JP2022014398A - Magnetic field measuring device, magnetic field measuring system, control method for magnetic field measuring device, and control program for magnetic field measuring system - Google Patents

Abstract

To certainly acquire biological information with a simple operation.SOLUTION: A magnetic field measuring device has a plurality of signal processing units that generate magnetic field data according to a magnetic field measured by a plurality of superconductive quantum interference elements. Each of the plurality of signal processing units has: an integrator that integrates a voltage value output from the superconductive quantum interference element according to a change in the magnetic field and changing with a flux quantum as a period to generate the magnetic field data; a counter that counts the number of changes of the flux quantum based on a change of the magnetic field data generated by the integrator; and a correction unit that corrects the magnetic field data generated by the integrator according to the number of changes of the flux quantum counted by counters of a predetermined number of other signal processing units.SELECTED DRAWING: Figure 1

Description

The present invention relates to a magnetic field measuring device, a magnetic field measuring system, a control method of the magnetic field measuring device, and a control program of the magnetic field measuring system.

In biomagnetic field measurement, which measures a very weak magnetic field generated by nerves, brains, or muscles, there is a method of electrically stimulating nerves as a means of generating a stable biomagnetic field. However, when noise called an artifact, which is not derived from a living body, is generated by electrical stimulation, the waveform of the biomagnetic field is greatly disturbed. Therefore, in order to suppress the decrease in the measurement accuracy of the magnetic field, it is necessary to reduce the artifacts.

For example, in a magnetic sensor using a magnetic resistance element, the environmental noise measured by the external magnetic resistance element that detects the magnetic field strength in the external environment is subtracted from the measurement result of the magnetic field of the measurement sample, so that highly accurate magnetic field information of the measurement sample is obtained. Is obtained. At this time, by weighting the output of each magnetoresistive element and the output of the external magnetoresistive element, more accurate magnetic field information can be obtained.

When a superconducting QUantum Interference Device (SQUID), which is a superconducting ring having a Josephson junction, is used for measuring a biomagnetic field, the measurement characteristics become non-linear. Therefore, linearization is performed using an FLL (Flux Locked Loop) circuit, and the magnetic field is measured. Hereinafter, the superconducting quantum interference device is also referred to as SQUID.

The FLL circuit includes an analog FLL system composed of only an analog circuit and a digital FLL system composed of a circuit that is once digitized and then digitized again. In the digital FLL method, when a magnetic field equal to or larger than the threshold value is applied to the SQUID, the magnetic flux quantum penetrating the SQUIID is increased or decreased to jump the operating point. At this time, the number of changes in the magnetic flux quantum that increases or decreases is counted by FQC (Flux Quanta Counting), and the digital integrator is reset for each magnetic flux quantum to secure a dynamic range that is several hundred times or more that of the analog FLL method. Will be possible.

However, since the adjacent SQUID sensor detects the step-like noise generated when the number of changes of the magnetic flux quantum penetrating the SQUID increases or decreases, there is a problem that the measurement accuracy of the magnetic field is lowered.

The disclosed technology was made in view of the above problems, and aims to suppress noise generated when the number of changes in the magnetic flux quantum penetrating the superconducting quantum interference element increases or decreases, and to improve the measurement accuracy of the magnetic field. And.

In order to solve the above technical problem, the magnetic field measuring device of one embodiment of the present invention is a magnetic field measuring device having a plurality of signal processing units that generate magnetic field data according to the magnetic fields measured by a plurality of superconducting quantum interference elements. Each of the plurality of signal processing units integrates a voltage value that changes with a magnetic flux quantum as a period, which is output from a superconducting quantum interference element in response to a change in a magnetic field, and generates the magnetic field data. A device, a counter that counts the number of changes in the magnetic flux quantum based on changes in the magnetic field data generated by the integrator, and a counter of a predetermined number of other signal processing units that count the magnetic field data generated by the integrator. It has a correction unit that corrects according to the number of changes in the counted magnetic field quantum.

It is possible to suppress the noise generated when the number of changes of the magnetic flux quantum penetrating the superconducting quantum interference element increases or decreases, and improve the measurement accuracy of the magnetic field.

It is a block diagram which shows an example of the magnetic field measurement system which concerns on 1st Embodiment of this invention. It is explanatory drawing which shows an example of the arrangement of SQUID of FIG. It is a block diagram which shows an example of the main part of the magnetic field measuring apparatus of FIG. It is a block diagram which shows an example of the data correction part of CH2 of FIG. It is a waveform diagram which shows an example of φ-V characteristic of SQUID of FIG. It is explanatory drawing which shows an example of the influence on the magnetic field waveform of the artifact generated by the operation of the FQC counter of FIG. It is explanatory drawing which shows an example of the magnetic field waveform which the artifact was removed by the data correction part of FIG. It is a block diagram which shows an example of the magnetic field measurement system which concerns on 2nd Embodiment of this invention. It is a block diagram which shows an example of the magnetic field measurement system which concerns on 3rd Embodiment of this invention. It is a block diagram which shows an example of the hardware composition of the data processing apparatus of FIG. 1, FIG. 8 and FIG.

Hereinafter, embodiments will be described with reference to the drawings. In each drawing, the same components may be designated by the same reference numerals and duplicate explanations may be omitted. Hereinafter, the code indicating a signal is also used as a code indicating a signal value or a code indicating a signal line. The code indicating a voltage is also used as a code indicating a voltage value or a code indicating a voltage line to which a voltage is supplied.

