JP2023034042A - Brain measuring device and brain measuring method - Google Patents

Abstract

To efficiently achieve magnetoencephalographic measurement and MRI measurement.SOLUTION: A brain measuring device M1 includes: a magnetoencephalography including a plurality of optical excitation magnetic sensors 1A for measuring a brain magnetic field, a plurality of correction magnetic sensors 2 for measuring geomagnetism and a variable magnetic field at each position of the plurality of optical excitation magnetic sensors 1A, and a correction coil for correcting the geomagnetism and the variable magnetic field; an MRI device including a static magnetic field coil for applying a static magnetic field, a gradient magnetic field coil for applying a gradient magnetic field, and a transmission/reception coil for transmitting a transmission pulse of a predetermined frequency and detecting a nuclear magnetic-resonance signal generated by the transmission of the transmission pulse; and a control device 4 for controlling an electric current supplied to the correction coil on the basis of a measurement value of the geomagnetism and a measurement value of the variable magnetic field by the plurality of correction magnetic sensors 2 when measuring a brain magnetic field, controlling an electric current supplied to the static magnetic field coil and the gradient magnetic field coil when measuring an MR image, and generating the MR image on the basis of the output of the transmission/reception coil.SELECTED DRAWING: Figure 1

Description

The present invention relates to a brain measurement device and a brain 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. An optically excited magnetic sensor measures a small magnetic field by detecting 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. Also, recently, research has been conducted to combine a magnetoencephalograph and an MRI (Magnetic Resonance Imaging) device using SQUID (see Non-Patent Document 1 below).

Japanese Patent No. 5823195

“SQUIDs in biomagnetism: a roadmap towards improved healthcare”, Supercond. Sci. Technol. 29 (2016) 113001 (30pp)

Here, in order to avoid the influence of magnetic noise stronger than the brain magnetic field, magnetoencephalography measurement must be performed in a state in which magnetic noise including geomagnetism is reduced. On the other hand, MRI measurement must be performed in a state in which a static magnetic field, a gradient magnetic field, and the like are generated. When trying to realize an apparatus in which a magnetoencephalograph and an MRI apparatus are integrated, it is required to efficiently reduce magnetic noise and apply a static magnetic field, a gradient magnetic field, and the like.

The present embodiment has been made in view of the above circumstances, and aims to provide a brain measurement apparatus and a brain measurement method that can efficiently realize magnetoencephalography and MRI measurement.

A brain measurement device according to an aspect of an embodiment includes: a plurality of optically excited magnetic sensors that measure brain magnetic fields; a plurality of corrective magnetic sensors that measure geomagnetism and varying magnetic fields at respective positions of the plurality of optically excited magnetic sensors; and a correction coil for correcting the fluctuating magnetic field, a magnetoencephalograph having a static magnetic field coil for applying a static magnetic field, a gradient magnetic field coil for applying a gradient magnetic field, and transmitting a transmission pulse of a predetermined frequency and a transmission/reception coil for detecting a nuclear magnetic resonance signal generated by the transmission of the transmission pulse; Based on the output of the transmission/reception coil, the current supplied to the correction coil is controlled, and when measuring an MR image, the current supplied to the static magnetic field coil and the gradient magnetic field coil is controlled to control the static magnetic field and the gradient magnetic field. a controller for generating MR images.

Alternatively, a brain measurement method according to another aspect of the embodiment includes a plurality of optically-excited magnetic sensors that measure brain magnetic fields, and a plurality of corrective magnetic sensors that measure 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, a magnetoencephalograph having a static magnetic field coil for applying a static magnetic field, a gradient magnetic field coil for applying a gradient magnetic field, and transmitting a predetermined frequency and a transmitting/receiving coil for transmitting a pulse and detecting a nuclear magnetic resonance signal generated by the transmission of the transmitted pulse, wherein a brain magnetic field is measured using a plurality of correction magnets. The current supplied to the correction coil is controlled based on the measured value of the geomagnetism and the measured value of the fluctuating magnetic field by the sensor. A gradient magnetic field is controlled and an MR image is generated based on the output of the receiving coil.

According to the above aspect or another aspect, the geomagnetism and the fluctuating magnetic field are measured at respective positions of the plurality of optically-excited magnetic sensors that measure brain magnetic fields. When the brain magnetic field is measured, the current flowing through the correction coil is controlled based on the measured value of the geomagnetism and the measured value of the fluctuating magnetic field, and a magnetic field is generated in the correction coil. As a result, the geomagnetism and the fluctuating magnetic field are corrected by the magnetic fields generated in the correction coils at the positions of the plurality of optically excited magnetic sensors. By correcting the geomagnetism and the fluctuating 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 fluctuating magnetic field.

On the other hand, according to the above aspect or another aspect, when measuring an MR image, the static magnetic field and the gradient magnetic field are applied by controlling the current flowing through the static magnetic field coil and the gradient magnetic field coil, and by transmitting the transmission pulse, Resulting nuclear magnetic resonance signals are detected. As a result, an MR image can be measured based on the output of the transmission/reception coil.

According to such a brain measurement device and brain measurement method, magnetoencephalography and MRI measurement can be efficiently realized using the same device. In particular, MRI measurement does not require a superconducting static magnetic field coil, a magnetic shield room for reducing magnetic noise during brain magnetic field measurement is not required, and coolant such as liquid helium required when using SQUID is not required. As a result, miniaturization and cost reduction are possible. Furthermore, since brain magnetic field measurement and MRI measurement can be sequentially performed on the same subject using the same apparatus, registration errors in both measurement results can be reduced.

