JPH0690916A - Cerebral magnetic field measuring instrument - Google Patents

Abstract

PURPOSE:To eliminate the interference of external magnetic noises of the cerebral magnetic field measuring instrument for which a superconductive quantum interferometer (SQUID) fluxmeter is used and to enhance the accuracy of cerebral magnetic field measurement by enabling the installation of a long-sized highly critical temp. oxide superconductor sufficient for decreasing the external magnetic noises. CONSTITUTION:The cup-shaped highly critical temp. oxide superconductor 1 of a hollow tubular body closed at one end is held at a differential temp. by the liquid nitrogen sealed into an external cryostat 2a enclosing the conductor. A cup-shaped internal cryostat 2b thermally insulated from the outside field of room temp. is placed therein via an ice-bag-shaped liquid helium container 7 housing a SQUID chip 4 within liquid helium and a pickup coil 5 connected thereto. The helium container 7 and the internal cryostat 2b are formed to a recessed shape so as to enclose the patient's head. The SQUID fluxmeter 3 is constituted of the helium container 7, the hemispherical end of the external cryostat 2a and the internal cryostat 2b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to SQUID (Super Co
nducting Quantum Interference Device: Superconducting Quantum Interference Device) This is a device for measuring a brain magnetic field using a flux meter. When the magnetic flux passing through the superconducting circuit including the weakly coupled Josephson element changes, the current signal changes accordingly. The SQUID magnetometer is a device that measures an extremely small change in magnetic flux by the quantum interference phenomenon.

[0002]

2. Description of the Related Art FIG. 3 shows an open type brain magnetic field measuring apparatus (Japanese Patent Application No. 2-38108) using a conventional SQUID magnetometer. In the figure, 1 is a high critical temperature oxide superconductor (ceramic), 2 is an adiabatic container or cryostat containing liquid nitrogen to keep it at an operating temperature,
These constitute a high critical temperature superconductor magnetic shield device. As shown in the figure, SQ
Combined with a UID magnetometer. The SQUID magnetometer includes a hollow container 3 that thermally insulates liquid helium, an SQUID chip 4 immersed in liquid helium in the inner space of the hollow container, and a brain magnetic field detection pickup coil 5 connected to the SQUID chip. ing. The hollow container 3 is provided with a transfer tube 6 for inserting liquid helium into the internal space of the hollow container, and a vertical hole 8 for inserting and removing the pickup coil 5 and the SQUID chip 4 into the internal space of the hollow container. The vertical hole 8 is provided with a heat shield plate 9 for preventing evaporation of liquid helium. In addition,
Although not shown in the figure, a ferromagnetic mu metal or Helmholtz coil is arranged around the cryostat 2 for the purpose of perfect magnetic shielding. However, even in such a case, this open-type brain magnetic field measurement apparatus has a problem that external magnetic noise intrudes from above and below. External magnetic noise is terrestrial magnetism or environmental magnetic noise, and in particular, environmental magnetic noise is a low frequency noise of 0.1 to 100 Hertz that can be compared with the frequency of the brain magnetic field, which causes a measurement error.

FIG. 4 shows another conventional vertical cerebral magnetic field measurement apparatus utilizing a SQUID magnetometer.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to actually install a long high-critical-temperature oxide superconductor that is sufficient to reduce external magnetic noise, and to eliminate external magnetic noise interference. Then, the accuracy of the brain magnetic field measurement is improved, and the brain magnetic field measurement device of a realistic price and size is provided.

[0005]

Means for Solving the Problems A brain magnetic field measuring apparatus of the present invention which achieves this object is a cup-shaped high critical temperature oxide superconductor having a hollow tubular body which is closed at one end and opened at the other end. A magnetic shield device consisting of a cup-shaped external cryostat that keeps this at operating temperature with liquid nitrogen is placed laterally, and in the conventional brain magnetic field measurement device, the SQUID magnetometer is a magnetic shield device that is configured separately from the magnetic shield device. The magnetic shield device and SQ
Liquid nitrogen cooling the high critical temperature oxide superconductor by SQU
It is also used to prevent the evaporation of liquid helium in the ID magnetometer, and more advantageously, the diameters of the high critical temperature oxide superconductor and the outer cryostat surrounding the supercritical temperature oxide are limited to the limit size that forms a space enough to accommodate a patient. Not only was it possible to reduce the size and design the magnetic shield device to be relatively small,
The ceramic firing of high critical temperature oxide superconductors can be reduced to a realistic price.

That is, according to the present invention, an ice bag type liquid helium container for accommodating a SQUID chip and a pickup coil, and a cup-shaped internal cryostat for thermally insulating the ice bag type liquid helium container from the ambient environment are provided,
The inner cryostat is placed coaxially with the outer cryostat, and the ice bag-shaped liquid helium container is placed in the space between the closed ends of the outer cryostat and the inner cryostat so that the ice bag-shaped liquid helium container and the adjacent outer cryostat have a hemispherical end. The SQUID magnetometer is composed of the part and the internal cryostat.