(First Embodiment)
FIG. 1 is a block diagram showing an example of a magnetic field measurement system according to the first embodiment of the present invention. For example, the magnetic field measuring system 100 shown in FIG. 1 includes a magnetic field measuring device 200 and a data processing device 300. The magnetic field measuring device 200 has a plurality of SQUIDs 10 (superconducting quantum interference elements) and a plurality of digital FLL circuits 20 each of the plurality of SQUIDs 10. The SQUID 10 and the digital FLL circuit 20 shown in FIG. 1 show one channel of the magnetic field measuring device 200. Although not particularly limited, for example, the magnetic field measuring device 200 has tens to hundreds of channels. The digital FLL circuit 20 is an example of a signal processing unit.

The magnetic field measurement system 100 is applicable to a magnetoencephalogram (MEG: Magnetoencephalograph), a magnetoencephalogram (MSG: Magnetospinograph) or a magnetoencephalogram (MCG: Magnetocardiograph). The magnetic field measurement system 100 may be applied to a myomagnetometer.

The SQUID 10 is a high-sensitivity magnetic sensor that detects a magnetic flux generated from a living body and penetrates a superconducting ring having a Josephson junction. For example, the SQUID 10 is configured by providing Josephson junctions at two points on the superconducting ring. The SQUID 10 generates a voltage that changes periodically with respect to a change in the magnetic flux penetrating the superconducting ring. Therefore, the magnetic flux penetrating the superconducting ring can be obtained by measuring the voltage across the superconducting ring with the bias current flowing through the superconducting ring. Hereinafter, the characteristic of the periodic voltage change in which the SQUID 10 is generated is also referred to as a φ-V characteristic, and one cycle of the periodic voltage change in which the SQUID 10 is generated is also referred to as a magnetic flux quantum φ0 (one cycle of the output voltage of the SQUID 10).

The digital FLL circuit 20 includes an amplifier 21, an AD (Analog-to-Digital) converter 22, a digital integrator 23, a data correction unit 24, an FQC counter 25, a DA (Digital-to-Analog) converter 26, and a voltage-current conversion. It has a device 27 and a feedback coil 28. For example, the dashed frame showing the digital FLL circuit 20 shows the control board. The feedback coil 28 is shown outside the broken line frame because it is physically separated from the control board of the digital FLL circuit 20 and is arranged close to the FIRD 10, but is included in the digital FLL circuit 20.

The amplifier 21 amplifies the voltage generated by the SQUID 10 according to the magnetic flux (magnetic field) penetrating the SQUID 10, and outputs the amplified voltage to the AD converter 22. The AD converter 22 converts an analog signal from the amplifier 21 into a digital signal (voltage value) by sampling at a predetermined sampling frequency, and outputs the digital signal to the digital integrator 23. That is, the AD converter 22 converts the voltage output from the SQUID 10 into a digital value according to the change in the magnetic field.

The digital integrator 23 integrates the voltage value from the AD converter 22 and outputs the integrated voltage value as magnetic field data to the data correction unit 24, the FQC counter 25, and the DA converter 26. Here, the digital integrator 23 integrates the change in the voltage of SQUID 10 (to be exact, the amplified voltage output from the amplifier 21) from the lock point (lock start point) which is the starting point of the magnetic flux quantum φ0. .. The digital integrator 23 resets the integrator value every time the count value CNT output by the FQC counter 25 is updated, and returns the integrator value to the initial value. The number of updates of the count value CNT indicates the number of changes (difference) in the magnetic flux quantum φ0.

The data correction unit 24 corrects the magnetic field data (integrated value) received from the digital integrator 23 based on the count value CNT received from the FQC counter 25 of the other digital FLL circuit 20, and obtains the corrected magnetic field data MDT as data. Output to the processing device 300.

The FQC counter 25 receives the magnetic field data (digital value) output by the digital integrator 23, and updates the count value CNT when the amount of increase or decrease of the digital value exceeds a predetermined threshold value. Thereby, the number of periodic changes in the φ-V characteristic of SQUID 10 (that is, the number of changes in the magnetic flux quantum φ0) can be shown as the count value CNT. The amount of increase or decrease (that is, the threshold value) of the digital value corresponding to the magnetic flux quantum φ0 output by the digital integrator 23 has been evaluated in advance.

The FQC counter 25 outputs the count value CNT to the digital integrator 23 and the data correction unit 24 of a predetermined number of other digital FLL circuits 20. The FQC counter 25 is an example of a counter that counts the number of changes in the magnetic flux quantum φ0 based on the changes in the magnetic field data generated by the digital integrator 23. The number and range of other digital FLL circuits 20 for which the FQC counter 25 outputs count value CNTs will be described in FIG.

The DA converter 26 converts the integrated value (magnetic field data) integrated by the digital integrator 23 into a voltage, and outputs the converted voltage to the voltage-current converter 27. The voltage-current converter 27 converts the voltage received from the DA converter 26 into a current, and outputs the converted current to the feedback coil 28.

