JP7002416B2 - Magnetic field measuring device - Google Patents

Description

The present invention is a magnetic field measuring device that estimates an approximate value of an environmental magnetic field signal measured by a magnetic field measuring device from an environmental magnetic field signal measured by a reference magnetic sensor, and detects the presence or absence of an environmental magnetic field using the approximate value. Regarding.

A magnetocardiogram has been developed as a magnetic field measuring device that measures a weak magnetic field from a subject's measurement target and evaluates the electrophysiological activity of the measurement target non-invasively. A magnetocardiogram is a device that non-contactly measures a weak magnetic field (magnetocardiography) generated by an electromotive force (current bipolar) associated with the electrophysiological activity of the heart, and is a space by simultaneous measurement of multiple magnetic sensors. Evaluation with excellent resolution is possible. An image of the temporal change and spatial distribution of this magnetocardiography is called a magnetocardiogram. Since the magnetic permeability in the living body is almost equal to that of vacuum, the magnetocardiogram is less affected by the peripheral organs of the heart (bones, lungs, etc.) than the electrocardiogram, and reflects the current associated with the electrophysiological activity of the heart with high sensitivity. do. Taking advantage of this magnetocardiography, many clinical effectiveness of the magnetocardiography has been shown.

In order to accurately and stably evaluate the electrophysiological activity of the heart by this magnetocardiographic examination, it is necessary to sufficiently reduce the environmental magnetic field mixed in the magnetocardiogram. The intensity of the heart magnet is very weak, the intensity of the adult QRS complex (wave reflecting the electrical activity of the ventricle) is several tens of pT, and the intensity of the P wave (wave reflecting the electrical activity of the atrium) is several pT. The intensity of the fetal P wave is about 0.1 pT. On the other hand, the environmental magnetic field is generated by the geomagnetic DC magnetic field, the magnetic field caused by the transmission / return current of the train, the magnetic field generated by the movement of objects made of magnetic materials such as automobiles, elevators and iron doors, and the current of the transmission line. There are magnetic fields, magnetic fields generated by rotating bodies of fans and pumps, and so on. The environmental magnetic field is much larger than that of magnetocardiography. It is reported to be 1.4 μT at the site. In order to reduce these environmental magnetic fields mixed in the magnetocardiogram, the magnetocardiogram usually has a magnetically shielded room (MSR), a gradiometer of the magnetic sensor section, and an analog filter (High pass). It is equipped with environmental magnetic field reduction technology such as filter: HPF, Low pass filter: LPF) and digital filter to reduce the mixed environmental magnetic field. In addition, as an environmental magnetic field reduction technology that complements the MSR, an environmental magnetic field reduction method (hereinafter referred to as "reduction method") that estimates and removes an approximate value of the environmental magnetic field signal of the biomagnetic measuring device from the environmental magnetic field signal measured by the reference magnetic sensor. ") Has been developed (Patent Document 1, etc.).

On the other hand, in order to reduce the influence of the environmental magnetic field mixed in the magnetocardiogram, there is a method of detecting the presence or absence of the generation of the environmental magnetic field affecting the magnetocardiographic examination and notifying the user of the detection state. Specifically, a magnetic field measuring device is used to measure the environmental magnetic field outside the MSR, detect the environmental magnetic field above a certain threshold value, output the detected signal, and display it based on the detected signal. The display based on the detection signal is connected to a display device (indicator, alarm and buzzer) and a magnetocardiograph to notify the user of the presence or absence of an environmental magnetic field. The user confirms whether or not an environmental magnetic field is generated by the display device and the magnetocardiograph, conducts a magnetocardiographic inspection during the time when the environmental magnetic field is not generated, and analyzes the magnetocardiographic data during the time when the environmental magnetic field is not generated. It is possible to reduce the influence of the environmental magnetic field on the magnetocardiographic inspection.

Japanese Unexamined Patent Publication No. 2016-217930

Since the magnetic field from the living body is weak, even if the environmental magnetic field reduction technology or the reduction method that estimates and removes the environmental magnetic field is applied, measurement is performed with the environmental magnetic field as small as possible, or the magnitude of the environmental magnetic field is grasped. It is desirable to analyze the obtained data after this.

