Brain measurement device and brain measurement method

Abstract

A brain measurement device and a brain measurement method are provided. A brain measurement device for generating an MR image and a brain magnetic field distribution of a subject includes: an MRI module having a transmission coil for transmitting a transmission pulse to the subject and a detection coil for detecting a nuclear magnetic resonance signal generated in the subject by the transmission pulse; an optically pumped magnetic sensor for detecting a brain magnetic field of the subject; a generation unit for generating the MR image based on the nuclear magnetic resonance signal detected by the detection coil and generating the brain magnetic field distribution based on the brain magnetic field detected by the optically pumped magnetic sensor; a marker capable of being displayed on the MR image generated by the generation unit; and a helmet-type frame on which the detection coil, the optically pumped magnetic sensor, and the marker are mounted and which is worn on the head of the subject.

Description

Technical Field

[0001] This invention relates to brain measurement devices and brain measurement methods. Background Technology

[0002] Patent document 1 (Japanese Patent No. 5823195) describes a MEG (Magnetoencephalography) device using a photoexcited magnetic sensor. In this MEG device, the distribution of a tiny magnetic field on the sensor surface is measured by the photoexcited magnetic sensor. Here, by aligning this magnetic field distribution with an MR image obtained by taking pictures of the brain structure of a subject using an MRI (Magnetic Resonance Imaging) device, the magnetic field source generated by the neural activity in the subject's brain can be assumed to be an equivalent current dipole moment vector, and its position and orientation can be obtained. In addition, non-patent document 1 (“SQUIDs in biomagnetism: a roadmap towards improved healthcare”, Supercond. Sci. Technol. 29(2016) 113001(30pp)) describes a study on integrating a MEG device and an MRI device. Summary of the Invention

[0003] Typically, MEG and MRI devices are separate devices. Therefore, in order to obtain the magnetic field distribution (brain magnetic field distribution) accompanying neural activity in the subject's brain, in addition to measurements in both devices, it is necessary to perform additional measurements to align the brain magnetic field distribution, based on the magnetic field measured on the sensor surface, with the subject's brain MR image. However, in this alignment based on the measurement, the additional measurements and the integrated processing of the brain magnetic field distribution based on the measurement with the brain morphology MR image become new major causes of error. Furthermore, Non-Patent Document 1 describes that even when the MEG and MRI devices are integrated, it is still necessary to improve the accuracy of the aforementioned alignment.

[0004] Therefore, the purpose of this invention is to provide a brain measurement device and method that can more accurately align the brain magnetic field distribution with MR images.

[0005] The brain measurement device of the present invention is a brain measurement device for generating MR images and brain magnetic field distribution of a subject, comprising: an MRI module having a transmitting coil for transmitting a transmitting pulse to the subject and a detection coil for detecting the MRI signal generated in the subject by transmitting the pulse; a photomagnetic sensor for detecting the brain magnetic field of the subject; a generation unit for generating an MR image based on the MRI signal detected by the detection coil and generating a brain magnetic field distribution based on the brain magnetic field detected by the photomagnetic sensor; a marker capable of being displayed on the MR image generated by the generation unit; and a helmet-type frame having the detection coil, the photomagnetic sensor, and the marker mounted thereon and worn on the head of the subject.

[0006] Alternatively, the brain measurement method of the present invention is a brain measurement method for generating MR images and brain magnetic field distributions of a subject, comprising: a first step, in a state where a helmet-type frame provided with a photomagnetic sensor and a marker is worn on the head of a subject, generating an MR image showing the marker based on the MRI signal generated by the subject and the marker, and generating a brain magnetic field distribution based on the brain magnetic field by detecting the subject's brain magnetic field using the photomagnetic sensor; and a second step, aligning the MR image generated in the first step with the brain magnetic field distribution.

[0007] In this brain measurement device and method, since the marker and photomagnetic sensor are mounted on a frame, the positional relationship between the marker and the photomagnetic sensor is determined within the frame with mechanical precision. This means that the position of the marker can be obtained with high precision in the brain magnetic field distribution generated based on the brain magnetic field detected by the photomagnetic sensor. Furthermore, the marker is displayed in the MR image. Therefore, information regarding the positional relationship between the brain magnetic field distribution and the MR image can be obtained based on the position of the marker in the brain magnetic field distribution and the position of the marker in the MR image. Thus, the brain magnetic field distribution can be aligned with the MR image with higher precision. In addition, in MRI and MEG measurements, the subject's head position sometimes changes relative to the tilting magnetic field coil, making alignment of the MR image with the brain magnetic field distribution difficult. In contrast, in this brain measurement device and method, since the marker is mounted on a helmet-shaped frame with a photomagnetic sensor fixed to it, the position of the marker is displayed in the MR image. Therefore, the brain magnetic field distribution can be aligned with the MR image with higher precision.

[0008] In the brain measurement device of the present invention, the generation unit may also perform: extraction processing, extracting markers from an MR image; acquisition processing, acquiring the position of the markers extracted in the extraction processing in an MRI coordinate system, which serves as a coordinate system on the MR image; estimation processing, estimating transformation information for transforming the MRI coordinate system to the MRI coordinate system based on the position of the markers in the MRI coordinate system, which serves as a coordinate system on the brain magnetic field distribution, and the position of the markers in the MRI coordinate system acquired in the acquisition processing; and alignment processing, using the transformation information estimated in the estimation processing, projecting the brain magnetic field distribution onto the MRI coordinate system to align the brain magnetic field distribution with the MR image. Alternatively, the brain measurement method of the present invention may also include, in the second step: an extraction step, extracting markers from an MR image; an acquisition step, acquiring the position of the markers extracted in the extraction step in an MRI coordinate system, which serves as the coordinate system on the MR image; an estimation step, estimating transformation information for transforming the MRI coordinate system to the MRI coordinate system based on the position of the markers in the MRI coordinate system, which serves as the coordinate system on the brain magnetic field distribution, and the position of the markers in the MRI coordinate system acquired in the acquisition step; and an alignment step, using the transformation information estimated in the estimation step, projecting the brain magnetic field distribution onto the MRI coordinate system to align the brain magnetic field distribution with the MR image. In these cases, transformation information for transforming the MRI coordinate system to the MRI coordinate system is estimated based on the positions of the markers 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 this transformation information, thereby enabling high-precision alignment of the MR image and the brain magnetic field distribution.

[0009] In the brain measurement device of the present invention, multiple markers may be installed at different positions on the frame. In this case, since there are multiple reference points for aligning the brain magnetic field distribution with the MR image, the alignment of the brain magnetic field distribution with the MR image can be performed with higher precision, for example, compared to the case where there is only one marker.

[0010] In the brain measurement device of the present invention, the multiple markers may also include at least three markers that are not on the same straight line. In this case, the three reference points required for the alignment of the brain magnetic field distribution with the MR image are obtained more accurately, so the alignment of the brain magnetic field distribution with the MR image can be performed with higher precision, for example, compared to the case where there are two markers.

[0011] In the brain measurement device of the present invention, the markers may also include Beekley markers or Magnevist solution capsules. In this case, the markers are displayed more clearly as bright dots in the MR image, so the position of the markers is determined with higher precision. Therefore, the brain magnetic field distribution can be aligned with the MR image with higher precision.

[0012] According to the present invention, a brain measurement device and a brain measurement method are provided that enable higher-precision alignment of the brain magnetic field distribution with MR images. Attached Figure Description

[0013] Figure 1 This is a diagram showing the structure of the brain measurement device according to the embodiment.

[0014] Figure 2 (a) is a schematic diagram showing an example of a non-magnetic frame for an implementation method.

[0015] Figure 2 (b) is a schematic diagram showing an example of an MR image acquired in the control device of the embodiment.

[0016] Figure 3 This is a schematic diagram showing the structure of the OPM module in the implementation method.

[0017] Figure 4 (a) is a schematic diagram showing an example of a non-magnetic frame for an implementation method.

[0018] Figure 4 (b) is a schematic diagram showing an example of an MR image acquired in the control device of the embodiment.

[0019] Figure 5 (a) is a schematic diagram showing an example of a non-magnetic frame for an implementation method.

[0020] Figure 5 (b) is a schematic diagram showing an example of an MR image acquired in the control device of the embodiment.

[0021] Figure 6 This is a flowchart illustrating the operation of the brain measurement device according to the implementation method.

[0022] Figure 7 This is a flowchart illustrating the operation of the brain measurement device according to the implementation method.

[0023] Figure 8 This is a flowchart illustrating the operation of the brain measurement device according to the implementation method. Detailed Implementation

[0024] Hereinafter, one embodiment will be described in detail with reference to the accompanying drawings. Furthermore, in the description of the drawings, the same or repeated elements will be labeled with the same reference numerals, and repeated descriptions will sometimes be omitted. Additionally, in the following drawings, an orthogonal coordinate system defined by the X-axis, Y-axis, and Z-axis may sometimes be shown.

