Brain measuring device and brain measuring method

Abstract

To provide a brain measurement device and a brain measurement method which can accurately align a brain magnetic field distribution with an MR image.SOLUTION: A brain measurement device M1 for generating an MR image and a brain magnetic field distribution of a subject comprises: an MRI module which has a transmitter coil 21 for transmitting a transmission pulse to the subject and a detection coil 22 for detecting a nuclear magnetic resonance signal generated in the subject with the transmission pulse; an optical excitation magnetic sensor 1A which detects a brain magnetic field of the subject; a generation unit 51 which generates the MR image on the basis of the nuclear magnetic resonance signal detected by the detection coil 22 and generates a brain magnetic field distribution on the basis of the brain magnetic field detected by the optical excitation magnetic sensor 1A; a marker 16 which is displayed on the MR image generated by the generation unit 51; and a helmet-type frame 4 to which the detection coil 22, the optical excitation magnetic sensor 1A and the marker 16 are attached and which is attached to the head of the subject.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a brain measuring apparatus and a brain measuring method. [Background technology]

[0002] Patent Document 1 describes a MEG (Magnetoencephalography) device using an optically excited magnetic sensor. In this MEG device, the distribution of a minute magnetic field on a sensor surface is measured by an optically excited magnetic sensor. Here, the magnetic field distribution is aligned (registered) with an MR image, which is an image of the brain structure of a subject captured using an MRI (Magnetic Resonance Imaging) device, and the position and direction of a magnetic field source generated by neural activity in the brain of the subject can be obtained by assuming the source to be an equivalent current dipole moment vector. In addition, Non-Patent Document 1 describes a study on integrating an MEG device with an MRI device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5823195 [Non-patent literature]

[0004] [Non-Patent Document 1] “SQUIDs in biomagnetism: a roadmap towards improved healthca re” ,Supercond. Sci. Technol.29 (2016) 113001 (30pp) Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, since the MEG device and the MRI device are separate devices, in order to obtain the magnetic field distribution (magnetic field distribution) associated with the neural activity in the brain of the subject, in addition to the measurements by both devices, a separate measurement is required for aligning the magnetic field distribution by the magnetic field measured on the sensor surface with the MR image of the brain of the subject. However, in the alignment by the measurement, the separate measurement and the integration process of the magnetic field distribution and the brain morphological MR image based on the measurement become new sources of error. In addition, Non-Patent Document 1 describes that even when the MEG device and the MRI device are integrated, it is necessary to improve the accuracy of the above alignment.

[0006] Therefore, an object of the present invention is to provide a brain measuring apparatus and a brain measuring method that enable more accurate alignment between the brain magnetic field distribution and an MR image. [Means for solving the problem]

[0007] The brain measuring device of the present invention is a brain measuring device for generating an MR image and brain magnetic field distribution of a subject, and is equipped with an MRI module having a transmitting coil for transmitting a transmission pulse to the subject and a detecting coil for detecting a nuclear magnetic resonance signal generated in the subject by the transmitting pulse, an optically excited magnetic sensor for detecting the subject's brain magnetic field, a generating unit for generating an MR image based on the nuclear magnetic resonance signal detected by the detecting coil and for generating a brain magnetic field distribution based on the brain magnetic field detected by the optically excited magnetic sensor, a marker displayed on the MR image generated by the generating unit, and a helmet-type frame to which the detecting coil, the optically excited magnetic sensor, and the marker are attached and which is worn on the subject's head.

[0008] Alternatively, the brain measurement method of the present invention is a brain measurement method for generating an MR image and brain magnetic field distribution of a subject, and includes a first step of detecting nuclear magnetic resonance signals generated by the subject and the markers while the subject is wearing a helmet-type frame equipped with an optically excited magnetic sensor and a marker on his / her head, thereby generating an MR image displaying the markers based on the nuclear magnetic resonance signals, and detecting the subject's brain magnetic field with the optically excited magnetic sensor, thereby generating a brain magnetic field distribution based on the brain magnetic field, and a second step of aligning the MR image generated in the first step with the brain magnetic field distribution.

[0009] In this brain measurement device and method, the marker and the optically excited magnetic sensor are attached to a frame, so that the positional relationship between the marker and the optically excited magnetic sensor is determined in the frame with machining accuracy. This means that the position of the marker can be acquired with high precision with machining accuracy in the brain magnetic field distribution generated based on the brain magnetic field detected by the optically excited magnetic sensor. Meanwhile, the marker is displayed on the MR image. Therefore, based on the position of the marker in the brain magnetic field distribution and the position of the marker in the MR image, information on the positional relationship between the brain magnetic field distribution and the MR image can be acquired. Therefore, it is possible to align the brain magnetic field distribution and the MR image with higher accuracy. Note that the subject's head position may vary with respect to the gradient magnetic field coil during the measurement of MRI and MEG, so it is not easy to align the MR image and the brain magnetic field distribution. In contrast, in this brain measurement device and method, the marker installed on a helmet-type frame to which the optically excited magnetic sensor is fixed is used, so that the position of the marker is displayed on the MR image. Therefore, it is possible to align the brain magnetic field distribution and the MR image with higher accuracy.

[0010] In the brain measuring device of the present invention, the generation unit may execute an extraction process to extract markers from an MR image, an acquisition process to acquire positions of the markers extracted in the extraction process in an MRI coordinate system, which is a coordinate system on the MR image, an estimation process to estimate conversion information for converting the brain magnetic coordinate system into the MRI coordinate system based on the positions of the markers in the brain magnetic coordinate system, which is a coordinate system on the brain magnetic field distribution, and the positions of the markers in the MRI coordinate system acquired in the acquisition process, and an alignment process to project the brain magnetic field distribution onto the MRI coordinate system using the conversion information estimated in the estimation process and align the brain magnetic field distribution with the MR image. In addition, the brain measurement method according to the present invention may include the following in the second step: an extraction step of extracting a marker from an MR image; an acquisition step of acquiring the position of the marker extracted by the extraction process in an MRI coordinate system, which is a coordinate system on the MR image; an estimation step of estimating conversion information for converting the magnetic brain coordinate system into the MRI coordinate system based on the position of the marker in the magnetic brain coordinate system, which is a coordinate system on the magnetic brain distribution, and the position of the marker in the MRI coordinate system acquired in the acquisition step; and an alignment step of projecting the magnetic brain distribution onto the MRI coordinate system using the conversion information estimated in the estimation step to align the magnetic brain distribution with the MR image. In these cases, the conversion information for converting the magnetic brain coordinate system into the MRI coordinate system is estimated from the positions of the markers in the MR image and the magnetic brain distribution, and the magnetic brain distribution is projected onto the MRI coordinate system based on the change information, thereby enabling the MR image and the magnetic brain distribution to be aligned with high accuracy.

[0011] The brain measuring device according to the present invention may include a plurality of markers attached to different positions on the frame. In this case, since there are a plurality of reference points for alignment between the brain magnetic field distribution and the MR image, it is possible to align the brain magnetic field distribution and the MR image with higher accuracy than when there is only one marker.

[0012] In the brain measuring device according to the present invention, the multiple markers may include at least three markers that are not on the same line. In this case, the three reference points required for alignment of the brain magnetic field distribution and the MR image are more accurately obtained, so that the brain magnetic field distribution and the MR image can be aligned more accurately than when there are two markers.

[0013] In the brain measuring device according to the present invention, the marker may include a Beakley marker or a Magnevist solution capsule. In this case, the marker is more clearly displayed as a bright point in the MR image, so that the position of the marker can be specified more accurately. Therefore, the brain magnetic field distribution and the MR image can be aligned more accurately. Effect of the Invention

[0014] According to the present invention, it is possible to provide a brain measuring apparatus and a brain measuring method that enable more accurate alignment between the brain magnetic field distribution and an MR image. [Brief description of the drawings]

[0015] [Figure 1] 1 is a diagram showing a configuration of a brain measuring apparatus according to an embodiment. [Diagram 2] 1A is a schematic diagram showing an example of a non-magnetic frame 4 according to an embodiment, and FIG. 1B is a schematic diagram showing an example of an MR image acquired in a control device 5. [Diagram 3] 2 is a schematic diagram showing a configuration of an OPM module 23 according to the embodiment. FIG. [Figure 4] 1A is a schematic diagram showing an example of a non-magnetic frame 4 according to an embodiment, and FIG. 1B is a schematic diagram showing an example of an MR image acquired in a control device 5. [Diagram 5] 1A is a schematic diagram showing an example of a non-magnetic frame 4 according to an embodiment, and FIG. 1B is a schematic diagram showing an example of an MR image acquired in a control device 5. [Figure 6] 4 is a flowchart showing the operation of the brain measuring apparatus according to the embodiment. [Figure 7] 4 is a flowchart showing the operation of the brain measuring apparatus according to the embodiment. [Figure 8] 4 is a flowchart showing the operation of the brain measuring apparatus according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] An embodiment will be described in detail below with reference to the drawings. In the description of the drawings, the same or overlapping elements are given the same reference numerals, and overlapping descriptions may be omitted. In addition, the drawings may show an orthogonal coordinate system defined by an X-axis, a Y-axis, and a Z-axis.

