JP2001112731A - Magnetic field measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic field measuring method capable of accurately canceling interfering magnetic fields. SOLUTION: A first SQUID fluxmeter 9 for detecting magnetic field components in a normal direction and a second SQUID fluxmeter 10 for detecting interfering magnetic fields in the normal direction are provided. First signal processing is performed in which signals produced by the second SQUID fluxmeter and signals produced by the first SQUID fluxmeter are used and the interfering magnetic fields are canceled from mixed magnetic fields by the method of least squares, and second signal processing is performed in which a waveform B (t) representative of variation in the interfering magnetic field with time (t) is approximated by B (t)=-A.t2.exp (-t/T), in the vicinity of initial time when the occurrence of the interfering magnetic fields starts; using the magnetic field waveform produced through the first signal processing, amplitude A and a time constant T are determined by the method of least squares; and using B (t) produced by the method of least squares, the interfering magnetic fields resulting from a frequency characteristic are canceled from the magnetic field waveform produced by the first signal processing. The interfering magnetic fields resulting from the frequency characteristic of a shielded room are canceled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SQUID (Super) which is a superconducting device for detecting a biomagnetic field such as a cardiac magnetic field or a brain magnetic field, a geomagnetic field, or a weak magnetic field such as a nondestructive test.
conducting Quantum Interf
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field measuring device using a flux meter, and more particularly to a magnetic field measuring method for canceling a disturbing magnetic field and a magnetic field measuring device. More specifically, the present invention relates to a signal processing method for canceling a disturbance magnetic field.

[0002]

2. Description of the Related Art In the measurement of a weak magnetic field by a magnetic field measuring device using SQUID, 40 to 50 dB (decibel) is used.
The measurement of a weak cerebral magnetic field, a heart magnetic field, and the like is performed inside the magnetically shielded room having the above-described magnetic field attenuation rate. As a detection coil for detecting a biomagnetic field, a primary differential detection coil for detecting a difference between a one-turn detection coil and a coil wound in the opposite direction is often used. The primary differential detection coil cancels the disturbing magnetic field from a distant magnetic field source,
A magnetic field generated from the vicinity of the heart, the brain, and the like has a characteristic that a signal can be detected without large cancellation, and the influence of a disturbing magnetic field can be easily reduced. Usually, the first-order differential detection coil is about 40 dB to 50 for a uniform magnetic field.
It has an attenuation of dB.

[0003] As described above, by combining the magnetic shield room and the first-order differential detection coil, the interference magnetic field can be canceled by about 80 dB to 100 dB or more. However, when an object that generates a large magnetic field, such as a train or a car, passes about 50 m to 100 m from the magnetically shielded room, an interfering magnetic field that is tens of times larger than the magnetic field generated from a living body is observed. Various methods have been attempted in order to cancel the above-mentioned disturbing magnetic field having a large intensity.

For example, using a signal of a magnetic field detected from a flux gate disposed outside a magnetic shield room, a feedback current is caused to flow through a cancel coil wound around the magnetic shield room, and the output of the flux gate becomes zero. (Prior Art 1: Meas. Sci. Technol.
Vol. 2, pp. 596-601 (1991)).

[0005] In addition, a method of softly canceling using a signal of a reference coil using a SQUID sensor (prior art 2: Clin. Phys. Physio)
l. Meas. , Vol. 12, Suppl. B, p
p. 81-86 (1991)), but the details of the reference coil are not mentioned.

Japanese Patent Application Laid-Open No. 11-47108 (Prior Art 3) describes a biomagnetic field measuring apparatus for reducing an error in removing environmental magnetic field noise caused by a coil balance disorder. JP-A-11-47108 discloses the following. Several coils that artificially generate an extraneous magnetic field
For example, it is mounted at a known position on the outer peripheral surface of the dure. Driving is performed by supplying a driving current to a plurality of coils. The sensitivity and the coil balance of the detection coil are measured with high accuracy using the detection value of the detection coil and the drive current value for the external magnetic field generated from the plurality of coils. The effect of the coil imbalance is corrected with high accuracy from the measured values of the biomagnetic field obtained from the detection values of the detection coil, and as a result, the error in removing the environmental magnetic field noise caused by the coil imbalance is reduced, and the biomagnetic field is reduced. Measurement accuracy has been improved. In the vacuum insulated container, a plurality of detection coils for measuring a biomagnetic field, which mainly measure a biomagnetic field, are arranged on a side close to the subject, and at a position further away from the subject than the detection coil, A plurality of reference coils for mainly measuring the environmental magnetic field are arranged.

Japanese Unexamined Patent Application Publication No. 11-83965 (prior art 4) discloses an environmental magnetic field canceling system capable of measuring a weak magnetic field from an object accurately and with high accuracy without being affected by environmental magnetic fields in different frequency bands. A magnetic measurement device is described. JP-A-11-83965 has the following description. Environmental magnetic fields having different magnetic field strengths and frequency bands are detected by a plurality of SQUID magnetometers for measuring environmental magnetic fields having different dynamic ranges and slew rates, and electric signals corresponding to the environmental magnetic fields are measured. A reverse magnetic field is generated via a pair of active shield coils based on the added electric signal obtained by adding the measured electric signals, or the electric signal is added from the magnetic signal measured by the SQUID magnetometer for magnetic measurement. By subtracting the signal, environmental magnetic fields having different magnetic field strengths and frequency bands can be canceled.

Japanese Unexamined Patent Application Publication No. 9-84777 (Prior Art 5) describes a biomagnetic field measuring apparatus capable of accurately estimating a deep current dipole even when a plurality of current dipoles overlap in the depth direction. Have been. JP-A-9-84777 has the following description. A pickup coil that detects magnetic flux from a biological magnetic field source
A pickup coil array is used in which a plurality of types of pickup coils different in at least one of the differential order and the base line are arranged in combination.

[0009]

In the prior art 1, the output of the flux gate disposed outside the magnetically shielded room becomes zero by supplying a feedback current to the cancel coil disposed outside the magnetically shielded room. Therefore, in a multi-channel magnetic field measuring apparatus having a SQUID magnetometer composed of a plurality of differential detection coils such as a plurality of primary differential detection coils, the cancellation rate of the differential detection coil in each channel is adjusted. There is a problem that it is difficult to correct the variation.

[0010] In the prior art 2, there is no description about the specific configuration of the reference coil, and only data when no magnetically shielded room is used is shown.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic field measuring device capable of canceling an interference magnetic field with high accuracy, and to provide a cancellation ratio of a differential detection coil in each channel of a multi-channel magnetic field measuring device and a base line. Provided is a magnetic field measuring apparatus capable of canceling a disturbing magnetic field in consideration of variation and removing distortion of a magnetic field waveform caused by frequency characteristics of a magnetic shield room.

[0012]

Means for Solving the Problems Terms used in the following description will be explained.

"Differential detection coil" means a primary differential detection coil or a secondary differential detection coil.

(1) When the differential detection coil is a primary differential detection coil.

(1.1) “Fluxmeter for detection” (first SQ
The UID magnetometer is a first-order differential SQUID magnetometer, and means a magnetometer that detects a z-direction magnetic field component of a disturbing magnetic field and a z-direction magnetic field component of a biological magnetic field generated from a living body.

(1.2) "Compensation magnetometer" (second SQ
UID magnetometer) is a first-order differential SQUID magnetometer, and means a magnetometer that detects a magnetic field component of a disturbing magnetic field in the z direction.

(1.3) "Input coil of detection magnetometer"
Means the first coil arranged at the position closest to the inspection target among the coils constituting the primary differential detection coil constituting the detection magnetometer.

(1.4) "Input coil of compensating magnetometer"
Means the first coil arranged at the position closest to the inspection target among the coils constituting the primary differential detection coil constituting the compensating magnetometer.

(1.5) "Compensation coil of detection magnetometer"
Is located at a position farther from the test object than the first coil and has a surface parallel to the surface of the second coil. 2 coils.

(1.6) "Compensation coil of compensating magnetometer"
Among the coils constituting the primary differential detection coil constituting the compensating magnetometer, the coil arranged at a position farther from the test object than the first coil and having a plane parallel to the plane of the second coil. 2 coils.

(1.7) "Output of detection magnetometer" means the output of the primary differential detection coil constituting the detection magnetometer.

(1.8) “Output of compensating magnetometer” means the output of the primary differential detection coil constituting the compensating magnetometer.

(1.9) "Baseline of magnetic fluxmeter for detection" means the baseline of the primary differential type detection coil constituting the magnetic fluxmeter for detection, the surface of the first coil and the second coil. Is the distance from the plane.

(1.10) “Baseline of compensating magnetometer” means the baseline of the primary differential detection coil constituting the compensating magnetometer, the surface of the first coil and the second coil. Is the distance from the plane.

(2) When the differential detection coil is a secondary differential detection coil.

(2.1) "Detection magnetometer" (first SQ
The UID magnetometer is a second-order differential SQUID magnetometer, and refers to a magnetometer that detects a z-direction magnetic field component of a disturbing magnetic field and a z-direction magnetic field component of a biological magnetic field generated from a living body.

(2.2) “Compensation magnetometer” (second SQ
The UID magnetometer is a second-order differential SQUID magnetometer, and means a magnetometer that detects a magnetic field component of a disturbing magnetic field in the z direction.

(2.3) "Input coil of detection magnetometer"
Means the first coil arranged at the position closest to the inspection target among the coils constituting the secondary differential detection coil constituting the detection magnetometer.

(2.4) "Input coil of compensating magnetometer"
Means the first coil arranged at the position closest to the inspection target among the coils constituting the secondary differential detection coil constituting the compensating magnetometer.

(2.5) "Compensation coil of detection magnetometer"
Are sequentially arranged at positions farther from the object to be inspected than the first coil, and have a surface parallel to the surface of the second coil. Mean second, third and fourth coils. In the present invention, the area of the second coil is equal to the area of the coil of the third coil.

(2.6) "Compensation coil of compensating magnetometer"
Among the coils constituting the secondary differential detection coil constituting the compensating magnetometer, are sequentially arranged at positions farther from the inspection object than the first coil, and have a surface parallel to the surface of the second coil. Mean second, third and fourth coils. In the present invention, the area of the second coil is equal to the area of the coil of the third coil.

(2.7) “Output of detection magnetometer” means the output of the secondary differential detection coil constituting the detection magnetometer.

(2.8) "Output of compensating magnetometer" means the output of the secondary differential detection coil constituting the compensating magnetometer.

(2.9) "Baseline of magnetic fluxmeter for detection" means the baseline of the secondary differential type detection coil constituting the magnetic fluxmeter for detection, and the surface of the first coil and the second coil And the distance between the surface of the third coil and the surface of the fourth coil. In the present invention, the distance between the surface of the first coil and the surface of the second coil is equal to the distance between the surface of the third coil and the surface of the fourth coil.

(2.10) "Baseline of compensating magnetometer" means the baseline of the secondary differential detection coil which constitutes the compensating magnetometer, the surface of the first coil and the second coil. And the distance between the surface of the third coil and the surface of the fourth coil. In the present invention, the distance between the surface of the first coil and the surface of the second coil is equal to the distance between the surface of the third coil and the surface of the “fourth coil”. .

