Brain measurement device and brain measurement method

Abstract

A brain measuring apparatus (M1) has a magnetoencephalograph having light-excited magnetic sensors (1A), magnetic sensors (2) measuring a static magnetic field of positions of the light-excited magnetic sensors (1A), and a correction coil (16) for correcting the static magnetic field, an MRI apparatus having a permanent magnet for applying a static magnetic field, a gradient magnetic field coil (8) for applying a gradient magnetic field, a transmission coil (21) for transmitting a transmission pulse, and a reception coil (22) for detecting a nuclear magnetic resonance signal produced by transmission of the transmission pulse, and a control apparatus (5) which, at the time of measurement of a magnetoencephalograph, controls a current supplied to the correction coil (16) based on a measurement value of the magnetic sensors (2) so as to cancel a static magnetic field related to the geomagnetism of each position of the light-excited magnetic sensors (1A) and a static magnetic field applied by the permanent magnet, and, at the time of measurement of an MR image, controls a current supplied to the gradient magnetic field coil (8) and the gradient magnetic field, and generates an MR image based on an output of the reception coil (22).

Description

Technical Field

[0001] One aspect of this disclosure relates to a brain measurement device and a brain measurement method. Background Technology

[0002] In the past, superconducting quantum interference devices (SQUIDs) were used as magnetoencephalometers (MEGs) to measure the minute magnetic fields in the brain. In recent years, MEGs using optically excited magnetometers instead of SQUIDs have been studied. Optically excited magnetometers measure minute magnetic fields by using the spin polarization of alkali metal atoms excited by optical pumping. For example, Patent Document 1 discloses a MEG using an optically pumped magnetometer. Furthermore, there has been recent research on using SQUIDs to fuse MEGs with MRI (Magnetic Resonance Imaging) (see Non-Patent Document 1 below).

[0003] Patent Document 1: Japanese Patent No. 5823195

[0004] Non-licensed reference 1: “SQUIDs in biomagnetism: a roadmap towards improved healthcare”, Superconductor Sci. and Technol. 29(2016)113001(30pp) Summary of the Invention

[0005] To avoid the influence of magnetic fields stronger than the brain's magnetic field, measurements using a magnetoencephalometer (MEG) must be performed under conditions that minimize the ambient magnetic field, which includes the Earth's magnetic field. Conversely, measurements using an MRI must be performed under conditions that generate static and tilting magnetic fields. In realizing a device that integrates the MEG and MRI equipment, the aim is to effectively reduce the ambient magnetic field and apply static and tilting magnetic fields.

[0006] In view of the above actual situation, this embodiment was made, and its purpose is to provide a brain measurement device and brain measurement method, which can effectively realize brain magnetic measurement and MRI measurement.

[0007] One embodiment of the brain measurement device includes: a magnetoencephalometer having: a plurality of photoexcited magnetic sensors for measuring the brain magnetic field, a plurality of static magnetic field correction magnetic sensors for measuring the static magnetic field at each location of the plurality of photoexcited magnetic sensors, and a static magnetic field correction coil for correcting the static magnetic field; an MRI device having: a permanent magnet for applying the static magnetic field, a tilting magnetic field coil for applying the tilting magnetic field, a transmitting coil for transmitting a transmitting pulse at a predetermined frequency, and a receiving coil for detecting the magnetic resonance signal generated by the transmission of the transmitting pulse; and a control device that, during the measurement of the brain magnetic field, controls the current supplied to the static magnetic field correction coil based on the measurement values ​​of the plurality of static magnetic field correction magnetic sensors, and operates in a manner that cancels the geomagnetically related static magnetic field at each location of the plurality of photoexcited magnetic sensors and the static magnetic field applied by the permanent magnet, and during the measurement of MR images, controls the current supplied to the tilting magnetic field coil and controls the tilting magnetic field, and generates MR images based on the output of the receiving coil.

[0008] Alternatively, another embodiment of the brain measurement method involves a brain measurement method using a magnetoencephalometer (MEG) and an MRI apparatus. The MEG includes: multiple photoexcited magnetic sensors for measuring the brain magnetic field; multiple static magnetic field correction magnetic sensors for measuring the static magnetic field at each location of the multiple photoexcited magnetic sensors; and a static magnetic field correction coil for correcting the static magnetic field. The MRI apparatus includes: a permanent magnet for applying the static magnetic field; a tilting magnetic field coil for applying the tilting magnetic field; a transmitting coil for transmitting a transmitting pulse at a predetermined frequency; and a receiving coil for detecting the magnetic resonance signal generated by the transmission of the transmitting pulse. During the measurement of the brain magnetic field, the current supplied to the static magnetic field correction coil is controlled based on the measurement values ​​of the multiple static magnetic field correction magnetic sensors, and the operation is performed in a manner that cancels the geomagnetically related static magnetic field at each location of the multiple photoexcited magnetic sensors and the static magnetic field applied by the permanent magnet. During the measurement of the MR image, the current supplied to the tilting magnetic field coil is controlled and the tilting magnetic field is controlled, and the MR image is generated based on the output of the receiving coil.

[0009] According to one or other methods described above, the static magnetic field at each location of multiple photomagnetic sensors used to measure the brain magnetic field can be measured. Furthermore, during the measurement of the brain magnetic field, based on multiple measured values ​​of the static magnetic field, the current flowing through the static magnetic field correction coil is controlled to generate a magnetic field in each coil. At the locations of the multiple photomagnetic sensors, the magnetic field generated by the static magnetic field correction coil cancels out the geomagnetic-related static magnetic field and the static magnetic field applied by the permanent magnet. As a result, by correcting the static magnetic field at the locations of the multiple photomagnetic sensors, the multiple photomagnetic sensors can measure the brain magnetic field while avoiding the influence of ambient magnetic fields. In this case, the geomagnetic-related static magnetic field and the static magnetic field applied by the permanent magnet can be corrected together by the static magnetic field correction coil.

[0010] On the other hand, according to one or other methods described above, during MR image measurement, a tilted magnetic field is applied by controlling the current flowing through the tilted magnetic field while a static magnetic field is applied using a permanent magnet, and the nuclear magnetic resonance signal generated by transmitting a transmission pulse is detected by a receiving coil. As a result, the MR image can be measured based on the output of the receiving coil. In particular, because a static magnetic field is generated using a permanent magnet, compared to a structure that generates a static magnetic field using an electromagnet, it is possible to achieve miniaturization of the device while reducing power consumption.

[0011] Based on this brain measurement device and method, both magnetoencephalography (MEG) and MRI measurements can be efficiently performed using the same device. In particular, during MRI measurements, superconducting coils are unnecessary, as are magnetic shielding chambers for reducing magnetic noise during MEG measurements, and coolants such as liquid helium required when using SQUIDs are also eliminated, allowing for miniaturization and cost reduction. Furthermore, since MEG and MRI measurements can be performed sequentially on the same subject using the same device, registration errors between the two measurements can be reduced. Attached Figure Description

[0012] Figure 1 This is a schematic diagram showing the structure of the brain measurement device involved in the embodiment.

[0013] Figure 2 This is a schematic diagram showing the structure of the static magnetic field correction coil according to the embodiment.

[0014] Figure 3 This is a schematic diagram showing the structure of the OPM module 23 according to the embodiment.

[0015] Figure 4 This is a flowchart illustrating the operation of the brain measurement device involved in the embodiment.

[0016] Figure 5 This is a flowchart illustrating the operation of the brain measurement device involved in the embodiment. Detailed Implementation

[0017] In the following description, the methods for carrying out the invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals, and repeated descriptions are omitted.