The environmental magnetic field measured by the magnetocardiogram inside the MSR is reduced by various environmental magnetic field reduction technologies (MSR, gradiometer of magnetic sensor unit, analog filter and digital filter). These environmental magnetic field reduction technologies have different reduction effects with respect to the frequency of the environmental magnetic field. Therefore, depending on the frequency characteristics of the environmental magnetic field, the pattern of the environmental magnetic field outside the MSR and the pattern of the environmental magnetic field measured by the magnetocardiogram inside the MSR may differ, and the time when the strength of the environmental magnetic field inside and outside the MSR is strong may not correspond. .. That is, the magnitude of the environmental magnetic field observed outside the MSR and the presence or absence of the generation of the environmental magnetic field that affects the magnetocardiographic examination do not always match.

The magnetic field measuring device according to the embodiment of the present invention includes an MSR, a magnetic sensor arranged inside the MSR, a reference magnetic sensor arranged outside the MSR, magnetic field time series data from the magnetic sensor, and magnetic field time series data. It has an arithmetic unit for inputting the environmental magnetic field time-series data from the reference magnetic sensor, and the arithmetic unit performs threshold processing on the estimated environmental magnetic field time-series data inside the MSR estimated from the environmental magnetic field time-series data. To create a detection signal, the estimated environmental magnetic field time-series data is required to minimize the predetermined evaluation function of the magnetic field time-series data and the estimated environmental magnetic field time-series data, and the estimated environmental magnetic field time-series data. In obtaining the above, the magnetic field reduction effect for each frequency of the MSR is applied to the environmental magnetic field time series data.

Using a reference magnetic sensor outside the MSR, it is possible to detect the presence or absence of an environmental magnetic field that affects the measurement of the magnetic field measuring device inside the MSR.

Other issues and novel features will become apparent from the description and accompanying drawings herein.

It is a schematic diagram which shows the whole structure of a magnetocardiogram. It is a figure which shows the arrangement of the magnetic sensor and the arrangement example with respect to a subject. It is a schematic diagram which shows the whole structure of the magnetocardiogram which concerns on Example 1. FIG. It is a figure which shows the processing flow which detects the presence or absence of the generation of an environmental magnetic field using a reference magnetic sensor. (A) Environmental magnetic field waveform from the train measured by the magnetocardometer (channel of maximum magnetic field strength), (b) Environmental magnetic field waveform from the train measured by the 3-axis fluxgate magnetic flux meter outside the MSR, (c) This implementation The environmental magnetic field waveform from the train on the magnetocardometer, estimated by applying the processing flow of the example. (A) The waveform of the detection signal created by applying the processing flow of this embodiment, and (b) the environmental magnetic field waveform (channel of the maximum magnetic field strength) from the train actually measured by the magnetocardiograph. It is a figure which shows an example of the display screen which displays the measurement result of a magnetocardiogram. It is a figure which shows an example of the display screen which sets the reduction effect of the environmental magnetic field of a magnetocardiogram. It is a schematic diagram which shows the whole structure of the magnetocardiography which concerns on Example 2.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

FIG. 1 is a schematic view showing the overall configuration of a magnetic field measuring device (magnetocardiography). The components of the magnetocardiogram 1 are arranged separately inside and outside the MSR2. The MSR2 has a length of, for example, about 3 m on each side, and a plurality of SQUID magnetometers 3 (hereinafter referred to as “magnetic sensors”) are arranged inside the MSR2 to maintain an extremely low temperature. A cryostat 4, a gantry 5 holding the cryostat 4, and a bed 6 on which the subject (not shown) lies are arranged. The bed 6 moves in the short axis (A direction, x direction) of the bed 6, moves in the long axis (B direction, y direction) of the bed 6, and moves in the vertical direction (C direction, z direction) of the bed 6. It is possible to move the subject and a plurality of magnetic sensors can be easily aligned with each other.

Outside the MSR2, there is a drive circuit 7 that drives the magnetic sensor 3 arranged in the cryostat 4, an amplifier filter unit 8 that amplifies and filters the output from the drive circuit 7, and an output from the amplifier filter unit 8. A calculation device 9 that collects signal data, analyzes and processes the collected data (hereinafter referred to as "magnetic field time series data"), and controls each part of the magnetometer 1, and an analysis result analyzed and processed by the calculation device 9. The display device 10 for displaying the above is mainly arranged.