The feedback coil 28 generates a magnetic field by the current received from the voltage-current converter 27, and feeds back the generated magnetic field to the SQUID 10. That is, the feedback coil 28 generates a magnetic field received by the SQUID 10 based on the current from the voltage-current converter 27. When measuring a biomagnetic field or the like by the digital FLL circuit 20, the voltage generated by SQUID 10 can be maintained near the lock point (linear region) of the φ-V characteristic, and the biomagnetic field signal can be obtained accurately. can.

The digital FLL circuit 20 generates magnetic field data from the magnetic field measured by the FIRST 10 by the FQC method. In the FQC method, when the magnitude of the observed magnetic field signal reaches the magnetic flux quantum φ0, the digital integrator 23 is reset and feedback is applied again to prevent the digital FLL circuit 20 from being saturated. Further, by combining the count value CNT in the FQC counter 25, which is the number of resets, and the amount of feedback data, the magnetic field data, which is the amount of change from the start of magnetic field measurement, can be calculated.

As a result, in the FQC method, magnetic field signal data corresponding to a plurality of magnetic flux quantum φ0 can be calculated, and the dynamic range of the digital FLL circuit 20 can be expanded beyond the maximum count value of the digital integrator 23. For example, a spinometer inputs an electrical stimulus from the outside and measures the biomagnetic field evoked by the electrical stimulus. In this case, the artifact (noise) caused by the electrical stimulation affects the measurement result. In general, artifacts are larger than the biomagnetic field and therefore require a wide dynamic range.

The data processing device 300 stores the magnetic field data MDT and the count value CNT received from the plurality of digital FLL circuits 20 included in the magnetic field measuring device 200 in a storage device (not shown). For example, the data processing device 300 generates image data using the magnetic field data and the count value CNT stored in the storage device, and displays the image represented by the generated image data on a display device (not shown).

FIG. 2 is an explanatory diagram showing an example of the arrangement of the SQUID 10 in FIG. For example, the magnetic field measuring device 200 has 44 SQUIDs 10 arranged in a matrix in the measuring region A of the biomagnetic field. FIG. 2 shows a state in which the SQUID 10 is viewed from the tip side, and the numerical value attached to each SQUID 10 indicates the channel CH number. The number and shape of arrangements of the SQUID 10 are not limited to FIG.

In FIG. 2, the region indicated by the arc or the circle of the broken line indicates the range of the channel CH that outputs the count value CNT received by the data correction unit 24 of the channel CH located at the center. For example, the data correction unit 24 of the channel CH2 receives the count value CNT from the FQC counters 25 of the channels CH5, CH6, and CH10 located around the channel CH2. The data correction unit 24 of the channel CH5 receives the count value CNT from the FQC counters 25 of the channels CH1, CH2, CH9, CH10, and CH13 located around the channel CH5. The data correction unit 24 of the channel CH10 receives the count value CNT from the FQC counters 25 of the channels CH2, CH5, CH6, CH13, CH14, and CH18 located around the channel CH10.

Other channel CHs also receive count value CNTs from up to 6 channel CHs located in the surroundings. Note that FIG. 2 shows an example in which the data correction unit 24 of each channel CH receives count value CNTs from a maximum of six channel CHs for the sake of clarity, but the number of channel CHs that receive count value CNTs is shown. Is not limited to FIG. The data correction unit 24 of each channel CH may receive the count value CNT from the FQC counter 25 corresponding to a predetermined number of SQUID 10s located in a predetermined range around the SQUID 10 of each channel CH. For example, as shown by the alternate long and short dash line, the data correction unit 24 of each channel CH may receive count value CNTs from a maximum of 18 channel CHs located around each channel CH. Further, the data correction unit 24 of each channel CH may receive the count value CNT from the FQC counter 25 of all the other channel CHs.

FIG. 3 is a block diagram showing an example of a main part of the magnetic field measuring device 200 of FIG. FIG. 3 shows an example in which the data correction unit 24 of the channel CH2 of FIG. 2 receives the count values CNT5, CNT6, and CNT10 from the channels CH5, CH6, and CH10 in the region shown by the arc of the thick broken line in FIG. The data correction unit 24 of the channel CH5 receives the count values CNT1, CNT2, CNT9, CNT10, and CNT13 from the channels CH1, CH2, CH9, CH10, and CH13 in the region shown by the arc of the thin broken line in FIG.

The data correction unit 24 of the channel CH6 receives the count values CNT2, CNT3, CNT10, CNT11, and CNT14 from the channels CH2, CH3, CH10, CH11, and CH14 in the region shown by the arc of the thin broken line in FIG. The data correction unit 24 of the channel CH10 receives the count values CNT2, CNT5, CNT6, CNT13, CNT14, and CNT18 from the channels CH2, CH5, CH6, CH13, CH14, and CH18 in the region shown by the arc of the thin broken line in FIG. .. Each data correction unit 24 outputs the corrected magnetic field data MDT (MDT2, MDT5, MDT6, MDT10) to the data processing device 300.

FIG. 4 is a block diagram showing an example of the data correction unit 24 of CH2 of FIG. For example, the channel CH2 is the correction target of the magnetic field data. The data correction unit 24 of the channel CH 2 has a coefficient holding unit 241, three multipliers 242, and three adders 243. For example, the coefficient holding unit 241 is configured by a register or a memory.

The coefficient holding unit 241 holds the coefficients WF5, WF6, and WF10 corresponding to the count values CNT5, CNT6, and CNT10 received from the other channel CH, respectively. The three multipliers 242 output a correction value obtained by multiplying the coefficient WF5 and the count value CNT5, the coefficient WF6 and the count value CNT6, and the coefficient WF10 and the count value CNT 10, respectively, to the corresponding adder 243.

