JP2020008304A - Magnetic field measurement device - Google Patents

Abstract

To detect whether there was generated an environmental magnetic field affecting measurement of a magnetic field measurement device inside a magnetic shield room (MSR) using a magnetic sensor for reference outside the MSR.SOLUTION: A magnetic field measurement device comprises an MSR 2, a magnetic sensor 3 provided inside the MSR, a magnet sensor 15 for reference provided outside the MSR, and an arithmetic device 9 to which magnetic field time-series data from the magnetic sensor and environmental magnetic field time-series data from the magnetic sensor for reference are input. The arithmetic device creates a detection signal by subjecting estimated environmental magnetic field time-series data inside the MSR estimated from the environmental magnetic time-series data to threshold value processing (107). The estimated environmental magnetic field time-series data is calculated so as to minimize prescribed evaluation functions of the magnetic field time-series data and the estimated environmental magnetic field time-series data. When the estimated environmental magnetic field time-series data is calculated, a magnetic field reduction effect per MSR frequency is applied to the environmental magnetic field time-series data (103).SELECTED DRAWING: Figure 4

Description

  The present invention relates to 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 whether an environmental magnetic field is generated using the approximate value. About.

  2. Description of the Related Art A magnetocardiograph has been developed as a magnetic field measurement device that measures a weak magnetic field from a measurement target of a subject and non-invasively evaluates the electrophysiological activity of the measurement target. The magnetocardiograph is a device that non-contactly measures a weak magnetic field (cardiac magnet) generated by a cardiac electromotive force (current dipole) accompanying the electrophysiological activity of the heart. Evaluation with excellent resolution is possible. An image of the temporal change and spatial distribution of the magnetocardiogram is called a magnetocardiogram. Because the permeability in the living body is almost equal to vacuum, the magnetocardiogram is less susceptible to the surrounding organs (bones, lungs, etc.) than the electrocardiogram, and reflects the current associated with the electrophysiological activity of the heart with high sensitivity I do. Taking advantage of the advantages of the magnetocardiogram, many clinical effectiveness of the magnetocardiogram have been shown.

  In order to accurately and stably realize the evaluation of the electrophysiological activity of the heart by the magnetocardiography, it is necessary to sufficiently reduce the environmental magnetic field mixed in the magnetocardiogram. The intensity of the magnetocardiogram is very weak, the intensity of the QRS wave (wave reflecting the electrical activity of the ventricle) of an adult is several tens of pT, and the intensity of the P wave (wave reflecting the electrical activity of the atria) 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 a dc magnetic field of the earth magnetism, a magnetic field caused by a transmission / return current of a train, a magnetic field generated by moving an object made of a magnetic material such as an automobile, an elevator and an iron door, and a current of a transmission line. There are a magnetic field, a magnetic field generated by a rotating body of a fan and a pump, and the like. The environmental magnetic field is much larger than the magnetocardiogram. For example, the DC magnetic field of the geomagnetism is about 50 μT (more than about 1,000,000 times the magnetocardiogram), and the fluctuation width of the magnetic field due to the transmission and return current of the train is 50 m from the orbit. It is reported to be 1.4 μT at the point. In order to reduce these environmental magnetic fields mixed in the magnetocardiograph, the magnetocardiograph usually includes a magnetically shielded room (MSR), a gradiometer of a magnetic sensor unit, an analog filter (High pass). An environmental magnetic field reduction technology such as a filter: HPF, a low pass filter (LPF), and a digital filter is mounted 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 a “reduction method”) that estimates and removes an approximate value of an environmental magnetic field signal in a biomagnetic measurement device from an environmental magnetic field signal measured by a 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 into the magnetocardiograph, there is a method of detecting the presence or absence of an environmental magnetic field that affects the magnetocardiogram inspection and notifying the user of the detection state. Specifically, an environmental magnetic field is measured outside the MSR using a magnetic field measuring device, an environmental magnetic field equal to or higher than a certain threshold is detected, a detected signal is output, and a display is performed based on the detected signal. The display based on the detection signal is connected to a display device (indicator lamp, alarm and buzzer) and a magnetocardiograph, and notifies a user whether or not an environmental magnetic field is generated. The user confirms the presence or absence of an environmental magnetic field using the display device and the magnetocardiograph, conducts a magnetocardiogram 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 To reduce the influence of the environmental magnetic field on the magnetocardiogram inspection.