With this configuration, the diameter of the magnetic shield device is limited to a diameter enough to accommodate a patient as compared with a horizontal brain magnetic field measurement device (FIG. 5) in which the magnetic shield device and the SQUID magnetometer are separately configured. It can be reduced to a relatively small diameter. If the diameter is large, the S from the open end must be increased unless the depth of the ceramic tube is increased in proportion to it.
It cannot prevent the magnetic field from entering the QUID magnetometer. For this reason, in the lateral brain magnetic field measurement device in which the magnetic shield device and the SQUID magnetometer are independently configured, the ceramic tube body becomes long and the volume increases as the cube of the length thereof.
Even if a high-critical-temperature oxide superconductor is fired in an electric furnace, its production becomes prohibitive in terms of cost. The ceramic tube body has a realistic size due to the integral structure of the magnetic shield device and the SQUID magnetometer according to the present invention.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. As shown in the figure, the outer cryostat 2a (stainless steel) surrounding the cup-shaped high-critical-temperature oxide superconductor 1 of the hollow tubular body which is closed at one end and open at the other end is a sealed liquid. Nitrogen-based supercritical oxide superconductor 1
Is kept at the operating temperature. Ice bag type liquid helium container 7
(Glass, reinforced plastic) is SQ in liquid helium
The UID chip 4 and the pickup coil 5 connected thereto are housed. A cup-shaped internal cryostat 2b that thermally insulates the ice bag type liquid helium container 7 from the outside at room temperature is arranged coaxially with the external cryostat 2a. A transfer tube is inserted using the annular space S between the outer cryostat 2a and the inner cryostat 2b, and liquid helium is injected into the ice bag-shaped liquid helium container 7 through the opening O of the ice bag-shaped liquid helium container 7.
H indicates the liquid level of liquid helium.

The closed ends of the ice bag type liquid helium container 7 and the internal cryostat 2b are recessed so as to surround the patient's head, and the pick-up coil 5 of the ice bag type liquid helium container 7 is surrounded so as to surround the head part. Place it in the recess. As a result, the cerebral magnetic field is detected in a state in which the penetrating external magnetic field is the weakest and closest to the patient's head. As shown in FIG. 1, the ice-sac-type liquid helium container 7 is disposed in the space between the closed end of the outer cryostat 2a and the closed end of the inner cryostat 2b, so that the ice-sac-type liquid helium container 7 and the external adjacent space The hemispherical end of the cryostat and the internal cryostat 2b constitute the SQUID magnetometer 3 as shown by the broken line.

Reference numeral 12 is a carrier for accommodating the patient in the hollow space and for carrying the patient out of the hollow space. As shown in FIG. 2, when the carrier 12 is connected to the shaft 11 slidably inserted in the slide bearing 10 arranged along the tubular surface of the magnetic shield device to reduce the size of the entire device including the gantry 13. Good. By adopting this folding-back type parallel movement mechanism, the total length of the brain magnetic field measurement apparatus can be shortened to about 2 meters, and the installation area can be significantly reduced.

[0011]

EFFECTS OF THE INVENTION By arranging a high critical temperature oxide superconductor (ceramic) horizontally according to the present invention, it is possible to avoid the instability of installation and the disadvantages of constructing a dedicated building when vertically arranged. You can Due to the inseparable structure of the magnetic shield device and the SQUID magnetometer according to the present invention, the ceramic tube body has a size that can be practically fired, and the size of the brain magnetic field measuring device is also large enough to accommodate a patient. It can be reduced to the limit towards a sufficient spatial size. Also, the liquid helium in the ice bag type liquid helium container is effectively cooled by the liquid nitrogen through the hemispherical end portion of the outer cryostat adjacent thereto, thereby preventing the evaporation of the liquid helium,
It enables long-term measurement.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of a brain magnetic field measuring apparatus of the present invention.

FIG. 2 is a perspective view of another embodiment of the brain magnetic field measuring apparatus of the present invention.

FIG. 3 is a schematic diagram showing an example of a conventional brain magnetic field measurement apparatus.

FIG. 4 is a schematic diagram showing another example of a conventional brain magnetic field measurement apparatus.

FIG. 5 is a vertical cross-sectional view of a horizontal cerebral magnetic field measurement apparatus in which a magnetic shield device and a SQUID magnetometer are independent and independent.

[Explanation of symbols]

 1 High Critical Temperature Oxide Superconductor 2 Cryostat 2a External Cryostat 2b Internal Cryostat 3 SQUID Magnetometer 4 SQUID Chip 5 Pickup Coil 6 Transfer Tube 7 Ice Bag Type Liquid Helium Container 8 Vertical Hole 9 Heat Shield Plate 10 Slide Bearing 11 Shaft 12 Carrier stand 13

Claims (2)

[Claims] 1. A cup-shaped horizontal type high critical temperature oxide superconductor magnetic shield device having a hollow tubular body closed at one end and opened at the other end, and an ice bag type liquid helium container accommodating a SQUID chip and a pickup coil. And a cup-shaped internal cryostat that thermally insulates this ice bag type liquid helium container from the outside at room temperature, the magnetic shield device is a cup-shaped high-critical-temperature oxide superconductor, and this to the operating temperature. And a cup-shaped outer cryostat, wherein the inner cryostat is arranged coaxially with the outer cryostat, and the ice-sac-type liquid helium container is arranged in a space between the outer cryostat and the closed end of the inner cryostat. An apparatus for measuring brain magnetic fields, which comprises an SQUID magnetometer. 2. A hollow tube magnetic shield device has a slide bearing disposed along its tubular surface and a shaft slidably inserted into the slide bearing, to which a carrier is connected. The brain magnetic field measuring apparatus according to claim 1, wherein the magnetic shield apparatus can be horizontally inserted and taken out from the open end of the magnetic shield apparatus.