JPH11128193A - Biomagnetism measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the magnetism shut-off effect by corresponding to changes of the environment after installing a second magnetism shut-off means which shuts off magnetism locally and furthermore concerning magnetism component in the direction in which it is detected by a magnetic sensor by providing the second magnetism shut-off means in a magnetism shut-off region by means of a first magnetism shut-off means. SOLUTION: A bed for examination 3, a cryostat 4, a gantry 6, and a local magnetism shield device 12 of square cylindrical type are stored in a magnetism shield room 1 which is a first magnetism shut-off means. The local magnetism shield device 12 forms a cryostat insertion hole opened toward the vertical direction for a square cylindrical shaft in a central part of a square cylindrical type magnetism shield material 12a of which both ends are opened, surrounds the circumference thereof by an insertion hole magnetism shield material 12b, and is put on the bed for examination 3. The cryostat 4 is put in such a way that a measuring face is positioned on the chest of a subject 2 by inserting a tip part where a magnetic sensor is positioned into the insertion hole through the insertion hole magnetism shield material 12b by inserting the tip part first.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biomagnetism measuring apparatus for measuring biomagnetism generated in response to nerve activity or myocardial activity of a living body's brain or heart, and more particularly to shielding of external magnetic noise.

[0002]

2. Description of the Related Art When a magnetic sensor using a superconducting quantum interference device (SQUID) is used, it is possible to measure an extremely low magnetic phenomenon of about 10 pT. Utilizing this, an apparatus has been developed for measuring weak magnetism generated by nerve activity or cardiac activity of the brain or heart of a living body. In order to stably perform such weak magnetic measurement, it is extremely important to severely suppress the influence of magnetic field fluctuation (magnetic noise) in the external environment.

FIG. 3 shows an example of a conventional biomagnetism measuring device. 1 is a magnetic shield room for maintaining a low magnetic field environment around the magnetic detection unit, 2 is a subject, 3 is a subject 2
Is a test bed on which a superconducting quantum interference device (S
5 is a refrigerant replenishing device, 6 is a gantry holding the cryostat 4, 7 is a controller for controlling the magnetic sensor, and amplifies an electric signal output from the magnetic sensor. Reference numeral 9 denotes a data processing device for setting measurement conditions and processing measurement data, and 10 denotes a printer for printing and outputting measurement data and measurement conditions.

As means for reducing (shielding) the influence of external magnetic field fluctuation in biomagnetism measurement, there are the following magnetic shielding means conventionally used.

[0005] One of them uses a magnetically shielded chamber 1 for magnetically shielding the entire measurement space as shown in FIG. A biomagnetic measurement device that measures magnetism generated from the brain and heart of a human body using a magnetic sensor using a SQUID has a built-in magnetic sensor as a component around the measurement site in addition to the subject and the magnetic sensor. Cryostat 4 to maintain the superconducting state by
A gantry 6 for holding the subject 2 in a predetermined posture in a measurement space, an inspection bed 3 for placing and holding the subject 2 and the like are required, and the magnetic shield room 1 has one Construct a large magnetic shielding space.

[0006] One such large magnetic shield room 1
Is usually used, the spatial three-directional components are usually 40 to 5
It is possible to obtain a magnetic shielding ratio of about 0 dB. Whether this shielding factor is sufficient for the desired magnetic measurement,
It is considered to be a boundary value depending on the surrounding environment. In a magnetically quiet environment with little artificial magnetic noise, an environment necessary for performing biomagnetic measurement can be obtained. In addition, since the entire large measurement space is magnetically shielded, the number of parameters affecting the measurement space is small, and stable magnetic measurement is possible.

However, in an environment where the external fluctuating magnetic field is large, it is insufficient, and a higher magnetic shielding rate may be required. In the case of one large magnetic shield room 1 as shown in FIG. 3, in order to enhance the magnetic shielding performance, it is necessary to adopt a multilayer shield wall configuration and to increase the thickness and the layer interval of the shield material. Yes, and very expensive. In addition, it is difficult to modify the apparatus to enhance the magnetic shielding performance after installing the apparatus, and it is difficult to cope with environmental degradation after installation.