JP-A-2006-217930

  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 determined. It is desirable to analyze the obtained data.

  The environmental magnetic field measured by the magnetocardiograph inside the MSR is reduced by various environmental magnetic field reduction techniques (MSR, gradiometer of magnetic sensor unit, analog filter, and digital filter). These environmental magnetic field reduction techniques have different reduction effects on 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 magnetocardiograph inside the MSR are different, 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 does not always coincide with the presence / absence of the environmental magnetic field affecting the magnetocardiogram inspection.

  A magnetic field measuring apparatus according to one embodiment of the present invention includes an MSR, a magnetic sensor disposed inside the MSR, a reference magnetic sensor disposed outside the MSR, magnetic field time-series data from the magnetic sensor, An arithmetic unit to which environmental magnetic field time-series data from the reference magnetic sensor is input, wherein 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 generate 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 the estimated environmental magnetic field time series data Is applied to the environmental magnetic field time series data, the magnetic field reduction effect for each frequency of the MSR is applied.

  Using a reference magnetic sensor outside the MSR, the presence or absence of an environmental magnetic field that affects the measurement of the magnetic field measurement device inside the MSR can be detected.

  Other problems and novel features will be apparent from the description of this specification and the accompanying drawings.

It is the schematic which shows the whole structure of a magnetocardiograph. It is a figure showing an example of arrangement of a magnetic sensor and arrangement with respect to a subject. FIG. 1 is a schematic diagram illustrating an entire configuration of a magnetocardiograph according to a first embodiment. It is a figure which shows the processing flow which detects presence / absence of an environmental magnetic field using a reference magnetic sensor. (A) Environmental magnetic field waveform from a train measured by a magnetocardiograph (the channel of the maximum magnetic field strength), (b) Environmental magnetic field waveform from a train measured by a three-axis fluxgate magnetometer outside the MSR, (c) this implementation It is the environmental magnetic field waveform from the electric train by the magnetocardiograph estimated by applying the processing flow of the example. (A) is a waveform of a detection signal created by applying the processing flow of the present embodiment, and (b) is an environmental magnetic field waveform (a channel of the maximum magnetic field intensity) from a train measured by a magnetocardiograph. It is a figure showing an example of a display screen which displays a measurement result of a magnetocardiograph. It is a figure which shows an example of the display screen which sets the reduction effect of the environmental magnetic field of a magnetocardiograph. FIG. 7 is a schematic diagram illustrating the entire configuration of a magnetocardiograph according to a second embodiment.

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

  FIG. 1 is a schematic diagram showing the overall configuration of a magnetic field measuring device (magnetocardiograph). The components of the magnetocardiograph 1 are arranged separately inside and outside the MSR 2. The MSR 2 has, for example, a length of about 3 m on each side, and a plurality of SQUID magnetometers 3 (hereinafter, referred to as “magnetic sensors”) are arranged inside the MSR 2 to maintain the temperature at a very low temperature. A cryostat 4, a gantry 5 holding the cryostat 4, and a bed 6 on which a subject (not shown) lie down 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 up and down (C direction, z direction) of the bed 6. And the positioning of the subject and the plurality of magnetic sensors can be easily performed.

  Outside the MSR 2, a drive circuit 7 for driving the magnetic sensor 3 disposed in the cryostat 4, an amplifier filter unit 8 for amplifying and filtering an output from the drive circuit 7, and an output from the amplifier filter unit 8 An arithmetic unit 9 that collects signals, analyzes the collected data (hereinafter referred to as “magnetic field time series data”) and controls each unit of the magnetocardiograph 1, and an analysis result analyzed by the arithmetic unit 9 Is mainly disposed.

  The magnetic sensor 3 of the magnetocardiograph 1 is not limited to the SQUID magnetometer, but may be a sensor using a magnetoresistive element, an optical pumping magnetometer, a fluxgate magnetometer, or a magnetic sensor using a magnetic impedance element. Can be. The magnetic field generated from the heart is very weak (0.1 to several tens pT), and the noise level of the magnetic sensor of the magnetocardiograph is desired to be several pT / √Hz or less. Further, the frequency band of the magnetic sensor of the magnetocardiograph is desired to be DC to several hundred Hz similarly to the frequency band of the electrical activity of the heart.

