Cerebral measurement device

Abstract

A brain measurement apparatus includes: a geomagnetic correction coil; a geomagnetic gradient correction coil; a transmission coil; a reception coil; a plurality of resonance adjustment circuits respectively provided corresponding to the reception coil and configured to output a signal of a prescribed resonance frequency of a current output from the reception coil; a plurality of OPM modules respectively provided corresponding to the plurality of resonance adjustment circuits and configured to detect a signal of the resonance frequency output from the resonance adjustment circuit; and a control device configured to generate an MR image based on the signal detected by the OPM module, wherein, in a case where a direction parallel to a central axis of a head of a subject is a Z-axis direction, a resonance frequency involved in each of the plurality of resonance adjustment circuits is set in accordance with a position in the Z-axis direction of the corresponding reception coil and a magnetic field gradient in the Z-axis direction generated by control of a gradient magnetic field.

Description

Technical Field

[0001] This invention relates to a brain measurement device. Background Technology

[0002] For a long time, superconducting quantum interference devices (SQUIDs) have been used as magnetoencephalography (MEG) devices to measure the tiny magnetic fields in the brain. In recent years, MEG devices using optically excited magnetic sensors to replace SQUIDs have been under research. Optically excited magnetic sensors measure tiny magnetic fields by detecting the spin polarization of alkali metal atoms excited by optical pumping. For example, Patent Document 1 (Japanese Patent No. 5823195) discloses a MEG device using an optically pumped magnetometer. In addition, recently, research has been conducted attempting to integrate MEG devices and MRI (Magnetic Resonance Imaging) devices using SQUIDs ("SQUIDs in biomagnetism: a roadmap towards improved healthcare", Supercond.Sci.Technol.29(2016)113001(30pp)).

[0003] In neurometry devices such as MRI, improving detection sensitivity is crucial. However, typically, increasing detection sensitivity narrows the detectable bandwidth (i.e., the field of view). Thus, achieving both high detection sensitivity and a sufficient field of view has historically been challenging in neurometry devices. Summary of the Invention

[0004] The present invention was made in view of the above-mentioned actual situation, and its object is to provide a brain measurement device that can improve detection sensitivity and ensure sufficient FOV.

[0005] One aspect of the present invention provides a brain measurement device comprising: a static magnetic field coil for applying a static magnetic field; a tilted magnetic field coil for applying a tilted magnetic field; a transmitting coil for transmitting a transmitting pulse at a predetermined frequency; a plurality of receiving coils for detecting and converting an MRI signal generated by transmitting the transmitting pulse into an electric current; a plurality of resonance modulation circuits respectively disposed corresponding to the plurality of receiving coils and for outputting a signal of a predetermined resonance frequency of the current output from the receiving coils; a plurality of detection units respectively disposed corresponding to the plurality of resonance modulation circuits and for detecting the signal of the resonance frequency output from the resonance modulation circuits; and a control device that controls the static magnetic field and the tilted magnetic field by controlling the current supplied to the static magnetic field coil and the tilted magnetic field coil, and controls the current supplied to the transmitting coil to transmit the transmitting pulse to the head of a subject, generates an MRI image based on the signal detected by the detection units, and, with the Z-axis direction parallel to the central axis of the subject's head as the Z-axis direction, sets the resonance frequency involved in each of the plurality of resonance modulation circuits according to the position of the corresponding receiving coil in the Z-axis direction and the magnetic field gradient in the Z-axis direction generated by controlling the tilted magnetic field.

[0006] In one aspect of the brain measurement device of the present invention, a resonance modulation circuit is provided to extract a signal at a predetermined resonance frequency of the current output from the receiving coil. Furthermore, the resonance frequency of each of the plurality of resonance modulation circuits is set according to the Z-axis position of the corresponding receiving coil and the magnetic field gradient in the Z-axis direction. Thus, by setting the resonance frequency of the resonance modulation circuit considering the position of the corresponding receiving coil and the generated magnetic field gradient, the sensitivity of the signal detected in the detection unit corresponding to the resonance modulation circuit can be improved. Here, when sensitivity is improved by the resonance modulation circuit, the bandwidth is limited to about a few kHz. Regarding this, in one aspect of the brain measurement device of the present invention, because the plurality of receiving coils with different resonance frequencies are arranged according to the magnetic field gradient, sensitivity can be improved, and a sufficient bandwidth, i.e., FOV (Field of View), can be ensured overall. As described above, according to one aspect of the brain measurement device of the present invention, detection sensitivity can be improved, and a sufficient FOV can be ensured.

[0007] Alternatively, among multiple detection units, one detection unit can be included to detect signals from two or more receiving coils that have the same resonant frequency as the resonant modulation circuit by adjusting the phase. In this way, by using the same detection unit to detect signals from receiving coils with the same resonant frequency while adjusting the phase, the number of detection units can be reduced and brain measurements can be performed with a simple structure.

[0008] Alternatively, the detection sensitivity of the detection unit can be maximized within its maximum frequency band, including the resonant frequency involved in the corresponding resonant adjustment circuit. This would further improve the detection sensitivity of the detection unit.

[0009] Alternatively, the receiving coil can be configured such that the maximum area and number of turns on the surface orthogonal to the direction of the generated static magnetic field are constant. With this structure, the sensitivity of the receiving coil becomes more uniform, enabling more appropriate brain measurements.

[0010] The receiving coil can also be a phased array coil. With this structure, induced electromotive forces from adjacent coils can be canceled, allowing brain measurements to be performed with minimal electrical interference.

[0011] According to the present invention, a brain measurement device is provided that can improve detection sensitivity and ensure adequate FOV. Attached Figure Description

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

[0013] Figure 2 This is a schematic diagram showing the structure of the OPM module 23 in the implementation method.

[0014] Figure 3 This is a flowchart illustrating the operation of the brain measurement device according to the implementation method.

[0015] Figure 4 This is a flowchart illustrating the operation of the brain measurement device according to the implementation method.

[0016] Figure 5 This is a graph representing an example of detection sensitivity corresponding to the detection frequency band.

[0017] Figure 6 This is a diagram illustrating the frequency-encoded MR signal.

[0018] Figure 7 This is a schematic diagram showing a portion of a brain measurement device that includes a resonance modulation circuit.

[0019] Figure 8 This is a diagram illustrating an example of the structure of a resonant modulation circuit.

[0020] Figure 9 This is a diagram illustrating an example of the structure of a resonant modulation circuit.

[0021] Figure 10 It means Figure 9 The diagram shows the detailed circuit structure of the resonance modulation circuit.

[0022] Figure 11This is a diagram illustrating the effects of the brain measurement device according to the implementation method.

[0023] Figure 12 This is a diagram showing the detailed circuit structure of the modified resonance modulation circuit.

[0024] Figure 13 This is a diagram showing the structure of the receiving coil in a modified example. Detailed Implementation

[0025] Hereinafter, the embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals, and repeated descriptions are omitted.