Further, there is a weak point that the apparatus is easily affected by floor vibration at the installation place. If there is floor vibration at the installation location,
The vibration of the wall surface of the magnetic shield caused by the floor vibration modulates the magnetic distribution in the magnetic shield chamber 1 by the vibration frequency. Therefore, magnetic noise (magnetic fluctuation) corresponding to the floor vibration frequency is generated at the position of the magnetic sensor,
It will interfere with the weak biomagnetic measurement.

The other is to use a cylindrical magnetic shield having one end closed / other end or both ends opened.
In a superconducting magnetic shielding device using an oxide superconductor as a magnetic shielding material, a high shielding performance can be obtained by a shielding current flowing in a circumferential direction with respect to a magnetic flux entering from an opening. As an example, it has been reported that in the case of a cylindrical superconducting magnetic shield having a diameter of 90 cm and a length of 2 m with one end open and the other end closed, a high magnetic shield performance of 100 dB or more can be obtained.

However, since the subject and the superconducting magnetic sensor must be inserted into the elongated cylinder,
There are significant restrictions on the application to biomagnetic measurement. For example,
In the above-described example, at the time of measurement, the subject is inserted to the closed end portion 2 m deep of the cylindrical superconducting magnetic shield having a diameter of 90 cm and an open / closed end. In the narrowly closed measurement space at the closed end, the subject receives a very strong feeling of pressure, and it is difficult to insert a cryostat (containing a magnetic sensor) having a practical refrigerant capacity. Further, it is difficult to keep the cryostat in a stable state. For this reason, it is difficult to configure a practical biomagnetism measuring device.

[0011]

As described above, as described above,
A biomagnetism measuring device using a large magnetic shield room surrounding the entire measuring unit as a magnetic shielding means does not give a feeling of oppression to the subject and fixes a cryostat having a necessary refrigerant capacity in the measuring unit. However, it is expensive to construct a magnetically shielded room with a high magnetic shielding rate, and it is difficult to improve the performance enhancement in response to environmental changes. There is a problem that noise is easily generated.

Further, in a biomagnetism measuring apparatus using a cylindrical superconducting magnetic shield as a magnetic shielding means, the subject has a very strong feeling of pressure due to its narrow and closed measurement space, and is a practical refrigerant. Since it is difficult to insert a cryostat having a capacity and to stably hold the cryostat, it is difficult to configure a biomagnetism measuring device capable of continuous measurement.

Accordingly, it is an object of the present invention to provide a biomagnetism measuring device which can obtain a high magnetic shielding effect with a small increase in price.

Another object of the present invention is to provide a biomagnetism measuring apparatus which can easily enhance the magnetic shielding effect in response to environmental changes after installation.

Still another object of the present invention is to provide a biomagnetism measuring apparatus capable of obtaining a magnetic shielding effect capable of performing stable magnetic measurement against vibration.

Still another object of the present invention is to provide a biomagnetism measuring apparatus which does not give a feeling of mental pressure to a subject.

[0017]

SUMMARY OF THE INVENTION The present invention provides a biomagnetism measuring apparatus comprising a magnetic sensor, subject support means for supporting a subject to be measured magnetically, and first magnetic shielding means for housing the same. In the above, the magnetic component is installed in a magnetic shielding area by the first magnetic shielding means, and at least a magnetic component in a direction to be detected by the magnetic sensor is limited only in an area near the measurement section and the magnetic sensor section of the subject. A second magnetic shielding means for locally performing magnetic shielding is provided. The combination of these two magnetic shielding means can provide a high magnetic shielding effect with a small increase in price. In addition, a second magnetic shielding means is added to increase the magnetic shielding effect in response to an environmental change after the apparatus is installed, or a modification for enhancing the magnetic shielding performance is facilitated.

Further, the second magnetic shielding means is configured to be compact and rigid, thereby obtaining magnetic shielding performance capable of performing stable magnetic measurement against vibration.

Furthermore, the second magnetic shielding means exposes the subject's head to prevent giving the subject a feeling of mental oppression.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) FIG. 1 shows an embodiment of a biomagnetism measuring apparatus employing a composite magnetic shield according to the present invention.