An example of an arrangement of the magnetic sensor array used in the magnetocardiograph 1 and an arrangement with respect to a 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 at the bottom of the cryostat 4 (see FIG. 1), and generate a magnetic field component _Bz in the z direction perpendicular to the chest wall 11 of the subject. Measure over time. The plurality of magnetic sensors are arranged at equal intervals in the x direction and the y direction so that the distance change amount of the magnetic field can be accurately detected. It is also possible to apply the magnetic sensor over time measure the magnetic field component B _y of the magnetic field components B _x and y directions parallel x-direction relative to the chest wall 11.

  In the example of FIG. 2, the distance between the magnetic sensors is 0.025 m, the measurement surface is 0.175 m × 0.175 m, and the magnetic sensor array 12 of 64 channels in which the magnetic sensors are arranged in an 8 × 8 array. Is shown. 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 seventh row and the third column indicated by the reference numeral 13 is located directly above the swordlike protrusion 14 on the chest. Do. The magnetic sensor in the first row and the eighth column is defined as the origin O of the coordinate system.

  First Embodiment As a first embodiment, a description will be given of a magnetic field measuring device that detects the presence or absence of an environmental magnetic field using a reference magnetic sensor installed outside the MSR 2. The same components as those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. FIG. 3 is a schematic diagram showing the overall configuration of a magnetic field measuring device (cardiac magnetometer) in which a reference magnetic sensor is installed outside the MSR.

  A three-axis fluxgate magnetometer 15 (hereinafter, referred to as a “reference magnetic sensor”) for measuring an environmental magnetic field, a drive circuit 16 for driving the reference magnetic sensor, and an output from the drive circuit 16 are provided outside the MSR 2. An amplifier filter unit 17 that amplifies and filters the signal is arranged, and an 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 element or a magnetic sensor using a sensor using a magnetic impedance element can be applied. The reference magnetic sensor 15 is installed in a place where there is no source of an environmental magnetic field (such as an electric device or a cancel coil of an active magnetic cancel system) around the outside of the MSR. The difference between the position of the magnetic sensor array 12 of the magnetocardiograph 1 and the position of the reference magnetic sensor 15 is negligible in terms of the magnetic field strength from the position of the source of the environmental magnetic field. even only observed magnetic field component B _z of the z direction of the magnetic sensor of the magnetometer 1, environmental magnetic components in three axes (the magnetic field components B _x, the magnetic field component B _y, the magnetic field component B _z) by correcting by, The influence of the environmental magnetic field on the magnetic sensor of the magnetocardiograph 1 can be obtained more accurately. Of course, the present invention is applicable even when the number of axes of the reference magnetic sensor 15 is one or two. Further, a plurality of reference magnetic sensors 15 may be used.

  FIG. 4 shows a flowchart of the environmental magnetic field detection processing procedure using the reference magnetic sensor 15 outside the MSR 2. First, the process is started (101), and magnetic field time-series data generated from the subject's heart (hereinafter, referred to as “cardiac magnetic field time-series data”) using a magnetocardiograph (see FIG. 3) and a reference magnetic field outside the MSR2. Using the sensor 15, time series data of the environmental magnetic field (hereinafter, referred to as “environmental magnetic field time series data”) is simultaneously measured (102).

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

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

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

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

Next, the magnetic field reduction effect of the magnetic sensor (gradiometer structure) of the magnetocardiograph is applied to the environmental magnetic field time-series data to which the magnetic field reduction effect of the MSR has been applied (104). The gradiometer structure is a configuration in which a magnetic flux detected by a differential detection coil made of a superconducting wire is transmitted to a SQUID magnetometer. By using the differential detection coil, the spatial gradient of the magnetic field can be detected, and the uniform environmental magnetic field can be reduced. The magnetic field reduction rate D _g by this gradiometer can be considered as a constant independent of frequency, unlike the magnetic field reduction effect of the MSR described above. Therefore, multiplying the time-series data x '(t) in the magnetic field reduction ratio D _g gradiometer environmental magnetic field to which the magnetic field reduction effect of MSR obtained in process 103 (5) that the magnetic field reduces the gradiometer 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 filter (HPF and LPF) of the magnetocardiograph is applied to the environmental magnetic field time-series data to which the magnetic field reduction effect of the magnetic sensor has been applied (105). Specifically, it can be obtained by applying a digital filter similar in filter type and filter order to the analog filter of the magnetocardiograph to the time-series data x ″ (t) of the environmental magnetic field obtained in the processing 104. For example, when an FIR (Finite Impulse Response) filter is used as a digital filter, 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, the a _m is the filter coefficient determined from the filter type and filter order.