[0026] [Basic Structure of a Brain Measurement Device]

[0027] Figure 1 This is a schematic diagram illustrating the structure of the brain measurement device M1 according to an embodiment. The brain measurement device M1 is an example of an alternating current magnetic field measurement device, used to measure the brain magnetic field and MR (Magnetic Resonance) images of a subject. The brain measurement device M1 includes: a magnetoencephalometer module having multiple OPM (optically pumped magnetometer) modules 1, multiple geomagnetic correction magnetic sensors 2, multiple active shielding magnetic sensors 3, a non-magnetic frame 4, a pair of geomagnetic correction coils 7, a pair of geomagnetic gradient correction coils 8, and a pair of variable magnetic field correction coils 9; and an MRI module having a transmitting coil 21, multiple receiving coils 22, multiple OPM modules 23 (detection units), multiple output coils 24, and multiple resonance adjustment circuits 50. The OPM modules 23 serving as detection units may also be replaced by amplifiers (not shown). Furthermore, the brain measurement device M1 includes a control unit 5, a coil power supply 6, a pump laser 10, a probe laser 11, amplifiers 12A and 12B, a heater controller 13, an electromagnetic shield 14, and a transmitting coil controller 15. Among these, in reference... Figure 1 The description of the resonance adjustment circuit 50 is omitted in the following description (the resonance adjustment circuit 50 will be described later).

[0028] In the following description, let the direction that is approximately parallel to the central axis of the subject's head be the Z-axis, and let the directions that are perpendicular to the Z-axis and perpendicular to each other be the X-axis and Y-axis.

[0029] OPM module 1 includes a photoexcited magnetic sensor 1A, a heat insulation element 1B, and a readout circuit 1C. Multiple OPM modules 1 are arranged, for example, along the scalp at predetermined intervals.

[0030] The photomagnetic sensor 1A is a sensor that measures the brain's magnetic field using optical pumping, and has a sensitivity of approximately 10 fT to 10 pT. A heat shield 1B prevents thermal movement and heat transfer of the photomagnetic sensor 1A. The readout circuit 1C is a circuit that obtains the detection result of the photomagnetic sensor 1A. The photomagnetic sensor 1A excites the alkali metal by irradiating a unit containing alkali metal vapor with pump light. The excited alkali metal is in a spin-polarized state, and when subjected to a magnetic field, the tilt of the spin polarization axis of the alkali metal atoms changes accordingly. This tilt of the spin polarization axis can be detected by a probe light that is irradiated separately from the pump light. The photomagnetic sensor 1A is configured to apply a predetermined bias magnetic field in the direction of the pump light irradiation, thereby achieving sensitivity to magnetic fields with frequencies ranging from 0 to 200 Hz. The readout circuit 1C uses a photodiode to receive the probe light passing through the alkali metal vapor and obtains the detection result. The readout circuit 1C outputs the detection result to an amplifier 12A.

[0031] The photomagnetic sensor 1A can also be, for example, an axial gradiometer. The axial gradiometer has a measurement area and a reference area coaxially arranged in a direction perpendicular to the subject's scalp (measurement site). The measurement area is, for example, the part of the axial gradiometer closest to the subject's scalp where the brain magnetic field is measured. The reference area is, for example, a part of the axial gradiometer at a predetermined distance (e.g., 3 cm) from the measurement area relative to the direction away from the subject's scalp where the brain magnetic field is measured. The axial gradiometer outputs the respective results measured in the measurement area and the reference area to the amplifier 12A. Here, in the presence of common-mode noise, its effect is manifested in the output results of the measurement area and the reference area, respectively. Common-mode noise is removed by obtaining the difference between the output results of the measurement area and the reference area. By removing common-mode noise, for example, in the case of measurement in a magnetic noise environment of 1 pT, the photomagnetic sensor 1A can obtain a sensitivity of approximately 10 fT / √Hz.

[0032] The geomagnetic correction magnetic sensor 2 is a sensor that measures the magnetic field involved in the geomagnetic field at a position corresponding to the photo-excited magnetic sensor 1A. It is, for example, composed of a fluxgate sensor with a sensitivity of approximately 1 nT to 100 μT. The position corresponding to the photo-excited magnetic sensor 1A is the periphery (nearby) of the area where the photo-excited magnetic sensor 1A is located. The geomagnetic correction magnetic sensor 2 can be set up in a one-to-one correspondence with the photo-excited magnetic sensor 1A, or in a one-to-many correspondence (one geomagnetic correction magnetic sensor 2 for multiple photo-excited magnetic sensors 1A). The geomagnetic correction magnetic sensor 2 measures, for example, the geomagnetic field and the geomagnetic gradient magnetic field (hereinafter simply referred to as "gradient magnetic field") involved in the geomagnetic field, and outputs the measured value to the control device 5. The measured value of the geomagnetic correction magnetic sensor 2 can be represented by a vector having direction and magnitude. The geomagnetic correction magnetic sensor 2 can also continuously measure and output at predetermined time intervals.

[0033] The active shielding magnetic sensor 3 is a sensor that measures a changing magnetic field at a position corresponding to the photoexcited magnetic sensor 1A. It has a sensitivity of approximately 100 fT to 10 nT and is composed of a photoexcited magnetic sensor different from the photoexcited magnetic sensor 1A. The position corresponding to the photoexcited magnetic sensor 1A is the periphery (nearby) of the area where the photoexcited magnetic sensor 1A is located. The active shielding magnetic sensor 3 can be set up in a one-to-one correspondence with the photoexcited magnetic sensor 1A, or in a one-to-many correspondence (one active shielding magnetic sensor 3 relative to multiple photoexcited magnetic sensors 1A). The active shielding magnetic sensor 3, as a magnetic field for measuring, for example, noise (AC) components below 200 Hz, outputs the measured value to the control device 5. The measured value of the active shielding magnetic sensor 3 can be represented by a vector having direction and magnitude. The active shielding magnetic sensor 3 can continuously measure and output at predetermined time intervals.

[0034] The non-magnetic frame 4 is a frame covering the entire area of ​​the subject's scalp, which is the object of the brain magnetic field measurement. It is made of a non-magnetic material such as graphite, whose relative permeability is close to 1 and will not disturb the magnetic field distribution. For example, the non-magnetic frame 4 can be a helmet-shaped frame that surrounds the entire area of ​​the subject's scalp and is mounted on the subject's head. In the non-magnetic frame 4, multiple photo-excited magnetic sensors 1A are fixed close to the subject's scalp. Furthermore, in the non-magnetic frame 4, a geomagnetic correction magnetic sensor 2 is fixed so as to be able to measure the magnetic field involved in the geomagnetism at the respective positions of the multiple photo-excited magnetic sensors 1A, and an active shielding magnetic sensor 3 is fixed so as to be able to measure the changing magnetic field at the respective positions of the multiple photo-excited magnetic sensors 1A. Because the deviation of the changing magnetic field from the static magnetic field based on the position is smaller, the number of active shielding magnetic sensors 3 can also be reduced in the non-magnetic frame 4 compared to the number of geomagnetic correction magnetic sensors 2. Furthermore, within the non-magnetic frame 4, on the scalp side of the subject's multiple photoexcited magnetic sensors 1A, a receiving coil 22 for detecting nuclear magnetic resonance signals is fixed for MR image measurement. This receiving coil 22 detects the nuclear magnetic resonance signal of protons and converts it into an electric current. To improve the detection sensitivity of the nuclear magnetic resonance signal, the receiving coil 22 is preferably positioned on the scalp side of the photoexcited magnetic sensor 1A near the subject's head.

