Brain measurement device

Abstract

To provide a brain measurement device in which power consumption can be reduced.SOLUTION: A brain measurement device M1 comprises: a static magnetic field formation part 50 which forms a static magnetic field; a gradient magnetic field correction coil 8 which forms a gradient magnetic field; a transmission coil 21 which transmits a transmission pulse to a subject; a reception coil 22 which detects a nuclear magnetic resonance signal generated in the subject; and a control device 5 which generates an MR image on the basis of the nuclear magnetic resonance signal. The static magnetic field formation part 50 comprises: a first magnetic pole 51 and a second magnetic pole 52 which are arranged so as to face each other; a first coil 53 which generates a magnetic flux; and a first holding member 54 in which a magnetic path for guiding the magnetic flux generated in the first coil 53 to each of the first magnetic pole 51 and the second magnetic pole 52 is formed.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a brain measurement device. [Background technology]

[0002] Patent Document 1 describes a magnetic resonance imaging apparatus. This apparatus includes a gantry in which an imaging region is formed, a cylindrical static magnetic field magnet that forms a static magnetic field in the imaging region, a cylindrical gradient magnetic field coil that forms a gradient magnetic field in the imaging region, and a WB coil that transmits RF magnetic field pulses to the entire imaging region, all built in coaxially. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-239723 [Non-patent literature]

[0004] [Non-Patent Document 1] Sarracanie et al., Low-CostHigh-Performance MRI, SCIENTICFIC REPORTS, 15 October 2015, p1-9. Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, Non-Patent Document 1 points out that when a magnet for a static magnetic field is powerful and huge, very strict infrastructure requirements are imposed. In response to this, Non-Patent Document 1 proposes using a simple coil-shaped electromagnet of about 6.5 mT. However, in this case, power consumption becomes large, for example, 6 kW to 7 kW, when generating the static magnetic field.

[0006] Therefore, an object of the present disclosure is to provide a brain-measuring device that enables low power consumption. [Means for solving the problem]

[0007] The brain measurement device of the present disclosure comprises a static magnetic field forming unit for forming a static magnetic field in a measurement area, a gradient magnetic field coil for forming a gradient magnetic field in the measurement area, a transmitting coil for transmitting a transmit pulse toward a subject in the measurement area, a detecting coil for detecting a nuclear magnetic resonance signal generated in the subject by transmitting the transmit pulse, and a generating unit for generating an MR image based on the nuclear magnetic resonance signal detected by the detecting coil, and the static magnetic field forming unit comprises a first magnetic pole and a second magnetic pole arranged to face each other across the measurement area, a first coil for generating magnetic flux, and a first holding member that holds the first magnetic pole and the second magnetic pole and forms a magnetic path for guiding the magnetic flux generated in the first coil to each of the first magnetic pole and the second magnetic pole.

[0008] In this brain measuring device, when generating an MR image of a subject in a measurement area, a static magnetic field is formed in the measurement area by a static magnetic field forming unit. In the static magnetic field forming unit, magnetic flux generated by a first coil is guided to first and second magnetic poles arranged opposite each other across the measurement area by a magnetic path formed in a first holding member. As a result, a static magnetic field is formed between the first and second magnetic poles in the measurement area. In this way, in this brain measuring device, a static magnetic field is formed using a pair of magnetic poles arranged to sandwich the measurement area. As a result, this brain measuring device can achieve low power consumption.

[0009] In the brain-measuring apparatus according to the present disclosure, the first holding member may include a first body portion extending along a first direction in which a first magnetic pole and a second magnetic pole face each other, a first extension portion extending from one end of the first body portion along a second direction intersecting the first direction, and a second extension portion extending from the other end of the first body portion along the second direction, wherein the first magnetic pole is connected to and held by the first extension portion, the second magnetic pole is connected to and held by the second extension portion, and the first coil may be wound around the first body portion. In this way, by connecting the first magnetic pole and the second magnetic pole to the first extension portion and the second extension portion extending from both ends of the first body portion of the first holding member along one direction, respectively, and providing a first coil on the first body portion to guide magnetic flux to the first magnetic pole and the second magnetic pole, respectively, a more uniform (homogenous) static magnetic field can be formed in the measurement area.

[0010] In the brain-measuring device according to the present disclosure, the first coil may be provided in the first body so as to be symmetrical with respect to a reference line along the second direction, which is a line passing through a midpoint between the first magnetic pole and the second magnetic pole in the first direction. In this case, the path lengths from the first coil to the first magnetic pole and the second magnetic pole are made uniform, thereby further improving the uniformity (homogeneity) of the static magnetic field formed in the measurement area.

[0011] In the brain measuring device according to the present disclosure, the first extension portion may include a first bent portion bent toward the second magnetic pole at an end of the first extension portion opposite the first main body portion, the second extension portion may include a second bent portion bent toward the first magnetic pole at an end of the second extension portion opposite the first main body portion, the first magnetic pole may be circular when viewed from the first direction and may be connected to and held at the tip of the first bent portion at the center of the circle, and the second magnetic pole may be circular when viewed from the first direction and may be connected to and held at the tip of the second bent portion at the center of the circle. In this case, the magnetic flux from the first coil is guided to the centers of the first magnetic pole and the second magnetic pole, thereby further improving the uniformity of the static magnetic field formed in the measurement area.

[0012] In the brain measurement device according to the present disclosure, the first extension portion and the second extension portion may extend linearly along the second direction, the first magnetic pole may be connected to and held at the tip of the front first extension portion at the outer edge of the first magnetic pole on the first extension portion side, and the second magnetic pole may be connected to and held at the tip of the second extension portion at the outer edge of the second magnetic pole on the second extension portion side. In this case, the magnetic paths from the first coil to each of the first magnetic pole and the second magnetic pole can be made shorter, thereby improving the magnetic field strength of the static magnetic field formed in the measurement area.

[0013] In the brain measurement apparatus according to the present disclosure, the static magnetic field generating unit includes a second coil for generating magnetic flux and a second holding member in which a magnetic path is formed for guiding the magnetic flux generated in the second coil to each of the first and second magnetic poles, the second holding member including a second main body portion extending along the first direction, a third extension portion extending linearly from one end of the second main body portion along the second direction, and a fourth extension portion extending linearly from the other end of the second main body portion along the second direction, wherein a tip of the third extension portion is connected to an outer edge of the first magnetic pole on the third extension portion side, and a tip of the fourth extension portion is connected to an outer edge of the second magnetic pole on the fourth extension portion side, and the second coil may be wound around the second main body portion. In this case, coils are disposed on both sides of the first and second magnetic poles, and magnetic flux is guided from each coil to the first and second magnetic poles, thereby further improving the uniformity of the static magnetic field formed in the measurement area.

[0014] In the brain measurement device according to the present disclosure, the size of the first magnetic pole and the size of the second magnetic pole when viewed from the opposing direction of the first magnetic pole and the second magnetic pole may be larger than the distance between the first magnetic pole and the second magnetic pole. In this case, it becomes possible to selectively use the central area between the first magnetic pole and the second magnetic pole, where a more uniform static magnetic field is formed. [Effects of the Invention]

[0015] According to the present disclosure, a brain-measuring device that enables low power consumption can be provided. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram showing a brain-measuring apparatus according to one embodiment. [Figure 2] FIG. 2 is a diagram showing a specific example of the configuration of the OPM module shown in FIG. [Figure 3] FIG. 3 is a side view showing the static magnetic field generating unit shown in FIG. [Figure 4] FIG. 4 is a graph showing the magnetic flux density distribution due to the magnetic field formed by the static magnetic field forming unit. [Figure 5] FIG. 5 is a graph showing the magnetic flux density distribution due to the magnetic field formed by the static magnetic field forming unit. [Figure 6] FIG. 6 is a graph showing the magnetic flux density distribution due to the magnetic field formed by the static magnetic field forming unit. [Figure 7] FIG. 7 is a flowchart showing one step of a brain measurement method according to one embodiment. [Figure 8] FIG. 8 is a flowchart showing one step of a brain measurement method according to one embodiment. [Figure 9] FIG. 9 is a side view showing a static magnetic field generating unit according to a modified example. [Figure 10] FIG. 10 is a graph showing the magnetic flux density distribution due to the magnetic field formed by the static magnetic field forming unit shown in FIG. [Figure 11] FIG. 11 is a graph showing the magnetic flux density distribution due to the magnetic field formed by the static magnetic field forming unit shown in FIG. [Figure 12] FIG. 12 is a side view showing a static magnetic field generating unit according to another modified example. [Figure 13] 13 is a graph showing the magnetic flux density distribution due to the magnetic field formed by the static magnetic field forming unit shown in FIG. [Figure 14] 14 is a graph showing a magnetic flux density distribution due to the magnetic field formed by the static magnetic field forming unit shown in FIG. 12. DETAILED DESCRIPTION OF THE INVENTION

[0017] A brain-measuring device and a brain-measuring method according to one embodiment will be described below with reference to the drawings. In the description of each drawing, identical or corresponding elements may be assigned the same reference numerals, and redundant description may be omitted. In addition, each drawing may show a Cartesian coordinate system defined by the X-axis, Y-axis, and Z-axis. In the following description, the direction roughly parallel to the central axis of the subject's head is referred to as the Z-axis direction, and directions perpendicular to the Z-axis and perpendicular to each other are referred to as the X-axis direction and the Y-axis direction.

