JP3379519B2 - Magnetic field measurement device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SQUID (Super) device which is a superconducting device for detecting a biological magnetic field such as a cardiac magnetic field and a brain magnetic field, a geomagnetic field, and a weak magnetic field such as a nondestructive test.
conducting Quantum Interf
(Field Device: Superconducting Quantum Interference Element) Field of the Invention The present invention relates to a magnetic field measuring apparatus using a flux meter, and particularly to a magnetic field measuring apparatus for canceling a disturbing 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 dB to 50 dB (decibels)
Weak brain magnetic fields and cardiac magnetic fields are measured inside the magnetically shielded room with the above magnetic field attenuation rates. As the detection coil for detecting the biomagnetic field, a primary differential type detection coil for detecting the difference between the one-turn detection coil and the coil wound in the opposite direction is often used. The first-order differential type detection coil cancels the disturbing magnetic field from the distant magnetic field source,
With respect to the magnetic field generated from the vicinity of the heart, brain, etc., there is a feature that the signal can be detected without large cancellation, and the influence of the disturbing magnetic field can be easily reduced. Normally, the first-order differential type detection coil is about 40 dB to 50 dB for a uniform magnetic field.
Has attenuation of dB.

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

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

In addition, a method of soft cancellation using a signal from a reference coil using an SQUID sensor (prior art 2: Clin. Phys. Physio)
l. Meas. , Vol. 12, Suppl. B, p
p. 81-86 (1991)) has been devised, but details of the reference coil are not mentioned.

Japanese Unexamined Patent Publication 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 loss of coil balance. Japanese Patent Laid-Open No. 11-47108 has the following description. Multiple coils that artificially generate an external magnetic field
For example, at a known location on the outer surface of the dure. A drive current is applied to a plurality of coils to drive them. By using the detection value of the detection coil and the drive current value with respect to the external magnetic field generated from the plurality of coils, the sensitivity and the coil balance of the detection coil are measured with high accuracy. The effect of the coil imbalance is corrected with high accuracy from the biomagnetic field measurement value obtained from the detection value of the detection coil, and as a result, the error of the environmental magnetic field noise removal caused by the imbalance of the coil balance is reduced, and the biomagnetic field is reduced. The measurement accuracy of is improved. Inside the vacuum heat insulation container, a plurality of detection coils for biomagnetic field measurement mainly measuring the biomagnetic field are arranged on the side close to the subject, and at a position farther from the detection coil with respect to the subject, A plurality of reference coils that mainly measure the environmental magnetic field are arranged.

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

Japanese Unexamined Patent Publication No. 9-84777 (Prior Art 5) describes a biomagnetic field measuring apparatus capable of accurately estimating a current dipole at a deep position even when a plurality of current dipoles are positioned to overlap each other in the depth direction. Has been done. Japanese Unexamined Patent Publication No. 9-84777 discloses the following. A pickup coil that detects the magnetic flux from the magnetic field source of the living body,
A pickup coil array in which a plurality of types of pickup coils different from each other in at least one of the differential order and the baseline are arranged is used.

[0009]

In the prior art 1, the feedback current is passed through the cancel coil arranged outside the magnetic shield room so that the output of the flux gate arranged outside the magnetic shield room becomes zero. Therefore, in a multi-channel magnetic field measurement device having a SQUID magnetometer composed of a plurality of differential detection coils such as first-order differential detection coils, the cancel ratio of the differential detection coils in each channel is There is a problem that it is difficult to correct variations.

In the prior art 2, there is no description about the specific structure of the reference coil, and only the data when the magnetic shield room is not used is shown.

It is an object of the present invention to provide a magnetic field measuring apparatus capable of canceling a disturbing magnetic field with high accuracy. The cancel ratio of the differential detection coil in each channel of the multi-channel magnetic field measuring apparatus and the baseline. Provided is a magnetic field measuring apparatus capable of canceling a disturbing magnetic field in consideration of variations and removing distortion of a magnetic field waveform caused by a frequency characteristic of a magnetic shield room.

[0012]

The terms used in the following description will be explained.

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

(1) When the differential type detection coil is a first-order differential type detection coil.

(1.1) "Magnetometer for detection" (first SQ
UID magnetometer) is a first-order differential type SQUID magnetometer, and means a magnetometer that detects a magnetic field component in the z direction of a disturbing magnetic field and a magnetic field component in the z direction of a biomagnetic field generated from a living body.

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

(1.3) "Input coil of magnetic flux meter for detection"
Means a first coil of the coils constituting the first-order differential type detection coil constituting the detection magnetometer, which is arranged at a position closest to the inspection object.

(1.4) "Input coil of compensating magnetometer"
Means the first coil, which is arranged at the position closest to the inspection object, among the coils forming the first-order differential type detection coil forming the compensating magnetometer.

(1.5) "Compensation coil of the magnetic flux meter for detection"
Is the first coil of the first-order differential type detection coil constituting the detection magnetometer, which is arranged at a position farther from the inspection target than the first coil and has a plane parallel to the plane of the second coil. Means 2 coils.

(1.6) "Compensation coil of compensating magnetometer"
Is a first coil having a plane parallel to the plane of the second coil, which is arranged farther from the inspection target than the first coil, among the coils constituting the first-order differential type detection coil constituting the compensating magnetometer. Means 2 coils.

(1.7) "Output of the magnetic flux meter for detection" means the output of the primary differential type detection coil constituting the magnetic flux meter for detection.

(1.8) "Output of compensating magnetometer" means the output of the first-order differential type detecting coil constituting the compensating magnetometer.

(1.9) "Base line of the detecting magnetometer" means the baseline of the first-order differential type detecting coil which constitutes the detecting magnetometer, and the surface of the first coil and the second coil. Is the distance from the plane.

(1.10) "Base line of compensating magnetometer" means the baseline of the first-order differential type detection coil which constitutes the compensating magnetometer, and the surface of the first coil and the second coil. Is the distance from the plane.

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

(2.1) "Magnetometer for detection" (first SQ
UID magnetometer) is a second-order differential SQUID magnetometer and means a magnetometer that detects a magnetic field component in the z direction of a disturbing magnetic field and a magnetic field component in the z direction of a biomagnetic field generated from a living body.

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

(2.3) "Input coil of magnetic flux meter for detection"
Means a first coil of the coils forming the second-order differential type detection coil forming the detection magnetometer, which is arranged at the position closest to the inspection target.

(2.4) "Input coil of compensating magnetometer"
Means a first coil of the coils forming the second-order differential type detection coil forming the compensating magnetometer, which is arranged at the position closest to the inspection target.

(2.5) "Compensation coil for detecting magnetometer"
Are sequentially arranged at positions farther from the inspection target than the first coil among the coils constituting the second-order differential type detection coil constituting the detection magnetometer, and have a plane parallel to the plane of the second coil. It means the 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"
Are sequentially arranged at positions farther from the inspection target than the first coil among the coils constituting the second-order differential type detection coil constituting the compensating magnetometer, and have a plane parallel to the plane of the second coil. It means the 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 the magnetic flux meter for detection" means the output of the secondary differential type detection coil constituting the magnetic flux meter for detection.

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

(2.9) "Baseline of detecting magnetometer" means the baseline of the second-order differential type detecting coil which constitutes the detecting magnetometer, and the surface of the first coil and the second coil. 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) "Base line of compensating magnetometer" means the baseline of the second-order differential type detecting coil which constitutes the compensating magnetometer, and the surface of the first coil and the second coil. 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, a plurality of differential type detection coils (first-order differential type detection coil or second-order differential type detection coil) are used to detect a disturbing magnetic field and a magnetic field generated from a living body. SQUID magnetometer (first SQUID
ID magnetometer) and a differential type detection coil (first differential type detection coil or second differential type detection coil), and one or a plurality of SQUID magnetometers (second SQUID magnetometer) for detecting an interfering magnetic field. ) And are arranged inside the cryostat, and cryogenic refrigerants such as liquid helium and liquid nitrogen are stored inside the cryostat, or a refrigerator is arranged. The cryostat is held in the gantry.

The second SQUID magnetometer is configured so that the baseline of the differential detecting coil of the second SQUID magnetometer is shorter than the baseline of the differential detecting coil of the first SQUID magnetometer. The configuration is such that the magnetic field emitted 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 detected by the first SQUID magnetometer, which is a mixture of the magnetic field emitted from the living body and the disturbing magnetic field. , The least fitting method is applied to find the optimum fitting parameter, and the disturbing magnetic field is canceled (removed) from the detected mixed magnetic field (first disturbing magnetic field canceling method).