[0017] 1 is a schematic diagram showing the configuration of a brain measuring device M1 according to an embodiment. The brain measuring device M1 is a device for measuring the brain magnetic field and measuring MR (Magnetic Resonance) images of a subject. In other words, the brain measuring device M1 is a device for generating the brain magnetic field distribution and MR images of a subject. The brain measuring device M1 includes a magnetoencephalograph module having a plurality of OPM (optically pumped magnetometer) modules 1, a plurality of geomagnetic field correction magnetic sensors 2, a plurality of active shield magnetic sensors 3, a non-magnetic frame 4 (frame), a pair of geomagnetic field correction coils 7, a pair of gradient magnetic field correction coils 8 (geomagnetic field correction coils), and a pair of active shield coils 9, and an MRI module having a transmission coil 21, a reception coil 22 (detection coil), an OPM module 23, and an output coil 24. Furthermore, the brain-measuring device M1 includes a control device (generation unit) 5, a coil power supply 6, a pump laser 10, a probe laser 11, amplifiers 12A, 12B, a heater controller 13, an electromagnetic shield 14, a transmitting coil controller 15, a marker 16, and a magnetic shield 25.

[0018] In the following description, the direction roughly 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.

[0019] The OPM module 1 includes an optically excited magnetic sensor 1A, a thermal insulator 1B, and a readout circuit 1C. A plurality of OPM modules 1 are arranged at predetermined intervals along the scalp, for example.

[0020] The optically excited magnetic sensor 1A is a sensor that measures the brain magnetic field by utilizing optical pumping. That is, the optically excited magnetic sensor 1A is a sensor for detecting the brain magnetic field of a subject. The optically excited magnetic sensor 1A has a sensitivity of, for example, about 10 fT to 10 pT. The heat insulating material 1B prevents heat movement and heat transfer of the optically excited magnetic sensor 1A. The readout circuit 1C is a circuit that acquires the detection result of the optically excited magnetic sensor 1A. The optically excited magnetic sensor 1A excites the alkali metal by irradiating a cell containing alkali metal vapor with pump light. The excited alkali metal is in a spin-polarized state, and when it receives a magnetic field, the tilt of the spin polarization axis of the alkali metal atom changes according to the magnetic field. The tilt of the spin polarization axis is detected by a probe light that is irradiated separately from the pump light. The optically excited magnetic sensor 1A is configured so that a predetermined bias magnetic field is applied in the irradiation direction of the pump light so that it has sensitivity to a magnetic field with a frequency in 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, obtains the detection result, and outputs the detection result to the amplifier 12A.

[0021] The optically excited magnetic sensor 1A may be, for example, an axial gradiometer. The axial gradiometer has a measurement region and a reference region on the same axis and in a direction perpendicular to the subject's scalp (measurement location). The measurement region is, for example, a location closest to the subject's scalp among the locations where the axial gradiometer measures the brain magnetic field. The reference region is, for example, a location at a predetermined distance (for example, 3 cm) from the measurement region in a direction away from the subject's scalp among the locations where the axial gradiometer measures the brain magnetic field. The axial gradiometer outputs the results of measurements in the measurement region and the reference region to the amplifier 12A. Here, if common mode noise is included, its influence is indicated in the output result of the measurement region and the output result of the reference region, respectively. The common mode noise is removed by acquiring the difference between the output result of the measurement region and the output result of the reference region. By removing the common mode noise, for example, when measurement is performed in a magnetic noise environment of 1 pT, the optically excited magnetic sensor 1A can obtain a sensitivity of about 10 fT / √Hz.

[0022] The geomagnetic field correcting magnetic sensor 2 is a sensor that measures a magnetic field related to geomagnetism at a position corresponding to the optically excited magnetic sensor 1A, and is composed of a fluxgate sensor having a sensitivity of, for example, about 1 nT to 100 μT. 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 geomagnetic field correcting magnetic sensor 2 may be provided in one-to-one correspondence with the optically excited magnetic sensor 1A, or in one-to-multiple correspondence (one geomagnetic field correcting magnetic sensor 2 for multiple optically excited magnetic sensors 1A). The geomagnetic field correcting magnetic sensor 2 measures, for example, geomagnetism and a geomagnetic gradient magnetic field (hereinafter simply referred to as a "gradient magnetic field") as a magnetic field related to geomagnetism, and outputs the measurement value to the control device 5. The measurement value of the geomagnetic field correcting magnetic sensor 2 can be expressed by a vector having a direction and a magnitude. The geomagnetic field correcting magnetic sensor 2 may continuously perform measurement and output at a predetermined time interval.

[0023] The magnetic sensor 3 for active shield is a sensor that measures a fluctuating magnetic field at a position corresponding to the optically excited magnetic sensor 1A, and is composed of an optically excited magnetic sensor different from the optically excited magnetic sensor 1A, having a sensitivity of, for example, about 100 fT to 10 nT. 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 magnetic sensor 3 for active shield may be provided in one-to-one correspondence with the optically excited magnetic sensor 1A, or in one-to-multiple correspondence (one magnetic sensor 3 for active shield for multiple optically excited magnetic sensors 1A). The magnetic sensor 3 for active shield measures a magnetic field of noise (AC) components of, for example, 200 Hz or less as a fluctuating magnetic field, and outputs the measurement value to the control device 5. The measurement value of the magnetic sensor 3 for active shield can be expressed by a vector having a direction and a magnitude. The magnetic sensor 3 for active shield may continuously perform measurement and output at a predetermined time interval.

[0024] The marker 16 is a marker displayed on the MR image acquired by the control device 5, and includes, for example, a Beakley marker or a Magnevist solution capsule. The marker 16 is, for example, spherical. The marker 16 including the Beakley marker or the Magnevist solution capsule has sufficient proton density and a suitable longitudinal relaxation time T1 and transverse relaxation time T2, and is therefore displayed as a bright point in the MR image.

[0025] The non-magnetic frame 4 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 that has a relative permeability close to 1 and does not disturb the magnetic field distribution. The non-magnetic frame 4 can be, for example, a helmet-type frame that surrounds the entire scalp of the subject and is worn on the subject's head. A plurality of optically excited magnetic sensors 1A are fixed to the non-magnetic frame 4 so as to be close to the subject's scalp. Furthermore, a geomagnetic field correction magnetic sensor 2 is fixed to the non-magnetic frame 4 so as to be able to measure the magnetic field related to the geomagnetism at each position of the plurality of optically excited magnetic sensors 1A, and an active shield magnetic sensor 3 is fixed to be able to measure the fluctuating magnetic field at each position of the plurality of optically excited magnetic sensors 1A. Since the fluctuating magnetic field has less variation in magnetic field strength depending on the position than the static magnetic field, the number of active shield magnetic sensors 3 may be fixed to the non-magnetic frame 4 so that the number of geomagnetic field correction magnetic sensors 2 is less.

[0026] In addition, one or more markers 16 are attached to the non-magnetic frame 4 at different positions. Here, multiple markers 16 are used. In the example shown in FIG. 1 and FIG. 2(a), the multiple markers 16 include at least three markers 16 that are not on the same line in the non-magnetic frame 4. A receiving coil 22 for detecting nuclear magnetic resonance signals for MR image measurement is fixed to the scalp side of the subject of the multiple optically excited magnetic sensors 1A in the non-magnetic frame 4. This receiving coil 22 is a coil for detecting nuclear magnetic resonance signals generated in the subject. This receiving coil 22 detects nuclear magnetic resonance signals of protons, which will be described later, and converts them into electric current. In order to improve the detection sensitivity of the nuclear magnetic resonance signals, it is preferable that the receiving coil 22 is provided on the side of the optically excited magnetic sensor 1A close to the scalp of the subject's head. In this way, at least the receiving coil 22, the optically excited magnetic sensor 1A, and the marker 16 are attached to the non-magnetic frame 4.

[0027] FIG. 2(a) is a diagram showing an example of a non-magnetic frame 4. In the example shown in FIG. 2(a), the non-magnetic frame 4 is a helmet-shaped frame, and multiple OPM modules 1 and three markers 16, markers P1, P2, and P3, are attached to the non-magnetic frame 4. The non-magnetic frame 4 is worn by a subject. The multiple OPM modules 1 are attached at predetermined intervals, for example, along the outer surface of the frame. Marker P1 is attached at a position corresponding to the space between the eyebrows of the subject, and markers P2 and P3 are attached at positions corresponding to the left and right temples of the subject's head.

[0028] Referring again to FIG. 1, the transmission coil 21 is a coil that irradiates an RF pulse (transmission pulse) of a predetermined frequency (e.g., about 300 kHz) to the subject's head during MR image measurement. That is, the transmission coil 21 is a coil for transmitting a transmission pulse toward the subject. Then, the transmission pulse generates a nuclear magnetic resonance signal from the subject. This transmission coil 21 is disposed, for example, outside the non-magnetic frame 4 and above the subject's head.

