JPH0632426B2 - Magnetic shield room door - Google Patents

Description

TECHNICAL FIELD The present invention relates to a door of a room in which a strong magnetic field generator such as a magnetic resonance diagnostic apparatus is installed, and in particular, a magnetic field is applied from a door portion by using a superconducting plate. It was designed so as not to leak.

“Prior Art” Recently, in a hospital, a magnetic resonance diagnostic apparatus (hereinafter referred to as MRI) is installed. However, in a hospital, there is a patient wearing a pacemaker, and a magnetic field such as a computer causes adverse effects. There are many devices to receive. Therefore, as shown in FIG. 4, in order to prevent the leakage magnetic field from the MRI from leaking to the outside, a magnetic shield A made of a ferromagnetic material such as pure iron is provided on the 4th or 6th surface of the chamber, and the influence of external radio waves is reduced. Electromagnetic shields B are provided on the six sides of the chamber for the purpose of shutting off.

Even in a room where the magnetic shield A and the radio wave shield B are provided, if there is a gap at the entrance and exit of the room, both shield effects will be significantly reduced. For this reason, the gaps in the chamber where the MRI and the like are installed are all welded, all soldered, etc. to eliminate the gaps for magnetic leakage. In addition, the openings such as the entrance and exit of the room are also provided with a radio wave shield by a stainless plate, shield glass, finger contacts, and the like.

However, since a heavy magnetic material is used for the magnetic shield, it is difficult to magnetically shield the door portion of the entrance / exit. At the entrance and exit of the MRI room, a stretcher carrying a patient and treatment equipment go in and out, so the size is, for example, 1400 mm wide,
The height is about 2100 mm, and a large door is required. When such a large door is made of a magnetic material, it is pulled by a magnet and opening and closing becomes extremely difficult. Therefore, it is unavoidable that the door is not magnetically shielded.

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

That is, as shown in Fig. 4, MR of 1.5T (Tesla)
When I was installed, the 5G (Gauss) line, which is a controlled area where pacemaker wearers are prohibited from entering the area, and a guideline for computer installation, expanded greatly from the door part, and there was a large problem in management.

Further, if the door is separated from the MRI as much as possible and the leakage magnetic field is suppressed to be small by utilizing the distance attenuation, the position of the door is restricted, which causes a problem in construction planning. Further MRI
A large distortion occurs in the magnetic field distribution in the chamber, and it was difficult to adjust the shim coil to prevent distortion in the MRI image.

In order to suppress the magnetic field generated from the MRI, it is possible to shut off the power supplied to the MRI when the door is opened and closed. However, the superconducting type MRI that generates a strong magnetic field uses a superconducting electromagnet to apply a permanent current to it. Since it was flowed, it was fully operated for 24 hours, and the magnetic field leaked from MRI could not be suppressed.

Therefore, it is an object of the present invention to provide a magnetic shield on the door of an MRI room and to easily open and close the door.

"Means for Solving the Problem" A door for a magnetically shielded room according to the present invention is formed by forming a non-magnetic plate into a hollow shape, and a superconducting member having substantially the same plane shape as the door in the central portion in the thickness direction inside the hollow portion of the door. A plate is arranged, and a refrigerant for cooling the superconducting plate to a critical temperature or lower is appropriately filled in the hollow part of the door,
Allowed to be discharged.

The super motor plate can be formed by depositing a superconducting thin film on the surface of a non-magnetic stainless plate. Also, to prevent the refrigerant injected into the hollow part of the door from receiving external heat,
A vacuum heat insulating layer may be formed between the hollow portion and both inner and outer surfaces of the door. In order to properly fill and discharge the refrigerant in the hollow part of the door, the refrigerant tank and the hollow part of the door are connected by a conduit, a pump is provided in the middle of the conduit, and an outlet having an on-off valve is provided at the bottom of the door. Good.

[Operation] In the magnetic shield room door of the above means, when the door is closed, the pump is driven to fill the hollow portion of the door with the refrigerant from the refrigerant tank. This refrigerant cools the super-electric plate in the hollow portion of the door to a temperature below the critical temperature, and the super-electric plate eliminates the magnetic field lines by not accepting them due to the super-electric Meissner effect (complete diamagnetism). Therefore, the door portion can be magnetically shielded by the super-electric plate, and the magnetic field of MRI in the room will not be leaked to the outside from the door portion.

When opening the door, open the on-off valve at the bottom of the door and discharge the refrigerant in the hollow part from the discharge port to the outside by its own weight. Will pass through the interior. Therefore,
The door is light and has no ferromagnetism, so it can be opened and closed easily without being pulled by magnetic force.

Here, the minor effect of the superconductor will be described with reference to FIG. FIG. 3 (A) shows a case where the superconductor is cooled to a critical temperature or lower. In that case, the superconductor becomes a superconductor, and the magnetic force lines pass through the outer peripheral portion without passing through the superconductor. Therefore, by enclosing it in a box-like shape with a superconductor, a complete magnetic shield can be made without the lines of magnetic force inside. Fig. 3 (B)
Is the case where the superconductor becomes above the critical temperature, in which case the superconductor becomes a normal conductor and the magnetic field lines pass through without changing the direction. Such complete diamagnetism and paramagnetism suddenly occur at the critical temperature of the superconductor and are reversible.