[0025] Figure 1This is a schematic diagram illustrating the structure of the brain measurement device M1 according to an embodiment. The brain measurement device M1 is a device for measuring the brain magnetic field and MR (Magnetic Resonance) images of a subject. That is, the brain measurement device M1 is a device for generating the brain magnetic field distribution and MR images of a subject. The brain measurement device M1 includes: a magnetoencephalometer module having: multiple OPM (optically pumped magnetometer) modules 1, multiple magnetic sensors for geomagnetic field correction 2, multiple magnetic sensors for active shielding 3, a non-magnetic frame 4 (frame), a pair of geomagnetic correction coils 7, a pair of gradient magnetic field correction coils 8 (geomagnetic field correction coils), and a pair of active shielding coils 9; and an MRI module having: a transmitting coil 21, a receiving coil 22 (detection coil), an OPM module 23, and an output coil 24. In addition, the brain measurement device M1 includes: a control unit (generation unit) 5, a coil power supply 6, a pump laser 10, a probe laser 11, amplifiers 12A and 12B, a heater controller 13, an electromagnetic shield 14, a transmitting coil controller 15, a marker 16, and a magnetic shield 25.

[0026] In the following description, the direction that is generally parallel to the central axis of the subject's head is defined as the Z-axis, and the directions that are perpendicular to the Z-axis and perpendicular to each other are defined as the X-axis and Y-axis.

[0027] OPM module 1 includes a photoexcited magnetic sensor 1A, a heat-insulating material 1B, and a readout circuit 1C. Multiple OPM modules 1 are arranged, for example, along the scalp at predetermined intervals.

[0028] The photo-induced magnetosensor 1A is a sensor that uses optical pumping to measure the brain's magnetic field. That is, the photo-induced magnetosensor 1A is a sensor used to detect the brain's magnetic field in a subject. The photo-induced magnetosensor 1A has a sensitivity of, for example, approximately 10 fT to 10 pT. A heat-insulating material 1B prevents thermal movement and heat transfer in the photo-induced magnetosensor 1A. A readout circuit 1C is a circuit that obtains the detection result of the photo-induced magnetosensor 1A. The photo-induced magnetosensor 1A excites the alkali metal by irradiating a pump light into a cell containing alkali metal vapor. The excited alkali metal is in a spin-polarized state, and when it receives magnetism, the tilt of the spin polarization axis of the alkali metal atoms changes according to the magnetism. This tilt of the spin polarization axis is detected by a probe light irradiated separately from the pump light. Furthermore, the photo-induced magnetosensor 1A is configured to apply a predetermined bias magnetic field in the direction of the pump light irradiation to have sensitivity to magnetic fields with frequencies ranging from 0 to 200 Hz. The readout circuit 1C receives the detection light passing through the alkali metal vapor via a photodiode and obtains the detection result. The readout circuit 1C outputs the detection result to the amplifier 12A.

[0029] The photoexcited magnetic sensor 1A can also be used as an axial gradiometer, for example. The axial gradiometer has a measurement region and a reference region coaxially arranged in a direction perpendicular to the subject's scalp (measurement site). The measurement region is, for example, the part of the axial gradiometer that measures the brain magnetic field closest to the subject's scalp. The reference region is, for example, the part of the axial gradiometer that measures the brain magnetic field at a predetermined distance (e.g., 3 cm) from the measurement region, relative to the direction away from the subject's scalp. The axial gradiometer outputs the respective results of measurements in the measurement region and the reference region to the amplifier 12A. Here, in the case of common-mode noise, the effect on the output results in the measurement region and the reference region is shown. Common-mode noise is removed by obtaining the difference between the output results in the measurement region and the output results in the reference region. By removing common-mode noise, for example, in the case of measurement in a magnetic noise environment of 1 pT, the photoexcited magnetic sensor 1A can obtain a sensitivity of approximately 10 fT / √Hz.

[0030] The geomagnetic field correction magnetic sensor 2 is a sensor that measures the geomagnetic magnetic field at a position corresponding to the photoexcited magnetic sensor 1A, and is configured, for example, by a fluxgate sensor with a sensitivity of approximately 1 nT to 100 μT. The position corresponding to the photoexcited magnetic sensor 1A refers to the periphery (nearby) of the area where the photoexcited magnetic sensor 1A is located. The geomagnetic field correction magnetic sensor 2 can be set up one-to-one with the photoexcited magnetic sensor 1A, or it can be set up in a one-to-many manner (one geomagnetic field correction magnetic sensor 2 corresponds to multiple photoexcited magnetic sensors 1A). The geomagnetic field correction magnetic sensor 2 measures, as a geomagnetic magnetic field, such as the geomagnetic gradient magnetic field (hereinafter simply referred to as "gradient magnetic field"), and outputs the measured value to the control device 5. The measured value of the geomagnetic field correction magnetic sensor 2 can be represented by a vector having direction and magnitude. The geomagnetic field correction magnetic sensor 2 can also continuously measure and output at predetermined time intervals.

[0031] The active shielding magnetic sensor 3 is a sensor that measures a changing magnetic field at a position corresponding to the photoexcited magnetic sensor 1A, and is configured, for example, by a photoexcited sensor having a sensitivity of approximately 100 fT to 10 nT, which is different from the photoexcited magnetic sensor 1A. The position corresponding to the photoexcited magnetic sensor 1A refers to the periphery (nearby) of the area where the photoexcited magnetic sensor 1A is located. The active shielding magnetic sensor 3 can be set one-to-one with the photoexcited magnetic sensor 1A, or it can be set in a one-to-many manner (one active shielding magnetic sensor 3 corresponds to multiple photoexcited magnetic sensors 1A). The active shielding magnetic sensor 3 measures the magnetic field as a noise (AC) component, for example, below 200 Hz, which is a changing magnetic field, and outputs the measured value to the control device 5. The measured value of the active shielding magnetic sensor 3 can be represented by a vector having direction and magnitude. The active shielding magnetic sensor 3 can also continuously measure and output at predetermined time intervals.

[0032] The marker 16 is a marker displayed in the MR image acquired by the control device 5, for example, including a Beekley marker or a Magnevisist solution capsule. The marker 16 is, for example, spherical. The marker 16 containing the Beekley marker or Magnevisist solution capsule has sufficient proton density and moderate longitudinal relaxation time T1 and lateral relaxation time T2, so it appears as a bright dot in the MR image.

[0033] The non-magnetic frame 4 is a frame that covers the entire area of ​​the scalp of the subject, which is the object of the brain magnetic field measurement, and is made of a non-magnetic material such as graphite with a relative magnetic permeability close to 1 that does not interfere with the magnetic field distribution. The non-magnetic frame 4 can be, for example, a helmet-type frame that surrounds the entire area of ​​the subject's scalp and is worn on the subject's head. In the non-magnetic frame 4, multiple photoexcited magnetic sensors 1A are fixed close to the subject's scalp. In addition, in the non-magnetic frame 4, a geomagnetic magnetic field correction magnetic sensor 2 is fixed so as to be able to measure the geomagnetic magnetic field at each position of the multiple photoexcited magnetic sensors 1A, and an active shielding magnetic sensor 3 is fixed so as to be able to measure the changing magnetic field at each position of the multiple photoexcited magnetic sensors 1A. Since the deviation of the magnetic field strength of the changing magnetic field according to the position is smaller than that of the static magnetic field, the non-magnetic frame 4 can also be fixed in such a way that the number of active shielding magnetic sensors 3 is less than the number of geomagnetic magnetic field correction magnetic sensors 2.

[0034] Furthermore, one or more markers 16 are mounted on the non-magnetic frame 4 at different locations. Multiple markers 16 are used here. Figure 1 and Figure 2In the example shown in (a), the plurality of markers 16 include at least three markers 16 that are not collinear within the non-magnetic frame 4. Additionally, a receiving coil 22 for detecting nuclear magnetic resonance signals for MR image measurement is fixed to the scalp side of the subject for the plurality of photoexcited magnetic sensors 1A within the non-magnetic frame 4. This receiving coil 22 is used to detect the nuclear magnetic resonance signal generated by the subject. The receiving coil 22 detects the nuclear magnetic resonance signal of protons (described later) and converts it into an electric current. To improve the detection sensitivity of the nuclear magnetic resonance signal, the receiving coil 22 is preferably positioned on the scalp side of the subject's head close to the photoexcited magnetic sensor 1A. Thus, at least the receiving coil 22, the photoexcited magnetic sensor 1A, and the markers 16 are mounted on the non-magnetic frame 4.

[0035] Figure 2 Figure (a) is an example of a nonmagnetic frame 4. Figure 2 In the example shown in (a), a non-magnetic frame 4, serving as a helmet-type frame, is depicted. Multiple OPM modules 1 and markers P1, P2, and P3, serving as three markers 16, are mounted on the non-magnetic frame 4. The non-magnetic frame 4 is mounted on the subject. The multiple OPM modules 1 are mounted, for example, along the outer surface of the frame at predetermined intervals. Marker P1 is mounted at a position corresponding to the subject's brow, and markers P2 and P3 are mounted at positions corresponding to the left and right temples of the subject's head.