[0035] The receiving coil 22 is configured such that the maximum area and the number of turns on the surface orthogonal to the direction of the generated static magnetic field, i.e., the X-axis (details will be explained later), are constant. The maximum area is determined, for example, by the size, shape (ellipse), position, and axial orientation of the receiving coil 22. With this structure, the sensitivity of the receiving coil 22 becomes uniform.

[0036] The transmitting coil 21 is a coil that irradiates the subject's head with RF pulses (transmit pulses) of a specified frequency (e.g., about 300 kHz) during MR image measurements. The transmitting coil 21 is, for example, positioned above the subject's head outside the non-magnetic frame 4.

[0037] The output coil 24 is electrically connected to both ends of the receiving coil 22 via a cable, receives the current flowing through both ends of the receiving coil 22, converts the current back into a magnetic signal, and outputs it. Specifically, the output coil 24 and the receiving coil 22 are connected via a resonance adjustment circuit 50, but the description of the resonance adjustment circuit 50 is omitted here (the resonance adjustment circuit 50 will be described later).

[0038] Like OPM module 1, OPM module 23 includes a photoexcited magnetic sensor 23A, a heat insulation element 23B, and a readout circuit 23C. OPM module 23 is housed, for example, outside the non-magnetic frame 4, together with the output coil 24, within a magnetic shield 25 that shields against the static magnetic field described below. The magnetic shield 25 is made of, for example, a high-permeability alloy with a relative magnetic permeability greater than 1.

[0039] The photo-excited magnetometer 23A is a sensor that measures magnetic signals using optical pumping. Specifically, the photo-excited magnetometer 23A is configured to apply a predetermined bias magnetic field in the direction of the pump light, thereby achieving sensitivity to magnetic fields with frequencies ranging from 20 kHz to 500 kHz. For example, applying a bias magnetic field of approximately 40 μT achieves sensitivity to electromagnetic waves emitted by protons at a frequency of 300 kHz. The readout circuit 23C outputs the detection result of the photo-excited magnetometer 23A to the amplifier 12B.

[0040] Figure 2 A specific example illustrating the structure of the OPM module 23 is shown below. The photoexcited magnetosensor 23A includes: an elongated unit 26 containing a gas of an alkali metal whose polarization direction varies according to the measured magnetic field; a heater 27 that heats the entire unit 26 to a predetermined temperature (e.g., 180 degrees Celsius); a polarizing beam splitter 28; and a photodetector 29. In this unit 26, pump light L1 is introduced from the outside along its long side direction, and probe light L2 from the outside is branched and irradiated relative to each of the multiple (e.g., four) intersection regions 26A divided along the long side direction. The probe light L2 passing through these intersection regions 26A is detected by the polarizing beam splitter 28 and the photodetector 29, which are correspondingly arranged for each intersection region 26A. That is, the polarizing beam splitter 28 separates the probe light L2 into two linearly polarized components that are orthogonal to each other. The photodetector 29 uses two built-in PDs (photodiodes) to detect the intensity of the two linearly polarized components, and detects the magneto-optical rotation angle of the probe light L2 based on the ratio of the detected intensities. In the OPM module 23, a circuit port 30 is also provided, through which the readout circuit 23C outputs the magneto-optical rotation angle of each detected probe light L2 according to each intersection region 26A.

[0041] The output coil 24 is fixed within the magnetic shield 25, opposite to the intersection regions 26A of the units 26 of the OPM module 23, which have the structure described above. With this structure, the magnetic signal BOUT generated by the output coil 24 based on the electromagnetic field BOUT detected by the receiving coil 22 is detected based on the magneto-optical rotation angle of the probe light L2, which varies accordingly with the tilt of the spin polarization axis of the alkali metal atom. Here, in Figure 2In the example, the number of divisions of the intersecting region 26A is 4, but it can be changed to any number. Alternatively, multiple units 26 can be arranged side by side, and the intersecting regions 26A can be arranged in two dimensions (e.g., 4×4=16).

[0042] When measuring the brain magnetic field, the control device 5 determines the current for various coils based on the measured values ​​output from the geomagnetic correction magnetic sensor 2 and the active shielding magnetic sensor 3, and outputs a control signal for the output current to the coil power supply 6. Based on the measured values ​​from the multiple geomagnetic correction magnetic sensors 2, the control device 5 determines the current for the geomagnetic correction coil 7 and the geomagnetic gradient correction coil 8 to generate a magnetic field that cancels out the magnetic field involved in the geomagnetism. Furthermore, based on the measured values ​​from the multiple active shielding magnetic sensors 3, the control device 5 determines the current for the variable magnetic field correction coil 9 to generate a magnetic field that cancels out the variable magnetic field. The control device 5 outputs a control signal corresponding to the determined current to the coil power supply 6.

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

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

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

[0046] Furthermore, the control device 5 uses the signal output from the amplifier 12A to obtain information about the magnetic field detected by the photoexcited magnetic sensor 1A. When the photoexcited magnetic sensor 1A is an axial slope measuring instrument, the control device 5 can also remove common-mode noise by obtaining the difference between the output result of the measurement area and the output result of the reference area. The control device 5 can also control the irradiation timing and duration of the pump laser 10 and the probe laser 11.

[0047] Furthermore, when measuring MR images, the control device 5 determines the current supplied to the geomagnetic correction coil 7 and the geomagnetic gradient correction coil 8, which operate as coils for applying static and tilted magnetic fields respectively, and outputs a control signal for outputting the current to the coil power supply 6. That is, the control device 5 determines the current flowing into the geomagnetic correction coil 7 by applying a magnetic field of a predetermined intensity (e.g., 7 mT) in the X-axis direction as a static magnetic field to the subject's head. Furthermore, the control device 5 selectively determines the magnetic field gradient (dBx / dX), the magnetic field gradient (dBx / dY), and the magnetic field gradient (dBx / dZ) in the X-axis direction as a tilted magnetic field, and determines the current flowing into the geomagnetic gradient correction coil 8. Thus, the position of the slice in the MR image can be determined, and the position within the slice plane is encoded through phase encoding and frequency encoding. During MR image measurement, the control device 5 outputs a control signal such that no current is supplied to the variable magnetic field correction coil 9, which removes low-frequency noise.