[0018] Figure 1 This is a schematic diagram showing the structure of the brain measurement device M1 according to the embodiment. Figure 2This is a schematic diagram showing the structure of the static magnetic field correction coil 16 included in the brain measurement device M1. The brain measurement device M1 is a device for measuring the brain magnetic field and MR (Magnetic Resonance) images of a subject. The brain measurement device M1 includes: a magnetoencephalometer module, including: multiple OPM (optically pumped magnetometer) modules 1, multiple magnetic sensors for static magnetic field correction 2, multiple magnetic sensors for active shielding 3, a non-magnetic frame 4, the static magnetic field correction coil 16, and a pair of active shielding coils 9; and an MRI module, including: a pair of permanent magnets 7, a pair of tilting magnetic field coils 8, a transmitting coil 21, a receiving coil 22, an OPM module 23, and an output coil 24. In addition, the brain measurement device M1 includes: a control device 5, a coil power supply 6, a pump laser 10, a probe laser 11, amplifiers 12A and 12B, a heater controller 13, an electromagnetic shield 14, and a transmitting coil controller 15.

[0019] In the following description, the direction generally parallel to the central axis of the subject's head is defined as the Z-axis, and the directions perpendicular to the Z-axis and perpendicular to each other are defined as the X-axis and Y-axis.

[0020] OPM module 1 includes a photoexcited magnetic sensor 1A, a heat-insulating material 1B, and a readout circuit 1C. Multiple OPM modules 1 are arranged, for example, along the scalp at predetermined intervals.

[0021] The photo-induced magnetosensor 1A is a sensor that uses optical pumping to measure the brain's magnetic field and has a sensitivity of, for example, about 10 fT to 10 pT. A thermal insulation material 1B prevents thermal movement and heat transfer of the photo-induced magnetosensor 1A. A readout circuit 1C is a circuit that obtains the detection result of the photo-induced magnetosensor 1A. The photo-induced magnetosensor 1A excites the alkali metal by irradiating a pump light into a unit containing alkali metal vapor. The excited alkali metal is in a spin-polarized state, and when it receives magnetism, the tilt of the spin polarization axis of the alkali metal atoms changes according to the magnetism. This tilt of the spin polarization axis is detected by a probe light irradiated separately from the pump light. Furthermore, the photo-induced magnetosensor 1A is configured to be sensitive to magnetic fields with frequencies ranging from 0 to 200 Hz by applying a predetermined bias magnetic field to the irradiation direction of the pump light through a static magnetic field correction coil 16 provided for each OPM module 1. The readout circuit 1C receives the probe light passing through the alkali metal vapor via a photodiode and obtains the detection result. The reading circuit 1C outputs the detection result to the amplifier 12A.

[0022] The photoexcited magnetic sensor 1A can also be used as an axial gradiometer, for example. The axial gradiometer has a measurement region and a reference region coaxially arranged in a direction perpendicular to the subject's scalp (measurement site). The measurement region refers to the part of the axial gradiometer that is closest to the subject's scalp when measuring the brain magnetic field. The reference region refers to the part of the axial gradiometer that is at a predetermined distance (e.g., 3 cm) from the measurement region, relative to the direction away from the subject's scalp. The axial gradiometer outputs the respective results of measurements in the measurement region and the reference region to the amplifier 12A. Here, in the case of common-mode noise, this effect is shown in the respective output results of the measurement region and the reference region. Common-mode noise is removed by obtaining the difference between the output results of the measurement region and the output results of the reference region. By removing common-mode noise, for example, in the case of measurement in a magnetic noise environment of 1 pT, the photoexcited magnetic sensor 1A can obtain a sensitivity of approximately 10 fT / √Hz.

[0023] The magnetic sensor 2 for static magnetic field correction is a sensor that measures the combined magnetic field containing the static magnetic field related to the Earth's magnetism and the static magnetic field applied by the permanent magnet 7 at a position corresponding to the photo-excited magnetic sensor 1A, and is configured, for example, by a fluxgate sensor having a sensitivity of about 1 nT to 10 mT. The position corresponding to the photo-excited magnetic sensor 1A refers to the periphery (nearby) of the area where the photo-excited magnetic sensor 1A is located. The magnetic sensor 2 for static magnetic field correction can be set one-to-one with the photo-excited magnetic sensor 1A, or it can be set in a one-to-many manner (one magnetic sensor 2 for static magnetic field correction corresponds to multiple photo-excited magnetic sensors 1A). In addition to the static magnetic field, the magnetic sensor 2 for static magnetic field correction also measures the gradient magnetic field of the Earth's magnetism (hereinafter simply referred to as "gradient magnetic field") and outputs their measured values ​​to the control device 5. The measured values ​​of the magnetic sensor 2 for static magnetic field correction can be represented by a vector having direction and magnitude. The magnetic sensor 2 for static magnetic field correction can also continuously measure and output at predetermined time intervals.

[0024] The active shielding magnetic sensor 3 is a sensor that measures a changing magnetic field at a position corresponding to the photoexcited magnetic sensor 1A, and is configured, for example, by a photoexcited sensor having a sensitivity of approximately 100 fT to 10 nT, which is different from the photoexcited magnetic sensor 1A. The position corresponding to the photoexcited magnetic sensor 1A refers to the periphery (nearby) of the area where the photoexcited magnetic sensor 1A is located. The active shielding magnetic sensor 3 can be set one-to-one with the photoexcited magnetic sensor 1A, or it can be set in a one-to-many manner (one active shielding magnetic sensor 3 corresponds to multiple photoexcited magnetic sensors 1A). The active shielding magnetic sensor 3 measures the magnetic field as a noise (AC) component, for example, below 200 Hz, which is a changing magnetic field, and outputs the measured value to the control device 5. The measured value of the active shielding magnetic sensor 3 can be represented by a vector having direction and magnitude. The active shielding magnetic sensor 3 can also continuously measure and output at predetermined time intervals.

[0025] The non-magnetic frame 4 is a frame that covers the entire area of ​​the scalp of the subject, which is the object of the brain magnetic field measurement, and is made of a non-magnetic material such as graphite with a relative magnetic permeability close to 1 that does not interfere with the magnetic field distribution. The non-magnetic frame 4 can be, for example, a helmet-type frame that surrounds the entire area of ​​the subject's scalp and is worn on the subject's head. In the non-magnetic frame 4, multiple photoexcited magnetic sensors 1A are fixed close to the subject's scalp. In addition, in the non-magnetic frame 4, a static magnetic field correction magnetic sensor 2 is fixed so that the static magnetic field at each position of the multiple photoexcited magnetic sensors 1A can be measured, and an active shielding magnetic sensor 3 is fixed so that the changing magnetic field at each position of the multiple photoexcited magnetic sensors 1A can be measured. Since the deviation of the magnetic field strength of the changing magnetic field according to the position is smaller than that of the static magnetic field, the non-magnetic frame 4 can be fixed in such a way that the number of active shielding magnetic sensors 3 is less than the number of static magnetic field correction magnetic sensors 2.

[0026] Additionally, a receiving coil 22 for detecting nuclear magnetic resonance signals used for MR image measurement is fixed to the scalp side of the subject within the non-magnetic frame 4, where multiple photoexcited magnetic sensors 1A are located. This receiving coil 22 detects the nuclear magnetic resonance signal of protons (described later) and converts it into an electric current. To improve the detection sensitivity of the magnetic resonance signal, the receiving coil 22 is preferably positioned close to the scalp side of the subject near the photoexcited magnetic sensor 1A.