The three adders 243 correct the magnetic field data by sequentially adding the correction values from the respective multipliers 242 to the magnetic field data output from the digital integrator 23, and the corrected magnetic field data MDT is used as the data processing device 300. Output to. The number and count values of the coefficient WF held by the coefficient holding unit 241 are different for each channel CH. Further, the number of multipliers 242 and the number of adders 243 are equal to the number of count value CNTs received by the data correction unit 24, and differ depending on the channel CH.

Since the data correction unit 24 corrects the digital magnetic field data generated by the digital integrator 23 by using the digital coefficient WF, the data correction unit 24 can be configured by a simple multiplier 242 and an adder 243. Further, since the coefficient WF of another channel CH different for each channel CH of interest is stored in the coefficient holding unit 241, the magnetic field data is appropriately stored for each channel CH of interest according to the positional relationship and the variation of the characteristics of the adjacent SQUID 10. Can be corrected to. This makes it possible to improve the measurement accuracy of the biomagnetic field.

For example, in the channel CH5 shown in FIG. 3, the coefficient holding unit 241 holds the coefficients WF1, WF2, WF9, WF10, and WF13 corresponding to the count values CNT1, CNT2, CNT9, CNT10, and CNT13. In the channel CH6, the coefficient holding unit 241 holds the coefficients WF2, WF3, WF10, WF11, and WF14 corresponding to the count values CNT2, CNT3, CNT10, CNT11, and CNT14.

In the channel CH10, the coefficient holding unit 241 holds the coefficients WF2, WF5, WF6, WF13, WF14, and WF18 corresponding to the count values CNT2, CNT5, CNT6, CNT13, CNT14, and CNT18. The coefficient holding unit 241 of the other channel CH holds the coefficient WF corresponding to the received count value CNT. As shown in FIG. 2, by configuring the data correction unit 24 according to the number of adjacent channel CHs that differ depending on the position of the SQUID 10, the magnetic field data can be appropriately corrected for each SQUAD 10.

FIG. 5 is a waveform diagram showing an example of the φ-V characteristic of the SQUID 10 of FIG. For example, the horizontal axis of FIG. 5 indicates the magnitude of the input magnetic field of SQUID 10, and the magnetic field gradually increases from left to right. The vertical axis of FIG. 5 shows the output voltage (analog value) of SQUID 10 when the input magnetic field changes. The vertical axis of FIG. 5 may be the output voltage (analog value) of the amplifier 21 or the output voltage (digital value) of the AD converter 22.

The magnetic flux quantum φ0 is obtained by applying a gradually increasing magnetic field or a gradually decreasing magnetic field to the SQUID 10 via the feedback coil 28 and measuring the cycle of change in the voltage value output from the AD converter 22. In the evaluation mode for evaluating the magnetic flux quantum φ0 in the magnetic field measuring device 200, the lock of the digital FLL circuit 20 for keeping the output voltage of the SQUID 10 constant is released, and the feedback of the integrated value by the digital integrator 23 is stopped. ..

The operating region of the SQUID 10 in the measurement mode for measuring the biomagnetic field is near the lock point of the φ-V characteristic by feeding back the magnetic field generated from the feedback coil 28 by the current corresponding to the output voltage of the digital integrator 23 to the SQUID 10. Maintained in (linear region). As a result, the magnetic field measurement system 100 can accurately obtain the biomagnetic field signal. The lock point (lock start point) of the φ—V characteristic is set at a position where a predetermined output voltage value is obtained, for example, in a region where the waveform is the steepest (either rising or falling).

FIG. 6 is an explanatory diagram showing an example of the influence of the artifact generated by the operation of the FQC counter 25 of FIG. 1 on the magnetic field waveform. For example, FIG. 6 shows an example of a change in the magnetic field measured by the SQUID 10 of the adjacent channel CH adjacent to the SQUID 10 of the channel CH of interest when an artifact is applied to the SQUID 10 of the channel CH of interest.

The magnetic field waveforms of the adjacent channels CHa, CHb, and CHc do not include artifacts such as an external magnetic field (environmental noise). Further, in FIG. 6, three adjacent channels CHa, CHb, and CHc are shown for the sake of clarity. For example, the adjacent channels CHa, CHb, and CHc are the channels CH5, CH6, and CH10 in FIG. 2, and the channel CH of interest is the channel CH2 in FIG. The adjacent channel CH is not limited to the SQUID 10 located next to the SQUID 10 of the channel CH of interest, and may be the SQUID 10 located in a predetermined range around the SQUID 10 of the channel CH of interest.

When the magnetic flux penetrating the SQUID 10 of the channel of interest changes beyond the magnetic flux quantum φ0 due to the generation of an artifact such as an external magnetic field, the FQC counter 25 of the channel of interest counts up or down, and the count value CNT changes. The digital integrator 23 is reset by the change of the count value CNT, the current flowing through the feedback coil 28 via the DA converter 26 changes, and the magnetic field generated from the feedback coil 28 changes.