[0018] FIG. 1 is a schematic diagram showing a brain-measuring apparatus according to one embodiment. As shown in FIG. 1, the brain-measuring apparatus M1 is an apparatus for acquiring the position and direction of a magnetic field source generated in association with neural activity in the brain of a subject, assuming the source to be an equivalent current dipole moment vector, and acquiring MRI (magnetic resonance imaging) of the subject. The brain-measuring apparatus M1 includes a plurality of OPM (optically pumped magnetometer) modules 1, a plurality of geomagnetic field correction magnetic sensors 2, a plurality of active shield magnetic sensors 3, a non-magnetic frame 4, a pair of gradient magnetic field correction coils 8 (geomagnetic field correction coils), a pair of active shield coils 9, a static magnetic field generating unit 50, a transmitting coil 21, a receiving coil 22 (detection coil), an OPM module 23, and an output coil 24. The brain-measuring apparatus M1 further includes a control device (generator) 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, and a power supply unit 100.

[0019] The OPM module 1 has an optically excited magnetic sensor 1A, a heat insulating material 1B, and a readout circuit 1C. Multiple OPM modules 1 are arranged, for example, at predetermined intervals along the scalp. The optically excited magnetic sensor 1A is a sensor that measures the brain's magnetic field using optical pumping, and has a sensitivity of, for example, approximately 10 fT to 10 pT. The heat insulating material 1B prevents heat transfer and heat transfer from the optically excited magnetic sensor 1A. The readout circuit 1C is a circuit that acquires the detection results of the optically excited magnetic sensor 1A. The optically excited magnetic sensor 1A excites the alkali metal by irradiating pump light onto a cell containing alkali metal vapor.

[0020] Excited alkali metals are spin-polarized, and when exposed to a magnetic field, the tilt of the electron spin polarization axis of the alkali metal atoms changes in response to the magnetic field. The tilt of this electron spin polarization axis is detected by a probe light irradiated separately from the pump light. The optically excited magnetic sensor 1A is configured to apply a predetermined bias magnetic field in the direction of the pump light irradiation so that it is sensitive to magnetic fields with frequencies in the range of 0 to 200 Hz. The readout circuit 1C receives the probe light that has passed through the alkali metal vapor using a photodiode and obtains the detection result. The readout circuit 1C outputs the detection result to the amplifier 12A.

[0021] The optically excited magnetic sensor 1A may be, for example, an axial gradiometer. The axial gradiometer has a measurement region and a reference region on the same axis in a direction perpendicular to the subject's scalp (measurement location). The measurement region is, for example, a location closest to the subject's scalp among the locations where the axial gradiometer measures the brain magnetic field. The reference region is, for example, a location at a predetermined distance (for example, 3 cm) from the measurement region in a direction away from the subject's scalp among the locations where the axial gradiometer measures the brain magnetic field.

[0022] The axial gradiometer outputs the results of measurements taken in the measurement region and the reference region to the amplifier 12A. If common mode noise is present, its influence is indicated in the output results of the measurement region and the reference region. The common mode noise is removed by obtaining the difference between the output results of the measurement region and the reference region. By removing the common mode noise, the optically excited magnetic sensor 1A can achieve a sensitivity of approximately 10 fT / √Hz when measuring in a magnetic noise environment of, for example, 1 pT.

[0023] The geomagnetic field compensating magnetic sensor 2 is a sensor that measures a magnetic field related to geomagnetism at a position corresponding to the optically excited magnetic sensor 1A, and is configured by, for example, a fluxgate sensor with a sensitivity of about 1 nT to 100 μT. The position corresponding to the optically excited magnetic sensor 1A is a position on the periphery (vicinity) of the area where the optically excited magnetic sensor 1A is arranged. The geomagnetic field compensating magnetic sensors 2 may be provided in one-to-one correspondence with the optically excited magnetic sensors 1A, or in one-to-multiple correspondence (one geomagnetic field compensating magnetic sensor 2 for multiple optically excited magnetic sensors 1A).

[0024] The geomagnetic field correcting magnetic sensor 2 measures the geomagnetic field and the geomagnetic gradient magnetic field (hereinafter, may be simply referred to as "gradient magnetic field") as a magnetic field related to the geomagnetic field, and outputs the measurement values ​​to the control device 5. The measurement values ​​of the geomagnetic field correcting magnetic sensor 2 can be represented by a vector having a direction and a magnitude. The geomagnetic field correcting magnetic sensor 2 may perform measurement and output continuously at predetermined time intervals.

[0025] The magnetic sensor 3 for the active shield is a sensor that measures a fluctuating magnetic field at a position corresponding to the optically excited magnetic sensor 1A, and has a sensitivity of, for example, about 100 fT to 10 nT, and is configured by an optically excited magnetic sensor different from the optically excited magnetic sensor 1A. The position corresponding to the optically excited magnetic sensor 1A is a position on the periphery (vicinity) of the area where the optically excited magnetic sensor 1A is arranged. The magnetic sensors 3 for the active shield may be provided in one-to-one correspondence with the optically excited magnetic sensors 1A, or in one-to-multiple correspondence (one magnetic sensor 3 for the active shield for multiple optically excited magnetic sensors 1A).

[0026] The active shield magnetic sensor 3 measures a fluctuating magnetic field, for example, a magnetic field of noise (AC) components of 200 Hz or less, and outputs the measurement value to the control device 5. The measurement value of the active shield magnetic sensor 3 can be expressed as a vector having a direction and a magnitude. The active shield magnetic sensor 3 may perform measurement and output continuously at predetermined time intervals.

[0027] The non-magnetic frame 4 is a frame that covers the entire scalp of the subject whose brain magnetic field is to be measured, and is made of a non-magnetic material such as graphite that has a relative permeability close to 1 and does not disturb the magnetic field distribution. The non-magnetic frame 4 can be, for example, a helmet-type frame that surrounds the entire scalp of the subject and is worn on the subject's head. Multiple optically excited magnetic sensors 1A are fixed to the non-magnetic frame 4 so that they are close to the subject's scalp. Furthermore, a geomagnetic field correction magnetic sensor 2 is fixed to the non-magnetic frame 4 so that the magnetic field related to the geomagnetism can be measured at each position of the multiple optically excited magnetic sensors 1A, and an active shield magnetic sensor 3 is fixed to the non-magnetic frame 4 so that the fluctuating magnetic field can be measured at each position of the multiple optically excited magnetic sensors 1A.

[0028] Because the magnetic field strength of a variable magnetic field varies less with position than that of a static magnetic field, the number of active shield magnetic sensors 3 may be fixed to the non-magnetic frame 4 so that it is fewer than the number of geomagnetic field correction magnetic sensors 2. In addition, a receiver coil 22 for detecting nuclear magnetic resonance signals for MR image measurement is fixed to the scalp side of the subject of the multiple optically excited magnetic sensors 1A in the non-magnetic frame 4. This receiver coil 22 detects nuclear magnetic resonance signals of protons, which will be described later, and converts them into electric current. In order to improve the detection sensitivity of the nuclear magnetic resonance signals, the receiver coil 22 is preferably provided on the side of the optically excited magnetic sensor 1A that is closer to the scalp of the subject's head.