The magnetic sensor 3 of the magnetometer 1 is not limited to the SQUID magnetometer, but a sensor using a magnetoresistive effect element, an optical pumping magnetometer, a flux gate magnetometer, and a magnetic sensor using a magnetic impedance element are also applied. Can be done. The magnetic field generated from the heart is very weak (0.1 to several tens of pT), and the noise level of the magnetic sensor of the magnetocardometer is preferably several pT / √Hz or less. Further, the frequency band of the magnetic sensor of the magnetocardiograph is preferably DC to several hundred Hz, which is the same as the frequency band of the electrical activity of the heart.

An example of the arrangement of the magnetic sensor array used in the magnetocardiograph 1 and the arrangement for the subject will be described with reference to FIG. The plurality of magnetic sensors constituting the magnetic sensor array are vertically suspended along the z direction on the inner wall of the bottom of the cryostat 4 (see FIG. 1), and the magnetic field component B _z in the z direction perpendicular to the chest wall 11 of the subject is generated. Measure over time. The plurality of magnetic sensors are arranged at equal intervals in the x-direction and the y-direction so that the amount of change in the distance of the magnetic field can be accurately captured. It should be noted that a magnetic sensor that measures the magnetic field component B _x in the x direction parallel to the chest wall 11 and the magnetic field component By in the _y direction over time can also be applied.

In the example of FIG. 2, a 64-channel magnetic sensor array 12 in which the distance between the magnetic sensors is 0.025 m, the measurement surface is 0.175 m × 0.175 m, and the magnetic sensors are arranged in an array of 8 × 8 is provided. Shows. In the coordinate system of the magnetic sensor array 12, for example, the magnetic sensor array 12 is aligned so that the magnetic sensor located in the 7th row and 3rd column indicated by reference numeral 13 is located directly above the xiphoid process 14 on the chest. conduct. The magnetic sensor in the 1st row and 8th column is set as the origin O of the coordinate system.

As the first embodiment, a magnetic field measuring device for detecting the presence or absence of an environmental magnetic field by using a reference magnetic sensor installed outside the MSR2 will be described. The components common to those in FIG. 1 are designated by the same reference numerals, and duplicate description will be omitted. FIG. 3 is a schematic view showing the overall configuration of a magnetic field measuring device (magnetocardiography) in which a reference magnetic sensor is installed outside the MSR.

Outside the MSR2, there is a 3-axis flux gate magnetometer 15 (hereinafter referred to as "reference magnetic sensor") for measuring the environmental magnetic field, a drive circuit 16 for driving the reference magnetic sensor, and an output from the drive circuit 16. The amplifier filter unit 17 for amplifying and filtering the magnet is arranged, and the output signal from the amplifier filter unit 17 is collected by the arithmetic unit 9.

As the reference magnetic sensor 15, a sensor using a magnetoresistive effect element and a magnetic sensor using a sensor using a magnetic impedance element can also be applied. The reference magnetic sensor 15 is installed in a place where there is no source of an environmental magnetic field (such as a cancel coil of an electric device or an active magnetic cancel system) around the outside of the MSR. The deviation between the position of the magnetic sensor array 12 of the magnetometer 1 and the position of the reference magnetic sensor 15 is negligible in terms of magnetic field strength from the position of the source of the environmental magnetic field, but since the measurement position is different, the heart Even if only the magnetic field component B _z in the _z direction of the magnetometer 1 is observed, it can be corrected by the environmental magnetic component (magnetic field component B _x , magnetic field component By, magnetic field component B _z ) in three axes. The influence of the environmental magnetic field on the magnetic sensor of the electrocardiograph 1 can be obtained more accurately. Of course, it is possible to apply even if the number of axes of the reference magnetic sensor 15 is 1 axis and 2 axes. Further, a plurality of reference magnetic sensors 15 may be used.

FIG. 4 shows a flowchart of an environmental magnetic field detection processing procedure using the external reference magnetic sensor 15 of the MSR2. First, processing is started (101), and magnetic field time series data (hereinafter referred to as “cardiac magnetic field time series data”) generated from the subject's heart using a magnetocardometer (see FIG. 3) and external reference magnetism of MSR2. The sensor 15 is used to simultaneously measure the time-series data of the environmental magnetic field (hereinafter referred to as "environmental magnetic field time-series data") (102).

