JPH1189810A - Current source estimator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly accurately estimate the depthwise position of a current source without the causing local minimum and global minimum. SOLUTION: In this current source estimator, the position of the current source is estimated based on a weak magnetic signal generated from the current source in a measuring object. This device has coils 6c1 -6c3 for signal detection arranged at mutually different positions along with the depthwise direction of the measuring object and pickup coils 6a1 -6a3 connected to each other at the interval of a base line while winding coils 6d1 -6d3 for compensation with mutually inverse phases, and is provided with SQUID magnetic flux gauges 2a1 -2a3 for outputting electric signals by detecting the weak magnetic signal generated from the measuring object through these coils 6c1 -6c3 for signal detection and coils 6d1 -6d3 for compensation of the pickup coils 6a1 -6a3 with mutually different magnetic field sensitivities and a data processor 16 for estimating the depthwise position of the current source based on electric signals Vout1-Vout3 respectively outputted from these SQUID magnetic flux gauges 2a1 -2a3 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures a weak magnetic field emitted from a measurement object such as a living body by using a magnetic signal detecting means such as a SQUID magnetometer (superconducting quantum interferometer) for detecting a weak magnetic signal. Also, the present invention relates to a current source estimating device for estimating a position in a depth direction of a current source which is a magnetic field generating source in a measurement object from the measured magnetic field.

[0002]

2. Description of the Related Art SQUI is a highly sensitive magnetic field measuring device.
When using a D magnetometer to measure a weak magnetic field (biomagnetic field) emitted from a measurement site in a measurement target such as a living body (hereinafter referred to as a living body), put the living body and the SQUID magnetometer in a magnetically shielded room. In this state, a detection coil (pickup coil) of the SQUID magnetometer is arranged around the measurement site of the living body, and the detection coil detects a magnetic flux based on the biomagnetic field emitted from the measurement site.

At this time, as a conventional pickup coil, the magnetic field in the normal direction is differentiated in the normal direction from the spatial differentiation of the magnetic field ｛the body table (normal direction component pickup coil), and the pickup coil in the tangential direction is obtained from the body surface. A gradiometer that detects a magnetic field differentiated in the normal direction (a tangential component pickup coil) or the like is often used.

[0004] This gradiometer is for attenuating signals (magnetic noise) from sources other than the living body.
As shown in FIG. 2, a plurality of (for example, two) coils 70a and 70b at positions separated from each other are wound in opposite phases and are coupled at an interval (baseline) BL. And
A biomagnetic signal and a noise component are detected by one coil (hereinafter, referred to as a signal detection coil) 70a disposed close to the living body H, and the other coil (hereinafter, a compensation coil) disposed far from the living body H (Referred to as a reference) 70b, and only the biomagnetic signal is detected by detecting only the noise component and taking the difference. Note that a gradiometer that takes a difference between two magnetic fields based on two coils, such as the gradiometer shown in FIG. 14, is called a first-order differential gradiometer. For example, two gradiometers are prepared and each other is prepared. The gradiometer that takes the difference is called a second-order gradiometer.

[0005] Incidentally, the pickup coil and the SQ
When estimating a current source in a measurement site of a living body based on a measurement magnetic field obtained through a SQUID element of a UID magnetometer, a drive circuit, and the like, a current dipole is generated by using a homogeneous or multilayer concentric conductive sphere. A magnetic field generated from a measurement site is calculated as a source, and a current dipole having a minimum difference from the measured magnetic field is set as an estimated position of the current source. At this time,
As a method for avoiding repeated calculations in a nonlinear system, there is known a method in which the position of a current dipole is fixed and the problem is replaced with a linear system. This method is described in detail in the following document.

(1) Brain Jeffs, et al: "An Evaluati
on of Methods for NeuromagneticImage Reconstructio
n ", IEEE Transactions on Biomadecal Engineering, V
ol.BME-34, No. 9, Sep.1987; (2) Warren E. Smith, et al: "Linear estimation the
ory applied to the reconstruction of a 3-D vector
current distribution ", Applied Optics, Vol. 29, No.
5 (1990); (3) Jukka Sarvas: "Basic mathematical and electr
omagnetic concepts of the biomagnetic inverse probl
em ", Phys. Med. & Biol., Vol. 32, Jan., 1987.

Here, in the method using the singular value decomposition of the matrix, the distribution of the current dipole is fixed in order to express the measured magnetic field picked up by the pickup coil and the current dipole density on the lattice point in the discretized model by a linear simultaneous equation. 3
Place on a dimensional grid point. Now, assuming that a matrix Q representing the current density in each of the three directions of the current dipole, a matrix A represented by a linear equation determined by the position of the pickup coil and the position of the current dipole, and a measurement magnetic field B, these relationships are simultaneous. Linear equation

## EQU2 ## B = AQ (2) Therefore, if the inverse matrix of A exists,

## EQU3 ## Q = A ^-1 B (3) However, in general, since the coefficient matrix A is a singular matrix in which each column is not independent, there is no inverse matrix. In such a case, there is a method of obtaining a unique solution that minimizes the sum of squares of the measured magnetic field and the calculated magnetic field from the singular value decomposition (method using the least square method).