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. In such a configuration, the geomagnetism correction coil and the static magnetic field coil can be shared depending on the situation, so in this case, further miniaturization and further cost reduction of the device are possible. According to such a configuration, 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 such a configuration, the geomagnetic gradient correction coil and the gradient magnetic field coil can be shared depending on the case, so in this case, further miniaturization and further cost reduction of the device are possible. Further, uniform magnetic field correction (zero-order correction) is performed by controlling the current to the correction coil, and furthermore, the gradient of the geomagnetism is corrected by controlling the current to the geomagnetic gradient correction coil, taking into account the difference in the position of each optically excited magnetic sensor. (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 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 (0th-order correction) is performed by controlling the current to the correction coil, and furthermore, by controlling the current to the fluctuation magnetic field gradient correction coil, the fluctuation magnetic field considering the difference in the position of each photoexcited magnetic sensor. is corrected (primary correction) for the gradient of . 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 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 transmit/receive coils may include transmit coils for transmitting transmit pulses and receive coils for detecting nuclear magnetic resonance signals. In this case, for example, the receiving coil can be placed at a location close to the object to be measured, and the transmitting coil can be placed at a different location from the receiving coil, thereby improving the degree of freedom in design. Moreover, when a plurality of small receiving coils are arranged to surround the object to be measured, the sensitivity of the receiving coils can be improved and noise can be reduced.

The transmission/reception coil may serve as both a coil for transmitting transmission pulses and a coil for detecting nuclear magnetic resonance signals. In this case, it is possible to further reduce the size and cost of the device.

The transmitting/receiving coil may be spirally formed and arranged so as to surround the object to be measured. In this case, since the transmitting/receiving coil can be placed near the object to be measured, the accuracy of MRI measurement can be improved.

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.

An output coil that is electrically connected to the transmission/reception coil and outputs a magnetic signal based on a current flowing through the transmission/reception coil, and another optically excited magnetic sensor that detects the magnetic signal output by the output coil. . The controller may generate an MR image based on magnetic signals detected by another optically-excited magnetic sensor. According to such a configuration, the signal can be received by another photoexcited magnetic sensor having a high sensitivity of fT order, so that the accuracy of MR image measurement can be improved. In addition, since another photoexcitation magnetic sensor is placed at a position away from the transmitting and receiving coil to which a static magnetic field of mT order is applied, it is possible to adjust the sensitivity band of the sensor without being affected by the static magnetic field. .

The plurality of optically excited magnetic sensors may be configured to have a bias magnetic field applied such that they are sensitive to frequencies in the range of 0-200 Hz. Another optically excited magnetic sensor may be configured to have a bias magnetic field applied such that it is sensitive to frequencies in the range of 20 kHz to 500 kHz. With such a configuration, the sensitivity of brain magnetic field measurement can be enhanced, and at the same time, the accuracy of MRI measurement can be enhanced.

The plurality of optically excited magnetic sensors, the plurality of correction magnetic sensors, and the receiving coil may be fixed to a helmet-shaped non-magnetic frame worn on the subject's head. According to such a configuration, the non-magnetic frame attached to the head and the sensors and receiving coils fixed to the non-magnetic frame move according to the movement of the subject's head, so that the subject's head moves. Even in this case, correction of geomagnetism and fluctuating magnetic fields, brain magnetic field measurement, and MRI measurement can be performed appropriately at the positions of a plurality of optically excited magnetic sensors. As a result, registration errors in both measurements can be suppressed.

An electromagnetic shield for shielding high-frequency electromagnetic noise may be further provided. According to such a configuration, it is possible to prevent high-frequency electromagnetic noise, which cannot be measured by a magnetoencephalograph, from entering the plurality of optically-excited magnetic sensors. As a result, brain magnetic field measurement can be stably operated by a plurality of optically-excited magnetic sensors. On the other hand, in MRI measurement, it is possible to prevent the intrusion of noise in the signal range of 20 kHz to 500 kHz.

ADVANTAGE OF THE INVENTION According to this invention, the brain measuring device and brain measuring method which can implement|achieve magnetoencephalography and MRI measurement efficiently can be provided.

1 is a schematic diagram showing the configuration of a brain measurement device according to an embodiment; FIG. FIG. 2 is a schematic diagram showing a configuration for the connection between the fluxgate sensor and the controller; 3 is a schematic diagram showing the configuration of an OPM module 23 according to the embodiment; FIG. It is a flow chart which shows operation of a brain measurement device concerning an embodiment. It is a flow chart which shows operation of a brain measurement device concerning an embodiment. It is a schematic diagram showing the configuration of a brain measurement device according to another embodiment. It is a schematic diagram showing the configuration of a brain measurement device according to another embodiment. 9 is a flow chart showing the operation of a brain measurement device according to another embodiment; It is a schematic diagram showing the configuration of a brain measurement device according to a modification. It is a schematic diagram showing the configuration of a brain measurement device according to a modification. It is a schematic diagram showing the configuration of a brain measurement device 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 brain measurement device M1 according to an embodiment. The brain measurement device M1 is a device that measures brain magnetic fields and MR (Magnetic Resonance) images of a subject. The brain measurement device M1 includes a plurality of OPM (optically pumped magnetometer) modules 1, a plurality of correction magnetic sensors 2, a non-magnetic frame 3, a pair of geomagnetic correction coils 6, a pair of geomagnetic gradient correction coils 7, and a pair of fluctuating magnetic field correction. It comprises a magnetoencephalography module having a coil 8 and a pair of fluctuating magnetic field gradient correction coils 9, and an MRI module (MRI apparatus) having a transmitting coil 21, a receiving coil 22, an OPM module 23, and an output coil 24. Furthermore, the brain measurement device M1 includes a control device 4, a coil power supply 5, a pump laser 10, a probe laser 11, amplifiers 12A and 12B, a heater controller 13, an electromagnetic shield 14, an excitation coil controller 15, Prepare.

In the following description, the direction approximately parallel to the central axis of the subject's head is defined as the Z-axis direction, and the directions perpendicular to the Z-axis and perpendicular to each other are defined as the X-axis direction and the Y-axis direction.