  The signals obtained by the above-described processes 103 to 105 reflect the reduction effect of the environmental magnetic field reduction technique applied to the magnetocardiograph 1, and the estimated values of the environmental magnetic field measured by the magnetocardiograph (hereinafter, referred to as “cardiac magnetometer 1”) Estimated environmental magnetic field "). Next, a weighting coefficient for each channel is calculated for the time-series data of the environmental magnetic field estimated by the magnetocardiograph (106).

This weighting coefficient can be obtained in advance by minimizing the difference between the time series data of the environmental magnetic field estimated by the magnetocardiograph and the environmental magnetic field time series data actually measured in each channel of the magnetocardiograph without a subject. it can. When a three-axis (x-axis, y-axis, and z-axis) magnetic sensor is used as the reference magnetic sensor 15, a weight coefficient vector W (W = [ _Wx , _Wy , _Wz ]) 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 t-th (t = 1 to T) sampling point in the n-th (n = 1 to 64) channel of the magnetocardiograph. I have. 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 x-axis, y-axis, and z-axis reference magnetic sensors. Each represents a magnetic field. Further, W _{x, n} , W _{y, n} and W _{z, n} are relative to the magnetocardiographic estimated environment magnetic field of the x-axis, y-axis, and z-axis reference magnetic sensors in the n-th (n = 1 to 64) channel. Weight coefficients (hereinafter referred to as “weight coefficients for each channel”).

Time-series data of magnetocardiograph estimated environmental magnetic field multiplied by the weighting coefficient for each the channel _{^{(B ref x, t × W}} x, n + B ref y, t × W y, n + B ref z, t × W z, n) , A threshold signal is applied to generate a detection signal (107). As the detection signal, for example, a signal that is 1 when the value is equal to or more than the threshold and 0 when it is less than the threshold can be used. As the threshold value of the threshold value processing, an appropriate value is set depending on a measurement target (for example, an adult and a fetus) and an analysis target (a ventricle and an atrium). As a result, threshold processing according to the magnitude of the cardiac magnetic field to be measured can be performed.

  Finally, the heart magnetic field time series data, the magnetocardiography estimated environmental magnetic field time series data and the detection signal are displayed (108), and the processing is terminated (109).

  In addition, as a frequency analysis method applied to the environmental magnetic field time series data in the process 103, there are a well-known fast Fourier transform method and a periodogram method, and the Fourier spectrum and power spectrum density are calculated, and the frequency of the environmental magnetic field time series data is calculated. Data in the area can be obtained. Processing based on these frequency analysis methods has become feasible with the recent improvement in the processing capability of personal computers. In order to calculate the magnetic field reduction effect for each frequency of the MSR, for example, a catalog value of the magnetic shield ratio of the MSR or actual measurement data acquired in advance can be used. Further, in calculating the magnetic field reduction effect, phase change information for each frequency of the MSR can be used.

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

  In order to calculate the magnetic field reduction effect of the analog filter with respect to the environmental magnetic field time-series data in the process 105, for example, it is possible to use the same type, cutoff frequency, and magnetic field reduction rate obtained from a digital filter of the same order as the analog filter of the magnetocardiograph it can.

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

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

  FIG. 5A shows an environmental magnetic field waveform 18 (a channel having the maximum magnetic field intensity) from a train measured by a 64-channel magnetocardiograph. 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 from a train by a reference magnetic sensor outside the MSR. The horizontal axis is time (seconds) and the vertical axis is magnetic field (μT). When compared with the environmental magnetic field waveform 18 measured by the magnetocardiograph, it can be seen that the environmental magnetic field waveform measured by the reference magnetic sensor outside the MSR has a different waveform pattern.

