JPH0718302B2 - 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 particularly, a superconducting thin film is provided in the door to remove the door from a door portion. This is to prevent the magnetic field from leaking.

“Prior art” Recently, a magnetic resonance diagnostic device (hereinafter referred to as MRI) has been installed in a hospital, but there are patients with pacemakers installed in the hospital, and magnetic effects such as computers can cause adverse effects. There are many devices to receive. Therefore, as shown in Fig. 4, in order to prevent the leakage magnetic field from 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 side of the room, and the influence of external radio waves is reduced. A radio wave shield B is provided on the six sides of the room 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 room where the MRI, etc. are installed are all welded, all soldered, etc. to eliminate the gaps for magnetic and radio wave 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. The entrance and exit of the MRI room is for entry and exit of the stretcher and treatment equipment on which the patient is placed, so the size is, for example, 1400 mm,
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 the door is not magnetically shielded as in the conventional MRI room, a large magnetic field leaks at the door.

That is, as shown in Fig. 4, when a 1.5T (Tesla) MRI is installed, a 5G (Gauss) line, which is a controlled area for pacemaker wearers and a standard for computer installation, greatly expands from the door, There was a big management problem.

In addition, if the door is separated from the MRI as much as possible and the distance attenuation is used to suppress the leakage magnetic field, the position of the door is restricted, which causes a problem in construction planning. Furthermore, it was difficult to adjust the shim coil to prevent distortion in the MRI image.

Since the magnetic field is generated from the MRI, M when opening and closing the door
It is possible to cut off the power supplied to the RI, but the superconducting type MRI that generates a strong magnetic field uses a superconducting electromagnet to send a permanent current to it, so it will be in full operation for 24 hours,
The stray magnetic field from the MRI could not be reached.

Therefore, an object of the present invention is to make a door of an MRI room magnetically shielded, and to easily open and close the door so that the door is not magnetically affected when the door is opened and closed.

"Means for Solving the Problem" The magnetic shield room door of the present invention is provided with a superconducting thin film in the door of a room equipped with a strong magnetic field generator, and in the case of magnetic shielding, the superconducting thin film via an electrode. A current below the critical current density can be supplied, and a current above the critical current density can be supplied when the door is opened and closed.

In order to increase the current density of the superconducting thin film, a part of the cross section may be made small, and if a plurality of superconducting thin films having different planar shapes are wrapped by the notches or the like, the magnetism will not leak from the notches or the like. In order to generate the superconducting Meissner effect in the superconducting thin film, the superconducting thin film is covered with a refrigerant.

"Operation" In the magnetic shield room door of the above means, when the door is closed, a current not higher than the critical current density is supplied to the superconducting thin film through the electrode to bring the superconducting state. At this time, the superconducting thin film becomes a perfect diamagnetic material due to the Meissner effect,
The leakage magnetic field from the door is greatly reduced. In order to show the characteristics of superconductivity, not only the critical current density but also the critical temperature and the critical magnetic field must be satisfied, and the critical temperature is kept at a predetermined value by the refrigerant, and the critical magnetic field is also predetermined. Is set to.

When the door is opened and closed, a current having a critical current density or more is passed through the superconducting thin film through the electrode to make it a non-conducting non-magnetic substance, so that the superconducting thin film can pass magnetism. Therefore, the door is not absorbed or repelled by the leakage magnetic field from the strong magnetic field generator.

The switching of the superconducting thin film to complete diamagnetism and paramagnetism is a reversible phenomenon and is controlled by the manufacturing method at the critical current density (specific to the substance, several hundred to several hundred thousand A / cm ^2). It can happen).

[Example] An example 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 a magnetic shield wall A made of pure iron and a radio wave shield wall B made of copper foil or the like, The door 2 was magnetically shielded by the following constitution.

In addition, a stainless frame 3 is provided around the opening of the chamber peripheral wall where the door 2 is provided, a high magnetic permeability material 4 such as amorphous permalloy is further provided along the stainless frame 3, and an electromagnetic field is provided between the stainless frame 3 and the door. By providing finger contacts 5 that are electrically connected, the peripheral edge of the door is magnetically shielded and radio wave shielded.