[0008]

In the current source estimating method using the above singular value decomposition (least squares method), it is difficult to accurately estimate the position with a deep current source, and therefore, for example, the position is generated from the heart. It has been difficult to accurately estimate the position of a current dipole having a depth of several cm required for medical diagnosis from a magnetic field or a magnetic field generated from a deep part of the brain.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 05-297091 (see FIG. 15), the plurality of pickup coils (pickup coil groups) 75A and 75B of the SQUID magnetometer are arranged on two different planes in the depth direction. By measuring the biomagnetic field by arranging it along two stages (the side closer to the living body as the lower coil group and the side farther from the living body as the upper coil group), the estimation accuracy of the deep current source of the living body is improved. Devices are known.

However, Japanese Patent Application Laid-Open No. 05-2970 describes
In the device disclosed in Japanese Patent Publication No. 91, the pickup coil composed of the signal detection coil and the compensation coil is simply arranged in a plurality of stages, so that the difference between the measurement magnetic field and the calculation magnetic field is locally reduced to a minimum value. There is still a high risk of falling into an inappropriate solution, that is, a local minimum, and it has been difficult to perform accurate current source estimation. In addition, as described in
For the same reason, the apparatus disclosed in Japanese Patent Application Laid-Open No. 5-297091 also has a risk of falling into a global minimum (in this specification, it takes a long time to reach a global true minimum). Still strong and not practical.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and highly accurately estimates a depth direction position of a current source distributed in a deep part of an object to be measured such as a living body without causing a local minimum and a global minimum. It is an object of the present invention to provide a current source estimating device which makes it possible to perform a current source estimation.

[0012]

In recent years, the performance of a magnetically shielded room has been improved, and active shield technology for environmental magnetic field canceling has been implemented. The necessity of removing noise components with a gradiometer, that is, a signal detection coil and a compensation coil has been reduced.

Therefore, it has become important to consider the new role of gradiometers that were initially developed for environmental magnetic field canceling.

The present inventor has given a new role to the gradiometer by changing the detection sensitivity (magnetic field sensitivity) of each coil (signal detection coil and compensation coil) of the gradiometer with respect to the magnetic field. Then, they came to think that the position of the current source in the depth direction of the living body in the depth direction could be estimated with high accuracy.

Now, according to the Biot-Savart formula, the magnetic field vector B1 generated from the current dipole dI is

[Number 4] _{B1 = (μ 0 · dI)} / (4πX 2) represented by the ... (4). Note that μ ₀ = 4π × 10 ⁻⁷ (zero isomagnetic susceptibility),
X is the distance along the depth direction between the current dipole dI and (the first coil of) the pickup coil (hereinafter, referred to as the focal length). Here, assuming that the baseline of the pickup coil is b, the magnetic field vector B2 measured by the pickup coil is

(Equation 5)

Therefore, from equations (4) and (5),

As [6] ^{B2 / B1 = X 2 / (} X + b) 2 ...... (6), expressed.

From the equation (6), the magnetic field sensitivity S2 of the compensation coil in the pickup coil is calculated as (X + b) ² / X ² of the magnetic field sensitivity S1 of the signal detection coil, that is,

S2 = S1 × {(X + b) ² / X ² } (7) If the following equation is set, the magnetic field generated from the current dipole located at a distance X from the pickup coil and detected by the pickup coil is: It can be seen that the signal is canceled by the signal detection coil and the compensation coil and becomes zero. That is,
By setting the magnetic field sensitivity of the signal detection coil and the compensation coil in the pickup coil of the SQUID magnetometer to the focal length X to be measured, the current source at the focal length X can be recognized.

The advantages of changing the sensitivity of each coil of the above-described gradiometer will be described with reference to FIGS.

FIGS. 16A and 16B show the relationship between the baseline length and the sensitivity distribution in the depth direction of a conventional first-order differential gradiometer (pickup coil) for a tangential component, for example. It is a figure which shows the sectional view which met in the depth direction immediately below the installation part of the said pick-up coil, respectively. FIG. 16A is a diagram when the base line length of the pickup coil is set to 5 cm, and FIG. 16B is a diagram when the base line length of the pickup coil is changed to 7 cm. Also,
The distance along the depth direction between the measurement object and the pickup coil is set to 2 cm, and L0 indicates a sensitivity zero line.

As shown in FIG. 16A, the sensitivity in the depth direction based on the conventional pickup coil is R1 (−2.5 × 10
^-12 [T] to 2.0 × 10 ^-12 [T]), R2 (-2.0 × 10 ^-12 [T] to)
-1.5 × 10 ^-12 [T]), R3 (-1.5 × 10 ^-12 [T] to -1.0 ×
^{10 -12 [T]), R4} (-1.0 × 10 -1 2 [T] ~ -0.5 × 10
^-12 [T]), R5 (-0.5 × 10 ^-12 [T] to 0 [T]), R6 (0 [T] to
0.5 × 10 ⁻¹² [T]).

At this time, as shown in FIG. 16B, the sensitivity distribution R in the depth direction based on the conventional pickup coil is obtained.
1 'to R6' are constant despite the change in the baseline length (R1 '= R1, R2' = R2, R3 '= R3, R4' =
R4, R5 '= R5, R6' = R6), and it is difficult to accurately estimate current sources having different depths in a living body to be measured.