The magnetic field reduction effect of MSR is applied to the environmental magnetic field time series data (103). Since the magnetic field reduction effect of MSR has frequency characteristics, frequency analysis is applied to the environmental magnetic field time series data to convert it into data in the frequency domain, and the converted frequency domain data is multiplied by the magnetic field reduction rate for each frequency by MSR. Then, apply frequency analysis and convert it to data in the time domain again. Specifically, it is as follows. Assuming that the environmental magnetic field time series data is given by T sample points (digital signal sequence) x (t) (t = 1 to T) sampled at predetermined time intervals, the discrete Fourier spectrum X of x (t) (k) (k = 0, 1, ... K-1) can be obtained from (Equation 1).

Here, K discrete frequency spectra (filter functions) F (k) are set as shown in (Equation 2) based on the frequency characteristic D _M (w _k ) of the magnetic field reduction rate of the MSR.

By multiplying the filter function F (k) shown in (Equation 2) and the discrete Fourier spectrum X (k) shown in (Equation 1) (Equation 3), the discrete frequency spectrum to which the magnetic field reduction effect of MSR is applied is applied. You can get X'(k).

By inverse Fourier transforming the discrete frequency spectrum X'(k) based on (Equation 4), time series data x'(t) of the environmental magnetic field to which the magnetic field reduction effect of MSR is applied can be obtained.

Next, the magnetic field reduction effect of the magnetic sensor (gravimeter structure) of the magnetocardiogram is applied to the environmental magnetic field time series data to which the magnetic field reduction effect of MSR is applied (104). The gradiometer structure is a configuration in which the magnetic flux detected by the difference type detection coil created by the superconducting wire is transmitted to the SQUID magnetic flux meter. By using the difference type detection coil, the spatial gradient of the magnetic field can be detected and a uniform environmental magnetic field can be reduced. The magnetic field reduction rate D _g by this gradiometer can be considered as a frequency-independent constant, unlike the magnetic field reduction effect of MSR described above. Therefore, by multiplying the time-series data x'(t) of the environmental magnetic field to which the magnetic field reduction effect of MSR obtained in the process 103 is applied by the magnetic field reduction rate D _g of the gradimeter (Equation 5), the magnetic field of the gradimeter is reduced. Time series data x'' (t) of the environmental magnetic field to which the effect is applied can be obtained.

Next, the magnetic field reduction effect of the analog filters (HPF and LPF) of the magnetometer is applied to the environmental magnetic field time series data to which the magnetic field reduction effect of the magnetic sensor is applied (105). Specifically, it can be obtained by applying a digital filter having a filter type and filter order similar to the analog filter of the electrocardiograph to the time series data x'' (t) of the environmental magnetic field obtained in the process 104. For example, when an FIR (Finite Impulse Response) filter is used as a digital filter, the time-series data x'''(t) of the environmental magnetic field to which the FIR filter is applied can be obtained from (Equation 6). Here, m is the filter order, and a _m is the filter coefficient determined by the filter type and the filter order.

The signals obtained by the processes 103 to 105 so far reflect the reduction effect of the environmental magnetic field reduction technology applied to the magnetocardiogram 1, and the estimated value of the environmental magnetic field measured by the magnetocardometer (hereinafter referred to as "magnetocardiography meter"). It can be regarded as "estimated environmental magnetic field"). Next, the weighting coefficient for each channel is calculated for the time-series data of the magnetocardiographic estimation environmental magnetic field (106).

This weighting factor can be obtained in advance by minimizing the difference between the time-series data of the estimated ambient magnetic field of the magnetocardiogram and the time-series data of the environmental magnetic field actually measured in each channel of the magnetocardiography without a subject. can. When a 3-axis (x-axis, y-axis and z-axis) magnetic sensor is used as the reference magnetic sensor 15, the weighting coefficient vector W (W = [W _x , W _y , W _z ]) for each channel of each axis. Can be obtained as a value that minimizes the evaluation function (Equation 7).

