阅读说明：本技术 脑磁计和脑磁场测定方法 (Brain magnetometer and method for measuring brain magnetic field ) 是由 森谷隆广 笈田武范 齐藤右典 须山本比吕 小林哲生 于 2021-06-15 设计创作，主要内容包括：脑磁计(M1),具备：多个光激发磁传感器(1A),测量脑磁场；多个地磁磁场修正用磁传感器(2),测量多个光激发磁传感器(1A)的各个的位置处的与地磁相关的磁场；多个有源屏蔽用磁传感器(3),测量多个光激发磁传感器(1A)的各个的位置处的变化磁场；地磁磁场修正线圈；有源屏蔽线圈(9)；控制装置(5),基于多个地磁磁场修正用磁传感器(2)的测量值,确定产生抵消与地磁相关的磁场的磁场的电流,并且基于多个有源屏蔽用磁传感器(3)的测量值,确定产生抵消与变化磁场的磁场的电流,并且输出对应于确定的电流的控制信号；以及线圈电源(6),根据控制信号,将电流输出至各线圈。(A brain magnetometer (M1) is provided with: a plurality of photo-excited magnetic sensors (1A) for measuring the magnetic field of the brain; a plurality of geomagnetic-field-correction magnetic sensors (2) that measure magnetic fields relating to geomagnetism at respective positions of the plurality of optically-excited magnetic sensors (1A); a plurality of active shielding magnetic sensors (3) for measuring a changing magnetic field at each position of the plurality of photo-excitation magnetic sensors (1A); a geomagnetic field correction coil; an active shield coil (9); a control device (5) that determines a current that generates a magnetic field that cancels a magnetic field associated with geomagnetism, based on the measurement values of the plurality of magnetic sensors (2) for geomagnetic field correction, and determines a current that generates a magnetic field that cancels and varies the magnetic field, based on the measurement values of the plurality of magnetic sensors (3) for active shielding, and outputs a control signal corresponding to the determined current; and a coil power supply (6) that outputs a current to each coil in accordance with the control signal.)

1. A brain magnetometer, characterized in that,

the disclosed device is provided with:

a plurality of light-excited magnetic sensors for measuring the magnetic brain field,

a plurality of geomagnetic-field-correction magnetic sensors that measure magnetic fields associated with geomagnetism at respective positions of the plurality of photo-excitation magnetic sensors,

a plurality of active shielding magnetic sensors that measure a changing magnetic field at a position of each of the plurality of photo-excitation magnetic sensors,

a geomagnetic field correction coil for correcting the magnetic field associated with geomagnetism,

an active shield coil for modifying the varying magnetic field,

control means for determining a current to the geomagnetic field correction coil so as to generate a magnetic field that cancels the magnetic field associated with geomagnetism, based on the measurement values of the plurality of geomagnetic field correction magnetic sensors, and determining a current to the active shield coil so as to generate a magnetic field that cancels the varying magnetic field, based on the measurement values of the plurality of active shield magnetic sensors, and outputting a control signal corresponding to the determined current; and

and a coil power supply that outputs a current to the geomagnetic field correction coil and the active shield coil according to the control signal output by the control device.

2. The brain magnetometer of claim 1,

the geomagnetic field correction coil includes a geomagnetic field correction coil for correcting a magnetic field of the geomagnetism and a gradient magnetic field correction coil for correcting a gradient magnetic field of the geomagnetism,

the control device determines the current to the geomagnetic correction coil so that an average value of the measurement values of the plurality of geomagnetic correction magnetic sensors is approximately zero, and determines the current to the gradient magnetic field correction coil so that a deviation from the average value of the measurement values of the plurality of geomagnetic correction magnetic sensors is minimized.

3. The brain magnetometer of claim 2,

the geomagnetic correction coil and the gradient magnetic field correction coil are each a pair of coils disposed so as to sandwich the plurality of optically excited magnetic sensors.

4. The brain magnetometer of claim 1,

the geomagnetic field correction coil includes a coil system capable of applying a magnetic field in three orthogonal directions, which are respectively orthogonal and circumferentially arranged, to each of the plurality of photo-excitation magnetic sensors,

the control device determines the current to the coil system for each of the plurality of optical excitation sensors so that the measurement values of the plurality of magnetic sensors for geomagnetic field correction are approximately zero.

5. The brain magnetometer according to any one of claims 1 to 4,

the control device determines the current to the active shield coil so that an average value of the measurement values of the plurality of magnetic sensors for active shield is approximately zero.

6. The brain magnetometer according to any one of claims 1 to 5,

the plurality of photo-excitation magnetic sensors are axial gradiometers having a measurement region and a reference region in a direction perpendicular to the scalp and coaxially.

7. The brain magnetometer according to any one of claims 1 to 6,

the plurality of photoexcited magnetic sensors, the plurality of magnetic sensors for geomagnetic field correction, and the plurality of magnetic sensors for active shielding are fixed to a helmet-type non-magnetic frame that is attached to the head of a subject, has a relative magnetic permeability close to 1, and does not disturb magnetic field distribution.

8. The brain magnetometer according to any one of claims 1 to 7,

the electromagnetic shield is also provided for shielding high-frequency electromagnetic noise.

9. A method for measuring a brain magnetic field is characterized in that,

the method comprises the following steps:

a step of measuring a magnetic field associated with geomagnetism at a position of each of the plurality of photo-excitation magnetic sensors;

a step of determining a current to the geomagnetic field correction coil based on the plurality of measurement values of the geomagnetic-related magnetic field so as to generate a magnetic field that cancels the geomagnetic-related magnetic field, and outputting a control signal for geomagnetic field correction corresponding to the determined current;

outputting a current to the geomagnetic field correction coil according to the geomagnetic field correction control signal;

a step of measuring a changing magnetic field at a position of each of the plurality of photo-excitation magnetic sensors;

a step of determining a current to the active shield coil based on the plurality of measured values of the varying magnetic field so as to generate a magnetic field that cancels the varying magnetic field, and outputting a varying magnetic field correction control signal corresponding to the determined current;

outputting a current to the active shield coil according to the control signal for correcting the changing magnetic field; and

a step of measuring a brain magnetic field by the plurality of optically-excited magnetic sensors.

10. The method for measuring a brain magnetic field according to claim 9,

determining the current to the geomagnetic field correction coil so as to generate a magnetic field that cancels the magnetic field associated with geomagnetism includes: determining a current to a geomagnetic correction coil constituting the geomagnetic field correction coil so that an average value of a plurality of measurement values of the magnetic field related to geomagnetism is approximately zero; the current to the gradient magnetic field correction coil constituting the geomagnetic field correction coil is determined so that a deviation from an average value of the measurement values of the magnetic field related to geomagnetism is minimized.

11. The method for measuring a brain magnetic field according to claim 9,

determining the current to the geomagnetic field correction coil so as to generate a magnetic field that cancels the magnetic field associated with geomagnetism includes: determining, for each of the plurality of photo-excited magnetic sensors, a current for a respective coil system arranged orthogonally and circumferentially in such a manner that a plurality of measured values of the magnetic field associated with geomagnetism are approximately zero.

Technical Field

One embodiment of the present invention relates to a brain magnetometer and a brain magnetic field measurement method.

Background

In the related art, a superconducting quantum interference device (SQUID) is used as a brain magnetometer to measure minute magnetic properties. In recent years, a brain magnetometer using an optically excited magnetic sensor instead of the SQUID has been studied. The optical excitation magnetic sensor measures minute magnetism by using spin polarization of atoms of alkali metal excited by an optical pump. For example, patent document 1 discloses a brain magnetometer using an optical pump magnetometer.

Patent document 1: japanese patent No. 5823195

Disclosure of Invention

In order to avoid the influence of magnetic noise stronger than the brain magnetic field, measurement by a brain magnetometer is performed in a magnetic shield room that shields the magnetic noise. However, the arrangement of the magnetic shield room is limited from the viewpoint of weight, price, and the like.