The disturbing magnetic field that cannot be canceled by the first canceling magnetic field canceling method described above, that is, the disturbing magnetic field generated due to the frequency characteristic of the magnetic shield room, is calculated as follows: The amplitude A and the time constant T are approximated by the theoretical waveform representing the change by the least square method, and the disturbing magnetic field is removed.

[0040]

[Number 1] B (t) = - A · t 2 · exp (-t / T) ... ( Equation 1) where, in the prior art 1 the prior art 5, a feature of the present invention, detects a disturbance magnetic field A configuration in which 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 that detects a biomagnetic field, and differential with different baselines The configuration using a plurality of second SQUID magnetometers equipped with the type detection coil, and the configuration for canceling the disturbing magnetic field generated due to the frequency characteristics of the magnetic shield room,
Not disclosed.

The first configuration of the magnetic field measuring apparatus of the present invention comprises a plurality of first SQUID magnetometers for detecting a magnetic field in the normal direction generated from an object to be inspected, and a second magnetic field measuring apparatus for detecting a disturbing magnetic field in the normal direction. SQUID magnetometer and first and second SQUIS
A cryogenic container for cooling the D magnetometer and first and second SQUs
Drive circuit for driving the ID magnetometer, and first and second SQ
The first and second SQUID magnetometers are equipped with a compensation coil and are provided with a computer that collects signals detected by the UID magnetometer and perform signal processing, and display means for displaying the result of the signal processing. A coil (first differential type detection coil or second differential type detection coil), and the length of the baseline of the differential type detection coil of the second SQUID magnetometer is
Is shorter than the length of the baseline of the differential detection coil of the SQUID magnetometer.

In the first configuration of the present invention, (1) the magnetic field in the normal direction generated from the inspection target is detected inside the magnetic shield room, and one or more second SQUID magnetometers are provided. , The calculator is a signal of the interfering magnetic field detected by the second SQUID magnetometer, and a signal of the mixed magnetic field in the normal direction in which the magnetic field emitted from the living body and the interfering magnetic field are detected by the first SQUID magnetometer. And the first signal processing for canceling the disturbing magnetic field from the mixed magnetic field by applying the least squares method, and the initial time when the generating of the disturbing magnetic field caused by the frequency characteristic of the magnetic shield room starts. , The waveform B (t) representing the waveform of the disturbing magnetic field generated due to the frequency characteristics, the amplitude A, the time constant T,
B (t) = − A · t ² · exp, where t is a time variable
The amplitude A and the time constant T are approximated by (-t / T) and the magnetic field waveform obtained by the first signal processing is used to obtain the amplitude A and the time constant T by the method of least squares, and the value of B is determined by the method of least squares.
Using (t), from the magnetic field waveform obtained by the first signal processing, performing the second signal processing for canceling the disturbing magnetic field generated due to the frequency characteristic, and
(2) The computer estimates the initial time, and the estimated initial time is displayed on the time axis of the magnetic field waveform in which the disturbing magnetic field is 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 of the present invention is to provide a plurality of first SQUID magnetometers for detecting a magnetic field in the normal direction generated from an inspection target inside the magnetically shielded room, and a magnetic field in the normal direction. A second SQUID magnetometer for detecting the disturbing magnetic field; a cryogenic container for cooling the first and second SQUID magnetometers; a drive circuit for driving the first and second SQUID magnetometers; And a computer that collects signals detected by the second SQUID magnetometer and performs signal processing, and a display unit that displays the result of the signal processing. The first and second SQUID magnetometers have compensating coils. The differential type detection coil (first differential type detection coil, second differential type detection coil) which has, the length of the baseline of the differential type detection coil of the second SQUID magnetometer is the first SQUID magnetic flux. Differential type detection carp Shorter than the length of the baseline, computer, a plurality of first SQUID magnetometers normal direction of the magnetic field waveform obtained by, considering the difference in cancellation rates between the first SQUID magnetometer signal processing to cancel the interference field Te and (b), the resulting magnetic field waveform by the signal processing (i), the signal processing for canceling the interfering magnetic field is generated due to the frequency characteristics of the magnetically shielded room (b) It is characterized by performing and.

In the second configuration of the present invention, (1) the computer estimates the initial time when the generation of the disturbing magnetic field caused by the frequency characteristic starts, and the estimated initial time is the signal processing. The interference magnetic field is displayed on the time axis of the magnetic field waveform canceled by (a) and (b), and (2) second
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 of the present invention is to provide 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, and a magnetic field in the normal direction. Second and third S detecting the disturbing magnetic field
QUID magnetometer and first, second, and third SQUIDs
A cryogenic container for cooling the magnetometer, a drive circuit for driving the first, second, and third SQUID magnetometers, first, second,
And a computer that collects signals detected by the third SQUID magnetometer and performs signal processing, and a display unit that displays the result of the signal processing. The first, second, and third SQs are provided.
The UID magnetometer is a differential type detection coil (1
Second derivative type detection coil, second derivative type detection coil),
The baseline length of the differential detection coil of the second and third SQUID magnetometers is shorter than the baseline length of the differential detection coil of the first SQUID magnetometer, and the second SQUID magnetic flux The length of the differential detection coil baseline of the meter is shorter than the baseline length of the differential detection coil of the third SQUID magnetometer, and the calculator obtains by the plurality of first SQUID magnetometers. From the obtained magnetic field waveform in the normal direction, the signal processing (a) for canceling the disturbing magnetic field in consideration of the difference in the cancellation rate between the first SQUID magnetometers and the magnetic field obtained by the signal processing (a). From the waveform, signal processing for canceling the disturbing magnetic field in consideration of 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 ( b 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 the initial time when the generation of the disturbing magnetic field caused by the frequency characteristic starts, and the estimated initial time is the signal processing. (A), (b), and (c) show that the disturbance 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 of the present invention is a plurality of first SQUID magnetometers for detecting a magnetic field in a normal direction generated from an inspection target inside an electromagnetic shield room for blocking high frequency electromagnetic waves. , A plurality of second SQUID magnetometers for detecting a disturbing magnetic field in a normal direction, and first and second S
A cryogenic container for cooling the QUID magnetometer, a drive circuit for driving the first and second SQUID magnetometers, and a cancel coil for generating a magnetic field in the normal direction for arranging the inspection target from above and below and canceling the disturbing magnetic field And a computer that collects signals detected by the first and second SQUID magnetometers and performs signal processing, and first and second SQUs.
The ID magnetometer has a differential detection coil (first differential detection coil, second differential detection coil) with a compensation coil, and the length of the baseline of the differential detection coil of the second SQUID magnetometer. Is shorter than the length of the baseline of the differential detection coil of the first SQUID magnetometer, and the control means outputs the current flowing in the cancel coil to the output of one SQUID magnetometer of the plurality of second SQUID magnetometers. The cancellation coil is characterized by generating a magnetic field in the normal direction opposite to the disturbing magnetic field.

In the fourth structure of the present invention, (1) second
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 the cancel coil is
It is also characterized in that it doubles as a feedback coil used in an independently provided drive circuit, and (3) the cancel coil is arranged inside or outside the electromagnetic shield room.

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

In the fifth structure of the present invention, the predetermined direction is at least one of the x, y, and z directions. Further, the predetermined direction is the normal direction and / or the tangential direction, and the normal direction and / or the tangential direction component of the magnetic field generated from the inspection target 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.

A typical configuration of the present invention is summarized below with reference to FIG. A plurality of first SQUID magnetometers 9 for detecting biomagnetic fields and disturbing magnetic fields, a plurality of second SQUID magnetometers 10 for detecting disturbing magnetic fields, and a drive 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 first-order differential type detection coil, and are the primary of the second SQUID magnetometer. The baseline of the differential type detection coil is shorter than the baseline of the primary differential type detection coil of the first SQUID magnetometer , and the plurality of first SQUID magnetometers 9 are used.
Considering the difference in the cancellation rate between the first-order differential type detection coils of the first SQUID magnetometer from the magnetic field waveform detected by
The process of canceling the disturbing magnetic field and the second SQU
A process of canceling the disturbing magnetic field in consideration of the difference in the baseline between the first-order differential type detection coils of the ID magnetometer ,
And a process of canceling an interfering magnetic field generated due to the frequency characteristic of the magnetic shield room. According to this configuration, it is possible to provide a magnetic field measuring apparatus that can cancel a disturbing magnetic field that is steep and has a large intensity and that can cancel the disturbing magnetic field with high accuracy.