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 of the optically excited magnetic sensor 1A. 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 photoexcited magnetic sensor 1A is configured so that a predetermined bias magnetic field is applied in the irradiation direction of the pump light so as to be sensitive to magnetic fields with frequencies within the range of 0 to 200 Hz. 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 12A.

The optically excited magnetic sensor 1A may be, for example, an axial gradiometer. The axial gradiometer has a measurement region and a reference region coaxially and perpendicularly to the subject's scalp (measurement point). 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 the results of measurements in the measurement area and the reference area to the amplifier 12A. 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 the subject whose brain magnetic field is to be measured, and is made of a non-magnetic material such as graphite whose relative magnetic permeability is close to 1 and does not disturb the magnetic field distribution. 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. In addition, a receiving coil 22 for detecting nuclear magnetic resonance signals for MR image measurement is fixed on the subject's scalp side of the plurality of optically excited magnetic sensors 1A in the non-magnetic frame 3 . The receiving coil 22 detects a proton nuclear magnetic resonance signal, which will be described later, and converts it into an electric current. In order to improve the detection sensitivity of the nuclear magnetic resonance signal, the receiving coil 22 is preferably provided on the side of the subject's head of the optically excited magnetic sensor 1A near the scalp.

The transmission coil 21 is a coil that irradiates the subject's head with an RF pulse (transmission pulse) of a predetermined frequency (for example, approximately 300 kHz) during MR image measurement. This transmission coil 21 is arranged above the subject's head outside the non-magnetic frame 3, for example.

The output coil 24 is electrically connected to both ends of the receiving coil 22 via a cable, receives a current flowing through both ends of the receiving coil 22, converts the current again into a magnetic signal, and outputs the magnetic signal.

The OPM module 23, like the OPM module 1, has an optical excitation magnetic sensor 23A, a heat insulating material 23B, and a read circuit 23C. For example, the OPM module 23 is housed in a magnetic shield 25 for shielding a static magnetic field, which will be described later, together with the output coil 24 outside the non-magnetic frame 3 . The magnetic shield 25 is made of, for example, mu-metal having a relative magnetic permeability greater than 1. As shown in FIG.

The optically excited magnetic sensor 23A is a sensor that measures a magnetic signal using optical pumping. The optically excited magnetic sensor 23A is configured such that a predetermined bias magnetic field is applied in the irradiation direction of the pump light so as to be sensitive to magnetic fields of frequencies within the range of 20 kHz to 500 kHz. For example, a bias magnetic field of about 40 μT is applied so as to be sensitive to the 300 kHz frequency of electromagnetic waves emitted by protons. 23 C of read-out circuits output the detection result by the optical excitation magnetic sensor 23A to the amplifier 12B.

FIG. 3 shows a specific example of the configuration of the OPM module 23. As shown in FIG. The optically excited magnetic sensor 23A includes a longitudinal cell 26 filled with a gas containing an alkali metal whose polarization direction changes depending on the magnetic field to be measured, and a heater that heats the entire cell 26 to a predetermined temperature (for example, 180 degrees). 27 , a polarizing beam splitter 28 and a photodetector 29 . Pump light LP is introduced from the outside along the longitudinal direction of the interior of the cell 26, and along the direction perpendicular to the longitudinal direction, the cell 26 is divided into a plurality of pieces (for example, divided into four) in the longitudinal direction. The probe light LB from the outside is branched and irradiated to each of the intersecting regions 26A. The probe beam LB transmitted through these intersection areas 26A has its magneto-rotation angle detected by the polarization beam splitter 28 and the photodetector 29 provided corresponding to each intersection area 26A. That is, the polarizing beam splitter 28 splits the probe light LB into two linearly polarized components orthogonal to each other, and the photodetector 29 uses two built-in PDs (photodiodes) to detect the intensity of the two linearly polarized components. The magneto-rotation angle of the probe light LB is detected based on the ratio of the detected intensities. The OPM module 23 is further provided with a circuit board 30, which outputs the magnetic rotation angle of the probe light LB detected for each intersection area 26A via a readout circuit 23C in the circuit board 30.

The output coil 24 is fixed within the magnetic shield 25 so as to face each intersection region 26A of the cells 26 of the OPM module 23 configured as described above. With such a configuration, the magnetic signal B _OUT generated by the output coil 24 based on the electromagnetic field B _IN detected by the receiving coil 22 changes according to the inclination of the spin polarization axis of the alkali metal atom. is detected based on the magnetic rotation angle of Here, in the example of FIG. 3, the number of divisions of the intersection area 26A is four, but it may be changed to any number. Alternatively, a plurality of cells 26 may be provided in parallel, and intersection regions 26A may be arranged two-dimensionally (for example, 4×4=16).

Returning to FIG. 1, the control device 4 controls the current supplied to the correction coil based on the measured values of the geomagnetism and the measured values of the fluctuating magnetic field by the plurality of correction magnetic sensors 2 when measuring the brain magnetic field. 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 .

In addition, the control device 4 uses the signal output from the amplifier 12A 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 .

Further, the control device 4 determines the current to be supplied to the geomagnetic correction coil 6 and the geomagnetic gradient correction coil 7 that operate as coils for applying the static magnetic field and the gradient magnetic field, respectively, and outputs the current when measuring an MR image. to the coil power supply 5. That is, the control device 4 determines the current to be applied to the geomagnetism correction coil 6 so as to apply a magnetic field in the X-axis direction of a predetermined strength (eg, 7 mT) to the subject's head as a static magnetic field. In addition, the control device 4 selectively determines the X-axis direction magnetic field gradient (dBx/dX), the Y-axis direction magnetic field gradient (dBx/dY), and the Z-axis direction magnetic field gradient (dBx/dZ) as the gradient magnetic field. , determine the current to be applied to the geomagnetic gradient correction coil 7 . This makes it possible to determine the slicing position in the MR image and encode the position within the slice plane by phase encoding and frequency encoding. Note that the control device 4 outputs a control signal so as not to supply current to the fluctuating magnetic field correction coil 8 and the fluctuating magnetic field gradient correction coil 9 that remove low-frequency noise during MR image measurement.

