Brain measurement device

Abstract

The brain measurement device (M1) comprises a magnetoencephalometer module and an MRI module, the magnetoencephalometer module comprising: a unit (2); a pump laser (4) that emits pump light; the detection laser (5) is used for emitting the detection light to a sensitivity area intersected with the pump light in the unit (2); a light sensor group (8) that detects the polarization surface angle of the probe light that has passed through the sensitivity region; and a bias magnetic field coil (11) that applies a bias magnetic field. The MRI module is provided with: a transmission coil (121) for transmitting an RF pulse of a prescribed frequency; and a reception coil (122) that detects a nuclear magnetic resonance signal generated by the transmission of the RF pulse. The magnetoencephalometer module and the MRI module are surrounded by a magnetic shield (115) containing a soft magnetic body.

Description

Technical Field

[0001] One aspect of the embodiments relates to a brain measurement device. Background Art

[0002] There are known optically excited magnetic sensors that can measure weak external magnetic fields (see, for example, Patent Documents 1 and 2). In optically excited magnetic sensors, alkali metal atoms in a cell are excited by pump light, and probe light irradiated to the cell in a manner intersecting with the pump light is measured by an optical sensor, and the intensity of the external magnetic field is detected based on the output of the optical sensor.

[0003] Patent Document 1: U.S. Patent Publication No. 2022 / 0091200

[0004] Patent Document 2: U.S. Patent No. 10,782,368 Summary of the invention

[0005] The inventors of this application have studied and explored a device that can measure brain magnetic fields and acquire brain morphological images by fusing an existing optically excited magnetic sensor such as the above-mentioned one with an MRI (Magnetic Resonance Imaging) device. In the case of wanting to realize a device that fuses an optically excited magnetic sensor with an MRI device, it is desired that the measurement using the MRI device does not affect the accuracy of the measurement using the optically excited magnetic sensor, and the accuracy of both measurements is maintained.

[0006] Therefore, one aspect of the embodiment is made in view of this technical problem, and its technical problem is to provide a brain measurement device that can measure brain magnetic fields and acquire brain morphological images with high accuracy.

[0007] A brain measurement device according to a first aspect of an embodiment includes a magnetoencephalometer and an MRI device, wherein the magnetoencephalometer includes: a cell in which alkali metal vapor is sealed; a pump laser that emits pump light for exciting alkali metal atoms constituting the alkali metal vapor; a detection laser that emits detection light for detecting changes in electron spins in an excited state of the alkali metal atoms to a sensitivity region within the cell that intersects with the pump light; a light sensor that detects the angle of the polarization plane of the detection light that has passed through the sensitivity region; and a bias magnetic field coil that applies a bias magnetic field in the same direction as the pump light to determine the resonance frequency of the electron spins, wherein the MRI device includes: a static magnetic field coil for applying a static magnetic field; a gradient magnetic field coil for applying a gradient magnetic field; a transmitting coil for transmitting a transmitting pulse of a specified frequency; and a receiving coil for detecting a nuclear magnetic resonance signal generated by the transmission of the transmitting pulse, wherein the magnetoencephalometer and the MRI device are surrounded by a magnetic shielding member containing a soft magnetic body.

[0008] According to the first aspect, pump light is emitted to a unit enclosed with an alkali metal under a bias magnetic field, thereby generating (excited) electron spins of alkali metal atoms. Furthermore, probe light is emitted to a sensitive region intersecting with the pump light in the unit, and the polarization plane angle of the probe light passing through the sensitive region is detected by an optical sensor. Based on the detected polarization plane angle, the intensity of the brain magnetic field in the sensitive region can be measured. In addition, according to the first aspect, a static magnetic field and a gradient magnetic field are applied by a static magnetic field coil and a gradient magnetic field coil, and a nuclear magnetic resonance signal generated by the transmission of a transmission pulse is detected by a receiving coil, thereby measuring a brain morphological image (MR image). Here, in the brain measurement device of the first aspect, the brain magnetometer and the MRI device are surrounded by a magnetic shield. The magnetic shield has the property of relatively large magnetic permeability and relatively small coercive force. Therefore, the influence of the environmental magnetic field during measurement can be reduced, and the magnetic shield can be prevented from being magnetized due to the static magnetic field applied during the measurement of the MR image when measuring the brain magnetic field. As a result, both the measurement of the brain magnetic field and the acquisition of the brain morphological image can be achieved with high precision.

[0009] In the first aspect, the soft magnetic material is preferably a material having a relative magnetic permeability of 1 or more and a coercive force smaller than that of a ferromagnetic material. In this case, both the measurement of the brain magnetic field and the acquisition of the brain morphological image can be achieved with higher accuracy.

[0010] In the first aspect, the soft magnetic material is preferably an amorphous magnetic material. In this case, both the measurement of the brain magnetic field and the acquisition of the brain morphological image can be achieved with higher accuracy.

[0011] Furthermore, in the first aspect, the soft magnetic material is preferably a nanocrystalline magnetic material. In this case, both the measurement of the brain magnetic field and the acquisition of the brain morphology image can be achieved with higher accuracy.

[0012] In addition, in the first aspect, the magnetoencephalometer preferably further includes a tilting unit that tilts the direction of the electron spin in a direction perpendicular to the pump light. In this case, by measuring the intensity of the brain magnetic field based on the frequency of the change in the polarization plane angle of the detected probe light, the measurement sensitivity of the brain magnetic field can be maintained without being affected by the environmental magnetic field.

[0013] In addition, in the first aspect, the magnetoencephalometer preferably has two or more sensitivity regions where the pump light and the detection light intersect, and measures the brain magnetic field based on the difference in outputs of the optical sensors corresponding to the two adjacent sensitivity regions. In this case, by using the difference in outputs of the optical sensors corresponding to the two adjacent sensitivity regions, it is possible to remove the common mode noise common to the two sensitivity regions, thereby achieving the measurement of the weak brain magnetic field.

[0014] In the first aspect, the tilting unit preferably emits an RF signal having the same frequency as the resonance frequency. In this case, the brain magnetic field can be measured based on the frequency of the change in the polarization angle of the probe light by a simple method.

[0015] In the first aspect, it is also preferable that the tilting means irradiates pulsed light. In this way, the brain magnetic field can be measured based on the frequency of the change in the polarization plane angle of the detection light by a simple method.

[0016] In the first aspect, the static magnetic field coil is preferably formed of the same coil as the bias magnetic field coil. In this case, the bias magnetic field and the static magnetic field can be stably applied by the dual-use coil, and stable measurement can be achieved with a compact device.

[0017] In the first aspect, the gradient magnetic field coil preferably corrects the gradient of the bias magnetic field when measuring the brain magnetic field. Thus, the gradient magnetic field coil can correct the gradient of the bias magnetic field when measuring the brain magnetic field, thereby achieving stable measurement of the brain magnetic field.

[0018] The brain measurement device of the embodiment is [1] "A brain measurement device, comprising a brain magnetometer and an MRI device, wherein the brain magnetometer comprises:

[0019] A unit enclosed with alkali metal vapor;

[0020] a pump laser emitting pump light for exciting alkali metal atoms constituting the alkali metal vapor;

[0021] a detection laser that emits a detection light for detecting a change in the electron spin of the alkali metal atom in an excited state toward a sensitive region in the cell that intersects with the pump light;

[0022] a light sensor that detects a polarization angle of the detection light that has passed through the sensitivity region; and

[0023] A bias magnetic field coil applies a bias magnetic field in the same direction as the pump light to determine the resonance frequency of the electron spin.

[0024] The MRI apparatus comprises:

[0025] A static magnetic field coil, which is used to apply a static magnetic field;

[0026] A gradient magnetic field coil, which is used to apply a gradient magnetic field;

[0027] a transmitting coil for transmitting a transmitting pulse of a prescribed frequency; and

[0028] a receiving coil that detects a nuclear magnetic resonance signal generated by the transmission of the transmission pulse,

[0029] The magnetoencephalometer and the MRI device are surrounded by a magnetic shielding member comprising a soft magnetic body.

