JP2023034039A - Magnetoencephalograph system and magnetoencephalography - Google Patents

Abstract

To provide a magnetoencephalograph system and a magnetoencephalography, capable of making high-accuracy measurement without using a magnetically shielded room.SOLUTION: A magnetoencephalograph system M1 includes a plurality of optical excitation magnetic sensors 1A that measures a brain magnetic field, a plurality of correcting magnetic sensors 2 that measures geomagnetism and a variable magnetic field at each position of the plurality of optical excitation magnetic sensors 1A, a correcting coil for correcting the geomagnetism and the variable magnetic field, a control device 4 that determines current for the correcting coil so as to generate a magnetic field that cancels the geomagnetism and the variable magnetic field on the basis of a measured value of the geomagnetism and a measured value of the variable magnetic field by the plurality of correcting magnetic sensors 2 to output a control signal according to the determined current, and a coil power supply 5 that outputs current to the correcting coil according to the control signal output by the control device 4.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a magnetoencephalograph and a brain magnetic field measurement method.

Conventionally, a superconducting quantum interference device (SQUID) has been used as a magnetoencephalograph to measure minute brain magnetic fields. In recent years, magnetoencephalographs using optically excited magnetic sensors instead of SQUIDs have been studied. Optically excited magnetic sensors measure minute magnetic fields by using the spin polarization of alkali metal atoms excited by optical pumping. For example, Patent Document 1 discloses a magnetoencephalograph using an optically pumped magnetometer.

Japanese Patent No. 5823195

Magnetoencephalography measurements are performed in a magnetically shielded room to shield against magnetic noise, which is stronger than the brain's magnetic field. However, the installation of the magnetic shield room is restricted from the viewpoint of weight, price, and the like.

The present disclosure has been made in view of the above circumstances, and aims to provide a magnetoencephalograph and a brain magnetic field measurement method capable of highly accurate measurement without using a magnetically shielded room.

A magnetoencephalograph according to an aspect of the present disclosure includes a plurality of optically-excited magnetic sensors that measure brain magnetic fields, a plurality of correction magnetic sensors that measure geomagnetism and varying magnetic fields at respective positions of the plurality of optically-excited magnetic sensors, geomagnetism and Based on the correction coil for correcting the fluctuating magnetic field and the measured value of the geomagnetism and the measured value of the fluctuating magnetic field by a plurality of correction magnetic sensors, the current for the correction coil is determined so as to generate a magnetic field that cancels the geomagnetism and the fluctuating magnetic field. a control device that outputs a control signal corresponding to the determined current; and a coil power supply that outputs a current to the correction coil according to the control signal output by the control device.

A magnetoencephalograph according to an aspect of the present disclosure measures geomagnetism and varying magnetic fields at respective positions of a plurality of optically-excited magnetic sensors that measure brain magnetic fields. Then, based on the measured values of the geomagnetism and the fluctuating magnetic field, a current for the correction coil is determined so as to generate a magnetic field that cancels the geomagnetism and the fluctuating 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 correction coil, a magnetic field is generated in the correction coil. As a result, the geomagnetism and the fluctuating magnetic field are canceled by the magnetic fields generated in the correction coils at the positions of the plurality of optically excited magnetic sensors. In this way, by canceling out the geomagnetism and the varying magnetic field at the positions of the plurality of optically excited magnetic sensors, the plurality of optically excited magnetic sensors can measure brain magnetic fields while avoiding the effects of the geomagnetism and the varying magnetic fields. . According to such a magnetoencephalograph, brain magnetic fields can be measured with high accuracy without using a magnetically shielded room.

The correction coils may include a geomagnetism correction coil for correcting geomagnetism and a fluctuating magnetic field correction coil for correcting a fluctuating magnetic field. Based on the measured value of the geomagnetism, the control device determines a current for the geomagnetism correction coil so as to generate a magnetic field that cancels the geomagnetism, and based on the measured value of the varying magnetic field, varies so as to generate a magnetic field that offsets the varying magnetic field. A current to the magnetic field correction coil may be determined. Even in this case, brain magnetic fields can be measured with high accuracy without using a magnetically shielded room. In addition, it is possible to optimize the number of turns of the geomagnetism correction coil for correcting the geomagnetism having an intensity of the order of 10 μT and the number of turns of the fluctuating magnetic field correction coil for correcting the fluctuating magnetic field having an intensity of the order of 10 nT. Therefore, geomagnetism and fluctuating magnetic fields can be accurately corrected.

The correction coil may comprise a geomagnetic gradient correction coil for correcting the geomagnetic gradient. The controller may determine a current to the geomagnetic gradient correction coil to generate a magnetic field that counteracts the geomagnetic gradient based on the geomagnetism measurements. In this case, uniform geomagnetism correction (zero-order correction) is performed by controlling the current to the geomagnetic correction coil, and furthermore, by controlling the current to the geomagnetic gradient correction coil, the gradient of the geomagnetism considering the difference in the position of each optically excited magnetic sensor. is corrected (primary correction). In this manner, the geomagnetism and the gradient of the geomagnetism are canceled step by step, so that the geomagnetism can be accurately corrected.

The correction coil may comprise a varying magnetic field gradient correction coil for correcting the gradient of the varying magnetic field. The controller may determine a current to the varying magnetic field gradient correction coil to generate a magnetic field that cancels the gradient of the varying magnetic field based on the measured value of the varying magnetic field. In this case, uniform fluctuation magnetic field correction (zero-order correction) is performed by controlling the current to the fluctuation magnetic field correction coil, and furthermore, the difference in the position of each photoexcited magnetic sensor is taken into account by controlling the current to the fluctuation magnetic field gradient correction coil. Correction of the gradient of the varying magnetic field (first-order correction) is performed. In this manner, the varying magnetic field and the gradient of the varying magnetic field are canceled step by step, so that the varying magnetic field can be corrected with high accuracy.

The correction coil may be composed of a pair of coils arranged with a plurality of optically-excited magnetic sensors interposed therebetween. In this case, the geomagnetism and the fluctuating magnetic field at the positions of the plurality of optically excited magnetic sensors sandwiched between the pair of correction coils are effectively corrected. As a result, it is possible to appropriately correct the geomagnetism and the fluctuating magnetic field with a simple configuration.

The correction coils may be a system of coils arranged in three orthogonal orientations, one for each of the plurality of optically excited magnetic sensors. The controller may determine currents to the coil system based on measurements of the earth's magnetic field to produce magnetic fields that counteract the earth's magnetic field and gradients of the earth's magnetic field. In this case, a coil system is arranged corresponding to each of the components of the three directions (x-axis, y-axis, and z-axis) of the geomagnetism for each optically excited magnetic sensor. Then, by controlling the current to each of the coil systems, a magnetic field is generated that cancels each of the x-axis component, y-axis component, and z-axis component of the geomagnetism for each optically excited magnetic sensor, Geomagnetism and geomagnetic gradients are corrected from three directions. As a result, the current can be finely controlled for each photoexcited magnetic sensor, and the correction accuracy of geomagnetism is improved. Moreover, since only the geomagnetism in the region related to the operation of the plurality of optically excited magnetic sensors is corrected, it is possible to suppress an increase in power consumption associated with unnecessary correction.

The correction magnetic sensor may be a fluxgate sensor that outputs a measured value of geomagnetism as a DC component and outputs a measured value of a varying magnetic field as an AC component. The dynamic range of a fluxgate sensor may include geomagnetic fields with strengths on the order of 10 μT and fluctuating magnetic fields at specific frequencies (eg, commercial frequencies) with strengths on the order of 10 nT. The fluctuating magnetic field of a specific frequency is a particularly large magnetic field among fluctuating magnetic fields. Such a fluxgate sensor can suitably measure geomagnetism and a varying magnetic field of a specific frequency.

The plurality of optically-excited magnetic sensors may be axial gradiometers having a measurement region and a reference region coaxially and perpendicularly to the object to be measured. In this case, since the influence of common mode noise is shown in the output result of the measurement area and the output result of the reference area, the common mode noise can be removed by obtaining the difference between the two output results. This improves the measurement accuracy of the brain magnetic field.

The plurality of optically-excited magnetic sensors and the plurality of correction magnetic sensors may be fixed to a helmet-shaped non-magnetic frame that is worn on the subject's head and has a relative magnetic permeability close to 1 and does not disturb the magnetic field distribution. In this case, the non-magnetic frame attached to the head and the sensors fixed to the non-magnetic frame move according to the movement of the subject's head. Correction of geomagnetism and fluctuating magnetic field at the position of the magnetic sensor and measurement of brain magnetic field can be performed appropriately.