Due to the change in the magnetic field, a stepped artifact (hereinafter referred to as FQC artifact) is applied to the SQUID 10 of the adjacent channel CH. As a result, the measured magnetic field measured by the digital FLL circuit 20 of the adjacent channel CH changes stepwise in synchronization with the change of the count value CNT of the channel CH of interest. When the measured magnetic field is affected by the change of the count value CNT, the detection accuracy of the magnetic field by the magnetic field measuring device 200 is lowered.

Since environmental noise and the like are applied to all SQUID10s, the change in the measured magnetic field in the adjacent channel CH generated by the change in the count value CNT of the channel CH of interest occurs in each channel CH. The shift amount of the measured magnetic field due to the influence of the FQC artifact received by the adjacent channel CH differs for each adjacent channel CH, but the shift amount of the measured magnetic field for each update of the count value CNT is the same for each channel CH (SQUID10). be.

For example, the amount of change in the measured magnetic field due to the count-up of the count value CNT of the channel CH of interest is -1500 fT for the adjacent channel CHa, −400 fT for the adjacent channel CHb, and +900 fT for the adjacent channel CHc. Further, the absolute value of the shift amount of the measured magnetic field due to the count-up and count-down of the count value CNT of the channel CH of interest is the same.

FIG. 7 is an explanatory diagram showing an example of a magnetic field waveform in which FQC artifacts have been removed by the data correction unit 24 of FIG. Note that, as in FIG. 6, the magnetic field waveforms of the adjacent channels CHa, CHb, and CHc do not include artifacts such as an external magnetic field (environmental noise).

For example, the data correction unit 24 of the adjacent channel CHa subtracts the magnetic field data corresponding to 1500 fT from the magnetic field data output from the digital integrator 23 when the count value CNT of the channel CH of interest counts up. Further, the data correction unit 24 of the adjacent channel CHa adds magnetic field data corresponding to 1500 fT to the magnetic field data output from the digital integrator 23 when the count value CNT of the channel CH of interest counts down. Here, the coefficient holding unit 241 (FIG. 4) of the adjacent channel CH holds the amount of change in the magnetic field data of the digital integrator 23 corresponding to 1500 fT as the coefficient WF of the channel CH of interest.

The data correction unit 24 of the other adjacent channels CHb and CHc also performs the same correction. Thereby, the influence of the FQC artifact on the adjacent channels CHa, CHb, and CHc generated by the change of the count value CNT of the channel CH of interest can be removed. As a result, in the magnetic field measuring device 200, it is possible to improve the measurement accuracy of the biomagnetic field when an artifact such as an external magnetic field is generated.

As described above, in the first embodiment, it is possible to reduce the influence of the FQC artifact generated when the count value CNT is updated by the FQC counter 25 of the channel of interest on the adjacent channel CH. That is, it is possible to remove noise generated when the magnetic flux quantum φ0 penetrating the SQUID 10 increases or decreases. Therefore, it is possible to improve the measurement accuracy of the biomagnetic field when the FQC artifact is generated due to the generation of an artifact such as an external magnetic field (environmental noise).

(Second embodiment)
FIG. 8 is a block diagram showing an example of a magnetic field measurement system according to a second embodiment of the present invention. Detailed description of the same elements as those in FIGS. 1 and 3 will be omitted. The magnetic field measurement system 100A shown in FIG. 8 includes a magnetic field measurement device 200A and a data processing device 300A. The magnetic field measuring device 200A has a plurality of SQUID 10s and a plurality of digital FLL circuits 20A each of the plurality of SQUAD 10s.

The digital FLL circuit 20A has the same configuration and function as the digital FLL circuit 20 of FIG. 1 except that it does not have the data correction unit 24. Each FQC counter 25 does not output the count value CNT to the other digital FLL circuit 20A, but outputs it to the data processing device 300A.

The data processing device 300A includes a data processing unit 31, a plurality of data correction units 24A, a magnetic field data storage unit 32, and a coefficient storage unit 33. The data processing unit 31 stores, for example, the magnetic field data MDT received from each digital FLL circuit 20A of the magnetic field measuring device 200A in the magnetic field data storage unit 32. The data processing unit 31 transfers the magnetic field data MDT stored in the magnetic field data storage unit 32 to the data correction unit 24A, and generates image data using the magnetic field data corrected by the data correction unit 24A. Then, the data processing unit 31 displays the image indicated by the generated image data on a display device (not shown).

The data correction unit 24A is provided in place of the data correction unit 24 of FIG. Therefore, the data processing device 300A has a plurality of data correction units 24A corresponding to the plurality of digital FLL circuits 20A mounted on the magnetic field measuring device 200A. The configuration of the data correction unit 24A is the same as that of FIG. 4, except that the data correction unit 24A does not have the coefficient holding unit 241. The magnetic field data input to the data correction unit 24A is transferred from the magnetic field data storage unit 32, and the coefficient WF input to the data correction unit 24A is transferred from the coefficient storage unit 33. That is, the coefficient storage unit 33 is provided in place of the coefficient holding unit 241 in FIG.

The number and count values of the coefficient WF transferred to each data correction unit 24A are different for each channel CH. The number of multipliers 242 and the number of adders 243 mounted on each data correction unit 24A are equal to the number of count value CNTs received by the data correction unit 24A, and differ depending on the channel CH. The coefficient storage unit 33 stores the coefficient WF used for correcting the magnetic field data for each channel CH. The coefficient WF stored in the coefficient storage unit 33 is determined by the evaluation of the FQC artifact described with reference to FIG.