[0030] The brain measurement device of the embodiment may also be [2] "The brain measurement device according to the above [1], wherein the soft magnetic body is a material having a relative magnetic permeability of 1 or more and a coercive force smaller than that of a ferromagnetic body.

[0031] The brain measurement device of the embodiment may also be [3] "the brain measurement device according to the above [2], wherein the soft magnetic material is an amorphous magnetic material."

[0032] The brain measurement device of the embodiment may also be [4] "the brain measurement device according to the above [3], wherein the soft magnetic body is a nanocrystalline magnet."

[0033] The brain measurement device of an embodiment may also be [5] "a brain measurement device according to any one of [1] to [4] above, wherein the brain magnetometer further has a tilting unit, and the tilting unit tilts the direction of the electron spin in a direction perpendicular to the pump light."

[0034] The brain measurement device of an embodiment may also be [6] "a brain measurement device according to any one of [1] to [5] above, wherein the brain magnetometer has two or more sensitivity areas where the pump light and the detection light intersect, and measures the brain magnetic field based on the difference in the output of the optical sensor corresponding to two adjacent sensitivity areas."

[0035] The brain measurement device of the embodiment may also be [7] "According to the brain measurement device described in [5] above, the tilting unit irradiates an RF signal having the same frequency as the resonance frequency."

[0036] The brain measurement device of the embodiment may also be [8] "the brain measurement device according to the above [5], wherein the tilting unit irradiates pulsed light."

[0037] The brain measurement device of an embodiment may also be [9] "A brain measurement device according to any one of [1] to [8] above, wherein the static magnetic field coil is composed of the same coil as the bias magnetic field coil."

[0038] The brain measurement device of an embodiment may also be

[10] "a brain measurement device according to any one of [1] to [9] above, wherein the gradient magnetic field coil corrects the gradient of the bias magnetic field when measuring the brain magnetic field." BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram showing the structure of a brain measurement device according to an embodiment.

[0040] Figure 2 Yes means Figure 1 A perspective view of the structure of the light-excited magnetic sensor 1.

[0041] Figure 3 Observed from the -y axis Figure 2 A top view of the first optical system 6.

[0042] Figure 4 Observed from the -z axis Figure 2 A top view of the second optical system 7, the optical sensor group 8 and the third optical system 9.

[0043] Figure 5 Yes means Figure 1 A three-dimensional diagram of the bias magnetic field gradient correction coil.

[0044] Fig. 6A It is a top view showing the second coil. Figure 6B It is a top view showing the first coil and the third coil.

[0045] Figure 7A to Figure 7C It means by Figure 2 A timing diagram showing the timings of pump light, RF signal, and probe light when the readout circuit 10 performs the measurement process of the brain magnetic field.

[0046] Figure 8 It means by Figure 2 FIG. 1 is a diagram of the FID obtained by the readout circuit 10 .

[0047] Fig. 9 Yes means Figure 1 A perspective view of the structure of the light-excited magnetic sensor 1A.

[0048] Fig.10 This is a flowchart showing the operation of the brain measurement device according to the embodiment.

[0049] Fig.11 This is a flowchart showing the operation of the brain measurement device according to the embodiment.

[0050] Fig.12 It is a perspective view showing the structure of a light-excited magnetic sensor according to a modified example.

[0051] Fig.13 It is a top view showing the structure of a brain measurement device according to a modified example.

[0052] Explanation of symbols

[0053] M1, M2…brain measuring device, 1, 1A, 1B…lightly excited magnetic sensor, 2…unit, 4…pump laser, 5…detection laser, 8…optical sensor group, 11, 11a~11d…bias magnetic field coil, 12, 13…bias magnetic field gradient correction coil, 114…electromagnetic shielding, 115…magnetic shielding, 121…transmitting coil, 122…receiving coil, 14…tilting coil (tilting unit), ARa~ARd…sensitivity area, Bm…magnetic field, Bz…bias magnetic field, PL, PLa~PLd…pump light, QLa~QLd…detection light, Rf…RF signal, S…head (subject). DETAILED DESCRIPTION

[0054] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same elements or elements having the same functions are denoted by the same reference numerals, and repeated descriptions are omitted.

[0055] Figure 1 1 is a schematic diagram showing the structure of a brain measurement device M1 according to an embodiment. The brain measurement device M1 is a device for measuring brain magnetic fields and MR (Magnetic Resonance) images as brain morphological images of a subject. The brain measurement device M1 includes: a brain magnetometer module having two optically pumped magnetometer sensors 1, 1A, a non-magnetic frame 104, a bias magnetic field coil 11, bias magnetic field gradient correction coils 12, 13, and a tilting coil 14; an MRI module having a transmitting coil 121, a plurality of receiving coils 122, and a receiving amplifier 124; an electromagnetic shield 114; and a magnetic shield 115. Furthermore, the brain measurement device M1 includes: a power supply device including a switch 105, an MRI power supply 106, a bias magnetic field power supply 107, and a gradient correction power supply 108; and a control device 109 for controlling the power supply device, etc.

[0056] In the following description, the direction substantially parallel to the central axis of the subject's head is defined as the y-axis direction, and the directions perpendicular to the y-axis and perpendicular to each other are defined as the z-axis direction and the x-axis direction. In the following description, the positive direction and the negative direction along the x-axis are defined as the +x-axis direction and the -x-axis direction, respectively, the positive direction and the negative direction along the y-axis are defined as the +y-axis direction and the -y-axis direction, respectively, and the positive direction and the negative direction along the z-axis are defined as the +z-axis direction and the -z-axis direction, respectively.

[0057] The non-magnetic frame 104 is a frame covering the entire area of ​​the scalp of the subject as the measurement object of the brain magnetic field, and is composed of a non-magnetic material such as graphite whose relative magnetic permeability is close to 1 and does not disturb the magnetic field distribution. The non-magnetic frame 104 can be set as a helmet-type frame that surrounds the entire area of ​​the subject's scalp and is worn on the subject's head. A plurality of optically excited magnetic sensors 1, 1A are fixed to the non-magnetic frame 104 in a manner close to the subject's scalp. Furthermore, a receiving coil 122 for detecting nuclear magnetic resonance signals for MR image measurement is fixed on the opposite side of the plurality of optically excited magnetic sensors 1, 1A in the non-magnetic frame 104 relative to the subject's scalp. The receiving coil 122 detects the nuclear magnetic resonance signals of the protons described below and converts them into electric current.

[0058] The plurality of optically excited magnetic sensors 1A are arranged at predetermined intervals around the y-axis so as to surround the head near the top of the subject's head. The plurality of optically excited magnetic sensors 1 are arranged at predetermined intervals around the y-axis so as to be separated in the -y-axis direction from the optically excited magnetic sensors 1A and surround the head.

[0059] Figure 2 1 is a perspective view showing the structure of the optically excited magnetic sensor 1 according to the embodiment. The optically excited magnetic sensor 1 is a device for measuring the brain magnetic field using optical pumping. The optically excited magnetic sensor 1 has a structure capable of measuring the brain magnetic field along the z-axis direction. As described later, the direction along the y-axis corresponds to the incident direction of the probe light in the measurement area, and the direction along the z-axis corresponds to the incident direction of the pump light in the measurement area.

[0060] like Figure 1 As shown, the optical excitation magnetization sensor 1 includes a unit 2, a heater 3, a pump laser 4, a detection laser 5, a first optical system 6, a second optical system 7, an optical sensor group 8, a third optical system 9, and a readout circuit 10. In addition, the pump laser 4, the detection laser 5, and the readout circuit 10 can also be shared with other optical excitation magnetization sensors 1 or with multiple optical excitation magnetization sensors 1A. The components of the optical excitation magnetization sensor 1 are described in detail below.

[0061] Unit 2 is a container for sealing alkali metal vapor. Unit 2 is arranged along the direction along the x-axis. Unit 2 has a roughly rectangular parallelepiped shape with a surface roughly parallel to the xy plane and a bottomed cylindrical shape. The cross section of unit 2 in a direction perpendicular to the length direction of unit 2 (in the direction along the yz plane) is, for example, a square. Unit 2 can be made of materials such as quartz, sapphire, silicon, kovar glass, borosilicate glass, etc. Unit 2 is translucent to the pump light and probe light described below. A heater 3 is installed on the side of unit 2 in the -z-axis direction. On the side of unit 2 in the -z-axis direction, the magnetic field Bm of the measurement object generated from the measurement object is incident along the +z-axis direction.