In the evaluation function (Equation 7), B ^MCG _{n, t} represents the environmental magnetic field measured at the tth (t = 1 to T) sampling point on the nth (n = 1 to 64) channel of the magnetocardiogram. There is. B ^ref _{x, t} , B ^ref _{y, t} and B ^ref _{z, t} are the magnetocardiograph estimation environment at the sampling point t of the magnetocardiograph 1 obtained from the magnetic field signals of the reference magnetic sensors of the x-axis, y-axis and z-axis. Each represents a magnetic field. Further, W _{x, n} , W _{y, n} and W _{z, n} are for the magnetocardiographic estimated environmental magnetic field of the reference magnetic sensor of the x-axis, y-axis and z-axis in the nth (n = 1 to 64) channel. Each represents a weighting coefficient (hereinafter referred to as "weighting coefficient for each channel").

Time-series data of the electrocardiograph estimated environmental magnetic field multiplied by the weighting factor for each channel (B ^ref _{x, t} × W _{x, n} ＋ B ^ref _{y, t} × W _{y, n} ＋ B ^ref _{z, t} × W _{z, n} ) The threshold value processing is applied to the above, and the detection signal is created (107). As the detection signal, for example, a signal in which 1 is set above the threshold value and 0 is set below the threshold value can be used. As the threshold value of the threshold value processing, an appropriate value is set depending on the measurement target (for example, adult and fetus) and the analysis target (ventricular and atriosphere). This makes it possible to perform threshold processing according to the magnitude of the cardiac magnetic field to be measured.

Finally, the cardiac magnetic field time-series data, the magnetocardiographic estimation environmental magnetic field time-series data and the detection signal are displayed (108), and the process is terminated (109).

As a frequency analysis method applied to the environmental magnetic field time series data of the process 103, there are well-known high-speed Fourier transform methods, periodogram methods, etc., and the Fourier spectrum and power spectrum density are calculated to calculate the frequency of the environmental magnetic field time series data. You can get the data in the area. Processing based on these frequency analysis methods has become feasible due to the recent improvement in the processing capacity of personal computers. Further, in order to calculate the magnetic field reduction effect for each frequency of the MSR, for example, the catalog value of the magnetic shield rate of the MSR or the actually measured data acquired in advance can be used. Further, in calculating the magnetic field reduction effect, the phase change information for each frequency of the MSR can also be used.

In order to calculate the magnetic field reduction effect of the magnetic sensor on the environmental magnetic field time series data of the process 104, for example, the catalog value of the magnetic field reduction rate of the magnetic sensor or the measured data acquired in advance can be used.

In order to calculate the magnetic field reduction effect of the analog filter on the environmental magnetic field time series data of the process 105, for example, the same type as the analog filter of the electrocardiograph, the cutoff frequency, the magnetic field reduction rate obtained from the digital filter of order, etc. can be used. can.

The weighting coefficient for each channel that minimizes the evaluation function (Equation 7) of the process 106 can be obtained, for example, by using the downhill simplex method, which is one of the linear programming methods.

The effectiveness of the method of detecting the environmental magnetic field using the reference magnetic sensor arranged outside the MSR described above was confirmed by using the measured data of the environmental magnetic field from the train.

FIG. 5A shows an environmental magnetic field waveform 18 (channel with maximum magnetic field strength) from a train measured by a 64-channel magnetocardiogram. The horizontal axis is time (seconds), and the vertical axis is magnetic field (pT). FIG. 5B shows an environmental magnetic field waveform 19 in the x direction, an environmental magnetic field waveform 20 in the y direction, and an environmental magnetic field waveform 21 in the z direction measured by a reference magnetic sensor outside the MSR. The horizontal axis is time (seconds), and the vertical axis is magnetic field (μT). Comparing with the environmental magnetic field waveform 18 measured by the magnetocardiogram, it can be seen that the waveform pattern of the environmental magnetic field waveform measured by the reference magnetic sensor outside the MSR is different.

FIG. 5C shows a magnetocardiograph-estimated environmental magnetic field waveform 22 of the same channel as in FIG. 5A calculated by applying the processing flow shown in FIG. Compared with the environmental magnetic field waveform 18 actually measured by the magnetocardiogram, the estimated ambient magnetic field waveform 22 of the magnetocardiogram and the actually measured waveform 18 were similar, and the correlation coefficient was 0.85.