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

Further, the distortion of the magnetic field waveform in the normal direction caused by the frequency characteristic of the magnetically shielded 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 sensitively measuring the weak magnetic field generated from the heart to be examined and the heart of the fetus in the mother's body.

[0055]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. First, as a differential type detection coil,
The case of using the secondary differential type detection coil will be described in detail, but the present invention can be applied to the case of using the secondary differential type detection coil as the differential type detection coil as described in detail later. .

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

Detecting magnetometer 9 and compensating magnetometer 10
Are driven by the drive circuit 6 via the connector 5, and the outputs of the detecting flux meter 9 and the compensating flux meter 10 are amplified by the amplifier filter unit 7 and filtered, and then collected by the computer 8. The computer 8 uses the output signal of the compensating magnetometer 10 to perform the canceling of the disturbing magnetic field, which will be described in detail later, on the output of the detecting magnetometer 9, and then estimates the average magnetic field and analyzes the magnetic field distribution. Etc. signal processing is performed and the processing result is displayed on the display device.

FIG. 2 is a diagram showing a configuration example of the detecting magnetometer and the compensating magnetometer according to the first embodiment of the present invention.
It is the figure which expanded and displayed the magnetic flux meter for detection 9 and the magnetic flux meter 10 for compensation which detect the biomagnetic field of z direction arrange | positioned inside the cryostat 1. As shown in FIG. Magnetic flux meters for detection 9-a, 9-b,
Base lines 11-c of 9-c and 9-d are 50 mm. Magnetic flux meters for detection 9-a, 9-b, 9-c, 9-d
Are arranged in a 2 × 2 matrix. The number and arrangement of the magnetic flux meters for detection are not limited to the example shown in FIG. For example, 9 to 64 in a 3 × 3 to 8 × 8 matrix.
The individual magnetometers for detection may be arranged, or may be arranged three-dimensionally. Further, the value of the baseline 11-c is not limited to 50 mm and may be 40 mm or the like.

The baselines 11-a and 11-b of the compensating magnetometers 10-a and 10-b are respectively the detecting magnetometers 9-a and 9-a.
-B, 9-c, 9-d are shorter than the baseline 11-c, and in the first embodiment, the baseline 11-a is 10 m.
m, and the baseline 11-b is 30 mm.
The baselines 11-a and 11-b of the compensating flux meter 10 (10-a, 10-b) are connected to the detecting flux meter 9 (9-a, 9-
-B, 9-c, 9-d) is shorter than the baseline 11-c so that the magnetic field generated from the heart is not mixed into the compensating magnetometer 10 and 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 arranged separated by 300 mm in the z direction. The distance between the surface of the input coil of the compensation magnetic flux meter 10 and the surface of the input coil of the detection magnetometers 9 is not limited to 300 mm, the compensation
The magnetic flux meter 10 can be set at an arbitrary distance so that the magnetic field generated from the heart is not mixed therein.

A method of canceling a disturbing magnetic field in the case where the gantry 3 holding the cryostat 1 is arranged inside the magnetic shield room and it is assumed that the magnetic shield room does not have frequency characteristics will be described below.

FIG. 3 shows the first embodiment of the present invention.
It is a figure which shows the magnetic field gradient inside a magnetically shielded 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]

In Equation 2] B (z) = βz + B (z 0) ... ( Equation 2) gradiometer consists first-order differential type detection coil, S ₁ the area of the input coil, the area of the compensation coil S _2, base When the line is d, the magnetic flux Φ detected by the magnetometer becomes (Equation 3). The surface of the input coil is z = z ₁ and the surface of the compensation coil is 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 × {β × (z ₁ + d ) + B (z ₀ )} = β × (S ₁ −S ₂ ) × z ₁ + (S ₁ −S ₂ ) × B (z ₀ ) −S ₂ × β × d (Equation 3) When defined by 4), B ₀ = Φ / S ₁ is obtained by (Equation 5).

[0065]

[Formula 4] α = S ₂ / S ₁ (Formula 4)

[0066]

[Equation 5] B ₀ = Φ / S ₁ = β × (1-α) × z ₁ + (1-α) × B (z ₀ ) −α × β × d (Equation 5) (Equation 5) In this case, the value of (1-α) indicates the cancellation rate for the uniform magnetic field of the first-order differential type detection coil.
When the magnetic field distribution in the space where the detecting magnetometer and the compensating magnetometer are arranged is shown by (Equation 2), as is clear from (Equation 5), the detected magnetic field has a cancellation rate (1-α).
And a term having a baseline d as a coefficient.

Further, the baseline 11 of the detecting magnetometer 9
-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. It is considered that by correcting the output of the compensating magnetometer 10 by the method described, only the term having the cancellation rate (1-α) as a coefficient remains. However, when measuring the magnetic field generated from the heart, even if the compensating flux meter 10 is placed at a position 300 mm away from the detecting flux meter 9,
When the baseline is set to 50 mm, the waveform of the magnetic field generated from the heart appears significantly, so that the magnetic flux generated from the heart is mixed in the compensating magnetometer 10, and therefore only the disturbing magnetic field cannot be detected.

Therefore, in order to prevent the magnetic field generated from the heart from entering the compensating magnetometer, the compensating magnetometer 10 is used.
(10-a, 10-b) baseline 11-a, 11
-B is made shorter than the baseline 11-c of the magnetic flux meter 9 for detection so that the length of the baseline 11-a and the baseline 1-c
Different from the length of 1-b.

For example, in the example shown in FIG. 2, the baseline 11-a is 10 mm and the baseline 11-b is 30 mm.
And Compensating magnetometer with different baseline values 1
By 0 multiple arrangement, it is possible to correct the difference in amount of mixed disturbance magnetic field and the detection magnetic flux meter 9 baseline and length of the compensation magnetometer 10 baseline is due to different.

The method of canceling the disturbing magnetic field using the magnetic field waveform measured by the compensating magnetometer (first canceling magnetic field canceling method) will be described below with reference to FIGS. 4 and 5. FIG. 4 is a diagram showing a flow chart showing an example of canceling a disturbing magnetic field by using the first compensating magnetometer of the first embodiment of the present invention, and FIG. 5 is a diagram of the first embodiment of the present invention. It is a figure which shows the flowchart which shows the example which cancels a disturbing magnetic field using the compensating magnetometer of FIG.

Here, the magnetic field waveforms detected by the magnetometers for detection 9-a, 9-b, 9-c, 9-d shown in FIG. 1 or 2 are 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 2 are G _1i and G _2i . F _1i , f _2i , f _3i , f _4i , g _1i , and g _2i shown in FIG. 4 and FIG.
4, with k = 1 to 2, the process of obtaining an average value and the process of subtracting each average value from each magnetic field waveform (Equation 6)
(Equation 9) It should be noted that the addition symbol Σ used in the following mathematical expressions indicates addition regarding i = 1 to i = N (N indicates the number of sampling points on the time axis of the magnetic field waveform).

[0072]

[ _Equation 6] F _j0 = Σ (F _ji ) / N ( _Equation 6)

[0073]

## _EQU7 ## G _k0 = Σ (G _ki ) / N ( _Equation 7)

[0074]

[ _Equation 8] f _ji = F _ji −F _j0 ( _Equation 8)

[0075]

G _ki = G _ki −G _k0 ( _Equation 9) The value of γ shown in (Processing 15) shown in FIG. 4 and the value of γ ′ shown in (Processing 19) shown in FIG. 5 are the least squares method. Can be determined by Magnetic field waveform F _ji (j
= 1 to 4, i = 1 to N), the magnetic field waveform f _ji (j = 1 to 4, i = 1 to 1) after removing the average value of the magnetic field waveform F _ji .
N) is f _i for simplification, and the magnetic field waveform g _ki after removing the average value of the magnetic field waveform G _ki from the magnetic field waveform G _ki (k = 1 to 2, i = 1 to N) obtained by the compensating magnetometer. (K =
1 to 2, i = 1 to N) is represented by g _i for simplicity,
When the value of γ that minimizes the evaluation function E of (Equation 10) is obtained by least-squares approximation, (Equation 11) is obtained. 4 and 5
Shows the procedure for canceling the disturbing magnetic field for each channel using (Equation 11).