[0062] The alkali metal constituting the alkali metal vapor sealed in the unit 2 may be, for example, at least one of lithium (Li), sodium (Na), potassium (K), rubidium (Rb) and cesium (Cs). For example, the alkali metal may be potassium and rubidium, or may be only potassium. The spin-destruction collision relaxation rate of potassium is also relatively small among the alkali metals used in the photoexcitation magnetic sensor. The spin-destruction collision relaxation rate of potassium is, for example, smaller than that of cesium and rubidium. Therefore, in the case of using a single alkali metal, the photoexcitation magnetic sensor using only potassium has a higher sensitivity than the photoexcitation magnetic sensor using only cesium or only rubidium.

[0063] In addition, the cell 2 contains a sealed gas. The sealed gas suppresses the relaxation of the spin polarization of the alkali metal vapor. In addition, the sealed gas protects the alkali metal vapor and suppresses noise emission. The sealed gas can be, for example, an inert gas such as helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), nitrogen (N2), etc. The sealed gas can be, for example, helium and nitrogen.

[0064] As described above, the unit 2 is provided with a heater 3. The heater 3 generates heat according to the current supplied from the heater power supply (not shown). The heater 3 controls the vapor density of the alkali metal by controlling the internal temperature of the unit 2. For example, when potassium is stored in the unit 2 as the alkali metal, the heater 3 heats the unit 2 so that the internal temperature of the unit 2 becomes 100°C.

[0065] The pump laser 4 emits pump light for exciting alkali metal atoms in the -z axis direction. That is, the pump laser 4 emits linearly polarized pump light, and the pump light is converted into circularly polarized light by the 1 / 4 wavelength plates 27a to 27d. The alkali metal atoms contained in the unit 2 are excited by the pump light in a polarization state set to circular polarization, generating spin polarization. The wavelength of the pump light is set according to the type of atoms constituting the alkali metal vapor (more specifically, the wavelength of the absorption line). For example, when the atoms constituting the alkali metal vapor are potassium, the wavelength of the pump light is set to 770.11nm that matches the resonance line of potassium. When the alkali metal atoms contained in the unit 2 are potassium and rubidium, the pump laser 4 can also excite the rubidium atoms and emit pump light for transferring the spin polarization of the rubidium atoms to the potassium atoms. In this case, the rubidium atoms are in an excited state by the pump light. Then, through the spin exchange interaction between potassium and rubidium, the spin polarization of the rubidium atoms is transferred to the potassium atoms, and the potassium atoms become excited.

[0066] The pump light from the pump laser 4 enters the cell 2 via the first optical system 6 . Figure 3It is a top view of the first optical system 6 observed from the -y axis direction. The first optical system 6 is configured to include a lens 21, a 1 / 2 wavelength plate 22, polarization beam splitters 23a, 23b, 23c, 1 / 2 wavelength plates 24a, 24b, a total reflection mirror 25, polarizers 26a, 26b, 26c, 26d and 1 / 4 wavelength plates 27a, 27b, 27c, 27d.

[0067] The lens 21 is disposed adjacent to the pump laser 4 in the -z axis direction, and focuses the pump light emitted from the pump laser 4. The 1 / 2 wavelength plate 22 is disposed adjacent to the lens 21 in the -z axis direction, and rotates the polarization plane so that the power of the pump laser is distributed to 1:3 by the polarization beam splitter 23a.

[0068] The polarization beam splitter 23a is arranged adjacent to the 1 / 2 wavelength plate 22 in the -z axis direction, and separates two mutually perpendicular linear polarization components from the polarization component of the pump light transmitted through the 1 / 2 wavelength plate 22, allowing one linear polarization component to be transmitted in the -z axis direction, and reflecting the other linear polarization component in the -x axis direction. The polarization beam splitters 23b, 23c and the total reflection mirror 25 are arranged in sequence in the -x axis direction relative to the polarization beam splitter 23a. The polarization beam splitters 23b and 23c respectively separate two mutually perpendicular linear polarization components from the pump light transmitted through the polarization beam splitters 23a and 23b, allowing one linear polarization component to be transmitted in the -x axis direction, and reflecting the other linear polarization component in the -z axis direction. The total reflection mirror 25 reflects the linear polarization pump light transmitted through the polarization beam splitter 23c in the -z axis direction.

[0069] The 1 / 2 wavelength plate 24a is disposed between the polarization beam splitter 23a and the polarization beam splitter 23b, and rotates the polarization plane of the linearly polarized pump light reflected by the polarization beam splitter 23a. Thus, the pump light can be separated into two linearly polarized polarization components by the polarization beam splitter 23b. The 1 / 2 wavelength plate 24b is disposed between the polarization beam splitter 23b and the polarization beam splitter 23c, and rotates the polarization plane of the linearly polarized pump light transmitted through the polarization beam splitter 23b. Thus, the pump light can be separated into two linearly polarized polarization components by the polarization beam splitter 23c.

[0070] The polarizer 26a and the quarter wavelength plate 27a are arranged adjacent to each other in the -z axis direction relative to the polarization beam splitter 23a. The polarizer 26a transmits a specific linearly polarized component of the pump light that has passed through the polarization beam splitter 23a, and the quarter wavelength plate 27a changes the polarization state of the pump light that has passed through the polarizer 26a into circularly polarized light, so that it is transmitted in the -z axis direction as the pump light PLa.

[0071] Polarizers 26b, 26c, 26d and quarter wavelength plates 27b, 27c, 27d are arranged adjacent to each other in the -z axis direction with respect to polarization beam splitters 23b, 23c and total reflection mirror 25. The functions of polarizers 26b, 26c, 26d and quarter wavelength plates 27b, 27c, 27d are the same as those of polarizer 26a and quarter wavelength plate 27a, respectively, and allow pump light PLb, PLc, PLd to pass in the -z axis direction.

[0072] The first optical system 6 having the above configuration is configured so that the four pump lights PLa to PLd transmitted through the four quarter-wave plates 27 a , 27 b , 27 c , and 27 d can be incident on regions separated in the longitudinal direction (direction along the x-axis) in the cell 2 .

[0073] The detection laser 5 emits a detection light in the -y-axis direction for detecting the precession of the spin when the electron spin in the excited state of the alkali metal atom is tilted by 90 degrees. That is, the detection laser 5 emits a linearly polarized detection light. When the detection light passes through the alkali metal vapor, it is affected by the state of the spin polarization of the alkali metal atom, and the magnetic rotation angle changes. By detecting the change in the magnetic rotation angle, the state of the precession of the spin can be derived. The wavelength of the detection light is set according to the type of atoms constituting the alkali metal vapor (more specifically, the wavelength of the absorption line). For example, when only potassium is contained as an alkali metal in the unit 2, the wavelength of the detection light is detuned from the wavelength of the pump light (for example, 770.11nm), for example, to about 770.05nm. By detuning the wavelength of the detection light from the wavelength of the pump light, it is possible to suppress the detection light from being absorbed by potassium.

[0074] In the case where potassium and rubidium are stored in the unit 2 as alkali metals, the detection laser 5 can also emit detection light for detecting the change of the magnetic rotation angle caused by spin polarization in the excited state of potassium atoms. The density of rubidium used for excitation is set to be smaller than the density of potassium used for detection. In the case where the density of rubidium is smaller than the density of potassium, the attenuation of the pump light caused by the excitation is suppressed. As a result, the optically excited magnetic sensor 1 can obtain uniform sensitivity within the unit 2.

[0075] The probe light from the probe laser 5 enters the cell 2 via the second optical system 7 . Figure 4 This is a top view of the second optical system 7, the optical sensor group 8, and the third optical system 9 as viewed from the -z axis direction. The second optical system 7 is configured to include 1 / 2 wavelength plates 31a, 31b, 31c, polarization beam splitters 32a, 32b, 32c, a total reflection mirror 33, and polarizers 34a, 34b, 34c, 34d.