FIG. 6A shows a detection signal 23 created by applying the processing flow shown in FIG. The horizontal axis is time (seconds), and the vertical axis is detection signal strength (arb. Unit.). FIG. 6B shows the environmental magnetic field waveform 18 measured by the magnetocardiograph. From FIG. 6, it can be seen that the time when the detection signal 23 outputs 1 corresponds to the time when the intensity of the environmental magnetic field waveform 18 measured by the magnetocardiograph is strong. By displaying this detection signal 23 at the same time as the magnetocardiographic waveform measured by the magnetocardiogram, it is possible to inform the user of the presence or absence of an environmental magnetic field that affects the magnetocardiographic examination.

From the above results, it was shown that the time when the environmental magnetic field affecting the magnetocardiographic examination can be accurately detected from the environmental magnetic field signal outside the MSR in the magnetocardiographic meter.

The interface applied to the magnetic field measuring device of the first embodiment will be described. FIG. 7 is an example of a display screen that displays the result of detecting the presence or absence of the generation of an environmental magnetic field that affects the magnetocardiographic examination using an external reference magnetic sensor of the MSR. The display screen 24 is displayed on the display device 10 of the magnetocardiogram.

The display screen 24 of the display device 10 applies the processing flow of FIG. 4 to the magnetocardiogram measurement data display field 25 that displays the magnetic field signal measured by the magnetocardiography and the environmental magnetic field measured by the reference magnetic sensor outside the MSR. The magnetocardometer estimated environmental magnetic field data display column 26 and the detection data display column 27 calculated in the above are included.

The magnetic field signal 28 measured by the magnetocardiography is displayed in the magnetocardiography measurement data display field 25. The channel of the magnetometer magnetic sensor displayed in the magnetocardiographic measurement data display field 25 can be switched by using the channel selection button 29. The signal of the magnetic sensor of "channel 1" selected by the channel selection button 29 is displayed as the magnetic field signal 28.

In the magnetocardiographic estimation environmental magnetic field data display column 26, the magnetocardiographic estimation environmental magnetic field signal 30 calculated by applying the processing flow of FIG. 4 to the environmental magnetic field measured by the reference magnetic field outside the MSR is displayed. The channel of the magnetometer magnetic sensor displayed in the magnetocardiographic estimation environment magnetic field data display field 26 is also switched by the channel selection button 29. The signal corresponding to the magnetic sensor of "channel 1" selected by the channel selection button 29 is displayed as the magnetocardiographic estimation environmental magnetic field signal 30. Further, a threshold value display field 32 for displaying a threshold value applied to the magnetocardiographic estimation environment magnetic field signal 30 is displayed. The value of this threshold can be set by the operator. Alternatively, the default value of the device may be set. The first threshold line 33 (line corresponding to the positive threshold value) and the second threshold line 34 (line corresponding to the negative threshold value) corresponding to this threshold value are magnetocardiographs. It is displayed in the estimated environmental magnetic field data display field 26.

In the detection data display field 27, the detection signal 35 created by applying the processing flow of FIG. 4 to the environmental magnetic field measured by the reference magnetic sensor outside the MSR is displayed. Further, the environmental magnetic field detection time range 36 is displayed in the magnetocardiographic measurement data display field 25 corresponding to the time range in which the detection signal 35 outputs 1. Since the change in the detection signal can be identified at a glance together with the magnetic field time series data, the operator can analyze the magnetocardiographic measurement data after grasping the time zone when the environmental magnetic field is large.

FIG. 8 sets the effect of reducing the environmental magnetic field of the magnetocardiograph used in the process of detecting the presence or absence of the generation of the environmental magnetic field that affects the magnetocardiographic examination according to the flow of FIG. 4 using the reference magnetic sensor outside the MSR. This is an example of a display screen. The display screen 37 is displayed on the display device 10 of the magnetocardiogram.