In the configuration of the magnetic field measuring apparatus of the present invention, the magnetic field measuring apparatus comprises a differential detection coil (primary differential detection coil or secondary differential detection coil), and detects a plurality of interference magnetic fields and magnetic fields generated from a living body. And one or a plurality of SQUID magnetometers (second SQUID magnetometers) for detecting an interfering magnetic field, each of the SQUID magnetometers comprising a SQUID magnetometer and a differential detection coil (primary or secondary differential detection coil). ) Is disposed inside the cryostat, and a cryogenic refrigerant such as liquid helium or liquid nitrogen is stored inside the cryostat, or a refrigerator is disposed. The cryostat is held in the gantry.

The baseline of the differential detection coil of the second SQUID magnetometer is made shorter than the baseline of the differential detection coil of the first SQUID magnetometer. The emitted magnetic field is not detected.

Using the signal of the disturbing magnetic field detected by the second SQUID magnetometer and the signal of the mixed magnetic field obtained by mixing the magnetic field emitted from the living body and the disturbing magnetic field detected by the first SQUID magnetometer. , An optimal fitting parameter is obtained by applying the least square method, and the interference magnetic field is canceled (removed) from the detected mixed magnetic field (first interference magnetic field cancellation method).

The remaining disturbing magnetic field which cannot be canceled by the above-described first disturbing magnetic field canceling method, that is, the disturbing magnetic field caused by the frequency characteristic of the magnetically shielded room is converted into the time of the magnetic field shown by (Equation 1). The amplitude A and the time constant T are determined by the least squares method by approximating the change with a theoretical waveform, and the disturbance magnetic field is removed.

[0040]

B (t) = − A · t ² · exp (−t / T) (Equation 1) Note that the prior arts 1 to 5 detect the disturbing magnetic field, which is a feature of the present invention. A configuration in which the baseline of the differential detection coil of the second SQUID magnetometer for detecting the biomagnetic field is shorter than the baseline of the differential detection coil of the first SQUID magnetometer for detecting the biomagnetic field. The configuration using a plurality of second SQUID magnetometers having the type detection coil and the configuration for canceling the disturbing magnetic field generated due to the frequency characteristics of the magnetically shielded room are as follows.
Not disclosed.

The first configuration of the magnetic field measuring apparatus according to the present invention comprises a plurality of first SQUID magnetometers for detecting a magnetic field in a normal direction generated from an object to be inspected and a second SQUID magnetometer for detecting a magnetic field in a normal direction. SQUID magnetometer and first and second SQUIDs
A cryogenic container for cooling the D magnetometer, and first and second SKUs
Driving circuit for driving the ID magnetometer, first and second SQs
A computer for collecting signals detected by the UID magnetometer and performing signal processing; and display means for displaying the result of the signal processing, wherein the first and second SQUID magnetometers are differential detectors having a compensation coil. A first differential detection coil or a second differential detection coil, and the length of the baseline of the differential detection coil of the second SQUID magnetometer is the first.
Is shorter than the base line length of the differential detection coil of the SQUID magnetometer.

In the first configuration of the present invention, (1) a magnetic field in a normal direction generated from an inspection target is detected inside a magnetic shield room, and one or more second SQUID magnetometers are provided. The computer calculates the signal of the interfering magnetic field detected by the second SQUID magnetometer and the signal of the mixed magnetic field in the normal direction where the magnetic field emitted from the living body and the interfering magnetic field are detected by the first SQUID magnetometer. The first signal processing for applying the least squares method to cancel the disturbing magnetic field from the mixed magnetic field, and the initial time when the generation of the disturbing magnetic field caused by the frequency characteristics of the magnetically shielded room starts. , The waveform B (t) representing the waveform of the disturbing magnetic field generated due to the frequency characteristic is represented by A, the time constant T,
Assuming that a time variable is t, B (t) = − A · t ² · exp
Using the magnetic field waveform obtained by the first signal processing approximated by (−t / T), the amplitude A and the time constant T are obtained by the least square method, and B determined by the least square method.
Using (t) to execute a second signal processing for canceling a disturbing magnetic field generated due to the frequency characteristic from a magnetic field waveform obtained by the first signal processing;
(2) The computer estimates the initial time, and the estimated initial time is displayed on the time axis of the magnetic field waveform from which the disturbing magnetic field has been canceled by the first and second signal processing. (3)
Another feature is that the area of the input coil of the differential detection coil of the second SQUID magnetometer is larger than the area of the input coil of the differential detection coil of the first SQUID magnetometer.

A second configuration of the magnetic field measuring apparatus according to the present invention comprises a plurality of first SQUID magnetometers for detecting a magnetic field in a normal direction generated from an object to be inspected inside a magnetically shielded room, A second SQUID magnetometer for detecting an interfering magnetic field, a low-temperature container for cooling the first and second SQUID magnetometers, a drive circuit for driving the first and second SQUID magnetometers, And a computer for collecting signals detected by the second SQUID magnetometer and performing signal processing, and display means for displaying a result of the signal processing. The first and second SQUID magnetometers each include a compensation coil. Having a differential detection coil (a primary differential detection coil and a secondary differential detection coil), and the base line length of the differential detection coil of the second SQUID magnetometer is equal to the first SQUID magnetic flux. Differential detection coil Is shorter than the base line length of the first SQUID magnetometer, the computer calculates the difference in the cancellation rate between the first SQUID magnetometers from the magnetic field waveform in the normal direction obtained by the plurality of first SQUID magnetometers. Signal processing (b) for canceling the disturbing magnetic field and signal processing (b) for canceling the disturbing magnetic field generated due to the frequency characteristics of the magnetically shielded room from the magnetic field waveform obtained by the signal processing (a) Is performed.

In the second configuration of the present invention, (1) the computer estimates an initial time at which the generation of the disturbing magnetic field generated due to the frequency characteristic starts, and the estimated initial time is used for signal processing. (B) the disturbing magnetic field is displayed on the time axis of the canceled magnetic field waveform according to (b).
Another feature is that the area of the input coil of the differential detection coil of the SQUID magnetometer is larger than the area of the input coil of the differential detection coil of the first SQUID magnetometer.

A third configuration of the magnetic field measuring apparatus according to the present invention comprises a plurality of first SQUID magnetometers for detecting a magnetic field in a normal direction generated from an object to be inspected inside a magnetic shield room; Second and third S for detecting disturbing magnetic field
QUID magnetometer and first, second, and third SQUID
A cryogenic vessel for cooling the magnetometer, a driving circuit for driving the first, second, and third SQUID magnetometers;
And a computer for collecting signals detected by the third SQUID magnetometer and performing signal processing, and display means for displaying a result of the signal processing, and the first, second, and third SQs are provided.
The UID magnetometer has a differential detection coil (1
Secondary differential detection coil, secondary differential detection coil)
The length of the baseline of the differential detection coil of the second and third SQUID magnetometers is shorter than the length of the baseline of the differential detection coil of the first SQUID magnetometer, and the second SQUID flux is The length of the baseline of the differential detection coil of the meter is shorter than the length of the baseline of the differential detection coil of the third SQUID magnetometer, and the computer obtains the data using the plurality of first SQUID magnetometers. Signal processing (a) for canceling the disturbing magnetic field caused by the difference in the cancellation rate between the first SQUID magnetometers from the obtained magnetic field waveform in the normal direction, and the magnetic field waveform obtained by the signal processing (a) The signal processing (b) cancels the disturbing magnetic field caused by the difference between the baseline of the differential detection coil of the second SQUID magnetometer and the baseline of the differential detection coil of the third SQUID magnetometer. If, from the resulting magnetic field waveform by the signal processing (b), and performing a signal processing for canceling the interfering magnetic field is generated due to the frequency characteristics of the magnetically shielded room (c).

In the third configuration of the present invention, (1) the computer estimates an initial time at which generation of a disturbing magnetic field generated due to frequency characteristics starts, and the estimated initial time is used for signal processing. (A), (b), and (c) that the disturbing magnetic field is displayed on the time axis of the canceled magnetic field waveform.
(2) The area of the input coil of the differential detection coil of the second and third SQUID magnetometers is larger than the area of the input coil of the differential detection coil of the first SQUID magnetometer. There is also a feature.

A fourth configuration of the magnetic field measuring apparatus according to the present invention comprises a plurality of first SQUID magnetometers for detecting a magnetic field in a normal direction generated from an inspection object in an electromagnetic shield room for blocking high-frequency electromagnetic waves. A plurality of second SQUID magnetometers for detecting a disturbing magnetic field in the normal direction, and first and second SQUID magnetometers;
A cryogenic container for cooling the QUID magnetometer, a drive circuit for driving the first and second SQUID magnetometers, and a cancel coil arranged to sandwich the test object from above and below to generate a magnetic field in the normal direction for canceling the disturbing magnetic field Control means for controlling a current flowing through the cancel coil, and a computer for collecting signals detected by the first and second SQUID magnetometers and performing signal processing, and the first and second SQUIDs are provided.
The ID magnetometer has a differential detection coil having a compensation coil (primary differential detection coil, secondary differential detection coil), and the length of the baseline of the differential detection coil of the second SQUID magnetometer. Is shorter than the base line length of the differential detection coil of the first SQUID magnetometer, and the control means outputs the current flowing through the cancel coil to the output of one SQUID magnetometer of the plurality of second SQUID magnetometers. , And the cancel coil generates a magnetic field in a normal direction opposite to the disturbing magnetic field.

In the fourth configuration of the present invention, (1) the second
That the area of the input coil of the differential detection coil of the SQUID magnetometer is larger than the area of the input coil of the differential detection coil of the first SQUID magnetometer; (2) a plurality of second SQUIDs; A drive circuit for driving one SQUID magnetometer of the magnetometer is provided independently, and a cancel coil is provided.
It is also characterized in that it also serves as a feedback coil used in an independently provided drive circuit, and (3) the cancel coil is arranged inside or outside the electromagnetically shielded room.

A fifth configuration of the magnetic field measuring apparatus according to the present invention comprises a plurality of first SQUID magnetometers for detecting a magnetic field in a predetermined direction generated from an inspection object, and a second SQUID magnetometer for detecting a disturbing magnetic field in a predetermined direction. SQUID magnetometer and first and second SQ
A cryogenic vessel for cooling the UID magnetometer, and first and second S
A driving circuit for driving the QUID magnetometer, a computer for collecting signals detected by the first and second SQUID magnetometers and performing signal processing, and a display means for displaying a result of the signal processing; And the second SQUID magnetometer has a differential detection coil, and the base line length of the differential detection coil of the second SQUID magnetometer is equal to the first SQUID magnetometer.
It is characterized in that it is shorter than the base line length of the differential detection coil of the magnetometer.

In the fifth configuration of the present invention, the predetermined direction is at least one of the x, y, and z directions. The predetermined direction is the normal direction and / or the tangential direction, and the component of the magnetic field generated from the inspection target in the normal direction and / or the tangential direction is detected, and the predetermined direction is the normal direction and / or the tangential direction. Signal processing for canceling the disturbing magnetic field is executed.

With reference to FIG. 1, a typical configuration of the present invention is summarized as follows. A plurality of first SQUID magnetometers 9 for detecting a biomagnetic field and a disturbing magnetic field, a plurality of second SQUID magnetometers 10 for detecting a disturbing magnetic field, and a driving circuit 6 for driving the first and second SQUID magnetometers And the first,
A computer 8 that collects detection signals from the second SQUID magnetometer and performs signal processing, and the first and second SQUID magnetometers have a primary differential detection coil, and the primary SQUID magnetometer has a primary differential detection coil. The baseline of the differential detection coil is shorter than the baseline of the primary differential detection coil of the first SQUID magnetometer, and the primary differential detection of the first SQUID magnetometer is detected from the detected biomagnetic field waveform. The disturbing magnetic field caused by the difference in the cancellation rate between the coils and the second SQUID
A process is performed to cancel the disturbing magnetic field caused by the difference in the baseline between the primary differential detection coils of the D magnetometer and the disturbing magnetic field generated by the frequency characteristics of the magnetic shield room. According to this configuration, it is possible to provide a magnetic field measuring device capable of canceling a steep and large-intensity disturbing magnetic field and accurately canceling the disturbing magnetic field.