A magnetic shield room 1 serving as a first magnetic shield means has an inspection bed 3 for placing a subject 2 and holding it in a measurement posture, and generates an electric signal in response to biomagnetism. A cryostat 4 which incorporates a magnetic sensor and maintains a superconducting state, a gantry 6 which supports the cryostat 4 at a predetermined position, and a rectangular cylindrical local magnetic shield device 12 which is a second magnetic shielding means are housed.

The magnetic shield chamber 1 is constructed by arranging a plate-like magnetic shield material made of permalloy in a two-layer structure with an appropriate interval (approximately 10 to 15 cm) between the ceiling, floor and side surfaces. The thickness of each permalloy magnetic shield plate is 1 to 2 mm, and the size of the internal space of the magnetic shield chamber 1 is approximately 2.5 mx 2.5 mx 2.5 m.

The cryostat 4 has a tip with a diameter of 2 mm.
It is 0 cm in length and 100 cm in length, and is held by the gantry 5 so that the bottom surface (the measuring side surface with a built-in magnetic sensor) is positioned 70 cm above the floor.

The local magnetic shield device 12 has a vertical
A rectangular cylindrical magnetic shield material 12a having both sides of 60 cm in width and 100 cm in length and made of permalloy and having both ends opened is mainly provided. The rectangular cylindrical magnetic shield material 12a is opened in a central portion thereof in a direction perpendicular to a rectangular cylinder axis. A cryostat insertion hole (not shown) is formed, and its periphery is surrounded by a permalloy insertion hole magnetic shield material 12b.
It is a T-shaped local magnetic shield device installed above. The rectangular cylindrical magnetic shield material 12a accommodates the subject 2 so as to expose the legs and the head of the subject 2 and magnetically shield the other portions, and the cryostat 4 is provided with a magnetic sensor. By inserting the distal end portion (measurement portion) into the insertion hole through the insertion hole magnetic shield material 12b first,
It is set so that the measurement surface is located on the chest of the subject 2.

In order to increase the magnetic shielding rate by itself, the rectangular cylindrical local magnetic shield device 12 having such a shape needs to have a sufficiently longer length than the inner diameter of the cylindrical portion. is there. For this reason, it is difficult to obtain the magnetic shielding rate required for biomagnetism measurement alone. However,
In this embodiment, the magnetic shielding performance of 40 to 60 dB is obtained by the magnetic shielding chamber 1 as the first magnetic shielding means, and the insufficient magnetic shielding effect is reduced by the local magnetic shielding means as the second magnetic shielding means. Since the local magnetic shield device 12 is obtained by the shield device 12,
It is sufficient that a magnetic shielding performance of about 0 dB can be obtained, and it can be easily adapted to this purpose.

On the other hand, the local magnetic shield device 12
Since the mechanical strength can be sufficiently increased due to the small size, it is possible to form firmly so as not to generate substantial distortion even under the influence of floor vibration, Magnetic noise generated when the magnetic shield room 1 vibrates on the floor can be shielded. It is easy to add the local magnetic shield device 12 to a conventional biomagnetism measuring device or to change its structure as necessary. As a result, the magnetic shield performance of the entire magnetic shield device is changed ( Reinforcement).

The same effect can be obtained from the rectangular cylindrical magnetic shield device 12 as a cylindrical magnetic shield device in which the rectangular cylindrical magnetic shield material 12a is transformed into a cylindrical magnetic shield material.

(Embodiment 2) FIG. 2 shows another embodiment of the present invention. The magnetic shield room 1 as the first magnetic shield means has the same configuration as the magnetic shield room 1 in the first embodiment. In this embodiment, as a local magnetic shield device 14 as a second magnetic shield means, an active shield method of generating a magnetic flux for compensating a change in an external magnetic field, suppressing a magnetic field change, and eliminating the influence of the external magnetic field change. Uses a local magnetic shield device. Aside from the magnetic sensor that generates an electric signal in response to the biomagnetism, a position for detecting the background generated in the cryostat 4 at a position above the magnetic sensor for detecting the biomagnetism where the subject 2 does not detect the biomagnetism is provided. Are provided.