[0076] The 1 / 2 wavelength plate 31a is arranged adjacent to the detection laser 5 in the -x axis direction, and the polarization plane is rotated in such a way that the power of the detection laser is distributed as 1:3 by the polarization beam splitter 32a. The polarization beam splitters 32a, 32b, and 32c are arranged in sequence in the -x axis direction relative to the 1 / 2 wavelength plate 31a, and two linear polarization components perpendicular to each other are separated from the polarization component of the detection light passing through the 1 / 2 wavelength plate 31a, so that one linear polarization component is transmitted in the -x axis direction, and the other linear polarization component is reflected in the -y axis direction. The 1 / 2 wavelength plate 31b is arranged between the polarization beam splitter 32a and the polarization beam splitter 32b, and the polarization plane of the linear polarization detection light passing through the polarization beam splitter 32a is rotated. As a result, the detection light can be separated into two linear polarization components by the polarization beam splitter 32b. The 1 / 2 wavelength plate 31c is disposed between the polarization beam splitter 32b and the polarization beam splitter 32c, and rotates the polarization plane of the linearly polarized probe light passing through the polarization beam splitter 32b. Thus, the probe light can be separated into two linearly polarized polarization components by the polarization beam splitter 32c. The total reflection mirror 33 reflects the linearly polarized probe light passing through the polarization beam splitter 32c in the -y axis direction.

[0077] The polarizers 34 a , 34 b , 34 c , and 34 d transmit specific linearly polarized components of the probe light reflected by the polarization beam splitters 32 a , 32 b , and 32 c and the total reflection mirror 33 , respectively.

[0078] The second optical system 7 of the above structure is configured to enable the four systems of detection light QLa~QLd transmitted through the four polarizers 34a, 34b, 34c, and 34d to be incident on the sensitive areas ARa~ARd arranged in the length direction (along the x-axis direction) in the unit 2 and intersecting with the pump light PLa~PLd.

[0079] Reference Figure 1 The bias magnetic field coil 11 is a coil that applies a bias magnetic field Bz in the direction along the z-axis inside the unit 2, and determines the resonance frequency of the electron spins of the alkali metal atoms excited inside the unit 2. By applying the bias magnetic field Bz in the same direction as the incident direction of the pump light by the bias magnetic field coil 11, the axis of the electron spins of the alkali metal atoms excited in the unit 2 is consistent with the direction along the z-axis. When the intensity of the bias magnetic field applied by the bias magnetic field coil 11 is 14μT and the alkali metal atom is potassium, the resonance frequency of the electron spin is 100kHz. In addition, as described later, the bias magnetic field coil 11 is also used as a static magnetic field coil used in the measurement of MR images using the MRI module.

[0080] The bias magnetic field gradient correction coils 12 and 13 are coil groups for correcting the gradient of the bias magnetic field Bz along the y-axis direction, along the z-axis direction, or along the x-axis direction. The bias magnetic field gradient correction coils 12 and 13 may be a coil group structure that includes a coil group that corrects the gradient of the bias magnetic field Bz along any one or two directions of the y-axis direction, along the z-axis direction, or along the x-axis direction, or may be a coil group structure that corrects the gradient in three directions. Due to the presence of the bias magnetic field gradient correction coils 12 and 13, even if the bias magnetic field Bz is not uniform due to the influence of the environmental magnetic field, etc., it can be corrected in a uniform manner, which can improve the detection sensitivity of the optically excited magnetic sensor 1 to the brain magnetic field. In addition, as described later, the bias magnetic field gradient correction coils 12 and 13 are also shared as the gradient magnetic field coils used when measuring MR images using the MRI module.

[0081] Here, the bias magnetic field gradient correction coils 12 and 13 will be described in detail.

[0082] like Figure 5 and Fig. 6A As shown, the bias magnetic field gradient correction coil 12 is a parallel flat plate type coil, including a second coil 12A. The second coil 12A is respectively provided on a pair of substrates opposite to each other in the x-axis direction across the unit 2. The second coil 12A is arranged on one side and the other side of the unit 2 in the x-axis direction. The second coil 12A corrects the change in the bias magnetic field Bz corresponding to the change in the position in the x-axis direction. In the example shown in the figure, the second coil 12A is a parallel four-wire coil.

[0083] like Figure 5 and Figure 6B As shown, the bias magnetic field gradient correction coil 13 is a parallel plate type coil, including a first coil 13A and a third coil 13B. The first coil 13A and the third coil 13B are respectively arranged on a pair of substrates opposite to each other in the z-axis direction across the unit 2. The first coil 13A is arranged on one side and the other side of the unit 2 in the z-axis direction. The first coil 13A corrects the change in the bias magnetic field Bz corresponding to the change in the position in the z-axis direction. In the example shown in the figure, the first coil 13A is a parallel four-wire coil. The third coil 13B is arranged on one side and the other side of the unit 2 in the z-axis direction. The third coil 13B corrects the change in the bias magnetic field Bz corresponding to the change in the position in the y-axis direction. In the example shown in the figure, the first coil 13A is a Maxell coil.

[0084] The first to third coils 13A, 12A, and 13B are coils for correcting the primary gradient magnetic field. Alternatively, the first to third coils 13A, 12A, and 13B may be coils for further correcting the secondary gradient magnetic field. In this case, the uniformity of the bias magnetic field Bz can be further improved. Figure 5 The arrows shown in the first to third coils 13A, 12A, and 13B in FIG. 1 indicate the directions of the currents to be applied.

[0085] The tilting coil 14 (see Figure 1 . ) In order to tilt the direction of the electron spin of the alkali metal atom excited in the unit 2 in a direction perpendicular to the incident direction of the pump light, an RF signal Rf is generated and irradiated. Specifically, the tilting coil 14 generates an RF signal Rf of the same frequency as the resonance frequency of the electron spin (100 kHz when the intensity of the bias magnetic field Bz is 14 μT and the alkali metal atom is potassium), and irradiates the RF signal Rf in the -x axis direction with the intensity and length required to tilt the electron spin by 90 degrees. In addition, as a tilting unit that tilts the direction of the electron spin instead of the tilting coil 14, a unit that irradiates other pulsed pump light from a direction perpendicular to the incident direction of the pump light may also be provided.

[0086] return Figure 4 , the structures of the optical sensor group 8 and the third optical system 9 are described.

[0087] The third optical system 9 is configured to include 1 / 2 wavelength plates 41a, 41b, 41c, 41d and polarization beam splitters 42a, 42b, 42c, 42d. The 1 / 2 wavelength plates 41a, 41b, 41c, 41d are respectively provided adjacent to the unit 2 in the -y axis direction on the optical paths of the probe lights QLa, QLb, QLc, QLd passing through the sensitive areas ARa to ARd of the unit 2, and rotate the polarization planes of the linearly polarized probe lights QLa, QLb, QLc, QLd passing through the unit 2. These 1 / 2 wavelength plates 41a, 41b, 41c, 41d are rotatably supported around an axis along the y axis so that the rotation angle of the polarization plane of the probe light can be adjusted. The polarizing beam splitters 42a, 42b, 42c, and 42d respectively separate two mutually perpendicular linear polarized components from the polarized components of the detection lights QLa, QLb, QLc, and QLd passing through the half-wavelength plates 41a, 41b, 41c, and 41d, so that one linear polarized component is transmitted in the -y-axis direction and the other linear polarized component is reflected in the z-axis direction.

[0088] The optical sensor group 8 is an element group that detects the polarization plane angle of the detection light QLa, QLb, QLc, and QLd that has passed through the sensitivity areas ARa to ARd, and is configured to include four optical sensor pairs 43a, 43b, 43c, and 43d. The optical sensor pair 43a includes two photodiodes 44a and 45a, and the photodiode 44a outputs a detection signal for detecting the intensity of the other linear polarization component of the detection light QLa, and the photodiode 45a outputs a detection signal for detecting the intensity of the one linear polarization component of the detection light QLa. Similarly, the optical sensor pairs 43b, 43c, and 43d include two photodiodes 44b and 45b, two photodiodes 44c and 45c, and two photodiodes 44d and 45d, respectively. The two photodiodes 44b and 45b respectively output detection signals for detecting the intensity of the two linearly polarized components of the detection light QLb, the two photodiodes 44c and 45c respectively output detection signals for detecting the intensity of the two linearly polarized components of the detection light QLc, and the two photodiodes 44d and 45d respectively output detection signals for detecting the intensity of the two linearly polarized components of the detection light QLd.