The magnetoencephalograph may further comprise an electromagnetic shield for shielding high frequency electromagnetic noise. In this case, it is possible to prevent high-frequency electromagnetic noise, which cannot be measured by magnetoencephalography, from entering the plurality of optically-excited magnetic sensors. This allows the plurality of optically excited magnetic sensors to operate stably.

A brain magnetic field measurement method according to an aspect of the present disclosure includes steps of measuring geomagnetism and a varying magnetic field at respective positions of a plurality of optically-excited magnetic sensors; determining a current to the correction coil to generate a magnetic field that cancels the magnetic field; outputting a control signal in response to the determined current; outputting a current to the correction coil in response to the control signal; and measuring brain magnetic fields with a magnetic sensor.

In a brain magnetic field measurement method according to an aspect of the present disclosure, geomagnetism and fluctuating magnetic fields are measured at respective positions of a plurality of optically-excited magnetic sensors that measure brain magnetic fields. Then, based on the measured values of the geomagnetism and the fluctuating magnetic field, a current for the correction coil is determined so as to generate a magnetic field that cancels the geomagnetism and the fluctuating magnetic field, and a control signal corresponding to the determined current is output. Then, when a current corresponding to the control signal is output to the correction coil, a magnetic field is generated in the correction coil. As a result, the geomagnetism and the fluctuating magnetic field are canceled by the magnetic fields generated in the correction coils at the positions of the plurality of optically excited magnetic sensors. In this way, by canceling out the geomagnetism and the varying magnetic field at the positions of the plurality of optically excited magnetic sensors, the plurality of optically excited magnetic sensors can measure brain magnetic fields while avoiding the effects of the geomagnetism and the varying magnetic fields. . According to such a brain magnetic field measurement method, a brain magnetic field can be measured with high accuracy without using a magnetically shielded room.

In the brain magnetic field measurement method, outputting the control signal determines a current for the geomagnetic correction coil so as to generate a magnetic field that cancels the geomagnetism based on the measured value of the geomagnetism; It may include determining a current for the fluctuating magnetic field correction coil so as to generate a magnetic field that cancels the magnetic field, and outputting a control signal for geomagnetism correction and a control signal for correcting the fluctuating magnetic field according to the determined current. Even in this case, brain magnetic fields can be measured with high accuracy without using a magnetically shielded room. In addition, it is possible to optimize the number of turns of the geomagnetism correction coil for correcting the geomagnetism having an intensity of the order of 10 μT and the number of turns of the fluctuating magnetic field correction coil for correcting the fluctuating magnetic field having an intensity of the order of 10 nT. Therefore, geomagnetism and fluctuating magnetic fields can be accurately corrected.

The brain magnetic field measurement method determines the current for the geomagnetic gradient correction coil so as to generate a magnetic field that cancels the gradient of the geomagnetism based on the measured value of the geomagnetism, and outputs a control signal for geomagnetic gradient correction according to the determined current. may further include the step of: In this case, uniform geomagnetism correction (zero-order correction) is performed by controlling the current to the geomagnetic correction coil, and furthermore, by controlling the current to the geomagnetic gradient correction coil, the gradient of the geomagnetism considering the difference in the position of each optically excited magnetic sensor. is corrected (primary correction). In this manner, the geomagnetism and the gradient of the geomagnetism are canceled step by step, so that the geomagnetism can be accurately corrected.

In the brain magnetic field measurement method, based on the measured value of the fluctuating magnetic field, a current for the fluctuating magnetic field gradient correction coil is determined so as to generate a magnetic field that cancels the gradient of the fluctuating magnetic field. A step of outputting a control signal may be further included. In this case, uniform fluctuation magnetic field correction (zero-order correction) is performed by controlling the current to the fluctuation magnetic field correction coil, and furthermore, the difference in the position of each photoexcited magnetic sensor is taken into account by controlling the current to the fluctuation magnetic field gradient correction coil. Correction of the gradient of the varying magnetic field (first-order correction) is performed. In this manner, the varying magnetic field and the gradient of the varying magnetic field are canceled step by step, so that the varying magnetic field can be corrected with high accuracy.

According to the present invention, it is possible to provide a magnetoencephalograph and a brain magnetic field measuring method capable of highly accurate measurement without using a magnetically shielded room.

1 is a schematic diagram showing the configuration of a magnetoencephalograph according to an embodiment; FIG. FIG. 2 is a schematic diagram showing a configuration for the connection between the fluxgate sensor and the controller; 4 is a flow chart showing the operation of the magnetoencephalograph according to the embodiment; FIG. 3 is a schematic diagram showing the configuration of a magnetoencephalograph according to another embodiment; Fig. 2 shows the arrangement of the coil system; 9 is a flow chart showing the operation of a magnetoencephalograph according to another embodiment; FIG. 11 is a schematic diagram showing the configuration of a magnetoencephalograph according to a modification; FIG. 11 is a schematic diagram showing the configuration of a magnetoencephalograph according to a modification;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments 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 overlapping descriptions are omitted.

FIG. 1 is a schematic diagram showing the configuration of a magnetoencephalograph M1 according to an embodiment. The magnetoencephalograph M1 is a device that measures a brain magnetic field using optical pumping while generating a magnetic field that cancels out magnetic noise. The magnetoencephalograph M1 includes a plurality of OPM (optically pumped atomic magnetometer) modules 1, a plurality of correction magnetic sensors 2, a nonmagnetic frame 3, a control device 4, a coil power source 5, and a pair of geomagnetism correction coils 6. , a pair of geomagnetic gradient correction coils 7, a pair of fluctuating magnetic field gradient correction coils 8, a pair of fluctuating magnetic field gradient correction coils 9, a pump laser 10, a probe laser 11, an amplifier 12, a heater controller 13, and an electromagnetic shield. 14 and.

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

The optically excited magnetic sensor 1A is a sensor that measures a brain magnetic field using optical pumping, and has a sensitivity of about 10 fT to 10 pT, for example. The heat insulating material 1B prevents heat transfer and heat transfer from the photoexcited magnetic sensor 1A heated to 180 degrees by a heater (not shown). 1 C of read-out circuits are circuits which acquire the detection result of 1 A of optical excitation magnetic sensors. The optically-excited magnetic sensor 1A excites the alkali metal by irradiating pump light onto a cell containing the alkali metal vapor. Alkali metals in an excited state are in a spin-polarized state, and when subjected to magnetism, the inclination of the spin-polarization axis of the alkali metal atoms changes according to the magnetism. The tilt of this spin polarization axis is detected by the probe light irradiated separately from the pump light. The readout circuit 1C receives the probe light that has passed through the alkali metal vapor with a photodiode and acquires the detection result. The readout circuit 1C outputs the detection result to the amplifier 12. FIG.

The optically excited magnetic sensor 1A may be, for example, an axial gradiometer. An axial gradiometer has a measurement region and a reference region that are coaxial and perpendicular to the object being measured. The measurement region is, for example, the location closest to the subject's scalp among the locations where the axial gradiometer measures brain magnetic fields. The reference area is, for example, a point at a predetermined distance (eg, 3 cm) from the measurement area in the direction away from the subject's scalp, among the points where the axial gradiometer measures brain magnetic fields. The axial gradiometer outputs to the amplifier 12 the results of measurements in the measurement area and the reference area. Here, when common mode noise is included, its influence is shown in the output result of the measurement area and the output result of the reference area. Common mode noise is removed by taking the difference between the measurement region output and the reference region output. By removing the common mode noise, the optical excitation magnetic sensor 1A can obtain a sensitivity of about 10 fT/√Hz when measured in a magnetic noise environment of 1 pT, for example.

The correction magnetic sensor 2 measures the geomagnetism and the fluctuating magnetic field at a position corresponding to the optically excited magnetic sensor 1A. The correction magnetic sensor 2 is, for example, a fluxgate sensor having a sensitivity of several pT to 100 μT. The dynamic range of a fluxgate sensor may include geomagnetic fields with strengths on the order of 10 μT, and varying magnetic fields at specific frequencies (eg, commercial frequencies of 50 Hz or 60 Hz) with strengths on the order of 10 nT. The fluctuating magnetic field of a specific frequency is a particularly large magnetic field among fluctuating magnetic fields. The position corresponding to the optically-excited magnetic sensor 1A is a position around (near) the area where the optically-excited magnetic sensor 1A is arranged. The correction magnetic sensor 2 may be provided in one-to-one correspondence with the optically excited magnetic sensor 1A, or may be provided in one-to-many correspondence (one correction magnetic sensor 2 for a plurality of optically excited magnetic sensors 1A). may be provided.