  FIG. 5C shows a magnetocardiographic estimated environment magnetic field waveform 22 of the same channel as that of FIG. 5A calculated by applying the processing flow shown in FIG. When compared with the environmental magnetic field waveform 18 actually measured by the magnetocardiograph, the estimated magnetic field waveform 22 of the magnetocardiograph was similar to the actually measured waveform 18, 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 represents time (seconds), and the vertical axis represents detection signal intensity (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 the detection signal 23 simultaneously with the magnetocardiogram waveform measured by the magnetocardiograph, it is possible to inform the user of the presence or absence of an environmental magnetic field that affects the magnetocardiogram inspection.

  From the above results, it was shown that the time at which the environmental magnetic field affecting the magnetocardiography was generated in the magnetocardiograph can be accurately detected from the environmental magnetic field signal outside the MSR.

  An interface applied to the magnetic field measurement device according to 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 an environmental magnetic field that affects the magnetocardiogram examination using a reference magnetic sensor external to the MSR. The display screen 24 is displayed on the display device 10 of the magnetocardiograph.

  The display screen 24 of the display device 10 applies the processing flow of FIG. 4 to a magnetocardiograph measurement data display column 25 for displaying a magnetic field signal measured by a magnetocardiograph and an environmental magnetic field measured by a reference magnetic sensor outside the MSR. A magnetic field data display field 26 and a detection data display field 27 are shown.

  A magnetic field signal 28 measured by the magnetocardiograph is displayed in the magnetocardiograph measurement data display column 25. The channel of the magnetic sensor of the magnetocardiograph displayed in the magnetocardiogram measurement data display field 25 can be switched 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 magnetocardiograph estimated environmental magnetic field data display field 26, a magnetocardiographic estimated environmental magnetic field signal 30 calculated by applying the processing flow of FIG. 4 to the environmental magnetic field measured by the reference magnetic sensor outside the MSR is displayed. The channel of the magnetic sensor of the magnetocardiograph displayed in the field 26 for displaying the estimated magnetic field data of the magnetocardiograph is also switched by the channel selection button 29. A signal corresponding to the magnetic sensor of “Channel 1” selected by the channel selection button 29 is displayed as a magnetocardiograph estimated environmental magnetic field signal 30. Further, a threshold value display column 32 for displaying a threshold value applied to the magnetocardiographic estimated environment magnetic field signal 30 is displayed. This threshold value can be set by the operator. Alternatively, a default value of the device may be determined. A first threshold line 33 (a line corresponding to a positive threshold) and a second threshold line 34 (a line corresponding to a negative threshold) corresponding to this threshold are magnetocardiographs. It is displayed in the estimated environmental magnetic field data display field 26.

  In the detection data display column 27, a 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, an environmental magnetic field detection time range 36 is displayed in the magnetocardiograph measurement data display column 25 in correspondence with the time range in which the detection signal 35 outputs 1. The operator can identify the change of the detection signal at a glance together with the magnetic field time-series data, so that the operator can analyze the magnetocardiograph measurement data after grasping the time zone in which 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 an environmental magnetic field that affects the magnetocardiography in accordance with the flow of FIG. 4 using the reference magnetic sensor external to the MSR. It is an example of a display screen. The display screen 37 is displayed on the display device 10 of the magnetocardiograph.

  The display screen 37 of the display device 10 has a frequency characteristic display field 38 of the magnetic shield rate of the MSR that displays the frequency characteristic of the shield rate of the MSR, and a reduction rate of the magnetic sensor that displays the magnetic field reduction rate of the magnetic sensor of the magnetocardiograph. A display field 39, a frequency characteristic display field 40 of the reduction rate of the high-pass filter that displays the frequency characteristic of the reduction rate of the high-pass filter of the amplifier filter unit of the magnetocardiograph, and a frequency characteristic of the reduction rate of the low-pass filter of the amplifier filter unit of the magnetocardiograph are displayed. And a frequency characteristic display column 41 of the reduction rate of the low-pass filter to be displayed.

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

  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 ratio of the MSR. In this case, a phase change information setting column for each frequency is displayed.