[0048] Furthermore, the control device 5 controls the measurement of MR images as follows: by outputting a control signal to the transmit coil controller 15 to control the power supplied to the transmit coil 21, a transmit pulse of a predetermined frequency (e.g., approximately 300 kHz in the case of a static magnetic field strength of 7 mT) is irradiated onto the subject's head. As a result, the proton resonance of the slice plane (the plane selected by the static magnetic field and the tilting magnetic field) causes the spin to tilt. Afterward, the control device 5 controls the power supply to the transmit coil 21 to be turned off. Thus, an MR image can be obtained by measuring the spin return pattern based on the output of the OPM module 23. More specifically, the control device 5 uses known spin echo sequences or gradient echo sequences, etc., to encode the position using frequency and phase, measures the nuclear magnetic resonance signal from the protons, and uses FFT to convert the measurement results into an MR image.

[0049] The control device 5 physically includes memory such as RAM and ROM, a processor (processor circuit) such as a CPU, a communication interface, and a storage unit such as a hard disk. Examples of devices that can be used as this control device 5 include personal computers, cloud servers, smartphones, and tablet terminals. The control device 5 functions by having the CPU of the computer system execute programs stored in its memory.

[0050] The coil power supply 6, based on the control signals output from the control device 5, outputs a specified current to the geomagnetic correction coil 7, the geomagnetic gradient correction coil 8, and the variable magnetic field correction coil 9, respectively. Specifically, the coil power supply 6 outputs current to the geomagnetic correction coil 7 according to the control signals related to the geomagnetic correction coil 7. The coil power supply 6 outputs current to the geomagnetic gradient correction coil 8 according to the control signals related to the geomagnetic gradient correction coil 8. The coil power supply 6 outputs current to the variable magnetic field correction coil 9 according to the control signals related to the variable magnetic field correction coil 9.

[0051] The transmitting coil controller 15 is electrically connected to the transmitting coil 21 and supplies power to the transmitting coil 21 according to the control signal output from the control device 5 so as to irradiate the transmitting pulse of a specified frequency.

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

[0053] Furthermore, the geomagnetic correction coil 7 functions as a static magnetic field coil for generating a static magnetic field in the X-axis direction during MR image measurements. The geomagnetic correction coil 7 generates a static magnetic field of a specified intensity in accordance with the current supplied by the coil power supply 6.

[0054] The geomagnetic gradient correction coil 8 is a coil used to correct the gradient magnetic field in the magnetic field involved in the geomagnetic field at the location of the photoexcited magnetometer 1A. The geomagnetic gradient correction coil 8 generates a magnetic field in response to the current supplied by the coil power supply 6, thereby eliminating the gradient magnetic field. The geomagnetic gradient correction coil 8 may have, for example, a pair of geomagnetic gradient correction coils 8A and 8B. The pair of geomagnetic gradient correction coils 8A and 8B are arranged such that they sandwich the photoexcited magnetometer 1A (e.g., on the left and right sides of the subject). The pair of geomagnetic gradient correction coils 8A and 8B generate magnetic fields of opposite direction and equal magnitude relative to the gradient magnetic field at the location of the photoexcited magnetometer 1A, in response to the current supplied by the coil power supply 6. The direction of the magnetic field is, for example, the X-axis direction, the Y-axis direction, and the Z-axis direction. The gradient magnetic field at the location of the photoexcited magnetometer 1A is canceled out by the magnetic field of opposite direction and equal magnitude generated by the geomagnetic gradient correction coil 8. Thus, the geomagnetic gradient correction coil 8 corrects the gradient magnetic field at the location of the photoexcited magnetometer 1A.

[0055] Furthermore, the geomagnetic gradient correction coil 8 functions as a tilting magnetic field coil for generating a tilting magnetic field during MR image measurements. The geomagnetic gradient correction coil 8, in accordance with the current supplied by the coil power supply 6, generates a tilting magnetic field with selective gradients in the X-axis, Y-axis, and Z-axis directions.

[0056] The variable magnetic field correction coil 9 is used to correct the variable magnetic field at the position of the photoexcited magnetic sensor 1A. The variable magnetic field correction coil 9 generates a magnetic field in response to the current supplied by the coil power supply 6, thereby eliminating the variable magnetic field. The variable magnetic field correction coil 9 may have a pair of variable magnetic field correction coils 9A and 9B. The pair of variable magnetic field correction coils 9A and 9B are arranged such that they sandwich the photoexcited magnetic sensor 1A (e.g., on the left and right sides of the subject). The pair of variable magnetic field correction coils 9A and 9B generate magnetic fields of opposite direction and equal magnitude relative to the variable magnetic field at the position of the photoexcited magnetic sensor 1A, in response to the current supplied by the coil power supply 6. The direction of the magnetic field is, for example, the X-axis direction, the Y-axis direction, and the Z-axis direction. The variable magnetic field at the position of the photoexcited magnetic sensor 1A is canceled out by the magnetic field of opposite direction and equal magnitude generated by the variable magnetic field correction coil 9. In this way, the variable magnetic field correction coil 9 corrects the variable magnetic field at the position of the photoexcited magnetic sensor 1A.

[0057] Pump laser 10 is a laser device that generates pump light. The pump light emitted from pump laser 10 passes through an optical fiber branch and is incident on multiple photoexcitation magnetometers 1A and 23A, respectively.

[0058] The probe laser 11 is a laser device that generates probe light. The probe light emitted from the probe laser 11 is branched through an optical fiber and incident on multiple photoexcited magnetic sensors 1A and 23A, respectively.

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

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

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

[0062] The electromagnetic shielding component 14 is a shielding member that blocks high-frequency (e.g., above 10kHz) electromagnetic noise. It is constructed, for example, from a mesh woven with metal wires or a non-magnetic metal plate such as aluminum. The electromagnetic shielding component 14 is arranged to surround the OPM modules 1 and 23, the transmitting coil 21, the receiving coil 22, the output coil 24, the geomagnetic correction magnetic sensor 2, the active shielding magnetic sensor 3, the non-magnetic frame 4, the geomagnetic correction coil 7, the geomagnetic gradient correction coil 8, and the variable magnetic field correction coil 9. Using this electromagnetic shielding component 14, during MR image measurements, noise in the 300kHz frequency band (the measurement frequency) can be prevented from incident on the receiving coil 22, thus preventing noise increase. Furthermore, during brain magnetic field measurements, high-frequency noise can be prevented from incident on the photoexcited magnetic sensor 1A, thus preventing unstable operation.

[0063] [Brain measurement methods implemented by brain measurement devices (brain measurement actions)]

[0064] Next, refer to Figure 3 and Figure 4 The brain measurement method using the brain measurement device M1 of the embodiment will be described. Figure 3 and Figure 4 This is a flowchart illustrating the actions of the brain measurement device M1.