[0089] Refer again Figure 2 The readout circuit 10 is a processing circuit that is electrically connected to the four optical sensor pairs 43a, 43b, 43c, and 43d that constitute the optical sensor group 8, and processes the detection signals output from the four optical sensor pairs 43a, 43b, 43c, and 43d. The readout circuit 10 may also be integrated with the control device 109. That is, the readout circuit 10 includes: a reading unit that reads the detection signals output from the four optical sensor pairs 43a, 43b, 43c, and 43d; and a measuring unit that performs measurement processing of the brain magnetic field in the sensitivity area ARa to ARd based on the detection signals. However, the measuring unit may also be configured to be provided outside the optical excitation magnetic sensor 1, and perform measurement processing based on the detection signals output from the optical excitation magnetic sensor 1.

[0090] The readout circuit 10 is physically configured to include a memory such as RAM, ROM, a processor such as a CPU (calculation circuit), a communication interface, a hard disk, an auxiliary storage device such as a semiconductor memory, etc. The readout circuit 10 can be implemented, for example, by a personal computer, a cloud server, a smart phone, a tablet terminal, etc. The function of the readout circuit 10 is implemented by the CPU of the computer system executing a program stored in the memory.

[0091] Reference Figure 7A to Figure 7C and Figure 8 The function of the brain magnetic field measurement process performed by the measurement unit of the readout circuit 10 will be described. Figure 7A to Figure 7C 1 and 2 show the timings of the pump light, the RF signal, and the probe light when the brain magnetic field is measured by the readout circuit 10. Fig. 7Arepresents the time when the pump light is generated, Figure 7B Indicates the time when the RF signal is generated, Figure 7C Indicates the readout time of the detection light. Figure 8 This is a diagram showing the temporal change of FID (Free Induction Decay) obtained by the readout circuit 10 .

[0092] When the brain magnetic field is measured by the readout circuit 10, the pump light is repeatedly turned on and off in a pulsed manner by a control circuit (not shown). Fig. 7A ), irradiate the RF signal in a pulsed manner just after the pump light is turned from on to off ( Figure 7B ), in a manner of reading out the probe light during a predetermined relaxation time after irradiation of the RF signal ( Figure 7C ) is controlled. Under such control, the readout circuit 10 obtains the detection signals output from the four light sensor pairs 43a, 43b, 43c, and 43d during the relaxation time. Then, the readout circuit 10 obtains the difference of the detection signals of the two photodiodes 44a and 45a constituting the light sensor pair 43a, thereby obtaining the FID ( Figure 8 ) Similarly, regarding the optical sensor pairs 43b, 43c, and 43d, the readout circuit 10 also obtains the FID by obtaining the difference between the detection signals of the two photodiodes.

[0093] The above-mentioned FID represents the situation of relaxation of the electron spin of the alkali metal atom. The frequency of the precession of the electron spin changes according to the change of the brain magnetic field in the sensitivity area ARa, and thus the frequency of the vibration changes due to the change of the brain magnetic field. For example, when the resonance frequency of the electron spin is 100kHz and the brain magnetic field changes from 0pT to 1pT, the frequency of the precession changes by about 0.007Hz. The readout circuit 10 uses this property to fit the waveform of the initial FID of the relaxation time using the function V shown in the following formula (in the above formula, t represents the time, and a0, a1, and a2 represent specified parameters),

[0094] [Formula 1]

[0095]

[0096] The frequency a1 of the vibration of the FID is derived, and the frequency a1 is obtained as the measured value of the brain magnetic field in the sensitivity area ARa. Similarly, the readout circuit 10 obtains the measured values ​​of the brain magnetic field in the sensitivity areas ARb, ARc, and ARd based on the detection signals output from the light sensor pairs 43b, 43c, and 43d. Furthermore, the readout circuit 10 can obtain time series data of the measured values ​​by repeating this operation at a frequency of 100 to 1000 Hz.

[0097] Next, refer to Fig. 9 The structure of the light-excited magnetic sensor 1A will be described. Fig. 9 1 is a perspective view showing the structure of the optical excitation magnetization sensor 1A. In the optical excitation magnetization sensor 1A, the incident direction of the pump light to the unit 2, the application direction of the bias magnetic field Bz to the unit 2, and the irradiation direction of the RF signal Rf to the unit 2 are different from those of the optical excitation magnetization sensor 1. In the following, only the structure that is different from the optical excitation magnetization sensor 1 is described.

[0098] The first optical system 6 is configured to include a lens 21, a 1 / 2 wavelength plate 22, a polarization beam splitter 23a, and a 1 / 4 wavelength plate 27a. The polarization beam splitter 23a is disposed adjacent to the 1 / 2 wavelength plate 22 in the -y axis direction, and reflects the linearly polarized component of the pump light that has passed through the 1 / 2 wavelength plate in the -z axis direction. The 1 / 4 wavelength plate 27a is disposed adjacent to the polarization beam splitter 23a in the -z direction, and changes the linearly polarized pump light reflected by the polarization beam splitter 23a into circularly polarized light, and transmits the pump light in the -z axis direction. The first optical system 6 of the above structure is configured so that a system of pump light can be incident in the longitudinal direction (along the z axis) of the unit 2.

[0099] The second optical system 7 is configured to include a lens 35, a half-wave plate 36, and a total reflection mirror 37 in addition to the half-wave plates 31a, 31b, and 31c, the polarization beam splitters 32a, 32b, and 32c, the total reflection mirror 33, and the polarizers 34a, 34b, 34c, and 34d. The lens 35 is disposed adjacent to the probe laser 5 in the -y-axis direction, and focuses the probe light emitted from the probe laser 5 in the -y-axis direction. The total reflection mirror 37 is disposed adjacent to the lens 35 in the -y-axis direction, and reflects the probe light transmitted through the lens 35 toward the half-wave plate 31a in the -z-axis direction. The second optical system 7 having such a configuration is configured to allow the four systems of probe light QLa to QLd transmitted through the four polarizers 34a, 34b, 34c, and 34d to be incident on four sensitivity regions arranged in the longitudinal direction (direction along the x-axis) in the unit 2 and intersecting with the pump light PL.

[0100] return Figure 1 , the structures of the MRI module, the power supply device group, and the control device 109 constituting the brain measurement device M1 are described.

[0101] The static magnetic field coil constituting the MRI module is constituted by a coil similar to the bias magnetic field coil 11 described above. The bias magnetic field coil 11 applies a static magnetic field in the z-axis direction during MR image measurement. The bias magnetic field coil 11 is switchably connected to either the MRI power supply 106 or the bias magnetic field power supply 107 via the switch 105. During MR image measurement, the bias magnetic field coil 11 is connected to the MRI power supply 106 under the control of the control device 109, thereby generating a static magnetic field of a predetermined intensity according to the current provided by the MRI power supply 106. During brain magnetic field measurement, the bias magnetic field coil 11 is connected to the bias magnetic field power supply 107 under the control of the control device 109, thereby generating a bias magnetic field of a predetermined intensity according to the current provided by the bias magnetic field power supply 107. Thus, even when the intensity of the bias magnetic field (e.g., 14 μT) and the intensity of the static magnetic field (e.g., 7 mT) are greatly different, the same number of turns of the coil can be shared, and MR image measurement and brain magnetic field measurement can be stably performed.