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

  In the frequency characteristic display column 40 of the reduction ratio of the high-pass filter, a reduction ratio 45 for each frequency of the high-pass filter is displayed. The reduction rate of each frequency displayed in the frequency characteristic display section 40 of the reduction rate of the high-pass filter is set in a filter type setting section 46 for setting the filter type of the high-pass filter, an order setting section 47 for setting the order of the high-pass filter, a high-pass filter. The value calculated based on the cut-off frequency setting field 48 for setting the cut-off frequency is displayed.

  In the frequency characteristic display column 41 of the reduction rate of the low-pass filter, a 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 field 41 of the reduction rate of the low-pass filter includes a filter type setting field 50 for setting the filter type of the low-pass filter, an order setting field 51 for setting the order of the low-pass filter, a low-pass filter. The value calculated based on the cut-off frequency setting column 52 for setting the cut-off frequency is displayed.

  Second Embodiment As a second embodiment, a magnetic field measuring device that detects the presence or absence of an environmental magnetic field using a reference magnetic sensor installed outside the MSR 2 and notifies the presence or absence of an environmental magnetic field within the MSR 2 using a detection result display device Will be described. 1 and 3 are denoted by the same reference numerals, and redundant description will be omitted. FIG. 9 is a schematic diagram showing the entire configuration of a magnetic field measurement device (cardiac magnetometer) 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 MSR 2, and the detection signal created by the arithmetic device 9 is input, and the detection result display device 53 displays or hides the detection result based on the detection signal. .

  An indicator light, an alarm, and a buzzer can be used as the detection result display device 53. The detection result display device 53 is desirably installed at a position where it is easy for the operator to confirm (upper wall of the room or upper outer wall of the MSR). A plurality may be installed.

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

1: magnetocardiograph, 2: magnetic shield room (MSR), 3: magnetic sensor, 4: cryostat, 5: gantry, 6: bed, 7: drive circuit, 8: amplifier filter unit, 9: arithmetic unit, 10: display Device, 12: magnetic sensor array, 15: magnetic sensor for reference, 16: drive circuit, 17: amplifier filter unit, 53: detection result display device.

Claims (8)

A magnetically shielded room,
A magnetic sensor disposed inside the magnetically shielded room,
Reference magnetic sensor disposed outside the magnetic shield room,
An arithmetic unit to which magnetic field time series data from the magnetic sensor and environmental magnetic field time series data from the reference magnetic sensor are input,
The arithmetic unit creates a detection signal by performing threshold processing on estimated environmental magnetic field time-series data inside the magnetically shielded room estimated from the environmental magnetic field time-series data,
The estimated environmental magnetic field time-series data is determined 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 upon obtaining the estimated environmental magnetic field time-series data, A magnetic field measuring apparatus, wherein a magnetic field reduction effect for each frequency of the magnetic shield room is applied to the environmental magnetic field time-series data. In claim 1,
The estimated environmental magnetic field time series data is a magnetic field to which the magnetic field reduction effect based on the structure of the magnetic sensor and the magnetic field reduction effect of an analog filter added to the output of the magnetic sensor are further applied to the environmental magnetic field time series data. Measuring device. In claim 1,
The magnetic sensor is a superconducting magnetic sensor that detects a uniaxial magnetic field component,
The reference magnetic sensor is a room-temperature magnetic sensor that detects magnetic components of a plurality of axes,
The magnetic field measurement device, wherein the predetermined evaluation function is represented as a sum of 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. In claim 1,
Having a detection result display device,
The magnetic field measurement device, wherein the detection result display device notifies the occurrence of an environmental magnetic field inside the magnetically shielded room based on the detection signal. In claim 4,
The detection result display device is a magnetic field measurement device that is at least one of an indicator light, an alarm, and a buzzer. In claim 1,
Having a display device,
The display device is a magnetic field measurement device that displays the magnetic field time series data, the estimated environmental magnetic field time series data, and the detection signal. In claim 6,
The magnetic field measuring device, wherein the display device displays a change in the detection signal on the magnetic field time-series data in a distinguishable manner. In claim 6,
The display device has a setting screen for the arithmetic device to determine the estimated environmental magnetic field time-series data,
A magnetic field measuring device for displaying a frequency characteristic of a magnetic shield rate of the magnetic shield room on the setting screen.

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