[0029] The transmitting coil 21 is a coil that irradiates the subject's head with RF pulses (transmitting pulses) of a predetermined frequency (for example, about 300 kHz) during MRI measurement. This transmitting coil 21 is placed, for example, above the subject's head outside the non-magnetic frame 4. The output coil 24 is electrically connected to both ends of the receiving coil 22 via a cable, receives the current flowing between both ends of the receiving coil 22, converts the current back into a magnetic signal, and outputs it.

[0030] Like the OPM module 1, the OPM module 23 has an optically excited magnetic sensor 23A, a heat insulating material 23B, and a readout circuit 23C. The OPM module 23 is housed together with the output coil 24 in a magnetic shield 25 that shields against a static magnetic field (described later) and is disposed, for example, outside the non-magnetic frame 4. The magnetic shield 25 is made of a material with a relative permeability greater than 1, such as mu metal.

[0031] The optically excited magnetic sensor 23A is a sensor that measures magnetic signals using optical pumping. The optically excited magnetic sensor 23A is configured so that a predetermined bias magnetic field is applied in the direction of irradiation with the pump light so that it is sensitive to magnetic fields with frequencies in the range of 20 kHz to 500 kHz. For example, a bias magnetic field of approximately 40 μT is applied so that it is sensitive to the 300 kHz frequency of electromagnetic waves emitted by protons. The readout circuit 23C outputs the detection result by the optically excited magnetic sensor 23A to the amplifier 12B.

[0032] Fig. 2 is a diagram showing a specific example of the configuration of the OPM module shown in Fig. 1. As shown in Fig. 2, the optically excited magnetic sensor 23A includes a longitudinal cell 26 filled with a gas containing an alkali metal whose polarization direction changes depending on the magnetic field to be measured, a heater 27 that heats the entire cell 26 to a predetermined temperature (e.g., 180 degrees), a polarizing beam splitter 28, and a photodetector 29. Pump light L1 is introduced from the outside into this cell 26 along the longitudinal direction thereof, and probe light L2 from the outside is branched and irradiated onto each of intersection regions 26A that are divided into a plurality of sections (e.g., four sections) along a direction perpendicular to the longitudinal direction.

[0033] The magnetic rotation angle of the probe light L2 transmitted through these intersection regions 26A is detected by a polarizing beam splitter 28 and a photodetector 29 provided corresponding to each intersection region 26A. That is, the polarizing beam splitter 28 splits the probe light L2 into two linearly polarized components that are orthogonal to each other, and the photodetector 29 detects the intensities of the two linearly polarized components using two built-in photodiodes (PDs) and detects the magnetic rotation angle of the probe light L2 based on the ratio of the detected intensities. The OPM module 23 is further provided with a circuit board 30, and the magnetic rotation angle of the probe light L2 detected for each intersection region 26A is output via a readout circuit 23C within this circuit board 30.

[0034] The output coil 24 is fixed in the magnetic shield 25 so as to face each intersection region 26A of the cells 26 of the OPM module 23 configured as described above. With this configuration, the electromagnetic field B OUT The magnetic signal B generated by the output coil 24 based on OUTis detected based on the magnetic rotation angle of the probe light L2, which changes depending on the tilt of the electron spin polarization axis of the alkali metal atom. Here, in the example of Fig. 2, the intersection region 26A is divided into four, but this may be changed to any number. Also, a plurality of cells 26 may be provided in parallel, and the intersection regions 26A may be arranged two-dimensionally (for example, 4 x 4 = 16).

[0035] When measuring the brain magnetic field, the control device 5 determines the currents to be supplied to the various coils based on the measurement values ​​output from the geomagnetic field correcting magnetic sensors 2 and the active shield magnetic sensors 3, and outputs control signals for outputting the currents to the coil power supply 6 and the power supply unit 100. Based on the measurement values ​​of the multiple geomagnetic field correcting magnetic sensors 2, the control device 5 determines the currents to be supplied to the static magnetic field generating unit 50 and the gradient magnetic field correction coil 8 so as to generate a magnetic field that cancels out the magnetic field associated with the geomagnetism. Details of the static magnetic field generating unit 50 will be described later. Based on the measurement values ​​of the multiple active shield magnetic sensors 3, the control device 5 also determines the current to be supplied to the active shield coil 9 so as to generate a magnetic field that cancels out the fluctuating magnetic field. The control device 5 outputs a control signal to the coil power supply 6 according to the determined current.

[0036] Specifically, the control device 5 determines the current for the static magnetic field generating unit 50 so that the average value of the measurement values ​​of the multiple geomagnetic field correcting magnetic sensors 2 approaches zero (as a result, a magnetic field is generated that is opposite to and has the same magnitude as the geomagnetism at the position of the optically excited magnetic sensor 1A). The control device 5 outputs a control signal (static magnetic field correction control signal) corresponding to the determined current for the static magnetic field generating unit 50 to the power supply unit 100.

[0037] The control device 5 also determines the current for the gradient magnetic field correction coil 8 so that the deviation from the average value of the measurement values ​​of the multiple geomagnetic field correcting magnetic sensors 2 is minimized (as a result, a magnetic field is generated that is opposite in direction to and has the same magnitude as the gradient magnetic field at the position of the optically excited magnetic sensor 1A). The control device 5 outputs a control signal (static magnetic field correction control signal) corresponding to the determined current for the gradient magnetic field correction coil 8 to the coil power supply 6.

[0038] Furthermore, the control device 5 determines the current for the active shield coil 9 so that the average value of the measurement values ​​of the multiple active shield magnetic sensors 3 approaches 0 (as a result, a magnetic field is generated that is opposite in direction to and has the same magnitude as the fluctuating magnetic field at the position of the optically excited magnetic sensor 1A). The control device 5 outputs a control signal (a fluctuating magnetic field correction control signal) to the coil power supply 6 according to the determined current for the active shield coil 9.

[0039] Furthermore, the control device 5 obtains information about the magnetism detected by the optically excited magnetic sensor 1A using the signal output from the amplifier 12A. When the optically excited magnetic sensor 1A is an axial gradiometer, the control device 5 may remove common mode noise by obtaining the difference between the output result of the measurement region and the output result of the reference region. The control device 5 may also control the operation of the pump laser 10 and the probe laser 11, such as the irradiation timing and irradiation time.

[0040] Furthermore, when measuring MR images, the control device 5 determines the current to be supplied to the static magnetic field generating unit 50 and the gradient magnetic field correction coil 8, which operate as coils for applying a static magnetic field and a gradient magnetic field, respectively, and outputs a control signal for outputting the current to the coil power supply 6 and the power supply unit 100. That is, the control device 5 determines the current to be passed through the static magnetic field generating unit 50 so as to apply a magnetic field in the X-axis direction of a predetermined strength (for example, 7 mT) to the head of the subject as the static magnetic field. Furthermore, the control device 5 determines the X-axis magnetic field gradient (dB X / dX), Y-axis magnetic field gradient (dB X / dY), and Z-axis magnetic field gradient (dB X / dZ) and determines the current to be passed through the gradient magnetic field correction coil 8. This allows the position to be determined in the MR image to be sliced, and the position within the slice plane to be encoded by phase encoding and frequency encoding. During MR image measurement, the control device 5 outputs a control signal so that no current is supplied to the active shield coil 9, which removes low-frequency noise.

[0041] Furthermore, when measuring an MR image, the control device 5 outputs a control signal to the transmit coil controller 15 to control the power supplied to the transmit coil 21, thereby controlling the transmit pulse to be irradiated onto the subject's head at a predetermined frequency (for example, approximately 300 kHz when the static magnetic field strength is 7 mT). As a result, protons in the slice plane (the plane selected by the static magnetic field and the gradient magnetic field) resonate and the spins tilt. Thereafter, the control device 5 controls the power of the transmit coil 21 to be turned off. This makes it possible to acquire an MR image by measuring the return of the spins based on the output of the OPM module 23. More specifically, the control device 5 measures the nuclear magnetic resonance signals from the protons by encoding their positions with frequency and phase using a known spin echo sequence or gradient echo sequence, and converts the measurement results into an MR image using FFT.

[0042] The control device 5 is physically configured to include memories such as RAM and ROM, a processor (arithmetic circuit) such as a CPU, a communication interface, and a storage unit such as a hard disk. Examples of such a control device 5 include a personal computer, a cloud server, a smartphone, and a tablet terminal. The control device 5 functions by executing a program stored in the memory with the CPU of the computer system.