[0029] The output coil 24 is electrically connected to both ends of the receiving coil 22 via a cable, receives the current flowing through both ends of the receiving coil 22, converts the current back into a magnetic signal, and outputs it.

[0030] Like OPM module 1, OPM module 23 has optically excited magnetic sensor 23A (another optically excited magnetic sensor), thermal insulation material 23B, and readout circuit 23C. OPM module 23 is arranged, for example, outside non-magnetic frame 4, housed together with output coil 24 in magnetic shield 25 that shields from a static magnetic field, which will be described later. Magnetic shield 25 is made of, for example, mu metal or the like, whose relative permeability is greater than 1.

[0031] The optically excited magnetic sensor 23A is a sensor that measures a magnetic signal by utilizing optical pumping. The optically excited magnetic sensor 23A is configured so that a predetermined bias magnetic field is applied in the direction of the pump light irradiation so that the sensor is sensitive to a magnetic field having a frequency in the range of 20 kHz to 500 kHz. For example, a bias magnetic field of about 40 μT is applied so that the sensor is sensitive to a frequency of 300 kHz of the electromagnetic wave emitted by the protons. The optically excited magnetic sensor 23A detects the magnetic signal output by the output coil 24. The readout circuit 23C outputs the detection result by the optically excited magnetic sensor 23A to the amplifier 12B.

[0032] 3 shows a specific example of the configuration of the OPM module 23. 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, a heater 27 for heating the entire cell 26 to a predetermined temperature (e.g., 180 degrees), a polarizing beam splitter 28, and a photodetector 29. Pump light L1 is introduced from the outside along the longitudinal direction of the inside of the cell 26, and probe light L2 from the outside is split and irradiated along a direction perpendicular to the longitudinal direction to each of a plurality of intersection regions 26A divided in the longitudinal direction (e.g., into four). The magnetic rotation angle of the probe light L2 transmitted through these intersection regions 26A is detected by the polarizing beam splitter 28 and the photodetector 29 provided corresponding to each intersection region 26A. That is, the polarizing beam splitter 28 splits the probe light L2 into two linearly polarized components that are orthogonal to each other, and the photodetector 29 detects the intensities of the two linearly polarized components using two built-in PDs (photodiodes) and detects the magnetic rotation angle of the probe light L2 based on the ratio of the detected intensities. The OPM module 23 is further provided with a circuit board 30, and the magnetic rotation angle of the probe light L2 detected for each intersection region 26A is output via a readout circuit 23C in the circuit board 30.

[0033] The output coil 24 is fixed in 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 this configuration, the electromagnetic field E OUT A magnetic signal B is generated by the output coil 24 based on OUT is detected based on the magnetic rotation angle of the probe light L2, which changes according to the inclination of the spin polarization axis of the alkali metal atom. Here, in the example of Fig. 3, the number of divisions of the intersection region 26A is four, but this may be changed to any number. Also, a plurality of cells 26 may be provided in parallel, and the intersection regions 26A may be arranged two-dimensionally (for example, 4 x 4 = 16).

[0034] When measuring the brain magnetic field, the control device 5 determines the currents for the various coils based on the measurement values ​​output from the geomagnetic field correction magnetic sensor 2 and the active shield magnetic sensor 3, and outputs a control signal for outputting the current to the coil power supply 6. Based on the measurement values ​​of the multiple geomagnetic field correction magnetic sensors 2, the control device 5 determines the currents for the geomagnetic field correction coils 7 and the gradient magnetic field correction coil 8 so as to generate a magnetic field that cancels out the magnetic field related to the geomagnetism. Based on the measurement values ​​of the multiple active shield magnetic sensors 3, the control device 5 also determines the current for the active shield coil 9 so as to generate a magnetic field that cancels out the fluctuating magnetic field. The control device 5 outputs a control signal to the coil power supply 6 according to the determined current.

[0035] Specifically, the control device 5 determines the current for the geomagnetic correction coil 7 so that the average value of the measurement values ​​of the multiple geomagnetic field correcting magnetic sensors 2 approaches zero (as a result, a magnetic field is generated that is opposite to and has the same magnitude as the geomagnetic field at the position of the optically excited magnetic sensor 1A). The control device 5 outputs a control signal (static magnetic field correction control signal) corresponding to the determined current for the geomagnetic correction coil 7 to the coil power supply 6.

[0036] The control device 5 also determines the current for the gradient magnetic field correction coil 8 so that the deviation from the average value of the measurement values ​​of the multiple geomagnetic field correction magnetic sensors 2 is minimized (as a result, a magnetic field is generated that is opposite to and has the same magnitude as the gradient magnetic field at the position of the optically excited magnetic sensor 1A). The control device 5 outputs a control signal (static magnetic field correction control signal) corresponding to the determined current for the gradient magnetic field correction coil 8 to the coil power supply 6.

[0037] Furthermore, the control device 5 determines the current for the active shield coil 9 so that the average value of the measurement values ​​of the multiple active shield magnetic sensors 3 approaches 0 (as a result, a magnetic field is generated that is opposite in direction and has the same magnitude as the fluctuating magnetic field at the position of the optically excited magnetic sensor 1A). The control device 5 outputs a control signal (a fluctuating magnetic field correction control signal) to the coil power supply 6 according to the determined current for the active shield coil 9.

[0038] Furthermore, the control device 5 obtains information on the magnetism detected by the optically excited magnetic sensor 1A using the signal output from the amplifier 12A. The control device 5 then generates a brain magnetic field distribution based on the brain magnetic field detected by the optically excited magnetic sensor 1A (based on information on the magnetism). When the optically excited magnetic sensor 1A is an axial gradiometer, the control device 5 may remove common mode noise by obtaining the difference between the output result of the measurement region and the output result of the reference region. The control device 5 may control the operation of the pump laser 10 and the probe laser 11, such as the irradiation timing and irradiation time. Furthermore, the process of generating a brain magnetic field distribution from information on the magnetism detected by the optically excited magnetic sensor 1A can be performed using existing technology.

[0039] In addition, when measuring an MR image, the control device 5 determines the current to be supplied to the geomagnetic correction coil 7 and the gradient magnetic field correction coil 8, which respectively operate as coils for applying a static magnetic field and a gradient magnetic field, and outputs a control signal for outputting the current to the coil power supply 6. That is, the control device 5 determines the current to be passed through the geomagnetic correction coil 7 so as to apply a magnetic field in the X-axis direction of a predetermined strength (for example, 7 mT) to the subject's head as a static magnetic field. In addition, the control device 5 selectively determines the X-axis magnetic field gradient (dBX / dX), the Y-axis magnetic field gradient (dBX / dY), and the Z-axis magnetic field gradient (dBX / dZ) as gradient magnetic fields, and determines the current to be passed through the gradient magnetic field correction coil 8. This allows the position to be sliced ​​in the MR image to be determined, and the position in the slice plane to be encoded by phase encoding and frequency encoding. In addition, the control device 5 outputs a control signal so as not to supply a current to the active shield coil 9, which removes low-frequency noise, when measuring an MR image.

[0040] Furthermore, when measuring an MR image, the control device 5 controls the transmission coil controller 15 to irradiate the subject's head with a transmission pulse of a predetermined frequency (for example, about 300 kHz when the static magnetic field strength is 7 mT) by outputting a control signal to control the power supplied to the transmission coil 21. As a result, protons on a slice plane (a plane selected by the static magnetic field and the gradient magnetic field) resonate and the spins tilt. Thereafter, the control device 5 controls the power of the transmission coil 21 to be turned off. This makes it possible to obtain an MR image by measuring the return of the spins based on the output of the OPM module 23. That is, the control device 5 generates an MR image based on the magnetic signal detected by the optically excited magnetic sensor 23A. In other words, the control device 5 is also a generating unit that generates an MR image based on the nuclear magnetic resonance signal (output of the receiving coil 22) detected by the receiving coil 22. More specifically, the control device 5 measures the nuclear magnetic resonance signal from the protons by encoding the position with the frequency and phase using a known spin echo sequence or gradient echo sequence, and converts the measurement result into an MR image using FFT.

[0041] The control device 5 is physically configured to include memories such as RAM and 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 5 include a personal computer, a cloud server, a smartphone, and a tablet terminal. The control device 5 functions by executing a program stored in the memory with the CPU of a computer system.

[0042] The coil power supply 6 outputs a predetermined current to each of the geomagnetic correction coil 7, the gradient magnetic field correction coil 8, and the active shield coil 9 in response to a control signal output from the control device 5. Specifically, the coil power supply 6 outputs a current to the geomagnetic correction coil 7 in response to a control signal related to the geomagnetic correction coil 7. The coil power supply 6 outputs a current to the gradient magnetic field correction coil 8 in response to a control signal related to the gradient magnetic field correction coil 8. The coil power supply 6 outputs a current to the active shield coil 9 in response to a control signal related to the active shield coil 9.