[0065] First, when the measurement of the brain magnetic field begins with the non-magnetic frame 4 installed on the subject, the geomagnetic correction magnetic sensor 2 measures the magnetic field involved in the geomagnetism, which is a static magnetic field (step S11). The geomagnetic correction magnetic sensor 2 measures the geomagnetic and gradient magnetic fields at their respective positions of the photoexcited magnetic sensor 1A and outputs the measured values ​​to the control device 5.

[0066] Control device 5 and coil power supply 6 control the current to geomagnetic correction coil 7 (step S12). Control device 5 determines the current to geomagnetic correction coil 7 based on the measurements from geomagnetic correction magnetic sensor 2, in a manner that generates a magnetic field of the same magnitude but in the opposite direction to the geomagnetic field at the location of photoexcited magnetic sensor 1A. More specifically, control device 5 determines the current to geomagnetic correction coil 7, for example, in a manner that makes the average of the measurements from multiple geomagnetic correction magnetic sensors 2 approximately zero. Control device 5 outputs a control signal corresponding to the determined current to coil power supply 6. Coil power supply 6 outputs a predetermined current to geomagnetic correction coil 7 according to the control signal output by control device 5. Geomagnetic correction coil 7 generates a magnetic field corresponding to the current supplied by coil power supply 6. The geomagnetic field at the location of photoexcited magnetic sensor 1A is canceled out by the magnetic field of the same magnitude but in the opposite direction generated by geomagnetic correction coil 7.

[0067] Control device 5 and coil power supply 6 control the current to the geomagnetic gradient correction coil 8 (step S13). Control device 5 determines the current to the geomagnetic gradient correction coil 8 based on the measurements from the geomagnetic correction magnetic sensor 2, in a manner that generates a magnetic field of the same magnitude but in the opposite direction to the gradient magnetic field at the position of the photoexcited magnetic sensor 1A. More specifically, control device 5 determines the current to the geomagnetic gradient correction coil 8, for example, in a manner that minimizes the deviation of the measurements from the average value of the multiple geomagnetic correction magnetic sensors 2. Control device 5 outputs a control signal corresponding to the determined current to the coil power supply 6. The coil power supply 6 outputs a predetermined current to the geomagnetic gradient correction coil 8 according to the control signal output by control device 5. The geomagnetic gradient correction coil 8 generates a magnetic field corresponding to the current supplied by the coil power supply 6. The gradient magnetic field at the position of the photoexcited magnetic sensor 1A is canceled out by the magnetic field of the same magnitude but in the opposite direction generated by the geomagnetic gradient correction coil 8.

[0068] Control device 5 determines whether the measured value of the corrected static magnetic field (the magnetic field involved in geomagnetism) is below a reference value (step S14). The measured value of the corrected static magnetic field is the value measured by the geomagnetic correction magnetic sensor 2 after the static magnetic field has been corrected by the geomagnetic correction coil 7 and the geomagnetic gradient correction coil 8. The reference value is the magnitude of the magnetic field in which the photoexcited magnetic sensor 1A operates normally, for example, it can be set to 1 nT. If the measured value of the static magnetic field is not below the reference value ("No" in step S14), return to step S11. If the measured value of the static magnetic field is below the reference value ("Yes" in step S14), proceed to step S15.

[0069] Active shielding magnetic sensor 3 measures the changing magnetic field (step S15). Active shielding magnetic sensor 3 measures the changing magnetic field at the respective positions of photoexcited magnetic sensor 1A and outputs the measured value to control device 5.

[0070] Control device 5 and coil power supply 6 control the current to the variable magnetic field correction coil 9 (step S16). Control device 5 determines the current to the variable magnetic field correction coil 9 based on the measurements from the active shielding magnetic sensor 3, in a manner that generates a magnetic field of the same magnitude but in the opposite direction to the variable magnetic field at the position of the photoexcitation magnetic sensor 1A. More specifically, control device 5 determines the current to the variable magnetic field correction coil 9, for example, in a manner that makes the average of the measurements from the plurality of active shielding magnetic sensors 3 approximately zero. Control device 5 outputs a control signal corresponding to the determined current to coil power supply 6. Coil power supply 6 outputs a predetermined current to the variable magnetic field correction coil 9 according to the control signal output by control device 5. The variable magnetic field correction coil 9 generates a magnetic field corresponding to the current supplied by coil power supply 6. The variable magnetic field at the position of the photoexcitation magnetic sensor 1A is canceled out by the magnetic field of the same magnitude but in the opposite direction generated by the variable magnetic field correction coil 9.

[0071] The control device 5 determines whether the measured value of the corrected variable magnetic field is below the reference value (step S17). The measured value of the corrected variable magnetic field is the value measured by the active shielding magnetic sensor 3 after the variable magnetic field has been corrected by the variable magnetic field correction coil 9. The reference value is the noise level at which the brain magnetic field can be measured, for example, it can be set to 1 pT. If the measured value of the variable magnetic field is not below the reference value ("No" in step S17), return to step S15. If the measured value of the variable magnetic field is below the reference value ("Yes" in step S17), proceed to step S18.

[0072] The photomagnetic 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 is a storage device such as a memory or hard disk of the control device 5, an output device such as a display, or an external device such as a terminal device connected via a communication interface. Up to this point, because the static magnetic field (the magnetic field involved in geomagnetism) and the fluctuating magnetic field at the location of the photomagnetic sensor 1A are canceled out in a manner that is below a predetermined reference value, the photomagnetic sensor 1A can measure the brain magnetic field without the influence of the static magnetic field (the magnetic field involved in geomagnetism) and the fluctuating magnetic field.

[0073] Transfer to Figure 4 While the non-magnetic frame 4 is still mounted on the subject, the MR image measurement begins. The control device 5 determines the current supplied to the geomagnetic correction coil 7 for applying the static magnetic field, and controls the generation of the static magnetic field in the X-axis direction in the subject's head by outputting a control signal to the coil power supply 6 (step S19). Next, the control device 5 determines the current supplied to the geomagnetic gradient correction coil 8 for generating the tilted magnetic field, and controls the generation of the magnetic field gradient (dBx / dX) in the X-axis direction by outputting a control signal to the coil power supply 6 (step S20). Simultaneously, the control device 5 controls the transmission by outputting a control signal to the transmission coil controller 15 to control the power supplied to the transmission coil 21, and irradiating the subject's head with a transmission pulse (step S21). As a result, protons in the specified slice area are excited.

[0074] Furthermore, the control device 5 determines the current supplied to the geomagnetic gradient correction coil 8 used to generate the tilted magnetic field, and controls the generation of the magnetic field gradient (dBx / dY) in the Y-axis direction on the slice surface by outputting a control signal to the coil power supply 6 (step S22). Phase encoding is then performed. Next, the control device 5 determines the current supplied to the geomagnetic gradient correction coil 8 used to generate the tilted magnetic field, and controls the generation of the magnetic field gradient (dBx / dZ) in the Z-axis direction on the slice surface by outputting a control signal to the coil power supply 6 (step S23). Frequency encoding is then performed.

