JPH02162798A - Door of magnetically shielding room - Google Patents

Abstract

PURPOSE:To provide a magnetic shield to the door of an MRI room and to easily open the door by a method wherein a superconductive plate is provided on the inside of the door and properly cooled down by a coolant to its critical temperature or lower. CONSTITUTION:A high magnetic permeability material 5 such as amorphous or the like is provided along a stainless steel frame 4, and a finger contact 6 is provided between the stainless steel frame 4 and a door 2 to electrically and magnetically shield the periphery of the door 2. The door 2 is formed of a non-magnetic stainless steel plate and has a cavity 9, and a non-magnetic stainless steel plate 7 is provided on the inside and the outside of the door 2 separating from the inner and the outer face by a certain space respectively. The spaces between the plates 7 and the door 2 are made to serve as vacuum heat insulating layers 8. A superconductive plate 10 almost the same as the door 2 in planar shape is provided to the thicknesswise center of the cavity 9. The superconductive plate 10 is formed in such a manner that a superconductive thin film 10b is made to adhere to the peripheral face of a non- magnetic stainless steel plate 10a. Coolant such as liquid nitrogen or liquid helium is filled into the cavity on both the sides of the superconductive plate 10 to cool down the plate 10 to its critical temperature.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to a door for a room in which a strong magnetic field generating device such as a magnetic resonance diagnostic device is installed, and in particular a superconducting plate is used to generate a magnetic field from the door. This is to prevent leakage.

"Prior Art" Recently, hospitals have begun to install magnetic resonance diagnostic equipment (hereinafter referred to as MHI), but in addition to patients with pacemakers, there are also devices such as computers that are adversely affected by magnetism. There are many devices available. Therefore, as shown in Figure 4, in order to prevent the leakage magnetic field from the MHI from leaking outside, a magnetic shield A made of ferromagnetic material such as pure iron is installed on the 4th or 6th side of the chamber, and the influence of external radio waves is prevented. Radio wave shields B are installed on six sides of the room for the purpose of blocking.

Even in a room where magnetic shield A and radio wave shield B are installed, if there is a gap at the entrance or exit of the room, the effectiveness of both shields will be significantly reduced. Therefore, all gaps in the room where MHI etc. are installed are welded and all hangs are installed. In addition, openings such as the entrance and exit of the room are also shielded from radio waves using stainless steel plates, shielding glass, finger contacts, etc.

However, since magnetic shielding uses heavy magnetic materials, it is difficult to magnetically shield the entrance/exit door.The entrance/exit of an MRI room is large, as stretchers carrying patients and treatment equipment enter and exit. Width 1400■
I, the height will be about 2100m+s, and a large door will be required. If such a large door is made of magnetic material, it will be pulled by the magnet and will be extremely difficult to open and close. Therefore, the reality is that it is unavoidable that magnetic shielding is not applied to the doors.

``Problems to be Solved by the Invention'' When the door is not magnetically shielded as in a conventional MRI room, a large amount of magnetic field leaks at the door.

In other words, as shown in Figure 4, if a 1.5 T (Tesla) MHI is installed, it will be a controlled area where pacemaker wearers are prohibited from entering, and a 5.
The G (Gauss) line spread out from the door, posing a major management problem.

Furthermore, if an attempt is made to keep the leakage magnetic field small by placing the door as far away from the MHI as possible and utilizing distance attenuation, problems will arise in terms of architectural planning due to constraints on the position of the door. Furthermore, MRI
Large distortions occurred in the magnetic field distribution in the chamber, and it was difficult to make adjustments using shim coils to prevent distortions from occurring in MHI images.

In addition, in order to suppress the generation of magnetic fields from the MHI, it is possible to cut off the power supplied to the MHI when opening and closing the door, but superconducting type MHIs that generate strong magnetic fields use superconducting electromagnets to flow a persistent current through them. Therefore, it was in full operation for 24 hours, and it was not possible to suppress the leakage magnetic field from the MHI.

Therefore, an object of the present invention is to provide a magnetic shield to the door of an MRI room and to enable the door to be opened and closed easily.