[0076]

(Equation 10) 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 magnetometer 9 for detection
Compensating 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 compensating magnetometer 10-b is used.
The magnetic field waveform detected by (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 in order to cancel the disturbing magnetic field mainly in consideration of the difference in the cancellation rate.

(Processing 15): Using (Equation 11), [gamma] ([gamma] ₁ , with respect to each detecting magnetometer 9 and compensating magnetometer 10-a.
Calculate the values of γ ₂ , γ ₃ , γ ₄ , γ ₅ ). γ ₁ , γ ₂ , γ ₃ ,
γ ₄ and γ ₅ are given by (Equation 12) to (Equation 16).

[0079] (processing 16): the difference between the mainly cancellation rate
Considering this, the disturbing magnetic field can be canceled for each of the channels 1 to 4, and the magnetic field waveforms f ′ _1i , f ′ _2i , f ′ _3i and f ′
_4i , _g'2i are obtained. _f'1i , _f'2i ,
f ′ _3i , f ′ _4i , and g ′ _2i are ( _Equation 17) to (Equation 21)
Given by. It is considered that a magnetic field component due to the difference in 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 ( _Equation 17)

[0086]

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

[0087]

F ′ _3i = f _3i −γ ₃ × g _1i ( _Equation 19)

[0088]

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

[0089]

G ′ _2i = g _2i −γ ₅ × g _1i ( _Equation 21) Next, moving to # 1 (reference numeral 18) in FIG. 5, (Processing 1
Similarly to 5), (Processing 19) and (Processing 20) are executed.

[0090] (processing _{19): γ '1, γ} ' 2, γ '3, γ'
₄ is obtained by (Equation 22) to (Equation 25).

[0091] (processing 20): the magnetic field waveform g to cancel the interference field from 'the _2i as reference data, the magnetic field waveform f after performing the (process 16)' _1i, f _'2i, f' _3i, f _'4i F " _1i , f" _2i , f " _3i , f" _4i
6) to (Equation 29).

[0092]

Γ ′ ₁ = Σ (f ′ _1i × g ′ _2i ) / Σ (g ′ _2i ) ² ( _Equation 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]

[ _Equation 26] f " _1i = f ' _1i -γ' ₁ × g ' _2i ( _Equation 26)

[0097]

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

[0098]

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

[0099]

F ′ _4i = f ′ _4i −γ ′ ₄ × g ′ _2i ( _Equation 29) The above-described method assumes that the magnetic shield room has no frequency characteristic, and the baseline length is different. 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 a disturbing magnetic field, which cancels the disturbing magnetic field depending on the frequency characteristic of the magnetic shield room, which cannot be canceled only by the above first canceling magnetic field canceling method.

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 an RC circuit with resistors and capacitors. That is, when a step function-like disturbing magnetic field enters the magnetically shielded room, the magnetic field waveform B _r observed inside the magnetically shielded room is given by (Equation 30) where t is time and T is time constant. It is considered to have a magnetic field waveform. For ease of understanding (Equation 30), the amplitude value is set to 1 (assuming that a disturbing magnetic field represented by a unit step function enters the magnetic shield 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 time constants of the input coil and the compensation coil of the magnetic flux meter for detection are T ₁ and T ₂ , respectively. Taylor expansion of (Equation 31) results in (Equation 32).

[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₎ ... (number 31)

[0104]

B ₁ (t) = (1 / T ₂ −1 / T ₁ ) × t × exp (−t / T ₁ ) ... (Equation 32) Similarly, the input coil of the compensating magnetometer and the compensation When the time constants of the coils are 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 ) ... (Equation 33) Magnetic field waveform B ₁ (measured by the magnetometer for detection From t), the magnetic field waveform B ₂ (t) of the disturbing magnetic field measured by the compensating magnetometer is canceled using δ defined by (Equation 34), and the magnetic field waveform (B ₁ −δB ₂ ) is ( (Number 35)
Becomes Taylor expansion of (Equation 35) into (Equation 32) yields (Equation 36).

[0106]

Equation 34] _{δ = (1 / T 2 -1} / T 1) / (1 / T 4 -1 / T 3) ... ( number 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) ...} ( number 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) Letting η (Equation 37) be the term that does not depend on time among the amplitude values of (Equation 36), (Equation 36) becomes the function shown in (Equation 38). As described above, (Equation 38) uses the fitting parameter δ obtained by (Equation 34) to calculate B ₁
A magnetic field waveform in which the disturbing magnetic field B ₂ (t) is canceled from (t) is shown.

[0109]

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

[0110]

(B ₁ −δB ₂ ) = − η × t ² × exp (−t / T ₃ ) ... (Formula 38) FIG. 6 shows theoretical calculation in the first embodiment of the present invention. It is a figure which shows the example of the magnetic field waveform of the disturbance magnetic field calculated | required. Figure 6
In the figure, the horizontal axis indicates time (seconds) and the vertical axis indicates (Equation 30).
As shown in, the magnetic field strength derived from the function having an amplitude value of 1 is shown.

FIG. 6A shows the magnetic field waveform B _r (t) (obtained by (Equation 30)) obtained by theoretical calculation (the magnetic field waveform of the observed disturbing magnetic field), and FIG. ，
FIG. 6C shows a magnetic field waveform B ₁ (t) (obtained by (Equation 32)) measured by a first-order differential SQUID magnetometer (detection magnetometer). The magnetic field waveform B ₂ (t) is used to cancel the disturbing magnetic field with respect to the magnetic field waveform B ₁ (t) measured by the magnetic flux meter for detection, that is, (Equation 38).
Magnetic field waveform {(B ₁ (t) −δB
₂ (t)} is shown.

In an actual measurement system, a high-pass filter (HPF) is used to measure the biomagnetic field.
In FIG. 6D, in order to simulate the actually measured magnetic field waveform, the magnetic field waveform measured by the compensating magnetometer is used to compare the disturbance magnetic field waveform with the magnetic field waveform measured by the detecting magnetometer. Magnetic field waveform after cancellation is performed, that is, magnetic field waveform {B obtained by (Equation 38)
₁ shows a magnetic field waveform after passing ₁ (t) −δB ₂ (t)} through a 0.1 Hz second-order Butterworth type high-pass filter.

In the above calculation, the time constant at B _r is T = 0.2 seconds, and the time constant at B ₁ is T ₁ = 0.
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 the observed disturbing magnetic field, which is a magnetic field waveform calculated by simulation assuming that the disturbing 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 Brakes et al. (Meas. Sc) at Twente University.
i. Technol. , Vol. 2, pp. 596-6
01 (1991)) and the magnetic field waveform actually measured is in good agreement.

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

(Process 302): The point at which the data in which the magnetic field waveform is distorted starts (the initial point at which the disturbing magnetic field occurs) (in the example shown in FIG. 6, the horizontal axis is equal to 10 seconds) is obtained.
In process 302, a secondary differential waveform with respect to time of the measured magnetic field waveform (the magnetic field waveform before the cancellation of the first disturbing magnetic field) is calculated to detect a peak, and the time of the peak point is set to the start point (initial point) of the data. ). 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 the flux gate installed outside the magnetic shield room may be used.

(Processing 303): j channel (j = 1 to 1)
4) regarding the amplitude η _j , the time constant T _j (T _j is T ₃ (Equation 38) of the j channel), and the initial value (the data point at the beginning of the data where the distortion of the magnetic field waveform occurs). Set. For example, η _j = 1 and T _j = 0.2 seconds are set.

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

(Process 305): Perform a high-pass filter process.

(Process 306): The evaluation function E is calculated from the least square sum of the measured values B _mes , _j , _i and B _est , _j , _i according to ( _Equation 40).
Calculate _j . In addition, in (Formula 40), the addition symbol Σ is
It is assumed that i = 1 to i = N ′ (N ′ represents the number of sampling points t _i on the time axis of the magnetic field waveform of the measured value B _mes , _j , _i ).

[0121]

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

[0122]

Equation 40] _{E j = Σ (B mes,} j, i -B est, j, i) 2 ... ( number 40) (process 307): _{E j>} preset reference value (e.g.,
When E _j > 10 ⁻⁴ ), (Process 308) is executed, and E _j
When ≦ preset reference value (for example, E _j ≦ 10 ⁻⁴ ), (Process 309) is executed.