An object of one embodiment of the present invention is to provide a brain magnetometer and a brain magnetic field measurement method that can perform measurement with high accuracy without using a magnetic shield room.

A brain magnetometer according to an embodiment of the present invention includes: a brain magnetometer having: a plurality of light-excited magnetic sensors for measuring the magnetic brain field; a plurality of geomagnetic-field-correction magnetic sensors that measure magnetic fields relating to geomagnetism at positions of the plurality of photo-excitation magnetic sensors, respectively; a plurality of active shielding magnetic sensors that measure a changing magnetic field at each of the plurality of photo-excitation magnetic sensors; a geomagnetic field correction coil for correcting a magnetic field associated with geomagnetism; an active shield coil for modifying the varying magnetic field; a control device that determines a current to the geomagnetic field correction coil based on measurement values of the plurality of geomagnetic field correction magnetic sensors in such a manner as to generate a magnetic field that cancels a magnetic field associated with geomagnetism, and determines a current to the active shield coil based on measurement values of the plurality of active shield magnetic sensors in such a manner as to generate a magnetic field that cancels a varying magnetic field, and outputs a control signal corresponding to the determined current; and a coil power supply that outputs a current to the geomagnetic field correction coil and the active shield coil, based on a control signal output by the control device.

In the brain magnetometer according to one aspect of the present invention, the magnetic field related to the geomagnetism and the varying magnetic field can be measured at each position of the plurality of optically excited magnetic sensors for measuring the brain magnetic field. Further, in the present brain magnetometer, the current to the geomagnetic field correction coil is determined so as to generate a magnetic field that cancels the magnetic field associated with the geomagnetism, based on the plurality of measurement values of the magnetic field associated with the geomagnetism, and the current to the active shield coil is determined so as to generate a magnetic field that cancels the varying magnetic field, based on the plurality of measurement values of the varying magnetic field, and a control signal corresponding to the determined current may be output. When a current corresponding to the control signal is output to the geomagnetic field correction coil and the active shield coil, a magnetic field is generated in each coil, and at the position where the plurality of optical excitation magnetic sensors are located, the magnetic field related to the geomagnetism is cancelled by the magnetic field generated in the geomagnetic field correction coil, and the varying magnetic field is cancelled by the magnetic field generated in the active shield coil. As described above, by canceling the magnetic field related to the geomagnetism and the varying magnetic field at the positions of the plurality of photo-excitation magnetic sensors, the plurality of photo-excitation magnetic sensors can measure the brain magnetic field while avoiding the influence of the magnetic field related to the geomagnetism and the influence of the varying magnetic field. According to such a brain magnetometer, it is possible to measure a brain magnetic field with high accuracy without using a magnetic shield room.

The geomagnetic field correction coil includes a geomagnetic correction coil for correcting a magnetic field of geomagnetism and a gradient magnetic field correction coil for correcting a gradient magnetic field of geomagnetism, and the control device may determine the current to the geomagnetic correction coil so that an average value of the measurement values of the plurality of geomagnetic field correction magnetic sensors is approximately zero, and may determine the current to the gradient magnetic field correction coil so that a deviation from the average value of the measurement values of the plurality of geomagnetic field correction magnetic sensors is minimized. With this configuration, the same magnetic field correction (0-time correction) is performed by controlling the current of the geomagnetic correction coil, and the correction (1-time correction) is performed by controlling the current of the gradient magnetic field correction coil, taking into account the different gradient magnetic fields at the positions of the respective optically excited magnetic sensors. In this way, by gradually canceling the gradient magnetic field of the geomagnetism and the geomagnetism, the magnetic field relating to the geomagnetism can be corrected with high accuracy.

The geomagnetic correction coil and the gradient magnetic field correction coil may be a pair of coils arranged with the plurality of optically excited magnetic sensors interposed therebetween. According to such a configuration, the magnetic field relating to the geomagnetism at the position where the plurality of optically excited magnetic sensors are sandwiched between the pair of geomagnetic field correction coils and the pair of gradient magnetic field correction coils is effectively corrected. Thus, the magnetic field associated with the geomagnetism can be appropriately corrected with a simple configuration.

The geomagnetic field correction coil includes a coil system capable of applying a magnetic field in three orthogonal directions, which are respectively orthogonal and circumferentially arranged, to each of the plurality of photo-excitation magnetic sensors, and the control device may determine a current to the coil system for each of the plurality of photo-excitation magnetic sensors so that a measurement value of each of the plurality of geomagnetic field correction magnetic sensors is approximately zero. With this configuration, the coil system is arranged for each of the plurality of photo-excitation magnetic sensors in accordance with each of the components in the three directions (x-axis, y-axis, and z-axis) of the static magnetic field. Then, by controlling the current corresponding to each of the coil systems, magnetic fields that cancel each of the x-axis direction component, the y-axis direction component, and the z-axis direction component of the magnetic field associated with the geomagnetism are generated for each of the plurality of photo-excited magnetic sensors, and the magnetic field associated with the geomagnetism is corrected from three directions. This makes it possible to finely control the current for each of the plurality of photo-excitation magnetic sensors and improve the accuracy of correction of the magnetic field associated with the geomagnetism. In addition, since only the magnetic field relating to the geomagnetism in the region relating to the operation of the plurality of photoexcited magnetic sensors is corrected, an increase in power consumption relating to unnecessary correction can be suppressed.

The control device may determine the current to the active shield coil so that an average value of the measurement values of the plurality of magnetic sensors for active shield is approximately zero. According to such a configuration, by controlling the current to the active shield coil, the changing magnetic field at the position of the plurality of photo-excitation magnetic sensors is effectively corrected. Thus, the varying magnetic field can be appropriately corrected with a simple configuration.

The plurality of photoexcited magnetic sensors may be axial gradiometers having a measurement region and a reference region in a direction perpendicular to the scalp and coaxially. According to such a configuration, since the influence of the common mode noise is shown in each of the output result of the measurement region and the output result of the reference region, the common mode noise can be removed by obtaining a difference between the output results of the both. This improves the measurement accuracy of the brain magnetic field.

The plurality of photoexcited magnetic sensors, the plurality of magnetic sensors for geomagnetic field correction, and the plurality of magnetic sensors for active shielding may be fixed to a helmet-type non-magnetic frame that is attached to the head of the subject and has a relative magnetic permeability close to 1 and does not disturb the magnetic field distribution. According to such a configuration, since the non-magnetic frame attached to the head and the sensors fixed to the non-magnetic frame move in accordance with the movement of the head of the subject, even when the head of the subject moves, it is possible to appropriately perform correction of the magnetic field and the varying magnetic field related to the geomagnetism and measurement of the brain magnetic field at the positions where the plurality of photo-excitation magnetic sensors are located.

The electromagnetic shielding device may further include an electromagnetic shield for shielding high-frequency electromagnetic noise. With this configuration, it is possible to prevent high-frequency electromagnetic noise that cannot be measured from entering the plurality of photoexcited magnetic sensors in the brain magnetometer. This makes it possible to stably operate the plurality of photo-excitation magnetic sensors.

A method for measuring a brain magnetic field according to an embodiment of the present invention includes: a step of measuring a magnetic field associated with geomagnetism at a position of each of the plurality of photo-excitation magnetic sensors; a step of determining a current to the geomagnetic field correction coil based on a plurality of measurement values of the magnetic field related to geomagnetism so as to generate a magnetic field that cancels the magnetic field related to geomagnetism, and outputting a control signal for geomagnetic field correction corresponding to the determined current; outputting a current to the geomagnetic field correction coil according to the geomagnetic field correction control signal; a step of measuring a changing magnetic field at a position of each of the plurality of photo-excitation magnetic sensors; a step of determining a current to the active shield coil based on the plurality of measured values of the varying magnetic field so as to generate a magnetic field that cancels the varying magnetic field, and outputting a control signal for varying magnetic field correction corresponding to the determined current; outputting a current to the active shield coil according to the control signal for correcting the changing magnetic field; and a step of measuring a brain magnetic field by a plurality of optically-excited magnetic sensors.