[0043] The transmitting coil controller 15 is electrically connected to the transmitting coil 21, and supplies power to the transmitting coil 21 in response to a control signal output from the control device 5 so as to irradiate a transmitting pulse of a predetermined frequency.

[0044] The geomagnetic correction coil 7 is a coil for correcting the geomagnetic field among the magnetic fields related to the geomagnetism at the position of the optically excited magnetic sensor 1A. The geomagnetic correction coil 7 generates a magnetic field according to the current supplied from the coil power supply 6 to cancel the geomagnetic field. The geomagnetic correction coil 7 has, for example, a pair of geomagnetic correction coils 7A and 7B. The pair of geomagnetic correction coils 7A and 7B are arranged to sandwich the optically excited magnetic sensor 1A (for example, on the left and right of the subject). The pair of geomagnetic correction coils 7A and 7B generate a magnetic field that is opposite to and has the same magnitude as the geomagnetic field at the position of the optically excited magnetic sensor 1A according to the current supplied from the coil power supply 6. The direction of the magnetic field is, for example, the X-axis direction, the Y-axis direction, and the Z-axis direction. The geomagnetic field at the position of the optically excited magnetic sensor 1A is canceled by the magnetic field that is opposite to and has the same magnitude as the geomagnetic field generated by the geomagnetic correction coil 7. In this way, the geomagnetic correction coil 7 corrects the geomagnetic field at the position of the optically excited magnetic sensor 1A.

[0045] The geomagnetic correction coil 7 also serves as a static magnetic field coil for generating a static magnetic field in the X-axis direction during MR image measurement. The geomagnetic correction coil 7 generates a static magnetic field of a predetermined intensity in response to the current supplied from the coil power supply 6.

[0046] The gradient magnetic field correction coil 8 is a coil for correcting the gradient magnetic field of the magnetic field related to the geomagnetism at the position of the optically excited magnetic sensor 1A. The gradient magnetic field correction coil 8 generates a magnetic field according to the current supplied from the coil power supply 6, and cancels the gradient magnetic field. The gradient magnetic field correction coil 8 has, for example, a pair of gradient magnetic field correction coils 8A and 8B. The pair of gradient magnetic field correction coils 8A and 8B are arranged to sandwich the optically excited magnetic sensor 1A (for example, on the left and right of the subject). The pair of gradient magnetic field correction coils 8A and 8B generate a magnetic field that is opposite to and has the same magnitude as the gradient magnetic field at the position of the optically excited magnetic sensor 1A according to the current supplied from the coil power supply 6. The direction of the magnetic field is, for example, the X-axis direction, the Y-axis direction, and the Z-axis direction. The gradient magnetic field at the position of the optically excited magnetic sensor 1A is canceled by the magnetic field that is opposite to and has the same magnitude generated by the gradient magnetic field correction coil 8. In this way, the gradient magnetic field correction coil 8 corrects the gradient magnetic field at the position of the optically excited magnetic sensor 1A.

[0047] The gradient magnetic field correction coil 8 also serves as a gradient magnetic field coil for generating a gradient magnetic field during MR image measurement. The gradient magnetic field correction coil 8 generates a gradient magnetic field having selective gradients in the X-axis direction, the Y-axis direction, and the Z-axis direction according to the current supplied from the coil power supply 6.

[0048] The active shield coil 9 is a coil for correcting the fluctuating magnetic field at the position of the optically excited magnetic sensor 1A. The active shield coil 9 generates a magnetic field in response to the current supplied from the coil power supply 6, and cancels the fluctuating magnetic field. The active shield coil 9 has, for example, a pair of active shield coils 9A and 9B. The pair of active shield coils 9A and 9B are arranged to sandwich the optically excited magnetic sensor 1A (for example, on the left and right of the subject). The pair of active shield coils 9A and 9B generate a magnetic field that is opposite to and has the same magnitude as the fluctuating magnetic field at the position of the optically excited magnetic sensor 1A in response to the current supplied from the coil power supply 6. 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 optically excited magnetic sensor 1A is canceled out by the magnetic field generated by the active shield coil 9 in the opposite direction and has the same magnitude. In this way, the active shield coil 9 corrects the fluctuating magnetic field at the position of the optically excited magnetic sensor 1A.

[0049] 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 the optically excited magnetic sensor 23A via fiber branching.

[0050] 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 multiple optically excited magnetic sensors 1A and the optically excited magnetic sensor 23A via fiber branching.

[0051] The amplifier 12A is a device or circuit that amplifies the signal resulting from the output from the OPM module 1 (specifically, the readout circuit 1C) and outputs the amplified signal to the control device 5.

[0052] 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 the amplified signal to the control device 5.

[0053] The heater controller 13 is a temperature control device connected to heaters for heating the cells of the photoexcited magnetic sensor 1A and the cells of the photoexcited magnetic sensor 23A, and to thermocouples (not shown) for measuring the temperatures of the respective cells. The heater controller 13 receives cell temperature information from the thermocouples, and adjusts the heating of the heater based on the temperature information to adjust the cell temperature.

[0054] The electromagnetic shield 14 is a shielding member that blocks electromagnetic noise of high frequencies (for example, 10 kHz or more), and is made of, for example, a mesh woven with metal threads, or a non-magnetic metal plate such as aluminum. The electromagnetic shield 14 is disposed so as to surround the OPM modules 1, 23, the transmitting coil 21, the receiving coil 22, the output coil 24, the geomagnetic field correction magnetic sensor 2, the active shield magnetic sensor 3, the non-magnetic frame 4, the geomagnetic correction coil 7, the gradient magnetic field correction coil 8, and the active shield coil 9. This electromagnetic shield 14 can prevent noise in the 300 kHz band, which is the measurement frequency, from entering the receiving coil 22 during MR image measurement, causing an increase in noise. In addition, it can prevent high-frequency noise from entering the optically excited magnetic sensor 1A during brain magnetic field measurement, causing the operation to become unstable.

[0055] Next, a characteristic process performed by the control device 5 will be described. The control device 5 generates a brain magnetic field distribution and an MR image as described above. Then, the control device 5 aligns the generated brain magnetic field distribution with the MR image. In the MEG coordinate system (magnetic brain coordinate system), which is a coordinate on the brain magnetic field distribution, the positions of the optically excited magnetic sensor 1A and the marker 16 are determined in advance when the non-magnetic frame 4 is designed. The MEG coordinate system (magnetic brain coordinate system) is a coordinate system that specifies the relative positional relationship between the optically excited magnetic sensor 1A and the measured brain magnetic field distribution.

[0056] First, the control device 5 executes an extraction process to extract the marker 16 from the generated MR image. Then, the control device 5 executes an acquisition process to acquire the position of the marker 16 extracted in the extraction process in the MRI coordinate system, which is the coordinate system on the MR image. FIG. 2(b) is a diagram showing an MR image. The control device 5 extracts markers Q1, Q2, and Q3, which are the markers 16 displayed in the MR image. The control device 5 acquires the position coordinates of the markers Q1, Q2, and Q3 in the MRI coordinate system based on the extraction result.

[0057] Next, the control device 5 executes an estimation process to estimate conversion information for converting the MEG coordinate system into the MRI coordinate system based on the position of the marker 16 in the MEG coordinate system and the position of the marker 16 in the MRI coordinate system acquired in the acquisition process.

[0058] In the estimation process, first, the control device 5 acquires the position coordinates of the marker 16 in the MEG coordinate system. In the example shown in Fig. 2(a), an MEG coordinate system is shown which is a coordinate system corresponding to the non-magnetic frame 4. The control device 5 acquires in advance the position coordinates of the markers P1, P2, and P3 in the MEG coordinate system from the design information of the non-magnetic frame 4.

[0059] Next, the control device 5 estimates an affine transformation matrix T, which is transformation information for transforming the MEG coordinate system into the MRI coordinate system, from the position coordinates of markers P1, P2, and P3 in the MEG coordinate system and the position coordinates of markers Q1, Q2, and Q3 in the MRI coordinate system, using the following equation (1). P MRI =TP MEG (1)

[0060] In the above formula (1), P MRI is the position vector in the MRI coordinate system, P MEGindicates a position vector in the MEG coordinate system, and T indicates an affine transformation matrix (transformation information). The affine transformation matrix T can be determined if the positional relationship between three points between the MRI coordinate system and the MEG coordinate system is known. In the example shown in FIG. 2, the three points in the MRI coordinate system can be markers P1, P2, and P3, and the three points in the MEG coordinate system can be markers Q1, Q2, and Q3. Therefore, the control device 5 can estimate the affine transformation matrix T by using the marker 16.

[0061] The number of markers 16 arranged on the non-magnetic frame 4 may be at least one. When the number of markers 16 is one, the substitute for the other two markers 16 may be anything that is displayed in the MR image, such as the subject's left and right ears. In the example shown in FIG. 4, the marker P1 arranged at a position corresponding to the subject's eyebrows is the marker 16 arranged on the non-magnetic frame 4, and is displayed as marker Q1 in the MR image. The control device 5 can estimate the affine transformation matrix T using this one marker 16 and two parts such as the subject's left and right ears.