For example, the data processing unit 31 and the data correction unit 24A are realized by a control program executed by the data processing device 300A. The magnetic field data storage unit 32 and the coefficient storage unit 33 are allocated to the memory mounted on the data processing device 300A. The magnetic field data storage unit 32 may be assigned to the volatile memory, and the coefficient storage unit 33 may be assigned to the electrically rewritable non-volatile memory. Further, the control program may be stored in the memory to which the magnetic field data storage unit 32 and the coefficient storage unit 33 are assigned.

The data correction unit 24A corresponding to the digital FLL circuit 20A of the channel CH of interest responds to the change in the count value CNT counted by the FQC counter 25 of another predetermined number of channels CH in the magnetic field data MDT generated by the digital integrator 23. To correct. By realizing the data correction unit 24A by a control program, for example, the number of adjacent channel CHs can be changed from a maximum of 6 (broken line) in FIG. 2 to a maximum of 18 (dashed line). Further, the multiplier 242 and the adder 243 in FIG. 4 can be increased or decreased according to the number of adjacent channel CHs.

The functions of the multiplier 242 and the adder 243 are realized by the control program executing the multiplication instruction and the addition instruction. As a result, for example, the number of adjacent channel CHs can be easily changed according to the magnitude of the artifact (environmental noise), and the magnetic field data can be appropriately corrected.

As described above, in the second embodiment as in the first embodiment, it is possible to reduce the influence of the FQC artifact on the adjacent channel CH. Further, in the second embodiment, the data correction unit 24A can be realized by the control program by providing the data correction unit 24A in the data processing device 300A. Thereby, the number of adjacent channel CHs can be easily changed according to the magnitude of the artifact (environmental noise), and the magnetic field data can be appropriately corrected.

Further, since the data correction unit 24A does not have to be provided in each digital FLL circuit 20A, the hardware cost of the magnetic field measuring device 200A can be reduced. For example, when the magnetic field measuring device 200A has the SQUID 10 of 44 channels as shown in FIG. 2, 44 data correction units 24 can be reduced as compared with the magnetic field measuring device 200 of FIG.

(Third embodiment)
FIG. 9 is a block diagram showing an example of a magnetic field measurement system according to a third embodiment of the present invention. Detailed description of the same elements as those in FIGS. 1, 3 and 8 will be omitted. The magnetic field measurement system 100B shown in FIG. 9 includes a magnetic field measurement device 200B and a data processing device 300B. The magnetic field measuring device 200B has a plurality of SQUID 10s and a plurality of digital FLL circuits 20B each of the plurality of SQUAD 10s.

The digital FLL circuit 20B has the same configuration and function as the digital FLL circuit 20A of FIG. 8 except that the signal switch 29 is added. The signal switch 29 outputs the magnetic field data (digital value) output from the digital integrator 23 to the DA converter 26 in the measurement mode for measuring the biomagnetic field.

The signal switch 29 outputs the calibration data CAL (digital value) generated by the calibration processing unit 34 of the data processing device 300B to the DA converter 26 in the coefficient determination mode for determining the coefficient WF to be stored in the coefficient storage unit 33. .. The calibration data CAL is supplied to the DA converter 26 from the feedback coil 28 in order to generate an external magnetic field (environmental noise) in a pseudo manner. That is, the signal switch 29 selects the magnetic field data or the calibration data CAL and outputs it to the DA converter 26.

The data processing device 300B has the same configuration and function as the data processing device 300A of FIG. 8 except that the calibration processing unit 34 is added. The calibration processing unit 34 is realized by a control program executed by the data processing device 300B together with the data processing unit 31 and the data correction unit 24A. The calibration processing unit 34 connects the input of the signal switch 29 to the data processing device 300B in the coefficient determination mode.

Further, the calibration processing unit 34 supplies the calibration data CAL to the DA converter 26 of the channel CH of interest, generates an artifact in a pseudo manner only in the channel CH of interest, and the count value CNT of the channel CH of interest is shown in FIG. Increase or decrease as follows. The calibration processing unit 34 controls the data processing unit 31 to measure the magnetic field data generated by the FQC artifact applied to the SQUID 10 of the adjacent channel CH.

Then, the calibration processing unit 34 obtains the amount of change in the magnetic field data that changes due to the change in the count value CNT of the channel CH of interest for each adjacent channel CH, and obtains the coefficient WF. The calibration processing unit 34 stores the obtained coefficient WF in the coefficient storage unit 33. In this embodiment, the calibration processing unit 34 outputs the calibration data CAL to the DA converter 26 of the channel CH of interest.

From this, an artifact can be generated in a pseudo manner only in the channel CH of interest, and as described with reference to FIG. 6, the amount of change in the magnetic field data of the adjacent channel CH due to the change in the count value CNT can be detected. As a result, the optimum coefficient WF for correcting the magnetic field data of the adjacent channel CH can be obtained for each channel CH of interest, and the measurement accuracy of the magnetic field can be improved.