In the magnetoencephalography measurement method according to one embodiment of the present invention, a magnetic field and a varying magnetic field relating to geomagnetism at respective positions of a plurality of optically excited magnetic sensors for measuring a magnetoencephalography field are measured. Further, according to the present brain magnetic field measurement method, the current to the geomagnetic field correction coil is determined so as to generate a magnetic field that cancels the geomagnetic-related magnetic field based on the plurality of measurement values of the geomagnetic-related magnetic field, and a control signal corresponding to the determined current is output. When a current corresponding to the control signal is output to the geomagnetic field correction coil, a magnetic field is generated in the geomagnetic field correction coil, and the magnetic field associated with the geomagnetism is cancelled by the magnetic field generated in the geomagnetic field correction coil at the position where the plurality of optical excitation magnetic sensors are located. In addition, based on the plurality of measured values of the varying magnetic field, a current to the active shielding coil is determined in such a manner as to generate a magnetic field that cancels the varying magnetic field, and a control signal corresponding to the determined current is output. When a current corresponding to the control signal is output to the active shield coil, a magnetic field is generated in the active shield coil, and the varying magnetic field is cancelled by the magnetic field generated in the active shield coil at the position where the plurality of photo-excitation magnetic sensors are located. As described above, by canceling the magnetic field related to the geomagnetism and the varying magnetic field at the positions of the plurality of photo-excitation magnetic sensors, the plurality of photo-excitation magnetic sensors can measure the brain magnetic field in a state of avoiding the influence of the magnetic field related to the geomagnetism and the influence of the varying magnetic field. According to such a brain magnetic field measurement method, a brain magnetic field can be measured with high accuracy without using a magnetic shield room.

Determining the current to the geomagnetic field correction coil so as to generate a magnetic field that cancels the magnetic field associated with geomagnetism may include: the current to the geomagnetic correction coil constituting the geomagnetic field correction coil is determined so that an average value of a plurality of measurement values of the magnetic field related to geomagnetism is approximately zero, and the current to the gradient magnetic field correction coil constituting the geomagnetic field correction coil is determined so that a deviation from the average value of the measurement values of the magnetic field related to geomagnetism is minimized. With this method, the same magnetic field correction (0-time correction) is performed by controlling the current of the geomagnetic correction coil, and the correction (1-time correction) is performed by controlling the current of the gradient magnetic field correction coil, taking into account the different gradient magnetic fields at the positions of the respective optically excited magnetic sensors. With such a method, by gradually canceling the geomagnetic field and the gradient magnetic field of the geomagnetism, the magnetic field relating to the geomagnetism can be corrected with high accuracy.

Determining the current to the geomagnetic field correction coil so as to generate a magnetic field that cancels the magnetic field associated with the geomagnetism may include: the current for each of the coil systems arranged orthogonally and circumferentially is determined for each of the plurality of photo-excited magnetic sensors in such a manner that a plurality of measured values of a magnetic field associated with geomagnetism are approximated to zero. According to such a method, the coil system is arranged for each of the plurality of photo-excitation magnetic sensors in accordance with each of the components in three directions (x-axis, y-axis, and z-axis) of the static magnetic field. Then, by controlling the current corresponding to each of the coil systems, magnetic fields that cancel each of the x-axis direction component, the y-axis direction component, and the z-axis direction component of the magnetic field associated with the geomagnetism are generated for each of the plurality of photo-excited magnetic sensors, and the magnetic field associated with the geomagnetism is corrected from three directions. Thereby, it is possible to finely control the current for each of the plurality of photo-excitation magnetic sensors and improve the correction accuracy of the magnetic field relating to the geomagnetism. In addition, since only the magnetic field relating to the geomagnetism in the region relating to the operation of the plurality of photoexcited magnetic sensors is corrected, an increase in power consumption relating to unnecessary correction can be suppressed.

According to one embodiment of the present invention, a brain magnetometer and a brain magnetic field measurement method capable of high-precision measurement without using a magnetic shield room can be provided.

Drawings

Fig. 1 is a schematic diagram showing the structure of a brain magnetometer according to an embodiment.

Fig. 2 is a flowchart illustrating an operation of the brain magnetometer according to the embodiment.

Fig. 3 is a schematic diagram showing a configuration of a brain magnetometer according to another embodiment.

Fig. 4 is a diagram showing the configuration of the coil system.

Fig. 5 is a flowchart showing the operation of the brain magnetometer according to the other embodiment.

Detailed Description

Hereinafter, modes for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

Fig. 1 is a schematic diagram showing the structure of a brain magnetometer M1 according to the embodiment. The brain magnetic meter M1 is a device that measures a brain magnetic field with an optical pump while generating a magnetic field that cancels magnetic noise. The brain magnetometer M1 includes: a plurality of OPM (optical pumped atomic magnetometer) modules 1, a plurality of magnetic sensors 2 for geomagnetic correction, a plurality of magnetic sensors 3 for active shielding, a nonmagnetic frame 4, a control device 5, a coil power supply 6, a pair of geomagnetic correction coils 7 and a pair of gradient magnetic correction coils 8 (geomagnetic correction coils), a pair of active shielding coils 9, a pump laser 10, a probe laser 11, an amplifier 12, a heater controller 13, and an electromagnetic shield 14.

The OPM module 1 has an optically excited magnetic sensor 1A, a heat insulating material 1B, and a read circuit 1C. The plurality of OPM modules 1 are arranged at predetermined intervals along the scalp, for example.

The optically-excited magnetic sensor 1A is a sensor for measuring a brain magnetic field with optical pumping, and has a sensitivity of about 10fT to 10pT, for example. The heat insulating material 1B prevents heat movement and heat transfer of the photo-excitation magnetic sensor 1A heated to 180 degrees by a heater (not shown). The reading circuit 1C is a circuit that obtains a detection result of the photoexcited magnetic sensor 1A. The optically-excited magnetic sensor 1A irradiates the cell in which the alkali metal vapor is sealed with pumping light to bring the alkali metal into an excited state. The alkali metal in an excited state is in a spin-polarized state, and when receiving magnetism, the inclination of the spin-polarized axis of the alkali metal atom changes according to the magnetism. The inclination of the spin polarization axis is detected by probe light irradiated separately from the pump light. The reading circuit 1C receives the probe light by the alkali metal vapor through the photodiode, and obtains a detection result. The read circuit 1C outputs the detection result to the amplifier 12.

The optically excited magnetic sensor 1A may be, for example, a Gradiometer (Gradiometer). The axial gradiometer has a measurement region and a reference region in a direction perpendicular to the scalp (measurement site) of a subject and coaxially. The measurement region refers to, for example, a portion closest to the scalp of the subject among portions where the axis type gradiometer measures the brain magnetic field. The reference region is, for example, a region that is a predetermined distance (for example, 3cm) from the measurement region in a direction away from the scalp of the subject, among the regions where the axis gradiometer measures the cerebral magnetic field. The axis type gradiometer outputs each result measured at the measurement region and the reference region to the amplifier 12. Here, when the common mode noise is included, the influence thereof is shown in each of the output result of the measurement region and the output result of the reference region. The common mode noise is removed by obtaining a difference between the output result of the measurement area and the output result of the reference area. By removing common mode noise, for example, in the case of measurement under a magnetic noise environment of 1pT, the photoexcitation magnetic sensor 1A can obtain a sensitivity of about 10fT/√ Hz.