[0043] The coil power supply 6 outputs a predetermined current to each of the gradient magnetic field correction coil 8 and the active shield coil 9 in response to a control signal output from the control device 5. Furthermore, the power supply unit 100 outputs a current to the static magnetic field generating unit 50 in response to a control signal related to the static magnetic field generating unit 50. Furthermore, the coil power supply 6 outputs a current to the gradient magnetic field correction coil 8 in response to a control signal related to the gradient magnetic field correction coil 8. Furthermore, the coil power supply 6 outputs a current to the active shield coil 9 in response to a control signal related to the active shield coil 9.

[0044] The transmitting coil controller 15 is electrically connected to the transmitting coil 21, and supplies power to the transmitting coil 21 in response to a control signal output from the control device 5 so as to irradiate a transmitting pulse of a predetermined frequency.

[0045] The static magnetic field generating unit 50 is also configured to correct the geomagnetic field among the geomagnetic fields at the position of the optically excited magnetic sensor 1A. The static magnetic field generating unit 50 generates a magnetic field in response to the current supplied from the power supply unit 100 to cancel the geomagnetic field. The static magnetic field generating unit 50 will be described in detail later. Here, the static magnetic field generating unit 50 has a pair of first and second magnetic poles 51 and 52. The pair of first and second magnetic poles 51 and 52 are arranged to sandwich the optically excited magnetic sensor 1A (for example, on the left and right sides of the subject). The pair of first and second magnetic poles 51 and 52 generate a magnetic field in the opposite direction to and of approximately the same magnitude as the geomagnetic field at the position of the optically excited magnetic sensor 1A in response to the current supplied from the power supply unit 100. The magnetic field direction is, for example, the X-axis direction, Y-axis direction, and Z-axis direction. The geomagnetic field at the position of the optically excited magnetic sensor 1A is canceled out by the magnetic field generated by the first and second magnetic poles 51 and 52, which is in the opposite direction and of approximately the same magnitude.

[0046] In this way, the static magnetic field generating unit 50 can also correct the geomagnetism at the position of the optically excited magnetic sensor 1A. The static magnetic field generating unit 50 also serves to generate a static magnetic field in the X-axis direction during MR image measurement. The static magnetic field generating unit 50 generates a static magnetic field of a predetermined strength in accordance with the current supplied from the power supply unit 100.

[0047] The gradient magnetic field correction coil 8 is a coil for correcting the gradient magnetic field, which is a magnetic field associated with geomagnetism at the position of the optically excited magnetic sensor 1A. The gradient magnetic field correction coil 8 generates a magnetic field in response to a current supplied from the coil power supply 6, thereby canceling the gradient magnetic field. The gradient magnetic field correction coil 8 has, for example, a pair of gradient magnetic field correction coils 8A and 8B. The pair of gradient magnetic field correction coils 8A and 8B are arranged on either side of the optically excited magnetic sensor 1A (for example, on the left and right of the subject). The pair of gradient magnetic field correction coils 8A and 8B generate a magnetic field that is opposite in direction to and approximately equal in magnitude to the gradient magnetic field at the position of the optically excited magnetic sensor 1A in response to the current supplied from the coil power supply 6. The magnetic field direction is, for example, the X-axis direction, Y-axis direction, and Z-axis direction. The gradient magnetic field at the position of the optically excited magnetic sensor 1A is canceled out by the magnetic field generated by the gradient magnetic field correction coil 8, which is opposite in direction to and approximately equal in magnitude.

[0048] In this way, the gradient magnetic field correction coil 8 corrects the gradient magnetic field at the position of the optically excited magnetic sensor 1A. The gradient magnetic field correction coil 8 also serves as a gradient magnetic field coil for generating a gradient magnetic field during MR image measurement. The gradient magnetic field correction coil 8 generates a gradient magnetic field having selective gradients in the X-axis, Y-axis, and Z-axis directions according to the current supplied from the coil power supply 6.

[0049] The active shield coil 9 is a coil for correcting a fluctuating magnetic field at the position of the optically excited magnetic sensor 1A. The active shield coil 9 generates a magnetic field in response to a current supplied from the coil power supply 6, thereby canceling the fluctuating magnetic field. The active shield coil 9 includes, for example, a pair of active shield coils 9A and 9B. The pair of active shield coils 9A and 9B are arranged on either side of the optically excited magnetic sensor 1A (for example, on the left and right sides of the subject). The pair of active shield coils 9A and 9B generate a magnetic field in response to a current supplied from the coil power supply 6, the magnetic field being opposite in direction and of approximately the same magnitude as the fluctuating magnetic field at the position of the optically excited magnetic sensor 1A. The magnetic field direction may be, for example, the X-axis direction, the Y-axis direction, or the Z-axis direction. The fluctuating magnetic field at the position of the optically excited magnetic sensor 1A is canceled out by the magnetic field generated by the active shield coil 9, which is opposite in direction and of approximately the same magnitude. In this way, the active shield coil 9 corrects the fluctuating magnetic field at the position of the optically excited magnetic sensor 1A.

[0050] The pump laser 10 is a laser device that generates pump light. The pump light emitted from the pump laser 10 is incident on each of the multiple optically excited magnetic sensors 1A and the optically excited magnetic sensor 23A via a fiber branch. The probe laser 11 is a laser device that generates probe light. The probe light emitted from the probe laser 11 is incident on each of the multiple optically excited magnetic sensors 1A and the optically excited magnetic sensor 23A via a fiber branch.

[0051] Amplifier 12A is a device or circuit that amplifies the signal output from OPM module 1 (specifically, readout circuit 1C) and outputs it to control device 5. Amplifier 12B is a device or circuit that amplifies the signal output from OPM module 23 (specifically, readout circuit 23C) and outputs it to control device 5.

[0052] The heater controller 13 is a temperature control device connected to heaters for heating the cells of the photoexcited magnetic sensor 1A and the photoexcited magnetic sensor 23A, and to thermocouples (not shown) for measuring the temperatures of the respective cells. The heater controller 13 receives cell temperature information from the thermocouples, and adjusts the heating of the heater based on the temperature information to adjust the temperature of the cells.

[0053] The electromagnetic shield 14 is a shielding member that blocks high-frequency (e.g., 10 kHz or higher) electromagnetic noise and is made of, for example, a mesh of woven metal threads or a nonmagnetic metal plate such as aluminum. The electromagnetic shield 14 is arranged to surround the OPM modules 1 and 23, the transmitter coil 21, the receiver coil 22, the output coil 24, the geomagnetic field correction magnetic sensor 2, the active shield magnetic sensor 3, the nonmagnetic frame 4, the static magnetic field generator 50, the gradient magnetic field correction coil 8, and the active shield coil 9. This electromagnetic shield 14 prevents noise in the 300 kHz band, which is the measurement frequency, from entering the receiver coil 22 during MR image measurement, which would increase the noise level. It also prevents high-frequency noise from entering the optically excited magnetic sensor 1A and causing unstable operation during brain magnetic field measurement.

[0054] Next, the static magnetic field generating unit 50 will be described in detail. FIG. 3 is a side view showing the static magnetic field generating unit shown in FIG. 1. As shown in FIG. 3, the static magnetic field generating unit 50 has a first magnetic pole 51, a second magnetic pole 52, a first coil 53, and a first holding member 54. The first magnetic pole 51 and the second magnetic pole 52 are disposed opposite each other and spaced apart from each other along the X-axis direction. As a result, a static magnetic field is generated between the first magnetic pole 51 and the second magnetic pole 52 during MR image measurement. Therefore, the area between the first magnetic pole 51 and the second magnetic pole 52 is a measurement area AR. In other words, the first magnetic pole 51 and the second magnetic pole 52 are disposed opposite each other across the measurement area AR.

[0055] 1, when viewed at least from the Y direction, the gradient magnetic field correction coil 8 and the active shield coil 9 are disposed between the first magnetic pole 51 and the second magnetic pole 52. Therefore, while the static magnetic field forming unit 50 is for forming a static magnetic field in the measurement area AR, the gradient magnetic field correction coil 8 is also a gradient magnetic field coil for forming a gradient magnetic field in the measurement area AR during MR image measurement. The transmitting coil 21 is disposed facing the measurement area AR and is for transmitting transmission pulses toward the subject in the measurement area AR during MR image measurement. The receiving coil 22 is for detecting nuclear magnetic resonance signals generated in the subject by transmitting the transmission pulses during MR image measurement. Furthermore, the control device (generating unit) 5 generates an MR image based on the nuclear magnetic resonance signals detected by the receiving coil 22.