On the other hand, FIG. 17 shows a pickup coil (sensitivity change pickup coil) in which the sensitivities of the signal detecting coil and the compensating coil in the primary differential gradiometer (pickup coil) for the tangential direction component are changed as described above. 3) is a diagram for illustrating the sensitivity distribution in the depth direction, and is a cross-sectional view along the depth direction immediately below the installation portion of the pickup coil. 17 (a) and 17 (b) show a case where the base line length is set to a constant 5 cm, and FIG. 17 (a) shows that the focal length is 5c.
m, FIG. 17B is a diagram when the sensitivity of the compensation coil is adjusted so that the focal length becomes 7 cm. The distance between the measurement object and the pickup coil along the depth direction is set to 2 cm, and L1 indicates a sensitivity zero line.

As shown in FIG. 17A, the sensitivity in the depth direction based on the sensitivity change pickup coil described above is R
10 (-0.8 × 10 ^-12 [T] to -0.6 × 10 ^-12 [T]), R11 (-
0.6 × 10 ^-12 [T] to -0.4 × 10 ^-12 [T]), R12 (-0.4 × 1
0 ^-12 [T] to -0.2 × 10 ^-12 [T]), R13 (-0.2 × 10
^-12 [T] to 0 [T]) and R14 (0 [T] to 0.2 × 10 ^-12 [T]).

At this time, as shown in FIG. 17 (b), the sensitivity distributions R10 'to R14' in the depth direction based on the sensitivity change pickup coil having the changed focal length are obtained by changing the above-mentioned R10's according to the change of the focal length. To change from R14 (R10 '(-0.6
^{× 10 -12 [T] ~ -0.4} × 10 -1 2 [T]), R11 '(- 0.4 × 10
^-12 [T] to -0.2 × 10 ^-12 [T]), R12 '(-0.2 × 10
^-12 [T] to 0 [T]), R13 '(0 [T] to 0.2 × 10 ^-12 [T]), R
14 ′ (0.2 × 10 ⁻¹² [T] to 0.4 × 10 ⁻¹² [T])}, it is possible to accurately estimate current sources having different positions in the depth direction in the living body to be measured.

Based on the above idea, according to the current source estimating apparatus according to the present invention for solving the above-mentioned problems,
In a current source estimating device for estimating the position of the current source based on a weak magnetic signal emitted from the current source in the measurement target, a plurality of components disposed at different positions along the depth direction of the measurement target A magnetic signal detecting unit having a coil, detecting weak magnetic signals emitted from the measurement target through the plurality of coils with different magnetic field sensitivities, and outputting an electric signal; and a magnetic signal output from the magnetic signal detecting unit. Estimating means for estimating the position of the current source in the depth direction based on the obtained electric signal.

Preferably, the magnetic signal detecting means includes a pickup coil in which a signal detecting coil and a compensating coil constituting the plurality of coils are wound in opposite phases to each other and connected with a base line, and Magnetic field measuring means having a SQUID element for outputting an electric signal in accordance with a magnetic flux based on a weak magnetic signal detected by the coil;
SQUID driving means for making the electric signal an output signal proportional to the weak magnetic signal by feeding back the electric signal output from the SQUID element as a magnetic flux to the SQUID element, wherein the magnetic field of the signal detection coil itself is provided. The sensitivity and the magnetic field sensitivity of the compensation coil itself are set to be different from each other.

Preferably, the magnetic field sensitivity of the signal detection coil itself and the magnetic field sensitivity of the compensation coil itself are set such that the magnetic field sensitivity of the compensation coil is higher than the magnetic field sensitivity of the signal detection coil. The pickup coil is a first-order differential type pickup coil in which one signal detection coil and one compensation coil are wound in opposite phases to each other and connected with a baseline, and the signal detection coil is It is arranged so as to be closer to the current source in the measurement object than to the compensation coil.

In particular, the distance between the signal detection coil and the compensation coil of the pickup coil (base line)
Is BL, the distance along the depth direction between the signal detection coil and the measurement object is F, the magnetic field sensitivity of the signal detection coil of the pickup coil is Z1, and the magnetic field sensitivity of the compensation coil is Z2. , The magnetic field sensitivity Z1
And the magnetic field sensitivity Z2 is expressed by the following equation: “Z2 / Z1 = (BL + F) ²
/ F ² ”is set.

[0029] More preferably, the plurality of coils include a first coil disposed in close proximity to a current source in the object to be measured.
And a second pickup coil disposed at a predetermined distance from the first pickup coil along the depth direction, and the magnetic signal detecting means includes a first pickup coil. A plurality of magnetic field measuring means provided for each of the second pickup coils and having a SQUID element for outputting an electric signal in accordance with a magnetic flux based on each weak magnetic signal detected by each pickup coil, and the plurality of SQUID elements Each SQUID as a magnetic flux using each electric signal output from
A plurality of SQUID driving means for converting each of the electric signals into an output signal in proportion to each of the weak magnetic signals by feeding back to each element, and the estimating means comprises:
Gain adjusting means for adjusting the gain of at least one of the electric signals output from the plurality of SQUID driving means to change the magnetic field sensitivity related to the electric signals;
And an arithmetic processing means for obtaining the position of the current source in the depth direction by arithmetic processing based on the gain value of each electric signal adjusted by the gain adjusting means.

