, is contained in the refrigerant container  20 . In addition, a superconducting coil  24  for generating a main magnetic field for magnetic resonance imaging is immersed in the liquid refrigerant  22 . The heat shield layer  30  is made of aluminum and arranged between the casing  10  and the refrigerant container  20 , and is connected to a first-stage cold head of a refrigerator in a turret  40 ; the refrigerant container  20  is connected to a second-stage cold head of the refrigerator. When the magnetic resonance imaging apparatus is energized, the temperature of the heat shield layer is cooled to 50 K to block thermal radiation from the casing  10 , and the temperature of the refrigerant container  20  is cooled to 4.2 K to keep the superconducting coil  24  in a superconducting state. 
     In addition, as shown in  FIG.  1   , the casing  10  has a suction hole  14  for evacuating the chamber  12 , and the suction hole  14  is blocked by a sealing cover  16  in a detachable manner. During the manufacture of the magnetic resonance imaging apparatus, it is necessary to use the suction hole  14  to evacuate the chamber  12  to a vacuum state, so as to reduce the transfer of heat from the casing  10  to the refrigerant container  20 . However, after the chamber  12  has been evacuated, when the refrigerator is working, the chamber  12  can maintain a relatively good vacuum state, but when the refrigerator stops working, the vacuum state of the chamber  12  will gradually be destroyed. Consequently, external heat from the casing  10  is rapidly transferred to the refrigerant container  20 , with the result that the temperature of the superconducting coil  24  in the refrigerant container  20  rises. The inventors of the present invention have discovered through research that this is because, when the refrigerator is working, hydrogen that separates out of the stainless steel used to make the casing  10  or the refrigerant container  20  gathers in a static state on the surface of the low-temperature refrigerant container  20 ; at this time, the chamber  12  can maintain a good degree of vacuum. However, when the refrigerator is not working, for example, when the temperature of the refrigerant container  20  reaches 20 K, the hydrogen that separates out will change to a free state, and this will cause the vacuum state of the chamber  12  to be destroyed, and the transfer of heat from the casing  10  or the heat shield layer  30  to the refrigerant container  20  is restored. Therefore, when transporting over a long distance, the vacuum state of the chamber  12  will be gradually destroyed due to the refrigerator not working for a long time, and heat outside the apparatus will be transferred to the refrigerant container  20  via the casing  10  and the heat shielding layer 30; at this time, the temperature of the superconducting coil  24  will reach several tens of degrees Celsius, and in this situation, the superconducting coil  24  might malfunction as a result. In view of this, the inventors of the present invention have provided an adsorption chamber  161  at the side of the sealing cover  16  that faces the chamber  12 , and stored in the adsorption chamber  161  an adsorbent that can effectively adsorb hydrogen, such as a silver zeolite  162 . Thus, during long-distance transportation, the adsorbent can effectively adsorb free hydrogen, to maintain the degree of vacuum of the chamber  12 , and reduce the transfer of heat from the casing  10  to the refrigerant container  20 . 
       FIG.  2    shows a schematic explanatory view of the sealing cover  16  according to the present invention. As shown in  FIG.  2   , the sealing cover  16  of the present invention comprises a cap body  160 , and the adsorption chamber  161  having an opening facing the chamber side. The adsorption chamber  161  contains the silver zeolite  162 , which has a very good adsorption effect on elemental hydrogen, as the adsorbent. The opening of the adsorption chamber  161  is covered by a mesh sheet  162  with mesh. Furthermore, the mesh sheet  162  is fixed so as to cover the opening of the adsorption chamber  161  by an annular pressure plate  163  using screws  164 . 
     In the present invention, the case where the casing  10  and the refrigerant container  20  are made of stainless steel, and the stainless steel releases hydrogen, is shown as an example; in this case, the silver zeolite is used as the adsorbent. However, when the casing  10  or the refrigerant container  20  or the heat shield layer  30  is made of another material and releases another element, an adsorbent with a good adsorption effect corresponding to the other element can also be selected accordingly. 
     According to the structure of the cryostat  1  of the present invention, since the adsorbent provided in the sealing cover is used to adsorb free elements that separate out from the casing or the refrigerant container or the heat shield layer, it is possible to ensure that the cryostat  1  can still keep the vacuum degree of the chamber in a satisfactory state, and reduce the transfer of heat from the casing to the refrigerant container, when the refrigerator is not working for a long period of time (e.g. several tens of days). Therefore, even after long-distance transportation, such as 60 days of sea transportation, the superconducting coil can be kept at a temperature not exceeding a specified temperature, such as 40 degrees. In addition, using the cryostat structure of the present invention, since the vacuum degree of the chamber is maintained effectively and the transfer of heat from the casing to the refrigerant container is reduced, it is not necessary to inject expensive liquid helium into the refrigerant container when long-distance transportation takes place, thus liquid helium loss is reduced and costs are further lowered. 
     In the above embodiment, the case where the casing and the refrigerant container are made of a stainless steel material and release elemental hydrogen is shown as an example. However, when the casing or the refrigerant container or the heat shield layer is made of another material and releases another element different from elemental hydrogen, a corresponding adsorbent capable of effectively adsorbing the other element may also be provided in the adsorption chamber. 
     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.