On the display screen 37 of the display device 10, the frequency characteristic display column 38 of the magnetic shield rate of the MSR that displays the frequency characteristic of the shield rate of the MSR and the reduction rate of the magnetic sensor that displays the magnetic field reduction rate of the magnetic sensor of the electrocardiograph are displayed. Display column 39, frequency characteristics of the reduction rate of the high-pass filter that displays the frequency characteristics of the reduction rate of the high-pass filter of the amplifier filter unit of the corer. The frequency characteristic display column 41 of the reduction rate of the low-pass filter to be displayed is included.

In the frequency characteristic display column 38 of the magnetic shield rate of the MSR, the magnetic shield rate 42 for each frequency of the MSR is displayed. The magnetic shield rate for each frequency displayed in the frequency characteristic display column 38 of the magnetic shield rate of the MSR can be set by using the magnetic shield rate setting column 43 for each frequency.

Further, when the phase change information is also used in calculating the magnetic field reduction effect of the MSR, the phase change information of the MSR can be displayed in the frequency characteristic display column 38 of the magnetic shield rate of the MSR. In this case, the phase change information setting column for each frequency is displayed.

In the reduction rate display column 39 of the magnetic sensor, the reduction rate for each channel of the magnetic sensor of the magnetocardiograph is displayed. The channel of the magnetocardiogram displayed in the reduction rate display field 39 of the magnetic shield rate can be switched and displayed by using the channel selection button 44.

In the frequency characteristic display column 40 of the reduction rate of the high-pass filter, the reduction rate 45 for each frequency of the high-pass filter is displayed. The reduction rate for each frequency displayed in the frequency characteristic display column 40 of the reduction rate of the high-pass filter is the filter type setting column 46 for setting the filter type of the high-pass filter, the order setting column 47 for setting the order of the high-pass filter, and the high-pass filter. The value calculated based on the cutoff frequency setting field 48 for setting the cutoff frequency of is displayed.

In the frequency characteristic display column 41 of the reduction rate of the low-pass filter, the reduction rate 49 for each frequency of the low-pass filter is displayed. The reduction rate for each frequency displayed in the frequency characteristic display column 41 of the reduction rate of the low-pass filter is the filter type setting column 50 for setting the filter type of the low-pass filter, the order setting column 51 for setting the order of the low-pass filter, and the low-pass filter. The value calculated based on the cutoff frequency setting field 52 for setting the cutoff frequency of is displayed.

As the second embodiment, a magnetic field measuring device for detecting the presence or absence of an environmental magnetic field using a reference magnetic sensor installed outside the MSR2 and notifying the presence or absence of an environmental magnetic field in the MSR2 using a detection result display device. Will be explained. The components common to those in FIGS. 1 and 3 are designated by the same reference numerals, and redundant description will be omitted. FIG. 9 is a schematic view showing the overall configuration of a magnetic field measuring device (magnetocardiography) in which a reference magnetic sensor and a detection result display device are installed outside the MSR.

A detection result display device 53 is arranged outside the MSR2, a detection signal created by the arithmetic unit 9 is input, and the detection result display device 53 displays or hides the detection result based on the detection signal. ..

As the detection result display device 53, an indicator light, an alarm, and a buzzer can be used. It is desirable that the detection result display device 53 be installed at a position that is easy for the operator to check (the upper part of the wall surface of the room or the upper part of the outer wall surface of the MSR). Multiple installations may be made.

For example, the detection result display device 53 issues an alarm in a time zone (see FIG. 6) when the detection signal 23 outputs 1, and the operator avoids that time zone and starts measurement. This makes it possible to perform magnetocardiographic measurement while avoiding the time zone when the environmental magnetic field is generated.

1: Magnetometer 2: Magnetic shield room (MSR) 3: Magnetic sensor 4: Cryostat 5: Gantry, 6: Bed, 7: Drive circuit, 8: Amplifier filter unit, 9: Computing device, 10: Display Device, 12: magnetic sensor array, 15: reference magnetic sensor, 16: drive circuit, 17: amplifier filter unit, 53: detection result display device.