[0027] Additionally, around the OPM module 1 containing multiple photoexcited magnetic sensors 1A within the non-magnetic frame 4, a static magnetic field correction coil 16 is provided. During brain magnetic field measurement, this coil corrects the static magnetic field and applies a predetermined bias magnetic field to the photoexcited magnetic sensors 1A. The static magnetic field correction coil 16 is a coil system (e.g., a 3-axis Helmholtz coil or a planar coil system) that is orthogonal and can apply magnetic fields to three orthogonally arranged around it. Figure 2 As shown, the static magnetic field correction coil 16 specifically comprises coil systems 16X, 16Y, and 16Z. Coil systems 16X, 16Y, and 16Z are respectively arranged in a dashed configuration for each OPM module 1. As described above, coil systems 16X, 16Y, and 16Z are orthogonally and surrounding each other for each OPM module 1 (photoexcited magnetic sensor 1A). Coil system 16X is a coil used to correct the x-axis component of the static magnetic field. Similarly, coil systems 16Y and 16Z are coils used to correct the y-axis and z-axis components of the static magnetic field, respectively.

[0028] The static magnetic field correction coil 16 corrects the static magnetic field at the location of the photoexcitation magnetometer 1A and applies a predetermined bias magnetic field to the photoexcitation magnetometer 1A. The static magnetic field correction coil 16 generates a magnetic field based on the current supplied from the coil power supply 6 to cancel the static magnetic field. The coil system 16X, 16Y, and 16Z included in the static magnetic field correction coil 16 generates a magnetic field of the same magnitude and opposite direction to the electrostatic field at the location of the photoexcitation magnetometer 1A, based on the current supplied from the coil power supply 6. The direction of the magnetic field is, for example, the X-axis, Y-axis, and Z-axis. Furthermore, the static magnetic field correction coil 16 generates a predetermined bias magnetic field for the photoexcitation magnetometer 1A along the irradiation direction of the pump light, based on the current supplied from the coil power supply 6. The static magnetic field at the location of the photoexcitation magnetometer 1A is canceled by the opposite magnetic field of the same magnitude generated by the static magnetic field correction coil 16.

[0029] The transmitting coil 21 is a coil that irradiates an RF pulse (transmit pulse) of a specified frequency (e.g., about 300 kHz) onto the subject's head during MR image measurement. The transmitting coil 21 is, for example, positioned above the subject's head outside the non-magnetic frame 4.

[0030] The output coil 24 is electrically connected to both ends of the receiving coil 22 via a cable, and receives the current flowing through both ends of the receiving coil 22, converts the current back into a magnetic signal and outputs it.

[0031] Like OPM module 1, OPM module 23 includes a photoexcited magnetic sensor 23A, a heat-insulating material 23B, and a readout circuit 23C. OPM module 23, for example, is housed outside the non-magnetic frame 4, together with the output coil 24, within a magnetic shield 25 that shields against the static magnetic field described later. The magnetic shield 25 is made of a metal with a relative permeability greater than 1, such as μ metal.

[0032] The photoexcited magnetosensor 23A is a sensor that uses optical pumping to measure magnetic signals. Furthermore, the photoexcited magnetosensor 23A is configured to apply a predetermined bias magnetic field in the direction of the pump light to be sensitive to magnetic fields with frequencies ranging from 20 kHz to 500 kHz. For example, applying a bias magnetic field of approximately 40 μT provides sensitivity to a frequency of 300 kHz emitted by protons. The readout circuit 23C outputs the detection result from the photoexcited magnetosensor 23A to the amplifier 12B.

[0033] exist Figure 3 The diagram illustrates a specific example of the structure of the OPM module 23. The photoexcited magnetosensor 23A comprises: a strip-shaped unit 26 encapsulated with a gas containing an alkali metal whose polarization direction changes according to the measured magnetic field; a heater 27 that heats the entire unit 26 to a predetermined temperature (e.g., 180 degrees Celsius); a polarizing beam splitter 28; and a photodetector 29. In this unit 26, pump light L1 is introduced from the outside along its long side, and along a direction perpendicular to its length, corresponding to each of several (e.g., four equal parts) intersecting regions 26A, branches illuminate the probe light L2 from the outside. The probe light L2 passing through these intersecting regions 26A is detected by the polarizing beam splitter 28 and photodetector 29, which are respectively arranged corresponding to each intersecting region 26A. That is, the polarization beam splitter 28 separates the probe light L2 into two linearly polarized components that are orthogonal to each other, and the photodetector 29 uses two built-in PDs (photodiodes) to detect the intensity of the two linearly polarized components, and detects the magneto-optical angle of the probe light L2 based on the ratio of the detected intensities. In the OPM module 23, a circuit board 30 is also provided, and the readout circuit 23C in the circuit board 30 outputs the magneto-optical angle of the probe light L2 detected for each of the respective cross regions 26A.

[0034] Within the magnetic shield 25, the output coil 24 is fixed in a manner opposite to the intersection regions 26A of the units 26 of the OPM module 23 described above. With this structure, the magnetic signal Bout generated by the output coil 24 is detected based on the magneto-optical angle of the probe light L2, which varies according to the tilt of the spin polarization axis of the alkali metal. Here, in Figure 3In the example, the number of divisions in the intersection region 26A is set to 4, but it can be changed to any number. In addition, multiple units 26 can be set side by side, and the intersection regions 26A can also be arranged in two dimensions (e.g., 4×4=16).

[0035] When measuring the brain magnetic field, the control device 5 determines the current corresponding to each coil based on the measured values ​​output from the magnetic sensor 2 for static magnetic field correction and the magnetic sensor 3 for active shielding, and outputs a control signal for outputting the current to the coil power supply 6. The control device 5 determines the current to the static magnetic field correction coil 16 based on the measured values ​​of the multiple magnetic sensors 2 for static magnetic field correction, in a manner that generates a magnetic field to counteract the static magnetic field. Additionally, the control device 5 determines the current to the active shielding coil 9 based on the measured values ​​of the multiple magnetic sensors 3 for active shielding, in a manner that generates a magnetic field to counteract the changing magnetic field. The control device 5 outputs a control signal corresponding to the determined current to the coil power supply 6.

[0036] Specifically, based on the measurements of multiple magnetic sensors 2 for static magnetic field correction, the current to the static magnetic field correction coil 16 is determined by generating a magnetic field of the same magnitude and opposite direction to the static magnetic field at the location of the photo-excited magnetic sensor 1A. This can be achieved by measuring the values ​​of the magnetic sensors 2 for static magnetic field correction and the magnetic field strength at the location of the photo-excited magnetic sensor 1A. The control device 5 outputs a control signal (static magnetic field correction control signal) corresponding to the determined current of the static magnetic field correction coil 16 to the coil power supply 6.

[0037] Furthermore, the control device 5 determines the current to the active shielding coil 9 in such a way that the average value of the measurements from the plurality of active shielding magnetic sensors 3 is approximately zero (as a result, in a way that generates a magnetic field that is opposite in direction and of the same magnitude as the changing magnetic field at the position of the photoexcitation magnetic sensor 1A). The control device 5 outputs a control signal (changing magnetic field correction control signal) corresponding to the determined current of the active shielding coil 9 to the coil power supply 6.

[0038] Furthermore, the control device 5 uses the signal output from the amplifier 12A to obtain information related to the magnetic field detected by the photoexcited magnetometer 1A. When the photoexcited magnetometer 1A is an axial gradiometer, the control device 5 can also remove common-mode noise by obtaining the difference between the output of the measurement area and the output of the reference area. In addition, the control device 5 can also control the operation of the pump laser 10 and the probe laser 11, including the irradiation time and duration.