[0030] In particular, the plurality of coils are a first pickup coil disposed close to a current source in the object to be measured, and a predetermined coil along the depth direction with respect to the first pickup coil. Second spaced apart
And the magnetic signal detecting means is provided for each of the first pickup coil and the second pickup coil, and is electrically connected to a magnetic flux based on each weak magnetic signal detected by each of the pickup coils. A plurality of magnetic field measuring means having a SQUID element for outputting a signal; and the electric signals output from the plurality of SQUID elements being fed back to the respective SQUID elements as magnetic fluxes to convert the electric signals to the respective weak magnetic signals. Output signals that are proportional to
QUID driving means, wherein the estimating means converts the electric signals into digital data, and performs the measurement based on the first digital data related to the first pickup coil in the converted digital data. Means for obtaining a magnetic field distribution (magnetic field mapping) in the object, and extracting a peak value on the magnetic field mapping,
Means for calculating a difference value between the value of the second digital data relating to the second pickup coil and the peak value; and setting the gain of the second digital data so that the obtained difference value becomes zero. Means for adjusting, and a position in a depth direction of the current source which performs an arithmetic process based on a gain value of the first digital data and a gain value of the second digital data when the difference value becomes zero. And arithmetic processing means for obtaining

[0031] Further, in particular, the plurality of coils are a first pickup coil disposed in close proximity to a current source in the object to be measured, and a predetermined pickup along the depth direction with respect to the first pickup coil. A second pickup coil disposed at an interval; and the magnetic signal detecting means is provided for each of the first pickup coil and the second pickup coil, and detects each weak magnetic field detected by each pickup coil. A plurality of magnetic field measuring means each having an SQUID element for outputting an electric signal in accordance with a magnetic flux based on a signal, wherein the estimating means samples and holds each electric signal output from the plurality of SQUID driving means Means for converting each electrical signal output from the sampling and holding means into digital data. Converting means for amplifying the second digital data related to the second pickup coil in each converted digital data and performing arithmetic processing on a ratio of the first digital data related to the first pickup coil to the first digital data; Arithmetic processing means for determining the position of the current source in the depth direction; converting means for converting the first and second digital data output via the arithmetic processing means into electric signals; A plurality of SQUID driving means for feeding back the electric signal as a magnetic flux to each of the SQUID elements to make the electric signal converted by the conversion means an output signal proportional to each of the weak magnetic signals.

[0032]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a first embodiment of the current source estimating apparatus according to the present invention.

According to FIG. 1, the current source estimating apparatus 1 of the present embodiment includes a plurality (three in this embodiment) of SQUIS for measuring a biomagnetic field emitted from a living body to be measured.
D magnetometers 2a1 to 2a3 are provided.

Each of the SQUID magnetometers 2a1 to 2a3 has 2
SQUID element 5 having two Josephson junctions and pickup coils 6 (6a1 to 6a3) for picking up a weak magnetic field (a weak magnetic signal) generated from a living body.
), And an input coil 7 for transmitting a magnetic flux based on the weak magnetic signal picked up by the pickup coil 6 to the SQUID element 5.

At this time, the SQUID magnetometers 2a1 to 2a-2
The pickup coils 6a1 to 6a3 of a3 (hereinafter, the pickup coil 6a1 will be described) are, as shown in FIG. 1, two different (separated) along the depth direction.
It has a first-order differential structure in which coils 6c1 and 6c2 positioned on a plane are wound in opposite phases and connected at intervals (baseline) BL, and are not shown in the normal direction (radial direction) of the body surface of a living body (not shown). In order to detect this magnetic field, the pickup coils 6a1 to 6a3 are arranged such that the normal direction of their coil surfaces coincides with the normal direction of the body surface.

The pickup coil 6a1 of the SQUID magnetometer 2a1 is configured such that the magnetic field sensitivity of each signal detection coil 6c1 and the magnetic field sensitivity of the compensation coil 6d1 are different from each other.

That is, the signal detecting coil 6c1 arranged close to the living body in the pickup coil 6a1
If the coil area of the compensation coil 6d1 is Sd1 and the coil area of the compensation coil 6d1 is Sd1,

(Equation 8) That is, the magnetic field sensitivity of the compensation coil 6d1 is equal to the magnetic field sensitivity of the signal detection coil 6c1 as "(X1 + BL) ² / (X1).
² times ". Where X1 is S
Represents the focal length of the QUID magnetometer 2a1.

Similarly, the pickup coil 6a2 of the SQUID magnetometer 2a2 has the coil area of the signal detection coil 6c2 as Sc2 and the coil area of the compensation coil 6d2 as S2.
Assuming d2,

(Equation 9) That is, the magnetic field sensitivity of the compensation coil 6d2 is equal to the magnetic field sensitivity of the signal detection coil 6c2 as "(X2 + BL) ² / (X2)
Is configured to be ^doubled ", SQUID magnetometer 2a3
Pickup coil 6a3 is a signal detection coil 6c
Assuming that the coil area of No. 3 is Sc3 and the coil area of the compensating coil 6d3 is Sd3,

(Equation 10) That is, the magnetic field sensitivity of the compensating coil 6d3 is equal to the magnetic field sensitivity of the signal detecting coil 6c3 as "(X3 + BL) ² / (X3).
² times ". Here, X2 and X3 represent the focal lengths of the SQUID magnetometers 2a2 and 2a3, respectively.