[0102] The gradient magnetic field coil constituting the MRI module is composed of the same coils as the above-mentioned bias magnetic field gradient correction coils 12 and 13. The bias magnetic field gradient correction coils 12 and 13 apply a gradient magnetic field when measuring MR images. The bias magnetic field gradient correction coils 12 and 13 generate a gradient magnetic field having a selective gradient in the x-axis direction, the y-axis direction, and the z-axis direction according to the current supplied from the gradient correction power supply 108. The gradient correction power supply 108 supplies the current used for the gradient correction of the bias magnetic field Bz to the bias magnetic field gradient correction coils 12 and 13 when measuring the brain magnetic field.

[0103] The transmission coil 121 is a coil that irradiates (transmits) an RF pulse (transmission pulse) of a predetermined frequency (eg, about 300 kHz) to the subject's head during MR image measurement. The transmission coil 121 is, for example, disposed above the subject's head outside the nonmagnetic frame 104 .

[0104] The receiving amplifier 124 is electrically connected to both ends of the receiving coil 122 via a cable, detects the current output from the receiving coil 122 , amplifies the detection result, and outputs it to the control device 109 .

[0105] The control device 109 controls the power supplied to various coils during brain magnetic field measurement and MR image measurement, and performs MR image measurement processing. The control device 109 is electrically connected to the switch 105, the MRI power supply 106, the bias magnetic field power supply 107, the gradient correction power supply 108, the power supply for the transmitting coil 121 (not shown), and the receiving amplifier 124. The control device 109 is configured to physically include a memory such as RAM, ROM, a processor such as a CPU (calculation circuit), a communication interface, a hard disk, a semiconductor memory, and other auxiliary storage devices. The control device 109 can be implemented, for example, by a personal computer, a cloud server, a smart phone, a tablet terminal, etc. The function of the control device 109 is implemented by executing a program stored in the memory by the CPU of the computer system.

[0106] Specifically, the control device 109 controls the switching of the switch 105 between the brain magnetic field measurement and the MR image measurement, connects the bias magnetic field coil 11 to the bias magnetic field power supply 107 when the brain magnetic field is measured, and connects the bias magnetic field coil 11 to the MRI power supply 106 when the MR image is measured. In addition, the control device 109 determines the current supplied to the bias magnetic field coil 11 and the bias magnetic field gradient correction coils 12 and 13, which respectively operate as coils for applying a static magnetic field and a gradient magnetic field, when the MR image is measured, and outputs a control signal for outputting the current to the MRI power supply 106 and the gradient correction power supply 108. That is, the control device 109 determines the current flowing through the bias magnetic field coil 11 so that a magnetic field in the z-axis direction of a predetermined intensity (for example, 7 mT) is applied to the head of the subject as a static magnetic field. In addition, the control device 109 selectively determines the magnetic field gradient in the x-axis direction, the magnetic field gradient in the y-axis direction, and the magnetic field gradient in the z-axis direction as the gradient magnetic field, and determines the current flowing through the bias magnetic field gradient correction coils 12 and 13. This makes it possible to determine the position of a slice in an MR image, and to encode the position in the slice plane by phase encoding and frequency encoding.

[0107] In addition, the control device 109 determines the current to be supplied to the bias magnetic field coil 11 and the bias magnetic field gradient correction coils 12 and 13 during brain magnetic field measurement, and outputs a control signal for outputting the current to the bias magnetic field power supply 107 and the gradient correction power supply 108. That is, the control device 109 determines the current to flow through the bias magnetic field coil 11 in such a manner as to apply a magnetic field in the z-axis direction of a predetermined intensity (e.g., 14 μT) as the bias magnetic field Bz. In addition, the control device 109 determines the current to be supplied to the bias magnetic field gradient correction coils 12 and 13 in order to correct the gradient of the bias magnetic field Bz in the direction along the x-axis, the direction along the y-axis, or the direction along the z-axis.

[0108] Furthermore, when measuring the MR image, the control device 109 controls the power supplied to the transmitting coil 121 so as to irradiate the head of the subject with RF pulses of a specified frequency (for example, about 300 kHz when the strength of the static magnetic field is 7 mT). As a result, the protons on the slice plane (the plane selected by the static magnetic field and the gradient magnetic field) resonate and the spins are tilted. Thereafter, the control device 109 controls the power of the transmitting coil 121 to be turned off. Therefore, it is possible to acquire an MR image by measuring the spin return based on the output of the receiving amplifier 124. More specifically, the control device 109 uses a well-known spin echo sequence or a gradient echo sequence, etc., to encode the position with frequency and phase, measure the nuclear magnetic resonance signal from the protons, and convert the measurement result into an MR image using FFT.

[0109] The electromagnetic shield 114 is a shielding component for shielding high-frequency (e.g., above 10kHz) electromagnetic noise, and is composed of, for example, a mesh of woven metal wires or a non-magnetic metal plate such as aluminum. The electromagnetic shield 114 is configured to surround the optically excited magnetic sensor 1, 1A, the transmitting coil 121, the receiving coil 122, the receiving amplifier 124, the non-magnetic frame 104, the bias magnetic field coil 11, the bias magnetic field gradient correction coils 12, 13, and the tilting coil 14. The electromagnetic shield 114 can prevent noise in the 300kHz band, which is the measurement frequency, from entering the receiving coil 122 and causing the noise to rise during MR image measurement. In addition, during brain magnetic field measurement, it is possible to prevent high-frequency noise from entering the optically excited magnetic sensor 1, 1A and causing the operation to become unstable.

[0110] The magnetic shield 115 is a shielding component for reducing the mixing of low-frequency magnetic noise of 100 Hz or less, which is equivalent to brain magnetism, and includes, for example, a high-permeability magnetic body composed of a soft magnetic body. The high-permeability magnetic body constituting the magnetic shield 115 is preferably a material with a relative permeability of 1 or more and a coercive force smaller than that of a ferromagnetic body. For example, the high-permeability magnetic body is preferably an amorphous magnetic body, and more preferably a nanocrystalline magnetic body. For example, the magnetic shield 115 has a laminated structure of a sheet containing the above-mentioned high-permeability magnetic body and a conductive film composed of aluminum in multiple layers. The magnetic shield 115 is configured to surround the brain magnetometer module including the optically excited magnetic sensor 1, 1A, the non-magnetic frame 104, the bias magnetic field coil 11, the bias magnetic field gradient correction coils 12, 13 and the tilting coil 14 from the outside of the electromagnetic shield 114, and the MRI module including the transmitting coil 121, the receiving coil 122 and the receiving amplifier 124. Through the magnetic shield 115, the S / N can be improved when measuring the brain magnetic field. Furthermore, the intensity of the geomagnetic field generated by direct current can be reduced to about 1 / 5, the current supplied to the bias magnetic field gradient correction coils 12 and 13 can be reduced to about 1 / 5, the overall current consumption of the device can be reduced, and the intensity of the inclined magnetic field noise caused by the noise generated by the gradient correction power supply 108 can be reduced to 1 / 5.

[0111] Next, refer to Fig.10 and Fig.11 , a brain measurement method using the brain measurement device M1 according to the embodiment is described. Fig.10 and Fig.11 This is a flowchart showing the operation of the brain measurement device M1.

[0112] First, when the measurement of the brain magnetic field is started with the non-magnetic frame 104 worn on the subject, the control device 109 connects the bias magnetic field coil 11 to the bias magnetic field power supply 107 (step S1). Next, the control device 109 determines the current to be supplied to the bias magnetic field coil 11 for applying the bias magnetic field, and outputs a control signal to the bias magnetic field power supply 107, thereby controlling the generation of the bias magnetic field of the bias magnetic field coil 11 (step S2). In addition, the control device 109 determines the current to be supplied to the bias magnetic field gradient correction coils 12 and 13 for correcting the gradient of the bias magnetic field, and controls the correction of the gradient of the bias magnetic field of the bias magnetic field gradient correction coils 12 and 13 by outputting a control signal to the gradient correction power supply 108 (step S3). In this state, the readout circuit 10 obtains the measured values ​​of the brain magnetic field in the multiple sensitivity areas of each optically excited magnetic sensor 1 and 1A in a time series (step S4). The readout circuit 10 outputs the obtained time series measured values ​​to a predetermined output destination. The predetermined output destination may be a storage device such as a memory or a hard disk of the read circuit 10 , an output device such as a display, or an external device such as a terminal device connected via a communication interface.