[0039] Furthermore, during MR image measurement, the control device 5 determines the current supplied to the tilted magnetic field coil 8 for applying the tilted magnetic field and outputs a control signal for the output current to the coil power supply 6. That is, the control device 5 selectively determines the magnetic field gradients (dBx / dX), (dBx / dY), and (dBx / dZ) along the X-axis, Y-axis, and Z-axis as the tilted magnetic field, and determines the current flowing through the tilted magnetic field coil 8. Therefore, the slice position in the MR image can be determined, and the position within the slice plane can be encoded using phase encoding and frequency encoding. Moreover, during MR image measurement, the control device 5 outputs a control signal without supplying current to the active shielding coil 9 for removing low-frequency noise.

[0040] Furthermore, during MR image measurement, the control device 5 controls the output of a control signal to the transmit coil controller 15 to control the power supplied to the transmit coil 21, thereby irradiating the subject's head with an RF pulse of a predetermined frequency (e.g., 300 kHz in the case of a static magnetic field strength of 7 mT). As a result, proton resonance and spin tilt occur in the slice plane (the plane selected by the static magnetic field and the tilting magnetic field). Subsequently, the control device 5 controls the power supply to the transmit coil 21 to be turned off. Thus, an MR image can be obtained by measuring the spin recovery morphology based on the output of the OPM module 23. More specifically, the control device 5 uses a known spin echo sequence or gradient echo sequence, etc., to encode the position by frequency and phase and measure the nuclear magnetic resonance signal from the protons, and converts the measurement result into an MR image using FFT.

[0041] The control device 5 is physically configured as a storage unit including a memory such as RAM and ROM, a processor (arithmetic circuit) such as a CPU, a communication interface, and a hard disk. Examples of related control devices 5 include personal computers, cloud servers, smartphones, and tablet computers. The control device 5 functions by having the CPU of the computer system execute programs stored in the memory.

[0042] The coil power supply 6 outputs a predetermined current to each of the static magnetic field correction coil 16, the tilted magnetic field coil 8, and the active shielding coil 9 according to the control signal output from the control device 5. Specifically, the coil power supply 6 outputs current to the static magnetic field correction coil 16 according to the control signal associated with the static magnetic field correction coil 16. The coil power supply 6 outputs current to the tilted magnetic field coil 8 according to the control signal associated with the active shielding coil 9.

[0043] The transmitting coil controller 15 is electrically connected to the transmitting coil 21 and supplies power to the transmitting coil 21 by irradiating electromagnetic waves of a specified frequency according to the control signal output from the control device 5.

[0044] As a static magnetic field, a permanent magnet 7 is constructed in a predetermined direction and with a specified strength (e.g., 7 mT) applied to the subject's head. The permanent magnet 7 may have, for example, a pair of permanent magnets 7A and 7B. The pair of permanent magnets 7A and 7B are configured to sandwich a light-excited magnetic sensor 1A (e.g., on the left and right sides of the subject). The pair of permanent magnets 7A and 7B, on the subject's head, generate, for example, a static magnetic field in the X-axis direction.

[0045] The tilting magnetic field coil 8 is a coil used to apply a tilting magnetic field to the subject's head during MR image measurement. The tilting magnetic field coil 8 generates a magnetic field based on the current supplied from the coil power supply 6. The tilting magnetic field coil 8 may have, for example, a pair of tilting magnetic field coils 8A and 8B. The pair of tilting magnetic field coils 8A and 8B are configured to sandwich a photoexcited magnetic sensor 1A (e.g., on the left and right sides of the subject). The tilting magnetic field coil 8 generates a tilting magnetic field with selective gradients in the X-axis, Y-axis, and Z-axis directions based on the current supplied from the coil power supply 6.

[0046] The active shielding coil 9 is a coil used to correct the changing magnetic field at the position of the photoexcited magnetometer 1A. The active shielding coil 9 generates a magnetic field based on the current supplied from the coil power supply 6 to cancel the changing magnetic field. The active shielding coil 9 may have a pair of active shielding coils 9A and 9B. The pair of active shielding coils 9A and 9B are configured to sandwich the photoexcited magnetometer 1A (e.g., on the left and right sides of the subject). The pair of active shielding coils 9A and 9B generate a magnetic field of the same magnitude and opposite direction to the changing magnetic field at the position of the photoexcited magnetometer 1A, based on the current supplied from the coil power supply 6. The direction of the magnetic field is, for example, the X-axis, Y-axis, and Z-axis directions. The changing magnetic field at the position of the photoexcited magnetometer 1A is canceled by the opposing magnetic field of the same magnitude generated by the active shielding coil 9. In this way, the active shielding coil 9 corrects the changing magnetic field at the position of the photoexcited magnetometer 1A.

[0047] Pump laser 10 is a laser device that generates pump light. The pump light emitted from pump laser 10 passes through an optical fiber branch and is incident on each of the multiple photoexcited magnetosensors 1A and 23A.

[0048] The probe laser 11 is a laser device that generates probe light. The probe light emitted from the probe laser 11 passes through an optical fiber branch and is incident on each of the multiple photoexcited magnetosensors 1A and 23A.

[0049] Amplifier 12A is a device or circuit that amplifies the signal from the output of OPM module 1 (specifically, readout circuit 1C) and outputs it to control device 5.

[0050] Amplifier 12B is a device or circuit that amplifies the signal from the output of OPM module 23 (specifically, read circuit 23C) and outputs it to control device 5.

[0051] The heater controller 13 is a temperature control device connected to the heaters for heating the units of photomagnetic sensor 1A and photomagnetic sensor 23A, as well as thermocouples (not shown) for measuring the temperature of each unit. The heater controller 13 receives temperature information of the unit from the thermocouples and adjusts the temperature of the unit based on this temperature information by adjusting the heating of the heater.

[0052] Electromagnetic shield 14 is a shielding member that blocks high-frequency (e.g., above 10kHz) electromagnetic noise. It is constructed, for example, of a mesh woven from metal wires or a non-magnetic metal plate such as aluminum. Electromagnetic shield 14 is configured to surround OPM modules 1 and 23, transmitting coil 21, receiving coil 22, output coil 24, magnetic sensor 2 for static magnetic field correction, magnetic sensor 3 for active shielding, non-magnetic frame 4, permanent magnet 7, tilting magnetic field coil 8, active shielding coil 9, and static magnetic field correction coil 16. This electromagnetic shield 14 prevents noise in the 300kHz frequency band (the measurement frequency) from entering the receiving coil 22 and causing noise increase during MR image measurement. Furthermore, it prevents high-frequency noise from entering the photoexcited magnetic sensor 1A and causing operational instability during brain magnetic field measurement.

[0053] Next, refer to Figure 4 and Figure 5 A brain measurement method using the brain measurement device M1 according to the embodiment will be described. Figure 4 and Figure 5 This is a flowchart illustrating the operation of the brain measurement device M1.

[0054] First, refer to Figure 4 When the measurement of the brain magnetic field begins with the non-magnetic frame 4 worn on the subject, the static magnetic field correction magnetic sensor 2 measures the static magnetic field and its gradient magnetic field (step S11). The static magnetic field correction magnetic sensor 2 measures the static magnetic field and gradient magnetic field at various locations of the photoexcited magnetic sensor 1A and outputs the measured values ​​to the control device 5.

[0055] Control device 5 and coil power supply 6 control the current to the static magnetic field correction coil 16 for each photoexcited magnetic sensor 1A (step S12). Control device 5 determines the current to the static magnetic field correction coil 16 based on the measured value of the static magnetic field correction magnetic sensor 2, in a manner that generates magnetic fields of opposite magnitude and opposite direction in the three directions (x-axis, y-axis, and z-axis) of the static magnetic field at the location of the photoexcited magnetic sensor 1A. This can be achieved by measuring the measured value of the static magnetic field correction magnetic sensor 2 and the magnetic field strength at the photoexcited magnetic sensor 1A. Control device 5 outputs control signals corresponding to the determined currents associated with each of the coil systems 16X, 16Y, and 16Z to the coil power supply 6. The coil power supply 6 outputs the specified current to each of the coil systems 16X, 16Y, and 16Z according to the control signals output by control device 5. The coil systems 16X, 16Y, and 16Z generate magnetic fields according to the current supplied from the coil power supply 6. The three directional components of the static magnetic field at the location of the photoexcited magnetic sensor 1A are counteracted by the opposing and equally magnituded magnetic fields generated by the coil systems 16X, 16Y, and 16Z.