In general, the biomagnetism generated from the subject 2 is very weak and is localized in the body of the subject 2, so that the biomagnetism is detected only by the magnetic sensor for biomagnetism disposed on the bottom surface of the cryostat 4. . On the other hand, the fluctuation of the external magnetic field is considered to be an effect of a fluctuation source far away from the subject 2, and includes a magnetic sensor for biomagnetism detection and a magnetic sensor 14a for background detection. It is considered to be primarily uniform around the sensor.
To this end, the magnetic sensor 1 for detecting each background
At 4a, only the change in the external magnetic field is detected without the biomagnetism from the subject 2 acting. The output signal of the background detection magnetic sensor 14a is negatively fed back to the compensation magnetic field generating coil 14b placed outside the cryostat 4 via an amplification circuit and a feedback current control circuit (not shown) in the measurement control circuit 7. The feedback current generates a magnetic field that compensates for external magnetic field fluctuation. With this control system, the magnetic field at the position of the magnetic sensor 14a for background detection is controlled so as to have a constant value, so that the influence of the fluctuation of the external magnetic field is avoided (shielded).

The magnetic shielding performance obtained by such an active shield depends on the degree of correlation of the externally changing magnetic field between the position of the magnetic sensor for detecting biomagnetism and the position of the magnetic sensor 14a for detecting background. It is difficult to obtain the shielding performance required for biomagnetic measurement by using the active shield alone. However, also in the second embodiment, as in the first embodiment, by using the magnetic shield chamber 1 as the first magnetic shield means in combination as an auxiliary means, the magnetic shield performance of the magnetic shield chamber 1 is insufficient. Even in such a case, the measurement unit can obtain magnetic shielding performance that provides a magnetic field sufficient for biomagnetism measurement. Further, by changing the shape of the compensation magnetic field generating coil 14b, it is possible to change the magnetic shielding space. Also,
Since the output signal of the magnetic sensor 14a for background detection is used as a compensation signal, the influence of the magnetic field modulation due to the vibration of the wall surface of the magnetic shield room 1 can be removed at the same time. Furthermore, since there is no special restriction on the size of the cryostat 4, the cryostat 4 having a sufficient refrigerant capacity for continuous magnetic measurement can be used.

(Other Embodiments) As the local magnetic shield device, a local magnetic shield device utilizing a superconducting magnetic shielding effect can be combined. That is, instead of the rectangular (or cylindrical) magnetic shield material 12a and the insertion hole magnetic shield material 12c made of permalloy in the first embodiment, for example, a magnetic shield material having both ends opened by an oxide superconductor may be used. . In this case, the magnetic shield material needs to be kept at a low temperature, and a heat insulating structure made of a cylinder or a square tube is provided, and the magnetic shield material is fixed and held inside the structure. A similar magnetic shielding effect can be obtained.

The inspection bed is adapted to the form of measurement,
It can be replaced by a chair or other form of subject support.

[0034]

According to the present invention, a large magnetic shielding means such as a magnetic shielding room for accommodating a subject, measuring equipment and auxiliary means and a local magnetic shielding for local magnetic shielding limited to the vicinity of the measuring unit. By combining the shields, it is possible to obtain the magnetic shield performance required for biomagnetism measurement by compensating for the disadvantages of each of them alone. In particular, the large magnetic shield means
A relatively large magnetic shielding effect can be obtained in spite of a small mental pressure on the subject. In addition, the local magnetic shielding means enhances the magnetic shielding effect of the measuring unit without giving a large feeling of oppression to the subject, and reduces floor vibration so as to reduce the effect of magnetic field fluctuation due to floor vibration in the large magnetic shielding means. It can be formed firmly so that it does not respond to changes in the magnetic environment.It is also easy to flexibly change its magnetic shielding performance in response to changes in the external magnetic environment. It becomes easy to obtain shielding performance.

It is also possible to use a cryostat having a refrigerant capacity necessary for continuous magnetic measurement.

[Brief description of the drawings]

FIG. 1 is a perspective view of a biomagnetism measuring apparatus according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a biomagnetism measuring device according to a second embodiment of the present invention.