[0075] Simultaneously, from the OPM module 23, via the receiving coil 22 and the output coil 24, a nuclear magnetic resonance (NMR) signal from the protons is output, and the control device 5 acquires the NMR signal data (step S24). Then, the control device 5 determines whether NMR signal data for other slice planes has been acquired (step S25). If the determination is successful and NMR signal data for other slice planes has been acquired ("Yes" in step S25), the process returns to step S20. On the other hand, if NMR signal data for other slice planes has not been acquired ("No" in step S25), an MR image is acquired by performing a Fourier transform on the acquired NMR signal data (step S26). The control device 5 outputs the acquired MR image to a predetermined output destination. The predetermined output destination is a storage device such as the control device 5's memory or hard disk, an output device such as a display, or an external device such as a terminal device connected via a communication interface.

[0076] [Structure of the Resonance Adjustment Circuit]

[0077] As described above, the brain measurement device M1, as a structure included in the MRI module, includes a resonance modulation circuit 50 (see reference). Figure 1 The following section describes the details of the structure of the resonance modulation circuit 50. First, refer to... Figure 5 and Figure 6 The purpose of setting up the resonance adjustment circuit 50 will be explained.

[0078] Figure 5 This is a diagram illustrating an example of detection sensitivity corresponding to the detection frequency band. As described above, the brain measurement device M1 can use either the OPM module 23 as the detection unit or an amplifier (not shown) instead of the OPM module 23. Figure 5 (a) shows an example of detection sensitivity corresponding to the detection band when an amplifier (not shown) is used as the detection unit. Figure 5 (b) shows an example of the detection sensitivity corresponding to the detection band when using OPM module 23 as the detection unit. Figure 5 In (a) and (b), the horizontal axis represents frequency (detection band), and the vertical axis represents amplitude (detection sensitivity). Figure 5 In (a), the amplitude is represented by the absolute value (mV). Figure 5 In (b), au represents the amplitude. Figure 5 The frequency ranges of the MR signals (nuclear magnetic resonance signals) represented in (a) and (b) are ranges specified by frequency encoding.

[0079] Here, in Figure 5In the example shown in (a), where an amplifier (not shown) is used as the detection unit, there is a frequency region in the frequency range of the MR signal where the sensitivity (SNR) drops significantly. The bandwidth (FWHM) of the portion where the sensitivity is 50% of the peak value is approximately 4.6 kHz. Furthermore, in Figure 5 In the example shown in (b) where OPM module 23 is used as the detection unit, there is also a frequency region in the frequency range of the MR signal where the sensitivity (SNR) drops significantly, with an FWHM of approximately 1060 Hz. Thus, in the detection unit, there is a frequency region in the frequency range of the MR signal where the sensitivity is insufficient.

[0080] Figure 6 This is a diagram illustrating the frequency-encoded MR signal. Current is supplied to the geomagnetic gradient correction coil 8, which is used to generate the tilted magnetic field, such as... Figure 6 As shown, a magnetic field gradient (dBx / dZ) is generated along the Z-axis and frequency encoded. During frequency encoding, the frequency band of the generated MR signal is determined based on its position along the Z-axis within the head. That is, as... Figure 6 As shown, for example, the lowermost part of the head is the range where an MR signal with a frequency near f1 is generated; the upper part of this range is the range where an MR signal with a frequency near f2 (f2 > f1) is generated; the upper part of this range is the range where an MR signal with a frequency near f3 (f3 > f2) is generated; and the upper part of this range is the range where an MR signal with a frequency near f4 (f4 > f3) is generated. Thus, if the generated Z-axis magnetic field gradient and the head position are determined, the frequency band of the generated MR signal can be determined. Therefore, by using a resonance adjustment circuit 50 that extracts a specific frequency band (resonance frequency) signal for each position (region), the frequency range of the MR signal can be detected with high sensitivity without omission. Hereinafter, refer to... Figures 7-10 The specific structural example of the resonance adjustment circuit 50 will be explained.

[0081] Figure 7 This is a schematic diagram showing a portion of a brain measurement device M1 including multiple resonance modulation circuits 50. The multiple resonance modulation circuits 50 are respectively arranged corresponding to multiple receiving coils 22, and are circuits used to extract and output a signal of a predetermined resonance frequency of the current output from the receiving coils 22. Figure 7 In this example, multiple resonance adjustment circuits 50 are shown, including resonance adjustment circuits 50a, 50b, 50c, and 50d. These resonance adjustment circuits 50 are arranged, for example, in a one-to-one correspondence with each receiving coil 22; however, in… Figure 7 The text only represents a portion of the resonance adjustment circuit 50, specifically four resonance adjustment circuits: 50a, 50b, 50c, and 50d.

[0082] The resonant frequencies of each of the multiple resonant adjustment circuits 50 are set according to the Z-axis position of the corresponding receiving coil 22 and the magnetic field gradient in the Z-axis direction generated by the control of the tilted magnetic field. As described above, when frequency encoding is performed by the control of the tilted magnetic field, the frequency band of the MR signal changes along the Z-axis direction (see reference). Figure 6 Therefore, by considering the position of the receiving coil 22 in the Z-axis direction and the magnetic field gradient, the resonant frequency of the resonance adjustment circuit 50 can be set, allowing the MR signal output from the receiving coil 22 to be appropriately extracted, and enabling high-sensitivity detection of the MR signal in the subsequent OPM module 23. The receiving coil 22, with a diameter of approximately 30-50 mm, is arranged to surround the head. The receiving coils 22 arranged at the same height in the Z-axis direction have the same resonant frequency in the resonance adjustment circuit 50. For example, the resonant frequency of the receiving coil 22 at the center of the head is 300 kHz, and the resonant frequency deviates by 1.5 kHz for every 30 mm deviation in the Z-direction. This allows for efficient detection of MR signals emitted from the brain near each receiving coil 22. Furthermore, the receiving coil 22 with a diameter of approximately 30-50 mm has high sensitivity in capturing MR signals generated near the coil, while having low sensitivity relative to noise generated far from the coil. Therefore, by arranging multiple such receiving coils 22, the SNR of the MR image can be improved.

[0083] like Figure 7 As shown, the OPM module 23, which consists of multiple detection units, and multiple resonance adjustment circuits 50 (in...) Figure 7 In this configuration, resonance adjustment circuits 50a, 50b, 50c, and 50d are respectively configured to detect the signal of the resonance frequency output from the resonance adjustment circuit 50. The detection sensitivity of the OPM module 23 covers the maximum frequency band, including the resonance frequency involved in the corresponding resonance adjustment circuit 50. The output coil 24 is fixed opposite to the OPM module 23. Each OPM module 23 can also be configured as follows: Figure 7 As shown, it is set up in a one-to-one correspondence with the resonance adjustment circuit 50.