[0056] Next, the photoexcited magnetic sensor 1A is tested (step S13). The photoexcited magnetic sensor 1A obtains a measurement of the residual magnetic field through the test operation and outputs it to the control device 5. The measured magnetic field value refers to the value measured by the photoexcited magnetic sensor 1A after the static magnetic field and gradient magnetic field have been corrected by the static magnetic field correction coil 16.

[0057] Control device 5 determines whether the measured values ​​of the corrected static magnetic field and gradient magnetic field are below the reference value (step S14). The measured values ​​of the corrected static magnetic field and gradient magnetic field refer to the values ​​measured by the photo-excited magnetic sensor 1A after the static magnetic field and gradient magnetic field are corrected by the static magnetic field correction coil 16. The reference value is the magnitude of the magnetic field in which the photo-excited magnetic sensor 1A operates normally, for example, it can be 1 nT. If the measured values ​​of the static magnetic field and gradient magnetic field are not below the reference value ("No" in step S14), return to step S11. If the measured value of the static magnetic field is below the reference value ("Yes" in step S14), proceed to step S15.

[0058] The active shielding magnetic sensor 3 measures the changing magnetic field (step S15). The active shielding magnetic sensor 3 measures the changing magnetic field at various locations of the photoexcited magnetic sensor 1A and outputs the measured values ​​to the control device 5.

[0059] Control device 5 and coil power supply 6 control the current to active shielding coil 9 (step S16). Control device 5 determines the current to active shielding coil 9 based on the measurements from active shielding magnetic sensor 3, in a manner that generates a magnetic field of the same magnitude and opposite direction to the changing magnetic field of photoexcitation magnetic sensor 1A. More specifically, control device 5 determines the current to active shielding coil 9, for example, by making the average of the measurements from multiple active shielding magnetic sensors 3 approximately zero. Control device 5 outputs a control signal corresponding to the determined current to coil power supply 6. Coil power supply 6 outputs a predetermined current to active shielding coil 9 according to the control signal output by control device 5. Active shielding coil 9 generates a magnetic field based on the current supplied from coil power supply 6. The changing magnetic field of the position of photoexcitation magnetic sensor 1A is canceled out by the opposing magnetic field of the active shielding coil 9.

[0060] Control device 5 determines whether the measured value of the corrected changed magnetic field is below a reference value (step S17). The measured value of the corrected changed magnetic field is the value measured by the active shielding magnetic sensor 3 after the changed magnetic field is corrected by the active shielding coil 9. The reference value is the noise level of the brain magnetic field that can be measured, for example, it can be set to 1 pT. If the measured value of the changed magnetic field is not below the reference value ("No" in step S17), return to step S15. If the measured value of the changed magnetic field is below the reference value ("Yes" in step S17), proceed to step S18.

[0061] The photomagnetic sensor 1A measures the brain's magnetic field (step S18). The control device 5 outputs the obtained measurement result to a predetermined output destination. The predetermined output destination can be an external device such as a storage device (e.g., a memory or hard disk of the control device 5) or an output device (e.g., a display), or a terminal device connected via a communication interface. Because the static magnetic field and changing magnetic field at the location of the photomagnetic sensor 1A are thus canceled out by becoming below a predetermined reference value, the photomagnetic sensor 1A can measure the brain's magnetic field while avoiding the influence of the electrostatic field and the changing magnetic field.

[0062] Move to Figure 5When MR image measurement continues while the non-magnetic frame 4 remains on the subject, the control device 5 sets the current to the static magnetic field correction coil 16 to 0 and, with a static magnetic field in the X-axis direction applied to the subject's head via the permanent magnet 7, determines the current supplied to the tilting magnetic field coil 8 for generating the tilting magnetic field, and controls, for example, the generation of the magnetic field gradient in the X-axis direction by outputting a control signal to the coil power supply 6 (step S19). Simultaneously, the control device 5 outputs a control signal to the transmitting coil controller 15 to control the power supplied to the transmitting coil 21, and controls this by irradiating the subject's head with a transmitting pulse (step 20). Thus, protons in the specified slice area are excited.

[0063] Furthermore, the control device 5 determines the current supplied to the tilted magnetic field coil 8 for generating the tilted magnetic field, and controls the generation of the tilted magnetic field on the slice surface, for example, the generation of the magnetic field gradient (dBX / dY) in the Y-axis direction, by outputting a control signal to the coil power supply 6 (step S21). Phase encoding is then performed. Additionally, the control device 5 determines the current supplied to the tilted magnetic field coil 8 for generating the tilted magnetic field, and controls the generation of the tilted magnetic field on the slice surface, for example, the generation of the magnetic field gradient (dBX / dZ) in the Z-axis direction, by outputting a control signal to the coil power supply 6 (step S22). Frequency encoding is then performed.

[0064] Simultaneously, from the OPM module 23, via the receiving coil 22 and the output coil 24, a nuclear magnetic resonance (NMR) signal from the protons is output, and the control device 5 subsequently acquires NMR signal data (step S23). Thereafter, the control device 5 determines whether NMR signal data related to other slice planes has been acquired (step S24). If the determination result is that NMR signal data related to other slice planes has been acquired ("Yes" in step S24), processing returns to step S19. On the other hand, if NMR signal data related to other slice planes has not been acquired ("No" in step S24), an MR image is obtained by performing a Fourier transform on the NMR signal data acquired so far (step S25). The control device 5 outputs the acquired MR image to a predetermined output destination. The predetermined output destination may be an external device such as a terminal device connected via a communication interface, in addition to a storage device such as the control device 5's memory or hard disk, or an output device such as a display.

[0065] [Effects]

[0066] Next, the effects of the brain measurement device described in the above embodiments will be explained.

[0067] According to the brain measurement device M1 of this embodiment, the static magnetic field is measured at each location of a plurality of photomagnetic sensors 1A that measure the brain magnetic field. Furthermore, during the measurement of the brain magnetic field, the current flowing through the static magnetic field correction coil 16 is controlled based on the multiple measured values ​​of the static magnetic field, and a magnetic field is generated in the static magnetic field correction coil 16. At the locations of the plurality of photomagnetic sensors 1A, the static magnetic field related to the Earth's magnetism and the static magnetic field caused by the permanent magnet 7 are counteracted by the magnetic field generated in the static magnetic field correction coil 16. As a result, by correcting the static magnetic field at the locations of the plurality of photomagnetic sensors 1A, the plurality of photomagnetic sensors 1A can measure the brain magnetic field while avoiding the influence of the ambient magnetic field. At this time, the static magnetic field related to the Earth's magnetism and the static magnetic field caused by the permanent magnet 7 can be corrected together by the static magnetic field correction coil 16.

[0068] On the other hand, according to one or other methods described above, when measuring MR images, a tilted magnetic field is applied by controlling the current flowing through the tilted magnetic field coil 8 while a static magnetic field is applied through the permanent magnet 7, and the nuclear magnetic resonance signal generated by the transmission of transmission pulses is detected by the receiving coil 22. As a result, the MR image can be measured based on the output of the receiving coil 22. In particular, because a static magnetic field is generated using the permanent magnet 7, compared with a structure that generates a static magnetic field through an electromagnet, it is possible to achieve miniaturization of the device and reduction of power consumption.