Each of the SQUID magnetometers 2a1 to 2a3
Is a current source 8 for flowing a bias current through the SQUID element 5.
And a drive circuit 11 composed of an amplifier (preamplifier) and an integrator for amplifying the voltage output from the SQUID element 5 and voltage signals Vout1 to Vout3 output from the integrator are converted into a voltage / current conversion circuit such as a resistor 12 (impedance). Zf0) and a SQUID drive circuit 15 having a first feedback circuit 14 that feeds a feedback current to the feedback coil 13 as a feedback current. The canceling feedback magnetic flux Φf is provided to the SQUID element 5. The SQUID magnetometers 2a2 and 2a3 are also SQUID magnetometers.
The configuration is the same as that of the D magnetometer 2a1.

Incidentally, the SQUID magnetometers 2a1 to 2a
3 pickup coils 6a1-6a3, input coil 7, SQUID element 5, and feedback coil 13
Are housed in a dewar (not shown), and are disposed in a magnetically shielded room R for magnetically shielding the dewar and the living body from the outside to shield environmental magnetic field noise.

Further, the current source estimating apparatus 1
Voltage signals Vout1 to Vout3 output from the drive circuit 11 (integrator) of the magnetometers 2a1 to 2a3 are input, data processing is performed based on the input voltage signals Vout1 to Vout3, and current in the depth direction in the living body is processed. A data processor 16 is provided for estimating the location of the source.

Next, the overall operation of the present configuration will be described.

According to the current source estimating apparatus of this configuration, the SQUID magnetometers 2a1 to 2a3 are attached to the living body with the dewar attached thereto.
By driving each of the SQUID driving circuits 15, weak magnetic signals emitted from the living body through the pickup coils 6a1 to 6a3 are detected.

The magnetic flux based on the magnetic signal detected by each of the pickup coils 6a1 to 6a3 is SQUID.
The voltage is transmitted to the D element 5 via the input coil 7 and is output based on the input magnetic flux. Then, this voltage output is amplified through the drive circuit 11 and the voltage signal V
out1 to Vout3.

At this time, the feedback circuit 14 outputs the voltage signals Vout1 to Vou output from the drive circuit 11.
t3 is supplied to the feedback coil 13 as a feedback current via the resistor 12, respectively. The feedback magnetic flux is supplied to the SQUID element 5, and the change in the measured magnetic signal is canceled.

The voltage signals Vout1 to Vout3 proportional to the feedback magnetic flux output from the drive circuit 11 are sent to the data processing device 16, respectively.

The data processing device 16 performs a process of inversely estimating the position of the current source in the living body using the above-described singular value decomposition (least square method) based on the transmitted voltage signals Vout1 to Vout3.

At this time, in this configuration, the compensation coil 6d1 of the pickup coil 6a1 of the SQUID magnetometer 2a1
Is (X1 + BL) ² / (X1) ² times the coil area Sc1 of the signal detection coil 6c1.
That is, since the magnetic field sensitivity of the compensation coil 6d1 to the weak magnetic signal is set to "(X1 + BL) ² / (X1) ² " times the magnetic field sensitivity of the signal detecting coil 6c1 to the weak magnetic signal, the current in the living body is increased. The source (current dipole) is at a focal length X1 with respect to the pickup coil 6a1.
In this case, the voltage signal Vout1 detected by the pickup coil 6a1 and measured via the SQUID magnetometer 2a1 becomes zero.

Similarly, the SQUID magnetometer 2a2,
2a3 pickup coil 6a2 compensation coil 6d2
And compensating coil 6d3 of pickup coil 6a3
The coil areas Sd2 and Sd3 of the signal detection coil 6c2
, 6c3 of the coil area Sc2, Sc3 "(X2 + B
L) ² / (X 2) ² ”times and“ (X 3 + BL) ² / (X
3) The magnetic field sensitivity of the compensation coils 6d2 and 6d3 to the weak magnetic signal is ² "times, that is, the signal detection coil 6c.
2, (c2) of the magnetic field sensitivity to the weak magnetic signal of 6c3
+ BL) ² / (X 2) ² ”times and“ (X 3 + BL) ² /
(X3) ² ”, the current is detected by the pickup coils 6a2 and 6a3 when the in-vivo current source is located at the focal distances X2 and X3 with respect to the pickup coils 6a2 and 6a3. SQUI
Voltage signal V measured via D magnetometers 2a2 and 2a3
out2 and Vout3 become zero.

Therefore, the data processing device 16
Based on the output values Vout1 to Vout3 of the QUID magnetometers 2a1 to 2a3, the output values Vout1 to Vout3 are used.
The focal lengths X1 to X3 at which t3 becomes zero, that is, the three current sources PS1 to PS3 having the focal lengths X1 to X3 in the depth direction can be easily and accurately obtained (estimated).

That is, according to the present configuration, a first-order differential pickup coil having two coils having different magnetic field sensitivities (coil areas) is placed on two separate planes along the depth direction. Since it is arranged so that it is located, the position of the current source in the depth direction can be directly obtained,
For example, it is possible to detect a position in the depth direction of the current source at a position deeper (away from the pickup coil coil) in the depth direction in the living body, such as a deep part of the heart or the brain, with high accuracy.