Furthermore, when measuring an MR image, the control device 4 outputs to the excitation coil controller 15 a control signal for controlling the power supplied to the transmission coil 21, thereby controlling a predetermined frequency (for example, when the strength of the static magnetic field is A transmission pulse of approximately 300 kHz for 7 mT) is controlled to irradiate the subject's head. As a result, the protons on the slice plane (the plane selected by the static magnetic field and the gradient magnetic field) resonate and the spins are tilted. After that, the control device 4 turns off the power of the transmission coil 21 . As a result, an MR image can be obtained by measuring how the spin returns based on the output of the OPM module 23 . More specifically, the control device 4 uses a known spin echo sequence, gradient echo sequence, or the like to encode the position with frequency and phase, measure nuclear magnetic resonance signals from protons, and use the fast Fourier transform. to convert the measurement result into an MR image.

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 excitation coil controller 15 is electrically connected to the transmission coil 21 and supplies power to the transmission coil 21 according to the control signal output from the control device 4 so as to irradiate transmission pulses of a predetermined frequency.

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 directions of the magnetic field are, for example, the X-axis direction, the Y-axis direction, and the Z-axis direction. 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 geomagnetism correction coil 6 also serves as a static magnetic field coil for generating a static magnetic field in the X-axis direction during MR image measurement. The geomagnetism correction coil 6 generates a static magnetic field with a predetermined intensity according to the current supplied from the coil power supply 5 .

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 opposite direction to the gradient at the position of the photoexcited magnetic sensor 1A and of the same magnitude according to the current supplied from the coil power supply 5. FIG. The directions of the magnetic field are, for example, the X-axis direction, the Y-axis direction, and the Z-axis direction. The gradient at the position of the photoexcited magnetic sensor 1A is canceled by a magnetic field of opposite direction and similar magnitude generated by the geomagnetic gradient correction coil 7. FIG. Thus, the geomagnetic gradient correction coil 7 corrects the gradient at the position of the optically excited magnetic sensor 1A.

The geomagnetic gradient correction coil 7 also serves as a gradient magnetic field coil for generating a gradient magnetic field during MR image measurement. The geomagnetic gradient correction coil 7 generates a gradient magnetic field having selective gradients in the X-axis direction, Y-axis direction, and Z-axis direction according to the current supplied from the coil power supply 5 .

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 directions of the magnetic field are, for example, the X-axis direction, the Y-axis direction, and the Z-axis direction. 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 is incident on each of the plurality of optically excited magnetic sensors 1A and 23A 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 and 23A through fiber branching.

The amplifier 12A 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 the amplified signal to the control device 4. FIG.

The amplifier 12B is a device or circuit that amplifies the signal of the output result from the OPM module 23 (specifically, the readout circuit 23C) and outputs it to the control device 4. FIG.

The heater controller 13 is a temperature control device connected to heaters for heating the cells of the photoexcited magnetic sensor 1A and the photoexcited magnetic sensor 23A, and thermocouples (not shown) for measuring the temperature of each 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 includes OPM modules 1 and 23, a transmission coil 21, a reception coil 22, an output coil 24, a correction magnetic sensor 2, a non-magnetic frame 3, a geomagnetic correction coil 6, a geomagnetic gradient correction coil 7, and a fluctuating magnetic field correction coil 8. , and the fluctuating magnetic field gradient correction coil 9 . The electromagnetic shield 14 can prevent noise in the 300 kHz band, which is the measurement frequency, from entering the receiving coil 22 and increasing the noise during MR image measurement. In addition, it is possible to prevent high-frequency noise from entering the optically excited magnetic sensor 1A and destabilizing its operation during brain magnetic field measurement.

Next, a brain measurement method using the brain measurement device M1 according to the embodiment will be described with reference to FIGS. 4 and 5. FIG. 4 and 5 are flowcharts showing the operation of the brain measurement device M1.

First, when the brain magnetic field measurement is started with the non-magnetic frame 3 worn on the subject, the correction magnetic sensor 2 measures the 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 7 so as to generate a magnetic field of the same magnitude and in the opposite direction to the gradient at the position of the optically excited magnetic sensor 1A. Determine the current for 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 gradient at the position of the photoexcited magnetic sensor 1A is canceled by a magnetic field of opposite direction and similar 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). The control device 4 outputs the acquired measurement result to a predetermined output destination. The predetermined output destination may be a storage device such as a memory or a hard disk of the control device 4, an output device such as a display, or an external device such as a terminal device connected via a communication interface. 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.

Referring to FIG. 5, when measurement of MR images is started with the non-magnetic frame 3 still attached to the subject, the control device 4 supplies current to the geomagnetism correction coil 6 for applying the static magnetic field. is determined, and a control signal is output to the coil power supply 5 to control the generation of the static magnetic field in the X-axis direction in the subject's head (step S20). Next, the control device 4 determines the current to be supplied to the geomagnetic gradient correction coil 7 for generating the gradient magnetic field, and outputs a control signal to the coil power supply 5 to generate the X-axis direction magnetic field gradient (dBx/dX). is controlled (step S21). At the same time, the control device 4 outputs a control signal for controlling the power supplied to the transmission coil 21 to the excitation coil controller 15, and controls the subject's head to be irradiated with the transmission pulse (step S22). This excites protons in a predetermined slice plane.