[0069] According to this brain measurement device M1 and brain measurement method, both magnetoencephalography (MEG) and MRI measurements can be effectively performed using the same device. In particular, in MRI measurements, because a photoexcited magnetic sensor is used, the high-sensitivity frequency band can be adjusted more widely than with a SQUID, thus reducing the limitation on the intensity of the applied static magnetic field, i.e., the resonant frequency of the protons. Because the pre-polarization coil required by the SQUID, which operates only at low resonant frequencies (i.e., low static magnetic fields), is unnecessary, and the coolant such as liquid helium required when using the SQUID is also unnecessary. Furthermore, because the frequency of the signal in MRI measurements is also relatively high, a magnetic shielding chamber for reducing magnetic noise during MRI and MEG measurements is not required. As a result, the device can be miniaturized and costs can be reduced. Additionally, because the time required for pre-polarization is approximately the same as the measurement time, in this embodiment, the measurement time can also be reduced to half.

[0070] Furthermore, in this embodiment, since the static magnetic field on the OPM module can be easily switched on / off by controlling the current flowing through the static magnetic field correction coil 16, brain magnetic field measurement and MRI measurement can be switched in a short time. Therefore, since brain magnetic field measurement and MRI measurement can be performed sequentially on the same subject using the same device, the registration error between the two measurement results can be reduced.

[0071] Furthermore, in this embodiment, during the measurement of the brain magnetic field, the current supplied to the active shielding coil 9 is controlled based on the measured value of the changing magnetic field to counteract the changing magnetic field on the multiple photoexcited magnetic sensors 1A. According to this structure, the brain magnetic field can be measured while reliably avoiding the influence of the changing magnetic field. As a result, the brain magnetic field can be measured with high precision without using a magnetic shielding chamber.

[0072] As described above, according to this embodiment, because MRI measurements can be performed in a low magnetic field, a special room is not required, and tomographic images with high T1 contrast can be easily obtained. Furthermore, by using the active shielding coil 9, magnetoencephalography (MEG) measurements are not required in a magnetically shielded room. Therefore, MEG and MRI measurements can be performed using the same device, and both measurements can be performed sequentially while the subject is seated in a chair or similar position. Additionally, the cost of the device can be reduced, and measurements can also be performed while the subject is in a vehicle or similar position. As a result, this can aid in the diagnosis of mental illnesses such as depression and schizophrenia, and neurodegenerative diseases such as dementia.

[0073] Here, the brain measurement device M1 uses a three-coil system 16X, 16Y, and 16Z, configured for each of the multiple photomagnetic sensors 1A, to correct the static magnetic field. This allows for precise local control of the current for each of the multiple photomagnetic sensors 1A, improving the accuracy of the static magnetic field correction. Furthermore, because the static magnetic field is corrected only in areas relevant to the operation of the multiple photomagnetic sensors 1A, the increase in power consumption associated with unnecessary corrections can be suppressed. Additionally, the static magnetic field correction coil 16 can also correct the gradient of the ambient magnetic field for each of the multiple photomagnetic sensors 1A.

[0074] Furthermore, an active shielding coil 9 is configured by sandwiching a pair of coils containing multiple photoexcitation magnetic sensors 1A. With this structure, the changing magnetic field at the positions of the multiple photoexcitation magnetic sensors 1A sandwiched between the pair of coils is effectively corrected. Thus, the changing magnetic field can be appropriately corrected with a simple structure.

[0075] In addition, the brain measurement device M1 also includes an output coil 24 electrically connected to the receiving coil 22 via a cable, and another photomagnetic sensor 23A for detecting the magnetic signal output by the output coil 24. With this structure, the influence of the applied static magnetic field on the detection signal of the other photomagnetic sensor 23A during MRI measurements can be avoided, thus improving the accuracy of MR image measurements. For example, with the application of a static magnetic field of 7 mT, the frequency of the proton-generated MRI signal is approximately 300 kHz. To maintain sensitivity of the photomagnetic sensor 23A to this frequency, a bias magnetic field of approximately 40 μT must be applied. When the photomagnetic sensor 23A is positioned near the subject's head, the coexistence of such a bias magnetic field and a static magnetic field is difficult. In this embodiment, the receiving coil 22, which is not sensitive to static magnetic fields, can be positioned near the head, and the photomagnetic sensor 23A can be separately positioned from the head, allowing for highly sensitive detection of the MRI signal.

[0076] Furthermore, the multiple photoexcited magnetic sensors 1A are axial gradiometers having a measurement region and a reference region coaxially arranged in a direction perpendicular to the subject's scalp. Based on this structure, since the influence of common-mode noise is evident in both the output of the measurement region and the output of the reference region, common-mode noise can be removed by obtaining the difference between the two outputs. This improves the measurement accuracy of the brain magnetic field.

[0077] Furthermore, multiple photoexcited magnetic sensors 1A, multiple static magnetic field correction magnetic sensors 2, multiple active shielding magnetic sensors 3, and a receiving coil 22 are fixed to a helmet-type non-magnetic frame 4 worn on the subject's head. With this structure, because the non-magnetic frame 4 worn on the head and the sensors 2, 3 fixed to it, as well as the receiving coil 22, move according to the movement of the subject's head, even when the subject's head moves, the static magnetic field correction for the position of the multiple photoexcited magnetic sensors 1A, the measurement of the brain magnetic field, and MRI measurements can be performed appropriately. As a result, registration errors in the two measurements can be suppressed.

[0078] Furthermore, an electromagnetic shield 14 for shielding high-frequency electromagnetic noise can be added. With this structure, high-frequency electromagnetic noise that cannot be measured can be prevented from intruding into the multiple photomagnetic sensors 1A. This allows for stable operation of the measurement of the brain magnetic field via the multiple photomagnetic sensors 1A. Simultaneously, it also prevents noise in the 300kHz frequency band, which is the measurement frequency for MRI, from incident on the receiving coil 22 and increasing the noise of the MRI measurement.

[0079] Furthermore, multiple photoexcited magnetic sensors 1A are configured to apply a bias magnetic field to be sensitive to frequencies in the range of 0–200 Hz, and another photoexcited magnetic sensor 23A is configured to apply a bias magnetic field to be sensitive to frequencies in the range of 20 kHz–500 kHz. With this structure, the sensitivity of brain magnetic field measurements can be improved, while the accuracy of MRI measurements can also be enhanced.

[0080] [Variation Example]

[0081] The embodiments described above have been explained in detail based on the present disclosure. However, the present disclosure is not limited to the above embodiments. Various modifications can be made without departing from the spirit of the present disclosure.

[0082] Although the active shielding coil 9 is described as a coil with a pair of active shielding coils 9A and 9B, each OPM module 1 (photomagnetic sensor 1A) can also be configured as a coil system consisting of three pairs of coils. In this case, the control device 5 determines the current to the active shielding coil 9 in a manner that generates a magnetic field with components of opposite directions (x-axis, y-axis, and z-axis) to the position of the photomagnetic sensor 1A and of equal magnitude. The control device 5 outputs a control signal to the coil power supply 6, the control signal corresponding to the determined current associated with each of the active shielding coils 9 configured as a coil system. With this structure, the power consumption for correcting the changing magnetic field is relatively small.

[0083] Furthermore, when measuring MR images, the control device 5 can either set the current flowing through the static magnetic field correction coil 16 by correcting for the geomagnetic gradient magnetic field, or it can set it without correcting for the geomagnetic gradient magnetic field. Because the magnitude of the gradient magnetic field in the measurement area is approximately several μT / m, which is about two orders of magnitude lower than the static magnetic field, high accuracy can be maintained even without correction when acquiring MR images.