[0036] Refer again Figure 1 The transmitting coil 21 is a coil that irradiates an RF pulse (transmit pulse) of a specified frequency (e.g., about 300 kHz) onto the subject's head during MR image measurement. That is, the transmitting coil 21 is a coil used to transmit the transmit pulse to the subject. An MRI signal is then generated from the subject through this transmit pulse. The transmitting coil 21 is, for example, positioned above the subject's head outside the non-magnetic frame 4.

[0037] The output coil 24 is electrically connected to both ends of the receiving coil 22 via a cable, and receives the current flowing through both ends of the receiving coil 22, converts the current back into a magnetic signal and outputs it.

[0038] Like OPM module 1, OPM module 23 includes a photoexcited magnetic sensor 23A (another photoexcited magnetic sensor), a heat-insulating material 23B, and a readout circuit 23C. OPM module 23, for example, is housed outside the non-magnetic frame 4, together with the output coil 24, within a magnetic shield 25 that shields against the static magnetic field described later. The magnetic shield 25 is made of a metal with a relative permeability greater than 1, such as μ metal.

[0039] The photo-excited magnetosensor 23A is a sensor that uses optical pumping to measure magnetic signals. Furthermore, the photo-excited magnetosensor 23A is configured to apply a predetermined bias magnetic field in the direction of the pump light to be sensitive to magnetic fields with frequencies ranging from 20 kHz to 500 kHz. For example, applying a bias magnetic field of approximately 40 μT provides sensitivity to electromagnetic waves emitted by protons at a frequency of 300 kHz. The photo-excited magnetosensor 23A detects the magnetic signal output by the output coil 24. The readout circuit 23C outputs the detection result from the photo-excited magnetosensor 23A to the amplifier 12B.

[0040] exist Figure 3 The diagram below illustrates a specific example of the structure of the OPM module 23. The photoexcited magnetic sensor 23A comprises: a strip-shaped unit 26 encapsulated with a gas containing an alkali metal whose polarization direction changes according to the measured magnetic field; a heater 27 that heats the entire unit 26 to a predetermined temperature (e.g., 180 degrees Celsius); a polarizing beam splitter 28; and a photodetector 29. In this unit 26, pump light L1 is introduced from the outside along its long side, and probe light L2 is branched out along a direction perpendicular to its length, corresponding to each of several (e.g., four equal parts) intersecting regions 26A divided along its long side. The probe light L2, passing through these intersecting regions 26A, is detected by the magneto-optical angle via the polarizing beam splitter 28 and photodetector 29, which are positioned corresponding to each intersecting region 26A. That is, the polarization beam splitter 28 separates the probe light L2 into two linearly polarized light components that are orthogonal to each other, and the photodetector 29 uses two built-in PDs (photodiodes) to detect the intensity of the two linearly polarized light components, and detects the magneto-optical angle of the probe light L2 based on the ratio of the detected intensities. In the OPM module 23, a circuit board 30 is also provided, and the readout circuit 23C in the circuit board 30 outputs the magneto-optical angle of each detected probe light L2 for each cross region 26A.

[0041] Within the magnetic shield 25, the output coil 24 is fixed in a manner opposite to the intersection regions 26A of the units 26 of the OPM module 23 described above. With this structure, the electromagnetic field E detected by the receiving coil 22 is detected based on the magneto-optical angle of the probe light L2, which varies according to the tilt of the spin polarization axis of the alkali metal atom. OUT The magnetic signal B generated by the output coil 24 OUT Here, in Figure 3 In the example, the number of divisions in the intersection region 26A is set to 4, but it can be changed to any number. In addition, multiple units 26 can be set side by side, and the intersection regions 26A can also be arranged in two dimensions (e.g., 4×4=16).

[0042] When measuring the brain magnetic field, the control device 5 determines the current corresponding to various coils based on the measured values ​​output from the magnetic sensor 2 for geomagnetic field correction and the magnetic sensor 3 for active shielding, and outputs a control signal for outputting the current to the coil power supply 6. The control device 5 determines the current for the geomagnetic correction coil 7 and the gradient magnetic field correction coil 8, which serve as geomagnetic field correction coils, based on the measured values ​​of the multiple magnetic sensors 2 for geomagnetic field correction, in a manner that generates a magnetic field to cancel out the magnetic field associated with the geomagnetic field. Furthermore, the control device 5 determines the current for the active shielding coil 9 based on the measured values ​​of the multiple magnetic sensors 3 for active shielding, in a manner that generates a magnetic field to cancel out the changing magnetic field. The control device 5 outputs a control signal corresponding to the determined current to the coil power supply 6.

[0043] Specifically, the control device 5 determines the current to the geomagnetic correction coil 7 in such a way that the average value of the measurements from the multiple geomagnetic field correction magnetic sensors 2 is approximately zero (as a result, to generate a magnetic field that is opposite in magnitude and opposite in magnitude to the geomagnetic field at the location of the photoexcited magnetic sensor 1A). The control device 5 outputs a control signal (static magnetic field correction control signal) corresponding to the determined current of the geomagnetic correction coil 7 to the coil power supply 6.

[0044] Furthermore, the control device 5 determines the current to the gradient magnetic field correction coil 8 in a manner that minimizes the deviation of the average value of the measurements from the multiple geomagnetic field correction magnetic sensors 2 (as a result, generating a magnetic field that is opposite in direction and of the same magnitude as the gradient magnetic field at the location of the photoexcited magnetic sensor 1A). The control device 5 outputs a control signal (static magnetic field correction control signal) corresponding to the determined current of the gradient magnetic field correction coil 8 to the coil power supply 6.

[0045] Furthermore, the control device 5 determines the current to the active shielding coil 9 in such a way that the average value of the measurements from the plurality of active shielding magnetic sensors 3 is approximately zero (as a result, in a way that generates a magnetic field that is opposite in direction and of the same magnitude as the changing magnetic field at the position of the photoexcitation magnetic sensor 1A). The control device 5 outputs a control signal (changing magnetic field correction control signal) corresponding to the determined current of the active shielding coil 9 to the coil power supply 6.

[0046] Furthermore, the control device 5 uses the signal output from the amplifier 12A to obtain magnetically correlated information detected by the photomagnetic sensor 1A. Moreover, the control device 5 generates a brain magnetic field distribution based on the brain magnetic field detected by the photomagnetic sensor 1A (based on the magnetically correlated information). In the case where the photomagnetic sensor 1A is an axial gradiometer, the control device 5 can also remove common-mode noise by obtaining the difference between the output result of the measurement area and the output result of the reference area. In addition, the control device 5 can also control the operation of the pump laser 10 and the probe laser 11, including the irradiation time and duration. Furthermore, the processing of generating the brain magnetic field distribution based on the magnetically correlated information detected by the photomagnetic sensor 1A can be performed using existing techniques.

[0047] Furthermore, during MR image measurement, the control device 5 determines the current supplied to the geomagnetic correction coil 7 and the gradient magnetic field correction coil 8. The geomagnetic correction coil 7 and the gradient magnetic field correction coil 8 operate as coils for applying static magnetic fields and tilted magnetic fields, respectively, and the control device 5 outputs a control signal for outputting the current to the coil power supply 6. That is, the control device 5 determines the current flowing through the geomagnetic correction coil 7 by applying a magnetic field of a predetermined intensity (e.g., 7 mT) in the X-axis direction as an electrostatic field to the subject's head. Additionally, the control device 5 selectively determines the X-axis magnetic field gradient (dBX / dX), Y-axis magnetic field gradient (dBX / dY), and Z-axis magnetic field gradient (dBX / dZ) as tilted magnetic fields and determines the current flowing through the gradient magnetic field correction coil 8. Therefore, the slice position in the MR image can be determined, and the position within the slice plane can be encoded through phase encoding and frequency encoding. Furthermore, during MR image measurement, the control device 5 outputs a control signal without supplying current to the active shielding coil 9, which removes low-frequency noise.

[0048] Furthermore, during MR image measurement, the control device 5 controls the transmission coil controller 15 by outputting a control signal to control the power supplied to the transmission coil 21, thereby irradiating the subject's head with a transmission pulse of a predetermined frequency (e.g., 300 kHz in the case of a static magnetic field strength of 7 mT). As a result, proton resonance and spin tilt occur in the slice plane (the plane selected by the static magnetic field and the tilting magnetic field). Subsequently, the control device 5 controls the power supply to the transmission coil 21 to be turned off. Thus, an MR image can be obtained by measuring the spin recovery morphology based on the output of the OPM module 23. That is, the control device 5 generates an MR image based on the magnetic signal detected by the photoexcited magnetic sensor 23A. In other words, the control device 5 is also a generation 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 uses a known spin echo sequence or gradient echo sequence, etc., to encode the position by frequency and phase and measure the nuclear magnetic resonance signal from the protons, and converts the measurement result into an MR image using FFT.

[0049] The control device 5 is physically configured as a storage unit including a memory such as RAM and ROM, a processor (arithmetic circuit) such as a CPU, a communication interface, and a hard disk. Examples of related control devices 5 include personal computers, cloud servers, smartphones, and tablet computers. The control device 5 functions by having the CPU of the computer system execute programs stored in the memory.