As shown in FIG. 2 , the correction magnetic sensor 2 branches the measured values of the geomagnetism and the fluctuating magnetic field and outputs them to the control device 4 . The correction magnetic sensor 2 outputs a measured value of geomagnetism as a DC (direct current) component, and outputs a measured value of a varying magnetic field as an AC (alternating current) component. A line L1 and a line L2 are formed by branching the wiring between the correction magnetic sensor 2 and the control device 4 . A capacitor C (capacitor) and an amplifier A are arranged on the line L2 in order from the correction magnetic sensor 2 side. The capacitor C cuts (blocks) the DC component. The amplifier A amplifies the AC component obtained by cutting the DC component from the output of the correction magnetic sensor 2 . The DC component is output to controller 4 via line L1. The AC component is output to controller 4 after being amplified on line L2. Although the AC component remains on the line L1, it is weaker than the DC component, so its influence on the DC component can be ignored. Alternatively, a low-pass filter that blocks AC components and allows only DC components to pass may be provided on line L1. Each measurement value of the correction magnetic sensor 2 can be represented in the control device 4 by a vector having a direction and magnitude. The control device 4 calculates a gradient of geomagnetism (hereinafter referred to as a “geomagnetic gradient”) based on measured values of geomagnetism by the plurality of correction magnetic sensors 2 . In addition, the control device 4 calculates the gradient of the varying magnetic field (hereinafter referred to as “variable magnetic field gradient”) based on the measured values of the varying magnetic field by the plurality of correction magnetic sensors 2 . The correction magnetic sensor 2 may continuously perform measurement and output at predetermined time intervals.

Returning to FIG. 1, the non-magnetic frame 3 is a frame that covers the entire scalp of a subject whose brain magnetic field is to be measured. be done. The non-magnetic frame 3 can be, for example, a helmet-type frame that surrounds the subject's entire scalp and is worn on the subject's head. A plurality of optically excited magnetic sensors 1A are fixed to the non-magnetic frame 3 so as to be close to the subject's scalp. Further, a correction magnetic sensor 2 is fixed to the non-magnetic frame 3 so as to be able to measure the geomagnetism and the varying magnetic field at each position of the plurality of optically excited magnetic sensors 1A.

The control device 4 controls the current supplied to the correction coils based on the measured values of the geomagnetism and the measured values of the varying magnetic field by the plurality of correction magnetic sensors 2 . That is, the control device 4 determines a current for the correction coil based on the measured value of the geomagnetism and the measured value of the fluctuating magnetic field so as to generate a magnetic field that cancels out the geomagnetism and the fluctuating magnetic field, and outputs a control signal corresponding to the determined current. Output to the coil power supply 5 . The correction coil is a coil for correcting geomagnetism and fluctuating magnetic fields. The correction coils include a geomagnetic correction coil 6 , a geomagnetic gradient correction coil 7 , a fluctuating magnetic field correction coil 8 and a fluctuating magnetic field gradient correction coil 9 .

Specifically, the control device 4 controls the geomagnetism so that the average value of the geomagnetism measured by the plurality of corrective magnetic sensors 2 approximates zero (as a result, the geomagnetism at the position of the optically excited magnetic sensor 1A is reversed and the same as the geomagnetism). A current to the geomagnetic correction coil 6 is determined such that a magnetic field of about the order of magnitude is generated. The control device 4 outputs a control signal (control signal for geomagnetism correction) corresponding to the determined current of the geomagnetism correction coil 6 to the coil power supply 5 .

In addition, the control device 4 controls the geomagnetism measured by the correction magnetic sensor 2 so that the deviation from the average value is minimized (as a result, the geomagnetic gradient at the position of the optically excited magnetic sensor 1A is reversed and approximately the same). ), the current to the geomagnetic gradient correction coil 7 is determined. The control device 4 outputs to the coil power supply 5 a control signal (control signal for geomagnetic gradient correction) corresponding to the determined current of the geomagnetic gradient correction coil 7 .

Furthermore, the control device 4 controls the average value of the measured values of the fluctuating magnetic field by the plurality of magnetic sensors for correction 2 to approximate zero (as a result, the fluctuating magnetic field at the position of the photoexcited magnetic sensor 1A The current to the fluctuating magnetic field correction coil 8 is determined such that a magnetic field of the magnitude of is generated. The control device 4 outputs a control signal (a control signal for correcting the fluctuating magnetic field) corresponding to the determined current of the fluctuating magnetic field correction coil 8 to the coil power supply 5 .

Furthermore, the control device 4 controls the measured value of the fluctuating magnetic field by the correction magnetic sensor 2 so that the deviation from the average value is minimized (as a result, the gradient of the fluctuating magnetic field at the position of the photoexcitation magnetic sensor 1A determine the current to the varying magnetic field gradient correction coil 9 such that a magnetic field of similar magnitude is generated. The controller 4 outputs a control signal (a control signal for correcting the fluctuating magnetic field gradient) corresponding to the determined current of the fluctuating magnetic field gradient correction coil 9 to the coil power supply 5 .

The control device 4 also uses the signal output from the amplifier 12 to obtain information about the magnetism detected by the optically excited magnetic sensor 1A. When the optically excited magnetic sensor 1A is an axial gradiometer, the control device 4 may remove common mode noise by acquiring the difference between the output results of the measurement region and the reference region. Note that the control device 4 may control operations such as irradiation timing and irradiation time of the pump laser 10 and the probe laser 11 .

The control device 4 physically includes a memory such as a RAM and a ROM, a processor (arithmetic circuit) such as a CPU, a communication interface, and a storage unit such as a hard disk. Examples of such a control device 4 include a personal computer, a cloud server, a smart phone, a tablet terminal, and the like. The control device 4 functions by causing the CPU of the computer system to execute a program stored in memory.

The coil power supply 5 outputs a predetermined current to each correction coil according to the control signal output from the control device 4 . Specifically, the coil power supply 5 outputs a current to the geomagnetism correction coil 6 according to the control signal for the geomagnetism correction coil 6 . The coil power supply 5 outputs a current to the geomagnetic gradient correction coil 7 according to a control signal for the geomagnetic gradient correction coil 7 . The coil power supply 5 outputs a current to the fluctuating magnetic field correction coil 8 according to the control signal for the fluctuating magnetic field correction coil 8 . The coil power supply 5 outputs a current to the fluctuating magnetic field gradient correction coil 9 according to a control signal for the fluctuating magnetic field gradient correction coil 9 .

The geomagnetism correction coil 6 is a coil for correcting the geomagnetism at the position of the optically excited magnetic sensor 1A. The geomagnetism correction coil 6 generates a magnetic field according to the current supplied from the coil power supply 5 to cancel the geomagnetism. The geomagnetism correction coil 6 has, for example, a pair of geomagnetism correction coils 6A and 6B. A pair of geomagnetism correction coils 6A and 6B are arranged so as to sandwich the optically excited magnetic sensor 1A (for example, on the left and right sides of the subject). A pair of geomagnetism correction coils 6A and 6B generate a magnetic field of the same magnitude and in the opposite direction to the geomagnetism at the position of the optically excited magnetic sensor 1A according to the current supplied from the coil power source 5. FIG. The direction of the magnetic field is, for example, from one geomagnetism correction coil 6A to the other geomagnetism correction coil 6B. The geomagnetism at the position of the optically excited magnetic sensor 1A is canceled by a magnetic field of the opposite direction and the same magnitude generated by the geomagnetism correction coil 6. FIG. Thus, the geomagnetism correction coil 6 corrects the geomagnetism at the position of the optically excited magnetic sensor 1A.