[0084] Alternatively, one OPM module 23 may be included among multiple OPM modules 23, which detects signals from two or more receiving coils 22 that have the same resonant frequency as the resonant adjustment circuit 50 by adjusting their phase. As described above, the resonant frequency of each resonant adjustment circuit 50 is determined by considering the position of the corresponding receiving coil 22 in the Z-axis direction. Therefore, two or more resonant adjustment circuits 50 with the same resonant frequency can be, in other words, two or more resonant adjustment circuits 50 whose corresponding receiving coils 22 are positioned at the same (or approximately) positions in the Z-axis direction. When only one OPM module 23 is used to detect signals from two or more receiving coils 22, there is a concern that the signals may cancel each other out because their phases are different. Therefore, when using one OPM module 23 to detect signals from two or more receiving coils 22, the phases of these signals are adjusted to prevent them from canceling out.

[0085] Figure 8 and Figure 9 This is a diagram illustrating an example of the structure of the resonance modulation circuit 50. Figure 8 This section illustrates an example of a resonance adjustment circuit 50 that uses an amplifier (not shown) as the detection unit. Specifically, it shows a parallel resonance circuit in which a capacitor C is connected in parallel relative to a receiving coil 22, which is connected in series with a resistor Rin and an inductor Lin. In such a parallel resonance circuit, for example, with a resistor Rin = 0.64Ω and an inductor Lin = 105μH, the value of the capacitor C is set according to the formula C = 1 / ω²Lin to achieve a predetermined resonant frequency (e.g., 300kHz).

[0086] Figure 9 This is an example of a resonance adjustment circuit 50 in which OPM module 23 is used as the detection unit. Figure 9 The resonant adjustment circuit 50 shown includes: an input-side circuit 52 in which capacitors Cs1 and Cp1 are connected in series and parallel with respect to the receiving coil 22; an output-side circuit 55 in which capacitors Cs2 and Cp2 are connected in series and parallel with respect to the output coil 24; and a coaxial cable 51 connecting the input-side circuit 52 and the output-side circuit 55. Figure 9 In the structure shown, the receiving coil 22 and the input side circuit 52 are surrounded by the same electromagnetic shielding, the output side circuit 55 is surrounded by an aluminum shell, and the output coil 24 and the OPM module 23 are surrounded by an OPM magnetic shielding.

[0087] Figure 10 It means Figure 9 A detailed circuit diagram of the resonance modulation circuit is shown. Figure 10As shown, in the receiving coil 22, the resistor Rin and the inductor Lin are connected in series. Furthermore, in the output coil 24, the resistor Rout and the inductor Lout are connected in series. Thus, as described above, the resonant adjustment circuit 50 includes: an input-side circuit 52 in which capacitors Cs1 and Cp1 are connected in series and parallel with respect to the receiving coil 22; an output-side circuit 55 in which capacitors Cs2 and Cp2 are connected in series and parallel with respect to the output coil 24; and a coaxial cable 51 connecting the input-side circuit 52 and the output-side circuit 55.

[0088] In this resonant adjustment circuit 50, the capacitances of capacitors Cs1 and Cp1 in the input-side circuit 52 are adjusted so that the impedance of the input-side circuit 52 and the receiving coil 22 as viewed from the coaxial cable 51, i.e., the input impedance, is the same as the impedance of the coaxial cable 51 at the resonant frequency. Furthermore, in the resonant adjustment circuit 50, the capacitances of capacitors Cs2 and Cp2 in the output-side circuit 55 are adjusted so that the impedance of the output-side circuit 55 and the output coil 24 as viewed from the coaxial cable 51, i.e., the output impedance, is the same as the impedance of the coaxial cable 51 at the resonant frequency. By adjusting the capacitances of capacitors Cs1 and Cp1 in the input-side circuit 52 and capacitors Cs2 and Cp2 in the output-side circuit 55 in this way, the input impedance and output impedance as viewed from the coaxial cable 51 are the same as the impedance of the coaxial cable 51 at the resonant frequency, thus suppressing signal reflection of the signal component at the resonant frequency. The impedance of the coaxial cable 51 is, for example, 50Ω.

[0089] exist Figure 10 In the structure shown, specifically, the capacitances of capacitors Cs1 and Cp1 in the input-side circuit 52 are determined to satisfy the following equations (1) and (2). In equation (1), 50 on the right-hand side represents the impedance of the coaxial cable 51. ω represents the angular frequency, which is determined based on the resonant frequency. Furthermore, the capacitances of capacitors Cs2 and Cp2 in the output-side circuit 55 can also be determined based on the same equation.

[0090] Z+1 / jωCs1=50 (1)

[0091] Z=(1 / jωCp1) / / (Rin+jωLin) (2)

[0092] Here, for example, let Lin = 105.7 μH, Rin = 0.77 Ω, LOUT = 3.0 μH, ROUT = 0.18 Ω, and resonant frequency = 300 kHz. According to the above equations (1) and (2), we can obtain Cp1 = 2.3 nF, Cs1 = 330 pF, Cp2 = 89 nF, and Cs2 = 6.6 nF.

[0093] Next, the effects of the brain measurement device M1 in this embodiment will be explained.

[0094] In the brain measurement device M1 of this embodiment, a resonance adjustment circuit 50 is provided to extract a signal with a predetermined resonance frequency from the current output from the receiving coil 22. Furthermore, the resonance frequency of each of the plurality of resonance adjustment circuits 50 is set according to the position of the corresponding receiving coil 22 in the Z-axis direction and the magnetic field gradient in the Z-axis direction. Thus, by setting the resonance frequency of the resonance adjustment circuit 50 considering the position of the corresponding receiving coil 22 and the generated magnetic field gradient, the sensitivity of the signal detected in the OPM module 23, which is provided corresponding to the resonance adjustment circuit 50, can be improved. Here, while the sensitivity is improved by the resonance adjustment circuit 50, the bandwidth is limited to about a few kHz. Regarding this, in the brain measurement device M1 of this embodiment, because the plurality of receiving coils 22 with different resonance frequencies are arranged according to the magnetic field gradient, the sensitivity can be improved, and a sufficient bandwidth, i.e., FOV (Field of View), can be ensured overall. As described above, the brain measurement device M1 according to this embodiment can improve detection sensitivity and ensure a sufficient FOV.

[0095] The multiple OPM modules 23 may also include a single OPM module 23 that detects signals from two or more receiving coils 22 that have the same resonant frequency as the resonant adjustment circuit 50 by adjusting the phase. In this way, by detecting signals from receiving coils 22 that have the same resonant frequency using the same OPM module 23 while adjusting the phase, the number of OPM modules 23 serving as detection units can be reduced, and brain measurements can be performed with a simple structure.

[0096] The detection sensitivity of the OPM module 23 reaches its maximum frequency band, which may also include the resonant frequency involved in the corresponding resonant adjustment circuit 50. This further improves the detection sensitivity of the detection unit.