[0050] The coil power supply 6 outputs a specified current to each of the geomagnetic correction coil 7, the gradient magnetic field correction coil 8, and the active shielding coil 9 according to the control signal output from the control device 5. Specifically, the coil power supply 6 outputs current to the geomagnetic correction coil 7 according to the control signal associated with the geomagnetic correction coil 7. The coil power supply 6 outputs current to the gradient magnetic field correction coil 8 according to the control signal associated with the gradient magnetic field correction coil 8. The coil power supply 6 outputs current to the active shielding coil 9 according to the control signal associated with the active shielding coil 9.

[0051] The transmitting coil controller 15 is electrically connected to the transmitting coil 21 and supplies power to the transmitting coil 21 by irradiating transmitting pulses of a predetermined frequency according to the control signal output from the control device 5.

[0052] The geomagnetic correction coil 7 is a coil used to correct the geomagnetic field in the magnetic field associated with the location of the photomagnetic sensor 1A. The geomagnetic correction coil 7 generates a magnetic field based on the current supplied from the coil power supply 6 to cancel the geomagnetic field. The geomagnetic correction coil 7 may have a pair of geomagnetic correction coils 7A and 7B. The pair of geomagnetic correction coils 7A and 7B are configured to sandwich the photomagnetic sensor 1A (e.g., on the left and right sides of the subject). The pair of geomagnetic correction coils 7A and 7B generate a magnetic field of the same magnitude and opposite direction to the geomagnetic field at the location of the photomagnetic sensor 1A, based on the current supplied from the coil power supply 6. The direction of the magnetic field is, for example, the X-axis, Y-axis, and Z-axis directions. The geomagnetic field at the location of the photomagnetic sensor 1A is canceled by the opposite magnetic field of the same magnitude generated by the geomagnetic correction coil 7. In this way, the geomagnetic correction coil 7 corrects the geomagnetic field at the location of the photomagnetic sensor 1A.

[0053] In addition, the geomagnetic correction coil 7 also functions as a static magnetic field coil, which is used to generate 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 specified intensity based on the current supplied from the coil power supply 6.

[0054] The gradient magnetic field correction coil 8 is used to correct the gradient magnetic field in the geomagnetic magnetic field related to the location of the photoexcited magnetic sensor 1A. The gradient magnetic field correction coil 8 generates a magnetic field based on the current supplied from the coil power supply 6 to cancel the gradient magnetic field. The gradient magnetic field correction coil 8 may have a pair of gradient magnetic field correction coils 8A and 8B. The pair of gradient magnetic field correction coils 8A and 8B are configured to sandwich the photoexcited magnetic sensor 1A (e.g., on the left and right sides of the subject). The pair of gradient magnetic field correction coils 8A and 8B generate a magnetic field of the same magnitude and opposite direction to the gradient magnetic field at the location of the photoexcited magnetic sensor 1A, based on the current supplied from the coil power supply 6. The direction of the magnetic field is, for example, the X-axis, Y-axis, and Z-axis directions. The gradient magnetic field at the location of the photoexcited magnetic sensor 1A is canceled by the opposite magnetic field of 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 location of the photoexcited magnetic sensor 1A.

[0055] Additionally, the gradient magnetic field correction coil 8 functions as a tilting magnetic field coil, which is used to generate a tilting magnetic field during MR image measurement. The gradient magnetic field correction coil 8 generates a tilting magnetic field with selective gradients in the X, Y, and Z axes, based on the current supplied from the coil power supply 6.

[0056] The active shielding coil 9 is a coil used to correct the changing magnetic field at the position of the photoexcited magnetometer 1A. The active shielding coil 9 generates a magnetic field based on the current supplied from the coil power supply 6 to cancel the changing magnetic field. The active shielding coil 9 may have a pair of active shielding coils 9A and 9B. The pair of active shielding coils 9A and 9B are configured to sandwich the photoexcited magnetometer 1A (e.g., on the left and right sides of the subject). The pair of active shielding coils 9A and 9B generate a magnetic field of the same magnitude and opposite direction to the changing magnetic field at the position of the photoexcited magnetometer 1A, based on the current supplied from the coil power supply 6. The direction of the magnetic field is, for example, the X-axis, Y-axis, and Z-axis directions. The changing magnetic field at the position of the photoexcited magnetometer 1A is canceled by the opposing magnetic field of the same magnitude generated by the active shielding coil 9. In this way, the active shielding coil 9 corrects the changing magnetic field at the position of the photoexcited magnetometer 1A.

[0057] Pump laser 10 is a laser device that generates pump light. The pump light emitted from pump laser 10 passes through an optical fiber branch and is incident on each of the multiple photoexcited magnetosensors 1A and 23A.

[0058] The probe laser 11 is a laser device that generates probe light. The probe light emitted from the probe laser 11 passes through an optical fiber branch and is incident on each of the multiple photoexcited magnetosensors 1A and 23A.

[0059] Amplifier 12A is a device or circuit that amplifies the signal from the output of OPM module 1 (specifically, read circuit 1C) and outputs it to control device 5.

[0060] Amplifier 12B is a device or circuit that amplifies the signal from the output of OPM module 23 (specifically, read circuit 23C) and outputs it to control device 5.

[0061] The heater controller 13 is a temperature control device connected to the heaters for heating the units of photoexcited magnetic sensor 1A and photoexcited magnetic sensor 23A, and to thermocouples (not shown) for measuring the temperature of each unit. The heater controller 13 receives temperature information of the unit from the thermocouples and adjusts the temperature of the unit based on this temperature information by adjusting the heating of the heater.

[0062] The electromagnetic shield 14 is a shielding member that blocks high-frequency (e.g., above 10kHz) electromagnetic noise. It is constructed, for example, of a mesh woven from metal wires or a non-magnetic metal plate such as aluminum. The electromagnetic shield 14 is configured to surround the OPM modules 1 and 23, the transmitting coil 21, the receiving coil 22, the output coil 24, the magnetic sensor 2 for geomagnetic field correction, the magnetic sensor 3 for active shielding, the non-magnetic frame 4, the geomagnetic correction coil 7, the gradient magnetic field correction coil 8, and the active shielding coil 9. This electromagnetic shield 14 prevents noise in the 300kHz frequency band (the measurement frequency) from entering the receiving coil 22 and causing noise increase during MR image measurement. Furthermore, it prevents high-frequency noise from entering the photoexcited magnetic sensor 1A and causing instability during brain magnetic field measurement.

[0063] Next, the characteristic processing performed by the control device 5 will be described. The control device 5 generates the brain magnetic field distribution and MR image as described above. Then, the control device 5 aligns the generated brain magnetic field distribution with the MR image. Furthermore, in the MEG coordinate system (magnetic-electromagnetic coordinate system) that serves as the coordinates on the brain magnetic field distribution, the positions of the photoexcited magnetic sensor 1A and the marker 16 are predetermined during the design of the non-magnetic frame 4. Additionally, the MEG coordinate system (magnetic-electromagnetic coordinate system) refers to the coordinate system that defines the relative positional relationship between the photoexcited magnetic sensor 1A and the measured brain magnetic field distribution.

[0064] First, the control device 5 performs an extraction process to extract marker 16 from the generated MR image. Then, the control device 5 performs an acquisition process in the coordinate system of the MR image, i.e., the MRI coordinate system, to obtain the position of the marker 16 extracted in the extraction process. Figure 2 (b) is a diagram representing an MR image. The control device 5 extracts the markers 16, namely markers Q1, Q2, and Q3, displayed in the MR image. Based on the extraction results, the control device 5 obtains the position coordinates of markers Q1, Q2, and Q3 in the MRI coordinate system.

[0065] Next, the control device 5 performs estimation processing to estimate transformation information for transforming the MEG coordinate system to 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 obtained in the acquisition process.

[0066] In the estimation process, firstly, the control device 5 obtains the position coordinates of the marker 16 in the MEG coordinate system. Figure 2 In the example shown in (a), the MEG coordinate system is represented as the coordinate system corresponding to the non-magnetic frame 4. The control device 5 obtains the position coordinates of markers P1, P2, and P3 in the MEG coordinate system in advance based on the design information of the non-magnetic frame 4.

[0067] Next, the control device 5 uses the following equation (1) to estimate the transformation information, namely the affine transformation matrix T, used to transform the MEG coordinate system into the MRI coordinate system, based on 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.

[0068] P MRI =TP MEG …(1)

[0069] In equation (1) above, P MRI P represents the position vector in the MRI coordinate system. MEG Let T represent the position vector in the MEG coordinate system, and let T represent the affine transformation matrix (transformation information). If the positional relationship between three points is known between the MRI and MEG coordinate systems, the affine transformation matrix T can be determined. Figure 2 of (a), Figure 2 In the example shown in (b), the three points in the MRI coordinate system can be designated as markers P1, P2, and P3, and the three points in the MEG coordinate system can be designated as markers Q1, Q2, and Q3. Therefore, the control device 5 can use the markers 16 to estimate the affine transformation matrix T.