In the present embodiment, three SQUID magnetometers having three pickup coils having different detection sensitivities (coil areas) are used. However, the present invention is not limited to this. It is also possible to use a plurality of SQUID magnetometers provided with a plurality of pickup coils having variously changed (coil areas) (for example, having detection sensitivities divided into a plurality of steps separated by a predetermined value), and further high accuracy Thus, the position in the depth direction of each of the different current sources can be estimated.

In this embodiment, the pickup coils 6a1 to 6a3 of the SQUID magnetometers 2a1 to 2a3 are used.
Is a pickup coil 6 for detecting a magnetic field in a radial direction for detecting a magnetic field in a normal direction (radial direction) of a body surface of a living body.
Although a1 to 6a3 have been described, the present invention is not limited to this. For example, as shown in FIG. 2, pickup coils 20a1 to 20a3 of a type for detecting a magnetic field in the tangential direction (tangential direction) of the body surface. Is also applicable.

That is, according to FIG. 2, the pickup coils 20a1 to 20a3 are obtained by winding two coils 20c1 and 20c2 at opposite positions in opposite phases as shown in FIG. In order to detect a magnetic field in a tangential direction of a body surface of a living body (not shown), each of the pickup coils 6a1 to 6a3 has a normal direction of the coil surface thereof in a tangential direction of the body surface. They are arranged to match.

The pickup coil 20a1 of the SQUID magnetometer 2a1 has a coil area Sc1 'for the signal detection coil 20c1 arranged close to the living body in the coil 20a1, and a compensation coil 20d1 arranged far from the living body. Let Sd1 'be the coil area of

[Equation 11] It is configured to satisfy. Where X1A is S
Represents the focal length of the QUID magnetometer 2a1.

Similarly, in the pickup coil 20a2 of the SQUID magnetometer 2a2, if the coil area of the signal detection coil 20c2 is Sc2 'and the coil area of the compensation coil 20d2 is Sd2',

(Equation 12) And the pickup coil 20a3 of the SQUID magnetometer 2a3 is connected to the signal detection coil 6c.
3 is Sc3 ', and the coil area of the compensation coil 20d3 is Sd3'.

(Equation 13) It is configured to satisfy. Here, X1B and X1C represent the focal lengths of the SQUID magnetometers 2a2 and 2a3, respectively.

It should be noted that the above-described pickup coil for detecting the magnetic field in the radial direction and the pickup coil for detecting the magnetic field in the tangential direction can be used in combination.

Further, a plurality of pickup coils 20a1 to 20an having different detection sensitivities, in other words, different focal lengths X11, X12,.
In the case where SQUID magnetometers 2a1 to 2an each having a pickup coil in the tangential direction of the body surface are used, the pickup coils 20a
As shown in FIGS. 3 (a) and 3 (b) (n = 12 in FIG. 3), 1 to 20an may be arranged so that their coil surfaces are arranged concentrically at predetermined intervals. .

Further, as shown in FIG. 4, a plurality of pickup coils (21a1 to 21a2) having different detection sensitivities are provided.
1an) each having a SQUID magnetometer 2a1'-2
an 'are provided (SQUID magnetometers 2A1 to 2Am) and their pickup coil groups 21A1 to 21Am
(M = 7 in the figure) may be arranged in the minutely important structure. Further, the pickup coil group 21A
1 to 21 Am may be set on grid points in the above-described discretized model.

(Second Embodiment) SQUID of the Present Invention
FIG. 5 shows a second embodiment relating to a current source estimating apparatus using a magnetometer.

According to FIG. 5, the current source estimating device 25 of the present embodiment includes a plurality of (two in this embodiment) SQUAs for measuring a biomagnetic field emitted from a living body to be measured.
ID magnetometers 30a1 to 30a2 are provided.

Each SQUID magnetometer 30a1, 30a2
Is a SQUID element 5 having two Josephson junctions.
And a first pickup coil 32a for picking up a weak magnetic field (a weak magnetic signal) emitted from the living body
1, a second pickup coil 32a2, and an input coil 7 for transmitting a magnetic flux based on a weak magnetic signal picked up by the first pickup coil 32a1 and the second pickup coil 32a2 to the SQUID element 5, respectively. I have.

The first pickup coil 32a1 and the second pickup coil 32a2 of each of the SQUID magnetometers 30a1 and 30a2 are different from those of the first embodiment in that they are configured as so-called magnetometers which detect a magnetic field with a single coil. Have been.

Pickup coils 32a1, 32a2
Are located on two different (separated) planes along the depth direction, the pickup coil 32a1 is arranged at a position close to the living body, and the pickup coil 32a2 is arranged at a position separated from the living body, not shown. The magnetic field in the normal direction of the body surface of the living body is detected.

Further, the pickup coil 32a2 is disposed with the base line (BL) placed with respect to the pickup coil 32a1 as in the first embodiment.

The SQUID magnetometers 30a1, 30a
The other configuration is the same as the configuration of the SQUID magnetometers 2a1 and 2a2 in the first embodiment, and a description thereof will be omitted.

Further, the current source estimating device 25
Drive circuit 11 for D fluxmeters 30a1 to 30a2 (integrator)
Is provided with a data processing device 31 for inputting the voltage signals Vout1 to Vout2 output from the controller, performing data processing based on the input voltage signals Vout1 to Vout2, and estimating the position of the current source in the living body.