"Means for Solving the Problems" The layer for a magnetically shielded room of the present invention has a door formed in a hollow shape by a non-magnetic plate, and a layer approximately coplanar with the door in the center part in the thickness direction within the hollow part of the door. Place the superconducting plate and fill the hollow part of the door with a refrigerant that cools the superconducting material below the critical temperature.
Made possible to eject.

It can be formed by depositing a superconducting thin film on the surface of a non-magnetic stainless steel plate that can be treated as a superconductor. In addition, in order to prevent the refrigerant injected into the hollow part of the door from receiving external heat,
It is sufficient to form a vacuum insulation layer between the hollow part and both the inside and outside surfaces of the door.In order to fill and discharge the refrigerant appropriately into the hollow part of the door, the refrigerant tank and the hollow part of the door are connected through a conduit. A pump may be provided in the middle of the conduit, and a discharge port with an on-off valve may be provided at the bottom of the door.

"Operation" In the magnetically shielded room layer of the above means, when the door is closed, the pump is driven to fill the hollow part of the door with refrigerant from the refrigerant tank. This refrigerant cools the superconducting plate in the hollow part of the door below the critical temperature, and the superconducting plate rejects magnetic lines of force without letting them in due to the Meissner effect (perfect diamagnetic) of superconductivity. Therefore, the door part can be magnetically shielded with a superconducting plate, and the magnetic field of the MHI inside the room will not leak from the door part to the outside.

When opening the door, open the opening/closing valve at the bottom of the door and discharge the refrigerant inside the hollow part to the outside from the discharge port under its own weight.The air temperature will cause the superconducting plate to reach a critical temperature or higher, and it will become a normal conductor and cause magnetic field lines. begins to pass through the interior. Therefore,
The door is lighter, and since it is not ferromagnetic, it is not pulled by magnetic force (the door can be opened and closed easily).

Here, the minor effects of superconductors will be explained with reference to FIG. FIG. 3(A) shows the case where the superconductor is cooled to below the critical temperature, in which case it becomes a superconductor and the lines of magnetic force pass through the outer periphery of the superconductor without passing through it. Therefore, if you surround it in a box shape with superconductors, you can create a complete magnetic shield with no magnetic lines of force inside. Figure 3 (B) is
This is the case when a superconductor reaches a temperature higher than its critical temperature. In that case, the superconductor becomes a normal conductor and the lines of magnetic field do not change direction (they pass through as they are. Such perfect diamagnetism and paramagnetism occur at the critical temperature of the superconductor. It occurs suddenly depending on the temperature and is reversible.

"Example" An embodiment of the present invention will be explained with reference to FIG. 1.2.

In order to install a device that generates a strong magnetic field, such as a magnetic resonance diagnostic instrument (MHI), in a room equipped with a magnetic shield wall A and a radio wave shield wall B, the door 2 of room 1 is magnetically shielded with the following configuration. I let it happen. A stainless steel frame 4 is provided around the opening of the peripheral wall of the chamber where the door 2 is provided, with a heat insulating material 3 interposed therebetween, and a high magnetic permeability material 5 such as amorphous is further installed along the stainless steel frame 4.
At the same time, a finger contact 6 is provided between the stainless steel frame 4 and the door, so that the peripheral edge of the door is magnetically shielded and radio wave shielded.

The door 2 is formed in a hollow shape by a non-magnetic stainless steel plate, and further non-magnetic stainless steel plates 7 are provided at intervals on both the indoor and outdoor sides of the door. Then, a vacuum was created between these two spaces of the door 2 to form a vacuum heat insulating layer 8. In this embodiment, the superconducting plate lO, which is substantially flush with the door 2, is arranged in the center in the thickness direction of the central hollow part 9 of the ff12. It is formed by attaching. The hollow portions on both sides of the superconducting plate IO are filled with a coolant such as liquid nitrogen or liquid helium, so that the superconducting plate IO is cooled to below a critical temperature and brought into a superconducting state.