(Processing 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, and the (processing 304) ) Is executed.

(Processing 309): Using the amplitude η _j , the time constant T _j , and the point (initial point) of the beginning of the data, which is obtained as the optimum solution, theoretically the magnetic field waveform B is calculated by (Equation 39).
_est , _j , _i is calculated, and according to (Equation 41), B _est , _j , _i is subtracted from the magnetic field waveform B _mes , _j , _i obtained by the method of canceling the first disturbing magnetic field. As a result, the interference time is canceled by the second interference magnetic field canceling method, j
Get B _c , _j , _i for the channel (j = 1 to 4).

[0125]

[Expression 41] B _c , _j , _i = B _mes , _j , _i- B _est , _j , _i (Expression 41) The method described above occurs depending on the frequency characteristics of the magnetically shielded room. 2 is a description of a second method of canceling a disturbing magnetic field, in which the remaining disturbing magnetic field is canceled by the canceling magnetic field canceling method of FIG.

(Second Embodiment) Next, the result of the above-mentioned processing will be described below by using the data measured with the arrangement of the SQUID magnetometer shown in FIGS. 1 and 2. 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 the magnetic field measuring apparatus according to the second embodiment of the present invention. The sensor unit 102 of the fluxgate magnetometer was installed outside about 5 m away from the magnetic shield room, and the magnetic field in the same z direction as the magnetic field detection direction of the first-order differential type SQUID magnetometer inside the magnetic shield room was detected. Fluxgate magnetometer sensor unit 102
Is operated by the main body 101 of the fluxgate magnetometer. The output of the main body 101 is passed through a low-pass filter having a corner frequency of 100 Hz only and the computer 8
Captured in. The layout of the first-order differential SQUID magnetometer is
As described with reference to FIGS. 1 and 2, the output of the SQUID magnetometer was taken into the computer 8 through a bandpass 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 cycle 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 about 50 minutes away from the magnetic shield room at intervals of about 10 minutes.

FIG. 10 shows a flux gate magnetometer and a SQUID in the magnetic field measuring apparatus according to the second embodiment of the present invention.
It is a figure which shows 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 magnetic field strength (pT (picotesla) in FIG. 10 (A),
(B) shows μT). FIG. 10 shows the magnetic field waveform recorded in the measurement section 201 shown in FIG. 9, and the magnetic field waveform detected by the detection flux meter and the magnetic field waveform measured by the fluxgate magnetometer (enlargement of the measurement section 201 in FIG. 9). Figure) is shown. The measurement of the magnetic field was carried out when the examination subject was not lying on the bed.

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

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

Ch. 1 to ch. The cause of the difference in the magnitude of the disturbing magnetic field even when using the magnetic flux for detection with the same baseline as in the magnetic field waveform of 4 is mainly due to the difference in the cancellation rate between the channels from the consideration of (Equation 5). it is conceivable that.

The detection coil, the input coil and the compensation coil of the compensating flux meter 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), a slight difference in the cancellation rate is largely reflected as a difference in the magnitude of the magnetic field waveform. In the case of a handmade coil, such a difference in cancellation rate between channels is an unavoidable problem. If each cancellation rate is adjusted,
In a uniform magnetic field of 10 ⁻³ or less, it is necessary to adjust the coil in the superconducting state, which is a very difficult work in reality.

When there is a strong non-uniform magnetic field, the magnitude of the output of the magnetometer changes greatly due to the difference in the canceling ratio between the channels. Therefore, a reference for estimating the magnetic field for one specific channel is used. It is difficult to accurately cancel the disturbing magnetic field by a method of using as a channel and using the output of the reference channel to subtract the output signal of the reference channel from the output signal of each channel. Therefore, in the multi-channel magnetic field measuring device, it is necessary to determine the optimum canceling amount of the disturbing magnetic field for each channel.

FIG. 11 shows, in the magnetic field measuring apparatus of the second embodiment of the present invention, the SQUI in a state different from the example shown in FIG. 10 in a state where the inspection object is not lying on the bed.
It is a figure which shows the example of the magnetic field waveform measured by the D magnetometer. In FIG. 11, the horizontal axis represents time (seconds) and the vertical axis represents magnetic field strength (pT). 11 (a), (b),
(C) and (d) are the magnetic flux meters for detection 9-a (ch. 1), 9-b (ch. 2), and 9-b (ch. 2) shown in FIGS. 1, 2, and 8, respectively.
It corresponds to the magnetic field waveforms f _1i , f _2i , f _3i , and f _4i by 9-c (ch. 3) and 9-d (ch. 4), and FIG.
(E) and (f) are compensating magnetometers 10-a (r), respectively.
ef. ch. 1) and 10-b (ref.ch.2), which correspond to the magnetic field waveforms g _1i and g _2i .

Ref. ch. 1 magnetic field waveform g _1i (Fig. 11
(E)) and ref. ch. 2 magnetic field waveform g _2i (Fig. 11
In (f), a large disturbing magnetic field of about 100 pT is generated around time 16 seconds. Baseline is 10 mm
Waveform g by the compensating magnetometer (ref.ch1.)
_Although the magnitude of the magnetic field waveform of _1i (FIG. 11 (e)) is the smallest, the magnetic field waveform of FIG.
h. 1) to 11 (d) (ch. 4), the waveforms of the disturbing magnetic field having the same shapes as the waveforms f _1i , f _2i , f _3i , and f _4i appear.

FIG. 12 shows an example of a magnetic field waveform after performing the interference magnetic field cancellation (FIG. 4) using the first compensating magnetometer of the first embodiment on the magnetic field waveform shown in FIG. 11 of the present invention. FIG. In FIG. 12, the horizontal axis represents time (second) and the vertical axis represents magnetic field strength (pT). 12 is shown in FIG.
Ref. The results of executing (Processing 15) and (Processing 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) and (Equation 21), f ′ _1i , f ′ _2i , f ′ _3i ,
_f'4i and _g'2i are shown.

The magnetic field waveforms of FIGS. 12 (a), 12 (b), 12 (c) and 12 (d) are shown in FIGS. 11 (a), 11 (b), 11 (c) and 11 (d).
Although the disturbing magnetic field is about 1/4 of that of the magnetic field waveform of, the large disturbing magnetic field still remains.

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

According to the result shown in FIG. 13, the large disturbing magnetic field is almost canceled, but 20 p near time 15 seconds.
A disturbing magnetic field of about T remains. FIG. 13 (a),
The waveforms of the disturbing magnetic fields remaining in (b), (c), and (d) are
It closely resembles the magnetic field waveform shown in FIG. 6D obtained by simulation. The waveform of the residual disturbing magnetic field shown in FIG. 13 is a magnetic field waveform generated when the disturbing magnetic field mixed in a step function is distorted 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 this residual disturbing magnetic field is
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 result shown in FIG. 13, the channel number of the magnetometer for detecting, that is, the magnetometer for detecting is It changes depending on the position where it is placed.

Therefore, the waveform of the disturbing magnetic field remaining due to the canceling of the disturbing magnetic field using the first and second compensating magnetometers of the first embodiment has a positional relationship between the detecting magnetometer and the compensating magnetometer. It also means that it changes depending on. FIG.
In order to cancel the remaining disturbing magnetic field shown in (1), (processing 302) to (processing 309) shown in FIG. 7 are executed.

FIG. 14 is a diagram showing an example of the magnetic field waveform after canceling the disturbing magnetic field caused by the frequency characteristic of the magnetic shield room (FIG. 7) 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),
The results obtained by executing the processes shown in (Formula 39) to (Formula 41) are shown in FIGS. 14 (a), (b), (c), and (d).

As is clear from FIGS. 14 (a), (b), (c) and (d), the disturbing magnetic field is almost canceled, but ch. 1-ch. In the magnetic field waveform of each channel of No. 4, a sharp peak remains as a disturbing magnetic field at around 15 seconds, which is considered to be an initial point where the disturbing magnetic field is mixed in a step function. It is considered that the disturbing magnetic field having a sharp peak remaining until the end is caused by the difference in the time constant T ₁ of the input coil of the magnetometer for detection.