Furthermore, the control device 4 determines the current to be supplied to the geomagnetic gradient correction coil 7 for generating the gradient magnetic field, and outputs a control signal to the coil power supply 5, thereby controlling the Y-axis direction magnetic field gradient (dBx/ dY) is controlled (step S23). Phase encoding is thereby performed. Then, the control device 4 determines the current to be supplied to the geomagnetic gradient correction coil 7 for generating the gradient magnetic field, and outputs a control signal to the coil power supply 5 so that the Z-axis direction magnetic field gradient (dBx/ dZ) is controlled (step S24). Thereby, frequency encoding is performed.

At the same time, the OPM module 23 detects nuclear magnetic resonance signals from protons via the receiving coil 22 and the output coil 24 and outputs the detection results. Data is acquired (step S25). After that, the controller 4 determines whether to acquire nuclear magnetic resonance signal data for another slice plane (step S26). As a result of the determination, if nuclear magnetic resonance signal data regarding another slice plane is to be acquired ("YES" in step S26), the process returns to step S21. On the other hand, if the nuclear magnetic resonance signal data for other slice planes are not to be acquired ("NO" in step S26), the nuclear magnetic resonance signal data acquired so far are Fourier transformed to acquire an MR image (step S27). . The control device 4 outputs the acquired MR image to a predetermined output destination. The predetermined output destination may be a storage device such as a memory or a hard disk of the control device 4, an output device such as a display, or an external device such as a terminal device connected via a communication interface.

FIG. 6 is a schematic diagram showing the configuration of a brain measurement device M2 according to another embodiment. The brain measurement device M2 differs from the brain measurement device M1 in that the receiving coil 22 is omitted. Further, the brain measurement device M2 includes a transmission/reception switch SW. In the brain measurement device M2, the transmission coil 21A is a transmission/reception coil that serves both as a transmission coil for transmitting transmission pulses and as a reception coil for detecting nuclear magnetic resonance signals. That is, the transmission coil 21A further has a role as the reception coil 22. FIG.

The transmission/reception switch SW is electrically connected to the excitation coil controller 15 and the transmission coil 21A via wiring that connects the excitation coil controller 15 and the transmission coil 21A. The transmission/reception switch SW is also electrically connected to the output coil 24 via wiring. The transmission/reception switch SW switches the connection destination of the transmission coil 21A between the excitation coil controller 15 and the output coil 24 . Specifically, when the transmission/reception switch SW is switched to the excitation coil controller 15 side, the transmission/reception switch SW electrically connects the excitation coil controller 15 and the transmission coil 21A. On the other hand, when the transmission/reception switch SW is switched to the output coil 24 side, the transmission/reception switch SW electrically connects the transmission coil 21A and the output coil 24 . The setting of the transmission/reception switch SW is switched by the control device 4 .

When the transmission/reception switch SW is switched to the excitation coil controller 15 side, the excitation coil controller 15 is electrically connected to the transmission coil 21A via the transmission/reception switch SW. The excitation coil controller 15 supplies power (current C1) to the transmission coil 21A according to the control signal output from the control device 4 so as to irradiate a transmission pulse of a predetermined frequency. After that, the control device 4 turns off the power of the transmission coil 21A and switches the transmission/reception switch SW to the output coil 24 side.

When the transmission/reception switch SW is switched to the output coil 24 side, the transmission coil 21A is electrically connected to the output coil 24 via the transmission/reception switch SW. The transmission coil 21A detects a proton nuclear magnetic resonance signal and converts it into a current C2. The transmission coil 21A outputs the current C2 to the output coil 24. FIG. The output coil 24 receives the current C2 from the transmission coil 21A, converts the current C2 into a magnetic signal again, and outputs the magnetic signal.

FIG. 7 is a schematic diagram showing the configuration of a brain measurement device M3 according to another embodiment. The brain measurement device M3 includes a transmission coil 21B as a transmission/reception coil instead of the transmission coil 21A in the brain measurement device M2. The transmission coil 21B is spirally formed and arranged so as to surround the object to be measured. The transmission coil 21B is fixed on the subject's scalp side within the non-magnetic frame 3, for example. The transmission coil 21B has the same function as the transmission coil 21A in the brain measurement device M2.

Next, a brain measurement method using the brain measurement device M2 or M3 according to the embodiment will be described with reference to FIG. FIG. 8 is a flow chart showing the operation of the brain measurement device M2 or M3. Since the operation of the brain measurement device M2 or M3 when measuring the brain magnetic field is the same as that of the brain measurement device M1, the description is omitted. Also, only points different from the operation of the brain measurement device M1 will be described.

Simultaneously with the processing of step S21, the control device 4 switches the transmission/reception switch SW to the excitation coil controller 15 side, outputs a control signal for controlling the power (current C1) supplied to the excitation coil controller 15 for transmission and reception, Control is performed to irradiate the subject's head with the transmission pulse (step S32). This excites protons in a predetermined slice plane.

Simultaneously with the processing of step S24, the control device 4 switches the transmission/reception switch SW to the output coil 24 side. From the OPM module 23, the detection result of the nuclear magnetic resonance signal from protons is output via the transmission/reception coil and the output coil 24, and the controller 4 accordingly acquires the data of the nuclear magnetic resonance signal (step S35). ).
[Effect]
Next, the effects of the brain measurement device according to the above-described embodiment will be described.

According to the brain measurement devices M1, M2, and M3 according to the present embodiment, the geomagnetism and the varying magnetic field are measured at respective positions of the plurality of optically-excited magnetic sensors 1A that measure brain magnetic fields. When the brain magnetic field is measured, the current flowing through the correction coil is controlled based on the measured value of the geomagnetism and the measured value of the fluctuating magnetic field, and a magnetic field is generated in the correction coil. As a result, the geomagnetism and the fluctuating magnetic field are corrected by the magnetic fields generated in the correction coils at the positions of the plurality of optically excited magnetic sensors 1A. By correcting the geomagnetism and the fluctuating magnetic field at the positions of the plurality of optically-excited magnetic sensors 1A, the plurality of optically-excited magnetic sensors 1A can measure brain magnetic fields while avoiding the effects of the geomagnetism and the fluctuating magnetic field.