[0056] Continuing with reference to FIG. 3, the first coil 53 generates a magnetic flux when supplied with power from the power supply unit 100. The first coil 53 is wound around a first holding member 54. The first holding member 54 holds the first magnetic pole 51 and the second magnetic pole 52, and forms a magnetic path for guiding the magnetic flux generated in the first coil 53 to each of the first magnetic pole 51 and the second magnetic pole 52. This generates a magnetic field between the first magnetic pole 51 and the second magnetic pole 52 (measurement area AR).

[0057] The first holding member 54 includes a first main body portion 55 extending along the X-axis direction (first direction) in which the first magnetic pole 51 and the second magnetic pole 52 face each other, a first extension portion 56 extending from one end of the first main body portion 55 along the Z-direction (second direction) intersecting the X-axis direction, and a second extension portion 57 extending from the other end of the first main body portion 55 along the Y-axis direction. As an example, the first extension portion 56 and the second extension portion 57 are approximately parallel to each other. The first magnetic pole 51 is connected to and held by the first extension portion 56, and the second magnetic pole 52 is connected to and held by the second extension portion 57.

[0058] More specifically, the first extension portion 56 includes a first bent portion 58 that bends toward the second magnetic pole 52 at an end of the first extension portion 56 opposite the first main body portion 55, and the second extension portion 57 includes a second bent portion 59 that bends toward the first magnetic pole at an end of the second extension portion 57 opposite the first main body portion 55. As a result, the first holding member 54 is configured to be approximately C-shaped as a whole. The first magnetic pole 51 is connected to and held by the tip of the first bent portion 58, and the second magnetic pole 52 is connected to and held by the tip of the second bent portion 59.

[0059] In particular, here, the first magnetic pole 51 and the second magnetic pole 52 each have a disk shape and are connected to the first bent portion 58 and the second bent portion 59 at approximately the center of the circular shape. Therefore, the measurement area AR formed between the first magnetic pole 51 and the second magnetic pole 52 can be formed, for example, in a roughly cylindrical shape. As an example, the first holding member 54 has a rod shape with a circular cross section. The first magnetic pole 51, the second magnetic pole 52, and the first holding member 54 are formed in a solid shape from a magnetic material (e.g., steel) that has high magnetic permeability and allows magnetic flux to pass easily.

[0060] Here, there is one first coil 53, and it is provided at the center of the first main body portion 55. However, there may be multiple first coils 53, and in that case, it is sufficient that they are provided in the first main body portion 55 so as to be symmetrical with respect to a reference line along the Z direction that passes through the midpoint between the first magnetic pole 51 and the second magnetic pole 52 in the X-axis direction. The number of turns of the first coil 53 is, for example, 1000 turns, and a current of about 3 A flows through it. In this case, the power consumption can be about 50 W.

[0061] Here, the size of the first magnetic pole 51 and the size of the second magnetic pole 52 when viewed from the opposing direction of the first magnetic pole 51 and the second magnetic pole 52 (X-axis direction) are larger than the distance Da between the first magnetic pole 51 and the second magnetic pole 52. As an example, the distance Da between the first magnetic pole 51 and the second magnetic pole 52 is approximately 300 mm, and the diameter φa of the first magnetic pole 51 and the second magnetic pole 52 is approximately 600 mm. That is, in this example, the size of the first magnetic pole 51 and the second magnetic pole 52 is approximately twice the distance Da between the first magnetic pole 51 and the second magnetic pole 52. The thickness T of the first magnetic pole 51 and the second magnetic pole 52 is uniform, for example, approximately 75 mm. However, the thickness T of the first magnetic pole 51 and the second magnetic pole 52 does not have to be uniform. As an example, the first magnetic pole 51 and the second magnetic pole 52 may be formed so as to be relatively thicker near their peripheral edges. In this case, the decrease in the uniformity of the static magnetic field near the periphery is suppressed, and the uniformity of the static magnetic field formed in the measurement area AR is further improved. In this example, the first magnetic pole 51 and the second magnetic pole 52 have the same shape.

[0062] The diameter φb of the first holding member 54 is, for example, approximately 50 mm to 100 mm, and is, for example, approximately 75 mm. The length La of the first extension portion 56 and the second extension portion 57 is, for example, approximately 600 mm. Furthermore, the distance Db between the first extension portion 56 and the second extension portion 57 along the X-axis direction is approximately 600 mm. Therefore, the length La of the first extension portion 56 and the second extension portion 57, the diameter φa of the first magnetic pole 51 and the second magnetic pole 52, and the distance Db between the first extension portion 56 and the second extension portion 57 can be approximately the same. The length Lb of the range in which the first coil 53 is provided in the first main body portion 55 is, for example, approximately 150 mm.

[0063] Next, the magnetic field generated by the static magnetic field generating unit 50 configured as described above will be described. FIG. 4 is a graph showing the magnetic flux density distribution in the measurement area due to the magnetic field generated by the static magnetic field generating unit. In FIG. 4(a), the horizontal axis represents the position in the X-axis direction, and in FIG. 4(b), the horizontal axis represents the position in the Z-axis direction. In both cases, the center is 0. Therefore, in both FIG. 4(a) and FIG. 4(b), the range from 0 mm to ±150 mm corresponds to a range of approximately 150 mm radially from the center of the circle of the first magnetic pole 51 and the second magnetic pole 52.

[0064] 4, it can be seen that with the static magnetic field generating unit 50 configured as described above, a uniform magnetic flux density distribution can be obtained in the XZ plane at about 3 mT when the diameter φb of the first holding member 54 is 50 mm, at about 6.5 mT to 7 mT when the diameter φb is 75 mm, and at about 9 mT when the diameter φb is 100 mm. In particular, as shown in FIGS. 5 and 6, it can be seen that when the diameter φb of the first holding member 54 is 75 mm, a substantially uniform magnetic flux density distribution of 6.7 mT can be obtained in the measurement area RA over a range of at least about φ200 mm in the XZ plane.

[0065] Next, a brain measuring method according to an embodiment will be described with reference to Figures 7 and 8. Figures 7 and 8 are flowcharts showing one step of a brain measuring method according to an embodiment.

[0066] First, when measurement of the brain magnetic field is started with the non-magnetic frame 4 attached to the subject, the geomagnetic field correcting magnetic sensor 2 measures the geomagnetic field, which is a static magnetic field (step S11). The geomagnetic field correcting magnetic sensor 2 measures the geomagnetic field and the gradient magnetic field at each position of the optically excited magnetic sensor 1A, and outputs the measurement values ​​to the control device 5.

[0067] The control device 5 and the coil power supply 6 control the current to the static magnetic field generating unit 50 (step S12). Based on the measurement values ​​of the geomagnetic field correcting magnetic sensor 2, the control device 5 determines the current to the static magnetic field generating unit 50 (i.e., the first coil 53) so as to generate a magnetic field of the same magnitude and in the opposite direction to the geomagnetism at the position of the optically excited magnetic sensor 1A. More specifically, the control device 5 determines the current to the static magnetic field generating unit 50 so that, for example, the average value of the measurement values ​​of the multiple geomagnetic field correcting magnetic sensors 2 approaches zero. The control device 5 outputs a control signal according to the determined current to the power supply unit 100. The power supply unit 100 outputs a predetermined current to the first coil 53 in response to the control signal output by the control device 5. The first coil 53 generates magnetic flux according to the current supplied from the power supply unit 100. The magnetic flux generated in the first coil 53 is guided by the first holding member 54 to the first magnetic pole 51 and the second magnetic pole 52. This generates a magnetic field between the first magnetic pole 51 and the second magnetic pole 52. The geomagnetism at the position of the optically excited magnetic sensor 1A is cancelled out by the magnetic field of the same magnitude and in the opposite direction generated by the first coil 53. In this way, the static magnetic field generating unit 50 also functions as a geomagnetic field correction coil for correcting the magnetic field related to the geomagnetism.