According to each of the configurations of the present invention described above, the disturbance magnetic field is detected by the SQUID magnetometer that detects the magnetic field in the normal direction generated from the living body, and the disturbance magnetic field mixed with the disturbance magnetic field in the normal direction is detected. The normal magnetic field signal can be separated and extracted using the signal of the normal magnetic field that is detected by the SQUID magnetometer that detects the magnetic field.

Further, the distortion of the magnetic field waveform in the normal direction caused by the frequency characteristic of the magnetic shield room can be removed by using a theoretical calculation formula.

Further, according to each configuration of the present invention, it is possible to realize a biomagnetic field measuring apparatus capable of measuring a weak magnetic field generated from the heart to be examined and the fetal heart in the mother with high sensitivity.

[0055]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. First, as a differential detection coil, 1
Although the case where the secondary differential detection coil is used will be described in detail, the present invention is also applicable to the case where a secondary differential detection coil is used as the differential detection coil, as described later in detail. .

(First Embodiment) FIG. 1 is a diagram showing a configuration example of a magnetic field measuring apparatus according to a first embodiment of the present invention. Bed 4 on which inspection object lies inside magnetic shield room 2
And a gantry 3 holding a cryostat (dur) 1. Four magnetometers 9 for detection are arranged in a 2 × 2 array at the bottom inside the cryostat 1. Above the detecting magnetometer 9, two compensating magnetometers 10 are arranged at the same height. The configurations of the detecting magnetometer 9 and the compensating magnetometer 10 will be described later in detail with reference to FIG.

Detection magnetometer 9 and compensation magnetometer 10
Is driven by a drive circuit 6 via a connector 5, and the outputs of the detection magnetometer 9 and the compensating magnetometer 10 are amplified by the amplifier filter unit 7, filtered, and then collected by the computer 8. The computer 8 uses the output signal of the compensating magnetometer 10 to cancel the disturbing magnetic field, which will be described in detail later, with respect to the output of the detecting magnetometer 9, and then estimates the average magnetic field and analyzes the magnetic field distribution. And the like, and display the processing result on a display device.

FIG. 2 is a diagram showing a configuration example of a detection magnetometer and a compensating magnetometer according to the first embodiment of the present invention.
FIG. 2 is an enlarged view of a detecting magnetometer 9 and a compensating magnetometer 10 arranged inside the cryostat 1 for detecting a biomagnetic field in the z direction. The detecting magnetometers 9-a, 9-b,
The baseline 11-c of 9-c and 9-d is 50 mm. Detection magnetometers 9-a, 9-b, 9-c, 9-d
Are arranged in a 2 × 2 matrix. The number and arrangement of the detection magnetometers are not limited to the example shown in FIG. For example, 9 to 64 in a matrix of 3 × 3 to 8 × 8
It is also possible to arrange the detection magnetometers, or to arrange them three-dimensionally. Also, the value of the baseline 11-c is not limited to 50 mm, and may be a length such as 40 mm.

The baselines 11-a and 11-b of the compensating magnetometers 10-a and 10-b correspond to the detecting magnetometers 9-a and 9-b.
−b, 9-c, 9-d, which are shorter than the baseline 11-c. In the first embodiment, the baseline 11-a is
m, and the baseline 11-b is 30 mm.
The baselines 11-a, 11-b of the compensating magnetometer 10 (10-a, 10-b) are connected to the detecting magnetometers 9 (9-a, 9-9).
-B, 9-c, 9-d), the magnetic field generated from the heart is prevented from entering the compensating magnetometer 10 by making the compensating magnetometer 10 shorter than the baseline 11-c, and almost only the disturbing magnetic field is detected. .

In the first embodiment, the surface of the input coil of the detecting magnetometer 9 and the surface of the input coil of the compensating magnetometer 10 are
They are separated by 300 mm in the z direction and arranged. The distance between the surface of the input coil of the detecting magnetometer 9 and the surface of the input coil of the compensating magnetometer 10 is not limited to 300 mm, but may be any distance that does not allow the magnetic field generated from the heart to enter.

A method of canceling a disturbing magnetic field when the gantry 3 holding the cryostat 1 is arranged inside a magnetically shielded room and the magnetically shielded room does not have frequency characteristics will be described below.

FIG. 3 shows a first embodiment of the present invention.
It is a figure showing a magnetic field gradient inside a magnetic shield room.
Consider a magnetic field gradient in which the intensity changes linearly in the z direction as shown in (Equation 2). The coordinate system (x, y, z) is as shown in FIGS. 1 and 2, and the coordinate point (x, y, z ₀ )
Is the bottom of the cryostat.

[0063]

B (z) = βz + B (z ₀ ) (Equation 2) In the magnetometer composed of the primary differential detection coil, the area of the input coil is S ₁ , the area of the compensation coil is S ₂ , and the base is When the line is d, the magnetic flux Φ detected by the magnetometer becomes (Equation 3). It is assumed that the plane of the input coil is at z = z ₁ and the plane of the compensation coil is at z = z ₂ = z ₁ + d.

[0064]

Φ = S ₁ × B (z ₁ ) −S ₂ × B (z ₁ + d) = S ₁ × {β × z ₁ + B (z ₀ )} − S ₂ × Δβ × (z ₁ + d ) + B (z ₀ )｝ = β × (S ₁ −S ₂ ) × z ₁ + (S ₁ −S ₂ ) × B (z ₀ ) −S ₂ × β × d (Expression 3) When defined by 4), B ₀ = Φ / S ₁ is obtained by (Equation 5).

[0065]

Α = S ₂ / S ₁ (Equation 4)

[0066]

B ₀ = Φ / S ₁ = β × (1−α) × z ₁ + (1−α) × B (z ₀ ) −α × β × d (Equation 5) Here, the value of (1−α) indicates the cancellation rate of the primary differential detection coil with respect to the uniform magnetic field.
When the magnetic field distribution in the space in which the detection magnetometer and the compensating magnetometer are arranged is expressed by (Equation 2), as apparent from (Equation 5), the detected magnetic field has a cancellation rate (1−α).
And a term using the baseline d as a coefficient.

Further, the baseline 11 of the magnetic flux meter 9 for detection is used.
If -c and the baselines 11-a and 11-b of the compensating magnetometers 10-a and 10-b have the same length, the output of the detecting magnetometer 9 will be described later with reference to FIGS. By correcting using the output of the compensating magnetometer 10 according to the method described, it is considered that only the term having the cancellation rate (1−α) as a coefficient remains. However, when measuring the magnetic field generated from the heart, even when the compensating magnetometer 10 is arranged at a position 300 mm away from the detecting magnetometer 9, the compensating magnetometer 10 is not used.
If the base line is set to 50 mm, the waveform of the magnetic field generated from the heart appears largely, and the magnetic field generated from the heart is mixed in the compensating flux meter 10, so that only the interference magnetic field cannot be detected.

In order to prevent the magnetic field generated from the heart from being mixed into the compensating magnetometer, the compensating magnetometer 10 is used.
Baselines 11-a, 11 of (10-a, 10-b)
−b is shorter than the baseline 11-c of the magnetometer 9 for detection, so that the length of the baseline 11-a and the baseline 1
1-b.

For example, in the example shown in FIG. 2, the base line 11-a is 10 mm, and the base line 11-b is 30 mm.
And Compensating magnetometer 1 with different values of baseline
By arranging a plurality of zeros, it is possible to correct the difference in the amount of interfering magnetic field caused by the difference between the base line of the detecting magnetometer 9 and the base line of the compensating magnetometer 10.

Hereinafter, a method of canceling the disturbing magnetic field using the magnetic field waveform measured by the compensating magnetometer (first disturbing magnetic field canceling method) will be described with reference to FIGS. FIG. 4 is a flowchart showing an example of canceling an interfering magnetic field using the first compensating magnetometer of the first embodiment of the present invention, and FIG. 5 is a flowchart of the first embodiment of the present invention. FIG. 9 is a flowchart illustrating an example of canceling a disturbing magnetic field using the compensating magnetometer of FIG.

Here, the magnetic field waveforms detected by the detection magnetometers 9-a, 9-b, 9-c, 9-d shown in FIG. 1 or FIG. 2 are represented by F _1i , F _2i , F _3i , F _4i, and the magnetic field waveforms detected by the compensating magnetometers 10-a and 10-b shown in FIG. 1 or FIG. 2 are G _1i and G _2i . F _1i , f _2i , f _3i , f _4i , g _1i , g _2i shown in FIGS.
4, assuming that k = 1 to 2, the average value is calculated, and the average value is subtracted from each magnetic field waveform.
数 (Equation 9). Note that the addition symbol Σ used in the following formulas indicates addition relating to i = 1 to i = N (N indicates the number of sampling points on the time axis of the magnetic field waveform).

[0072]

F _j0 = Σ (F _ji ) / N ( _Equation 6)

[0073]

G _k0 = Σ (G _ki ) / N ( _Equation 7)

[0074]

F _ji = F _ji −F _j0 ( _Equation 8)

[0075]

G _ki = G _ki −G _k0 ( _Equation 9) The value of γ shown in (Process 15) shown in FIG. 4 and the value of γ ′ shown in (Process 19) shown in FIG. Can be determined by The magnetic field waveform F _ji (j =
For the sake of simplicity, the magnetic field waveform f _ji (j = 1 to 4, i = 1 to N) after removing the average value of the magnetic field waveform F _ji from 1 to 4, i = 1 to N is denoted by f _i and the compensating magnetic flux. magnetic field waveform G _ki obtained by total (k = 1~2, i = 1~N ) from after the removal of the magnetic field waveform G _ki Contact average magnetic field waveform _{g ki (k = 1~2, i} = 1
ＮN) is represented by g _i for simplicity, and the value of γ at which the evaluation function E of (Equation 10) is minimized is obtained by (Equation 11) by least squares approximation. 4 and 5 show (Equation 11)
The procedure for canceling the disturbing magnetic field for each channel by using is described below.

[0076]

E = Σ (f _i −γ × g _i ) ² (Equation 10)

[0077]

Γ = Σ (f _i × g _i ) / Σ (g _i ) ² (Equation 11) A specific processing procedure will be described with reference to FIGS. 4 and 5. Length 50 of baseline 11-c of detection magnetometer 9
Compensation magnetometer 10 with a baseline shorter than 10 mm
The magnetic field waveform detected by −a (baseline 11-a is 10 mm) is g _1i, and the magnetic field waveform detected by the compensating magnetometer 10-b (baseline 11-b is 30 mm) is g _2i . First, the magnetic field waveform of the disturbing magnetic field measured by the compensating magnetometer 10-a having the shortest baseline is used to cancel the disturbing magnetic field mainly caused by the difference in the canceling rate.

(Processing 15): γ (γ ₁ , ₁ ) for each of the detection magnetometer 9 and the compensating magnetometer 10-a using (Equation 11).
γ ₂ , γ ₃ , γ ₄ , γ ₅ ) are obtained. γ ₁ , γ ₂ , γ ₃ ,
γ ₄ and γ ₅ are given by (Equation 12) to (Equation 16).