[0062] 5, markers P1 and P2 arranged at positions corresponding to the subject's eyebrows and the back of the head are markers 16 arranged on the non-magnetic frame 4, and are displayed as markers Q1 and Q2 in the MR image. When the number of markers 16 is two as described above, the control device 5 uses a part such as the left or right ear of the subject as a substitute for another marker 16. The control device 5 can estimate the affine transformation matrix T using these two markers 16 and one part such as the left or right ear of the subject.

[0063] The control device 5 executes a registration process for projecting the brain magnetic field distribution onto the MRI coordinate system and aligning the brain magnetic field distribution with the MR image using the transformation information estimated by the estimation process as described above. Specifically, the control device 5 projects the brain magnetic field distribution in the MEG coordinate system onto the MRI coordinate system using an affine transformation matrix T, which is information indicating the correspondence between the MEG coordinate system and the MRI coordinate system estimated by the estimation process.

[0064] Next, a brain measuring method using the brain measuring apparatus M1 according to the embodiment will be described with reference to Figures 6 to 8. Figures 6 to 8 are flow charts showing the operation of the brain measuring apparatus M1.

[0065] First, when measurement of the brain magnetic field is started with the non-magnetic frame 4 attached to the subject, the geomagnetic field correcting magnetic sensor 2 measures the magnetic field related to the geomagnetism, which is a static magnetic field (step S11). The geomagnetic field correcting magnetic sensor 2 measures the geomagnetism and the gradient magnetic field at each position of the optically excited magnetic sensor 1A, and outputs the measurement values ​​to the control device 5.

[0066] The control device 5 and the coil power supply 6 control the current to the geomagnetic correction coil 7 (step S12). Based on the measurement value of the geomagnetic field correcting magnetic sensor 2, the control device 5 determines the current to the geomagnetic correction coil 7 so as to generate a magnetic field of the same magnitude and in the opposite direction to the geomagnetic field at the position of the optically excited magnetic sensor 1A. More specifically, the control device 5 determines the current to the geomagnetic correction coil 7 so that, for example, the average value of the measurement values ​​of the multiple geomagnetic field correcting magnetic sensors 2 approaches zero. The control device 5 outputs a control signal according to the determined current to the coil power supply 6. The coil power supply 6 outputs a predetermined current to the geomagnetic correction coil 7 in response to the control signal output by the control device 5. The geomagnetic correction coil 7 generates a magnetic field in response to the current supplied from the coil power supply 6. The geomagnetic field at the position of the optically excited magnetic sensor 1A is canceled by the magnetic field generated by the geomagnetic correction coil 7, which is of the same magnitude and in the opposite direction.

[0067] The control device 5 and the coil power supply 6 control the current to the gradient magnetic field correction coil 8 (step S13). Based on the measurement value of the geomagnetic field correction magnetic sensor 2, the control device 5 determines the current to the gradient magnetic field correction coil 8 so as to generate a magnetic field having the same magnitude as and in the opposite direction to the gradient magnetic field at the position of the optically excited magnetic sensor 1A. More specifically, the control device 5 determines the current to the gradient magnetic field correction coil 8 so as to minimize the deviation from the average value of the measurement values ​​of the multiple geomagnetic field correction magnetic sensors 2. The control device 5 outputs a control signal according to the determined current to the coil power supply 6. The coil power supply 6 outputs a predetermined current to the gradient magnetic field correction coil 8 in response to the control signal output by the control device 5. The gradient magnetic field correction coil 8 generates a magnetic field in response to the current supplied from the coil power supply 6. The gradient magnetic field at the position of the optically excited magnetic sensor 1A is canceled by the magnetic field generated by the gradient magnetic field correction coil 8 having the same magnitude as and in the opposite direction.

[0068] The control device 5 judges whether the measured value of the static magnetic field (magnetic field related to geomagnetism) after correction is equal to or less than the reference value (step S14). The measured value of the static magnetic field after correction is the value measured by the geomagnetic field correction magnetic sensor 2 after the static magnetic field is corrected by the geomagnetic correction coil 7 and the gradient magnetic field correction coil 8. The reference value is the magnitude of the magnetic field at which the optically excited magnetic sensor 1A operates normally, and may be, for example, 1 nT. If the measured value of the static magnetic field is not equal to or less than the reference value ("NO" in step S14), the process returns to step S11. If the measured value of the static magnetic field is equal to or less than the reference value ("YES" in step S14), the process proceeds to step S15.

[0069] The active shield magnetic sensor 3 measures the fluctuating magnetic field at each position of the optically excited magnetic sensor 1A, and outputs the measurement value to the control device 5 (step S15).

[0070] The control device 5 and the coil power supply 6 control the current to the active shield coil 9 (step S16). Based on the measurement value of the active shield magnetic sensor 3, the control device 5 determines the current to the active shield coil 9 so as to generate a magnetic field having the same magnitude and in the opposite direction to the fluctuating magnetic field at the position of the optical excitation magnetic sensor 1A. More specifically, the control device 5 determines the current to the active shield coil 9 so that, for example, the average value of the measurement values ​​of the multiple active shield magnetic sensors 3 approaches zero. The control device 5 outputs a control signal according to the determined current to the coil power supply 6. The coil power supply 6 outputs a predetermined current to the active shield coil 9 in response to the control signal output by the control device 5. The active shield coil 9 generates a magnetic field in response to the current supplied from the coil power supply 6. The fluctuating magnetic field at the position of the optical excitation magnetic sensor 1A is canceled by the magnetic field generated by the active shield coil 9 having the same magnitude and in the opposite direction.

[0071] The control device 5 judges whether the measurement value of the variable magnetic field after correction is equal to or less than the reference value (step S17). The measurement value of the variable magnetic field after correction is the value measured by the active shield magnetic sensor 3 after the variable magnetic field is corrected by the active shield coil 9. The reference value is the noise level at which the brain magnetic field can be measured, and may be, for example, 1 pT. If the measurement value of the variable magnetic field is not equal to or less than the reference value ("NO" in step S17), the process returns to step S15. If the measurement value of the variable magnetic field is equal to or less than the reference value ("YES" in step S17), the process proceeds to step S18.

[0072] The optically excited magnetic sensor 1A measures the brain magnetic field (step S18). The control device 5 outputs the measurement result acquired by the optically excited magnetic sensor 1A to a predetermined output destination. The predetermined output destination may be the memory of the control device 5, a storage device such as a hard disk, an output device such as a display, or an external device such as a terminal device connected via a communication interface. Since the static magnetic field (magnetic field related to the geomagnetism) and the variable magnetic field at the position of the optically excited magnetic sensor 1A have been canceled so as to be equal to or less than a predetermined reference value, the optically excited magnetic sensor 1A can measure the brain magnetic field while avoiding the influence of the static magnetic field (magnetic field related to the geomagnetism) and the variable magnetic field. The control device 5 generates the brain magnetic field distribution of the subject based on the brain magnetic field acquired by the optically excited magnetic sensor 1A. The control device 5 can acquire information on the position of the marker 16 (on the MEG coordinate system) in the brain magnetic field distribution based on the positional relationship between the optically excited magnetic sensor 1A and the marker 16 in the non-magnetic frame 4.

[0073] 7, when the measurement of MR images is started while the non-magnetic frame 4 is still attached to the subject, the control device 5 determines the current to be supplied to the geomagnetic correction coil 7 for applying the static magnetic field, and controls the generation of the static magnetic field in the X-axis direction in the subject's head by outputting a control signal to the coil power supply 6 (step S19). Next, the control device 5 determines the current to be supplied to the gradient magnetic field correction coil 8 for generating the gradient magnetic field, and controls the generation of the X-axis magnetic field gradient (dBX / dX) by outputting a control signal to the coil power supply 6 (step S20). At the same time, the control device 5 outputs a control signal to the transmission coil controller 15 for controlling the power to be supplied to the transmission coil 21, and controls the transmission pulse to be irradiated to the subject's head (step S21). This excites protons on a predetermined slice plane.

[0074] Furthermore, the control device 5 determines the current to be supplied to the gradient magnetic field correction coil 8 for generating the gradient magnetic field, and outputs a control signal to the coil power supply 6 to control the generation of the Y-axis magnetic field gradient (dBX / dY) on the slice surface (step S22). This performs phase encoding. Then, the control device 5 determines the current to be supplied to the gradient magnetic field correction coil 8 for generating the gradient magnetic field, and outputs a control signal to the coil power supply 6 to control the generation of the Z-axis magnetic field gradient (dBX / dZ) on the slice surface (step S23). This performs frequency encoding.