On the other hand, according to the above aspect or another aspect, during measurement of an MR image, currents flowing through the geomagnetic correction coil 6 (static magnetic field coil) and the geomagnetic gradient correction coil 7 (gradient magnetic field coil) are controlled to generate a static magnetic field. A magnetic field and a gradient magnetic field are applied and nuclear magnetic resonance signals produced by transmission of the transmit pulse are detected. As a result, an MR image can be measured based on the output of the transmission/reception coil.

According to such a brain measurement device and brain measurement method, magnetoencephalography and MRI measurement can be efficiently realized using the same device. In particular, in MRI measurement, since a photoexcited magnetic sensor is used, it is possible to adjust a wider frequency band with higher sensitivity compared to SQUID, so there are few restrictions on the strength of the static magnetic field to be applied, that is, the resonance frequency of protons. A pre-polarization coil, which is necessary because the SQUID operates only at a low resonance frequency, that is, a low static magnetic field, is unnecessary, and a coolant such as liquid helium, which is necessary when using the SQUID, is also unnecessary. Furthermore, since the frequency of signals measured in MRI is relatively high, a magnetic shield room for reducing magnetic noise during MRI measurement and brain magnetic field measurement is not required. As a result, it is possible to reduce the size and cost of the device. In addition, since the time required for prepolarization is about the same as the measurement time, the measurement time can also be shortened to 1/2 in this embodiment.

Furthermore, in this embodiment, the static magnetic field can be easily turned on/off by turning on/off the current flowing through the geomagnetism correction coil 6, so that brain magnetic field measurement and MRI measurement can be switched in a short time. As a result, brain magnetic field measurement and MRI measurement can be sequentially performed on the same subject using the same apparatus, so registration errors in both measurement results can be reduced.

Thus, according to this embodiment, MRI measurement can be performed in a low magnetic field, so a special room is not required, and T1 contrast can be enhanced. Moreover, by using the fluctuating magnetic field correction coil 8, there is no need to perform magnetoencephalography in a magnetically shielded room. Therefore, the same apparatus can be used for magnetoencephalography and MRI, and both measurements can be performed sequentially while the subject is sitting on a chair or the like. In addition, the cost of the device can be reduced, and measurement can be performed while the subject is in a vehicle or the like. As a result, it can contribute to the diagnosis of mental disorders such as depression and schizophrenia, and neurodegenerative diseases such as dementia.

Here, the brain measurement device M1 uses a geomagnetic correction coil 6 for applying a static magnetic field and a geomagnetic gradient correction coil 7 for applying a gradient magnetic field. As a result, the geomagnetism correction coil for magnetoencephalography measurement and the MRI measurement coil can be used in common, so that the apparatus can be further miniaturized and further reduced in cost.

In addition, in the present embodiment, the geomagnetism and the varying magnetic field at the positions of the plurality of optically excited magnetic sensors 1A are canceled out during magnetoencephalography measurement, so that the plurality of optically excited magnetic sensors 1A are reliably free from the influence of the geomagnetism and the influence of the varying magnetic field. Brain magnetic field can be measured in the avoidance state. As a result, brain magnetic fields can be measured with high accuracy without using a magnetically shielded room. Such an effect can be realized even if the subject's head moves.

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. In such a configuration, the geomagnetism correction coil 6 and the static magnetic field coil can be used in common depending on the situation, and in this case, further miniaturization and further cost reduction of the device are possible. According to such a configuration, brain magnetic fields can be measured with high accuracy without using a magnetically shielded room.

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 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 such a configuration, the geomagnetic gradient correction coil 7 and the gradient magnetic field coil can be shared depending on the case, so in this case, further miniaturization and further cost reduction of the device are possible. In addition, uniform magnetic field correction (zero-order correction) is performed by controlling the current to the correction coil, and the gradient of the geomagnetism considering the difference in the position of each optically excited magnetic sensor 1A by controlling the current to the geomagnetic gradient correction coil 7. 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 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 varying magnetic field, the controller 4 may determine the current to the varying magnetic field gradient correction coil 9 so as to generate a magnetic field that cancels the gradient of the varying magnetic field. In this case, uniform fluctuation magnetic field correction (zero-order correction) is performed by controlling the current to the correction coil, and furthermore, by controlling the current to the fluctuation magnetic field gradient correction coil 9, the difference in the position of each photoexcited magnetic sensor 1A is taken into consideration. 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 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 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 brain measurement device M1 has a transmission coil 21 that transmits transmission pulses and a reception coil 22 that detects nuclear magnetic resonance signals. In this case, for example, the receiving coil 22 can be arranged at a location close to the object to be measured, and the transmitting coil 21 can be arranged at a different location from the receiving coil 22, thereby improving the degree of freedom in design. Also, when a plurality of small receiving coils 22 are arranged to surround the object to be measured, the sensitivity of the receiving coils 22 can be improved and noise can be reduced.

The transmitting/receiving coils of the brain measurement devices M2 and M3 serve both as coils for transmitting transmission pulses and as coils for detecting nuclear magnetic resonance signals. In this case, it is possible to further reduce the size and cost of the device.

The transmitting/receiving coil (transmitting coil 21B) is spirally formed and arranged so as to surround the object to be measured. In this case, since the transmitting/receiving coil can be placed near the object to be measured, the accuracy of MRI measurement can be improved.