As shown in FIG. 5, the data processing unit 31 has a gain control unit having a first gain controller 33a and a second gain controller 33b for setting the gains of the voltage signals Vout1 and Vout2 while controlling them individually. A / D converter 3 for converting voltage signals Vout1 'and Vout2', which have been gain-controlled by first gain controller 33a and second gain controller 33b, into digital data D1 and D2, respectively.
4, the digital data D1 and D2 converted by the A / D converter 34 and the first gain controller 3
3a, a control operation unit (for example, CPU, DSP) for estimating a three-dimensional position including a position in the depth direction of the current source based on each gain value set by the second gain controller 33b
Etc.) 35.

Next, the overall operation of the current source estimating device 25 of this configuration will be described, focusing on the processing of the control calculation unit 35.

According to the current source estimating device 25 of this configuration, as in the first embodiment, the dewar is attached to the living body and each SQ
By driving the SQUID drive circuits 15 of the UID magnetometers 30a1 and 30a2, weak magnetic signals emitted from the living body through the pickup coils 32a1 and 32a2 are detected.

The magnetic flux based on the magnetic signals detected by the pickup coils 32a1 and 32a2 is transmitted through the input coil 7 and the SQUID element 5, respectively, and a voltage based on the input magnetic flux is output. Then, this voltage output is amplified through the drive circuit 11 and becomes voltage signals Vout1 and Vout2 proportional to the feedback magnetic flux, respectively, as the first signals of the gain control unit 33 of the data processing device 16.
Are sent to the gain controller 33a and the second gain controller 33b, respectively.

First and second gain controllers 33
a and 33b are the voltage signals Vout1,
Gain values G1 and G2 are set for Vout2, respectively, and A / D are set as voltage signals Vout1 'and Vout2'.
Output to the converter 34. The A / D converter 34 converts the sent voltage signals Vout1 'and Vout2' into digital data D1 and D2 and sends them to the control operation unit 35 (FIG. 6;
Step S1).

The control operation unit 35 determines a difference value (digital difference value) between the transmitted digital data D1 and D2 (step S2), and based on the difference value, maps the magnetic field (maps the intensity of the digital difference value). , Which represents the magnetic field distribution in the living body) (step S
3).

Subsequently, the control calculation section 35 finds the value of the peak portion on the magnetic field mapping (step S4), and determines whether or not the value of the peak portion is zero (step S4).
5).

At this time, the control operation unit 35 in step S5
Is NO, that is, if the value of the peak portion is not zero, the gain setting value of the second gain controller 33b is changed from G2 to G2 ', and the process returns to step S2 (step S6). Repeat the process.

On the other hand, as a result of the determination in step S5, YE
S, that is, when the value of the peak portion is zero, the control calculation unit 35 performs the process of step S1 when the value of the peak portion is zero or the first gain controller 33a and the first gain controller 33a set in step S6. From the ratio {G2 (G2 ') / G1} of the gain values G1 and G2 (G2') of the second controller 33b, the position in the depth direction of the current source (focal length) is calculated by the above equation (6). XA) (step S7), and the processing for calculating the position of the current source in the depth direction is ended.

As described above, according to this configuration, the gain value of the signal detected via the two pickup coils arranged so as to be located on two separate planes along the depth direction is changed. By doing so, the magnetic field sensitivity of the signal detected via the two pickup coils can be changed, so that the position of the current source in the depth direction can be directly obtained. Therefore, similarly to the first embodiment, the depth direction position of the current source at a deep position in the depth direction in the living body can be detected with high accuracy.

In this embodiment, the gain controller 33
(The first and second gain controllers 33a and 33b) A / D convert the voltage signals Vout1 'and Vout2' whose gains have been controlled by the A / D converter 34, and convert the converted digital data D1 and D2. Although the difference value is obtained by the processing of the control operation unit 35, the present invention is not limited to this. For example, an analog difference circuit 40 is provided between the gain control unit 33 and the A / D converter 34.
May be provided. That is, as shown in FIG. 7, the voltage signal V that has been gain-controlled by the analog difference circuit 40 is used.
out1 'and Vout2' are sent to the A / D converter 34 as analog difference values via the analog difference circuit 40,
The data is converted into digital data (digital difference value) by the / D converter 34 and sent to the control operation unit 35. At this time, the control operation unit 35 can obtain the position of the current source in the depth direction by performing the processing after step S3 in FIG. 6 based on the sent digital difference value.

In this embodiment, the gain controller 33
The position of the current source in the depth direction is detected while controlling the gain of the voltage signals Vout1 and Vout2 using the (gain controllers 33a and 33b), but the present invention is not limited to this.

FIG. 8 shows a modification of the second embodiment. FIG.
Data processing device 31A of current source estimating device 25A shown in FIG.
Are voltage signals Vout1 to Vout2 output from the drive circuit 11 (integrator) of each of the SQUID magnetometers 30a1 to 30a2.
A / D converter 34A for converting the input voltage signals Vout1 to Vout2 into digital data D1 and D2, respectively, and a current based on the digital data D1 and D2 converted by the A / D converter 34A. Control operation unit (CP) for estimating a three-dimensional position including the position of the source in the depth direction
U / DSP) 35A. Note that the other configuration is similar to the configuration of the second embodiment (FIG. 5).
The description is omitted.