(Process 16): The disturbing magnetic field generated mainly due to the difference in the cancellation rate can be canceled for each of channels 1 to 4, and the magnetic field waveforms f ′ _1i , f ′ _2i , f ′ _3i , f ′.
_4i and g ′ _2i are obtained. f ′ _1i , f ′ _2i , f ′ _3i , f ′ _4i ,
g ′ _2i is given by ( _Equation 17) to (Equation 21). It is considered that a magnetic field component due to a difference between the baselines of the two compensating magnetometers remains in the magnetic field waveform g ′ _2i .

[0080]

Γ ₁ = Σ (f _1i × g _1i ) / Σ (g _1i ) ² ( _Equation 12)

[0081]

Γ ₂ = Σ (f _2i × g _1i ) / Σ (g _1i ) ² ( _Equation 13)

[0082]

Γ ₃ = Σ (f _3i × g _1i ) / Σ (g _1i ) ² ( _Equation 14)

[0083]

Γ ₄ = Σ (f _4i × g _1i ) / Σ (g _1i ) ² ( _Equation 15)

[0084]

Γ ₅ = Σ (g _2i × g _1i ) / Σ (g _1i ) ² ( _Equation 16)

[0085]

F ′ _1i = f _1i −γ ₁ × g _1i ( _Formula 17)

[0086]

F ′ _2i = f _2i −γ ₂ × g _1i ( _expression 18)

[0087]

F ′ _3i = f _3i −γ ₃ × g _1i (19)

[0088]

F ′ _4i = f _4i −γ ₄ × g _1i ( _Equation 20)

[0089]

G ′ _2i = g _2i −γ ₅ × g _1i ( _Equation 21) Next, the process proceeds to # 1 (reference numeral 18) in FIG.
(Process 19) and (Process 20) are executed in the same manner as in 5).

(Processing 19): γ ′ ₁ , γ ′ ₂ , γ ′ ₃ , γ ′
₄ is obtained from (Equation 22) to (Equation 25).

(Process 20): Using the magnetic field waveform g ' _2i as reference data, canceling of the disturbing magnetic field is performed based on the magnetic field waveforms f' _1i , f ' _2i , f' _3i , and f ' _4i after the execution of (Process 16). Then, f " _1i , f" _2i , f " _3i , f" _4i are _expressed by ( _Equation 2)
6) to (Equation 29).

[0092]

Γ ′ ₁ = Σ (f ′ _1i × g ′ _2i ) / Σ (g ′ _2i ) ² ( _Expression 22)

[0093]

Γ ′ ₂ = Σ (f ′ _2i × g ′ _2i ) / Σ (g ′ _2i ) ² ( _Equation 23)

[0094]

Γ ′ ₃ = Σ (f ′ _3i × g ′ _2i ) / Σ (g ′ _2i ) ² ( _Equation 24)

[0095]

Γ ′ ₄ = Σ (f ′ _4i × g ′ _2i ) / Σ (g ′ _2i ) ² ( _Equation 25)

[0096]

[ _Formula 26] f ″ _1i = f ′ _1i −γ ′ ₁ × g ′ _2i ( _Formula 26)

[0097]

F ′ _2i = f ′ _2i −γ ′ ₂ × g ′ _2i ( _Expression 27)

[0098]

F ′ _3i = f ′ _3i −γ ′ ₃ × g ′ _2i ( _Expression 28)

[0099]

F ′ _4i = f ′ _4i −γ ′ ₄ × g ′ _2i ( _Equation 29) The method described above assumes that the magnetic shield room has no frequency characteristics and the length of the baseline differs. This is a first method of canceling a disturbing magnetic field using a plurality of compensating magnetometers.

Next, a description will be given of a second method of canceling the disturbing magnetic field which cancels the disturbing magnetic field depending on the frequency characteristic of the magnetically shielded room, which cannot be canceled only by the above-described method for canceling the first disturbing magnetic field.

The magnetic shield room has the characteristics of a low-pass filter (LPF) having a cutoff frequency of 1 Hz or less. The characteristics of this low-pass filter show the same behavior as that of an RC circuit using a resistor and a capacitor. That is, when the step function-like disturbance magnetic field invading the magnetic shield room, the magnetic field waveform B _r observed inside the magnetic shield room, the time is T a time constant and t, as indicated by equation (30) It is considered to be a magnetic field waveform. In order to facilitate understanding (Equation 30), the amplitude value is set to 1 (assuming that a disturbing magnetic field represented by a unit step function enters the magnetically shielded room).

[0102]

B _r (t) = exp (−t / T) (Equation 30) Using the magnetic field waveform B _r (t) shown in (Equation 30), the magnetic field of the magnetic field measured by the magnetometer for detection The waveform B ₁ (t) can be calculated by (Equation 31). However, the input coils of the detection gradiometers, respectively and T ₁ and T ₂ the time constant of the compensation coil. When (Equation 31) is subjected to Taylor expansion, (Equation 32) is obtained.

[0103]

B ₁ (t) = exp (−t / T ₁ ) −exp (−t / T ₂ ) = {1−exp (−t (1 / T ₂ −1 / T ₁ ))} × exp (−t / T ₁ ) (Equation 31)

[0104]

B ₁ (t) = (1 / T ₂ −1 / T ₁ ) × t × exp (−t / T ₁ ) (Formula 32) Similarly, the input coil compensation coil of the compensating magnetometer Is defined as T ₃ and T ₄ , respectively, the magnetic field waveform B ₂ (t) measured by the compensating magnetometer can be calculated by (Equation 33).

[0105]

B ₂ (t) = (1 / T ₄ −1 / T ₃ ) × t × exp (−t / T ₃ ) (Formula 33) Magnetic field waveform B ₁ (measured by the detecting magnetometer) From t), the magnetic field waveform (B ₁ −δB ₂ ) obtained by canceling the magnetic field waveform B ₂ (t) of the disturbing magnetic field measured by the compensating magnetometer using δ defined by (Equation 34) is (Equation 35)
Becomes (Equation 35) is obtained by Taylor expansion of (Equation 32) in the same manner as (Equation 32).

[0106]

Δ = (1 / T ₂ −1 / T ₁ ) / (1 / T ₄ −1 / T ₃ ) (Expression 34)

[0107]

(B ₁ −δB ₂ ) = (1 / T ₄ −1 / T ₃ ) × δ × t × exp (−t / T ₁ ) −δ × (1 / T ₄ −1 / T ₃ ) × t × exp (−t / T ₃ ) = (1 / T ₄ −1 / T ₃ ) × δ × t × {exp (− (1 / T ₁ −1 / T ₃ ) × t) −1} × exp (−t / T ₃ ) (Expression 35)

[0108]

(B ₁ −δB ₂ ) = − (1 / T ₁ −1 / T ₃ ) × (1 / T ₄ −1 / T ₃ ) × δ × t ² × exp (−t / T ₃ ) .. (Equation 36) If a term that does not depend on time among the amplitude values of (Equation 36) is η (Equation 37), (Equation 36) becomes a function shown in (Equation 38). As described above, (Equation 38) uses the fitting parameter δ obtained by (Equation 34) to calculate B ₁
9 shows a magnetic field waveform in which the disturbing magnetic field B ₂ (t) is canceled from (t).

[0109]

Η = (1 / T ₁ −1 / T ₃ ) × (1 / T ₄ −1 / T ₃ ) × δ (Expression 37)

[0110]

(B ₁ −δB ₂ ) = − η × t ² × exp (−t / T ₃ ) (Equation 38) FIG. 6 shows a first embodiment of the present invention based on theoretical calculation. It is a figure showing the example of the magnetic field waveform of the interference magnetic field calculated | required. FIG.
, The horizontal axis represents time (seconds), and the vertical axis represents (Equation 30).
Shows the magnetic field strength derived from a function having an amplitude value of 1 as shown in FIG.

FIG. 6A shows a magnetic field waveform B _r (t) obtained by theoretical calculation (determined by (Equation 30)) (a magnetic field waveform of an observing magnetic field), and FIG. ,
FIG. 6C shows a magnetic field waveform B ₁ (t) (determined by (Equation 32)) measured by a first-order differential SQUID magnetometer (detector magnetometer), and FIG. The magnetic field waveform after canceling the disturbing magnetic field with respect to the magnetic field waveform B ₁ (t) measured by the detecting magnetometer using the magnetic field waveform B ₂ (t),
Magnetic field waveform ｛(B ₁ (t) −δB
₂ (t)｝.

In an actual measurement system, a biomagnetic field is measured using a high-pass filter (HPF).
FIG. 6 (d) shows a simulation of the magnetic field waveform actually measured, using the magnetic field waveform measured by the compensating magnetometer, and comparing the magnetic field waveform measured by the detecting magnetometer with the disturbance magnetic field. The magnetic field waveform after canceling, that is, the magnetic field waveform ｛B obtained by (Equation 38)
₁ (t) -δB ₂ (t)} shows a magnetic field waveform after passing through a 0.1 Hz secondary Butterworth type high-pass filter.

[0113] In the above calculations, the B _r of at time constant and T = 0.2 seconds, T ₁ = 0 the in time constant B _1.
2 seconds, T ₂ = 0.21 seconds, and the time constant in (B ₁ −δB ₂ ) was T ₃ = 0.2 seconds. FIG. 6A shows a magnetic field waveform of an observing magnetic field, which is a magnetic field waveform calculated by simulation on the assumption that the magnetic field is generated as a step function at time 10 seconds.

Magnetic field waveform B _r (t) and magnetic field waveform B ₁ (t)
Is a member of the University of Twente, such as Brake et al. (Meas.
i. Technol. , Vol. 2, pp. 596-6
01 (1991)), which is in good agreement with the magnetic field waveform actually measured.

FIG. 7 shows a first embodiment of the present invention.
It is a figure which shows the example of the flowchart of the method of canceling the disturbing magnetic field resulting from the frequency characteristic of a magnetic shield room (2nd disturbing magnetic field cancellation method). The second method of canceling the disturbing magnetic field will be described with reference to FIG. First, the processing of canceling the first disturbing magnetic field shown in FIGS. 4 and 5 is performed, and then the distortion of the magnetic field waveform caused by the frequency characteristic of the magnetic shield room is canceled based on (Equation 38). Go. j channel (j = 1 to
The following (process 302) to each channel of 4)
(Process 309) is performed.

(Process 302): The starting point of the data where the magnetic field waveform is distorted (the initial point where the disturbing magnetic field is generated) (in the example shown in FIG. 6, the horizontal axis is equal to 10 seconds) is determined.
In a process 302, a second derivative waveform with respect to the time of the measured magnetic field waveform (the magnetic field waveform before canceling the first disturbing magnetic field) is calculated, a peak is detected, and the time of the peak point is set to the start point of the data (the initial point). ). As the initial point, the peak point of the magnetic field waveform displayed on the display screen of the display device may be read, or the magnetic field waveform measured by a flux gate installed outside the magnetic shield room may be used.

(Process 303): j-channel (j = 1 to j)
Regarding 4), the initial values of the amplitude η _j , the time constant T _j (T _j is T ₃ (Equation 38) of the j channel), and the initial point (the data point at the beginning of the data in which the magnetic field waveform distortion occurs) are defined as Set. For example, η _j = 1 and T _j = 0.2 seconds are set.