The geomagnetic gradient correction coil 7 is a coil for correcting the gradient of geomagnetism at the position of the optically excited magnetic sensor 1A. The geomagnetic gradient correction coil 7 generates a magnetic field according to the current supplied from the coil power supply 5 to cancel the gradient. The geomagnetic gradient correction coil 7 has, for example, a pair of geomagnetic gradient correction coils 7A and 7B. A pair of geomagnetic gradient correction coils 7A and 7B are arranged so as to sandwich the optically excited magnetic sensor 1A (for example, on the left and right sides of the subject). A pair of geomagnetic gradient correction coils 7A and 7B generate a magnetic field of the same magnitude and in the opposite direction to the geomagnetic gradient at the position of the optically excited magnetic sensor 1A according to the current supplied from the coil power supply 5. The direction of the magnetic field is, for example, from one geomagnetic gradient correction coil 7A to the other geomagnetic gradient correction coil 7B. The geomagnetic gradient at the position of the optically excited magnetic sensor 1A is canceled by a magnetic field of the opposite direction and the same magnitude generated by the geomagnetic gradient correction coil 7 . Thus, the geomagnetic gradient correction coil 7 corrects the geomagnetic gradient at the position of the optically excited magnetic sensor 1A.

The fluctuating magnetic field correction coil 8 is a coil for correcting the fluctuating magnetic field at the position of the optically excited magnetic sensor 1A. The fluctuating magnetic field correction coil 8 generates a magnetic field according to the current supplied from the coil power supply 5 to cancel the fluctuating magnetic field. The fluctuating magnetic field correction coil 8 has, for example, a pair of fluctuating magnetic field correction coils 8A and 8B. A pair of fluctuating magnetic field correction coils 8A and 8B are arranged (for example, on the left and right sides of the subject) so as to sandwich the optically excited magnetic sensor 1A. A pair of fluctuating magnetic field correction coils 8A and 8B generate a magnetic field of the opposite direction to the fluctuating magnetic field at the position of the photo-excited magnetic sensor 1A in accordance with the current supplied from the coil power supply 5, but of the same magnitude. The direction of the magnetic field is, for example, from one fluctuating magnetic field correction coil 8A to the other fluctuating magnetic field correction coil 8B. The fluctuating magnetic field at the position of the photoexcited magnetic sensor 1A is canceled by a magnetic field of the opposite direction and similar magnitude generated by the fluctuating magnetic field correction coil 8. FIG. In this manner, the fluctuating magnetic field correction coil 8 corrects the fluctuating magnetic field at the position of the optically excited magnetic sensor 1A.

The fluctuating magnetic field gradient correction coil 9 is a coil for correcting the fluctuating magnetic field gradient at the position of the photoexcited magnetic sensor 1A. The fluctuating magnetic field gradient correction coil 9 generates a magnetic field according to the current supplied from the coil power supply 5 to cancel the fluctuating magnetic field gradient. The fluctuating magnetic field gradient correction coil 9 has, for example, a pair of fluctuating magnetic field gradient correction coils 9A and 9B. A pair of fluctuating magnetic field gradient correction coils 9A and 9B are arranged (for example, on the left and right sides of the subject) so as to sandwich the optically excited magnetic sensor 1A. The pair of fluctuating magnetic field gradient correction coils 9A and 9B generate a magnetic field of the opposite direction to the fluctuating magnetic field gradient at the position of the photo-excited magnetic sensor 1A and having approximately the same magnitude according to the current supplied from the coil power supply 5. The direction of the magnetic field is, for example, from one fluctuating magnetic field gradient correction coil 9A to the other fluctuating magnetic field gradient correction coil 9B. The varying magnetic field gradient at the position of the photoexcited magnetic sensor 1A is canceled by a magnetic field of the opposite direction and the same magnitude generated by the varying magnetic field gradient correction coil 9. FIG. Thus, the fluctuating magnetic field gradient correction coil 9 corrects the fluctuating magnetic field gradient at the position of the optically excited magnetic sensor 1A.

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

The probe laser 11 is a laser device that generates probe light. The probe light emitted from the probe laser 11 is incident on each of the plurality of optically excited magnetic sensors 1A through fiber branching.

The amplifier 12 is a device or circuit that amplifies the signal of the output result from the OPM module 1 (specifically, the readout circuit 1C) and outputs it to the control device 4 .

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

The electromagnetic shield 14 is a shielding member that shields high-frequency (for example, 10 kHz or higher) electromagnetic noise, and is composed of, for example, a mesh woven with metal thread, or a non-magnetic metal plate such as aluminum. The electromagnetic shield 14 is arranged to surround the optical excitation magnetic sensor 1A, the correction magnetic sensor 2, the nonmagnetic frame 3, the geomagnetic correction coil 6, the geomagnetic gradient correction coil 7, the fluctuating magnetic field gradient correction coil 8, and the fluctuating magnetic field gradient correction coil 9. be.

Next, a brain magnetic field measuring method using the magnetoencephalograph M1 according to the embodiment will be described with reference to FIG. FIG. 3 is a flow chart showing the operation of the magnetoencephalograph M1.

The correction magnetic sensor 2 measures geomagnetism (step S11). The correction magnetic sensor 2 measures the geomagnetism at each position of the optically excited magnetic sensor 1A and outputs the measured value of the geomagnetism to the control device 4 . The control device 4 calculates the geomagnetic gradient based on the geomagnetism measured by the plurality of correction magnetic sensors 2 .

The control device 4 and the coil power supply 5 control the current to the geomagnetism correction coil 6 (step S12). Based on the geomagnetism measured by the correction magnetic sensor 2, the control device 4 determines the current for the geomagnetism correction coil 6 so as to generate a magnetic field of the same degree and in the opposite direction to the geomagnetism at the position of the optically excited magnetic sensor 1A. do. More specifically, the control device 4 determines the current for the geomagnetism correction coil 6 so that the average value of the geomagnetism measured by the plurality of correction magnetic sensors 2 approximates zero. The control device 4 outputs a control signal corresponding to the determined current to the coil power supply 5 . The coil power supply 5 outputs a predetermined current to the geomagnetism correction coil 6 according to the control signal output from the control device 4 . The geomagnetism correction coil 6 generates a magnetic field according to the current supplied from the coil power supply 5 . The geomagnetism at the position of the optically excited magnetic sensor 1A is canceled by a magnetic field of the opposite direction and the same magnitude generated by the geomagnetism correction coil 6. FIG.

The control device 4 and the coil power supply 5 control the current to the geomagnetic gradient correction coil 7 (step S13). Based on the geomagnetism measured by the correction magnetic sensor 2, the control device 4 controls the geomagnetic gradient correction coil so as to generate a magnetic field of the same magnitude and in the opposite direction to the geomagnetic gradient at the position of the optically excited magnetic sensor 1A. Determine the current for 7. More specifically, the control device 4 determines the current for the geomagnetic gradient correction coil 7 so that the deviation from the average value of the geomagnetism measured by the correction magnetic sensor 2 is minimized. The control device 4 outputs a control signal corresponding to the determined current to the coil power supply 5 . The coil power supply 5 outputs a predetermined current to the geomagnetic gradient correction coil 7 according to the control signal output from the control device 4 . The geomagnetic gradient correction coil 7 generates a magnetic field according to current supplied from the coil power supply 5 . The geomagnetic gradient at the position of the photoexcited magnetic sensor 1A is canceled by a magnetic field of the opposite direction and the same magnitude generated by the geomagnetic gradient correction coil 7. FIG.

The control device 4 determines whether or not the measured value of geomagnetism after correction is equal to or less than a reference value (step S14). The measured value of the geomagnetism after correction is the measured value of the geomagnetism by the correction magnetic sensor 2 after the geomagnetism is corrected by the geomagnetism correction coil 6 and the geomagnetic gradient correction coil 7 . The reference value is the magnitude of the magnetic field at which the optically excited magnetic sensor 1A operates normally, and can be set to 1 nT, for example. If the measured value of geomagnetism is not equal to or lower than the reference value ("NO" in step S14), the process returns to step S11. If the measured value of geomagnetism is equal to or less than the reference value ("YES" in step S14), the process proceeds to step S15.

The correction magnetic sensor 2 measures the fluctuating magnetic field (step S15). The correction magnetic sensor 2 measures the varying magnetic field at each position of the optically excited magnetic sensor 1A and outputs the measured value of the varying magnetic field to the control device 4 . The control device 4 calculates the varying magnetic field gradient based on the measured values of the varying magnetic field by the plurality of correction magnetic sensors 2 .