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 brain measuring device M1 is electrically connected to the transmitting coil 21, and the brain measuring devices M2 and M3 are electrically connected to the transmitting/receiving coils (transmitting coils 21A and 21B, respectively). It further comprises an output coil 24 for output and another optically excited magnetic sensor 23A for detecting the magnetic signal output by the output coil 24 . The controllers 4 of the brain measuring devices M1, M2, M3 generate MR images based on magnetic signals detected by another optically-excited magnetic sensor 23A. According to such a configuration, the signal can be received by the separate photoexcited magnetic sensor 23A having a high sensitivity of fT order, so the accuracy of MR image measurement can be improved. In addition, since another photoexcitation magnetic sensor 23A is arranged at a position away from the transmission coil to which the static magnetic field of mT order is applied, it is possible to adjust the sensitivity band of the sensor without being affected by the static magnetic field. be.

A plurality of optically-excited magnetic sensors 1A are configured to be applied with a bias magnetic field so as to have sensitivity to frequencies within the range of 0 to 200 Hz. Another optically excited magnetic sensor 23A is configured to be biased magnetically sensitive to frequencies in the range of 20 kHz to 500 kHz. With such a configuration, the sensitivity of brain magnetic field measurement can be enhanced, and at the same time, the accuracy of MRI measurement can be enhanced.

Moreover, the plurality of optically excited magnetic sensors 1A, the plurality of correction magnetic sensors 2, and the receiving coil 22 are fixed to a helmet-shaped non-magnetic frame 3 that is worn on the subject's head. According to such a configuration, the non-magnetic frame 3 attached to the head and the correction magnetic sensors 2 and the receiving coils 22 fixed to the non-magnetic frame 3 move according to the movement of the subject's head. Even when the subject's head moves, correction of geomagnetism and fluctuating magnetic fields, brain magnetic field measurement, and MRI measurement at the positions of the plurality of optically-excited magnetic sensors 1A can be performed appropriately. As a result, registration errors in both measurements can be suppressed.

Furthermore, the brain measurement devices M1, M2, and M3 are further provided with an electromagnetic shield 14 for shielding high-frequency electromagnetic noise. According to such a configuration, it is possible to prevent high-frequency electromagnetic noise, which cannot be measured by a magnetoencephalograph, from entering the plurality of optically-excited magnetic sensors 1A. As a result, brain magnetic field measurement can be stably operated by the plurality of optically-excited magnetic sensors 1A. At the same time, it is possible to prevent noise in the 300 kHz band, which is the measurement frequency of MRI, from entering the receiving coil 22 and increasing the noise in the MRI measurement.
[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.

Although the geomagnetism correction coil 6 has been described as having a pair of geomagnetism correction coils 6A and 6B, it may be arranged as a three coil system for each OPM module 1 (optically excited 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 geomagnetism at the position of the optically excited magnetic sensor 1A. , determines the current for the geomagnetic correction coil 6 . The control device 4 outputs to the coil power supply 5 a control signal corresponding to the determined current for each of the geomagnetism correction coils 6 arranged as three coil systems. According to such a configuration, it is possible to relatively reduce power consumption for correction of geomagnetism.

The fluctuating magnetic field correction coil 8 has been described as having a pair of fluctuating magnetic field correction coils 8A and 8B, but may be arranged as a three coil system for each OPM module 1 (optically excited 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 for each of the fluctuating magnetic field correction coils 8 arranged as the three coil systems. According to such a configuration, the power consumption for correcting the fluctuating magnetic field can be made relatively small.

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.

Further, when measuring MR images, the control device 4 may set the current flowing through the geomagnetic gradient correction coil 7 so as to correct the gradient related to geomagnetism, or set the current flowing through the geomagnetic gradient correction coil 7 so as not to correct the gradient related to geomagnetism. May be set. Since the magnitude of the gradient magnetic field is about several μT, which is lower than that of the static magnetic field by about two orders of magnitude, high accuracy can be maintained without correction when acquiring an MR image.

Further, the brain measurement device M1 of the above embodiment may omit the optically excited magnetic sensor 23A, and may be configured such that the output from the receiving coil 22 is directly detected by the control device 4 via an amplifier. .

Further, the optically excited magnetic sensor 1A is not limited to a pump & probe type that uses pump light and probe light, and may be a zero-field type optically excited magnetic sensor that uses circularly polarized light that serves as pump light and probe light. . In this zero-field type, the cell is irradiated with light and a periodic bias magnetic field is applied, the magnetic field is lock-in detected, and the deviation from the zero magnetic field can be measured as the brain magnetic field.

Further, in the brain measurement device M1 of the above embodiment, the position of the non-magnetic frame 3 may be optically measurable. For example, markers attached to the lower end of the non-magnetic frame 3 at 120-degree intervals and a camera facing the non-magnetic frame 3 may be provided so that the positional change of the helmet can be measured using the camera. This measurement result can be used at the time of MRI measurement. For example, the controller 4 can use the measurement results to calculate the relative positions of the geomagnetic gradient correction coil 7 and the receiving coil 22 to calibrate the MR image. As a result, high-resolution MR images can be acquired even if the subject's head moves. This configuration is useful for MRI measurement of a subject such as an infant whose head is difficult to fix. In the magnetoencephalography measurement, even if the position of the head is shifted, the magnetic field at the position of the optically excited magnetic sensor 1A is corrected to be zero. Although the need for measurement is low, the positional information of the non-magnetic frame 3 may be used for zero magnetic field generation.

9 to 11 are diagrams showing brain measurement devices M4 to M6 according to modifications. The brain measurement devices M4 to M6 differ from the brain measurement devices M1 to M3 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. That is, the geomagnetism correction coil 6 may further serve as the fluctuating magnetic field correction coil 8 . Similarly, in the geomagnetic gradient correction coil 7, the magnetic field gradient may be corrected by DC current, and the varying magnetic field gradient may be corrected by superimposing an AC current component. That is, the geomagnetic gradient correction coil 7 may further serve as the fluctuating magnetic field gradient correction coil 9 . According to such brain measurement devices M4 to M6, for the same reason as the brain measurement devices M1 to M3, magnetoencephalography and MRI measurement can be efficiently realized using the same device. 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.