[0075] At the same time, the OPM module 23 outputs a nuclear magnetic resonance signal from the protons via the receiving coil 22 and the output coil 24, and the control device 5 acquires the nuclear magnetic resonance signal data accordingly (step S24). After that, the control device 5 judges whether to acquire nuclear magnetic resonance signal data related to other slice planes (step S25). If the result of the judgment is that nuclear magnetic resonance signal data related to other slice planes is to be acquired ("YES" in step S25), the process returns to step S20. On the other hand, if nuclear magnetic resonance signal data related to other slice planes is not to be acquired ("NO" in step S25), an MR image is acquired by Fourier transforming the nuclear magnetic resonance signal data acquired up to that point (step S26). That is, the control device 5 generates an MR image based on the nuclear magnetic resonance signal. The control device 5 outputs the acquired MR image to a predetermined output destination. The predetermined output destination may be a memory of the control device 5, a storage device such as a hard disk, an output device such as a display, or an external device such as a terminal device connected via a communication interface.

[0076] 8, the control device 5 extracts the marker 16 from the MR image (step S27). Then, the control device 5 acquires the position of the extracted marker 16 in the MRI coordinate system (step S28). Furthermore, the control device 5 estimates conversion information for converting the MEG coordinate system into the MRI coordinate system based on the position of the marker 16 in the MEG coordinate system and the acquired position of the marker 16 in the MRI coordinate system (step S29). After that, the control device 5 uses the estimated conversion information to project the brain magnetic field distribution onto the MRI coordinate system and align the brain magnetic field distribution with the MR image (step S30).

[0077] As described above, the brain measurement method of one embodiment includes a first step of detecting nuclear magnetic resonance signals generated in a subject while the helmet-type non-magnetic frame 4 having the optically excited magnetic sensor 1A and the markers 16 is attached to the head of the subject, thereby generating an MR image displaying the markers 16 based on the nuclear magnetic resonance signals (steps S19 to S26), and generating a brain magnetic field distribution based on the brain magnetic field by detecting the subject's brain magnetic field with the optically excited magnetic sensor 1A (steps S11 to S18), and a second step of aligning the MR image generated in the first step with the brain magnetic field distribution (steps S27 to S30). The second step includes an extraction step (step S27) of extracting markers from the MR image, an acquisition step (step S28) of acquiring the position of the marker 16 extracted by the extraction process in the MRI coordinate system, which is the coordinate system on the MR image, an estimation step (step S29) of estimating conversion information for converting the MEG coordinate system into the MRI coordinate system based on the position of the marker 16 in the MEG coordinate system, which is the coordinate system on the brain magnetic field distribution, and the position of the marker 16 in the MRI coordinate system acquired in the acquisition step, and an alignment step (step S30) of projecting the brain magnetic field distribution onto the MRI coordinate system using the conversion information estimated in the estimation step to align the brain magnetic field distribution with the MR image. A specific method of estimating the conversion information is as described above. [Effects] Next, the effects of the brain measuring apparatus according to the above-described embodiment will be described.

[0078] In the brain measuring device M1 and the brain measuring method according to the present embodiment, the marker 16 and the optically excited magnetic sensor 1A are attached to the non-magnetic frame 4, so that the positional relationship between the marker 16 and the optically excited magnetic sensor 1A is determined in the non-magnetic frame 4 with machining accuracy. This means that the position of the marker 16 can be acquired with high accuracy with machining accuracy in the brain magnetic field distribution generated based on the brain magnetic field detected by the optically excited magnetic sensor 1A. Meanwhile, the marker 16 is displayed in the MR image. Therefore, based on the position of the marker 16 in the brain magnetic field distribution and the position of the marker 16 in the MR image, information on the positional relationship between the brain magnetic field distribution and the MR image can be acquired. Therefore, it is possible to align the brain magnetic field distribution and the MR image with higher accuracy. Note that the position of the subject's head may change with respect to the gradient magnetic field coil during the measurement of MRI and MEG, so it is not easy to align the MR image and the brain magnetic field distribution. Since the marker 16 is installed on the helmet-type non-magnetic frame 4 to which the optically excited magnetic sensor 1A is fixed, the position of the marker 16 is displayed in the MR image. Therefore, it is possible to more accurately align the brain magnetic field distribution and the MR image. That is, it is possible to accurately estimate from which location in the subject's brain a magnetic signal is generated in the brain-measuring device M1. That is, it is possible to improve the accuracy of signal source estimation in the brain-measuring device M1.

[0079] In the brain measuring device M1 of this embodiment, the generation unit 51 may execute an extraction process to extract the marker 16 from the MR image, an acquisition process to acquire the position of the marker 16 extracted in the extraction process in the MRI coordinate system, which is a coordinate system on the MR image, an estimation process to estimate conversion information for converting the MEG coordinate system into the MRI coordinate system based on the position of the marker 16 in the MEG coordinate system, which is a coordinate system on the brain magnetic field distribution, and the position of the marker 16 in the MRI coordinate system acquired in the acquisition process, and an alignment process to project the brain magnetic field distribution onto the MRI coordinate system using the conversion information estimated in the estimation process and align the brain magnetic field distribution with the MR image. In addition, in the brain measurement method according to the present invention, the second step may include an extraction step of extracting the marker 16 from the MR image, an acquisition step of acquiring the position of the marker 16 extracted by the extraction process in the MRI coordinate system, which is the coordinate system on the MR image, an estimation step of estimating conversion information for converting the MEG coordinate system to the MRI coordinate system based on the position of the marker 16 in the MEG coordinate system, which is the coordinate system on the brain magnetic field distribution, and the position of the marker 16 in the MRI coordinate system acquired in the acquisition step, and an alignment step of projecting the brain magnetic field distribution onto the MRI coordinate system using the conversion information estimated in the estimation step to align the brain magnetic field distribution with the MR image. In this case, the conversion information for converting the MEG coordinate system into the MRI coordinate system is estimated from the position of the marker 16 in the MR image and the brain magnetic field distribution, and the brain magnetic field distribution is projected onto the MRI coordinate system based on the change information, thereby enabling the MR image and the brain magnetic field distribution to be aligned with high accuracy.

[0080] The brain-measuring apparatus M1 according to this embodiment may be provided with a plurality of markers 16 attached at different positions on the non-magnetic frame 4. In this case, the three reference points required for alignment of the brain magnetic field distribution with the MR image are acquired more accurately before measurement, so that the brain magnetic field distribution and the MR image can be aligned with higher accuracy than when there is, for example, one marker 16.

[0081] In the brain measuring device M1 according to this embodiment, the multiple markers 16 may include at least three non-collinear markers 16. In this case, the three reference points required for alignment of the brain magnetic field distribution with the MR image are acquired more accurately before measurement, and the three reference points are not on the same line, so that the brain magnetic field distribution and the MR image can be aligned more accurately than when there are two markers 16, for example.

[0082] In the brain measuring device M1 according to the present embodiment, the marker 16 may include a Beakley marker or a Magnevist solution capsule. In this case, the marker 16 is displayed more clearly in the MR image, so that the position of the marker 16 can be specified more accurately. Therefore, the brain magnetic field distribution and the MR image can be aligned more accurately.

[0083] According to the brain measuring device M1 of this embodiment, the magnetic field and the variable magnetic field related to the geomagnetism are measured at each position of the multiple optically excited magnetic sensors 1A that measure the brain magnetic field. Then, when measuring the brain magnetic field, the current flowing through the geomagnetic correction coil 7 and the gradient magnetic field correction coil 8 is controlled based on the multiple measured values ​​of the magnetic field related to the geomagnetism, and the current flowing through the active shield coil 9 is controlled based on the multiple measured values ​​of the variable magnetic field, and a magnetic field is generated in each coil 7, 8, 9, and at the positions of the multiple optically excited magnetic sensors 1A, the magnetic field related to the geomagnetism is corrected by the magnetic field generated in the geomagnetic correction coil 7 and the gradient magnetic field correction coil 8, and the variable magnetic field is corrected by the magnetic field generated in the active shield coil 9. As a result, the magnetic field and the variable magnetic field related to the geomagnetism at the positions of the multiple optically excited magnetic sensors 1A are corrected, and the multiple optically excited magnetic sensors 1A can measure the brain magnetic field in a state where the influence of the magnetic field related to the geomagnetism and the influence of the variable magnetic field are avoided.

[0084] On the other hand, according to the above one or other aspects, when measuring an MR image, a static magnetic field and a gradient magnetic field are applied by controlling the currents flowing through the geomagnetic correction coil 7 and the gradient magnetic field correction coil 8, and a nuclear magnetic resonance signal generated by the transmission of a transmission pulse is detected by the receiving coil 22. As a result, an MR image can be measured based on the output of the receiving coil 22.

[0085] According to such brain measuring device M1 and brain measuring method, the same device can be used to efficiently realize the magnetoencephalography and the MRI measurement. In particular, since the optically excited magnetic sensor is used in the MRI measurement, the frequency band with high sensitivity can be adjusted widely compared to the SQUID, so there is little restriction on the strength of the static magnetic field to be applied, i.e., the resonance frequency of the protons. A prepolarization coil, which is necessary because the SQUID operates only at a low resonance frequency, i.e., a low static magnetic field, is not required, and a coolant such as liquid helium, which is necessary when using the SQUID, is also not required. Furthermore, since the frequency of the signal measured in the MRI is relatively high, a magnetically shielded room for reducing magnetic noise during the MRI measurement and the brain magnetic field measurement is not required. As a result, the device can be made smaller and less expensive. In addition, since the time required for prepolarization is about the same as the measurement time, the measurement time can be shortened to 1 / 2 in this embodiment.