The control device 4 and the coil power supply 5 control the current to the fluctuating magnetic field correction coil 8 (step S16). The controller 4 corrects the fluctuating magnetic field based on the measured value of the fluctuating magnetic field by the correction magnetic sensor 2 so as to generate a magnetic field of the same magnitude and in the opposite direction to the fluctuating magnetic field at the position of the photoexcitation magnetic sensor 1A. Determine the current for the coil 8; More specifically, the control device 4 determines the current for the fluctuating magnetic field correction coil 8 so that the average value of the fluctuating magnetic field measured by the plurality of correction magnetic sensors 2 approximates zero. The control device 4 outputs a control signal corresponding to the determined current to the coil power supply 5 . The coil power supply 5 outputs a predetermined current to the fluctuating magnetic field correction coil 8 according to the control signal output from the control device 4 . The fluctuating magnetic field correction coil 8 generates a magnetic field according to the current supplied from the coil power supply 5 . The fluctuating magnetic field at the position of the photoexcited magnetic sensor 1A is canceled by a magnetic field of the opposite direction and similar magnitude generated by the fluctuating magnetic field correction coil 8. FIG.

The control device 4 and the coil power supply 5 control the current to the fluctuating magnetic field gradient correction coil 9 (step S17). Based on the measured value of the varying magnetic field by the correction magnetic sensor 2, the control device 4 controls the varying magnetic field so as to generate a magnetic field of the same magnitude and in the opposite direction to the varying magnetic field gradient at the position of the photoexcited magnetic sensor 1A. The current for the gradient correction coil 9 is determined. More specifically, the control device 4 determines the current for the fluctuating magnetic field gradient correction coil 9 so that the deviation from the average value of the fluctuating magnetic field measured by the correction magnetic sensor 2 is minimized. The control device 4 outputs a control signal corresponding to the determined current to the coil power supply 5 . The coil power supply 5 outputs a predetermined current to the fluctuating magnetic field gradient correction coil 9 according to the control signal output from the control device 4 . The variable magnetic field gradient correction coil 9 generates a magnetic field according to the current supplied from the coil power supply 5 . The varying magnetic field gradient at the position of the photoexcited magnetic sensor 1A is canceled by a magnetic field of the opposite direction and the same magnitude generated by the varying magnetic field gradient correction coil 9. FIG.

The control device 4 determines whether or not the corrected measured value of the fluctuating magnetic field is equal to or less than the reference value (step S18). The measured value of the fluctuating magnetic field after correction is the measured value of the fluctuating magnetic field by the correction magnetic sensor 2 after the fluctuating magnetic field is corrected by the fluctuating magnetic field correction coil 8 . The reference value is the noise level at which brain magnetic fields can be measured, and can be, for example, less than 1 nT, more specifically 10 pT. If the measured value of the fluctuating magnetic field is not equal to or less than the reference value ("NO" in step S18), the process returns to step S15. If the measured value of the fluctuating magnetic field is equal to or less than the reference value ("YES" in step S18), the process proceeds to step S19.

The optically excited magnetic sensor 1A measures brain magnetic fields (step S19). Since the geomagnetism and the fluctuating magnetic field at the position of the photoexcited magnetic sensor 1A have been canceled so far that they are equal to or less than the predetermined reference value, the photoexcited magnetic sensor 1A can detect the effects of the geomagnetism and the fluctuating magnetic field while avoiding the effects of the geomagnetism and the fluctuating magnetic field. Magnetic fields can be measured.

FIG. 4 is a schematic diagram showing the configuration of a magnetoencephalograph M2 according to another embodiment. The magnetoencephalography M2 is a device that measures a brain magnetic field using optical pumping while generating a magnetic field that cancels out magnetic noise, like the magnetoencephalography M1. The magnetoencephalograph M2 includes an OPM module 1, a correction magnetic sensor 2, a nonmagnetic frame 3, a control device 4, a coil power supply 5, a fluctuating magnetic field correction coil 8, a fluctuating magnetic field gradient correction coil 9, and a pump laser. 10, a probe laser 11, an amplifier 12, a heater controller 13, an electromagnetic shield 14, and a coil system 15 (correction coil). In the magnetoencephalograph M2, instead of the geomagnetic correction coil 6 and the geomagnetic gradient correction coil 7 of the magnetoencephalograph M1, a coil system 15 is arranged for each OPM module 1 (light-excited magnetic sensor 1A). The arrangement of the coil system 15 will now be described with reference to FIG.

FIG. 5 is a diagram showing the arrangement of the coil system 15 related to the magnetoencephalography M2. Coil system 15 is a coil system capable of applying magnetic fields in three orthogonal directions, each orthogonal and arranged in a circle (eg, a three-axis Helmholtz coil or a planar coil system). Coil system 15 specifically includes coil systems 15X, 15Y, and 15Z. In FIG. 5, coil systems 15X, 15Y, and 15Z are arranged with respect to OPM module 1, respectively, as indicated by dotted lines. In this way, the coil systems 15X, 15Y, and 15Z are arranged orthogonally and in a circle for each OPM module 1 (photoexcited magnetic sensor 1A). The coil system 15X is a coil for correcting the x-axis component of the geomagnetism and the gradient of the geomagnetism shown in FIG. Similarly, the coil systems 15Y and 15Z are coils for correcting the y-axis and z-axis components of the geomagnetism and the gradient of the geomagnetism, respectively.

Returning to FIG. 4, only the parts of the magnetoencephalograph M2 that differ from the magnetoencephalograph M1 will be described. The control device 4 determines currents for the coil systems 15X, 15Y, and 15Z for each of the plurality of optically excited magnetic sensors 1A so that the average value of the geomagnetism measured by the plurality of correction magnetic sensors 2 approximates zero. In addition, the control device 4 determines currents for the coil systems 15X, 15Y, and 15Z for each of the plurality of optically excited magnetic sensors 1A so that the deviation from the average value of the geomagnetism measured by the correction magnetic sensor 2 is minimized. do. Based on the geomagnetism measured by the correction magnetic sensor 2, the control device 4 generates a magnetic field of the opposite direction to the x-axis component of the geomagnetism and the geomagnetic gradient at the position of the optically excited magnetic sensor 1A and having a similar magnitude. Determine the current for the coil system 15X so that The control device 4 outputs a control signal (a control signal for geomagnetism correction) corresponding to the determined current to the coil power supply 5 . In addition, based on the measurement value of the geomagnetism by the correction magnetic sensor 2, the control device 4 generates a magnetic field having a direction opposite to the y-axis component of the geomagnetism and the geomagnetic gradient at the position of the optically excited magnetic sensor 1A and having a magnitude similar to that of the geomagnetism. Determine the current to the coil system 15Y so as to generate The control device 4 outputs a control signal (a control signal for geomagnetism correction) corresponding to the determined current to the coil power supply 5 . Furthermore, based on the geomagnetism measured by the correction magnetic sensor 2, the control device 4 generates a magnetic field having a direction opposite to the z-axis component of the geomagnetism and the geomagnetic gradient at the position of the optically excited magnetic sensor 1A and having a magnitude similar to that of the geomagnetism. Determine the current to the coil system 15Z so as to generate The control device 4 outputs a control signal (a control signal for geomagnetism correction) corresponding to the determined current to the coil power supply 5 .

The coil power supply 5 outputs a predetermined current to each of the coil systems 15X, 15Y, and 15Z according to the control signal output by the control device 4. FIG. Specifically, the coil power supply 5 outputs current to the coil system 15X according to a control signal related to the coil system 15X. The coil power supply 5 outputs current to the coil system 15Y according to the control signal for the coil system 15Y. The coil power supply 5 outputs current to the coil system 15Z according to the control signal for the coil system 15Z.

The coil system 15 generates a magnetic field according to the current supplied from the coil power supply 5 to cancel the geomagnetism and the geomagnetic gradient. Specifically, according to the current supplied from the coil power supply 5, the coil system 15X is configured such that the direction of the geomagnetism and the x-axis component of the geomagnetic gradient at the position of the optically excited magnetic sensor 1A is opposite to and of approximately the same magnitude. Generate a magnetic field. The x-axis components of the geomagnetism and the geomagnetic gradient at the location of the optically excited magnetic sensor 1A are canceled by the oppositely oriented and comparable magnitude magnetic field generated by the coil system 15X. Similarly, the coil systems 15Y and 15Z generate magnetic fields of the same magnitude and in opposite directions to the y-axis direction and z-axis direction components of the geomagnetism and the geomagnetic gradient at the position of the optically excited magnetic sensor 1A. Cancels the geomagnetic gradient. In this way, the coil system 15 corrects the geomagnetism and the geomagnetic gradient at the location of the optically excited magnetic sensor 1A. It should be noted that the magnetic field information generated by the coil system 15 is not included in the information about magnetism obtained by the control device 4 .