FIG. 15 shows the magnetic field generated from the heart to be examined in the magnetic field measuring apparatus according to the second embodiment of the present invention.
It is a figure which shows 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 time 14 seconds. Figure 15
Magnetic field waveforms of (a), (b), (c), (d), (e), and (f) are shown in FIGS. 11 (a), (b), (c), and FIG.
Waveforms similar to the magnetic field waveforms of (d), (e), and (f) are shown.

FIG. 16 shows the magnetic field waveform of FIG. 15 of the present invention after the disturbance magnetic field cancellation (FIG. 4) using the first compensating magnetometer of the first embodiment is executed. It is a figure which shows an example. In FIG. 16, the horizontal axis represents time (second) and the vertical axis represents magnetic field strength (pT). FIG. 12 (a),
15 (b), (c), (d), and (e) in the same manner as in FIG.
Ref. ch. 16 (a), (b), (c), the results of executing (Process 15) and (Process 16) shown in FIG. 4 by using the magnetic field waveform of No. 1 (FIG. 15 (e)).
Shown in (d) and (e). In the example shown in FIG. 16, the large disturbing magnetic field is almost canceled by only the process shown in FIG. 4, but the disturbing magnetic field of about 20 pT remains near 14 seconds.

FIG. 17 shows the magnetic field waveform of FIG. 16 of the present invention after the interference magnetic field cancellation (FIG. 5) using the second compensating magnetometer of the first embodiment is executed. It is a figure which shows an example. In FIG. 17, the horizontal axis represents time (seconds) and the vertical axis represents magnetic field strength (pT). FIG. 13 (a),
Similarly to (b), (c) and (d), r shown in FIG.
ef. FIG. 5 using the magnetic field waveform of ch2 (FIG. 16 (e))
Results of executing (Processing 19) and (Processing 20) shown in FIG. 17 are shown in FIGS. 17 (a), (b), (c), and (d). Similar to FIGS. 13 (a), 13 (b), 13 (c), and 13 (d), a waveform obtained by simulation that closely resembles the magnetic field waveform shown in FIG. b),
It remains in the magnetic field waveforms of (c) and (d).

FIG. 18 is a diagram showing an example of the magnetic field waveform after canceling the disturbing magnetic field caused by the frequency characteristic of the magnetic shield room (FIG. 7) from the magnetic field waveform shown in FIG. 17 of the present invention. In FIG. 18, the horizontal axis represents time (second) and the vertical axis represents magnetic field strength (pT). FIG. 17 (a),
In order to cancel the disturbing magnetic field remaining in the magnetic field waveforms in (b), (c), and (d), FIGS.
Similar to (c) and (d), it is shown in FIG.
The result of executing (Process 309) from 2) is shown in FIG.
Shown in (a), (b), (c) and (d).

As is clear from the result 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. However, similar to the result shown in FIG. A sharp peak of the disturbing magnetic field that could not be canceled in 8 seconds remains.

In the result shown in FIG. 16, since the large disturbing magnetic field is almost canceled by only the processing shown in FIG. 4, the magnetic fields shown in FIGS. 16 (a), 16 (b), 16 (c) and 16 (d) are obtained. In order to cancel the disturbing magnetic field of about 20 pT remaining near the time 14 seconds in the waveform, the same result can be obtained by canceling the disturbing magnetic field due to the frequency characteristic of the magnetic shield room (FIG. 7).

That is, the result of canceling the disturbing magnetic field using the first compensating magnetometer (FIG. 4) is judged, and the canceling magnetic field caused by the frequency characteristic of the magnetic shield room is cancelled (FIG. 4) based on the judgment result. 7) may be executed. As a result, when it is not necessary to cancel the disturbing magnetic field using the second compensating magnetometer shown in FIG. 5, the canceling of the disturbing magnetic field can be performed in a short time.

FIG. 22 shows the second embodiment of the present invention shown in FIG.
3, the time constant (T ₃ (unit: second) of (Equation 38)) obtained from the waveforms shown in FIG. 17, data1, data2
FIG. FIG. 22 is a result of summarizing the time constants estimated by using (Equation 38) for canceling the residual disturbing magnetic field in FIGS. 13 and 17. According to the result of FIG. 22, the detecting magnetometers 9-a (ch. 1) and 9-b (ch.
2), 9-c (ch.3 ), different it can be seen the value is little by little constant (T ₃₎ when determined from the magnetic field waveform by 9-d (ch.4).

Time constant T of the input coil of the compensating magnetometer
The magnitude of the influence of ₃ on each of the detection magnetometers differs for each of the detection magnetometers, and the magnitude of the influence of the time constant T ₃ varies depending on the position of the detection magnetometer. In order to evaluate the difference in these time constants, FIG. 13 and FIG.
Subtraction of 7 magnetic field waveforms between channels is performed.

FIG. 19 is a circuit diagram of FIG. 13 (a), (b),
It is a figure which shows the example of the magnetic field waveform after the differential process between the channels of the magnetic field waveform shown in (c) and (d). In FIG. 19, the horizontal axis represents time (seconds) and the vertical axis represents magnetic field strength (pT).
Indicates. 19 (a), (b), and (c) are the ch. 2, ch. 3, ch. 4 from the magnetic field waveform of ch. The result of subtracting (-1) times the magnetic field waveform of 1 is shown.

FIG. 20 is similar to FIG. 17 (a),
It is a figure which shows the example of the magnetic field waveform after the difference process between channels of the magnetic field waveform shown to (b), (c), (d). Figure 20
In the figure, the horizontal axis represents time (second) and the vertical axis represents magnetic field strength (pT). 20 (a), (b), and (c) are the ch. 2, ch. 3, ch. 4 from the magnetic field waveform of ch. The result of subtracting (-1) times the magnetic field waveform of 1 is shown.

In the example shown in FIGS. 19 and 20, the time constant T ₃
Of ch. 1 and ch. The disturbing magnetic field remains in the magnetic field waveforms (differences) in FIGS. 19C and 20C obtained by subtraction from the magnetic field waveform in FIG. From the above results, the time constant T estimated using the time constant ((Equation 38))
It is shown that the magnitude of the effect in ₃ ) varies depending on the position of the magnetometer for detection. That is, it can be seen that there is a spatial distribution of the influence 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 in the second embodiment of the present invention. An example of a display that makes it easy to understand is shown. In FIG. 21, the horizontal axis represents time (seconds) and the vertical axis represents magnetic field strength (pT). As shown in FIG. 21, a magnetic field in which the disturbing magnetic field has been canceled is displayed on the screen of the display device by a straight line 401 on the time of the initial point where the disturbing magnetic field is generated, by points, color points, dotted lines, colored lines, thick lines, etc. The configuration is such that it is displayed together with the waveform, and that there is a possibility that it is affected by the disturbing magnetic field near the initial point.

As the time displayed by the straight line 401,
The value obtained in (Process 303) shown in FIG. 7 is used. The time displayed by the straight line 401 may be detected from the time differential waveform of the magnetic field waveform measured by the fluxgate magnetometer shown in FIG.

(Third Embodiment) FIG. 23 shows the third embodiment of the present invention.
It is a figure which shows the structural example of the magnetic field measuring apparatus of the Example of. Third
In the first embodiment, the magnetically shielded room composed of a member having a high magnetic permeability such as permalloy, which is used in the first embodiment (FIG. 1) and the second embodiment (FIG. 8), is used. It is a configuration that does not. The compensating magnetometer 10 shown in FIG. 23 has a compensating magnetometer 10 (10-a, 10-b) in the first embodiment (FIG. 1) and the second embodiment (FIG. 8). )
The configuration is similar to.

Compensating magnetometer 10 (10-a, 10-b)
Has a shorter baseline 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 controller 604 controls the current flowing through the coils 603-a and 603-b to generate a magnetic field in the z direction opposite to the disturbing magnetic field, thereby reducing the disturbing magnetic field to 2
It is configured to cancel about 0 dB to 60 dB. The coils 603-a and 603-b can be arranged 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 baseline of the compensating magnetometer 601 is set to a value in the range of 0.5 mm to 1 mm, and the disturbing magnetic field is canceled by mainly considering only the canceling rate.

When the baseline of the compensating magnetometer 10 or 601 is shortened, the inductance of the coil becomes small and the effective area becomes small, and the minimum magnetic field resolution of the SQUID magnetometer (for example, 10 fT / √Hz). 23, the compensating magnetometer 10 (10-a, 10-b) and compensating magnetometer 601 are used in the configuration shown in FIG.
Is larger than the area of the magnetic flux meter for detection 9.