(Process 304): j channel (j = 1 to j)
For each channel of 4), the magnetic field waveform B _est , _j , _i obtained by theoretical calculation is calculated by (Equation 39).

(Process 305): High pass filter processing is performed.

(Process 306): The evaluation function E is obtained by the least square sum of the measured values B _mes , _j , _i and B _est , _j , _i according to ( _Equation 40).
Calculate _j . In equation (40), the addition symbol Σ
i = 1 to i = N '(N' indicates the number of sampling points t _i on the time axis of the magnetic field waveform of the measured values B _mes , _j , _i ).

[0121]

B _est , _j , _i = −η _j × t _i ² × exp (−t _i / T _j ) (Expression 39)

[0122]

E _j = Σ (B _mes , _j , _i −B _est , _j , _i ) ² (Equation 40) (Process 307): E _j > reference value set in advance (for example,
When (E _j > 10 ⁻⁴ ), (process 308) is executed, and when E _j ≦ a preset reference value (for example, E _j > 10 ⁻⁴ ), (process 309) is executed.

(Process 308): The amplitude η _j , the time constant T _j , and the start point (initial point) of the data are obtained by the simplex method so that the value E _{j of the} evaluation function becomes smaller. ).

(Process 309): Using the amplitude η _j , the time constant T _j , and the point at the beginning of the data (initial point) obtained as the optimal solution, the magnetic field waveform B is theoretically expressed by (Equation 39).
_est , _j , _i are calculated, and _Best , _j , _i is subtracted from the magnetic field waveform _Bmes , _j , _i obtained by the first interference magnetic field cancellation method according to (Equation 41). As a result, the interference time is canceled by the second interference magnetic field canceling method, j
Obtain B _c , _j , _i for the channel (j = 1 to 4).

[0125]

B _c , _j , _i = B _mes , _j , _i −B _est , _j , _i (Equation 41) The method described above occurs depending on the frequency characteristics of the magnetically shielded room. 4 is a description of a second method for canceling a disturbing magnetic field, in which the remaining disturbing magnetic field is canceled by the method for canceling a disturbing magnetic field according to the first embodiment.

(Second Embodiment) Next, the result of performing the above-described processing using the data measured by the arrangement of the SQUID magnetometers shown in FIGS. 1 and 2 will be described below. First, the waveform of the disturbing magnetic field was recorded simultaneously inside and outside the magnetically shielded room.

FIG. 8 is a diagram showing a configuration example of a magnetic field measuring apparatus according to a second embodiment of the present invention. The sensor unit 102 of the fluxgate magnetometer was installed outside about 5 m away from the magnetically shielded room, and a magnetic field in the same z-direction as that of the first-order differential SQUID magnetometer inside the magnetically shielded room was detected. Sensor unit 102 of fluxgate magnetometer
Is operated by the main body 101 of the fluxgate magnetometer. The output of the main unit 101 is passed through only a low-pass filter having a corner frequency of 100 Hz.
Was taken in. The arrangement of the first derivative SQUID magnetometer is
As described in FIG. 1 and FIG. 2, the output of the SQUID magnetometer was taken into the computer 8 through a band-pass filter of 0.1 Hz to 100 Hz and a notch filter of 50 Hz.

FIG. 9 is a diagram showing an example of a magnetic field waveform measured by a fluxgate magnetometer in the magnetic field measuring apparatus according to the second embodiment of the present invention. In FIG. 9, the horizontal axis represents time (minutes) and the vertical axis represents magnetic field strength (μT (microtesla)). In the example shown in FIG. 9, with a period of about 10 minutes,
A large magnetic field of 1.2 μT or more appears. This large magnetic field is a waveform of a magnetic field generated from a train running at a distance of about 10 minutes from a magnetic shield room at a distance of about 50 m.

FIG. 10 shows a magnetic field measuring apparatus according to a second embodiment of the present invention, in which a fluxgate magnetometer and a SQUID are used.
It is a figure showing the example of the magnetic field waveform measured by the magnetometer.
In FIG. 10, the horizontal axis represents time (seconds), and the vertical axis represents the magnetic field intensity (pT (picotesla in FIG. 10A), FIG.
(B) shows μT). FIG. 10 is a magnetic field waveform recorded in the measurement section 201 shown in FIG. 9, the magnetic field waveform detected by the detection magnetometer, and the magnetic field waveform measured by the fluxgate magnetometer (enlargement of the measurement section 201 in FIG. 9). Figure). The measurement of the magnetic field was performed with the test object not lying on the bed.

FIG. 10A shows waveforms measured by a first-order differential SQUID magnetometer measured inside the magnetically shielded room, where (A1), (A2), (A3), and (A4) indicate the detected waveforms, respectively. Flux meter (FIG. 2) 9-a (ch. 1), 9
-B (ch. 2), 9-c (ch. 3), 9-d (c
h. 4) corresponds to outputs f _1i , f _2i , f _3i , and f _4i . ch. i means i channel.

FIG. 10B shows a waveform measured by a flux gate magnetometer outside the magnetically shielded room. In FIG. 10B, at time A, time B, and time C, a disturbing magnetic field in the form of a step function is generated. FIG. 10 (A)
Ch. 1 to ch. Looking at the magnetic field waveforms related to 4,
It can be seen that a disturbing magnetic field is also generated inside the magnetically shielded room with time A and time B as initial points. c
h. 1 to ch. Comparing the intensities of the disturbing magnetic field waveforms with respect to No. 4, it can be seen that the magnitude of the disturbing magnetic field differs between the channels.

Ch. 1 to ch. The reason why the magnitude of the disturbing magnetic field differs even when using a detection magnetometer having the same baseline as the magnetic field waveform in Fig. 4 is mainly due to the difference in the cancellation rate between channels from the consideration of (Equation 5). it is conceivable that.

The input coil and the compensation coil of the detecting magnetometer and the compensating magnetometer shown in FIGS. 1, 2 and 8 are made by manually winding a superconducting wire, and the cancellation rate is about 10 ^-2.
To 10 ^-3 or less (40 dB to 60 dB), and a slight difference in the cancellation rate largely reflects as a difference in the magnitude of the magnetic field waveform. In the case of a handmade coil, such a difference in the cancellation rate between the channels is an unavoidable problem. Assuming that the cancellation rates are the same,
It is necessary to adjust the superconducting coil in a uniform magnetic field of 10 ⁻³ or less, which is a very difficult task in practice.

When there is a non-uniform strong disturbing magnetic field, the magnitude of the output of the magnetometer changes greatly due to the difference in the cancellation rate between the channels. It is difficult to accurately cancel the disturbing magnetic field by using a method of using as a channel and subtracting the output signal of the reference channel from the output signal of each channel using the output of the reference channel. Therefore, in a multi-channel magnetic field measuring apparatus, it is necessary to determine an optimal canceling amount of a disturbing magnetic field for each channel.

FIG. 11 shows the SQUID in the magnetic field measuring apparatus according to the second embodiment of the present invention in a state in which the object to be inspected is not lying on a bed and at a time different from the example shown in FIG.
It is a figure showing the example of the magnetic field waveform measured by D magnetometer. In FIG. 11, the horizontal axis represents time (seconds), and the vertical axis represents magnetic field strength (pT). FIGS. 11 (a), (b),
(C) and (d) show the detection magnetometers 9-a (ch. 1), 9-b (ch. 2), and 9-b (ch. 1) shown in FIGS.
FIG. 11 corresponds to the magnetic field waveforms f _1i , f _2i , f _3i , and f _{4i according} to 9-c (ch. 3) and 9-d (ch. 4).
(E) and (f) respectively show the compensating magnetometer 10-a (r
ef. ch. 1) and 10-b (ref. Ch. 2) correspond to the magnetic field waveforms g _1i and g _2i .

Ref. ch. The magnetic field waveform g _{1i of} FIG.
(E)) and ref. ch. The magnetic field waveform g _{2i of} FIG.
In (f)), a large disturbing magnetic field of about 100 pT is generated before and after the time of 16 seconds. Baseline is 10mm
Waveform g by the compensating magnetometer (ref.ch1.)
_1i (FIG. _11E ) has the smallest magnitude of the magnetic field waveform, but the magnetic field waveform of FIG.
h. 1) to 11 (d) (ch. 4), the waveforms of the disturbing magnetic fields having the same shape as the waveforms f _1i , f _2i , f _3i and f _4i appear.

FIG. 12 shows an example of the magnetic field waveform shown in FIG. 11 of the present invention after the interference magnetic field is canceled (FIG. 4) using the first compensating magnetometer of the first embodiment. FIG. In FIG. 12, the horizontal axis represents time (seconds), and the vertical axis represents magnetic field strength (pT). FIG.
Ref. The results of executing (Process 15) and (Process 16) shown in FIG. 4 according to (Equation 12) to (Equation 21) using the magnetic field waveform g _{1i of} ch1 are shown. That is, FIG.
2 (a), (b), (c), (d), and (e) are (Equation 17), (Equation 18), (Equation 19), and (Equation 2), respectively.
0), (Equation 21), f ′ _1i , f ′ _2i , f ′ _3i ,
f ′ _4i and g ′ _2i are shown.

In the magnetic field waveforms of FIGS. 12 (a), (b), (c) and (d), FIGS. 11 (a), (b), (c) and (d)
Although the disturbance magnetic field is about 1/4 as compared with the magnetic field waveform of the above, a large disturbance magnetic field still remains.

FIG. 13 shows the magnetic field waveform shown in FIG. 12 of the present invention, which is obtained by canceling the disturbing magnetic field (FIG. 5) using the second compensating magnetometer of the first embodiment. It is a figure showing an example. In FIG. 13, the horizontal axis represents time (seconds), and the vertical axis represents magnetic field strength (pT). FIG. 13 further illustrates
The ref. The result of executing (Process 19) and (Process 20) shown in FIG. 5 using the magnetic field waveform g ′ _2i of ch2 is shown. That is, FIGS. 13 (a), (b),
(C) and (d) are (Equation 26), (Equation 27),
As a result of (Equation 28) and (Equation 29), f " _1i , f" _2i ,
f " _3i and f" _4i .

In the result shown in FIG. 13, although the large interfering magnetic field is almost canceled, 20 p
A disturbance magnetic field of about T remains. FIG. 13 (a),
The waveforms of the disturbing magnetic fields remaining in (b), (c) and (d) are
This is very similar to the magnetic field waveform shown in FIG. The waveform of the remaining disturbing magnetic field shown in FIG. 13 is a magnetic field waveform generated by distorting the disturbing magnetic field mixed in a step function shape by the characteristics of the low-pass filter in the magnetic shield room, as described above with reference to FIG. it is conceivable that.

The waveform of the remaining disturbing magnetic field is given by (Equation 3)
As is clear from 8), it depends on the time constant T ₃ of the input coil of the compensating magnetometer, and as is clear from the results shown in FIG. 13, the channel number of the detecting magnetometer, that is, the detecting magnetometer is It changes depending on the position where it is arranged.

Accordingly, the waveform of the disturbance magnetic field remaining due to the cancellation of the disturbance magnetic field using the first and second compensating magnetometers of the first embodiment depends on the positional relationship between the detection magnetometer and the compensation magnetometer. Means that it also changes. FIG.
In order to cancel the remaining disturbing magnetic field shown in FIG. 7, (Process 302) to (Process 309) shown in FIG. 7 are executed.