[0070] Furthermore, the number of markers 16 disposed on the non-magnetic frame 4 need to be at least one. If there is only one marker 16, substitutes for the other two markers 16 can be displayed in the MR image, for example, on the left and right ears of the subject. Figure 4 of (a), Figure 4 In the example shown in (b), the marker P1 positioned corresponding to the subject's brow is marker 16 positioned on the non-magnetic frame 4, and is displayed as marker Q1 in the MR image. The control device 5 can use one marker 16 and two locations, namely the subject's left and right ears, to estimate the affine transformation matrix T.

[0071] In addition, Figure 5 of (a), Figure 5 In the example shown in (b), markers P1 and P2, positioned corresponding to the subject's brow and back of the head, are markers 16 disposed within the non-magnetic frame 4, and are displayed as markers Q1 and Q2 in the MR image. As described above, when there are two markers 16, the control device 5 uses a portion of the subject's left or right ear as a substitute for the other marker 16. The control device 5 can use these two markers 16 and a portion of the subject's left or right ear to estimate the affine transformation matrix T.

[0072] The control device 5 uses the transformation information estimated through the estimation process as described above to perform alignment processing to project the brain magnetic field distribution onto the MRI coordinate system, thereby aligning the brain magnetic field distribution with the MR image. Specifically, the control device 5 uses the affine transformation matrix T, which represents the correspondence between the MEG coordinate system and the MRI coordinate system estimated in the estimation process, to project the brain magnetic field distribution in the MEG coordinate system onto the MRI coordinate system.

[0073] Next, refer to Figures 6-8 The brain measurement method using the brain measurement device M1 according to the embodiment will be described. Figures 6-8 This is a flowchart illustrating the actions of the brain measurement device M1.

[0074] First, when the measurement of the brain magnetic field begins with the non-magnetic frame 4 worn on the subject, the geomagnetic field correction magnetic sensor 2 measures the magnetic field associated with the geomagnetic field as an electrostatic field (step S11). The geomagnetic field correction magnetic sensor 2 measures the geomagnetic and gradient magnetic fields at various locations of the photoexcited magnetic sensor 1A and outputs the measured values ​​to the control device 5.

[0075] Control device 5 and coil power supply 6 control the current to the geomagnetic correction coil 7 (step S12). Control device 5 determines the current to the geomagnetic correction coil 7 based on the measurements from the geomagnetic field correction magnetic sensor 2, in a manner that generates a magnetic field of the same magnitude and opposite direction to the geomagnetic field at the location of the photoexcited magnetic sensor 1A. More specifically, control device 5 determines the current to the geomagnetic correction coil 7, for example, by making the average of the measurements from the plurality of geomagnetic field correction magnetic sensors 2 approximately zero. Control device 5 outputs a control signal corresponding to the determined current to coil power supply 6. Coil power supply 6 outputs a predetermined current to the geomagnetic correction coil 7 according to the control signal output by control device 5. Geomagnetic correction coil 7 generates a magnetic field based on the current supplied from coil power supply 6. The geomagnetic field at the location of the photoexcited magnetic sensor 1A is canceled out by the magnetic field of the same magnitude and opposite direction generated by the geomagnetic correction coil 7.

[0076] Control device 5 and coil power supply 6 control the current to gradient magnetic field correction coil 8 (step S13). Control device 5 determines the current to gradient magnetic field coil 8 based on measurements from the geomagnetic field correction magnetic sensor 2, in a manner that generates a magnetic field of the same magnitude and opposite direction to the gradient magnetic field at the location of photoexcited magnetic sensor 1A. More specifically, control device 5 determines the current to gradient magnetic field correction coil 8, for example, in a manner that minimizes the deviation from the average of the measurements from multiple geomagnetic field correction magnetic sensors 2. Control device 5 outputs a control signal corresponding to the determined current to coil power supply 6. Coil power supply 6 outputs a predetermined current to gradient magnetic field correction coil 8 according to the control signal output by control device 5. Gradient magnetic field correction coil 8 generates a magnetic field based on the current supplied from coil power supply 6. The gradient magnetic field at the location of photoexcited magnetic sensor 1A is canceled out by a magnetic field of the same magnitude and opposite direction generated by gradient magnetic field correction coil 8.

[0077] Control device 5 determines whether the measured value of the corrected static magnetic field (magnetic field related to the Earth's magnetism) is below a reference value (step S14). The measured value of the corrected static magnetic field refers to the value measured by the magnetic sensor 2 using the geomagnetic magnetic field correction after the static magnetic field is corrected by the geomagnetic correction coil 7 and the gradient magnetic field correction coil 8. The reference value is the magnitude of the magnetic field in which the photoexcited magnetic sensor 1A operates normally, for example, it can be 1 nT. If the measured value of the static magnetic field is not below the reference value ("No" in step S14), the process returns to step S11. If the measured value of the static magnetic field is below the reference value ("Yes" in step S14), the process proceeds to step S15.

[0078] The active shielding magnetic sensor 3 measures the changing magnetic field (step S15). The active shielding magnetic sensor 3 measures the changing magnetic field at various locations of the photoexcited magnetic sensor 1A and outputs the measured values ​​to the control device 5.

[0079] Control device 5 and coil power supply 6 control the current to active shielding coil 9 (step S16). Control device 5 determines the current to active shielding coil 9 based on the measurements from active shielding magnetic sensor 3, in a manner that generates a magnetic field of the same magnitude and opposite direction to the changing magnetic field of photoexcitation magnetic sensor 1A. More specifically, control device 5 determines the current to active shielding coil 9, for example, by making the average of the measurements from multiple active shielding magnetic sensors 3 approximately zero. Control device 5 outputs a control signal corresponding to the determined current to coil power supply 6. Coil power supply 6 outputs a predetermined current to active shielding coil 9 according to the control signal output by control device 5. Active shielding coil 9 generates a magnetic field based on the current supplied from coil power supply 6. The changing magnetic field of the position of photoexcitation magnetic sensor 1A is canceled out by the opposing magnetic field of the active shielding coil 9.

[0080] The control device 5 determines whether the measured value of the corrected changed magnetic field is below a reference value (step S17). The measured value of the corrected changed magnetic field refers to the value measured by the active shielding magnetic sensor 3 after the changed magnetic field is corrected by the active shielding coil 9. The reference value is the noise level that can be measured in the brain magnetic field, for example, it can be set to 1 pT. If the measured value of the changed magnetic field is not below the reference value ("No" in step S17), the process returns to step S15. If the measured value of the changed magnetic field is below the reference value ("Yes" in step S17), the process proceeds to step S18.

[0081] The photomagnetic sensor 1A measures the brain magnetic field (step S18). The control device 5 outputs the measurement result obtained by the photomagnetic sensor 1A to a predetermined output destination. The predetermined output destination may be an external device such as a storage device (e.g., a memory or hard disk of the control device 5) or an output device (e.g., a display). Because the static magnetic field (magnetic field related to the Earth's magnetosphere) and the changing magnetic field at the location of the photomagnetic sensor 1A are canceled out by becoming below a predetermined reference value, the photomagnetic sensor 1A can measure the brain magnetic field while avoiding the influence of the electrostatic field (magnetic field related to the Earth's magnetosphere) and the changing magnetic field. Based on the brain magnetic field obtained by the photomagnetic sensor 1A, the control device 5 generates the brain magnetic field distribution of the subject. The control device 5 can obtain information related to the position of the marker 16 (in the MEG coordinate system) in the brain magnetic field distribution based on the positional relationship between the photomagnetic sensor 1A and the marker 16 in the non-magnetic frame 4.

[0082] Move to Figure 7 When MR image measurement continues while the non-magnetic frame 4 remains on the subject, the control device 5 determines the current supplied to the geomagnetic correction coil 7 for applying the static magnetic field, and controls the generation of an electrostatic field in the X-axis direction of 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 supplied to the gradient magnetic field correction coil 8 for generating the tilted magnetic field, and controls the generation of the magnetic field gradient (dBX / dX) in the X-axis direction by outputting a control signal to the coil power supply 6 (step S20). Simultaneously, the control device 5 outputs a control signal to the transmitting coil controller 15 to control the power supplied to the transmitting coil 21, and controls the transmission by irradiating the subject's head with a transmitting pulse (step 21). As a result, protons in the specified slice area are excited.

[0083] Furthermore, the control device 5 determines the current supplied to the gradient magnetic field correction coil 8 for generating the tilted magnetic field, and controls the generation of the Y-axis magnetic field gradient (dBX / dY) on the slice surface by outputting a control signal to the coil power supply 6 (step S22). Phase encoding is then performed. Additionally, the control device 5 determines the current supplied to the gradient magnetic field correction coil 8 for generating the tilted magnetic field, and controls the generation of the Z-axis magnetic field gradient (dBX / dZ) on the slice surface by outputting a control signal to the coil power supply 6 (step S23). Frequency encoding is then performed.