[0086] Furthermore, in this embodiment, the static magnetic field can be easily turned on / off by turning on / off the current flowing through the geomagnetic correction coil 7, so that it is possible to switch between the brain magnetic field measurement and the MRI measurement in a short time. This allows the brain magnetic field measurement and the MRI measurement to be performed sequentially on the same subject using the same device, so that registration errors in both measurement results can be reduced.

[0087] Thus, according to this embodiment, since MRI measurement can be performed in a low magnetic field, no special room is required, and the T1 contrast can be increased. In addition, by using the active shield coil 9, it is not necessary to perform the magnetoencephalography in a magnetically shielded room. Therefore, magnetoencephalography and MRI measurement can be realized with the same device, and both measurements can be performed sequentially while the subject is sitting in a chair or the like. In addition, the cost of the device can be reduced, and measurements can be performed while the subject is in a vehicle or the like. As a result, this can contribute to the diagnosis of mental disorders such as depression and schizophrenia, and neurodegenerative disorders such as dementia.

[0088] Here, the brain measuring device M1 uses a geomagnetic field correction coil 7 for applying a static magnetic field, and a gradient magnetic field correction coil 8 for applying a gradient magnetic field. This allows the coil for geomagnetic field correction for brain magnetism measurement and the coil for MRI measurement to be shared, making it possible to further reduce the size and cost of the device.

[0089] In addition, in this embodiment, the magnetic field and the fluctuating magnetic field related to the geomagnetism are cancelled out at the positions of the optically excited magnetic sensors 1A during the brain magnetic field measurement, so that the optically excited magnetic sensors 1A can measure the brain magnetic field in a state where the influence of the magnetic field related to the geomagnetism and the fluctuating magnetic field is reliably avoided. As a result, the brain magnetic field can be measured with high accuracy without using a magnetically shielded room. This effect can be achieved even if the subject's head moves.

[0090] Furthermore, the geomagnetic correction coil 7, the gradient magnetic field correction coil 8, and the active shield coil 9 are each configured as a pair of coils arranged to sandwich the multiple optically excited magnetic sensors 1A. With this configuration, the magnetic field and fluctuating magnetic field associated with the geomagnetism at the positions of the multiple optically excited magnetic sensors 1A sandwiched between the pair of coils are effectively corrected. This makes it possible to appropriately correct the magnetic field and fluctuating magnetic field associated with the geomagnetism with a simple configuration.

[0091] Furthermore, the brain measuring device M1 further includes an output coil 24 electrically connected to the receiving coil 22 via a cable, and another optically excited magnetic sensor 23A that detects the magnetic signal output by the output coil 24. With this configuration, it is possible to avoid the influence of the static magnetic field applied during MRI measurement on the detection signal in the other optically excited magnetic sensor 23A, thereby improving the accuracy of MR image measurement. That is, for example, the frequency of the nuclear magnetic resonance signal generated by protons due to the application of a static magnetic field of 7 mT is about 300 kHz, and in order to make the optically excited magnetic sensor 23A sensitive to this frequency, it is necessary to apply a bias magnetic field of about 40 μT. When the optically excited magnetic sensor 23A is placed near the head of the subject, it is difficult to achieve both the bias magnetic field and the static magnetic field. In this embodiment, the receiving coil 22, which is not sensitive to the static magnetic field, can be placed near the head, and the optically excited magnetic sensor 23A can be placed away from the head, and the nuclear magnetic resonance signal can be detected with high sensitivity.

[0092] Furthermore, the optically excited magnetic sensors 1A are axial gradiometers having a measurement region and a reference region on the same axis in a direction perpendicular to the subject's scalp. With this configuration, the effect of common mode noise is shown in the output result of the measurement region and the output result of the reference region, respectively, so that 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.

[0093] In addition, the optically excited magnetic sensors 1A, the geomagnetic field correcting magnetic sensors 2, the active shield magnetic sensors 3, and the receiving coil 22 are fixed to a helmet-type non-magnetic frame 4 worn on the head of the subject. With this configuration, the non-magnetic frame 4 worn on the head and the sensors 2, 3 and the receiving coil 22 fixed to the non-magnetic frame 4 move in response to the movement of the subject's head, so that even if the subject's head moves, it is possible to appropriately correct the magnetic field and fluctuating magnetic field related to the geomagnetism at the position of the optically excited magnetic sensors 1A, measure the brain magnetic field, and perform MRI measurement. As a result, it is possible to suppress registration errors in both measurements.

[0094] Furthermore, an electromagnetic shield 14 for blocking high-frequency electromagnetic noise may be further provided. With this configuration, high-frequency electromagnetic noise that is not the subject of measurement by the magnetoencephalograph can be prevented from entering the multiple optically excited magnetic sensors 1A. This allows the multiple optically excited magnetic sensors 1A to stably measure the brain magnetic field. At the same time, it is also 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.

[0095] Furthermore, the optically excited magnetic sensors 1A are configured to have a bias magnetic field applied thereto so that they are sensitive to frequencies in the range of 0 to 200 Hz, and another optically excited magnetic sensor 23A is configured to have a bias magnetic field applied thereto so that they are sensitive to frequencies in the range of 20 kHz to 500 kHz. This configuration can increase the sensitivity of the brain magnetic field measurement while also increasing the accuracy of MRI measurement.

[0096] [Variations] The above embodiment describes one aspect of the present invention. Therefore, the present invention is not limited to the above brain-measuring apparatus and brain-measuring method, and may be modified as desired.

[0097] The marker 16 is not limited to a Beakley marker or a Magnevist solution capsule, as long as it is displayed as a bright point in an MR image and contains a material having sufficient proton density and appropriate T1 and T2 times. The marker 16 may contain, for example, a liquid.

[0098] The shape of the marker 16 may be any shape as long as the center of gravity of the marker 16 can be derived in the MR image when the marker 16 is displayed in the MR image. The shape of the marker 16 is not limited to a sphere, and may be, for example, a rectangular parallelepiped or cubic shape, or any other shape other than the above.

[0099] As long as the marker 16 is displayed in the MR image, the position of the marker 16 on the non-magnetic frame 4 is not limited to the positions corresponding to the subject's eyebrows, the back of the head, and the temples. The position of the marker 16 on the non-magnetic frame 4 may be, for example, a position corresponding to the top of the subject's head, or any other position other than the above. In addition, as long as the substitute for the marker 16 is displayed in the MR image, it may be a part other than the subject's ear, or may be a structure of the frame 4 instead of a part of the subject.

[0100] When the number of markers 16 is less than three, the positions of substitutes for the markers 16 may be set in advance or may be specified by some method.

[0101] The transformation information may be any information for transforming the MEG coordinate system into the MRI coordinate system, and is not limited to the affine transformation matrix T. For example, the transformation information may be other information expressed other than a matrix.

[0102] Although the active shield coil 9 has been described as having a pair of active shield coils 9A and 9B, it may be arranged as a three-coil system for each OPM module 1 (optically excited magnetic sensor 1A). In this case, the control device 5 determines a current for the active shield coil 9 so as to generate a magnetic field having the same magnitude and in the opposite direction to the three-directional (x-axis, y-axis, and z-axis) components of the fluctuating magnetic field at the position of the optically excited magnetic sensor 1A. The control device 5 outputs a control signal corresponding to the determined current for each of the active shield coils 9 arranged as the three-coil system to the coil power supply 6. With such a configuration, the power consumption for correcting the fluctuating magnetic field can be made relatively small.

[0103] Furthermore, the control device 5 may set the current flowing through the gradient magnetic field correction coil 8 so as to correct the gradient magnetic field related to geomagnetism when measuring an MR image, or may set it so as not to correct the gradient magnetic field related to geomagnetism. Since the magnitude of the gradient magnetic field is about several μT, which is about two orders of magnitude lower than the static magnetic field, high accuracy can be maintained even without correction when acquiring an MR image.

[0104] Furthermore, the brain-measuring device M1 of the above embodiment may be configured so that the optically excited magnetic sensor 23A is omitted, and the control device 5 directly detects the output from the receiving coil 22 via an amplifier.

[0105] In addition, the optically excited magnetic sensor 1A is not limited to the pump-and-probe type that uses pump light and probe light, but may be a zero-field type optically excited magnetic sensor that uses circularly polarized light that serves as both pump light and probe light. In this zero-field type, a cell is irradiated with light and a periodic bias magnetic field is applied to perform lock-in detection of the magnetic field, and the deviation from the zero magnetic field can be measured as the brain magnetic field.