The electromagnetic shield 14 is arranged to surround the optically excited magnetic sensor 1A, the correction magnetic sensor 2, the non-magnetic frame 3, the fluctuating magnetic field correction coil 8, the fluctuating magnetic field gradient correction coil 9, and the coil system 15. FIG.

Next, a brain magnetic field measuring method using the magnetoencephalograph M2 according to the embodiment will be described with reference to FIG. FIG. 6 is a flow chart showing the operation of the magnetoencephalograph M2.

The correction magnetic sensor 2 measures geomagnetism (step S21). The correction magnetic sensor 2 measures the geomagnetism at each position of the optically excited magnetic sensor 1A and outputs the measured value of the geomagnetism to the control device 4 . The control device 4 calculates the geomagnetic gradient based on the geomagnetism measured by the plurality of correction magnetic sensors 2 .

The control device 4 and the coil power supply 5 control the current to the coil system 15 for each optically excited magnetic sensor 1A (step S22). Based on the measured value of the geomagnetism by the correction magnetic sensor 2, the control device 4 determines the components of the geomagnetism and the geomagnetic gradient in the three directions (x-axis, y-axis, and z-axis) at the position of the optically-excited magnetic sensor 1A. The currents to the coil system 15 are determined so as to generate magnetic fields of opposite direction and of similar magnitude. More specifically, the control device 4 controls the coil systems 15X, 15Y, and 15Z for each optically excited magnetic sensor 1A so that, for example, the average value of the geomagnetism measured by the plurality of correction magnetic sensors 2 approximates zero. Determine the current for In addition, the control device 4 determines currents for the coil systems 15X, 15Y, and 15Z for each of the plurality of optically excited magnetic sensors 1A so that the deviation from the average value of the geomagnetism measured by the correction magnetic sensor 2 is minimized. do. The control device 4 outputs to the coil power supply 5 control signals corresponding to the determined currents of the coil systems 15X, 15Y, and 15Z. The coil power supply 5 outputs a predetermined current to each of the coil systems 15X, 15Y, and 15Z according to the control signal output by the control device 4. FIG. Coil systems 15X, 15Y, and 15Z each generate a magnetic field in response to current supplied from coil power supply 5. FIG. The three-directional components of the geomagnetism and the geomagnetic gradient at the location of the optically excited magnetic sensor 1A are canceled by magnetic fields of opposite direction and similar magnitude generated by coil systems 15X, 15Y, and 15Z, respectively.

A test operation of the optically excited magnetic sensor 1A is performed (step S23). The photoexcited magnetic sensor 1A acquires the measured value of the residual magnetic field by the test operation and outputs it to the control device 4. FIG. The measured value of the magnetic field is the value measured by the optically excited magnetic sensor 1A after the coil system 15 corrects the geomagnetism and the geomagnetic gradient.

The control device 4 determines whether the measured value of the magnetic field is equal to or less than the reference value (step S24). The reference value is a level at which the optically excited magnetic sensor 1A operates normally, and can be set to 0.3 nT, for example. 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.

The subsequent steps S25 to S29 are the same processing as steps S15 to S19, so the explanation is simplified. The correction magnetic sensor 2 measures the fluctuating magnetic field (step S25). The controller 4 controls the current to the fluctuating magnetic field correction coil 8 (step S26). The controller 4 controls the current to the fluctuating magnetic field gradient correction coil 9 (step S27). The control device 4 determines whether or not the corrected measured value of the fluctuating magnetic field is equal to or less than the reference value (step S28). If the measured value of the fluctuating magnetic field is not equal to or less than the reference value ("NO" in step S28), the process returns to step S25. If the measured value of the fluctuating magnetic field is equal to or less than the reference value ("YES" in step S28), the process proceeds to step S29. The optically excited magnetic sensor 1A measures brain magnetic fields (step S29).

[Effect]
Next, functions and effects of the magnetoencephalograph according to the above-described embodiment will be described.

The magnetoencephalographs M1 and M2 according to this embodiment include a plurality of optically-excited magnetic sensors 1A for measuring brain magnetic fields, and a plurality of corrective magnetic sensors 2 for measuring geomagnetism and varying magnetic fields at respective positions of the plurality of optically-excited magnetic sensors 1A. and a correction coil for correcting the geomagnetism and the fluctuating magnetic field, and based on the measured value of the geomagnetism and the measured value of the fluctuating magnetic field by the plurality of correction magnetic sensors 2, correction to generate a magnetic field that cancels the geomagnetism and the fluctuating magnetic field. A control device 4 that determines a current for the coil and outputs a control signal corresponding to the determined current, and a coil power supply 5 that outputs a current to the correction coil according to the control signal output by the control device 4. .

The magnetoencephalographs M1 and M2 measure geomagnetism and varying magnetic fields at respective positions of a plurality of optically-excited magnetic sensors 1A that measure brain magnetic fields. Then, based on the measured values of the geomagnetism and the fluctuating magnetic field, a current for the correction coil is determined so as to generate a magnetic field that cancels the geomagnetism and the fluctuating 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 correction coil, a magnetic field is generated in the correction coil. As a result, at the positions of the plurality of optically excited magnetic sensors 1A, the geomagnetism and the fluctuating magnetic field are canceled by the magnetic fields generated in the correction coils. In this way, by canceling the geomagnetism and the varying magnetic field at the positions of the plurality of optically excited magnetic sensors 1A, the plurality of optically excited magnetic sensors 1A can measure the brain magnetic field in a state where the influence of the geomagnetism and the influence of the varying magnetic field are avoided. can be done. According to such magnetoencephalographs M1 and M2, brain magnetic fields can be measured with high accuracy without using a magnetically shielded room. In addition, since the sensor for measuring the geomagnetism and the fluctuating magnetic field can be shared by the correction magnetic sensor 2, an increase in the number of sensors can be suppressed.

The correction coils include a geomagnetism correction coil 6 for correcting geomagnetism and a fluctuating magnetic field correction coil 8 for correcting a fluctuating magnetic field. Based on the measured value of the geomagnetism, the control device 4 determines a current for the geomagnetism correction coil 6 so as to generate a magnetic field that cancels out the geomagnetism, and based on the measured value of the fluctuating magnetic field, generates a magnetic field that cancels out the fluctuating magnetic field. , the current for the fluctuating magnetic field correction coil 8 is determined. Even in this case, brain magnetic fields can be measured with high accuracy without using a magnetically shielded room. Also, the number of turns of the geomagnetism correction coil 6 for correcting the geomagnetism having an intensity of the order of 10 μT and the number of turns of the fluctuating magnetic field correction coil 8 for correcting the fluctuating magnetic field having an intensity of the order of 10 nT should be optimized. Therefore, the geomagnetism and the fluctuating magnetic field can be accurately corrected.

The correction coil has a geomagnetic gradient correction coil 7 for correcting the gradient of geomagnetism. Based on the measured value of the geomagnetism, the controller 4 determines the current to the geomagnetic gradient correction coil 7 so as to generate a magnetic field that cancels the gradient of the geomagnetism. In this case, uniform geomagnetism correction (zero-order correction) is performed by controlling the current to the geomagnetism correction coil 6, and furthermore, by controlling the current to the geomagnetic gradient correction coil 7, the difference in the position of each photoexcited magnetic sensor 1A is taken into consideration. Correction of the geomagnetic gradient (primary correction) is performed. In this manner, the geomagnetism and the gradient of the geomagnetism are canceled step by step, so that the geomagnetism can be accurately corrected.

The correction coil has a varying magnetic field gradient correction coil 9 for correcting the gradient of the varying magnetic field. Based on the measured value of the fluctuating magnetic field, the controller 4 determines the current to the fluctuating magnetic field gradient correction coil 9 so as to generate a magnetic field that cancels the gradient of the fluctuating magnetic field. In this case, the uniform variation magnetic field correction (zero-order correction) is performed by controlling the current to the variation magnetic field correction coil 8, and furthermore, by controlling the current to the variation magnetic field gradient correction coil 9, the position of each photoexcited magnetic sensor 1A is different. Correction (first-order correction) of the gradient of the fluctuating magnetic field in consideration of is performed. In this manner, the varying magnetic field and the gradient of the varying magnetic field are canceled step by step, so that the varying magnetic field can be corrected with high accuracy.

The correction coil is composed of a pair of coils arranged with a plurality of optically-excited magnetic sensors 1A interposed therebetween. In this case, the geomagnetism and the fluctuating magnetic field at the positions of the plurality of optically excited magnetic sensors 1A sandwiched between the pair of correction coils are effectively corrected. As a result, it is possible to appropriately correct the geomagnetism and the fluctuating magnetic field with a simple configuration.