[0084] Simultaneously, the OPM module 23 outputs a nuclear magnetic resonance (NMR) signal from the protons via the receiving coil 22 and the output coil 24, and the control device 5 subsequently acquires NMR signal data (step S24). Afterward, the control device 5 determines whether NMR signal data related to other slice planes has been acquired (step S25). If the determination result is that NMR signal data related to other slice planes has been acquired ("Yes" in step S25), the process returns to step S20. On the other hand, if NMR signal data related to other slice planes has not been acquired ("No" in step S25), an MR image is obtained by performing a Fourier transform on the NMR signal data acquired so far (step S26). That is, the control device 5 generates an MR image based on the NMR signal. The control device 5 outputs the acquired MR image to a predetermined output destination. The predetermined output destination may be an external device such as a memory, hard disk, or other storage device of the control device 5, or a display or other output device, or a terminal device connected via a communication interface.

[0085] Transferred to Figure 8 The control device 5 extracts marker 16 from the MR image (step S27). Next, the control device 5 obtains the position of the extracted marker 16 in the MRI coordinate system (step S28). Then, based on the position of marker 16 in the MEG coordinate system and the obtained position of marker 16 in the MRI coordinate system, the control device 5 estimates transformation information for transforming the MEG coordinate system to the MRI coordinate system (step S29). Afterwards, the control device 5 uses the estimated transformation information to project the brain magnetic field distribution onto the MRI coordinate system to align the brain magnetic field distribution with the MR image (step S30).

[0086] As described above, one embodiment of the brain measurement method includes: a first step, in which, with a helmet-type non-magnetic frame 4 equipped with a photomagnetic sensor 1A and a marker 16 worn on the head of a subject, an MR image displaying the marker 16 is generated based on the MRI signal generated by the subject (steps S19 to S26), and a brain magnetic field distribution is generated based on the brain magnetic field by detecting the subject's brain magnetic field with the photomagnetic sensor 1A (steps S11 to S18); and a second step, in which the MR image generated in the first step is aligned with the brain magnetic field distribution (steps S27 to S30). Furthermore, the second step includes: an extraction step (step S27), extracting marker 16 from the MR image; an acquisition step (step S28), acquiring the position of marker 16 extracted in the extraction step in the coordinate system of the MR image, i.e., the MRI coordinate system; an estimation step (step S29), estimating transformation information for transforming the MEG coordinate system to the MRI coordinate system based on the position of marker 16 in the coordinate system of the brain magnetic field distribution, i.e., the MEG coordinate system, and the position of marker 16 in the MRI coordinate system acquired in the acquisition step; and an alignment step (step S30), using the transformation information estimated in the estimation step, projecting the brain magnetic field distribution onto the MRI coordinate system to align the brain magnetic field distribution with the MR image. The specific method for estimating the transformation information is as described above.

[0087] [Effects]

[0088] Next, the effects of the brain measurement device described in the above embodiments will be explained.

[0089] In the brain measurement device M1 and brain measurement method of this embodiment, since the marker 16 and the photomagnetic sensor 1A are mounted on the non-magnetic frame 4, the positional relationship between the marker 16 and the photomagnetic sensor 1A is determined with mechanical precision within the non-magnetic frame 4. This means that the position of the marker 16 can be obtained with high precision in the brain magnetic field distribution generated based on the brain magnetic field detected by the photomagnetic sensor 1A. On the other hand, the marker 16 is displayed in the MR image. Therefore, information related to the positional relationship between the brain magnetic field distribution and the MR image can be obtained 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. Therefore, the brain magnetic field distribution can be aligned with the MR image with higher precision. Furthermore, in MRI and MEG measurements, the subject's head position sometimes changes relative to the tilting magnetic field coil, so alignment of the MR image with the brain magnetic field distribution is not easy. Since the marker 16 is provided on the helmet-type non-magnetic frame 4 on which the photomagnetic sensor 1A is fixed, the position of the marker 16 is displayed on the MR image. Therefore, the brain magnetic field distribution can be aligned with MR images with higher precision. That is, in the brain measurement device M1, it is possible to accurately estimate the location of the magnetic signal originating from the subject's brain. In other words, the accuracy of signal source estimation can be improved in the brain measurement device M1.

[0090] In the brain measurement device M1 of this embodiment, the generation unit may perform: extraction processing to extract marker 16 from the MR image; acquisition processing to acquire the position of marker 16 extracted by the extraction processing in the coordinate system on the MR image, i.e., the MRI coordinate system; estimation processing to estimate transformation information for transforming the MEG coordinate system to the MRI coordinate system based on the position of marker 16 in the coordinate system on the brain magnetic field distribution, i.e., the MEG coordinate system, and the position of marker 16 in the MRI coordinate system obtained by the acquisition processing; and alignment processing to project the brain magnetic field distribution onto the MRI coordinate system using the transformation information estimated by the estimation processing to align the brain magnetic field distribution with the MR image. Furthermore, in the brain measurement method of the present invention, the second step may also include: an extraction step, in which marker 16 is extracted from an MR image; an acquisition step, in which the position of marker 16 extracted in the extraction step is acquired in the coordinate system of the MR image, i.e., the MRI coordinate system; an estimation step, in which transformation information for transforming the MEG coordinate system to the MRI coordinate system is estimated based on the position of marker 16 in the coordinate system of the brain magnetic field distribution, i.e., the MEG coordinate system, and the position of marker 16 in the MRI coordinate system acquired in the acquisition step; and an alignment step, in which the brain magnetic field distribution is projected onto the MRI coordinate system using the transformation information estimated in the estimation step to align the brain magnetic field distribution with the MR image. In this case, transformation information for transforming the MEG coordinate system to the MRI coordinate system is estimated based on the MR image and the position of marker 16 in the brain magnetic field distribution, and the brain magnetic field distribution is projected onto the MRI coordinate system based on this transformation information, thereby enabling high-precision alignment of the MR image and the brain magnetic field distribution.

[0091] In the brain measurement device M1 of this embodiment, multiple markers 16 may be installed at different positions on the non-magnetic frame 4. In this case, three reference points required for the alignment of the brain magnetic field distribution with the MR image can be obtained more accurately before measurement, so the alignment of the brain magnetic field distribution with the MR image can be performed with higher precision, for example, compared to the case where there is only one marker 16.

[0092] In the brain measurement device M1 of this embodiment, the plurality of markers 16 may also include at least three markers 16 that are not on the same straight line. In this case, the three reference points required for the alignment of the brain magnetic field distribution with the MR image can be obtained more accurately before measurement. Since the three reference points are not on the same straight line, the alignment of the brain magnetic field distribution with the MR image can be performed with higher accuracy, for example, compared to the case where there are two markers 16.

[0093] In the brain measurement device M1 of this embodiment, the marker 16 may also include a Beekley marker or a Magnevist solution capsule. In this case, the marker 16 is displayed more clearly in the MR image, so the position of the marker 16 is determined with higher precision. Therefore, the brain magnetic field distribution can be aligned with the MR image with higher precision.

[0094] According to the brain measurement device M1 of this embodiment, the geomagnetically related magnetic field and the changing magnetic field are measured at various locations of multiple photomagnetically excited sensors 1A that measure the brain magnetic field. Furthermore, during the measurement of the brain magnetic field, the current flowing through the geomagnetically correcting coil 7 and the gradient magnetic field correcting coil 8 is controlled based on multiple measured values ​​of the geomagnetically related magnetic field, and the current flowing through the active shielding coil 9 is controlled based on multiple measured values ​​of the changing magnetic field. Magnetic fields are generated at each of the coils 7, 8, and 9. At the locations of the multiple photomagnetically excited sensors 1A, the geomagnetically related magnetic field is corrected by the magnetic field generated by the geomagnetically correcting coil 7 and the gradient magnetic field correcting coil 8, and the changing magnetic field is corrected by the magnetic field generated by the active shielding coil 9. As a result, by correcting the geomagnetically related magnetic field and the changing magnetic field at the locations of the multiple photomagnetically excited sensors 1A, the multiple photomagnetically excited sensors 1A can measure the brain magnetic field while avoiding the influence of the geomagnetically related magnetic field and the changing magnetic field.

[0095] On the other hand, according to one or other methods described above, when measuring MR images, a static magnetic field and a tilted magnetic field are applied by controlling the current flowing through the geomagnetic correction coil 7 and the gradient magnetic field correction coil 8, and the nuclear magnetic resonance signal generated by the transmission of transmission pulses is detected by the receiving coil 22. As a result, MR images can be measured based on the output of the receiving coil 22.

[0096] According to this brain measurement device M1 and brain measurement method, both magnetoencephalography (MEG) and MRI measurements can be effectively performed using the same device. In particular, in MRI measurements, because a photoexcited magnetic sensor is used, a wider range of highly sensitive frequency bands can be tuned compared to SQUID, thus reducing the limitation on the intensity of the applied static magnetic field, i.e., the resonant frequency of the protons. The pre-polarization coil required by SQUID, which operates only at low resonant frequencies (i.e., low static magnetic fields), is unnecessary, as is the coolant such as liquid helium required when using SQUID. Furthermore, because the frequency of the signal in MRI measurements is also relatively high, a magnetic shielding chamber for reducing magnetic noise during MRI and MEG measurements is not required. As a result, the device can be miniaturized and costs can be reduced. Additionally, because the time required for pre-polarization is approximately the same as the measurement time, in this embodiment, the measurement time can also be reduced to half.