[0084] Alternatively, the brain measurement device M1 described in the above embodiment may omit the photoexcitation magnetic sensor 23A, and may also be a structure in which the control device 5 directly detects the output from the receiving coil 22 via an amplifier.

[0085] Furthermore, the photoexcited magnetic sensor 1A is not limited to the pump & probe type that uses both pump light and probe light; it can also be a zero-field type photoexcited magnetic sensor that uses circularly polarized light, which combines pump light and probe light. In this zero-field type, light can be irradiated onto the cell and a periodic bias magnetic field can be applied and the detection magnetic field locked, and the deviation from the zero magnetic field can be measured as the brain magnetic field.

[0086] Furthermore, in the brain measurement device M1 of the above embodiment, the position of the non-magnetic frame 4 can also be measured optically. For example, markers installed at 120° intervals around the lower end of the non-magnetic frame 4 and a camera opposite to the non-magnetic frame 4 can be provided, making it possible to measure the positional changes of the helmet using the camera. This measurement result can be used during MRI measurement. For example, the control device 5 can use the measurement result to calculate the relative position of the tilting magnetic field coil 8 and the receiving coil 22, and correct the MR image. As a result, even if the subject's head moves, a high-resolution MR image can be obtained. This is a useful structure for MRI measurement of subjects whose heads are difficult to fix, such as young children. In addition, during magnetoencephalography (MEG) measurement, since the correction is performed in such a way that the magnetic field at the position of the photoexcited magnetic sensor 1A in the deviated state becomes zero even if the head position deviates, the positional information of the non-magnetic frame 4 can be used for zero magnetic field generation even though the necessity of measuring the position of the non-magnetic frame 4 is low.

[0087] Furthermore, in the brain measurement device M1 described in the above embodiment, the magnetic shield 25 is not necessarily required. If the magnetic shield 25 is omitted, a coil may be provided in the OPM module 23, which can apply a magnetic field in the opposite direction to eliminate the static magnetic field on the photoexcitation magnetic sensor 23A.

[0088] In the above embodiment, preferably, the static magnetic field correction coil for each of the plurality of photoexcited magnetic sensors includes a coil system that applies a magnetic field in three orthogonal directions arranged around the sensor, and a control device determines the current to the coil system such that the magnetic field at each position of the plurality of photoexcited magnetic sensors is approximately zero. According to this structure, the coil system is configured for each of the plurality of photoexcited magnetic sensors according to the components of the static magnetic field in the three directions (x-axis, y-axis, and z-axis). Furthermore, by controlling the current corresponding to each of the coil systems, magnetic fields are generated for each of the plurality of photoexcited magnetic sensors to cancel out the x-axis, y-axis, and z-axis components of the static magnetic field, and the static magnetic field is corrected from the three directions. Thus, the current can be precisely controlled for each of the plurality of photoexcited magnetic sensors, and the accuracy of the static magnetic field correction is improved. In addition, since the static magnetic field is corrected only in the region related to the operation of the plurality of photoexcited magnetic sensors, the increase in power consumption associated with unnecessary corrections can be suppressed. Furthermore, the static magnetic field correction coil can also correct the gradient of the ambient magnetic field for each of the plurality of photoexcited magnetic sensors.

[0089] Furthermore, preferably, the magnetoencephalometer also includes: multiple active shielding magnetic sensors for measuring the changing magnetic field at each position of the multiple photoexcited magnetic sensors; an active shielding coil for correcting the changing magnetic field; and a control device that, during magnetoencephalography measurement, controls the current supplied to the active shielding coil based on the measured values ​​of the multiple active shielding magnetic sensors to generate a magnetic field that cancels out the changing magnetic field at each position of the multiple photoexcited magnetic sensors, thereby determining the current supplied to the active shielding coil. With this structure, by canceling out the changing magnetic field at the positions of the multiple photoexcited magnetic sensors and the changing magnetic field, the multiple photoexcited magnetic sensors can reliably measure the brain magnetic field while avoiding the influence of the changing magnetic field. As a result, the brain magnetic field can be measured with high accuracy without using a magnetic shielding chamber.

[0090] Furthermore, the active shielding coils are preferably a pair of coils that sandwich multiple photoexcitation magnetic sensors. With this structure, the changing magnetic field at the positions of the multiple photoexcitation magnetic sensors sandwiched between the pair of active shielding coils is effectively corrected. Thus, the changing magnetic field can be appropriately corrected with a simple structure.

[0091] Furthermore, preferably, the device also includes: an output coil electrically connected to a receiving coil and outputting a magnetic signal based on the current flowing through the receiving coil; and another photoexcited magnetic sensor that detects the magnetic signal output by the output coil, and the control device generates an MR image based on the magnetic signal detected by the other photoexcited magnetic sensor. With this structure, since the signal can be received by another photoexcited magnetic sensor with a high sensitivity of fT or more, the accuracy of MR image measurement can be improved. Furthermore, since the other photoexcited magnetic sensor is positioned separately from the receiving coil where a static magnetic field of approximately mT is applied, the sensitivity band of the sensor can be adjusted regardless of the static magnetic field.

[0092] Furthermore, preferably, the multiple photoexcited magnetic sensors are axial gradiometers having a measurement region and a reference region coaxially in a direction perpendicular to the subject's scalp. With this structure, since the influence of common-mode noise is reflected in both the output of the measurement region and the output of the reference region, common-mode noise can be removed by obtaining the difference between the two outputs. This improves the accuracy of brain magnetic field measurement.

[0093] Furthermore, it is preferable to fix multiple photoexcited magnetic sensors, multiple static magnetic field correction magnetic sensors, and receiving coils to a helmet-type non-magnetic frame worn on the subject's head. With this structure, because the non-magnetic frame worn on the head and the sensors and receiving coils fixed to it move according to the movement of the subject's head, static magnetic field correction for the positions of the multiple photoexcited magnetic sensors, brain magnetic field measurement, and MRI measurements can be performed appropriately even when the subject's head moves. As a result, registration errors between the two measurements can be suppressed.

[0094] Furthermore, it can also incorporate electromagnetic shielding to block high-frequency electromagnetic noise. With such a structure, high-frequency electromagnetic noise that cannot be measured can be prevented from intruding into multiple photoexcited magnetic sensors in the magnetoencephalometer. This allows for stable operation of the measurement of the brain's magnetic field via multiple photoexcited magnetic sensors. On the other hand, in MRI measurements, noise in the 20kHz–500kHz frequency band, which constitutes the signal region, can be prevented from intruding.

[0095] Furthermore, it is preferable to configure a static magnetic field correction coil to apply a bias magnetic field to multiple photoexcited magnetic sensors in a manner that provides sensitivity to frequencies within the range of 0–200 Hz. This configuration improves the sensitivity of brain magnetic field measurements.

[0096] Alternatively, it is preferable to configure another photoexcited magnetic sensor to be sensitive to frequencies in the range of 20 kHz to 500 kHz by applying a bias magnetic field. In this case, the accuracy of MRI measurements can also be improved.

Claims

1. A brain measurement device, characterized in that, It includes: a magnetoencephalometer, an MRI machine, and a control device. The magnetoencephalometer has the following features: Multiple photoexcited magnetic sensors measure the brain's magnetic field. Multiple magnetic sensors for static magnetic field correction are used to measure the static magnetic field at various locations of the multiple photoexcited magnetic sensors, and A static magnetic field correction coil is used to correct the static magnetic field. The MRI device has: Permanent magnets are used to apply static magnetic fields. Inclined magnetic field coil, used to apply an inclined magnetic field. A transmitting coil, used to transmit pulses at a specified frequency, and A receiving coil detects the nuclear magnetic resonance signal generated by the transmission of the transmitted pulse; The control device, during the measurement of the brain magnetic field, controls the current supplied to the static magnetic field correction coil based on the measured values ​​of the plurality of static magnetic field correction magnetic sensors, and operates in a manner that cancels out the geomagnetic static magnetic field at each location of the plurality of photoexcited magnetic sensors and the static magnetic field applied by the permanent magnet. During MR image measurement, the current supplied to the tilted magnetic field coil is controlled and the tilted magnetic field is controlled, and the MR image is generated based on the output of the receiving coil.