The correction coils are coil systems 15 arranged around in three orthogonal directions for each of the plurality of optically excited magnetic sensors 1A. The controller 4 determines the current to the coil system 15 to generate a magnetic field that counteracts the geomagnetism and the gradient of the geomagnetism based on the geomagnetism measurements. In this case, the coil system 15 is arranged corresponding to each component of the three directions (x-axis, y-axis, and z-axis) of the geomagnetism for each optically excited magnetic sensor 1A. By controlling the current to each of the coil systems 15, a magnetic field is generated that cancels the x-axis component, y-axis component, and z-axis component of the geomagnetism for each optically excited magnetic sensor 1A. Then, the geomagnetism and the gradient of the geomagnetism are corrected from three directions. As a result, the current can be finely controlled for each optically excited magnetic sensor 1A, and the correction accuracy of geomagnetism is improved. Moreover, since only the geomagnetism in the region related to the operation of the plurality of optically excited magnetic sensors 1A is corrected, it is possible to suppress an increase in power consumption associated with unnecessary correction.

The correction magnetic sensor 2 is a fluxgate sensor that outputs a measured value of geomagnetism as a DC component and outputs a measured value of a varying magnetic field as an AC component. The dynamic range of a fluxgate sensor may include geomagnetic fields with strengths on the order of 10 μT and fluctuating magnetic fields at specific frequencies (eg, commercial frequencies) with strengths on the order of 10 nT. The fluctuating magnetic field of a specific frequency is a particularly large magnetic field among fluctuating magnetic fields. Such a fluxgate sensor can suitably measure geomagnetism and a varying magnetic field of a specific frequency.

The multiple optically-excited magnetic sensors 1A are axial gradiometers having a measurement region and a reference region coaxially in a direction perpendicular to the object to be measured. In this case, since the influence of common mode noise is shown in the output result of the measurement area and the output result of the reference area, the common mode noise can be removed by obtaining the difference between the two output results. This improves the measurement accuracy of the brain magnetic field.

The plurality of optically-excited magnetic sensors 1A and the plurality of correction magnetic sensors 2 are fixed to a helmet-shaped non-magnetic frame 3 that is worn on the subject's head and has a relative magnetic permeability close to 1 and does not disturb the magnetic field distribution. In this case, the non-magnetic frame 3 attached to the head and the sensors fixed to the non-magnetic frame 3 move according to the movement of the subject's head. Correction of the geomagnetism and the varying magnetic field at the position of the optically excited magnetic sensor 1A, and measurement of the brain magnetic field can be performed appropriately.

The magnetoencephalographs M1 and M2 may further comprise an electromagnetic shield 14 for shielding high frequency electromagnetic noise. In this case, it is possible to prevent high-frequency electromagnetic noise, which cannot be measured by the magnetoencephalographs M1 and M2, from entering the plurality of optically-excited magnetic sensors 1A. This allows the plurality of optically excited magnetic sensors 1A to operate stably.

A brain magnetic field measurement method according to an aspect of the present disclosure includes steps of measuring geomagnetism and varying magnetic fields at respective positions of a plurality of optically excited magnetic sensors 1A; determining a current for the correction coil so as to generate a magnetic field that cancels the fluctuating magnetic field; outputting a control signal according to the determined current; outputting the current to the correction coil according to the control signal; and measuring brain magnetic fields with the optically excited magnetic sensor 1A.

In the brain magnetic field measurement method according to one aspect of the present disclosure, geomagnetism and fluctuating magnetic fields are measured at respective positions of a plurality of optically-excited magnetic sensors 1A that measure brain magnetic fields. Then, based on the measured values of the geomagnetism and the fluctuating magnetic field, a current for the correction coil is determined so as to generate a magnetic field that cancels the geomagnetism and the fluctuating magnetic field, and a control signal corresponding to the determined current is output. Then, when a current corresponding to the control signal is output to the correction coil, a magnetic field is generated in the correction coil. As a result, at the positions of the plurality of optically excited magnetic sensors 1A, the geomagnetism and the fluctuating magnetic field are canceled by the magnetic fields generated in the correction coils. In this way, by canceling the geomagnetism and the varying magnetic field at the positions of the plurality of optically excited magnetic sensors 1A, the plurality of optically excited magnetic sensors 1A can measure the brain magnetic field in a state where the influence of the geomagnetism and the influence of the varying magnetic field are avoided. can be done. According to such a brain magnetic field measurement method, a brain magnetic field can be measured with high accuracy without using a magnetically shielded room.

In the brain magnetic field measurement method, outputting the control signal determines the current for the geomagnetic correction coil 6 so as to generate a magnetic field that cancels the geomagnetism based on the measured value of the geomagnetism, and based on the measured value of the fluctuating magnetic field, It includes determining a current for the fluctuating magnetic field correction coil 8 so as to generate a magnetic field that cancels the fluctuating magnetic field, and outputting a control signal for geomagnetism correction and a control signal for correcting the fluctuating magnetic field according to the determined current. Even in this case, brain magnetic fields can be measured with high accuracy without using a magnetically shielded room. Also, the number of turns of the geomagnetism correction coil 6 for correcting the geomagnetism having an intensity of the order of 10 μT and the number of turns of the fluctuating magnetic field correction coil 8 for correcting the fluctuating magnetic field having an intensity of the order of 10 nT should be optimized. Therefore, the geomagnetism and the fluctuating magnetic field can be accurately corrected.

The brain magnetic field measurement method determines a current for the geomagnetic gradient correction coil 7 so as to generate a magnetic field that cancels the gradient of the geomagnetism based on the measured value of the geomagnetism, and outputs a control signal for correcting the geomagnetic gradient according to the determined current. Further including the step of outputting. In this case, uniform geomagnetism correction (zero-order correction) is performed by controlling the current to the geomagnetism correction coil 6, and furthermore, by controlling the current to the geomagnetic gradient correction coil 7, the difference in the position of each photoexcited magnetic sensor 1A is taken into account. Correction of the geomagnetic gradient (primary correction) is performed. In this manner, the geomagnetism and the gradient of the geomagnetism are canceled step by step, so that the geomagnetism can be accurately corrected.

In the brain magnetic field measurement method, based on the measured value of the fluctuating magnetic field, a current for the fluctuating magnetic field gradient correction coil 9 is determined so as to generate a magnetic field that cancels the gradient of the fluctuating magnetic field. and outputting a control signal for . In this case, the uniform variation magnetic field correction (zero-order correction) is performed by controlling the current to the variation magnetic field correction coil 8, and furthermore, by controlling the current to the variation magnetic field gradient correction coil 9, the position of each photoexcited magnetic sensor 1A is different. Correction (first-order correction) of the gradient of the fluctuating magnetic field in consideration of is performed. In this manner, the varying magnetic field and the gradient of the varying magnetic field are canceled step by step, so that the varying magnetic field can be corrected with high accuracy.

[Modification]
The above has been described in detail based on the embodiments of the present disclosure. However, the present disclosure is not limited to the above embodiments. Various modifications can be made to the present disclosure without departing from the gist thereof.

In the embodiment, the magnetic sensor for correction 2 has a configuration in which the measured value is branched and output to the control device 4, but the magnetic sensor for correction 2 is configured to output the measured value to the control device 4 without branching. There may be. In such a configuration, the control device 4 extracts the DC component and the AC component based on the measured value output from the correction magnetic sensor 2, and uses the respective components as the measured value of the geomagnetism and the measured value of the fluctuating magnetic field. may be obtained. In this case, wiring for branching can be omitted.

The correction magnetic sensor 2 may be a fluxgate sensor that measures geomagnetism and an optically excited magnetic sensor that measures a varying magnetic field. The optically-excited magnetic sensor is a sensor different from the optically-excited magnetic sensor 1A that measures brain magnetic fields. Since the photoexcited magnetic sensor has higher sensitivity than the fluxgate sensor or the like, it can measure the fluctuating magnetic field with high accuracy. As a result, the fluctuating magnetic field and the fluctuating magnetic field gradient can be corrected more precisely.

The fluctuating magnetic field correction coil 8 has been described as having a pair of fluctuating magnetic field correction coils 8A and 8B, but like the coil system 15, it may be arranged as a coil system for each OPM module 1 (photoexcited magnetic sensor 1A). In this case, the controller 4 generates a magnetic field of the same magnitude and in the opposite direction to the components of the three directions (x-axis, y-axis, and z-axis) of the variable magnetic field at the position of the photoexcited magnetic sensor 1A. First, the current for the fluctuating magnetic field correction coil 8 is determined. The control device 4 outputs to the coil power supply 5 a control signal according to the determined current associated with each of the fluctuating magnetic field correction coils 8 arranged as a coil system.