FIG. 14 is a diagram showing an example of the magnetic field waveform after the cancellation of the disturbing magnetic field (FIG. 7) caused by the frequency characteristics of the magnetically shielded room from the magnetic field waveform shown in FIG. 13 of the present invention. In FIG. 14, the horizontal axis represents time (seconds), and the vertical axis represents magnetic field strength (pT). FIG. 13 (a),
For the magnetic field waveforms of (b), (c), and (d),
FIGS. 14A, 14B, 14C, and 14D show the results obtained by executing the processes shown in (Formula 39) to (Formula 41).

As is clear from FIGS. 14 (a), (b), (c) and (d), the interference magnetic field is almost cancelled. 1 to ch. In the magnetic field waveform of each channel of No. 4, a sharp peak remains as a disturbing magnetic field at around time 15 seconds, which is considered as an initial point where the disturbing magnetic field is mixed in a step function. Disturbance magnetic field having a sharp peak that remains until the end is considered to have occurred due to the difference of the constant T ₁ when the input coil of the detection gradiometers.

FIG. 15 shows a magnetic field measuring apparatus according to a second embodiment of the present invention in which the magnetic field generated from the heart to be examined is represented by S.
It is a figure showing the example of the magnetic field waveform measured by the QUID magnetometer. In FIG. 15, the horizontal axis represents time (seconds), and the vertical axis represents magnetic field strength (pT). In the example shown in FIG. 15, the disturbing magnetic field is generated near the time of 14 seconds. FIG.
The magnetic field waveforms of (a), (b), (c), (d), (e), and (f) are shown in FIGS. 11 (a), (b), (c), and (c), respectively.
It shows waveforms similar to the magnetic field waveforms of (d), (e), and (f).

FIG. 16 shows the magnetic field waveform shown in FIG. 15 according to the present invention, which is obtained by executing the canceling of the disturbing magnetic field (FIG. 4) using the first compensating magnetometer of the first embodiment. It is a figure showing an example. In FIG. 16, the horizontal axis represents time (seconds), and the vertical axis represents magnetic field strength (pT). FIG. 12 (a),
As in the case of (b), (c), (d), and (e), FIG.
Ref. ch. The results of executing (Process 15) and (Process 16) shown in FIG. 4 using the magnetic field waveform of FIG. 1 (FIG. 15 (E)) are shown in FIG. 16 (A), (B), (C),
(D) and (e) show. In the example illustrated in FIG. 16, the large interference magnetic field is almost completely canceled only by the processing illustrated in FIG. 4, but the interference magnetic field of about 20 pT remains near the time of 14 seconds.

FIG. 17 shows the magnetic field waveform shown in FIG. 16 of the present invention as the magnetic field waveform after the cancellation of the disturbing magnetic field (FIG. 5) using the second compensating magnetometer of the first embodiment. It is a figure showing an example. In FIG. 17, the horizontal axis represents time (seconds), and the vertical axis represents magnetic field strength (pT). FIG. 13 (a),
As shown in (b), (c) and (d), r shown in FIG.
ef. Using the magnetic field waveform of ch2 (FIG. 16 (e)), FIG.
17 (a), (b), (c), and (d) show the results of executing (Process 19) and (Process 20) shown in FIG. Similar to FIGS. 13 (a), 13 (b), (c), and (d), waveforms that are very similar to the magnetic field waveforms shown in FIG. b),
It remains in the magnetic field waveforms of (c) and (d).

FIG. 18 is a diagram showing an example of a magnetic field waveform after the disturbance magnetic field caused by the frequency characteristics of the magnetically shielded room (FIG. 7) is applied to the magnetic field waveform shown in FIG. 17 of the present invention. In FIG. 18, the horizontal axis represents time (seconds), and the vertical axis represents magnetic field strength (pT). FIG. 17 (a),
FIGS. 14 (a), 14 (b), 14 (b), 14 (c), and 14 (d) show how to cancel the disturbing magnetic field remaining in the magnetic field waveform in FIGS.
Similar to (c) and (d), FIG.
The result of executing (Process 309) from 2) is shown in FIG.
(A), (b), (c), and (d) show.

As is clear from the results shown in FIG. 18, the disturbing magnetic field is almost canceled, and the magnetic field generated from the heart to be examined is clearly detected. A sharp peak of the disturbing magnetic field that could not be completely canceled in .8 seconds remains.

In the results shown in FIG. 16, since the large interfering magnetic field is almost completely canceled only by the processing shown in FIG. 4, the magnetic fields shown in FIGS. 16 (a), (b), (c), and (d) are obtained. Similar results can be obtained by canceling the disturbance magnetic field caused by the frequency characteristics of the magnetically shielded room (FIG. 7) in order to cancel the disturbance magnetic field of about 20 pT remaining near the time of 14 seconds in the waveform.

That is, the result of the cancellation of the disturbing magnetic field using the first compensating magnetometer (FIG. 4) is determined, and the result of the determination is used to cancel the disturbing magnetic field due to the frequency characteristics of the magnetic shield room (FIG. 4). Step 7) may be performed. As a result, when there is no need to execute the disturbance magnetic field cancellation using the second compensating magnetometer shown in FIG. 5, the cancellation of the disturbance magnetic field can be executed in a short time.

FIG. 22 shows a second embodiment of the present invention.
3, time constants (T ₃ (unit: second) in (Equation 38)) obtained from the waveforms shown in FIG. 17, data1, data2
FIG. FIG. 22 is a result of summarizing the time constants estimated using (Equation 38) in order to cancel the disturbing magnetic field remaining in FIGS. 13 and 17. According to the results shown in FIG. 22, the detecting magnetometers 9-a (ch. 1) and 9-b (ch. 1) arranged as shown in FIGS.
2) It can be seen that the value of the time constant (T ₃ ) obtained from the magnetic field waveform according to 9-c (ch. 3) and 9-d (ch. 4) is slightly different.

The time constant T of the input coil of the compensating magnetometer
_3, the magnitude of the effect on each of the detection magnetic flux meter, are different for each detection gradiometers, the magnitude of the influence of the constant T ₃ time the position of the detection magnetometer indicates different. In order to evaluate the difference between these time constants, FIG. 13 and FIG.
The subtraction is performed between the channels of the magnetic field waveform of FIG.

FIGS. 19 (a), (b),
It is a figure which shows the example of the magnetic field waveform after difference processing between the channels of the magnetic field waveform shown to (c) and (d). In FIG. 19, the horizontal axis indicates time (seconds), and the vertical axis indicates magnetic field strength (pT).
Is shown. FIGS. 19 (a), (b) and (c) respectively show ch. 2, ch. 3, ch. 4 from the magnetic field waveform of ch. The result of subtracting (-1) times the magnetic field waveform of No. 1 is shown.

FIG. 20 is similar to FIG.
It is a figure which shows the example of the magnetic field waveform after the difference process between the channels of the magnetic field waveform shown to (b), (c), (d). FIG.
In the graph, the horizontal axis indicates time (seconds), and the vertical axis indicates magnetic field strength (pT). FIGS. 20 (a), (b) and (c) respectively show ch. 2, ch. 3, ch. 4 from the magnetic field waveform of ch. The result of subtracting (-1) times the magnetic field waveform of No. 1 is shown.

In the examples shown in FIGS. 19 and 20, the time constant T ₃
Ch. 1 and ch. The interference magnetic field remains in the magnetic field waveforms (differences) of FIGS. 19C and 20C obtained by subtraction from the magnetic field waveforms of FIG. From the above results, the time constant T estimated using the time constant ((Equation 38))
_This indicates that the magnitude of the effect of ₃ ) differs depending on the position of the detection magnetometer. That is, it can be seen that with the size of the spatial distribution of the effects of the time constant T _3.

FIG. 21 is a diagram showing a display example of the magnetic field waveform after canceling the disturbing magnetic field according to the second embodiment of the present invention. Here is a display example that can be easily understood. In FIG. 21, the horizontal axis represents time (seconds), and the vertical axis represents magnetic field strength (pT). As shown in FIG. 21, a line 401 is drawn on the time of the initial point at which the disturbing magnetic field is generated, and a point, a color point, a dotted line, a color line, a bold line, etc. It is configured to be displayed together with the waveform, and to indicate that it may be affected by the disturbing magnetic field near the initial point.

The time displayed by the straight line 401 is
The value obtained in (process 303) shown in FIG. 7 is used. Further, the time displayed by the straight line 401 may be detected from a time derivative waveform or the like of the magnetic field waveform measured by the fluxgate magnetometer shown in FIG.

(Third Embodiment) FIG. 23 shows a third embodiment of the present invention.
It is a figure showing an example of composition of a magnetic field measuring device of an example. Third
In the second embodiment, a magnetically shielded room made of a member having high magnetic permeability such as permalloy used in the first embodiment (FIG. 1) and the second embodiment (FIG. 8) is used. No configuration. The configuration of the compensating magnetometer 10 shown in FIG. 23 is different from the compensating magnetometer 10 (10-a, 10-b) in the first embodiment (FIG. 1) and the second embodiment (FIG. 8). )
The configuration is the same as described above.

Compensation magnetometer 10 (10-a, 10-b)
Is shorter than the baseline of the detecting magnetometer 9, and in the third embodiment, another compensating magnetometer 601 is arranged in addition to the compensating magnetometer 10. Using the output of the compensating magnetometer 601, the control device 604 controls the current flowing through the coils 603-a and 603-b to generate a magnetic field in the direction opposite to the disturbing magnetic field in the z direction.
It is configured to cancel about 0 dB to 60 dB. The coils 603-a and 603-b can be disposed inside or outside an electromagnetic shield room made of aluminum, copper, or the like that blocks high-frequency electromagnetic waves.

The baseline of the compensating magnetometer 601 is shorter than the baseline of the compensating magnetometer 10 (10-a, 10-b). For example, the base line of the compensating magnetometer 601 is set to a value in the range of 0.5 mm to 1 mm, and a disturbance magnetic field determined mainly by only the cancellation rate is cancelled.

When the baseline of the compensating magnetometer 10 or 601 is shortened, the inductance of the coil is reduced and the effective area is not reduced. The minimum magnetic field resolution of the SQUID magnetometer (for example, 10 fT / √Hz) 23, the compensating magnetometer 10 (10-a, 10-b) and the compensating magnetometer 601 are provided in the configuration shown in FIG.
Is larger than the area of the magnetic flux meter 9 for detection.

When the compensating magnetometer having the minimum magnetic field resolution smaller than the minimum magnetic field resolution of the detecting magnetometer is not used, the processing for canceling the disturbing magnetic field described with reference to FIGS. The coils 603-a and 60 shown in FIG.
When canceling the disturbing magnetic field by 3-b, SQ
There is a problem that the white noise of the UID magnetometer increases.

When the value of the white noise is large and poses a problem, the signal band of the output waveform of the compensating magnetometers 10-a, 10-b, and 601 is subjected to band limiting processing by analog or digital filtering processing. By doing so, it is possible to prevent an increase in white noise due to the canceling processing of the disturbing magnetic field. In many cases, a magnetic field of a low frequency (up to 1 Hz) becomes a main noise source and generates a disturbing magnetic field. Therefore, this band limiting process is a practical and effective method.

The execution of the band limiting process described above, and
The configuration in which the area of the compensating magnetometer is larger than the area of the detecting magnetometer 9 is not limited to the third embodiment (FIG. 23) and the fourth embodiment (FIG. 24) described below. The same applies to the first embodiment (FIGS. 1 and 2), and the interference magnetic field can be canceled without increasing the white noise.