The calibration processing unit 34 operates the data correction unit 24A using the coefficient WF stored in the coefficient storage unit 33, and confirms whether or not the corrected magnetic field data is an expected value (for example, FIG. 7). You may. Further, instead of providing the data correction unit 24A in the data processing device 300B, as shown in FIG. 3, the data correction unit 24 may be provided in each digital FLL circuit 20B. That is, the signal switch 29 may be added to the digital FLL circuit 20 of FIG. 3, and the calibration processing unit 34 may be added to the data processing device 300 of FIG. In this case, the calibration processing unit 34 stores the coefficient WF for each channel CH obtained in the coefficient determination mode in the coefficient holding unit 241 (FIG. 4) provided in the data correction unit 24 of each channel CH.

Further, the process of determining the coefficient WF by the calibration processing unit 34 may be executed when the magnetic field measurement system 100B is powered on, may be executed at a predetermined frequency, or may be executed when the SQUID 10 is replaced due to a failure or the like. good.

As described above, the same effects as those of the first and second embodiments can be obtained in the third embodiment. Further, in the third embodiment, the calibration data CAL output by the calibration processing unit 34 only to the channel CH of interest can generate a pseudo FQC artifact only in the channel CH of interest. That is, it is possible to evaluate the influence of the FQC artifact generated in the channel CH of interest when the external magnetic field is applied without applying the external magnetic field (environmental noise) to the SQUID 10.

Then, it is possible to detect the amount of change in the magnetic field data of the adjacent channel CH due to the change in the count value CNT of only the channel CH of interest. As a result, the optimum coefficient WF for removing the influence of the FQC artifact can be obtained from the magnetic field data of the adjacent channel CH for each channel CH of interest, and the measurement accuracy of the magnetic field can be improved.

Further, by realizing the data correction unit 24A by a control program, it is possible to easily increase or decrease the number of adjacent channel CHs and increase or decrease the multiplier 242 and the adder 243. Further, by providing the calibration processing unit 34 in the data processing apparatus 300B, the processing for determining the coefficient WF by the calibration processing unit 34 can be executed at an arbitrary timing.

FIG. 10 is a block diagram showing an example of the hardware configuration of the data processing devices 300, 300A, and 300B of FIGS. 1, 8 and 9. The data processing devices 300, 300A, and 300B are computers such as a PC (Personal Computer) or a server. Since the hardware configurations of the data processing devices 300, 300A, and 300B are similar to each other, the data processing device 300B will be described below.

The data processing device 300B has a CPU 301, a RAM 302, a ROM 303, an auxiliary storage device 304, an input / output interface 305, and a display device 306, which are connected to each other by a bus 307.

The CPU 301 controls the overall operation of the data processing device 300B. For example, the CPU 301 executes a control program stored in the ROM 303 or the auxiliary storage device 304 to realize the operations of the data processing unit 31, the data correction unit 24A, and the calibration processing unit 34 in FIG. Further, the CPU 301 executes a control program to display the corrected magnetic field data waveform, the uncorrected magnetic field data waveform, or the change of the count value CNT on the display device 306.

The RAM 302 is assigned a magnetic field data storage unit 32 that stores a control program and stores magnetic field data, and is also used as a work area of the CPU 301. The ROM 303 stores various programs, parameters used in the programs, and the like. The control program may be transferred from the ROM 303 to the RAM 302. The ROM 303 may be a non-volatile memory such as an electrically rewritable flash memory, and in this case, the coefficient storage unit 33 may be assigned to the ROM 303.

The auxiliary storage device 304 is a storage device such as an SSD (Solid State Drive) or an HDD (Hard Disk Drive). The auxiliary storage device 304 stores, for example, an OS (Operating System) that controls the operation of the data processing device 300B, a control program, various data, files, and the like necessary for the operation of the data processing device 300B. Various programs stored in the auxiliary storage device 304 are expanded in the RAM 302 and executed by the CPU 301.

The input / output interface 305 includes a user interface such as a touch panel, a keyboard, and operation buttons, and a communication interface for communicating with other electronic devices. Further, the input / output interface 305 may include an interface for connecting a recording medium in which the control program is stored. The recording medium is a CD (Compact Disc: registered trademark), a DVD (Digital Versatile Disc: registered trademark), a USB (Universal Serial Bus) memory, or the like.

For example, a stimulus application device that applies an electrical stimulus to a subject who measures a biomagnetic field may be connected to the communication interface. In this case, the data processing device 300B controls the magnetic field measuring device 200B and the stimulus applying device in synchronization with each other. The display device 306 displays a waveform or the like of the magnetic field data measured by the magnetic field measuring device 200B. Further, the display device 306 may display the waveforms shown in FIGS. 6 and 7.

Although the present invention has been described above based on each embodiment, the present invention is not limited to the requirements shown in the above embodiments. With respect to these points, the gist of the present invention can be changed to the extent that the gist of the present invention is not impaired, and can be appropriately determined according to the application form thereof.