The geomagnetic magnetic field correction magnetic sensor 2 is a sensor that measures a magnetic field related to geomagnetism at a position corresponding to the photo-excitation magnetic sensor 1A, and is configured of, for example, a Fluxgate sensor (Fluxgate sensor) having a sensitivity of about 1nT to 100 μ T. The position corresponding to the photoexcited magnetic sensor 1A is a position in the periphery (vicinity) of the region where the photoexcited magnetic sensor 1A is arranged. The geomagnetic-field-correction magnetic sensors 2 may be provided in one-to-one correspondence with the photo-excitation magnetic sensors 1A, or may be provided in one-to-many correspondence (1 geomagnetic-field-correction magnetic sensor 2 corresponds to a plurality of photo-excitation magnetic sensors 1A). The geomagnetic-field correction magnetic sensor 2 measures, for example, geomagnetic and a gradient magnetic field of the geomagnetic field (hereinafter, simply referred to as a "gradient magnetic field") as a magnetic field related to the geomagnetic field, and outputs the measured value to the control device 5. The measurement value of the magnetic sensor 2 for geomagnetic field correction may be represented by a vector having a direction and a magnitude. The geomagnetic field correction magnetic sensor 2 may continue to perform measurement and output at predetermined time intervals.

The active shielding magnetic sensor 3 is a sensor that measures a varying magnetic field at a position corresponding to the photo-excitation magnetic sensor 1A, and is constituted of, for example, a photo-excitation sensor having a sensitivity of about 100fT to 10nT in a frequency band of several hundred Hz or less and different from the photo-excitation magnetic sensor 1A. The position corresponding to the photoexcited magnetic sensor 1A is a position in the periphery (vicinity) of the region where the photoexcited magnetic sensor 1A is arranged. The active shielding magnetic sensors 3 may be provided in one-to-one correspondence with the photoexcited magnetic sensors 1A, or may be provided in one-to-many correspondence (1 active shielding magnetic sensor 3 corresponds to a plurality of photoexcited magnetic sensors 1A). The active shielding magnetic sensor 3 measures a magnetic field as a noise (alternating current) component of, for example, 200Hz or less, which is a changing magnetic field, and outputs the measured value to the control device 5. The measurement value of the magnetic sensor for active shielding 3 can be represented by a vector having a direction and a magnitude.

The nonmagnetic frame 4 is a frame covering the entire region of the scalp of a subject as a measurement target of a brain magnetic field, and is composed of a nonmagnetic material such as graphite having a relative permeability close to 1 and not disturbing the magnetic field distribution. The non-magnetic frame 4 may be, for example, a helmet-type frame that surrounds the entire area of the scalp of the subject and is mounted on the head of the subject. A plurality of photoexcited magnetic sensors 1A are fixed to the nonmagnetic frame 4 so as to be close to the scalp of the subject. In the non-magnetic frame 4, the geomagnetic field correction magnetic sensor 2 is fixed so as to be able to measure a magnetic field related to geomagnetism at each of the plurality of photoexcited magnetic sensors 1A, and the active shielding magnetic sensor 3 is fixed so as to be able to measure a varying magnetic field at each of the plurality of photoexcited magnetic sensors 1A. Since the variation of the magnetic field intensity in the varying magnetic field according to the position is smaller than that of the static magnetic field, the number of the active shielding magnetic sensors 3 may be fixed to the nonmagnetic frame 4 so as to be smaller than the number of the geomagnetic field correction magnetic sensors 2.

The control device 5 is a device that determines currents to the various coils based on the measurement values output from the magnetic sensor for geomagnetic field correction 2 and the magnetic sensor for active shielding 3, and outputs a control signal for outputting the currents to the coil power supply 6. The control device 5 determines currents to the geomagnetic correction coil 7 and the gradient magnetic field correction coil 8, which are geomagnetic correction coils, so as to generate magnetic fields that cancel magnetic fields related to geomagnetism, based on the measurement values of the plurality of geomagnetic correction magnetic sensors 2. The control device 5 determines the current to the active shield coil 9 so as to generate a magnetic field that cancels the changing magnetic field, based on the measurement values of the plurality of active shield magnetic sensors 3. The control device 5 outputs a control signal corresponding to the determined current to the coil power supply 6.

Specifically, the control device 5 determines the current to the geomagnetic correction coil 7 in such a manner that the average of the measurement values of the plurality of geomagnetic magnetic field correction magnetic sensors 2 is approximated to zero (as a result, in such a manner that a magnetic field of the same magnitude and opposite to the geomagnetism at the position of the photoexcited magnetic sensor 1A is generated). The control device 5 outputs a control signal (static magnetic field correction control signal) corresponding to the determined current of the geomagnetism correction coil 7 to the coil power supply 6.

The control device 5 determines the current to the gradient magnetic field correction coil 8 so that the deviation from the average of the measurement values of the plurality of geomagnetic field correction magnetic sensors 2 is minimized (so that a magnetic field having the same magnitude and opposite direction to the gradient magnetic field at the position of the optically excited magnetic sensor 1A is generated as a result). The control device 5 outputs a control signal (static magnetic field correction control signal) corresponding to the determined current of the gradient magnetic field correction coil 8 to the coil power supply 6.

Further, the control device 5 determines the current to the active shielding coil 9 so that the average value of the measurement values of the plurality of active shielding magnetic sensors 3 is approximately zero (as a result, a magnetic field having the same magnitude and the opposite direction to the changing magnetic field at the position of the photoexcitation magnetic sensor 1A is generated). The control device 5 outputs a control signal (control signal for varying magnetic field correction) corresponding to the determined current of the active shield coil 9 to the coil power supply 6.

Further, the control device 5 obtains information on the magnetism detected by the photoexcited magnetic sensor 1A by using the signal output from the amplifier 12. When the photoexcited magnetic sensor 1A is an axial gradiometer, the control device 5 may remove the common mode noise by obtaining a difference between the output result of the measurement region and the output result of the reference region. The control device 5 may control operations such as the irradiation timing and the irradiation time of the pump laser 10 and the probe laser 11.

The control device 5 is physically configured as a storage unit including a memory such as a RAM or a ROM, a processor (arithmetic circuit) such as a CPU, a communication interface, a hard disk, and the like. Examples of the control device 5 include a personal computer, a cloud server, a smart phone, and a tablet terminal. The control device 5 functions by the CPU of the computer system executing a program stored in the memory.

The coil power supply 6 outputs a predetermined current to each of the geomagnetism correction coil 7, the gradient magnetic field correction coil 8, and the active shield coil 9 in accordance with a control signal output from the control device 5. Specifically, the coil power supply 6 outputs a current to the geomagnetism correction coil 7 in accordance with a control signal related to the geomagnetism correction coil 7. The coil power supply 6 outputs a current to the gradient magnetic field correction coil 8 in accordance with a control signal related to the gradient magnetic field correction coil 8. The coil power supply 6 outputs a current to the active shield coil 9 in accordance with a control signal related to the active shield coil 9.

The geomagnetism correction coil 7 is a coil for correcting the magnetic field of geomagnetism among the magnetic fields associated with geomagnetism at the position of the optically excited magnetic sensor 1A. The geomagnetism correction coil 7 generates a magnetic field based on the current supplied from the coil power supply 6, and cancels the geomagnetism. The geomagnetic correction coil 7 has, for example, a pair of geomagnetic correction coils 7A and 7B. The pair of geomagnetic correction coils 7A and 7B is disposed so as to sandwich the optically excited magnetic sensor 1A (for example, on the left and right of the subject). The pair of geomagnetism correction coils 7A and 7B generate magnetic fields having the same magnitude and reverse direction to the geomagnetism at the position of the optically excited magnetic sensor 1A, based on the current supplied from the coil power supply 6. The direction of the magnetic field is, for example, from one geomagnetic correction coil 7A toward the other geomagnetic correction coil 7B. The geomagnetism at the position of the optically-excited magnetic sensor 1A is cancelled by the magnetic field of the same magnitude and in the opposite direction generated by the geomagnetism correction coil 7. In this way, the geomagnetism correction coil 7 corrects the geomagnetism at the position of the optically-excited magnetic sensor 1A.