2. The brain measurement device according to claim 1, characterized in that, The static magnetic field correction coil, for each of the plurality of photoexcited magnetic sensors, has a coil system that is orthogonal and capable of applying magnetic fields in three orthogonal directions arranged in a surrounding configuration. The control device determines the current to the coil system in such a way that the magnetic field at each position of the plurality of photoexcited magnetic sensors is approximately zero.

3. The brain measurement device according to claim 1, characterized in that, It also has: Multiple active shielding magnetic sensors are used to measure the changing magnetic field at various positions of the multiple photoexcited magnetic sensors, and An active shielding coil is used to correct the changing magnetic field, and The control device, when measuring the brain magnetic field, controls the current supplied to the active shielding coil based on the measured values ​​of the plurality of active shielding magnetic sensors, and determines the current supplied to the active shielding coil in a manner that generates a magnetic field that cancels out the changing magnetic field at each position of the plurality of photoexcitation magnetic sensors.

4. The brain measurement device according to claim 2, characterized in that, It also has: Multiple active shielding magnetic sensors are used to measure the changing magnetic field at various positions of the multiple photoexcited magnetic sensors, and An active shielding coil is used to correct the changing magnetic field, and The control device, when measuring the brain magnetic field, controls the current supplied to the active shielding coil based on the measured values ​​of the plurality of active shielding magnetic sensors, and determines the current supplied to the active shielding coil in a manner that generates a magnetic field that cancels out the changing magnetic field at each position of the plurality of photoexcitation magnetic sensors.

5. The brain measurement device according to claim 3, characterized in that, The active shielding coil is a pair of coils sandwiching the plurality of photoexcited magnetic sensing configurations.

6. The brain measurement device according to claim 4, characterized in that, The active shielding coil is a pair of coils sandwiching the plurality of photoexcited magnetic sensing configurations.

7. The brain measurement device according to claim 1, characterized in that, It also has: An output coil, electrically connected to the receiving coil, outputs a magnetic signal based on the current flowing through the receiving coil. Another optically excited magnetic sensor detects the magnetic signal output by the output coil. The control device generates the MR image based on the magnetic signal detected by the other photoexcited magnetic sensor.

8. The brain measurement device according to claim 2, characterized in that, It also has: An output coil, electrically connected to the receiving coil, outputs a magnetic signal based on the current flowing through the receiving coil. Another optically excited magnetic sensor detects the magnetic signal output by the output coil. The control device generates the MR image based on the magnetic signal detected by the other photoexcited magnetic sensor.

9. The brain measurement device according to claim 3, characterized in that, It also has: An output coil, electrically connected to the receiving coil, outputs a magnetic signal based on the current flowing through the receiving coil. Another optically excited magnetic sensor detects the magnetic signal output by the output coil. The control device generates the MR image based on the magnetic signal detected by the other photoexcited magnetic sensor.

10. The brain measurement device according to claim 4, characterized in that, It also has: An output coil, electrically connected to the receiving coil, outputs a magnetic signal based on the current flowing through the receiving coil. Another optically excited magnetic sensor detects the magnetic signal output by the output coil. The control device generates the MR image based on the magnetic signal detected by the other photoexcited magnetic sensor.

11. The brain measurement device according to any one of claims 1 to 10, characterized in that, The plurality of photoexcited magnetic sensors are axial gradient meters having a measurement area and a reference area on the same axis in a direction perpendicular to the subject's scalp.

12. The brain measurement device according to any one of claims 1 to 10, characterized in that, The plurality of photoexcited magnetic sensors, the plurality of static magnetic field correction magnetic sensors, and the receiving coil are fixed to a helmet-shaped non-magnetic frame worn on the subject's head.

13. The brain measurement device according to claim 11, characterized in that, The plurality of photoexcited magnetic sensors, the plurality of static magnetic field correction magnetic sensors, and the receiving coil are fixed to a helmet-shaped non-magnetic frame worn on the subject's head.

14. The brain measurement device according to any one of claims 1 to 10, characterized in that, It also has electromagnetic shielding for blocking high-frequency electromagnetic noise.

15. The brain measurement device according to claim 11, characterized in that, It also has electromagnetic shielding for blocking high-frequency electromagnetic noise.

16. The brain measurement device according to claim 12, characterized in that, It also has electromagnetic shielding for blocking high-frequency electromagnetic noise.

17. The brain measurement device according to claim 13, characterized in that, It also has electromagnetic shielding for blocking high-frequency electromagnetic noise.

18. The brain measurement device according to any one of claims 1 to 10, 13, 15 to 17, characterized in that, The static magnetic field correction coil is configured to apply a bias magnetic field to the plurality of photoexcited magnetic sensors in order to be sensitive to frequencies in the range of 0 to 200 Hz.

19. The brain measurement device according to claim 11, characterized in that, The static magnetic field correction coil is configured to apply a bias magnetic field to the plurality of photoexcited magnetic sensors in order to be sensitive to frequencies in the range of 0 to 200 Hz.

20. The brain measurement device according to claim 12, characterized in that, The static magnetic field correction coil is configured to apply a bias magnetic field to the plurality of photoexcited magnetic sensors in order to be sensitive to frequencies in the range of 0 to 200 Hz.

21. The brain measurement device according to claim 14, characterized in that, The static magnetic field correction coil is configured to apply a bias magnetic field to the plurality of photoexcited magnetic sensors in order to be sensitive to frequencies in the range of 0 to 200 Hz.

22. The brain measurement device according to claims 7-10, characterized in that, The other photoexcited magnetic sensor is configured such that a bias magnetic field is applied to it to make it sensitive to frequencies in the range of 20 kHz to 500 kHz.

23. A brain measurement method, characterized in that, It is a method that uses magnetoencephalography (MEG) and MRI equipment. The magnetoencephalometer has the following features: Multiple photoexcited magnetic sensors measure the brain's magnetic field. Multiple magnetic sensors for static magnetic field correction are used to measure the static magnetic field at various locations of the multiple photoexcited magnetic sensors, and A static magnetic field correction coil is used to correct the static magnetic field. MRI device, having: Permanent magnets are used to apply static magnetic fields. Inclined magnetic field coil, used to apply an inclined magnetic field. A transmitting coil, used to transmit pulses at a specified frequency, and A receiving coil detects the nuclear magnetic resonance signal generated by the transmission of the transmitted pulse; During the measurement of the brain magnetic field, the current supplied to the static magnetic field correction coil is controlled based on the measured values ​​of the plurality of static magnetic field correction magnetic sensors, and the operation is performed in a manner that cancels out the geomagnetic static magnetic field at each location of the plurality of photoexcited magnetic sensors and the static magnetic field applied by the permanent magnet. During MR image measurement, the current supplied to the tilted magnetic field coil is controlled and the tilted magnetic field is controlled, and the MR image is generated based on the output of the receiving coil.

24. The brain measurement method according to claim 23, characterized in that, The static magnetic field correction coil, for each of the plurality of photoexcited magnetic sensors, comprises a coil system that is orthogonal and capable of applying magnetic fields in three orthogonal directions arranged in a surrounding configuration, and The current to the coil system is determined in such a way that the magnetic field at each location of the plurality of optically excited magnetic sensors is approximately zero.

Images