10 SQUID
20, 20A, 20B Digital FLL circuit 21 Amplifier 22 AD converter 23 Digital adder 24, 24A Data correction unit 25 FQC counter 26 DA converter 27 Voltage current converter 28 Feedback coil 29 Signal switch 31 Data processing unit 32 Magnetic field data Storage unit 33 Coefficient storage unit 34 Calibration processing unit 100, 100A, 100B Magnetic field measurement system 200, 200A, 200B Magnetic field measurement device 241 Coefficient holding unit 242 Multiplier 243 Adder 300, 300A, 300B Data processing device 304 Auxiliary storage device 305 Output interface 306 Display device 307 Bus CAL Calibration data CH channel CNT Count value MDT Magnetic field data WF coefficient φ0 Magnetic flux quantum

International Publication No. 2018/199067

Claims (11)

It is a magnetic field measuring device having a plurality of signal processing units that generate magnetic field data according to the magnetic field measured by a plurality of superconducting quantum interference elements.
Each of the plurality of signal processing units
An integrator that generates the magnetic field data by integrating the voltage value that changes with the magnetic flux quantum as a period, which is output from the superconducting quantum interference element according to the change of the magnetic field.
A counter that counts the number of changes in the magnetic flux quantum based on the changes in the magnetic field data generated by the integrator.
A correction unit that corrects the magnetic field data generated by the integrator according to the number of changes in the magnetic flux quantum counted by the counters of a predetermined number of other signal processing units.
A magnetic field measuring device characterized by having. The correction unit corrects the magnetic field data by adding a correction value obtained by multiplying the change number of the magnetic flux quantum counted by the counter of the other signal processing unit by a predetermined coefficient to the magnetic field data. The magnetic field measuring device according to claim 1, wherein the magnetic field measuring device is to be used. The magnetic field measuring device according to claim 2, wherein the predetermined coefficient differs for each of the other signal processing units. The other signal processing unit is characterized in that it corresponds to a predetermined number of superconducting quantum interference elements located in a predetermined range around the superconducting quantum interference element corresponding to the signal processing unit to be corrected for the magnetic field data. The magnetic field measuring device according to any one of claims 1 to 3. Each of the plurality of signal processing units
It has an AD converter that converts the voltage output from the superconducting quantum interference element into a digital value.
The integrator is a digital integrator that integrates the digital values output by the AD converter.
The magnetic field measuring device according to any one of claims 1 to 4, wherein the counter is for counting the number of changes in magnetic flux quantum according to changes in magnetic field data output by the digital integrator. .. Each of the plurality of signal processing units
The magnetic field measuring device according to claim 5, further comprising a DA converter that converts magnetic field data output by the digital integrator into a voltage. In each of the plurality of signal processing units, the counter is characterized in that when the integral value output by the digital integrator exceeds a predetermined threshold value, the magnetic flux quantum is updated and the digital integrator is reset. The magnetic field measuring device according to claim 5 or 6. A plurality of superconducting quantum interference elements, a plurality of signal processing units that generate magnetic field data according to the magnetic fields measured by the plurality of superconducting quantum interference elements, and magnetic field data generated by the plurality of signal processing units, respectively. A magnetic field measurement system having a data processing device for processing,
Each of the plurality of signal processing units
An integrator that generates the magnetic field data by integrating the voltage value that changes with the magnetic flux quantum as a period, which is output from the superconducting quantum interference element according to the change of the magnetic field.
It has a counter that counts the number of changes in the magnetic flux quantum based on the changes in the magnetic field data generated by the integrator.
The data processing device corrects the magnetic field data generated by the integrator of each of the plurality of signal processing units according to the number of changes in the magnetic flux quantum counted by the counters of a predetermined number of other signal processing units. A magnetic field measurement system characterized by having a part. The correction unit obtains a correction value obtained by multiplying the magnetic field data of each of the plurality of signal processing units by a predetermined coefficient with the number of changes in the magnetic flux quantum counted by the counters of the other signal processing units. By adding, the magnetic field data is corrected and
Each of the plurality of signal processing units
A signal switch that selects the magnetic field data or calibration data generated by the integrator, and
The signal switch has a feedback coil that generates a magnetic field according to the selected magnetic field data or calibration data.
The data processing device applies calibration data to the signal switch of the signal processing unit of interest in order to apply an artifact to the superconducting quantum interference element of interest corresponding to the signal processing unit of interest among the plurality of signal processing units. A magnetic field is generated in the feedback coil by outputting, and the predetermined value is specified for each of the adjacent superconducting quantum interference elements based on the change in the voltage output by the adjacent superconducting quantum interference element adjacent to the superconducting quantum interference element of interest. The magnetic field measurement system according to claim 8, further comprising a calibration processing unit for obtaining a coefficient. A plurality of superconducting quantum It is a control method of the magnetic field measuring device that corresponds to each of the interfering elements.
For each of the plurality of signal processing units, the number of changes in the magnetic flux quantum is counted based on the changes in the magnetic field data generated by the integrator.
Control of a magnetic field measuring device characterized in that the magnetic field data generated by the integrator of the signal processing unit of interest is corrected according to the number of changes in the magnetic flux quantum counted by the counters of a predetermined number of other signal processing units. Method. Multiple signals including a plurality of superconducting quantum interference elements and an integrator that generates magnetic field data by integrating the voltage values that change with the magnetic flux quantum as a period, which are output from the superconducting quantum interference elements in response to changes in the magnetic field. Control of a magnetic field measurement system having a magnetic field measuring device having a processing unit corresponding to each of a plurality of superconducting quantum interference elements and a data processing device for processing magnetic field data generated by each of the plurality of signal processing units. It ’s a program,
The number of changes in the magnetic flux quantum measured based on the changes in the magnetic field data generated by the integrator is received from each of the plurality of signal processing units.
It is characterized by having a computer execute a process of correcting the magnetic field data generated by the integrator of the signal processing unit of interest according to the number of changes in the magnetic flux quantum counted by the counters of a predetermined number of other signal processing units. Control program for the magnetic field measurement system.

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