The gradient magnetic field correction coil 8 is a coil for correcting a gradient magnetic field in a magnetic field associated with the geomagnetism at the position of the optically-excited magnetic sensor 1A. The gradient magnetic field correction coil 8 generates a magnetic field based on the current supplied from the coil power supply 6, and cancels the gradient magnetic field. The gradient magnetic field correction coil 8 has, for example, a pair of gradient magnetic field correction coils 8A and 8B. The pair of gradient magnetic field correction coils 8A and 8B are disposed so as to sandwich the optically excited magnetic sensor 1A (for example, on the left and right of the subject). The pair of gradient magnetic field correction coils 8A and 8B generate magnetic fields having the same magnitude and the same direction as the gradient magnetic field at the position of the optically excited magnetic sensor 1A, based on the current supplied from the coil power supply 6. The direction of the magnetic field is, for example, from one gradient magnetic field correction coil 8A towards the other gradient magnetic field correction coil 8B. The gradient magnetic field at the position of the optically-excited magnetic sensor 1A is canceled by the magnetic field of the same magnitude and in the opposite direction generated by the gradient magnetic field correction coil 8. In this way, the gradient magnetic field correction coil 8 corrects the gradient magnetic field at the position of the optically-excited magnetic sensor 1A.

The active shield coil 9 is a coil for correcting a changing magnetic field at a position where the optically excited magnetic sensor 1A is located. The active shield coil 9 generates a magnetic field in accordance with the current supplied from the coil power supply 6, and cancels the changing magnetic field. The active shield coil 9 has, for example, a pair of active shield coils 9A and 9B. The pair of active shield coils 9A and 9B are disposed so as to sandwich the photoexcited magnetic sensor 1A (for example, on the left and right of the subject). The pair of active shield coils 9A and 9B generate a magnetic field having a magnitude opposite to and the same as the changing magnetic field at the position of the photoexcited magnetic sensor 1A, in accordance with the current supplied from the coil power supply 6. The direction of the magnetic field is, for example, from one active shield coil 9A towards the other active shield coil 9B. The changing magnetic field at the location of the optically excited magnetic sensor 1A is cancelled by the magnetic field of the same magnitude and in the opposite direction generated by the active shielding coil 9. In this way, the active shield coil 9 corrects the varying magnetic field at the position where the optically excited magnetic sensor 1A is located.

The pump laser 10 is a laser device that generates pump light. The pump light emitted from the pump laser 10 is branched by the fiber and enters each of the plurality of optically excited magnetic sensors 1A.

The probe laser 11 is a laser device that generates probe light. The probe light emitted from the probe laser 11 is branched by the fiber and enters each of the plurality of photoexcited magnetic sensors 1A.

The amplifier 12 is a device or a circuit that amplifies a signal of an output result from the OPM module 1 (specifically, the reading circuit 1C) and outputs to the control device 5.

The heater controller 13 is a temperature control device connected to a heater (not shown) for heating the cell of the photoexcited magnetic sensor 1A and a thermocouple (not shown) for measuring the temperature of the cell. The heater controller 13 receives temperature information of the cell from the thermocouple, and adjusts the temperature of the cell by adjusting heating of the heater based on the temperature information.

The electromagnetic shield 14 is a shield member that shields electromagnetic noise at high frequencies (for example, 10kHz or more), and is configured by, for example, a mesh woven with a metal wire, a non-magnetic metal plate made of aluminum or the like, or the like. The electromagnetic shield 14 is disposed so as to surround the photoexcited magnetic sensor 1A, the geomagnetic magnetic field correction magnetic sensor 2, the active shield magnetic sensor 3, the nonmagnetic frame 4, the geomagnetic correction coil 7, the gradient magnetic field correction coil 8, and the active shield coil 9.

Next, a brain magnetic field measurement method using the brain magnetometer M1 according to the embodiment will be described with reference to fig. 2. Fig. 2 is a flowchart showing the operation of the brain magnetometer M1.

The geomagnetic field correction magnetic sensor 2 measures a magnetic field associated with the geomagnetic field as an electrostatic field (step S11). The geomagnetic-field correction magnetic sensor 2 measures geomagnetism and a gradient magnetic field at each position of the optically-excited magnetic sensor 1A, and outputs the measured values to the control device 5.

The control device 5 and the coil power supply 6 control the current to the geomagnetism correction coil 7 (step S12). The control device 5 determines the current to the geomagnetic correction coil 7 based on the measurement value of the geomagnetic correction magnetic sensor 2 so as to generate a magnetic field having a magnitude that is opposite to and approximately equal to the geomagnetism at the position of the optically excited magnetic sensor 1A. More specifically, the control device 5 determines the current to the geomagnetic correction coil 7, for example, so that the average of the measurement values of the plurality of geomagnetic magnetic field correction magnetic sensors 2 is approximately zero. The control device 5 outputs a control signal corresponding to the determined current to the coil power supply 6. The coil power supply 6 outputs a predetermined current to the geomagnetism correction coil 7 in accordance with a control signal output from the control device 5. The geomagnetism correction coil 7 generates a magnetic field based on the current supplied from the coil power supply 6. The geomagnetism at the position of the optically-excited magnetic sensor 1A is cancelled by the magnetic field of the same magnitude and in the opposite direction generated by the geomagnetism correction coil 7.

The control device 5 and the coil power supply 6 control the current to the gradient magnetic field correction coil 8 (step S13). The control device 5 determines the current to the gradient magnetic field coil 8 so as to generate a magnetic field having a magnitude approximately equal to the magnitude of the gradient magnetic field at the position of the optically excited magnetic sensor 1A, based on the measurement value of the geomagnetic field correction magnetic sensor 2. More specifically, the control device 5 determines the current to the gradient magnetic field correction coil 8 so that, for example, the deviation from the average of the measurement values of the plurality of magnetic sensors 2 for geomagnetic field correction becomes minimum. The control device 5 outputs a control signal corresponding to the determined current to the coil power supply 6. The coil power supply 6 outputs a predetermined current to the gradient magnetic field correction coil 8 in accordance with a control signal output from the control device 5. The gradient magnetic field correction coil 8 generates a magnetic field based on the current supplied from the coil power supply 6. The gradient magnetic field at the position of the optically-excited magnetic sensor 1A is canceled by the magnetic field of the same magnitude and in the opposite direction generated by the gradient magnetic field correction coil 8.

The control device 5 determines whether or not the corrected measurement value of the static magnetic field (magnetic field related to geomagnetism) is equal to or less than a reference value (step S14). The corrected measurement value of the static magnetic field is a value measured by the geomagnetic correction magnetic sensor 2 after the static magnetic field is corrected by the geomagnetic correction coil 7 and the gradient magnetic field correction coil 8. The reference value is the magnitude of the magnetic field in which the photoexcited magnetic sensor 1A normally operates, and may be, for example, 1 nT. If the measured value of the static magnetic field is not equal to or less than the reference value (no in step S14), the process returns to step S11. If the measured value of the static magnetic field is equal to or less than the reference value (yes at step S14), the process proceeds to step S15.

The active shielding magnetic sensor 3 measures the changing magnetic field (step S15). The active shielding magnetic sensor 3 measures a changing magnetic field at each position of the photo-excitation magnetic sensor 1A, and outputs the measured value to the control device 5.