[0068] The control device 5 and the coil power supply 6 control the current to the gradient magnetic field correction coil 8 (step S13). Based on the measurement value of the geomagnetic field correcting magnetic sensor 2, the control device 5 determines the current to the gradient magnetic field correction coil 8 so as to generate a magnetic field that is opposite to and of approximately the same magnitude as the gradient magnetic field at the position of the optically excited magnetic sensor 1A. More specifically, the control device 5 determines the current to the gradient magnetic field correction coil 8 so as to minimize the deviation from the average value of the measurement values ​​of the multiple geomagnetic field correcting magnetic sensors 2. The control device 5 outputs a control signal according to the determined current to the coil power supply 6. The coil power supply 6 outputs a predetermined current to the gradient magnetic field correction coil 8 in accordance with the control signal output by the control device 5. The gradient magnetic field correction coil 8 generates a magnetic field in accordance with the current supplied from the coil power supply 6. The gradient magnetic field at the position of the optically excited magnetic sensor 1A is canceled out by the magnetic field generated by the gradient magnetic field correction coil 8, which is opposite to and of approximately the same magnitude.

[0069] The control device 5 determines whether the measured value of the static magnetic field (magnetic field related to geomagnetism) after correction is equal to or less than the reference value (step S14). The measured value of the static magnetic field after correction is the value measured by the geomagnetic field correcting magnetic sensor 2 after the static magnetic field has been corrected by the static magnetic field generating unit 50 and the gradient magnetic field correction coil 8. The reference value is the magnitude of the magnetic field at which the optically excited magnetic sensor 1A operates normally, and can be, for example, 1 nT. If the measured value of the static magnetic field is not equal to or less than the reference value ("NO" in step S14), the process returns to step S11. If the measured value of the static magnetic field is equal to or less than the reference value ("YES" in step S14), the process proceeds to step S15.

[0070] The active shield magnetic sensor 3 measures the fluctuating magnetic field at each position of the optically excited magnetic sensor 1A, and outputs the measurement values ​​to the control device 5 (step S15).

[0071] The control device 5 and the coil power supply 6 control the current to the active shield coil 9 (step S16). Based on the measurement values ​​of the active shield magnetic sensors 3, the control device 5 determines the current to be applied to the active shield coil 9 so as to generate a magnetic field of the same magnitude and in the opposite direction to the fluctuating magnetic field at the position of the optically excited magnetic sensor 1A. More specifically, the control device 5 determines the current to be applied to the active shield coil 9 so that, for example, the average value of the measurement values ​​of the multiple active shield magnetic sensors 3 approaches zero. The control device 5 outputs a control signal according to the determined current to the coil power supply 6. The coil power supply 6 outputs a predetermined current to the active shield coil 9 in response to the control signal output by the control device 5. The active shield coil 9 generates a magnetic field in response to the current supplied from the coil power supply 6. The fluctuating magnetic field at the position of the optically excited magnetic sensor 1A is canceled out by the magnetic field generated by the active shield coil 9 of the same magnitude and in the opposite direction.

[0072] The control device 5 determines whether the measured value of the variable magnetic field after correction is equal to or less than the reference value (step S17). The measured value of the variable magnetic field after correction is the value measured by the active shield magnetic sensor 3 after the variable magnetic field has been corrected by the active shield coil 9. The reference value is the noise level at which the brain magnetic field can be measured, and may be, for example, 1 pT. If the measured value of the variable magnetic field is not equal to or less than the reference value ("NO" in step S17), the process returns to step S15. If the measured value of the variable magnetic field is equal to or less than the reference value ("YES" in step S17), the process proceeds to step S18.

[0073] The optically excited magnetic sensor 1A measures the brain magnetic field (step S18). The control device 5 outputs the acquired measurement results to a predetermined output destination. The predetermined output destination may be the memory of the control device 5, a storage device such as a hard disk, an output device such as a display, or an external device such as a terminal device connected via a communication interface. Since the static magnetic field (magnetic field related to the earth's magnetism) and the variable magnetic field at the position of the optically excited magnetic sensor 1A have been canceled out so that they are below predetermined reference values, the optically excited magnetic sensor 1A can measure the brain magnetic field while avoiding the influence of the static magnetic field (magnetic field related to the earth's magnetism) and the variable magnetic field. In this way, the control device 5 also serves as a generation unit for generating the brain magnetic field distribution of the subject based on the brain magnetic field detection results obtained by the optically excited magnetic sensor 1A.

[0074] 8, when MR image measurement is initiated while the non-magnetic frame 4 is still attached to the subject, the control device 5 determines the current to be supplied to the static magnetic field generator 50 (i.e., the first coil 53) for applying a static magnetic field, and outputs a control signal to the power supply 100 to control the generation of a static magnetic field in the X-axis direction at the subject's head (step S19). In this way, the static magnetic field generator 50 also functions as a static magnetic field coil for applying a static magnetic field. Next, the control device 5 determines the current to be supplied to the gradient magnetic field correction coil 8 for generating a gradient magnetic field, and outputs a control signal to the coil power supply 6 to control the generation of the X-axis magnetic field gradient (dBx / dX) (step S20). At the same time, the control device 5 outputs a control signal to the transmit coil controller 15 to control the power to be supplied to the transmit coil 21, thereby controlling the transmit pulse to be irradiated onto the subject's head (step S21). This excites protons in a predetermined slice plane.

[0075] Furthermore, the control device 5 determines the current to be supplied to the gradient magnetic field correction coil 8 for generating the gradient magnetic field, and outputs a control signal to the coil power supply 6, thereby controlling the generation of the Y-axis magnetic field gradient (dBx / dY) on the slice surface (step S22). This performs phase encoding. Then, the control device 5 determines the current to be supplied to the gradient magnetic field correction coil 8 for generating the gradient magnetic field, and outputs a control signal to the coil power supply 6, thereby controlling the generation of the Z-axis magnetic field gradient (dBx / dZ) on the slice surface (step S23). This performs frequency encoding.

[0076] At the same time, nuclear magnetic resonance signals from protons are output from the OPM module 23 via the receive coil 22 and the output coil 24, and the control device 5 acquires the nuclear magnetic resonance signal data accordingly (step S24). The control device 5 then determines whether to acquire nuclear magnetic resonance signal data for other slice planes (step S25). If the determination result indicates that nuclear magnetic resonance signal data for other slice planes will be acquired ("YES" in step S25), the process returns to step S20. On the other hand, if nuclear magnetic resonance signal data for other slice planes will not be acquired ("NO" in step S25), an MR image is acquired by Fourier transforming the nuclear magnetic resonance signal data acquired up to that point (step S26). The control device 5 outputs the acquired MR image to a predetermined output destination. The predetermined output destination may be the memory of the control device 5, a storage device such as a hard disk, an output device such as a display, or an external device such as a terminal device connected via a communication interface. In this way, the control device 5 also functions as a generator that generates an MR image of the subject based on the nuclear magnetic resonance signals detected by the receive coil 22.

[0077] As described above, in the brain-measuring device M1, when generating an MR image of a subject in the measurement area AR, a static magnetic field is formed in the measurement area AR by the static magnetic field forming unit 50. In the static magnetic field forming unit 50, magnetic flux generated in the first coil 53 is guided to the first magnetic pole 51 and the second magnetic pole 52, which are arranged opposite each other across the measurement area AR, by a magnetic path formed in the first holding member 54. As a result, a static magnetic field is formed between the first magnetic pole 51 and the second magnetic pole 52 in the measurement area AR. In this way, in the brain-measuring device M1, a static magnetic field is formed using a pair of the first magnetic pole 51 and the second magnetic pole 52, which are arranged to sandwich the measurement area AR. Therefore, in the brain-measuring device M1, power consumption can be reduced by approximately 99% compared to, for example, a case in which a static magnetic field is formed by arranging an air-core coil to surround the measurement area AR.

[0078] Furthermore, in the brain-measuring device M1, the first holding member 54 includes a first main body portion 55 extending along the X-axis direction (first direction) in which the first magnetic pole 51 and the second magnetic pole 52 face each other, a first extension portion 56 extending from one end of the first main body portion 55 along the Z-axis direction (second direction) that intersects with the X-axis direction, and a second extension portion 57 extending from the other end of the first main body portion 55 along the Z-axis direction. The first magnetic pole 51 is connected to and held by the first extension portion 56, and the second magnetic pole 52 is connected to and held by the second extension portion 57. The first coil 53 is wound around the first main body portion 55. In this way, by connecting the first magnetic pole 51 and the second magnetic pole 52 to the first extension portion 56 and the second extension portion 57, which extend in one direction from both ends of the first main body portion 55 of the first holding member 54, and providing a first coil 53 in the first main body portion 55 to guide magnetic flux to the first magnetic pole 51 and the second magnetic pole 52, a more uniform (homogenous) static magnetic field can be formed in the measurement area AR.