The optically excited magnetic sensor 1A may have a plurality of measurement points within one housing. In this case, it is possible to narrow the distance between the measurement points, and to measure brain magnetic fields with high spatial resolution.

Although the coil system 15 associated with the magnetoencephalograph M2 has been described as correcting the geomagnetism and the geomagnetic gradient, only the geomagnetism may be corrected. A geomagnetic gradient correction coil 7 may be further provided to correct the geomagnetic gradient. Even in this case, brain magnetic fields can be measured with high accuracy without using a magnetically shielded room.

FIG. 7 is a diagram showing the configuration of a magnetoencephalograph M3 according to a modification. The magnetoencephalograph M3 differs from the magnetoencephalograph M1 in that the fluctuating magnetic field correction coil 8 and the fluctuating magnetic field gradient correction coil 9 are omitted. The geomagnetism correction coil 6 may correct the geomagnetism with a DC current and superimpose an AC current component to correct the fluctuating magnetic field. Similarly, in the geomagnetic gradient correction coil 7, a DC current may be used to correct the geomagnetic gradient, and an AC current component may be superimposed to correct the fluctuating magnetic field gradient. According to such a magnetoencephalograph M3, for the same reason as the magnetoencephalographs M1 and M2, it is possible to measure brain magnetic fields with high accuracy without using a magnetically shielded room. In addition, since an increase in the number of correction coils can be suppressed, geomagnetism and fluctuating magnetic fields can be appropriately corrected with a simple configuration.

FIG. 8 is a diagram showing the configuration of a magnetoencephalograph M4 according to a modification. The magnetoencephalograph M4 differs from the magnetoencephalograph M2 in that the fluctuating magnetic field correction coil 8 and the fluctuating magnetic field gradient correction coil 9 are omitted. The correction coil may be the coil system 15 alone. Based on the measured value of the measured value of the geomagnetism and the measured value of the varying magnetic field, the controller 4 controls the current to the coil system 15 so as to generate a magnetic field that cancels the geomagnetism, the gradient of the geomagnetic field, and the varying magnetic field and the gradient of the varying magnetic field. may be determined. In this case, the coil system 15 is arranged for each optically excited magnetic sensor 1A so as to correspond to each of the components in the three directions (x-axis, y-axis, and z-axis) of the geomagnetism and the varying magnetic field. Then, by controlling the current to each of the coil systems 15, the x-axis component, the y-axis component, and the z-axis component of the geomagnetism and the varying magnetic field are canceled for each photoexcited magnetic sensor 1A. A magnetic field is generated, and the geomagnetism and the gradient of the geomagnetism and the varying magnetic field and the gradient of the varying magnetic field are corrected from three directions. As a result, the current can be finely controlled for each photoexcited magnetic sensor 1A, and the correction accuracy of the geomagnetism and the fluctuating magnetic field is improved. Moreover, since only the geomagnetism and the varying magnetic field in the region related to the operation of the plurality of optically excited magnetic sensors 1A are corrected, it is possible to suppress an increase in power consumption associated with unnecessary correction.

1A Optical excitation magnetic sensor 2 Correction magnetic sensor 3 Nonmagnetic frame 4 Control device 5 Coil power supply 6 Geomagnetic correction coil 7 Geomagnetic gradient correction coil 8 Fluctuating magnetic field correction coil 9 ... fluctuating magnetic field gradient correction coil, 14 ... electromagnetic shield, 15 ... coil system.

Claims (14)

a plurality of optically excited magnetic sensors that measure brain magnetic fields;
a plurality of correction magnetic sensors for measuring geomagnetism and varying magnetic fields at respective positions of the plurality of optically excited magnetic sensors;
a correction coil for correcting the geomagnetism and the fluctuating magnetic field;
determining a current for the correction coil so as to generate a magnetic field that cancels out the geomagnetism and the varying magnetic field based on the measured values of the geomagnetism and the measured values of the varying magnetic field by the plurality of correcting magnetic sensors; and determining the determined current. a control device that outputs a control signal according to
a coil power supply that outputs a current to the correction coil according to the control signal output by the control device;
A magnetoencephalograph. The correction coil includes a geomagnetism correction coil for correcting the geomagnetism and a fluctuating magnetic field correction coil for correcting the fluctuating magnetic field,
The control device determines a current for the geomagnetism correction coil so as to generate a magnetic field that cancels the geomagnetism based on the measured value of the geomagnetism, and a magnetic field that cancels the varying magnetic field based on the measured value of the varying magnetic field. determining a current to the fluctuating magnetic field correction coil to generate
The magnetoencephalograph according to claim 1. The correction coil has a geomagnetic gradient correction coil for correcting the gradient of the geomagnetism,
The controller determines a current to the geomagnetic gradient correction coil based on the measured value of the geomagnetism so as to generate a magnetic field that cancels the gradient of the geomagnetism.
The magnetoencephalograph according to claim 2. The correction coil has a variable magnetic field gradient correction coil for correcting the gradient of the variable magnetic field,
The controller determines a current to the varying magnetic field gradient correction coil based on the measured value of the varying magnetic field so as to generate a magnetic field that cancels the gradient of the varying magnetic field.
The magnetoencephalograph according to claim 2 or 3. The magnetoencephalograph according to any one of claims 1 to 4, wherein said correction coil comprises a pair of coils arranged with said plurality of optically excited magnetic sensors interposed therebetween. The correction coil is a coil system arranged in three orthogonal directions for each of the plurality of optically-excited magnetic sensors,
the controller determines currents to the coil system to generate magnetic fields that counteract the geomagnetism and gradients of the geomagnetism based on the geomagnetism measurements;
The magnetoencephalograph according to claim 1. The correcting magnetic sensor according to any one of claims 1 to 6, wherein the magnetic sensor for correction is a fluxgate sensor that outputs the measured value of the geomagnetism as a DC component and outputs the measured value of the varying magnetic field as an AC component. magnetoencephalography. The magnetoencephalograph according to any one of claims 1 to 7, wherein said plurality of optically-excited magnetic sensors are axial gradiometers having a measurement region and a reference region coaxially and perpendicularly to the object to be measured. The plurality of optically excited magnetic sensors and the plurality of correction magnetic sensors are fixed to a helmet-shaped non-magnetic frame that is worn on the subject's head and has a relative magnetic permeability close to 1 that does not disturb the magnetic field distribution. The magnetoencephalograph according to any one of 1 to 8. The magnetoencephalograph according to any one of claims 1 to 9, further comprising an electromagnetic shield for shielding high-frequency electromagnetic noise. measuring geomagnetism and varying magnetic fields at respective positions of a plurality of optically excited magnetic sensors;
determining a current for a correction coil based on the measured value of the geomagnetism and the measured value of the varying magnetic field so as to generate a magnetic field that cancels the geomagnetism and the varying magnetic field, and outputting a control signal according to the determined current; and,
outputting a current to the correction coil in response to the control signal;
measuring brain magnetic fields with the plurality of optically-excited magnetic sensors;
A brain magnetic field measurement method, comprising: Outputting the control signal includes determining a current for a geomagnetism correction coil to generate a magnetic field that cancels the geomagnetism based on the measured value of the geomagnetism, and determining the varying magnetic field based on the measured value of the varying magnetic field. 12. The method according to claim 11, comprising determining a current for the fluctuating magnetic field correction coil so as to generate a magnetic field that cancels out the magnetic field, and outputting a control signal for geomagnetism correction and a control signal for correcting the fluctuating magnetic field according to the determined current. brain magnetic field measurement method. determining a current for a geomagnetic gradient correction coil based on the measured value of the geomagnetism so as to generate a magnetic field that cancels the gradient of the geomagnetism; and outputting a control signal for geomagnetic gradient correction according to the determined current. 13. The brain magnetic field measurement method according to claim 12, comprising: Based on the measured value of the fluctuating magnetic field, a current for the fluctuating magnetic field gradient correction coil is determined so as to generate a magnetic field that cancels the gradient of the fluctuating magnetic field, and a control signal for correcting the fluctuating magnetic field gradient is output according to the determined current. 14. The brain magnetic field measurement method according to claim 12 or 13, further comprising the step of:

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