"Embodiment" An embodiment of the present invention will be described with reference to FIGS. Since a device for generating a strong magnetic field, such as a magnetic resonance diagnostic device (MRI), is installed in a room provided with the magnetic shield wall A and the radio wave shield wall B, the door 2 of the room 1 is magnetically shielded by the following configuration. Let It should be noted that a stainless frame 4 is provided on the periphery of the opening of the chamber peripheral wall where the door 2 is provided via a heat insulating material 3, and a high magnetic permeability material 5 such as amorphous is further provided along the stainless frame 4, and the stainless frame 4 and the door are connected. A finger contact 6 is provided in between so that the peripheral portion of the door is magnetically shielded and radio waves are shielded.

Secondly, the non-magnetic stainless steel plate is formed in a hollow shape, and the non-magnetic stainless steel plate 7 is formed on the inner side of the door and on the inner side of the outer side of the door.
Provide one. Then, the inside of these two spaces of the door 2 was evacuated to form the vacuum heat insulating layer 8. A superconductor 10 having substantially the same plane as that of the door 2 is arranged in the central portion in the thickness direction of the central hollow portion 9 of the door 2. In this embodiment, the superconductor 10 is formed by adhering the superconducting thin film 10b to the outer peripheral surface of the non-magnetic stainless plate 10a. Then, the hollow portions on both sides of the superconductor 10 are filled with a coolant such as liquid nitrogen or liquid helium, and the superconductor 10 can be cooled to a critical temperature or lower to be in a superconducting state.

The door 2 is provided with inlets 11 at two upper ends of the hollow portion 9 in order to fill the hollow portion thereof with the refrigerant, and is provided at the lower portion of the hollow portion 9 for discharging the refrigerant in the hollow portion 9. A discharge port 12 is provided, and an air hole 13 that communicates the hollow portion 9 with the outside air is provided in the upper portion of the door 2. Note that the injection port 1
1 and two discharge ports 12 are provided in order to fill the hollow portions on both sides of the superconductor with the coolant and discharge the coolant, and the two discharge ports 12 are each provided with an on-off valve 12a. Has been.

In order to fill the inside of the hollow portion 9 of the door 2 with the refrigerant, the refrigerant tank 14 is connected to the inlet 11 of the hollow portion via the conduit 15 as shown in FIG. Then, the electromagnetic open / close valve 16 provided in the middle of the conduit 15 is opened by the microcomputer 17, and the pump 18 provided at the outlet of the refrigerant tank 14 is driven, 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 inlet 11 are not always communicated with each other, and the end of the conduit 15 is arranged in the stainless frame 4 on the outer periphery of the door 2. And conduit 15
The expansion tube 15a is provided at the end of the expansion tube 15a so that when the refrigerant is injected into the hollow portion 9 of the closed door, the expansion tube 15a can be extended and inserted into the injection port 11. The expandable tube 15a can be expanded and contracted by expanding and contracting a hydraulic cylinder, for example.

The outlet 12 at the bottom of the door 2 is communicated with a conduit 19 whose one end is open at the stainless frame 4, and the end of the conduit 19 also has a telescopic tube 19 similar to that described above.
a is provided, and after the door is closed, the expansion tube 19a extends and communicates with the discharge port 12. The refrigerant discharged from the discharge port can be recovered and reused.

The superconducting plate, the heat insulating structure of the outer surface of the door, the refrigerant injecting device into the hollow part of the door, the discharging device, and the like according to the present invention are not limited to the above-described embodiments, and may be converted by a known technique.

"Effect of the invention" In the electromagnetic shield room door of the present invention, since a superconducting plate is provided inside the door so that it can be cooled to a critical temperature or lower with a refrigerant, the Meissner effect of superconducting causes The leakage magnetic field can be greatly reduced, and the superconductor can be made paramagnetic when opening and closing the door, so that the door can be easily operated without being pulled or repulsed by magnetic force.

Also, since the door of the room can be magnetically shielded, M
Since it is not necessary to consider the distance attenuation of the magnetic field generated from RI etc., the area of the MRI chamber can be kept small,
Moreover, since the distortion of the magnetic field in the room becomes small, the adjustment by the shim coil is easy.

[Brief description of drawings]

FIG. 1 is a side sectional view of a magnetic shield room door of the present invention, FIG. 2 is an explanatory view showing a passage of a refrigerant for cooling the inside of a magnetic shield roof door, and FIG. 3 is an explanation showing a Meissner effect of a superconductor. FIG. 4 and FIG. 4 are explanatory views showing a magnetic field state in a conventional MRI chamber. 2: Door, 8: Thermal insulation layer 10: Superconducting plate, 11: Inlet port 12: Outlet port, 14: Refrigerant tank 18: Pump

Claims (4)

[Claims] 1. A door for a room in which a device for generating a strong magnetic field is installed, wherein the door is formed of a non-magnetic plate in a hollow shape, and a superconducting member having substantially the same plane as the door is formed in a central portion in a thickness direction inside the hollow portion of the door. A door for a magnetically shielded room, in which a plate is arranged, and a refrigerant for cooling the superconducting plate to a critical temperature or lower can be appropriately filled and discharged in a hollow portion 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 plate. 3. The magnetic material according to claim 1, wherein a non-magnetic plate is arranged with a space between the inner and outer surfaces of the door and the hollow portion, and vacuum heat insulating layers are formed on both sides of the hollow portion. Door for shield room. 4. A refrigerant tank and a hollow part of a door are connected by a conduit, a pump is provided in the middle of the conduit to allow a refrigerant to flow into the hollow part, and an outlet having an opening / closing valve is provided at the bottom of the hollow part of the door. The magnetic shield room door according to claim (1) or (2) or (3) provided.