(Fourth Embodiment) FIG. 24 shows a fourth embodiment of the present invention.
It is a figure showing an example of composition of a magnetic field measuring device of an example. Hereinafter, a configuration different from the configuration of the third embodiment (FIG. 23) will be described. In the configuration of the fourth embodiment, a drive circuit (FLL: Flux Locked Loop) that drives the compensating magnetometer 601 described in the third embodiment (FIG. 23).
The circuit 605 is provided independently, and the feedback coil (normally incorporated in the SQUID) used in the FLL circuit and the coils 603-a and 603-b are used. By using both the feedback coil and the coils 603-a and 603-b,
External magnetic field can be canceled without adjustment.

(Fifth Embodiment) FIG. 25 shows a fifth embodiment of the present invention.
FIG. 9 is a projection view showing an example of arrangement of a compensating magnetometer and a detecting magnetometer in the first embodiment (FIGS. 1 and 2) and the second embodiment (FIG. 8). FIG. 3 is a diagram showing a position where a compensating magnetometer is arranged, projected from above onto a surface on which a detection magnetometer is arranged (a surface parallel to the lower surface of the cryostat), and viewed from above. In the example shown in FIG. 25, a compensating magnetometer 10-a is provided above the detection magnetometer 9-a, and a compensation magnetometer 10-b is provided above the detection magnetometer 9-d. , Each is arranged. At the position where the detection magnetometers 9-a and 9-d are arranged, the magnitude of the magnetic field generated from the heart of the human body is small. Therefore, in the arrangement example shown in FIG. 25, the compensation magnetometers 10-a and 10-d are arranged. A magnetic field generated from the heart is hardly input to b, and an almost pure external interference magnetic field can be detected.

(Sixth Embodiment) FIG. 26 shows a sixth embodiment of the present invention.
FIG. 24 is a projection view showing an example of the arrangement of the compensating magnetometer and the detecting magnetometer in the third embodiment (FIG. 23) and the fourth embodiment (FIG. 24). FIG. 5 is a diagram in which a position where the meter is arranged is projected from above onto a surface on which the magnetic flux meter for detection is arranged (a surface parallel to the lower surface of the cryostat), and viewed from above. In the example shown in FIG. 26, in addition to the configuration of FIG. 25, a compensating magnetometer 601 is arranged near the compensating magnetometer 10-a. In the arrangement example shown in FIG.
In this case, almost no magnetic field generated from the heart is input, and almost pure external disturbance magnetic field can be detected.

(Seventh Embodiment) In each of the first to sixth embodiments described above, the number of detection magnetometers is set to four and four
Although the magnetic field measuring device of the channel has been described, the number of magnetometers for detection is not limited to this.
Either as 15, it is needless to say may be field measuring apparatus of n ² channels. Furthermore, a plurality of each of the compensating magnetometers 10-a, 10-b, and 601 may be used. That is, each of the embodiments described above is performed by using a plurality of compensating magnetometers having the same baseline size and using the average value of the magnetic field waveforms obtained by the plurality of compensating magnetometers having the same baseline size. The canceling of the disturbing magnetic field may be performed according to the method described in the above section.

(Eighth Embodiment) Each of the first to seventh embodiments described above comprises a detection magnetometer for detecting a component of a magnetic field in the normal direction (z direction) and a compensation magnetometer. Although the magnetic field detection system described above has been described as an example, the method of canceling the disturbing magnetic field of the present invention is based on a detection magnetometer and a compensating magnetometer that detect components in three directions (x, y, and z directions) of the magnetic field. Needless to say, the present invention can be applied to the configured magnetic field detection system in the same manner as in the first to seventh embodiments.

That is, using the signals detected by the second SQUID magnetometer for detecting the magnetic field components in the x, y, and z directions of the disturbing magnetic field, the x, y,
From each signal detected by the first SQUID magnetometer for detecting the magnetic field component in the z direction, the magnetic field component in each direction of the disturbing magnetic field is removed (canceled) for each direction, and the biomagnetic field for each direction is removed. The magnetic field component can be separated and extracted.

Furthermore, the distortion of the magnetic field waveform of the magnetic field components in the x, y, and z directions caused by the frequency characteristics of the magnetic shield room can be removed by using a theoretical calculation formula.

(Ninth Embodiment) In the configuration shown in FIG. 21 described in the second embodiment, a straight line is displayed on the screen of the display device at the time of the initial point where the disturbing magnetic field is generated. In the magnetic field measuring apparatus of each of the first to eighth embodiments described above, the magnetic field waveform measured by the fluxgate magnetometer (for example, FIG. 9), the fluxgate magnetometer, and the SQUID magnetometer were further measured. Magnetic field waveform (for example,
10), a magnetic field waveform measured by the SQUID magnetometer (for example, FIGS. 11 and 15), and a magnetic field waveform (for example, FIGS. 12 to 13,
16 to 17), a magnetic field waveform (for example, FIGS. 14, 18, and 21) indicating the result of canceling the disturbing magnetic field may be displayed on the screen of the display device. In such a configuration, analysis and evaluation of the situation of the occurrence of the disturbing magnetic field and the situation of the result of the cancellation of the disturbing magnetic field are performed. It can also be executed.

(Tenth Embodiment) In each of the first to ninth embodiments described above, the case where the primary differential detection coil is used as the differential detection coil has been described.
In each of the first to ninth embodiments, when the secondary differential detection coil is used as the differential detection coil, the cancellation of the disturbing magnetic field is executed in the same manner as in the first to ninth embodiments. it can.

When the differential detection coil is a secondary differential detection coil, the input coils of the detection magnetic flux meter and the compensating magnetic flux meter are the inspection target of the coils constituting the secondary differential detection coil. Is a first coil disposed at a position closest to the first coil.

Each of the compensating coils of the detecting magnetometer and the compensating magnetometer is sequentially disposed at a position farther from the test object than the first coil among the coils constituting the second-order differential detecting coil. Second, third, and fourth coils having a plane parallel to the plane of the coil. Here, the area of the second coil is equal to the area of the coil of the third coil.

The baselines of the detecting magnetometer and the compensating magnetometer mean the baseline of the secondary differential detecting coil, respectively, the distance between the surface of the first coil and the surface of the second coil, The distance between the surface of the third coil and the surface of the fourth coil. Here, the distance between the surface of the first coil and the surface of the second coil is equal to the distance between the surface of the third coil and the surface of the fourth coil.

In the magnetometer composed of the secondary differential detection coil, the area of the first coil (input coil) is s ₁ , the area of the second and third coils (compensation coils) is s ₂ , When the area of the coil (compensation coil) is s ₃ and the baseline is b, the magnetic flux φ detected by the magnetometer can be obtained in the same manner as in the magnetometer composed of the primary differential detection coil. (Equation 42). The surface of the first coil is z
= Z ₁ , the surface of the second coil is z = z ₂ = z ₁ + b,
Is located at z = z ₂ + Δ = z ₁ + b + Δ, and Δ ≒
0, and the surface of the fourth coil is at z = z ₂ + b = z ₁ + 2b.

[0179]

## EQU42 ## φ = s ₁ × B (z ₁ ) -2s ₂ × B (z ₁ + b) + s ₃ × B (z ₁ + 2b) = s ₁ × {β × z ₁ + B (z ₀ )}-2s ₂ × {β × (z ₁ + b) + B (z ₀ )} + s ₃ × {β × (z ₁ + 2b) + B (z ₀ )} = β × {(s ₁ −s ₂ ) − (s ₂ + s ₃₎ )｝ × z ₁ + {(s ₁ −s ₂ ) − (s ₂ −s ₃ )} × B (z ₀ ) −2 (s ₂ −s ₃ ) × β × b (Equation 42) (Equation 42) ), (S ₁ -s ₂ ) is replaced by S ₁ and (s ₂ -s
_{If (3} ) is replaced with S ₂ and (2 × b) is replaced with d, (Equation 42) is equivalent to (Equation 3).

If α ′ is defined by (Equation 43), B ′ ₀
= Φ / (s ₁ −s ₂ ) is obtained by (Equation 44).

[0181]

Α ′ = (s ₂ −s ₃ ) / (s ₁ −s ₂ ) (Expression 43)

[0182]

B ′ ₀ = φ / (s ₁ −s ₂ ) = β × (1−α ′) × z ₁ + (1−α ′) × B (z ₀ ) −2α ′ × β × b (Equation 44) In (Equation 44), when α ′ is replaced with α and 2 × b is replaced with d, (Equation 44) is equivalent to (Equation 5).

In (Equation 44), the value of (1−α ′) indicates the cancellation rate of the secondary differential detection coil with respect to the uniform magnetic field. When the magnetic field distribution in the space where the detection magnetometer and the compensating magnetometer are arranged is shown by (Equation 2),
As is apparent from (Equation 44), the detected magnetic field includes the term having the cancellation rate (1−α ′) as a coefficient and the baseline b.
And a term whose coefficient is.

As in the first embodiment, the base line of the compensating magnetometer is made shorter than that of the detecting magnetometer in order to prevent the magnetic field generated from the heart from entering the compensating magnetometer. For example, a plurality of compensating magnetometers having different baselines such as 10 mm and 30 mm are arranged. Therefore, as in the case of the first embodiment, FIG.
According to the first method of canceling the disturbing magnetic field according to the procedure shown in FIG. 5, the canceling of the disturbing magnetic field can be executed, and the disturbing magnetic field caused by the difference between the length of the baseline of the detecting magnetometer and the length of the baseline of the compensating magnetometer is different. The difference in the mixing amount can be corrected.

In the same manner as in the first embodiment, using the magnetic field waveform B _r (t) shown in (Equation 30), the magnetic field measured by the detection magnetometer constituted by the secondary differential detection coil is used. The magnetic field waveform B ′ ₁ (t) can be calculated by (Equation 45). However, the time constant of the first coil (input coil) of the second derivative detection coil constituting the detection magnetometer is t ₁ , the time constant of the second and third coils (compensation coil) is t ₂ , The time constant of the coil No. 4 (compensation coil) is t ₃ . When (Equation 45) is subjected to Taylor expansion, (Equation 46) is obtained.

[0186]

B ′ ₁ (t) = exp (−t / t ₁ ) −2 × exp (−t / t ₂ ) + exp (−t / t ₃ ) = − ｛1−exp (−t (1 / t) t ₁ −1 / t ₂ ))｝ × exp (−t / t ₂ ) − {1−exp (−t (1 / t ₃ −1 / t ₂ ))} × exp (−t / t ₂ ) (Equation 45)

[0187]

B ′ ₁ (t) = {(1 / t ₂ −1 / t ₁ ) − (1 / t ₃ −1 / t ₂ )} × t × exp (−t / t ₂ ) (number) 46) Similarly, the time constant of the first coil (input coil) of the secondary differential detection coil constituting the compensating magnetometer is t ′ ₁ , and the time constants of the second and third coils (compensation coils) Is t ′ ₂ and the time constant of the fourth coil (compensation coil) is t ′ ₃ , the magnetic field waveform B ′ ₂ (t) measured by the compensating magnetometer is
It can be calculated by (Equation 47).

[0188]

B ′ ₂ (t) = {(1 / t ′ ₂ −1 / t ′ ₁ ) − (1 / t ′ ₃ −1 / t ′ ₂ )} × t × exp (−t / t ′) ₂ )... (Equation 47) From the magnetic field waveform B ′ ₁ (t) measured by the detecting magnetometer, the magnetic field waveform B ′ ₂ (t) of the disturbing magnetic field measured by the compensating magnetometer is expressed by (Equation 48). The magnetic field waveform (B ′ ₁ −δ′B ′ ₂ ) canceled by using δ ′ defined by is represented by (Equation 49). When (Equation 49) is Taylor expanded, (Equation 5)
0).