M1 to M6...brain measuring device, 1A, 23A...light-excited magnetic sensor, 2...correction magnetic sensor, 3...non-magnetic frame, 4...control device, 5...coil power supply, 6...geomagnetic correction coil, 7...geomagnetic gradient correction Coils 8... fluctuating magnetic field correction coil 9... fluctuating magnetic field gradient correction coil 14... electromagnetic shield 21, 21A, 21B... transmission coil, 22... reception coil, 24... output coil.

Claims (22)

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 magnetoencephalograph having a correction coil for correcting the geomagnetism and the fluctuating magnetic field;
a static magnetic field coil for applying a static magnetic field;
a gradient magnetic field coil for applying a gradient magnetic field;
an MRI apparatus having a transmitting/receiving coil for transmitting a transmission pulse of a predetermined frequency and detecting a nuclear magnetic resonance signal generated by the transmission of the transmission pulse;
when measuring the brain magnetic field, controlling the current supplied to the correction coil based on the measured values of the geomagnetism and the measured values of the varying magnetic field by the plurality of correction magnetic sensors;
a control device that controls currents supplied to the static magnetic field coil and the gradient magnetic field coil to control the static magnetic field and the gradient magnetic field when measuring an MR image, and generates an MR image based on the output of the transmission/reception coil; ,
A brain measurement device with 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 brain measurement device 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 brain measuring device according to claim 1 or 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 brain measurement device according to any one of claims 1 to 3. 5. The brain measurement device according to claim 1, wherein said correction coil is composed of a pair of coils arranged with said plurality of optically excited magnetic sensors interposed therebetween. 6. The correction magnetic sensor according to any one of claims 1 to 5, 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. Brain measuring device. The brain measurement device according to any one of claims 1 to 6, wherein said transmission/reception coil includes a transmission coil for transmitting said transmission pulse and a reception coil for detecting said nuclear magnetic resonance signal. 7. The brain measurement device according to claim 1, wherein said transmission/reception coil serves both as a coil for transmitting said transmission pulse and as a coil for detecting said nuclear magnetic resonance signal. 9. The brain measurement device according to claim 8, wherein said transmitting/receiving coil is spirally formed and arranged so as to surround an object to be measured. The brain measurement device according to any one of claims 1 to 9, wherein said plurality of optically-excited magnetic sensors are axial gradiometers having a measurement region and a reference region coaxially and in a direction perpendicular to the object to be measured. an output coil that is electrically connected to the transmission/reception coil and that outputs a magnetic signal based on the current flowing through the transmission/reception coil;
and another optically excited magnetic sensor that detects the magnetic signal output by the output coil,
The controller generates the MR image based on the magnetic signal detected by the another optically-excited magnetic sensor.
The brain measurement device according to any one of claims 1 to 10. The plurality of optically excited magnetic sensors are configured to be applied with a bias magnetic field so as to be sensitive to frequencies in the range of 0 to 200 Hz,
wherein said another optically excited magnetic sensor is configured to have a bias magnetic field applied such that it is sensitive to frequencies included in the range of 20 kHz to 500 kHz;
The brain measurement device according to claim 11. 8. The brain measurement device according to claim 7, wherein said plurality of optically-excited magnetic sensors, said plurality of correction magnetic sensors, and said receiving coil are fixed to a helmet-shaped non-magnetic frame worn on the subject's head. . The brain measurement device according to any one of claims 1 to 12, further comprising an electromagnetic shield for shielding high-frequency electromagnetic noise. 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 magnetoencephalograph having a correction coil for correcting the geomagnetism and the fluctuating magnetic field;
a static magnetic field coil for applying a static magnetic field;
a gradient magnetic field coil for applying a gradient magnetic field;
and a transmission/reception coil for transmitting a transmission pulse of a predetermined frequency and detecting a nuclear magnetic resonance signal generated by the transmission of the transmission pulse, and an MRI apparatus comprising:
when measuring the brain magnetic field, controlling the current supplied to the correction coil based on the measured values of the geomagnetism and the measured values of the varying magnetic field by the plurality of correction magnetic sensors;
When measuring an MR image, controlling the current supplied to the static magnetic field coil and the gradient magnetic field coil to control the static magnetic field and the gradient magnetic field, and generating an MR image based on the output of the receiving coil;
Brain measurement method. 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,
Based on the measured value of the geomagnetism, a current for the geomagnetism correction coil is determined so as to generate a magnetic field that cancels the geomagnetism, and based on the measured value of the varying magnetic field, a magnetic field that cancels the varying magnetic field is generated. determining a current to the fluctuating magnetic field correction coil;
The brain measurement method according to claim 15. The correction coil has a geomagnetic gradient correction coil for correcting the gradient of the geomagnetism,
determining a current to the geomagnetic gradient correction coil based on the measured value of the geomagnetism to generate a magnetic field that cancels the gradient of the geomagnetism;
The brain measurement method according to claim 15 or 16. The correction coil has a variable magnetic field gradient correction coil for correcting the gradient of the variable magnetic field,
determining 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 brain measurement method according to any one of claims 15-17. The correction magnetic sensor according to any one of claims 15 to 18, 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. Brain measurement method. The brain measurement method according to any one of claims 15 to 19, wherein said transmission/reception coil has a transmission coil for transmitting said transmission pulse and a reception coil for detecting said nuclear magnetic resonance signal. The brain measurement method according to any one of claims 15 to 19, wherein said transmission/reception coil serves both as a coil for transmitting said transmission pulse and as a coil for detecting said nuclear magnetic resonance signal. The brain measurement method according to any one of claims 14-17. 22. The brain measurement method according to claim 21, wherein said transmitting/receiving coil is spirally formed and arranged so as to surround an object to be measured.

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