The door 2 is formed of a non-magnetic stainless plate in a hollow shape,
A plurality of superconducting thin films 6 were wrapped and arranged therein. The superconducting thin film 6 is adhered to both sides of a stainless steel supporting plate 7 having substantially the same plane as the door 2 by a sputtering method, for example, by a thickness of several tens of microns. In this embodiment, two superconducting thin films 6 are adhered to both sides. The support plate 7 of No. 2 was provided in the door 2. As shown in FIG. 2, electrodes 8 are provided on both ends of the superconducting thin film 6.
Is provided, and when a current having a critical current density or less is supplied from the DC power source 9 through them, the superconducting state is established and the Meissner effect is used to form a complete diamagnetic material, which has a magnetic shield function. Further, when a current having a critical current density or more is supplied to the superconducting thin film 6, the superconducting thin film 6 becomes a normal conducting non-magnetic material. In order to supply the superconducting thin film 6 with a current equal to or higher than the critical current density, the switch 10 is turned on and off, but the current value is controlled by a variable resistor instead of the switch. Good. Also, the smaller the critical current density of superconductivity, the smaller the current flowing, and the easier switching. Each superconducting thin film 6 has substantially the same plane shape as that of the door 2, but it may be cut out as shown in FIGS. You may.

Since the magnetism leaks from the cutout portion of the superconducting thin film 6 and the like, a plurality of superconducting thin film 6 having different notches and the like are wrapped in multiple layers to prevent leakage. The door 2 is opened and closed by swinging around the hinge portion as a fulcrum, and the electrode of each superconducting thin film and the power source are connected through the hinge portion.

In the door 2, each superconducting thin film 6 is a stainless steel case.
The superconducting thin film 6 is covered with the refrigerant 12 contained in 11 and can keep each superconducting thin film 6 at a critical temperature or lower. Superconducting thin film 6
If the critical temperature is 90 K to 120 K, liquid nitrogen can be used as the refrigerant 12. A vacuum layer 13 is provided between the stainless case 11 and the peripheral wall of the door 2 so that the superconducting thin film 6 can be effectively cooled. In order to bring each superconducting thin film 6 into a superconducting state, it is necessary not only to supply a current below the critical current density and keep it below the critical temperature but also to satisfy the condition of the critical magnetic field. However, although not shown, the condition of the critical magnetic field is satisfied.

Although the superconducting thin film is used in the above embodiment, a thin plate-like one may be used instead of the thin film.

"Effects of the Invention" In the magnetic shield room door of the present invention, a superconducting thin film is provided inside the door, and a diamagnetic substance due to the Meissner effect of superconductivity is provided by supplying a current equal to or lower than the critical current density or higher. And a non-magnetic material can be easily switched. Therefore, when the diamagnetic material is used, the door is magnetically shielded, and the leakage magnetic field from the door can be greatly reduced. Further, when the door for people and things to enter and exit is opened and closed, if the superconducting thin film is made of a non-magnetic material, the door will not be attracted to or repelled by the leakage magnetic field from the room.

Furthermore, since the door part of the room can be magnetically shielded, the distance attenuation of the magnetic field generated from MRI etc. need not be considered so much, the area of the MRI room can be kept small, and the distortion of the magnetic field inside the room can be reduced. Therefore, adjustment by the shim coil is easy.

[Brief description of drawings]

FIG. 1 is a side sectional view of a door for a magnetically shielded room according to the present invention, FIG. 2 is a circuit diagram showing a power feeding state to a superconducting thin film, and FIGS. 3 (a) and 3 (b) are superconducting thin films having different planar shapes. FIG. 4 is an explanatory view showing a magnetic field state of a conventional MRI room. 2; Door, 6; Superconducting thin film 8; Electrode, 12; Refrigerant 13; Vacuum layer

Claims (3)

[Claims] 1. In a door of a magnetically shielded room in which a strong magnetic field generator is installed, a superconducting thin film having substantially the same plane shape as that of the door is provided in the door, and electrodes are provided at both ends of the superconducting thin film through both electrodes. A door for a magnetically shielded room that can supply a current that is below or above the critical current density as appropriate. 2. The door for a magnetically shielded room according to claim 1, wherein a plurality of superconducting thin films are arranged so as to be wrapped with each other. 3. The door for a magnetically shielded room according to claim 1, wherein the superconducting thin film is covered with a refrigerant in the door.