The control device 5 and the coil power supply 6 control the current to the active shield coil 9 (step S16). The control device 5 determines the current to the active shielding coil 9 based on the measurement value of the active shielding magnetic sensor 3 so as to generate a magnetic field having a magnitude opposite to and approximately equal to the changing magnetic field at the position of the photoexcited magnetic sensor 1A. More specifically, the control device 5 determines the current to the active shield coil 9, for example, in such a manner that the average of the measurement values of the plurality of magnetic sensors for active shielding 3 is approximately zero. The control device 5 outputs a control signal corresponding to the determined current to the coil power supply 6. The coil power supply 6 outputs a predetermined current to the active shield coil 9 in accordance with a control signal output from the control device 5. The active shield coil 9 generates a magnetic field according to the current supplied from the coil power supply 6. The changing magnetic field at the location of the optically excited magnetic sensor 1A is cancelled by the magnetic field of the same magnitude and in the opposite direction generated by the active shielding coil 9.

The control device 5 determines whether or not the corrected measured value of the varying magnetic field is equal to or less than a reference value (step S17). The corrected measured value of the varying magnetic field is a value measured by the active shielding magnetic sensor 3 after the varying magnetic field is corrected by the active shielding coil 9. The reference value is a noise level at which the brain magnetic field can be measured, and may be set to 1pT, for example. If the measured value of the varying magnetic field is not equal to or less than the reference value (no in step S17), the process returns to step S15. If the measured value of the varying magnetic field is equal to or less than the reference value (yes in step S17), the process proceeds to step S18.

The optically-excited magnetic sensor 1A measures a cerebral magnetic field (step S18). Since the static magnetic field (magnetic field associated with geomagnetism) and the varying magnetic field at the position of the optically-excited magnetic sensor 1A are cancelled out so far as to become equal to or less than the predetermined reference value, the optically-excited magnetic sensor 1A can measure the brain magnetic field while avoiding the influence of the electrostatic field (magnetic field associated with geomagnetism) and the influence of the varying magnetic field.

Fig. 3 is a schematic diagram showing the structure of a brain magnetometer M2 according to another embodiment. The brain magnetic meter M2 is a device that measures a brain magnetic field with an optical pump while generating a magnetic field that cancels magnetic noise, as in the case of the brain magnetic meter M1. The brain magnetometer M2 includes: the OPM module 1, the magnetic sensor for geomagnetic field correction 2, the magnetic sensor for active shielding 3, the nonmagnetic frame 4, the control device 5, the coil power supply 6, the active shielding coil 9, the pump laser 10, the probe laser 11, the amplifier 12, the heater controller 13, the electromagnetic shield 14, and the coil system 15 (geomagnetic field correction coil). The brain magnetometer M2 has a coil system 15 disposed for each OPM module 1 (the optically excited magnetic sensor 1A) in place of the geomagnetic correction coil 7 and the gradient magnetic field correction coil 8 of the brain magnetometer M1. Here, the arrangement of the coil system 15 will be described with reference to fig. 4.

Fig. 4 is a diagram showing the arrangement of the coil system 15 according to the brain magnetometer M2. The coil system 15 is a coil system (for example, a 3-axis helmholtz coil or a planar-type coil system) that can apply magnetic fields to three orthogonal directions that are respectively orthogonal and circumferentially arranged. The coil system 15 has in particular coil systems 15X, 15Y and 15Z. In fig. 4, the coil systems 15X, 15Y, and 15Z are arranged in a dotted line manner for the OPM module 1, respectively. As described above, the coil systems 15X, 15Y, and 15Z are arranged orthogonally and circumferentially for each OPM module 1 (photo-excitation magnetic sensor 1A). The coil system 15X is a coil for correcting a component in the X-axis direction of the magnetic field associated with the geomagnetism as shown in fig. 4. Likewise, the coil systems 15Y and 15Z are coils for correcting components in the Y-axis direction and the Z-axis direction of the magnetic field associated with the geomagnetism, respectively.

Referring back to fig. 3, only the portion of the brain magnetometer M2 that is different from the brain magnetometer M1 will be described. The control device 5 determines currents to the coil systems 15X, 15Y, and 15Z for each of the plurality of photoexcited magnetic sensors 1A so that the measurement values of the plurality of geomagnetic-field-correcting magnetic sensors 2 are approximately zero. The control device 5 determines the current to the coil system 15X so as to generate a magnetic field having the same magnitude and opposite direction to the X-axis component of the magnetic field related to the geomagnetism at the position of the optically excited magnetic sensor 1A based on the measurement value of the geomagnetic field correction magnetic sensor 2. The control device 5 outputs a control signal (static magnetic field correction control signal) corresponding to the determined current to the coil power supply 6. Further, the control device 5 determines the current to the coil system 15Y so as to generate a magnetic field having the same magnitude and opposite direction to the Y-axis component of the magnetic field related to the geomagnetism at the position of the optically excited magnetic sensor 1A based on the measurement value of the geomagnetic field correction magnetic sensor 2. The control device 5 outputs a control signal (static magnetic field correction control signal) corresponding to the determined current to the coil power supply 6. Further, the control device 5 determines the current to the coil system 15Z based on the measurement value of the geomagnetic field correction magnetic sensor 2 so as to generate a magnetic field having a magnitude opposite to and the same as the Z-axis component of the magnetic field related to the geomagnetism at the position of the optically excited magnetic sensor 1A. The control device 5 outputs a control signal (control signal for varying magnetic field correction) corresponding to the determined current to the coil power supply 6.

The coil power supply 6 outputs a predetermined current to each of the coil systems 15X, 15Y, and 15Z in accordance with a control signal output from the control device 5. Specifically, the coil power supply 6 outputs a current to the coil system 15X according to a control signal related to the coil system 15X. The coil power supply 6 outputs a current to the coil system 15Y in accordance with a control signal related to the coil system 15Y. The coil power supply 6 outputs a current to the coil system 15Z in accordance with a control signal related to the coil system 15Z.

The coil system 15 generates a magnetic field based on the current supplied from the coil power supply 6, and cancels the magnetic field associated with the geomagnetism. Specifically, the coil system 15X generates a magnetic field having a magnitude opposite to and the same as the component in the X-axis direction of the magnetic field related to the geomagnetism at the position of the optically excited magnetic sensor 1A, based on the current supplied from the coil power supply 6. The component in the X-axis direction of the magnetic field associated with the geomagnetism at the position of the optically excited magnetic sensor 1A is cancelled by the magnetic field of the same magnitude and in the opposite direction generated by the coil system 15X. Similarly, the coil systems 15Y and 15Z generate magnetic fields having the same magnitude and opposite directions to the components in the Y-axis direction and the Z-axis direction of the magnetic field related to the geomagnetism at the positions of the respective photo-excitation magnetic sensors 1A, and cancel the magnetic field related to the geomagnetism. In this way, the coil system 15 corrects the magnetic field associated with the geomagnetism at the position of the optically excited magnetic sensor 1A. Furthermore, the magnetically relevant information obtained by the control device 5 does not contain the magnetic field generated by the coil system 15.

The electromagnetic shield 14 is disposed so as to surround the photoexcited magnetic sensor 1A, the geomagnetic field correction magnetic sensor 2, the active shield magnetic sensor 3, the nonmagnetic frame 4, the active shield coil 9, and the coil system 15.

Next, a brain measurement method using the brain measurement device M2 according to the embodiment will be described with reference to fig. 5. Fig. 5 is a flowchart showing the operation of the magnetoencephaloscope M2.

The geomagnetic-field correction magnetic sensor 2 measures a magnetic field associated with the magnetic field as a static magnetic field (step S21). The geomagnetic magnetic field correction magnetic sensor 2 measures a magnetic field related to geomagnetism including geomagnetism and a gradient magnetic field at each position of the optically excited magnetic sensor 1A, and outputs the measured value to the control device 5.