[0097] The receiving coil 22 can also be configured such that the maximum area and the number of turns on the surface orthogonal to the X-axis direction, which is the direction in which the static magnetic field is generated, are constant. With such a structure, the sensitivity of the receiving coil 22 becomes more uniform, enabling more appropriate brain measurements.

[0098] Furthermore, in the resonance adjustment circuit 50 of the brain measurement device M1 in this embodiment, the capacitances of capacitors Cs1 and Cp1 in the input-side circuit 52 can be adjusted such that the impedance (i.e., the input impedance) of the input-side circuit 52 and the receiving coil 22 as viewed from the coaxial cable 51 is the same as the impedance of the coaxial cable 51 at the resonant frequency. Similarly, the capacitances of capacitors Cs2 and Cp2 in the output-side circuit 55 can be adjusted such that the impedance (i.e., the output impedance) of the output-side circuit 55 and the output coil 24 as viewed from the coaxial cable 51 is the same as the impedance of the coaxial cable 51 at the resonant frequency. Thus, the capacitances of capacitors Cs1, Cp1, Cs2, and Cp2 in the input-side circuit 52 and the output-side circuit 55 can be adjusted such that the input impedance (i.e., the input impedance) of the input-side circuit 52 and the receiving coil 22 as viewed from the coaxial cable 51, and the output impedance (i.e., the output impedance) of the output-side circuit 55 and the output coil 24 as viewed from the coaxial cable 51 are both the same as the impedance of the coaxial cable 51 at the resonant frequency. Based on this structure, since the input impedance and output impedance seen from the coaxial cable 51 at the resonant frequency are the same as the impedance of the coaxial cable 51, the power loss caused by signal reflection can be suppressed and the detection sensitivity of the OPM module 23 can be improved for the resonant frequency component in the signal.

[0099] Figure 11 This is a diagram illustrating the effect of the brain measurement device M1 in the embodiment. Figure 11 (a) indicates the noise level of the structure (comparative example structure) in which a capacitor is connected in series between the receiving coil 22 and the output coil 24, forming a series resonance. Figure 11 (b) indicates that the resonance adjustment circuit 50 of this embodiment is included. Figure 9 and Figure 10 The noise level of the structure of the resonance modulation circuit 50 shown. Figure 11 In (a) and (b), the horizontal axis represents frequency, and the vertical axis represents magnetic noise density. For example... Figure 11 As shown in (a), in the comparative example structure, the noise level is 23 fT / Hz1 / 2 at a frequency of 300 kHz. In contrast, as... Figure 11 (b) As shown, in the structure of this embodiment, the noise level is 2.1 fT / Hz¹ / ² at a frequency of 300 kHz. Thus, compared to the comparative example, the SNR can be significantly improved in this embodiment. Specifically, in the structure of this embodiment, signal reflection between the FT input / output coils (receiving coil 22 and output coil 24) can be suppressed, and the FT gain is increased, thereby improving the sensitivity of the OPM module 23. Furthermore, since signal loss can be reduced even by lengthening the coaxial cable 51 between the FT input / output coils, the configuration freedom of the input / output coils and the OPM module 23 is increased.

[0100] The embodiments of the present invention have been described above; however, the present invention is not limited to the above embodiments. For example, a brain measurement device M1 including a resonance modulation circuit 50 has been described; however, the resonance modulation circuit 50 may also be equipped in other alternating current magnetic field measurement devices other than the brain measurement device M1.

[0101] Furthermore, the structure of the resonant modulation circuit is not limited to Figure 10 The structure. Figure 12 This is a diagram showing the detailed circuit structure of the modified resonance modulation circuit 500. For example... Figure 12 As shown, the resonance adjustment circuit 500 disposed between the receiving coil 22 and the output coil 240 includes an impedance matching circuit 260 connected to the receiving coil 22. The impedance matching circuit 260, viewed from the receiving coil 22, makes the downstream side (coaxial cable 51 side) have a high impedance. By providing such an impedance matching circuit 260, the current flowing into the coil can be reduced, and in the case of a coil array, the inductive coupling between the coils can be mitigated. Furthermore, even with this structure, by impedance matching between the coaxial cable 51 and the output coil 240, current can flow efficiently into the output coil 240.

[0102] In addition, the structure of the receiving coil can also be... Figure 13 The phased array coil shown. Figure 13 This is a diagram showing the structure of the receiving coil (phased array coil) in a modified example. Figure 13 In the structure of the phased array coil shown, considering the interference of adjacent coils 601, coils 601 are overlapped. In this way, by arranging the coils 601 with a specific overlap, the induced electromotive force from adjacent coils 601 can be canceled and the electrical interference can be suppressed to a minimum.

Claims

1. A brain measurement device, characterized in that, include: A static magnetic field coil, used to apply a static magnetic field; Inclined magnetic field coil, which is used to apply an inclined magnetic field; A transmitting coil, used to transmit pulses at a specified frequency; Multiple receiving coils are used to detect the nuclear magnetic resonance signal generated by the transmission of the transmission pulse and convert it into current; Multiple resonant adjustment circuits are respectively configured corresponding to the multiple receiving coils and are used to output a signal of a predetermined resonant frequency of the current output from the receiving coils; Multiple detection units are respectively arranged corresponding to the multiple resonance adjustment circuits and are used to detect the signal of the resonance frequency output from the resonance adjustment circuits; and A control device controls the current supplied to the static magnetic field coil and the tilted magnetic field coil to control the static magnetic field and the tilted magnetic field, and controls the current supplied to the transmitting coil to transmit the transmitting pulse to the subject's head, generating an MR image based on the signal detected by the detection unit. With the Z-axis direction being parallel to the central axis of the subject's head, the resonant frequency of each of the plurality of resonant adjustment circuits is set according to the position of the corresponding receiving coil in the Z-axis direction and the magnetic field gradient in the Z-axis direction generated by the control of the tilting magnetic field.

2. The brain measurement device as described in claim 1, characterized in that, The plurality of detection units include one detection unit that detects signals from two or more receiving coils that have the same resonant frequency as the resonant adjustment circuit by adjusting the phase.

3. The brain measurement device as described in claim 1, characterized in that, The detection sensitivity of the detection unit becomes the maximum frequency band, including the resonant frequency involved in the corresponding resonant adjustment circuit.

4. The brain measurement device as described in claim 2, characterized in that, The detection sensitivity of the detection unit becomes the maximum frequency band, including the resonant frequency involved in the corresponding resonant adjustment circuit.

5. The brain measurement device according to any one of claims 1 to 4, characterized in that, The receiving coil is configured such that the maximum area and the number of turns on the surface orthogonal to the direction in which the static magnetic field is generated are constant.

6. The brain measurement device as described in any one of claims 1 to 4, characterized in that, The receiving coil is a phased array coil.

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