When the compensating magnetometer having a value of the minimum magnetic field resolution smaller than the value of the minimum magnetic field resolution of the detecting magnetometer is not used, the process of canceling the disturbing magnetic field described in FIGS. 4 and 5 is performed. Coil 603-a, 60 shown in FIG.
When canceling the disturbing magnetic field by 3-b, SQ
The problem arises that the white noise of the UID magnetometer increases.

When the value of the white noise is large and causes a problem, the signal band of the output waveform of the compensating magnetometers 10-a, 10-b and 601 is band-limited by analog or digital filtering. By doing so, an increase in white noise due to the process of canceling the disturbing magnetic field can be prevented. In many cases, a magnetic field of low frequency (up to 1 Hz) becomes a main noise source to generate an interfering magnetic field, and thus this band limiting process is a practical and effective method.

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 can be applied to the first embodiment (FIGS. 1 and 2), and the interference magnetic field can be canceled without increasing white noise.

(Fourth Embodiment) FIG. 24 shows a fourth embodiment of the present invention.
It is a figure which shows the structural example of the magnetic field measuring apparatus of the Example of. The configuration different from that of the third embodiment (FIG. 23) will be described below. In the configuration of the fourth embodiment, a drive circuit (FLL: Flux Locked Loop) for driving the compensating flux meter 601 described in the third embodiment (FIG. 23).
The circuit 605 is independently provided, and the feedback coil (usually built in the SQUID) and the coils 603-a and 603-b used in this FLL circuit are also used. By using both the feedback coil and the coils 603-a and 603-b,
The external magnetic field can be canceled without adjustment.

(Fifth Embodiment) FIG. 25 shows the fifth embodiment of the present invention.
FIG. 9 is a projection view showing an arrangement example of the compensating magnetometer and the detecting magnetometer in the first embodiment (FIGS. 1 and 2) and the second embodiment (FIG. 8). It is the figure which projected the position where a compensating magnetometer is arrange | positioned from the upper side on the surface (plane parallel to the lower surface of a cryostat) where a magnetometer for detection is arrange | positioned, and was seen from above. In the example shown in FIG. 25, the compensating magnetic flux meter 10-a is provided above the detecting magnetic flux meter 9-a, and the compensating magnetic flux meter 10-b is provided above the detecting magnetic flux meter 9-d. 、 I have arranged each. Since the magnitude of the magnetic field generated from the heart of the human body is small at the positions where the detection magnetometers 9-a and 9-d are arranged, in the arrangement example shown in FIG. 25, the compensating magnetometers 10-a and 10- The magnetic field generated from the heart is hardly input to b, and a substantially pure external disturbance magnetic field can be detected.

(Sixth Embodiment) FIG. 26 shows a sixth embodiment of the present invention.
FIG. 24 is a projection diagram showing an example of arrangement of the compensating magnetometer and the detecting magnetometer in the third embodiment (FIG. 23) and the fourth embodiment (FIG. 24). It is the figure which projected the position where a meter is arrange | positioned from the upper side on the surface (plane parallel to the lower surface of a cryostat) in which a magnetism for detection is arrange | positioned, and was seen 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. 26, the compensating magnetometer 60 is used.
The magnetic field generated from the heart is hardly input to 1, and an almost pure external disturbance magnetic field can be detected.

(Seventh Embodiment) In each of the first to sixth embodiments described above, the number of detecting magnetometers is set to four, and four magnetometers are used.
Although the magnetic field measuring device for the channel has been described, the number of magnetic flux meters for detection is not limited to this, and for example, n = 1, 2,
It is needless to say that any one of the items 1 to 15 may be an n ² channel magnetic field measuring device. Further, a plurality of each of the compensating magnetometers 10-a, 10-b, 601 may be used. That is, a plurality of compensating magnetometers having the same baseline size are used, and the average value of the magnetic field waveforms by a plurality of compensating magnetometers having the same baseline is used to explain each of the embodiments described above. The disturbing magnetic field may be canceled in accordance with the method described in.

(Eighth Embodiment) In each of the above-described first to seventh embodiments, a magnetic flux meter for detection for detecting a component in the direction normal to the magnetic field (z direction) and a magnetic flux meter for compensation are used. Although the magnetic field detection system described above has been described as an example, the method of canceling a disturbing magnetic field of the present invention includes a detection magnetometer and a compensation magnetometer that detect components of the magnetic field in three directions (x, y, z directions). It goes without saying that it can be applied to the constructed magnetic field detection system in the same manner as in the first to seventh embodiments.

That is, by using the signal detected by the second SQUID magnetometer for detecting the magnetic field components in the x, y, z directions of the disturbing magnetic field, the x, y,
For each direction, the magnetic field component in each direction of the disturbing magnetic field is removed (cancelled) from the signal detected by the first SQUID magnetometer that detects the magnetic field component in the z direction, and Magnetic field components 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, which is 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, further, the magnetic field waveform measured by the fluxgate magnetometer (for example, FIG. 9), the fluxgate magnetometer and the SQUID magnetometer were measured. Magnetic field waveform (eg,
10), a magnetic field waveform measured by the SQUID magnetometer (for example, FIGS. 11 and 15), a magnetic field waveform showing the progress of the cancellation of the disturbing magnetic field (for example, FIGS. 12 to 13,
16 to 17), magnetic field waveforms indicating the results of canceling the disturbing magnetic field (for example, FIGS. 14, 18, and 21) and the like may be displayed on the screen of the display device. In such a configuration, the situation of generation of the disturbing magnetic field and the situation of the result of canceling the disturbing magnetic field are analyzed and evaluated, and the result of the signal processing is evaluated in detail as to whether or not a magnetic field waveform that can be normally diagnosed is obtained. You can also run

(Tenth Embodiment) In each of the first to ninth embodiments described above, the case where the first-order differential type detection coil is used as the differential type detection coil has been described.
In each of the eighth to eighth embodiments, even when the second differential type detection coil is used as the differential type detection coil, the interference magnetic field is canceled in the same manner as in the first to ninth examples. it can.

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

The compensating coils of the detecting magnetometer and the compensating magnetometer are sequentially arranged at positions farther from the object to be inspected than the first coil among the coils constituting the second-order differential type detecting coil, and the second coil. The second, third, and fourth coils have planes parallel to the planes of the coils. 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 baselines of the second-order differential type detecting coils, respectively, and the distance between the surface of the first coil and the surface of the second coil, It is 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 second-order differential type detection coil, the area of the first coil (input coil) is s ₁ , the area of the second and third coils (compensation coil) is s ₂ , and the area of the fourth coil is s ₂ . Where s ₃ is the area of the coil (compensation coil) and b is the baseline, the magnetic flux φ detected by the magnetometer is obtained in the same way as in the case of the magnetometer composed of the first-order differential type 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, the third
The coil surface of is at z = z ₂ + Δ = z ₁ + b + Δ, and Δ≈
0, and the surface of the fourth coil is z = z ₂ + b = z ₁ + 2b.

[0179]

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 (Expression 42) (Expression 42) ), (S ₁ -s ₂ ) becomes S ₁ and (s ₂ -s ₂
Replacing ₃ ) with S ₂ and 2 × b with d, (Equation 42) becomes 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 ) ... (Equation 43)

[0182]

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

In (Equation 44), the value of (1-α ') indicates the cancellation rate for the uniform magnetic field of the secondary differential type detection coil. When the magnetic field distribution in the space where the detecting magnetometer and the compensating magnetometer are arranged is expressed by (Equation 2),
As is clear from (Equation 44), the detected magnetic field has a term with the cancellation rate (1−α ′) as a coefficient and the baseline b.
And a term with a coefficient of.

As in the case of the first embodiment, in order to prevent the magnetic field generated from the heart from entering the compensating magnetometer, the baseline of the compensating magnetometer is made shorter than that of the detecting 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, as shown in FIG.
According canceling method of the first interference magnetic field by the procedure shown in FIG. 5, it can be performed to cancel the interference field, baseline baseline and compensation magnetometer for detection gradiometers length and the interference field by different The difference in the mixed amount can be corrected.

Similar to the first embodiment, by using the magnetic field waveform B _r (t) shown in (Equation 30), the magnetic field of the magnetic field measured by the detection magnetometer composed of the secondary differential type detection coil is calculated. 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-order differential type detection coil constituting the detection magnetometer is t ₁ , the time constants of the second and third coils (compensation coil) are t ₂ , The time constant of the 4th coil (compensation coil) is t ₃ . Taylor expansion of (Equation 45) gives (Equation 46).