[0189]

Δ ′ = {(1 / t ₂ −1 / t ₁ ) − (1 / t ₃ −1 / t ₂ )} / ｛(1 / t ′ ₂ −1 / t ′ ₁ ) − (1 / T ′ ₃ −1 / t ′ ₂ )｝ (Equation 48) In (Equation 48), (1 / t ₂ −1 / t ₁ ) is changed to (1 / T
₂ ), (1 / t ₃ -1 / t ₂ ) to (1 / T ₁ ) and (1 / T ₁ )
t ' ₂ -1 / t' ₁ ) to (1 / T ₄ ) and (1 / t ' ₃ -1 /
t ′ ₂ ) is replaced by (1 / T ₃ ), respectively.
8) is equivalent to (Equation 34).

[0190]

(B ′ ₁ −δ′B ′ ₂ ) = {(1 / t ′ ₂ −1 / t ′ ₁ ) − (1 / t ′ ₃ −1 / t ′ ₂ )} × δ ′ × t × exp (−t / t ₂ ) −δ ′ × {(1 / t ′ ₂ −1 / t ′ ₁ ) − (1 / t ′ ₃ −1 / t ′ ₂ )} × t × exp (−t / t ′ ₂ ) = {(1 / t ′ ₂ −1 / t ′ ₁ ) − (1 / t ′ ₃ −1 / t ′ ₂ )} × δ ′ × t × {exp (− (1 / t ₂ − 1 / t ′ ₂ ) × t) −1｝ × exp (−t / t ′ ₂ ) (Equation 49)

[0191]

(B ′ ₁ −δ′B ′ ₂ ) = − (1 / t ₂ −1 / t ′ ₂ ) × ｛(1 / t ′ ₂ −1 / t ′ ₁ ) − (1 / t ′) ₃ −1 / t ′ ₂ )｝ × δ ′ × t ² × exp (−t / t ′ ₂ ) (Equation 50) The term independent of time in the amplitude value of (Equation 50) is η ′
Assuming (Equation 51), (Equation 50) is a function shown in (Equation 52). As described above, (Equation 52) becomes (Equation 4)
8 shows a magnetic field waveform in which the disturbing magnetic field B ′ ₂ (t) is canceled from B ′ ₁ (t) using the fitting parameter δ ′ obtained in 8).

[0192]

Η ′ = − (1 / t ₂ −1 / t ′ ₂ ) × {(1 / t ′ ₂ −1 / t ′ ₁ ) − (1 / t ′ ₃ −1 / t ′ ₂ )} × δ '... (Equation 51)

[0193]

(B ′ ₁ −δ′B ′ ₂ ) = − η ′ × t ² × exp (−t / t ′ ₂ ) (Equation 52) In (Equation 52), η ′ is replaced by η. , T ′ ₂ are replaced with T ₃ , respectively, so that (Equation 52) is equivalent to (Equation 38).

Since (Equation 52) is equivalent to (Equation 38), the same applies to the case of using the secondary differential detection coil as the differential detection coil, as in the case of the first embodiment. The second method of canceling the disturbing magnetic field shown in FIG. 7 (a method of canceling the disturbing magnetic field caused by the frequency characteristics of the magnetically shielded room) can be applied.

As described above, in each of the first to ninth embodiments, even when the secondary differential detection coil is used as the differential detection coil, the differential detection coil is not limited to one.
In the same way as when using the second derivative detection coil,
Cancellation of the disturbing magnetic field can be executed. When a second-order differential detection coil is used in the present invention, a disturbing magnetic field from a wide range can be canceled.

[0196]

According to the present invention, interference is made by taking into account the difference in the cancellation rate of the differential detection coil constituting the SQUID magnetometer with respect to the uniform magnetic field and the difference in the baseline of the differential detection coil. Since the magnetic field is canceled, the disturbing magnetic field can be accurately canceled.

Further, the interference magnetic field caused by the frequency characteristics of the magnetically shielded room can be canceled with high accuracy, and the interference magnetic field having a steep and large strength can be canceled with high accuracy.

Further, it is possible to realize a biomagnetic field measuring apparatus capable of measuring a weak magnetic field generated from the heart to be examined and the heart of the fetus in the mother with high sensitivity.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a magnetic field measurement device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of a detecting magnetometer and a compensating magnetometer according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a magnetic field gradient inside a magnetically shielded room in the first embodiment of the present invention.

FIG. 4 is a flowchart showing an example of canceling a disturbing magnetic field by using the first compensating magnetometer according to the first embodiment of the present invention.

FIG. 5 is a flowchart showing an example of canceling an interfering magnetic field using the second compensating magnetometer according to the first embodiment of the present invention.

FIG. 6 is a diagram showing an example of a magnetic field waveform of a disturbing magnetic field obtained by a theoretical calculation in the first embodiment of the present invention.

FIG. 7 is a diagram showing an example of a flowchart for canceling an interfering magnetic field caused by frequency characteristics of a magnetically shielded room in the first embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration example of a magnetic field measurement device according to a second embodiment of the present invention.

FIG. 9 is a diagram showing an example of a magnetic field waveform measured by a fluxgate magnetometer in the magnetic field measurement device according to the second embodiment of the present invention.

FIG. 10 is a diagram showing an example of a magnetic field waveform measured by a fluxgate magnetometer and a SQUID magnetometer in the magnetic field measurement device according to the second embodiment of the present invention.

FIG. 11 is a diagram illustrating a magnetic field measuring apparatus according to a second embodiment of the present invention.
The figure which shows the example of the magnetic field waveform measured by ID magnetometer.

FIG. 12 is a diagram showing an example of the magnetic field waveforms of the magnetic field waveform shown in FIG. 11 of the present invention after executing a disturbance magnetic field canceling process (FIG. 4) using the first compensating magnetometer of the first embodiment.

FIG. 13 is a diagram showing an example of the magnetic field waveform shown in FIG. 12 of the present invention after the disturbance magnetic field cancellation processing (FIG. 5) using the second compensating magnetometer of the first embodiment is executed. .

FIG. 14 is a diagram showing an example of the magnetic field waveform after the cancellation processing (FIG. 7) of the magnetic field waveform shown in FIG. 13 of the present invention is performed for the disturbing magnetic field caused by the frequency characteristics of the magnetically shielded room.

FIG. 15 is a diagram showing an example of a magnetic field waveform obtained by measuring a magnetic field generated from a heart to be inspected by a SQUID magnetometer in the magnetic field measuring apparatus according to the second embodiment of the present invention.

16 is a diagram showing an example of a magnetic field waveform after executing a magnetic field waveform shown in FIG. 15 of the present invention and a disturbing magnetic field cancellation process (FIG. 4) using the first compensating magnetometer of the first embodiment; .

FIG. 17 is a diagram showing an example of the magnetic field waveform shown in FIG. 16 of the present invention after the disturbance magnetic field canceling process (FIG. 5) using the second compensating magnetometer of the first embodiment is executed (FIG. 5). .

18 is a diagram showing an example of a magnetic field waveform after executing the magnetic field waveform shown in FIG. 17 of the present invention after cancellation processing (FIG. 7) of a disturbing magnetic field caused by frequency characteristics of a magnetically shielded room.

19 is a diagram showing an example of a magnetic field waveform after the magnetic field waveform shown in FIG. 13 of the present invention is subjected to difference processing between channels.

FIG. 20 is a diagram showing an example of a magnetic field waveform after the magnetic field waveform shown in FIG. 17 of the present invention is subjected to difference processing between channels.

FIG. 21 is a diagram showing a display example of a magnetic field waveform after canceling out an interfering magnetic field in the second embodiment of the present invention.

22 and FIG. 17 of the second embodiment of the present invention.
FIG. 6 is a diagram showing a time constant obtained from the waveform shown in FIG.

FIG. 23 is a diagram illustrating a configuration example of a magnetic field measurement device according to a third embodiment of the present invention.

FIG. 24 is a diagram illustrating a configuration example of a magnetic field measurement apparatus according to a fourth embodiment of the present invention.

FIG. 25 is a fifth embodiment of the present invention, and shows the compensating magnetometer and the detecting magnetometer in the first embodiment (FIGS. 1 and 2) and the second embodiment (FIG. 8). FIG. 3 is a projection view showing an example of arrangement.

FIG. 26 is a sixth embodiment of the present invention, showing an example of the arrangement of the compensating magnetometer and the detecting magnetometer in the third embodiment (FIG. 23) and the fourth embodiment (FIG. 24). FIG.

[Explanation of symbols]

1 ... cryostat, 2 ... magnetic shield room, 3 ...
Gantry, 4 Bed, 5 Connector, 6 Drive circuit, 7 Amplifier filter unit, 8 Computer, 9, 9
−a, 9-b, 9-c, 9-d...
10-a, 10-b, 601 ... compensating magnetometer, 11-
a, 11-b, 11-c: Baseline, 12: Magnetic field gradient, 13: Position in z direction in magnetically shielded room, 1
4 ... magnetic field strength, 15, 16, 17, 18, 19, 20 ...
Processing, 101: fluxgate magnetometer main body, 102 ...
Fluxgate magnetometer sensor section, 201 ... measurement section,
301, 302, 303, 304, 305, 306, 3
07, 308, 309, 310... Processing, 401.
602: wiring, 603-a, 603-b: coil, 60
4. Control device, 605 FLL circuit.

Claims (1)

[Claims] A plurality of first sensors for detecting a component in a normal direction of a magnetic field generated from an inspection object inside a magnetic shield room.
A SQUID magnetometer, one or more second SQUID magnetometers for detecting the interfering magnetic field in the normal direction, and the first SQUID magnetometer.
A low-temperature container for cooling the first and second SQUID magnetometers, a drive circuit for driving the first and second SQUID magnetometers, and collecting signals detected by the first and second SQUID magnetometers. A computer for performing signal processing; and display means for displaying a result of the signal processing, wherein the first and second SQUID magnetometers have a differential detection coil, and the difference between the second SQUID magnetometer and the second SQUID magnetometer is provided. The magnetic field measuring method used in the magnetic field measuring device in which the length of the base line of the dynamic detection coil is shorter than the length of the base line of the differential detection coil of the first SQUID magnetometer is characterized in that the second SQUID
A signal of the disturbing magnetic field detected by the D magnetometer and a mixed magnetic field in which the normal component of the magnetic field emitted from the inspection object and the disturbing magnetic field detected by the first SQUID magnetometer are mixed. A first signal processing for applying the least squares method to cancel the disturbing magnetic field from the mixed magnetic field using a signal and generating the disturbing magnetic field caused by a frequency characteristic of the magnetically shielded room. In the vicinity of the initial time at which the time begins, a waveform B (t) representing the time change of the disturbing magnetic field generated due to the frequency characteristic is represented by
B (t), where A is the amplitude, T is the time constant, and t is the time variable
= −A · t ² · exp (−t / T), using the magnetic field waveform obtained by the first signal processing,
The amplitude A and the time constant T are obtained by the least square method, and using the B (t) determined by the least square method, from the magnetic field waveform obtained by the first signal processing,
And a second signal processing for canceling the disturbing magnetic field generated due to the frequency characteristic, by the computer.