[0079] Furthermore, in the brain-measuring device M1, the first coil 53 is provided in the first main body 55 so as to be symmetrical with respect to a reference line along the Z-axis direction, which is a line passing through the midpoint between the first magnetic pole 51 and the second magnetic pole 52 in the X-axis direction. Therefore, the path lengths from the first coil 53 to the first magnetic pole 51 and the second magnetic pole 52 are made uniform, and the uniformity (homogeneity) of the static magnetic field formed in the measurement area AR is further improved.

[0080] Furthermore, in the brain-measuring device M1, the first extension portion 56 includes a first bent portion 58 bent toward the second magnetic pole 52 at an end of the first extension portion 56 opposite the first main body portion 55, and the second extension portion 57 includes a second bent portion 59 bent toward the first magnetic pole 51 at an end of the second extension portion 57 opposite the first main body portion 55. The first magnetic pole 51 has a circular shape when viewed from the X-axis direction, and is connected to and held at the tip of the first bent portion 58 at the center of the circle. Furthermore, the second magnetic pole 52 has a circular shape when viewed from the X-axis direction, and is connected to and held at the tip of the second bent portion 59 at the center of the circle. Therefore, the magnetic flux from the first coil 53 is guided to the centers of the first magnetic pole 51 and the second magnetic pole 52, thereby further improving the uniformity of the static magnetic field formed in the measurement area AR.

[0081] Furthermore, in the brain-measuring device M1, the size (for example, diameter φa) of the first magnetic pole 51 and the size (for example, diameter φa) of the second magnetic pole 52 when viewed from the opposing direction (X-axis direction) of the first magnetic pole 51 and the second magnetic pole 52 are larger than the distance Da between the first magnetic pole 51 and the second magnetic pole 52. Therefore, it becomes possible to selectively use, of the area between the first magnetic pole 51 and the second magnetic pole 52, the area closer to the center where a more uniform static magnetic field is formed.

[0082] The above embodiment has described one aspect of the present invention. Therefore, the present invention is not limited to the above disclosure and can be modified as desired. Next, modifications will be described.

[0083] Fig. 9 is a side view showing a static magnetic field generating unit according to a modified example. The static magnetic field generating unit 50A shown in Fig. 9 is similar to the static magnetic field generating unit 50 according to the above embodiment except for the manner in which the first extension 56 is connected to the first magnetic pole 51 and the manner in which the second extension 57 is connected to the second magnetic pole 52.

[0084] More specifically, in the static magnetic field generating unit 50A, the first extension portion 56 and the second extension portion 57 extend linearly along the Z-axis direction. The first magnetic pole 51 is connected to and held by the tip of the first extension portion 56 at an outer edge 51s of the first magnetic pole 51 on the first extension portion 56 side. The second magnetic pole 52 is connected to and held by the tip of the second extension portion 57 at an outer edge 52s of the second magnetic pole 52 on the second extension portion 57 side. The length Le from the center of the first magnetic pole 51 and the second magnetic pole 52 in the Z-axis direction to the edge of the first extension portion 56 and the second extension portion 57 is, for example, about 600 mm, which may be approximately the same as the size (e.g., diameter φa) of the first magnetic pole 51 and the second magnetic pole 52.

[0085] 10 and 11 are graphs showing the magnetic flux density distribution due to the magnetic field formed by the static magnetic field forming unit shown in Fig. 9. As shown in Figs. 10 and 11, it can be seen that, with the static magnetic field forming unit 50A, when the diameter φb of the first holding member 54 is 75 mm, a substantially uniform magnetic flux density distribution of 7.3 mT can be obtained over a range of at least approximately φ200 mm in the XZ plane. In this way, with the static magnetic field forming unit 50A, the magnetic paths from the first coil 53 to the first magnetic pole 51 and the second magnetic pole 52 can be made shorter, thereby improving the magnetic field strength (magnetic flux density) of the static magnetic field and obtaining a uniform magnetic flux density distribution.

[0086] Fig. 12 is a side view showing a static magnetic field generating unit according to another modification. The static magnetic field generating unit 50B shown in Fig. 12 differs from the static magnetic field generating unit 50A shown in Fig. 9 in that it further includes a second coil 63 for generating magnetic flux and a second holding member 64 in which a magnetic path is formed for guiding the magnetic flux generated by the second coil 63 to each of the first magnetic pole 51 and the second magnetic pole 52, but is the same in other respects.

[0087] The second holding member 64 includes a second main body portion 65 extending along the X-axis direction (first direction), a third extension portion 66 extending linearly along the Z-axis direction from one end of the second main body portion 65, and a fourth extension portion 67 extending linearly along the Z-axis direction from the other end of the second main body portion 65. The material, shape and dimensions of each portion of the second holding member 64 may be the same as those of the first holding member 54.

[0088] In the static magnetic field generating unit 50B, the tip of the third extension portion 66 is connected to the outer edge 51r on the third extension portion 66 side of the first magnetic pole 51, and the tip of the fourth extension portion 67 is connected to the outer edge 52r on the fourth extension portion 67 side of the second magnetic pole 52. The second coil 63 is wound around the second main body portion 65, and the same coil as the first coil 53 can be used as the second coil 63.

[0089] 13 and 14 are graphs showing the magnetic flux density distribution due to the magnetic field generated by the static magnetic field generating unit shown in FIG. 12. As shown in FIGS. 13 and 14, when the diameter φb of the first holding member 54 and the second holding member 64 is 75 mm, the static magnetic field generating unit 50B can obtain a more uniform magnetic flux density distribution of 7.1 mT over a range of at least approximately φ200 mm in the XZ plane. As described above, the static magnetic field generating unit 50B has coils (first coil 53 and second coil 63) disposed on both sides of the first magnetic pole 51 and the second magnetic pole 52, and magnetic flux is guided from each coil to the first magnetic pole 51 and the second magnetic pole 52, thereby further improving the uniformity of the static magnetic field generated in the measurement area AR.

[0090] Although the above has described modified examples, any other modifications are possible. For example, the first coil 53 (or the second coil 63) may be distributed in multiple locations and provided in the first body portion 55 (or the second body portion 65). Even in this case, the distribution is symmetrical with respect to a reference line along the Z-axis direction that passes through the midpoint between the first magnetic pole 51 and the second magnetic pole 52 in the X-axis direction, thereby ensuring the uniformity of the static magnetic field formed in the measurement area AR.

[0091] Additionally, the shapes and dimensions of each of the static magnetic field generating units 50, 50A, 50B, such as the first holding member 54, the second holding member 64, or the first magnetic pole 51, the second magnetic pole 52, can be adjusted as desired.