FIG. 3 is a perspective view of a conventional biomagnetism measuring device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic shield room, 2 ... Examinee, 3 ... Bed, 4 ... Cryostat, 6 ... Gantry, 7 ... Measurement control circuit,
9: Computer, 12: Local magnetic shield device, 12a: Rectangular cylindrical magnetic shield material, 12b: Insertion hole magnetic shield material.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akihiko Kamtori 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside Central Research Laboratory, Hitachi, Ltd.

Claims (10)

[Claims] 1. A magnetic sensor including a superconducting quantum interference device (SQUID), a cryostat holding the SQUID in a cooling medium to maintain a superconducting state, a gantry holding the cryostat, and a subject. Biomagnetism measurement comprising: an inspection bed or chair for carrying and magnetic measurement, and first magnetic shielding means for housing the cryostat, gantry, bed or chair in its entirety and magnetically shielding the bed or chair from the outside. In the apparatus, at least a magnetic component detected by the magnetic sensor, which is installed in a magnetic shielding area by the first magnetic shielding means and is limited to at least a measured part of the subject and a magnetic sensor part of the cryostat. A biomagnetism measuring apparatus further comprising a second magnetic shielding means for performing local magnetic shielding. 2. The method according to claim 1, wherein the second magnetic shielding means for performing local magnetic shielding utilizes a superconducting magnetic shielding effect. A biomagnetism measurement apparatus characterized in that it is configured to maintain a conduction magnetic shielding state. 3. The magnetic sensor according to claim 1, wherein the second magnetic shielding means for performing local magnetic shielding comprises a material to be measured of the subject and a magnetic sensor in the cryostat made of a material having high magnetic permeability at room temperature. A biomagnetism measuring device characterized in that the magnetic field is locally shielded. 4. The external magnetic field fluctuation detecting means according to claim 1, wherein said second magnetic shielding means performs an external magnetic field fluctuation detecting means and an output signal of said external magnetic field fluctuation detecting means. A biomagnetism measuring apparatus characterized by comprising means for compensating for (1) and (2), by means of which the part to be measured of the subject and the magnetic sensor part in the cryostat are locally magnetically shielded. 5. The magnetic shielding means according to claim 1, wherein said second magnetic shielding means is combined substantially vertically with a cylindrical magnetic shielding member and an intermediate portion of said cylindrical magnetic shielding member, and has a cryostat inserted therein. A biomagnetism measuring device, which is a T-shaped magnetic shielding device provided with a shielding cylinder. 6. A biomagnetism measuring apparatus comprising: a magnetic sensor; subject support means for supporting a subject to be measured magnetically; and first magnetic shielding means for housing the magnetic sensor. The magnetic shield is installed in the magnetic shield area by the means, and further performs local magnetic shield on at least the magnetic component in the direction detected by the magnetic sensor only in the area near the measurement section and the magnetic sensor section of the subject. 2
A biomagnetism measuring device, comprising: a magnetic shielding means. 7. A structure according to claim 6, wherein said second magnetic shielding means utilizes a superconducting magnetic shielding effect, and maintains the superconducting state during magnetic measurement. A biomagnetism measuring device, characterized in that: 8. The apparatus according to claim 6, wherein the second magnetic shielding means is configured to locally magnetically shield the measurement portion and the magnetic sensor portion of the subject with a material having high magnetic permeability at room temperature. A biomagnetism measuring device, characterized in that: 9. The apparatus according to claim 6, wherein the second magnetic shielding means includes an external magnetic field fluctuation detecting means, and a compensation magnetic field generating means for compensating for the influence of the external magnetic field fluctuation using an output signal of the magnetic field fluctuation detecting means. A biomagnetism measuring apparatus comprising: a magnetic field shielding unit configured to locally shield a magnetic field of a measurement unit and a magnetic sensor unit of a subject from being affected by an external magnetic field. 10. The magnetic shielding means according to claim 6, wherein said second magnetic shielding means is combined substantially vertically with a cylindrical magnetic shielding member and an intermediate portion of said cylindrical magnetic shielding cylinder, and a magnetic sensor portion is inserted therein. A biomagnetism measuring device, which is a T-shaped magnetic shielding device provided with a magnetic shielding cylinder.