[0106] In addition, in the brain measuring device M1 of the above embodiment, the position of the non-magnetic frame 4 may be optically measurable. For example, markers attached at 120 degree intervals around the lower end of the non-magnetic frame 4 and a camera facing the non-magnetic frame 4 may be provided, and the positional fluctuation of the helmet may be measured 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 gradient magnetic field correction coil 8 and the receiving coil 22 to calibrate the MR image. As a result, a high-resolution MR image can be obtained even if the subject's head moves. This is a useful configuration for MRI measurement of subjects whose heads are difficult to fix, such as infants. Note that, during brain magnetism measurement, even if the head position is shifted, the magnetic field at the position of the optically excited magnetic sensor 1A in the shifted state is corrected to be zero, so there is little need to measure the position of the non-magnetic frame 4, but the position information of the non-magnetic frame 4 may be used to generate a zero magnetic field.

[0107] The following additional notes will be given regarding the above embodiment.

[0108] [Appendix 1] A magnetoencephalograph having a plurality of optically excited magnetic sensors for measuring a brain magnetic field, a plurality of geomagnetic field compensation magnetic sensors for measuring a magnetic field related to the geomagnetism at the respective positions of the plurality of optically excited magnetic sensors, a plurality of active shield magnetic sensors for measuring a fluctuating magnetic field at the respective positions of the plurality of optically excited magnetic sensors, a geomagnetic field compensation coil for compensating the magnetic field related to the geomagnetism, and an active shield coil for compensating 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 coil for transmitting a transmission pulse of a predetermined frequency. and a control device that, when measuring a brain magnetic field, controls a current supplied to the geomagnetic field correction coil and a current supplied to the active shield coil based on measurement values ​​of the plurality of geomagnetic field correction magnetic sensors and measurement values ​​of the plurality of active shield magnetic sensors, and, when measuring an MR image, controls 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 generates an MR image based on the output of the receiving coil.

[0109] [Appendix 2] The brain measuring device according to appendix 1, wherein the geomagnetic field correction coil is composed of a geomagnetic field correction coil for correcting the geomagnetic field and a gradient magnetic field correction coil for correcting the geomagnetic gradient magnetic field.

[0110] [Appendix 3] The brain measuring device described in Appendix 1 or 2, wherein the control device determines a current to be supplied to the geomagnetic field correction coil so as to generate a magnetic field that cancels out the magnetic field related to the geomagnetic field, and determines a current to be supplied to the active shield coil so as to generate a magnetic field that cancels out the fluctuating magnetic field.

[0111] [Appendix 4] A brain measuring device according to any one of appendices 1 to 3, wherein the geomagnetic field correction coil and the active shield coil are each a pair of coils arranged on either side of the multiple optically excited magnetic sensors.

[0112] [Appendix 5] A brain measuring device as described in any one of Appendices 1 to 4, further comprising an output coil electrically connected to the receiving coil and outputting a magnetic signal based on a current flowing through the receiving coil, and another optically excited magnetic sensor detecting the magnetic signal output by the output coil, wherein the control device generates the MR image based on the magnetic signal detected by the other optically excited magnetic sensor.

[0113] [Appendix 6] A brain measuring device described in any one of Appendices 1 to 5, wherein the plurality of optically excited magnetic sensors are axial gradiometers having a measurement area and a reference area in a direction perpendicular to the subject's scalp and on the same axis.

[0114] [Appendix 7] A brain measuring device as described in any one of Appendices 1 to 6, wherein the plurality of optically excited magnetic sensors, the plurality of magnetic sensors for geomagnetic field correction, the plurality of magnetic sensors for active shielding, and the receiving coil are fixed to a helmet-type non-magnetic frame that is worn on the subject's head.

[0115] [Appendix 8] The brain-measuring device according to any one of appendices 1 to 7, further comprising an electromagnetic shield for blocking high-frequency electromagnetic noise.

[0116] [Appendix 9] The brain measuring device described in Appendix 5, wherein the plurality of optically excited magnetic sensors are configured to have a bias magnetic field applied thereto so that they are sensitive to frequencies in the range of 0 to 200 Hz, and the other optically excited magnetic sensor is configured to have a bias magnetic field applied thereto so that it is sensitive to frequencies in the range of 20 kHz to 500 kHz.

[0117] [Appendix 10] A magnetoencephalograph having a plurality of optically excited magnetic sensors for measuring a brain magnetic field, a plurality of geomagnetic field compensation magnetic sensors for measuring a magnetic field related to the geomagnetism at the respective positions of the plurality of optically excited magnetic sensors, a plurality of active shield magnetic sensors for measuring a fluctuating magnetic field at the respective positions of the plurality of optically excited magnetic sensors, a geomagnetic field compensation coil for compensating the magnetic field related to the geomagnetism, and an active shield coil for compensating 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 coil for transmitting a transmission pulse of a predetermined frequency. and an MRI apparatus having a receiving coil for detecting a nuclear magnetic resonance signal generated by the transmission of the transmission pulse, the method comprising: when measuring the brain magnetic field, controlling a current supplied to the geomagnetic field correction coil and a current supplied to the active shield coil based on the measurement values ​​of the plurality of geomagnetic field correction magnetic sensors and the measurement values ​​of the plurality of active shield magnetic sensors; when measuring an MR image, controlling the 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, and generating an MR image based on the output of the receiving coil.

[0118] [Appendix 11] A brain measurement method as described in Appendix 10, wherein the geomagnetic field correction coil is composed of a geomagnetic field correction coil for correcting the geomagnetic field and a gradient magnetic field correction coil for correcting the geomagnetic gradient magnetic field. [Explanation of symbols]

[0119] M1...brain measuring device, 1A, 23A...optically excited magnetic sensor, 2...magnetic sensor for geomagnetic field correction, 3...magnetic sensor for active shield, 4...non-magnetic frame (frame), 5...control device, 6...coil power supply, 7...geomagnetic correction coil, 8...gradient magnetic field correction coil, 9...active shield coil, 14...electromagnetic shield, 16, P1, P2, P3, Q1, Q2, Q3...markers, 21...transmitting coil, 22...receiving coil (detection coil), 24...output coil.

Claims

1. A brain measuring apparatus for generating an MR image and a brain magnetic field distribution of a subject, comprising: an MRI module having a transmission coil for transmitting a transmission pulse toward the subject and a detection coil for detecting a nuclear magnetic resonance signal generated in the subject by the transmission pulse; an optically excited magnetic sensor for detecting the brain magnetic field of the subject; a generating unit for generating the MR image based on the nuclear magnetic resonance signal detected by the detection coil, and for generating the brain magnetic field distribution based on the brain magnetic field detected by the optically excited magnetic sensor; A marker to be displayed on the MR image generated by the generation unit; a helmet-type frame to which the detection coil, the optically excited magnetic sensor, and the markers are attached and which is worn on the head of the subject; Equipped with The generation unit is an extraction process for extracting the marker from the MR image; an acquisition process for acquiring positions of the markers extracted in the extraction process in an MRI coordinate system, which is a coordinate system on the MR image; an estimation process for estimating conversion information for converting the magnetic brain coordinate system into the MRI coordinate system based on the positions of the markers in a magnetic brain coordinate system, which is a coordinate system on the brain magnetic field distribution, and the positions of the markers in the MRI coordinate system acquired in the acquisition process; a registration process for projecting the brain magnetic field distribution onto the MRI coordinate system using the transformation information estimated in the estimation process, and performing registration between the brain magnetic field distribution and the MR image; A brain measurement device that performs the following:

2. A plurality of the markers are attached to the frame at different positions from each other. The brain measuring apparatus according to claim 1 .

3. the plurality of markers includes at least three of the markers that are not collinear; The brain measuring apparatus according to claim 2 .

4. The marker includes a Beakley marker or a Magnevist solution capsule; The brain measuring apparatus according to any one of claims 1 to 3.

5. A brain measurement method for generating an MR image and a brain magnetic field distribution of a subject, comprising: a first step of detecting nuclear magnetic resonance signals generated by the subject and the markers while the subject is wearing a helmet-type frame provided with an optically excited magnetic sensor and markers on his / her head, thereby generating the MR image in which the markers are displayed based on the nuclear magnetic resonance signals, and detecting the subject's brain magnetic field with the optically excited magnetic sensor, thereby generating the brain magnetic field distribution based on the brain magnetic field; a second step of aligning the MR image generated in the first step with the brain magnetic field distribution; Equipped with The second step comprises: extracting the markers from the MR image; an acquiring step of acquiring the position of the marker extracted in the extracting step in an MRI coordinate system which is a coordinate system on the MR image; an estimation step of estimating conversion information for converting the magnetic brain coordinate system into the MRI coordinate system based on the positions of the markers in a magnetic brain coordinate system, which is a coordinate system on the brain magnetic field distribution, and the positions of the markers in the MRI coordinate system acquired in the acquisition step; a registration step of projecting the brain magnetic field distribution onto the MRI coordinate system using the transformation information estimated in the estimation step, and performing registration between the brain magnetic field distribution and the MR image; A brain measurement method comprising:

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