[0092] The above-described embodiments are described below. In the brain-measuring apparatus and brain-measuring method described in the following notes, each element can be arbitrarily replaced with or applied to each element of the above-described embodiments. [Appendix 1] a plurality of optically excited magnetic sensors for measuring brain magnetic fields; a plurality of geomagnetic field correcting magnetic sensors for measuring magnetic fields related to geomagnetism at respective positions of the plurality of optically excited magnetic sensors; a plurality of magnetic sensors for an active shield that measure a fluctuating magnetic field at each position of the plurality of optically excited magnetic sensors; a geomagnetic field correction coil for correcting a magnetic field related to the geomagnetism; an active shield coil for correcting the fluctuating magnetic field; and a static magnetic field coil for applying a static magnetic field; a gradient coil for applying a gradient magnetic field; a transmission coil for transmitting a transmission pulse of a predetermined frequency; a receiving coil for detecting a nuclear magnetic resonance signal generated by the transmission of the transmission pulse; when measuring the brain magnetic field, controlling the current supplied to the geomagnetic field correction coil and the current supplied to the active shield coil based on the measurement values ​​of the plurality of geomagnetic field correction magnetic sensors and the measurement values ​​of the plurality of active shield magnetic sensors; a control device that controls the static magnetic field and the gradient magnetic field by controlling the currents supplied to the static magnetic field coil and the gradient magnetic field coil when measuring an MR image, and generates an MR image based on the output of the receiving coil; A brain measurement device comprising: [Appendix 2] the geomagnetic field correction coil is composed of a geomagnetic field correction coil for correcting the geomagnetic field and a gradient magnetic field correction coil for correcting the geomagnetic gradient magnetic field, 2. The brain measurement device according to claim 1. [Appendix 3] The control device determining a current to be supplied to the geomagnetic field correction coil so as to generate a magnetic field that cancels out the magnetic field associated with the geomagnetism, and determining a current to be supplied to the active shield coil so as to generate a magnetic field that cancels out the fluctuating magnetic field; 3. A brain measuring device according to claim 1 or 2. [Appendix 4] 4. The brain measuring device according to any one of appendices 1 to 3, wherein the geomagnetic field correction coil and the active shield coil are a pair of coils arranged to sandwich the plurality of optically excited magnetic sensors. [Appendix 5] an output coil electrically connected to the receiving coil, which outputs a magnetic signal based on the current flowing through the receiving coil; and a separate optically excited magnetic sensor for detecting the magnetic signal output by the output coil. the control device generates the MR image based on the magnetic signal detected by the other optically excited magnetic sensor. 5. The brain-measuring device according to any one of appendices 1 to 4. [Appendix 6] The plurality of optically excited magnetic sensors are axial gradiometers having a measurement region and a reference region coaxially aligned in a direction perpendicular to the scalp of the subject. 6. The brain-measuring device according to any one of appendices 1 to 5. [Appendix 7] The brain measurement device according to any one of appendices 1 to 6, wherein the plurality of optically excited magnetic sensors, the plurality of geomagnetic field correction magnetic sensors, the plurality of active shield magnetic sensors, and the receiving coil are fixed to a helmet-type non-magnetic frame that is worn on the subject's head. [Appendix 8] 8. The brain-measuring device according to any one of appendices 1 to 7, further comprising an electromagnetic shield for blocking high-frequency electromagnetic noise. [Appendix 9] The plurality of optically excited magnetic sensors are configured to be sensitive to a frequency in the range of 0 to 200 Hz, and a bias magnetic field is applied to the optically excited magnetic sensors. The other optically excited magnetic sensor is configured to have a bias magnetic field applied thereto so as to have sensitivity to frequencies within a range of 20 kHz to 500 kHz. 6. A brain measuring device according to claim 5. [Appendix 10] a plurality of optically excited magnetic sensors for measuring brain magnetic fields; a plurality of geomagnetic field correcting magnetic sensors for measuring magnetic fields related to geomagnetism at respective positions of the plurality of optically excited magnetic sensors; a plurality of magnetic sensors for an active shield that measure a fluctuating magnetic field at each position of the plurality of optically excited magnetic sensors; a geomagnetic field correction coil for correcting a magnetic field related to the geomagnetism; an active shield coil for correcting the fluctuating magnetic field; and a static magnetic field coil for applying a static magnetic field; a gradient coil for applying a gradient magnetic field; a transmission coil for transmitting a transmission pulse of a predetermined frequency; a receiving coil for detecting a nuclear magnetic resonance signal generated by transmitting the transmission pulse; and an MRI apparatus having the receiving coil, when measuring the brain magnetic field, controlling the current supplied to the geomagnetic field correction coil and the current supplied to the active shield coil based on the measurement values ​​of the plurality of geomagnetic field correction magnetic sensors and the measurement values ​​of the plurality of active shield magnetic sensors; When measuring an MR image, the static magnetic field and the gradient magnetic field are controlled by controlling the currents supplied to the static magnetic field coil and the gradient magnetic field coil, and an MR image is generated based on the output of the receiving coil. Brain measurement methods. [Appendix 11] the geomagnetic field correction coil is composed of a geomagnetic field correction coil for correcting the geomagnetic field and a gradient magnetic field correction coil for correcting the geomagnetic gradient magnetic field, 11. The brain measurement method according to claim 10. [Explanation of symbols]

[0093] M1...brain measuring device, 5...control device (generation unit), 8...gradient magnetic field correction coil (gradient magnetic field coil), 21...transmitting coil, 22...receiving coil (detection coil), 50, 50A, 50B...static magnetic field forming unit, 51...first magnetic pole, 51s, 51r...outer edge, 52...second magnetic pole, 52s, 52r...outer edge, 53...first coil, 54...first holding member, 55...first main body portion, 56...first extension portion, 57...second extension portion, 58...first bending portion, 59...second bending portion, 63...second coil, 64...second holding member, 65...second main body portion, 66...third extension portion, 67...fourth extension portion.

Claims

1. a static magnetic field forming unit for forming a static magnetic field in the measurement area; a gradient coil for forming a gradient magnetic field in the measurement area; a transmitting coil for transmitting a transmit pulse toward the subject in the measurement area; a detection coil for detecting a nuclear magnetic resonance signal generated in the subject by transmission of the transmission pulse; a generating unit that generates an MR image based on the nuclear magnetic resonance signal detected by the detection coil; an optically excited magnetic sensor for measuring the brain magnetic field of the subject; Equipped with The static magnetic field generating unit is a first magnetic pole and a second magnetic pole arranged to face each other across the measurement area; a first coil for generating a magnetic flux; a first holding member that holds the first magnetic pole and the second magnetic pole and that forms a magnetic path for guiding magnetic flux generated in the first coil to each of the first magnetic pole and the second magnetic pole; Equipped with the optically excited magnetic sensor is fixed to a frame worn on the head of the subject in the measurement area between the first magnetic pole and the second magnetic pole; the static magnetic field generating unit corrects the earth's magnetism at the position of the optically excited magnetic sensor when measuring the brain magnetic field, and generates a static magnetic field in the measurement area in the X-axis direction, which is the direction in which the first magnetic pole and the second magnetic pole face each other, when measuring an MR image. Brain measurement device.

2. The first holding member is a first main body portion extending along a first direction in which the first magnetic pole and the second magnetic pole face each other; a first extension portion extending from one end of the first main body portion along a second direction intersecting the first direction; a second extension portion extending from the other end of the first main body portion along the second direction; Including, the first magnetic pole is connected to and held by the first extension portion, the second magnetic pole is connected to and held by the second extension portion, The first coil is wound around the first body portion. The brain measuring apparatus according to claim 1 .

3. the first coil is provided in the first body portion so as to be symmetrical with respect to a reference line along the second direction, the reference line being a line passing through a midpoint between the first magnetic pole and the second magnetic pole in the first direction; The brain measuring apparatus according to claim 2 .

4. the first extension portion includes a first bent portion that is bent toward the second magnetic pole at an end of the first extension portion opposite to the first main body portion, the second extension portion includes a second bent portion that is bent toward the first magnetic pole at an end of the second extension portion opposite to the first main body portion, the first magnetic pole has a circular shape when viewed from the first direction, and is connected to and held by a tip of the first bent portion at a center of the circular shape, The second magnetic pole has a circular shape when viewed from the first direction, and is connected to and held by the tip of the second bent portion at the center of the circular shape. The brain measuring apparatus according to claim 2 or 3.

5. the first extension portion and the second extension portion extend linearly along the second direction, the first magnetic pole is connected to and held by a tip of the first extension portion at an outer edge of the first magnetic pole on the side of the first extension portion, The second magnetic pole is connected to and held by the tip of the second extension portion at an outer edge of the second magnetic pole on the second extension portion side. The brain measuring apparatus according to claim 2 or 3.

6. The static magnetic field generating unit is a second coil for generating a magnetic flux; a second holding member in which a magnetic path is formed for guiding the magnetic flux generated in the second coil to each of the first magnetic pole and the second magnetic pole; Equipped with The second holding member is a second main body portion extending along the first direction; a third extension portion extending linearly from one end of the second main body portion along the second direction; a fourth extension portion extending linearly from the other end of the second main body portion along the second direction; Including, a tip end of the third extension portion is connected to an outer edge of the first magnetic pole on the third extension portion side, a tip end of the fourth extension portion is connected to an outer edge of the second magnetic pole on the fourth extension portion side, the second coil is wound around the second body portion, the first holding member and the second holding member are connected to each other via the first magnetic pole and the second magnetic pole. The brain measuring apparatus according to any one of claims 2 to 5.

7. a size of the first magnetic pole and a size of the second magnetic pole when viewed from a direction in which the first magnetic pole and the second magnetic pole face each other are larger than a distance between the first magnetic pole and the second magnetic pole; The brain measuring apparatus according to any one of claims 1 to 6.

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