[0113] Move to Fig.11 After the measurement of the brain magnetic field is completed, when the measurement of the MR image is continued while the non-magnetic frame 104 is installed on the subject as it is, the control device 109 connects the bias magnetic field coil 11 to the MRI power supply 106 (step S5). Then, the control device 109 determines the current provided to the bias magnetic field coil 11 for applying the static magnetic field, and outputs the control signal to the MRI power supply 106, thereby controlling the generation of the static magnetic field in the z-axis direction of the subject's head (step S6). Next, the control device 109 determines the current provided to the bias magnetic field gradient correction coils 12 and 13 for generating the inclined magnetic field, and outputs the control signal to the gradient correction power supply 108, thereby controlling the generation of the magnetic field gradient in the z-axis direction (step S7). At the same time, the control device 109 controls to control the power provided to the transmitting coil 121 so that the RF pulse is irradiated on the subject's head (step S8). As a result, the protons of the specified slice plane are excited.

[0114] Furthermore, the control device 109 determines the current provided to the bias magnetic field gradient correction coils 12 and 13 for generating the gradient magnetic field, and outputs the control signal to the gradient correction power supply 108, thereby controlling the generation of the x-axis direction magnetic field gradient on the slice plane (step S9). Thus, phase encoding is performed. Then, the control device 109 determines the current provided to the bias magnetic field gradient correction coils 12 and 13 for generating the gradient magnetic field, and outputs the control signal to the gradient correction power supply 108, thereby controlling the generation of the y-axis direction magnetic field gradient on the slice plane (step S10). Thus, frequency encoding is performed.

[0115] At the same time, the detection signal of the nuclear magnetic resonance signal from the proton is output via the receiving coil 122 and the receiving amplifier 124, and the control device 109 obtains the data of the nuclear magnetic resonance signal (step S11). Then, the control device 109 determines whether to obtain the nuclear magnetic resonance signal data related to other slice planes (step S12). If the result of the determination is that the nuclear magnetic resonance signal data related to other slice planes is obtained ("yes" in step S12), the process returns to step S7. On the other hand, if the nuclear magnetic resonance signal data related to other slice planes is not obtained ("no" in step S12), the MR image is obtained by Fourier transforming the nuclear magnetic resonance signal data obtained so far (step S13). The control device 109 outputs the acquired MR image to a specified output destination. The specified output destination may be an external device such as a terminal device connected via a communication interface in addition to a storage device such as a memory, a hard disk, and an output device such as a display of the control device 109.

[0116] According to the brain measurement device M1 described above, pump light is emitted to the cell 2 enclosed with alkali metal in a state where a bias magnetic field with a corrected gradient is applied, thereby generating (exciting) the electron spin of the alkali metal atom. Furthermore, the probe light is emitted to the sensitive area intersecting with the pump light in the cell 2, and the polarization plane angle of the probe light passing through the sensitive area is detected by the optical sensor group 8. Based on the detected polarization plane angle, the intensity of the brain magnetic field in the sensitive area can be measured. In addition, according to the brain measurement device M1, a static magnetic field and a gradient magnetic field are applied by the bias magnetic field coil 11 and the bias magnetic field gradient correction coils 12 and 13, and the nuclear magnetic resonance signal generated by the transmission of the RF pulse is detected by the receiving coil 122, thereby measuring a brain morphological image (MR image). Here, in the brain measurement device M1, the brain magnetometer module and the MRI module are surrounded by a magnetic shield 115. The magnetic shield 115 has the property of relatively large magnetic permeability and relatively small coercive force. Therefore, the influence of the environmental magnetic field during brain magnetic field measurement can be reduced, and the static magnetic field applied during MR image measurement can prevent the magnetic shield 115 from being magnetized during brain magnetic field measurement. As a result, both brain magnetic field measurement and MR image acquisition can be achieved with high accuracy.

[0117] In the brain measurement device M1, the soft magnetic material included in the magnetic shield 115 is set to a material with a relative magnetic permeability of 1 or more and a coercive force smaller than that of a ferromagnetic material. In this case, both brain magnetic field measurement and MR image acquisition can be achieved with higher accuracy. In the case where a commonly used shielding material containing iron is used as a magnetic shield, if the brain magnetic field is measured after the MR image measurement, the magnetic shield is magnetized and the optically excited magnetic sensors 1 and 1A do not operate normally. In contrast, in the present embodiment, the magnetization of the magnetic shield caused by the measurement of the MR image can be avoided, and the influence of the earth's magnetism or the environmental magnetic field can be reduced.

[0118] In addition, in this embodiment, the magnetoencephalometer module is provided with a tilting coil 14, which is a tilting unit that tilts the direction of the electron spin in a direction perpendicular to the pump light. In this case, by measuring the intensity of the brain magnetic field based on the frequency of the change in the polarization plane angle of the detected detection light, the measurement sensitivity of the brain magnetic field can be maintained without being affected by the environmental magnetic field.

[0119] In addition, the optically excited magnetic sensor 1, 1A of the present embodiment has a sensitivity region divided into four in the direction along the length direction of the unit 2. Therefore, by obtaining the difference value of the measurement value of the brain magnetic field obtained for two adjacent sensitivity regions among the sensitivity regions divided into four, it is possible to remove the common mode noise.

[0120] In addition, in the present embodiment, a tilting coil 14 for irradiating an RF signal having the same frequency as the resonance frequency is provided as a tilting unit. In this case, the measurement of the brain magnetic field based on the frequency of the change in the polarization angle of the detection light can be achieved by a simple method. In addition, the tilting unit can also be a light source that irradiates pulsed light. In this case, the measurement of the brain magnetic field based on the frequency of the change in the polarization angle of the detection light can also be achieved by a simple method.

[0121] In this embodiment, the static magnetic field coil is formed of the same coil as the bias magnetic field coil 11. Thus, the bias magnetic field and the static magnetic field can be stably applied by the dual-use coil, and stable brain magnetic field and MR image measurement can be achieved.

[0122] In this embodiment, the gradient magnetic field coil is preferably formed of the same coil as the bias magnetic field gradient correction coils 12 and 13. Thus, the bias magnetic field gradient can be corrected and the gradient magnetic field can be applied stably by the dual-use coil, and stable brain magnetic field and MR image measurement can be achieved.

[0123] As mentioned above, although various embodiments of the present invention have been described, the present invention is not limited to the above-mentioned embodiments, and may be modified or applied to other modes within the scope of the gist of the present invention.

[0124] For example, the optically excited magnetic sensors 1 and 1A of the above-described embodiments have the four divided sensitive regions ARa to ARd, but may have any number of sensitive regions as long as there are two or more sensitive regions.

[0125] Furthermore, the optically excited magnetic sensor 1 of the above-described embodiment can also adopt the following modified configurations.

[0126] Fig.12 1 is a perspective view showing the structure of a modified optical excitation magnetometry sensor 1B. The optical excitation magnetometry sensor 1B is different from the optical excitation magnetometry sensor 1 in that it includes two units 2 arranged in parallel, four systems of pump light are incident on the two units 2 respectively, and the detection light is branched and incident on the two units 2 along the length direction thereof. In the following, only the structure different from the optical excitation magnetometry sensor 1 is described.

[0127] The optically excited magnetic sensor 1B includes a pump laser 4 and a first optical system 6 for causing four pump lights to be incident on regions separated in the longitudinal direction (direction along the x-axis) in the cell 2 corresponding to the two cells 2 , respectively.