[0097] Furthermore, in this embodiment, since the static magnetic field can be easily switched on and off by turning the current flowing through the geomagnetic correction coil 7, brain magnetic field measurement and MRI measurement can be switched in a short time. Therefore, since brain magnetic field measurement and MRI measurement can be performed sequentially on the same subject using the same device, the registration error between the two measurement results can be reduced.

[0098] As described above, according to this embodiment, because MRI measurements can be performed in a low magnetic field, a special room is not required, and T1 contrast can be improved. Furthermore, by using the active shielding coil 9, magnetoencephalography (MEG) measurements are not required in a magnetically shielded room. Therefore, MEG and MRI measurements can be performed using the same device, and both measurements can be performed sequentially while the subject is seated in a chair or similar position. Additionally, the cost of the device can be reduced, and measurements can also be performed while the subject is in a vehicle or similar position. As a result, this can aid in the diagnosis of mental illnesses such as depression and schizophrenia, and neurodegenerative diseases such as dementia.

[0099] Here, the brain measurement device M1 uses a geomagnetic correction coil 7 for applying a static magnetic field and a gradient magnetic field correction coil 8 for applying a tilted magnetic field. As a result, since the geomagnetic field correction coil for brain measurement and the coil for MRI measurement can be shared, the device can be further miniaturized and the cost can be further reduced.

[0100] Furthermore, in this embodiment, during magnetoencephalography (MEG) measurement, by canceling out the geomagnetic magnetic field and changing magnetic field at the positions of the multiple photoexcited magnetic sensors 1A, the multiple photoexcited magnetic sensors 1A can reliably measure the brain magnetic field while avoiding the influence of the geomagnetic magnetic field and changing magnetic field. As a result, the brain magnetic field can be measured with high precision without the use of a magnetic shielding chamber. This can be achieved even if the subject's head moves.

[0101] Furthermore, the geomagnetic correction coil 7, the gradient magnetic field correction coil 8, and the active shielding coil 9 are each configured as a pair of coils sandwiching multiple photoexcited magnetic sensors 1A. With this structure, the geomagnetic-related magnetic field and changing magnetic field at the positions of the multiple photoexcited magnetic sensors 1A sandwiched between the pair of coils are effectively corrected. Thus, it is possible to appropriately correct the geomagnetic-related magnetic field and changing magnetic field with a simple structure.

[0102] In addition, the brain measurement device M1 also includes an output coil 24 electrically connected to the receiving coil 22 via a cable, and another photomagnetic sensor 23A for detecting the magnetic signal output by the output coil 24. With this structure, the influence of the applied static magnetic field on the detection signal of the photomagnetic sensor 23A during MRI measurements can be avoided, thus improving the accuracy of MR image measurements. For example, with the application of a static magnetic field of 7 mT, the frequency of the proton-generated MRI signal is approximately 300 kHz. To maintain the sensitivity of the photomagnetic sensor 23A to this frequency, a bias magnetic field of approximately 40 μT must be applied. When the photomagnetic sensor 23A is positioned near the subject's head, the coexistence of such a bias magnetic field and a static magnetic field is difficult. In this embodiment, by positioning the receiving coil 22, which is not sensitive to static magnetic fields, near the head, and separating the photomagnetic sensor 23A from the head, high-sensitivity detection of MRI signals is possible.

[0103] Furthermore, the multiple photoexcited magnetic sensors 1A are axial gradiometers having a measurement region and a reference region coaxially arranged in a direction perpendicular to the subject's scalp. Based on this structure, since the influence of common-mode noise is represented in both the output of the measurement region and the output of the reference region, common-mode noise can be removed by obtaining the difference between the two outputs. This improves the accuracy of brain magnetic field measurement.

[0104] Furthermore, multiple photomagnetic sensors 1A, multiple geomagnetic field correction magnetic sensors 2, multiple active shielding magnetic sensors 3, and a receiving coil 22 are fixed to a helmet-type non-magnetic frame 4 worn on the subject's head. With this structure, because the non-magnetic frame 4 worn on the head and the sensors 2, 3, and receiving coil 22 fixed to it move according to the movement of the subject's head, even when the subject's head moves, it is possible to appropriately perform positional corrections for the multiple photomagnetic sensors 1A, corrections for geomagnetic-related magnetic fields and changing magnetic fields, measurements of the brain magnetic field, and MRI measurements. As a result, registration errors in the two measurements can be suppressed.

[0105] Furthermore, an electromagnetic shield 14 for shielding high-frequency electromagnetic noise can be added. With this structure, high-frequency electromagnetic noise that cannot be measured can be prevented from intruding into the multiple photomagnetic sensors 1A of the magnetoencephalometer. This allows for stable measurement of the brain magnetic field through the multiple photomagnetic sensors 1A. Simultaneously, it also prevents noise in the 300kHz frequency band, which is the measurement frequency for MRI, from incident on the receiving coil 22 and increasing the noise of the MRI measurement.

[0106] Furthermore, multiple photoexcited magnetic sensors 1A are configured to apply a bias magnetic field to be sensitive to frequencies in the range of 0–200 Hz, and another photoexcited magnetic sensor 23A is configured to apply a bias magnetic field to be sensitive to frequencies in the range of 20 kHz–500 kHz. With this structure, the sensitivity of brain magnetic field measurements can be improved while also increasing the accuracy of MRI measurements.

[0107] [Variation Example]

[0108] The above embodiments illustrate one aspect of the present invention. Therefore, the present invention is not limited to the brain measurement device and brain measurement method described above, and can be modified arbitrarily.

[0109] The marker 16 only needs to appear as a bright point in the MR image and contain material with sufficient proton density and appropriate T1 and T2 times, so it is not limited to containing Beekley markers or Magnevist solution capsules. The marker 16 may also contain liquids, for example.

[0110] The shape of marker 16 only needs to be such that its center of gravity can be derived in the MR image when displayed. The shape of marker 16 is not limited to a sphere; for example, it can be a cuboid or a cube, or other shapes besides those mentioned above.

[0111] The marker 16 only needs to be displayed in the MR image, so the position of the marker 16 in the non-magnetic frame 4 is not limited to the positions corresponding to the subject's eyebrows, back of the head, and temples. The position of the marker 16 in the non-magnetic frame 4 can be, for example, the position corresponding to the top of the subject's head, or other positions besides those mentioned above. Furthermore, substitutes for the marker 16 only need to be displayed in the MR image, so they can be locations other than the subject's ears, or even non-subject locations but structures within the non-magnetic frame 4.

[0112] Furthermore, when the number of markers 16 is less than 3, the position of the substitute for marker 16 can be preset or determined by some method.

[0113] Transformation information is only required to transform the MEG coordinate system to the MRI coordinate system, and is therefore not limited to the affine transformation matrix T. For example, transformation information can also be other information represented by a matrix.

[0114] Although the active shielding coil 9 is described as a coil with a pair of active shielding coils 9A and 9B, it is also possible to configure each OPM module 1 (photomagnetic sensor 1A) as a system of three coils. In this case, the control device 5 determines the current to the active shielding coil 9 in a manner that generates a magnetic field whose components in the three directions (x-axis, y-axis, and z-axis) of the changing magnetic field relative to the position of the photomagnetic sensor 1A are opposite in magnitude and equal in magnitude. The control device 5 outputs a control signal to the coil power supply 6, which corresponds to the determined current associated with each of the active shielding coils 9 configured as a system of three coils. With this structure, the power consumption for correcting the changing magnetic field is relatively small.

[0115] Furthermore, when measuring MR images, the control device 5 can either set the current flowing through the gradient magnetic field correction coil 8 by correcting for the geomagnetic gradient magnetic field, or it can set it without correcting for the geomagnetic gradient magnetic field. Because the magnitude of the gradient magnetic field is approximately several μT, which is about two orders of magnitude lower than that of the static magnetic field, high accuracy can be maintained even without correction when acquiring MR images.

[0116] Alternatively, the brain measurement device M1 described in the above embodiment may omit the photoexcitation magnetic sensor 23A, and may also be a structure in which the control device 5 directly detects the output from the receiving coil 22 via an amplifier.

[0117] Furthermore, the photoexcited magnetic sensor 1A is not limited to the pump & probe type that uses both pump light and probe light; it can also be a zero-field type photoexcited magnetic sensor that uses circularly polarized light, which combines pump light and probe light. In this zero-field type, light can be irradiated onto the cell and a periodic bias magnetic field can be applied and the detection magnetic field locked, and the deviation from the zero magnetic field can be measured as the brain magnetic field.