The control device 5 and the coil power supply 6 control the current to the coil system 15 for each of the optically excited magnetic sensors 1A (step S22). The control device 5 determines the current to the static magnetic field coil system 15 based on the measurement value of the geomagnetic field correction magnetic sensor 2 so as to generate magnetic fields having the same magnitude and opposite directions to the components in the three directions (x-axis, y-axis, and z-axis) of the magnetic field associated with the geomagnetism at the position of the optically excited magnetic sensor 1A. More specifically, the control device 5 determines to apply the current to the coil systems 15X, 15Y, and 15Z for each of the photo-excitation magnetic sensors 1A, for example, in such a manner that the measurement values of the plurality of magnetic sensors 2 for geomagnetic field correction are approximated to zero. The control device 5 outputs a control signal corresponding to the determined current associated with each of the coil systems 15X, 15Y, and 15Z to the coil power supply 6. The coil power supply 6 outputs a predetermined current to each of the coil systems 15X, 15Y, and 15Z in accordance with a control signal output from the control device 5. The coil systems 15X, 15Y, and 15Z generate magnetic fields in accordance with currents supplied from the coil power supply 6, respectively. Components in three directions of the magnetic field relating to the geomagnetism at the position of the photo-excitation magnetic sensor 1A are cancelled by the magnetic fields of the same magnitude and the opposite directions generated by each of the coil systems 15X, 15Y, and 15Z.

The test operation of the optically excited magnetic sensor 1A is performed (step S23). The photo-excitation magnetic sensor 1A obtains a measurement value of the residual magnetic field by a test operation, and outputs the measurement value to the control device 5. The measured value of the magnetic field is a value measured by optically exciting the magnetic sensor 1A after the static magnetic field is corrected by the coil system 15.

The control device 5 determines whether or not the measured value of the magnetic field is equal to or less than a reference value (step S24). The reference value is a value at which the photoexcited magnetic sensor 1A normally operates, and may be, for example, 0.3 nT. If the measured value of the magnetic field is not equal to or less than the reference value (no in step S24), the process returns to step S21. If the measured value of the magnetic field is equal to or less than the reference value (yes in step S24), the process proceeds to step S25.

Since the subsequent steps S25 to S28 are the same processes as steps S15 to S18, the description is omitted. The active shielding magnetic sensor 3 measures the changing magnetic field (step S25).

The control device 5 controls the current to the active shield coil 9 (step S26).

The control device 5 determines whether or not the corrected measured value of the varying magnetic field is equal to or less than a reference value (step S27). If the measured value of the varying magnetic field is not equal to or less than the reference value (no in step S27), the process returns to step S25. If the measured value of the varying magnetic field is equal to or less than the reference value (yes in step S27), the process proceeds to step S28.

The optically-excited magnetic sensor 1A measures a cerebral magnetic field (step S28).

[ Effect ]

Next, the operational effects of the brain magnetometer according to the above embodiment will be described.

The brain magnetometers M1 and M2 according to the present embodiment include: a plurality of optically excited magnetic magnetometers 1A measuring the brain magnetic field; a plurality of geomagnetic-magnetic-field correction magnetic sensors 2 that measure magnetic fields relating to geomagnetism at positions of the plurality of photo-excitation magnetic sensors 1A, respectively; a plurality of active shielding magnetic sensors 3 for measuring a changing magnetic field at each position of the plurality of photoexcited magnetic sensors 1A; a geomagnetic field correction coil for correcting a magnetic field associated with geomagnetism; an active shield coil 9 for correcting the varying magnetic field; a control device 5 that determines a current to the geomagnetic field correction coil based on the measurement values of the plurality of geomagnetic field correction magnetic sensors 2 so as to generate a magnetic field that cancels a magnetic field associated with geomagnetism, and determines a current to the active shield coil 9 based on the measurement values of the plurality of active shield magnetic sensors 3 so as to generate a magnetic field that cancels a varying magnetic field, and outputs a control signal corresponding to the determined current; and a coil power supply 6 that outputs a current to the geomagnetic field correction coil and the active shield coil 9 in accordance with a control signal output from the control device 5.

The magnetoencephalographs M1 and M2 according to the present embodiment measure a magnetic field and a varying magnetic field related to geomagnetism at positions of the plurality of photoexcited magnetic sensors 1A for measuring a cerebral magnetic field. In the present magnetoencephalography device, the current to the geomagnetic field correction coil is determined based on the plurality of measured values of the magnetic field related to the geomagnetism so as to generate a magnetic field that cancels the magnetic field related to the geomagnetism, and the current to the active shield coil 9 is determined based on the plurality of measured values of the varying magnetic field so as to generate a magnetic field that cancels the varying magnetic field, and a control signal corresponding to the determined current is output. When a current corresponding to the control signal is output to the geomagnetic field correction coil and the active shield coil 9, a magnetic field is generated in each coil, and at the position of the plurality of photoexcited magnetic sensors 1A, the magnetic field generated in the geomagnetic field correction coil cancels the magnetic field associated with the geomagnetism, and the magnetic field generated in the active shield coil 9 cancels the varying magnetic field. As described above, by canceling the magnetic field related to the geomagnetism and the varying magnetic field at the positions of the plurality of photo-excitation magnetic sensors 1A, the plurality of photo-excitation magnetic sensors 1A can measure the brain magnetic field while avoiding the influence of the magnetic field related to the geomagnetism and the influence of the varying magnetic field. According to the magnetoencephalographs M1 and M2, the brain magnetic field can be measured with high accuracy without using a magnetic shield room.

The geomagnetic field correction coil includes a geomagnetic correction coil 7 for correcting a magnetic field of geomagnetism and a gradient magnetic field correction coil 8 for correcting a gradient magnetic field of geomagnetism, and the control device 5 may determine the current to the geomagnetic correction coil 7 so that an average value of the measurement values of the plurality of geomagnetic field correction magnetic sensors 2 is approximately zero, and may determine the current to the gradient magnetic field correction coil 8 so that a deviation from the average value of the measurement values of the plurality of geomagnetic field correction magnetic sensors 2 is minimized. According to such a configuration, the same magnetic field correction (0-time correction) is performed by controlling the current of the geomagnetism correction coil 7, and the correction (1-time correction) is performed by controlling the current of the gradient magnetic field correction coil 8 in consideration of the different gradient magnetic fields at the positions of the respective photoexcited magnetic sensors 1A. With such a method, by gradually canceling the geomagnetic field and the gradient magnetic field of the geomagnetism, the magnetic field relating to the geomagnetism can be corrected with high accuracy.

The geomagnetism correction coil 7 and the gradient magnetic field correction coil 8 are a pair of coils disposed so as to sandwich the plurality of photoexcited magnetic sensors 1A, respectively. According to such a configuration, the magnetic field relating to the geomagnetism at the positions of the plurality of photoexcited magnetic sensors 1A sandwiched between the pair of geomagnetic field correction coils 7 and the pair of gradient magnetic field correction coils 8 is effectively corrected. Thus, the magnetic field associated with the geomagnetism can be appropriately corrected with a simple configuration.

The geomagnetic field correction coil includes, for each of the plurality of photo-excitation magnetic sensors 1A, a coil system 15 arranged orthogonally and circumferentially, and the control device 5 determines the current to the coil system 15 for each of the plurality of photo-excitation magnetic sensors 1A so that the measurement value of the plurality of magnetic field correction magnetic sensors 2 is approximately zero. With such a configuration, the coil system 15 is arranged for each of the plurality of photo-excitation magnetic sensors 1A in accordance with each of the components of the static magnetic field in three directions (x-axis, y-axis, and z-axis). Then, by controlling the currents corresponding to the respective coil systems 15, magnetic fields that cancel the components in the x-axis direction, the y-axis direction, and the z-axis direction of the magnetic field associated with the geomagnetism are generated for each of the plurality of photo-excited magnetic sensors 1A, and the magnetic field associated with the geomagnetism is corrected from three directions. Thereby, it is possible to finely control the current for each of the plurality of photo-excitation magnetic sensors 1A, and improve the correction accuracy of the magnetic field relating to the geomagnetism. In addition, since only the magnetic field relating to the geomagnetism in the region relating to the operation of the plurality of photoexcited magnetic sensors 1A is corrected, an increase in power consumption relating to unnecessary correction can be suppressed.