The door 2 is provided with two inlets 11 at the upper end of the hollow part 9 in order to fill the hollow part with refrigerant, and two inlets 11 in the lower part of the hollow part 9 to discharge the refrigerant in the hollow part 9. A discharge port 12 is provided, and an air hole 13 is further provided in the upper part of the door 2 to communicate the hollow part 9 with the outside air. In addition, injection port 1
The reason why two discharge ports 12 and two discharge ports 12 are provided is to fill the hollow portions on both sides of the superconducting plate with refrigerant and to discharge the refrigerant, and each of the two discharge ports 12 is provided with an on-off valve 12a. It is being

In order to fill the hollow part 9 of the door 2 with refrigerant, a refrigerant tank 14 is connected to the injection port 11 of the hollow part through a conduit 15, as shown in FIG. Then, the microcomputer 17 opens the electromagnetic on-off valve 16 provided in the middle of the conduit 15 and drives the pump 18 provided at the outlet of the refrigerant tank 14, so that the refrigerant can be injected into the hollow portion 9.

Since the door 2 is opened and closed, the conduit 15 and the injection port 11 are not always communicated with each other, and the end of the conduit 15 is placed in the stainless steel frame 4 on the outer periphery of the door 2. and conduit 15
A telescopic pipe 15a is provided at the end of the refrigerant, so that the telescopic pipe 15a can be extended and inserted into the injection port 11 when refrigerant is injected into the hollow part 9 of the closed door. Note that the telescopic pipe 15a can be expanded and contracted by, for example, expanding and contracting a hydraulic cylinder.

Further, the outlet 12 at the bottom of the door 2 is connected to a conduit 19 whose one end is opened in the stainless steel frame 4, and the end of this conduit 19 is also connected to a telescopic tube 19 similar to that described above.
a is provided, and after the door is closed, the telescopic tube 19a extends and communicates with the discharge port 12. Note that the refrigerant discharged from the discharge port can also be recovered and reused.

In the present invention, the superconducting plate, the heat insulating structure of the outer surface of the door, the injection and discharge device for refrigerant into the hollow part of the door, etc. are not limited to the above-mentioned embodiments, and may be modified using known techniques.

``Effects of the Invention'' In the magnetically shielded room layer of the present invention, a superconducting plate is provided inside the door and can be appropriately cooled to below the critical temperature with a refrigerant, so that the Meissner effect of superconductivity allows for leakage from the door part. The leakage magnetic field can be greatly reduced, and the superconductor can be made paramagnetic when opening and closing the door, so the door can be easily operated without being pulled or repelled by magnetic force.

In addition, by magnetically shielding the door of the room, M
Since there is no need to take into account the distance attenuation of the magnetic field generated from HI etc., the area of the MRI room can be kept small.
In addition, since the distortion of the indoor magnetic field is reduced, adjustment using shim coils is also easy.

[Brief explanation of the drawing]

Fig. 1 is a side cross-sectional view of the magnetically shielded room layer of the present invention, Fig. 2 is an explanatory diagram showing the path of a refrigerant that cools the inside of the magnetically shielded room door, and Fig. 3 is an explanatory diagram showing the Meissner effect of a superconductor. 4 are explanatory diagrams showing the magnetic field state of a conventional MRI room. 2: Door 8: Heat insulating layer 10; Superconducting plate 11: Inlet 12: Outlet 14: Refrigerant tank 18: Pump

Claims (4)

[Claims] (1) For the door of a room where a device that generates a strong magnetic field is installed, the door is formed into a hollow shape using a non-magnetic plate, and a superconducting plate that is almost flush with the door is placed in the center of the hollow part of the door in the thickness direction. A door for a magnetically shielded room, characterized in that the door is configured such that a refrigerant for cooling a superconducting plate below a critical temperature can be appropriately filled and discharged into a hollow part of the door. (2) The door for a magnetically shielded room according to claim (1), wherein the superconducting plate is formed by depositing a superconducting thin film on the surface of a non-magnetic stainless steel plate. (3) The magnetically shielded room according to claim (1) or (2), wherein a non-magnetic plate is arranged at a distance between the inner and outer surfaces of the door and the hollow part to form a vacuum insulation layer on both sides of the hollow part. door. (4) The refrigerant tank and the hollow part of the door are connected by a conduit, a pump is installed in the middle of the conduit to allow the refrigerant to flow into the hollow part as appropriate, and a discharge port with an on-off valve is provided at the bottom of the hollow part of the door. The magnetically shielded room door according to claim (1), (2), or (3).