[0186]

B ′ ₁ (t) = exp (−t / t ₁ ) −2 × exp (−t / t ₂ ) + exp (−t / t ₃ ) = − {1-exp (−t (1 / 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 second-order differential type detection coil constituting the compensating magnetometer is t ′ ₁ , and the time constants of the second and third coils (compensation coil). 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 calculated by (Equation 48) The magnetic field waveform (B ′ ₁ −δ′B ′ ₂ ) canceled by using δ ′ defined by Taylor expansion of (Equation 49) (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 ′ ₂ −1 / t ′ ₁ ) is set to (1 / T ₄ ), and (1 / t ′ ₃ −1 /)
Replacing t ′ ₂ ) with (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) Among the amplitude values of (Equation 50), the term that does not depend on time is η ′.
If (Equation 51) is used, (Equation 50) becomes the function shown in (Equation 52). As described above, (Equation 52) is (Equation 4)
8 shows a magnetic field waveform obtained by canceling the disturbing magnetic field B ′ ₂ (t) 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]

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

Since (Equation 52) is equivalent to (Equation 38), even when a second-order differential type detection coil is used as the differential type detection coil, as in the case of the first embodiment, The second method of canceling the disturbing magnetic field shown in 7 (method of canceling the disturbing magnetic field due to the frequency characteristic of the magnetic shield room) can be applied.

As described above, in each of the first to ninth embodiments, even when the secondary differential type detection coil is used as the differential type detection coil, the differential type detection coil is
Exactly the same as when using the second derivative type detection coil,
It is possible to cancel the disturbing magnetic field. When the second differential type detection coil is used in the present invention, the disturbing magnetic field from a wide range can be canceled.

[0196]

According to the present invention, the disturbance is taken into consideration by taking into consideration the difference in the cancellation rate for the uniform magnetic field of the differential type detection coil constituting the SQUID magnetometer and the difference in the baseline of the differential type detection coil. Since the magnetic field is canceled, the disturbing magnetic field can be canceled accurately.

Further, the canceling of the disturbing magnetic field caused by the frequency characteristic of the magnetically shielded room can be executed accurately, and the disturbing magnetic field having a steep and large strength can be canceled accurately.

Further, it is possible to realize a biomagnetic field measuring device which enables highly sensitive measurement of a weak magnetic field generated from the heart to be examined and the heart of a fetus in the mother's body.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a magnetic field measuring apparatus 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 in 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 view showing a flowchart showing an example of canceling a disturbing magnetic field using the first compensating magnetometer of the first embodiment of the present invention.

FIG. 5 is a view showing a flowchart showing an example of canceling a disturbing magnetic field by using the second compensating magnetometer of the first embodiment of the present invention.

FIG. 6 is a diagram showing an example of a magnetic field waveform of an interference magnetic field obtained by 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 the frequency characteristic of the magnetic shield room in the first embodiment of the present invention.

FIG. 8 is a diagram showing a configuration example of a magnetic field measuring apparatus 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 measuring apparatus according to the second embodiment of the present invention.

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

FIG. 11 is a SQU in a state where the inspection target is not lying on the bed in the magnetic field measuring apparatus according to the second embodiment of the present invention.
The figure which shows the example of the magnetic field waveform measured by the ID magnetometer.

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

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

FIG. 14 is a diagram showing an example of a magnetic field waveform after the process of canceling the disturbing magnetic field caused by the frequency characteristic of the magnetic shield room (FIG. 7) is performed on the magnetic field waveform shown in FIG. 13 of the present invention.

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

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

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

FIG. 18 is a diagram showing an example of a magnetic field waveform after executing the cancellation process (FIG. 7) of the magnetic field waveform shown in FIG. 17 of the present invention, which is caused by the frequency characteristic of the magnetic shield room.

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

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

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

FIG. 22 is a view showing a second embodiment of the present invention shown in FIGS. 13 and 17;
The figure which shows the time constant calculated from the waveform shown in FIG.

FIG. 23 is a diagram showing a configuration example of a magnetic field measuring apparatus according to a third embodiment of the present invention.

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

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

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

[Explanation of symbols]

1 ... Cryostat, 2 ... Magnetically shielded 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 ... Magnetic flux meter for detection 10,
10-a, 10-b, 601 ... Compensating magnetometer, 11-
a, 11-b, 11-c ... Baseline, 12 ... Magnetic field gradient, 13 ... Position in z direction in magnetic shield room, 1
4 ... Magnetic field strength, 15, 16, 17, 18, 19, 20, ...
Processing, 101 ... Fluxgate magnetometer main body, 102 ...
Fluxgate magnetometer sensor unit, 201 ... Measuring section,
301, 302, 303, 304, 305, 306, 3
07, 308, 309, 310 ... Processing, 401 ... Straight line,
602 ... Wiring, 603-a, 603-b ... Coil, 60
4 ... Control device, 605 ... FLL circuit.

Continuation of the front page (56) Reference JP-A-9-84777 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01R 33/035 ZAA

Claims (5)

(57) [Claims] 1. A plurality of first SQUID magnetometers for detecting a component in a predetermined direction of a magnetic field generated from an inspection target inside a magnetically shielded room, and a second and a second for detecting an interfering magnetic field in the predetermined direction. And a third SQUID magnetometer, a cryogenic container for cooling the first, second, and third SQUID magnetometers, and a drive circuit for driving the first, second, and third SQUID magnetometers. , The first, second, and third S
Comprising a computer for performing signal processing by collecting signals detected by QUID magnetometer, and display means for displaying the result of the signal processing, the first, second, and third SQU
The ID magnetometer has a differential type detection coil,
The baseline length of the differential detection coil of the SQUID magnetometer is shorter than the baseline length of the differential detection coil of the first SQUID magnetometer, and the second SQUID magnetometer is The length of the baseline of the differential detection coil is shorter than the length of the baseline of the differential detection coil of the third SQUID magnetometer. From the magnetic field waveform obtained by the SQUID magnetometer, the first SQUI
Considering the difference in the cancellation rate between the D magnetometers,
From the signal processing (a) for canceling the field and the magnetic field waveform obtained by the signal processing (a), the second SQU
Signal processing for canceling a disturbing magnetic field in consideration of the difference between the baseline of the differential detection coil of the ID magnetometer and the baseline of the differential detection coil of the third SQUID magnetometer (b) ) And the signal processing (c) for canceling the disturbing magnetic field generated due to the frequency characteristic of the magnetic shield room from the magnetic field waveform obtained by the signal processing (b). Magnetic field measuring device. 2. The magnetic field measuring device according to claim 1, wherein:
The computer estimates an initial time at which the generation of the disturbing magnetic field caused by the frequency characteristic starts, and the estimated initial time is the signal processing (a), (b), and (c). The magnetic field measuring apparatus is characterized in that the disturbing magnetic field is displayed on the time axis of the magnetic field waveform. 3. The magnetic field measuring device according to claim 1, wherein:
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. Characteristic magnetic field measurement device. 4. In the magnetic field measuring device according to claim 1,
Having a plurality of said second SQUID magnetometers
Magnetic field measuring device. 5. Is the inspection object inside the magnetically shielded room?
To detect the components of the magnetic field generated in a predetermined direction.
1 SQUID magnetometer and the disturbing magnetic field in the predetermined direction
Second and third SQUID magnetometers for detecting,
Low temperature cooling first, second and third SQUID magnetometers
Container and the first, second and third SQUID magnetometers
And a drive circuit for driving the first, second, and third S
The signal detected by the QUID magnetometer is collected and processed.
Table for displaying the result of the signal processing
Indicating means, and the first, second, and third SQUs.
The ID magnetometer has a differential type detection coil,
Of the differential detection coil of the SQUID magnetometer
The length of the in is the differential of the first SQUID magnetometer.
Shorter than the baseline length of the mold detection coil,
The differential type detection coil of the second SQUID magnetometer
The length of the baseline is the same as that of the third SQUID magnetometer.
Than the length of the baseline of the differential detection coil
Briefly, the differential of the second and third SQUID magnetometers
The area of the input coil of the mold detection coil is equal to the first SQUA
Area of the input coil of the differential detection coil of the ID magnetometer
A magnetic field measuring device characterized by being larger than