Claims (7)

Magnetic shield room and
The magnetic sensor arranged inside the magnetic shield room and
A reference magnetic sensor located outside the magnetically shielded room,
It has an arithmetic device for inputting magnetic field time series data from the magnetic sensor and environmental magnetic field time series data from the reference magnetic sensor.
The arithmetic unit performs threshold processing on the estimated environmental magnetic field time series data inside the magnetic shield room estimated from the environmental magnetic field time series data to create a detection signal.
The estimated environmental magnetic field time-series data is obtained so as to minimize a predetermined evaluation function of the magnetic field time-series data and the estimated environmental magnetic field time-series data, and in obtaining the estimated environmental magnetic field time-series data. The magnetic field reduction effect for each frequency of the magnetic shield room, the magnetic field reduction effect based on the structure of the magnetic sensor, and the magnetic field reduction effect of the analog filter added to the output of the magnetic sensor are applied to the environmental magnetic field time series data. Magnetic field measuring device. Magnetic shield room and
The magnetic sensor arranged inside the magnetic shield room and
A reference magnetic sensor located outside the magnetically shielded room,
It has an arithmetic device for inputting magnetic field time series data from the magnetic sensor and environmental magnetic field time series data from the reference magnetic sensor.
The arithmetic unit performs threshold processing on the estimated environmental magnetic field time series data inside the magnetic shield room estimated from the environmental magnetic field time series data to create a detection signal.
The estimated environmental magnetic field time-series data is obtained so as to minimize a predetermined evaluation function of the magnetic field time-series data and the estimated environmental magnetic field time-series data, and in obtaining the estimated environmental magnetic field time-series data. The magnetic field reduction effect for each frequency of the magnetic shield room is applied to the environmental magnetic field time series data, and the magnetic field reduction effect is applied.
The magnetic sensor is a superconducting magnetic sensor that detects a magnetic field component of one axis.
The reference magnetic sensor is a room temperature magnetic sensor that detects magnetic field components of a plurality of axes.
The predetermined evaluation function is a magnetic field measuring device represented as the sum of the differences between the magnetic field time series data and the estimated environmental magnetic field time series data for each of the plurality of axes weighted. Magnetic shield room and
The magnetic sensor arranged inside the magnetic shield room and
A reference magnetic sensor located outside the magnetically shielded room,
An arithmetic unit for inputting magnetic field time series data from the magnetic sensor and environmental magnetic field time series data from the reference magnetic sensor, and
It has a detection result display device and
The arithmetic unit performs threshold processing on the estimated environmental magnetic field time series data inside the magnetic shield room estimated from the environmental magnetic field time series data to create a detection signal.
The estimated environmental magnetic field time-series data is obtained so as to minimize a predetermined evaluation function of the magnetic field time-series data and the estimated environmental magnetic field time-series data, and in obtaining the estimated environmental magnetic field time-series data. The magnetic field reduction effect for each frequency of the magnetic shield room is applied to the environmental magnetic field time series data, and the magnetic field reduction effect is applied.
The detection result display device is a magnetic field measuring device that notifies the generation of an environmental magnetic field inside the magnetically shielded room based on the detection signal. In claim 3 ,
The detection result display device is a magnetic field measuring device that is at least one of an indicator lamp, an alarm, and a buzzer. Magnetic shield room and
The magnetic sensor arranged inside the magnetic shield room and
A reference magnetic sensor located outside the magnetically shielded room,
An arithmetic unit for inputting magnetic field time series data from the magnetic sensor and environmental magnetic field time series data from the reference magnetic sensor, and
Has a display device and
The arithmetic unit performs threshold processing on the estimated environmental magnetic field time series data inside the magnetic shield room estimated from the environmental magnetic field time series data to create a detection signal.
The estimated environmental magnetic field time-series data is obtained so as to minimize a predetermined evaluation function of the magnetic field time-series data and the estimated environmental magnetic field time-series data, and in obtaining the estimated environmental magnetic field time-series data. The magnetic field reduction effect for each frequency of the magnetic shield room is applied to the environmental magnetic field time series data, and the magnetic field reduction effect is applied.
The display device is a magnetic field measuring device that displays the magnetic field time series data, the estimated environmental magnetic field time series data, and the detection signal. In claim 5 ,
The display device is a magnetic field measuring device that can discriminately display changes in the detection signal on the magnetic field time series data. In claim 5 ,
The display device has a setting screen for the arithmetic unit to obtain the estimated environmental magnetic field time series data.
A magnetic field measuring device that displays the frequency characteristics of the magnetic shield rate of the magnetic shield room on the setting screen.

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