More specifically, the control device 5 may determine the current to the active shield coil 9 so that the average of the measurement values of the plurality of magnetic sensors for active shield 3 is approximately zero. According to such a configuration, by controlling the current to the active shield coil 9, the varying magnetic field at the position of the plurality of photo-excitation magnetic sensors 1A is effectively corrected. Thus, the varying magnetic field can be appropriately corrected with a simple configuration.

The plurality of photoexcitation magnetic sensors 1A may be axial gradiometers having a measurement region and a reference region in a direction perpendicular to the scalp and coaxially. According to such a configuration, since the influence of the common mode noise is shown in each of the output result of the measurement region and the output result of the reference region, the common mode noise can be removed by obtaining a difference between the output results of the both. This improves the measurement accuracy of the brain magnetic field.

The plurality of photoexcited magnetic sensors 1A, the plurality of magnetic sensors 2 for geomagnetic field correction, and the plurality of active shielding magnetic sensors 3 may be fixed to a helmet-type non-magnetic frame 4 attached to the head of the subject. According to such a configuration, since the non-magnetic frame 4 attached to the head and the sensors fixed to the non-magnetic frame 4 move in accordance with the movement of the head of the subject, even when the head of the subject moves, it is possible to appropriately perform the correction of the magnetic field and the varying magnetic field related to the geomagnetism and the measurement of the brain magnetic field at the positions of the plurality of photo-excitation magnetic sensors 1A.

An electromagnetic shield 14 for shielding high-frequency electromagnetic noise may be further provided. With this configuration, it is possible to prevent high-frequency electromagnetic noise that cannot be measured from entering the plurality of photoexcited magnetic sensors 1A in the magnetoencephalograph. This allows the plurality of photoexcited magnetic sensors 1A to operate stably.

The method for measuring a brain magnetic field according to the present embodiment includes: a step of measuring a magnetic field related to geomagnetism at a position of each of the plurality of photo-excitation magnetic sensors 1A; a step of determining a current to the geomagnetic field correction coil based on a plurality of measurement values of the geomagnetic-related magnetic field so as to generate a magnetic field that cancels the geomagnetic-related magnetic field, and outputting a control signal for geomagnetic field correction corresponding to the determined current; outputting a current to the geomagnetic field correction coil according to the geomagnetic field correction control signal; a step of measuring a changing magnetic field at each position of the plurality of photoexcitation magnetic sensors 1A; a step of determining a current to the active shield coil 9 based on the plurality of measured values of the varying magnetic field so as to generate a magnetic field that cancels the varying magnetic field, and outputting a control signal for varying magnetic field correction corresponding to the determined current; outputting a current to the active shield coil 9 based on the control signal for correcting the varying magnetic field; and a step of measuring the brain magnetic field by the plurality of photo-excitation magnetic sensors 1A.

With the brain magnetic field measurement method according to the present embodiment, it is possible to measure the magnetic field related to the geomagnetism and the varying magnetic field at the positions of the plurality of photoexcited magnetic sensors 1A for measuring the brain magnetic field. Then, according to the present brain magnetic field measurement method, the current to the geomagnetic field correction coil is determined so as to generate a magnetic field that cancels the geomagnetic-related magnetic field, based on the plurality of measurement values of the geomagnetic-related magnetic field, and a control signal corresponding to the determined current is output. When a current corresponding to the control signal is output to the geomagnetic field correction coil, a magnetic field is generated in the geomagnetic field correction coil, and the magnetic field associated with the geomagnetism is cancelled by the magnetic field generated in the geomagnetic field correction coil at the position where the plurality of photoexcited magnetic sensors 1A are located. In addition, based on a plurality of measured values of the varying magnetic field, a current to the active shielding coil 9 is determined in such a manner that a magnetic field that cancels the varying magnetic field is generated, and a control signal corresponding to the determined current is output. When a current corresponding to the control signal is output to the active shield coil 9, a magnetic field is generated in the active shield coil 9, and the magnetic field generated in the active shield coil 9 at the positions of the plurality of photoexcited magnetic sensors 1A cancels the varying magnetic field. As described above, by canceling the magnetic field related to the geomagnetism and the varying magnetic field at the positions of the plurality of photo-excitation magnetic sensors 1A, the plurality of photo-excitation magnetic sensors 1A can measure the brain magnetic field while avoiding the influence of the magnetic field related to the geomagnetism and the influence of the varying magnetic field. According to such a brain magnetic field measurement method, a brain magnetic field can be measured with high accuracy without using a magnetic shield room.

Determining the current to the geomagnetic field correction coil so as to generate a magnetic field that cancels the magnetic field associated with the geomagnetism may include: the current to the geomagnetic correction coil 7 constituting the geomagnetic field correction coil is determined so that an average value of a plurality of measurement values of the magnetic field related to geomagnetism is approximately zero, and the current to the gradient magnetic field correction coil 8 constituting the geomagnetic field correction coil is determined so that a deviation from the average value of the measurement values of the magnetic field related to geomagnetism is minimized. With this method, the same magnetic field correction (0-time correction) is performed by controlling the current of the geomagnetism correction coil 7, and the correction (1-time correction) is performed by controlling the current of the gradient magnetic field correction coil 8, taking into account the different gradient magnetic fields at the positions of the respective photoexcited magnetic sensors 1A. With such a method, by gradually canceling the geomagnetic field and the gradient magnetic field of the geomagnetism, the magnetic field relating to the geomagnetism can be corrected with high accuracy.

Determining the current to the geomagnetic field correction coil so as to generate a magnetic field that cancels the magnetic field associated with the geomagnetism may include: the current for each of the coil systems 15 arranged orthogonally and circumferentially is determined for each of the plurality of photo-excited magnetic sensors 1A in such a manner that a plurality of measurement values of the magnetic field associated with the geomagnetism are approximated to zero. According to such a method, the coil system 15 is arranged for each of the plurality of photo-excitation magnetic sensors 1A in accordance with each of the components of the static magnetic field in three directions (x-axis, y-axis, and z-axis). Then, by controlling the currents corresponding to the respective coil systems 15, magnetic fields that cancel the components in the x-axis direction, the y-axis direction, and the z-axis direction of the magnetic field associated with the geomagnetism are generated for each of the plurality of photo-excited magnetic sensors 1A, and the magnetic field associated with the geomagnetism is corrected from three directions. Thereby, it is possible to finely control the current for each of the plurality of photo-excitation magnetic sensors 1A, and improve the correction accuracy of the magnetic field relating to the geomagnetism. In addition, since only the magnetic field relating to the geomagnetism in the region relating to the operation of the plurality of photoexcited magnetic sensors 1A is corrected, an increase in power consumption relating to unnecessary correction can be suppressed.

[ modified examples ]

The above description is based on the embodiments of the present disclosure in detail. However, the present disclosure is not limited to the above embodiments. Various modifications may be made within a scope not departing from the gist of the present disclosure.

Although the active shield coil 9 is described as a coil having a pair of active shield coils 9A and 9B, each OPM module 1 (the optically-excited magnetic sensor 1A) may be configured as a coil system in the form of a coil system 15. In this case, the control device 5 determines the current to the active shield coil 9 in such a manner as to generate a magnetic field of the same magnitude and opposite to the components of the three directions (x-axis, y-axis, and z-axis) of the varying magnetic field at the position of the photoexcitation magnetic sensor 1A. The control device 5 outputs a control signal to the coil power supply 6, which control signal corresponds to a determined current associated with each of the active shielding coils 9 configured as a coil system.