[0128] In addition, the optically excited magnetic sensor 1B includes a second optical system 7 as an optical system for branching the detection light into two and injecting it into two units 2. The second optical system 7 is constructed to include a lens 35, a 1 / 2 wavelength plate 36, a polarization beam splitter 38 and total reflection mirrors 37a to 37c. The polarization beam splitter 38 is arranged adjacent to the 1 / 2 wavelength plate 36 in the -z axis direction, and separates two mutually perpendicular linear polarization components from the polarization component of the detection light passing through the 1 / 2 wavelength plate 36, so that one of the linear polarization components is transmitted in the -z axis direction, and the other linear polarization component is reflected in the +y axis direction. The total reflection mirror 37a reflects the linear polarization component of the detection light passing through the polarization beam splitter 38 in the -x axis direction, so that it is incident on one unit 2 along its length direction. Total reflection mirrors 37b and 37c continuously reflect the linearly polarized components of the probe light reflected by polarization beam splitter 38 in the -z-axis direction and the -x-axis direction, and make them incident on the other unit 2 along the longitudinal direction thereof. The second optical system 7 having such a structure is configured so that the probe lights of the two systems can be incident on four sensitive areas arranged in the longitudinal direction (along the x-axis direction) in the unit 2 and intersecting with the pump light.

[0129] In addition, four pairs of bias magnetic field coils 11a to 11d are respectively provided in the two units 2 included in the optically excited magnetic sensor 1B. These bias magnetic field coils 11a to 11d, together with the bias magnetic field coil 11, generate bias magnetic fields with different magnetic field strengths in a step-like manner in the four sensitive regions in the unit 2. Thus, the resonance frequencies of the electron spins in the four sensitive regions in the unit 2 can be set to different values, such as 98.5kHz, 99.5kHz, 100.5kHz, and 101.5kHz.

[0130] The optically excited magnetic sensor 1B includes two third optical systems 9 and two optical sensor pairs 43a and 43b corresponding to the two units 2. The third optical system 9 includes a total reflection mirror 46, a 1 / 2 wavelength plate 47, a polarization beam splitter 48 and a total reflection mirror 49. The total reflection mirror 46 reflects the detection light that has passed through the unit 2 along the -x axis direction toward the +z axis direction. The 1 / 2 wavelength plate 47 rotates the polarization plane of the detection light reflected by the total reflection mirror 46. The 1 / 2 wavelength plate 47 is rotatably supported around an axis along the z axis in a manner that can adjust the rotation angle of the polarization plane of the detection light. The polarization beam splitter 48 separates the detection light that passes through the 1 / 2 wavelength plate 47 into two linearly polarized components that are perpendicular to each other, so that one of the linearly polarized components is transmitted in the +z axis direction and incident on the optical sensor pair 43a or the optical sensor pair 43b, and the other linearly polarized component is reflected in the +x direction. The total reflection mirror 49 reflects the other linearly polarized light component reflected by the polarization beam splitter 48 in the +z-axis direction and causes the component to enter the optical sensor pair 43 a or the optical sensor pair 43 b .

[0131] In the optically excited magnetic sensor 1B having the above structure, by including the readout circuit 10, it is also possible to perform the measurement processing of the brain magnetic field related to the eight sensitivity areas of 4×2. That is, the readout circuit 10 extracts a specific frequency band corresponding to the resonance frequency of the electron spin in the sensitivity area based on the voltage signal generated based on the detection signal of each of the optical sensor pairs 43a and 43b, and obtains the measurement value of the brain magnetic field based on the voltage signal of the extracted frequency band. The readout circuit 10 repeatedly extracts the frequency band and obtains the measurement value for the eight sensitivity areas, thereby being able to obtain the measurement values ​​corresponding to the eight sensitivity areas.

[0132] According to the above-mentioned modification example, by obtaining the difference between the measurement values ​​related to two adjacent sensitivity areas, it is also possible to remove the common mode noise and improve the detection accuracy of the brain magnetic field.

[0133] In the above-described embodiment and the above-described modification, linearly polarized pump light is converted into circularly polarized light. However, circularly polarized pump light may be emitted from the pump laser.

[0134] In addition, the arrangement of the optically excited magnetic sensors 1 and 1A in the brain measurement device M1 can be changed in various ways. Fig.13 : is a top view showing the structure of a brain measurement device M2 of a modified example. The brain measurement device M2 includes a plurality of optical excitation magnetization sensors 1 and a plurality of optical excitation magnetization sensors 1A which are arranged in a manner that can be arranged around the head (subject) S of a subject. Two of the plurality of optical excitation magnetization sensors 1A are arranged in parallel in a predetermined direction (x-axis direction) at positions where their four sensitivity regions are close to each other and at positions where they are separated from each other relative to the head S. Two of the plurality of optical excitation magnetization sensors 1 are also arranged in parallel in a direction (z-axis direction) substantially perpendicular to the arrangement direction of the sensitivity regions in the optical excitation magnetization sensors 1 at positions where their four sensitivity regions are close to each other and at positions where they are separated from each other relative to the head S. In addition, a bias magnetic field coil 11, bias magnetic field gradient correction coils 12, 13, and a tilting coil 14 are shared between the plurality of optical excitation magnetization sensors 1 and the plurality of optical excitation magnetization sensors 1A. The bias magnetic field Bz is applied in the z-axis direction by the bias magnetic field coil 11.

[0135] According to the brain measurement device M2 of the above structure, it is possible to obtain the measurement value of the weak magnetic field from the head S. Specifically, according to Fig.13 In the configuration example, the measured value of the magnetic field in the z-axis direction in the sensitivity area of ​​8×4=32 can be obtained. In addition, by obtaining the difference between the measured value of the sensitivity area close to the head S and the measured value of the sensitivity area adjacent to the outside of the head S relative to the sensitivity area, the weak brain magnetic field with common mode noise removed can be measured.

[0136] In addition, in the brain measurement device M2, a structure can also be applied in which the optical excitation magnetometry sensor 1 and the optical excitation magnetometry sensor 1A are only arranged at a position close to the head S and are not arranged in parallel. In this case, by obtaining the difference in the measurement values ​​of two adjacent sensitivity areas of one optical excitation magnetometry sensor 1, 1A, it is possible to measure weak brain magnetometry with common mode noise removed.

Claims

1. A brain measurement device, characterized in that: Including magnetoencephalometer and MRI equipment, The magnetoencephalometer comprises: A unit enclosed with alkali metal vapor; a pump laser emitting pump light for exciting alkali metal atoms constituting the alkali metal vapor; a detection laser that emits a detection light for detecting a change in the electron spin of the alkali metal atom in an excited state toward a sensitive region in the cell that intersects with the pump light; a light sensor that detects a polarization angle of the detection light that has passed through the sensitivity region; and A bias magnetic field coil applies a bias magnetic field in the same direction as the pump light to determine the resonance frequency of the electron spin. The MRI apparatus comprises: A static magnetic field coil, which is used to apply a static magnetic field; A gradient magnetic field coil, which is used to apply a gradient magnetic field; a transmitting coil for transmitting a transmitting pulse of a prescribed frequency; and a receiving coil that detects a nuclear magnetic resonance signal generated by the transmission of the transmission pulse, The magnetoencephalometer and the MRI device are surrounded by a magnetic shield including a soft magnetic body.

2. The brain measurement device according to claim 1, characterized in that: The soft magnetic material is a material having a relative magnetic permeability of 1 or more and a coercive force smaller than that of a ferromagnetic material.

3. The brain measurement device according to claim 2, characterized in that: The soft magnetic body is an amorphous magnetic body.

4. The brain measurement device according to claim 3, characterized in that: The soft magnetic material is a nanocrystalline magnetic material.

5. The brain measurement device according to any one of claims 1 to 4, characterized in that: The magnetoencephalometer further includes a tilting unit that tilts the direction of the electron spin in a direction perpendicular to the pump light.

6. The brain measurement device according to any one of claims 1 to 5, characterized in that: The magnetoencephalometer has two or more sensitivity regions where the pump light and the probe light intersect, and measures the brain magnetic field based on a difference between outputs of the photosensors corresponding to two adjacent sensitivity regions.

7. The brain measurement device according to claim 5, characterized in that: The tilting unit irradiates an RF signal having the same frequency as the resonance frequency.

8. The brain measurement device according to claim 5, characterized in that: The tilting unit irradiates pulsed light.

9. The brain measurement device according to any one of claims 1 to 8, characterized in that: The static magnetic field coil is formed of the same coil as the bias magnetic field coil.

10. The brain measurement device according to any one of claims 1 to 9, characterized in that: The gradient magnetic field coil corrects the gradient of the bias magnetic field when measuring the brain magnetic field.

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