[0118] Furthermore, in the brain measurement device M1 of the above embodiment, the position of the non-magnetic frame 4 can also be measured optically. For example, markers installed at 120-degree intervals around the lower end of the non-magnetic frame 4 and a camera opposite to the non-magnetic frame 4 can be provided, making it possible to measure the positional changes of the helmet using the camera. This measurement result can be used during MRI measurement. For example, the control device 5 can use the measurement result to calculate the relative position of the gradient magnetic field correction coil 8 and the receiving coil 22, and correct the MR image. As a result, even if the subject's head moves, a high-resolution MR image can be obtained. This is a useful structure for MRI measurement of subjects whose heads are difficult to fix, such as young children. In addition, during magnetoencephalography (MEG) measurement, since the correction is performed in such a way that the magnetic field at the position of the photoexcited magnetic sensor 1A in the deviated state becomes zero even if the head position deviates, the positional information of the non-magnetic frame 4 can be used for zero magnetic field generation even though the necessity of measuring the position of the non-magnetic frame 4 is low.

[0119] The above implementation methods are described below.

[0120] [Appendix 1] A brain measurement device, comprising a magnetoencephalometer, an MRI device, and a control device, wherein the magnetoencephalometer includes: a plurality of photoexcited magnetic sensors for measuring the brain magnetic field; a plurality of geomagnetic field correction magnetic sensors for measuring the geomagnetic field at each position of the plurality of photoexcited magnetic sensors; a plurality of active shielding magnetic sensors for measuring the changing magnetic field at each position of the plurality of photoexcited magnetic sensors; a geomagnetic field correction coil for correcting the geomagnetic field; and an active shielding coil for correcting the changing magnetic field; the MRI device includes: a static magnetic field coil for applying a static magnetic field; and a tilting magnetic field coil for applying a tilting magnetic field. The system comprises: a tilted magnetic field coil for transmitting a transmission pulse at a specified frequency; and a receiving coil for detecting the magnetic resonance signal generated by the transmission pulse. During brain magnetic field measurement, the current supplied to the geomagnetic field correction coil and the current supplied to the active shielding coil are controlled based on the measurements of the plurality of geomagnetic field correction magnetic sensors and the plurality of active shielding magnetic sensors. During MR image measurement, the current supplied to the static magnetic field coil and the tilted magnetic field coil are controlled, and the static magnetic field and the tilted magnetic field are controlled. An MR image is generated based on the output of the receiving coil.

[0121] [Appendix 2] According to the brain measurement device described in Appendix 1, the geomagnetic field correction coil is composed of a geomagnetic field correction coil for correcting the magnetic field of the geomagnetic field and a gradient field correction coil for correcting the gradient magnetic field of the geomagnetic field.

[0122] [Appendix 3] According to the brain measurement device described in Appendix 1 or 2, the control device determines the current supplied to the geomagnetic field correction coil in a manner that generates a magnetic field to counteract the geomagnetic field associated with the geomagnetic field, and determines the current supplied to the active shielding coil in a manner that generates a magnetic field to counteract the changing magnetic field.

[0123] [Appendix 4] In the brain measurement device according to any one of Appendices 1 to 3, the geomagnetic field correction coil and the active shielding coil are a pair of coils that sandwich the plurality of photoexcited magnetic sensors.

[0124] [Appendix 5] The brain measurement device according to any one of Appendices 1 to 4 further comprises: 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 photoexcited magnetic sensor for 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 photoexcited magnetic sensor.

[0125] [Appendix 6] The brain measurement device according to any one of Appendices 1 to 5, wherein the plurality of photoexcited magnetic sensors are axial gradient meters having a measurement area and a reference area on the same axis in a direction perpendicular to the subject's scalp.

[0126] [Appendix 7] In the brain measurement device according to any one of Appendices 1 to 6, the plurality of photoexcited magnetic sensors, the plurality of geomagnetic field correction magnetic sensors, the plurality of active shielding magnetic sensors and the receiving coil are fixed to a helmet-type non-magnetic frame worn on the head of the subject.

[0127] [Note 8] The brain measurement device according to any one of Notes 1 to 7 further comprises electromagnetic shielding for shielding high-frequency electromagnetic noise.

[0128] [Appendix 9] According to the brain measurement device described in Appendix 5, the plurality of photoexcited magnetic sensors are configured to apply a bias magnetic field to be sensitive to frequencies in the range of 0 to 200 Hz, and the other photoexcited magnetic sensor is configured to apply a bias magnetic field to be sensitive to frequencies in the range of 20 kHz to 500 kHz.

[0129] [Appendix 10] A brain measurement method using a magnetoencephalometer (MEO) and an MRI apparatus, wherein the MEO comprises: a plurality of photoexcited magnetic sensors for measuring the brain magnetic field; a plurality of geomagnetic field correction magnetic sensors for measuring the geomagnetically related magnetic field at each position of the plurality of photoexcited magnetic sensors; a plurality of active shielding magnetic sensors for measuring the changing magnetic field at each position of the plurality of photoexcited magnetic sensors; a geomagnetic field correction coil for correcting the geomagnetically related magnetic field; and an active shielding coil for correcting the changing magnetic field; the MRI apparatus comprises: a static magnetic field coil for applying a static magnetic field; and a tilting magnetic field coil for applying a tilting magnetic field. The system includes a tilted magnetic field coil; a transmitting coil for transmitting transmission pulses at a specified frequency; and a receiving coil for detecting the magnetic resonance signal generated by the transmission of the transmission pulses. During brain magnetic field measurement, the current supplied to the geomagnetic field correction coil and the current supplied to the active shielding coil are controlled based on the measured values ​​of the plurality of geomagnetic field correction magnetic sensors and the plurality of active shielding magnetic sensors. During MR image measurement, the current supplied to the static magnetic field coil and the tilted magnetic field coil are controlled, and the static magnetic field and the tilted magnetic field are controlled. An MR image is generated based on the output of the receiving coil.

[0130] [Appendix 11] The brain measurement method according to Appendix 10 is characterized in that: the geomagnetic field correction coil is composed of a geomagnetic correction coil for correcting the magnetic field of the geomagnetic field and a gradient field correction coil for correcting the gradient magnetic field of the geomagnetic field.

Claims

1. A brain measurement device for generating MR images and brain magnetic field distribution of a subject, characterized in that, have: An MRI module having a transmitting coil for transmitting a transmitting pulse to the subject and a detection coil for detecting the magnetic resonance signal generated in the subject by the transmitting pulse; A photoexcited magnetic sensor is used to detect the subject's brain magnetic field; The generation unit is used to generate the MR image based on the nuclear magnetic resonance signal detected by the detection coil, and to generate the brain magnetic field distribution based on the brain magnetic field detected by the photoexcited magnetic sensor; A marker that can be displayed on the MR image generated by the generating unit; and A helmet-shaped frame, on which the detection coil, the photoexcited magnetic sensor, and the marker are mounted, is worn on the head of the subject. The generation unit performs: Extraction processing: Extracting the markers from the MR image; The process involves obtaining the position of the marker extracted during the extraction process in the MRI coordinate system, which serves as the coordinate system on the MR image. The estimation process, based on the position of the marker in the brain magnetic field coordinate system, which serves as the coordinate system on the brain magnetic field distribution, and the position of the marker in the MRI coordinate system obtained in the acquisition process, estimates transformation information for transforming the brain magnetic field coordinate system into the MRI coordinate system; and The alignment process uses the transformation information estimated in the estimation process to project the brain magnetic field distribution onto the MRI coordinate system to align the brain magnetic field distribution with the MR image.

2. The brain measurement device as described in claim 1, characterized in that: The frame has multiple markers installed at different locations.

3. The brain measurement device as described in claim 2, characterized in that: The plurality of markers includes at least three markers that are not on the same straight line.

4. The brain measurement device as described in any one of claims 1 to 3, characterized in that: The markers include Beekley markers or Magnevist solution capsules.

5. A brain measurement method for generating MR images and brain magnetic field distribution of a subject, characterized in that, have: In the first step, with the helmet-shaped frame equipped with a photomagnetic sensor and a marker worn on the head of the subject, the MR image showing the marker is generated based on the nuclear magnetic resonance signal generated by the subject and the marker by detecting the nuclear magnetic resonance signal generated by the subject and the marker, and the brain magnetic field distribution is generated based on the brain magnetic field by detecting the brain magnetic field of the subject by the photomagnetic sensor. and The second step involves aligning the MR image generated in the first step with the brain magnetic field distribution. The second step includes: The extraction process involves extracting the markers from the MR image; The acquisition process involves obtaining the position of the marker extracted in the extraction process within the MRI coordinate system, which serves as the coordinate system on the MR image. The estimation process, based on the position of the marker in the magnetoencephalogram (MEG) coordinate system (which serves as the coordinate system for the brain magnetic field distribution) and the position of the marker in the MRI coordinate system obtained in the acquisition process, estimates transformation information for transforming the MEG coordinate system to the MRI coordinate system; and In the alignment process, the transformation information estimated in the estimation process is used to project the brain magnetic field distribution onto the MRI coordinate system to align the brain magnetic field distribution with the MR image.

Images