Next, the overall operation of the current source estimating apparatus 25A of this configuration will be described, focusing on the processing of the control calculation section 35A.

According to the current source estimating device 25A of this configuration,
By the same operation as the first and second embodiments, the SQUID
When the weak magnetic signals emitted from the living body are detected by driving the D magnetometers 30a1 and 30a2, the voltage signals Vout1 and Vout2 based on the detected weak magnetic signals are converted into A / D converters of the data processing device 31A. 34A. A /
The D converter 34A converts the transmitted voltage signal Vout1 and voltage signal Vout2 into digital data D1 and D2, and sends them to the control operation unit 35A.

The control operation unit 35A is configured to control the first pickup coil 32 of the transmitted digital data D1 and D2.
magnetic field mapping (digital data D1) based on the digital data D1 based on the biomagnetic signal detected at a1
1 (representing the magnetic field distribution in the living body) (FIG. 9; step S10), and find the value of the peak portion in the magnetic field mapping (step S11).

On the other hand, the control calculation unit 35A adjusts (amplifies) the gain of the digital data D2 based on the biomagnetic signal detected by the second pickup coil 32a2 (the gain of the digital data D1 is constant (G10)). Then, a difference between the value of the peak portion (peak value) is obtained (step S12), and the gain of the digital data D2 related to the second pickup coil 32a2 is amplified so that the difference value becomes zero (step S12). Step S13).

Then, the control calculation unit 35A calculates the gain value (G1) of the digital data D1 when the difference value becomes zero.
0) and the amplification gain value (G2
0) and the position (focal length XB) in the depth direction of the current source by calculation using the above-mentioned formula (6) from the ratio (G20 / G10).
Is obtained (step S13), and the process of calculating the position of the current source in the depth direction ends.

As described above, in this modification,
As in the second embodiment, the depth direction position of the current source at a deep position in the depth direction in the living body can be detected with high accuracy. Further, in the present modification, it is not necessary to provide a gain control unit, and the circuit space of the current source estimating device can be reduced.

FIG. 10 shows a modification in which the data processing device according to the second embodiment is configured using a sample and hold circuit and the like.

The data processing device 51 of the current source estimating device 50 shown in FIG. 10 includes the SQUID magnetometers 30a1 to 30a.
A sample and hold circuit 52 that samples the voltage signals Vout1 and Vout2 amplified through the amplifier and integrator of the second drive circuit 11 in accordance with the sampling clock, and holds (holds) the output for a fixed time; An A / D converter 53 for converting the voltage signals Vout1 and Vout2 output from 52 into digital data D1 and D2, respectively, and at least one of the digital data D1 and D2 converted by the A / D converter 53. A control / operation unit (CPU / DSP) 54 for performing amplification processing as required and estimating a three-dimensional position including a position in the depth direction of the current source based on the amplified digital data D1 and D2; A monitor which is connected to the operation unit 54 and monitors digital data D1 and D2 inputted to the control operation unit 54 55.

Further, the data processing device 51 outputs the digital data D 1, D 2
And second latch circuits 56B and 56B that output after holding (latch) the digital data D1 and D2 respectively output from the first latch circuit 56A and the second latch circuit 56B. A first D / A converter (first DAC) 57A and a second D / A converter (second DAC) 57B for converting into an analog value (DC voltage signal); SKU
ID magnetometer 30a1 and second SQUID magnetometer 30
Each feedback circuit 14A converts the DC voltage signal output from the first DAC 57A and the second DAC 57B into a current via the resistor 12 (impedance Zf0) instead of the output voltage signal from the drive circuit 11. In addition, the feedback coil 13 is configured to flow as a feedback current. Note that the other configuration is similar to the configuration of the second embodiment (FIG. 5).
The description is omitted.

Next, the overall operation of the current source estimating apparatus 50 having this configuration will be described.

According to the current source estimating device 50 of the present configuration, similarly to the first and second embodiments, the dewar is mounted on the living body and the SQUID of each SQUID magnetometer 30a1, 30a2 is set.
By driving each of the D drive circuits 15, a weak magnetic signal emitted from a living body is detected through the pickup coils 32a1 and 32a2.

The magnetic flux based on the magnetic signals detected by the pickup coils 32a1 and 32a2 is transmitted via the input coil 7 and the SQUID element 5, respectively, and a voltage based on the input magnetic flux is output. Then, these voltage outputs Vout1 and Vout2 are amplified through the drive circuit 11.

At this time, the voltage signals Vout1 and Vout2 that have been amplified by the sample-and-hold circuit 52 are held (held) at the same timing according to the rise of the sent sample clock (for example, the n-th sampling clock). The signal is output to the output A / D converter 53 in response to the fall. The sent voltage signal Vout1 and voltage signal Vout2 are converted into digital data D1 and D2 via an A / D converter 53, and
4

The control operation unit 54 monitors the transmitted digital data D1 and D2 via the monitor 55, and amplifies at least one of the digital data D1 and D2 (for example, digital data D2) (D2 → D2a). ), The ratio of the data values (D2a / D1) is set so as to satisfy the focal length = X1 (for example, 3 cm) in equation (6).

Then, the control operation unit 54 converts the digital data D1 and D2a into the first latch circuit 56A, respectively.
And output to the second latch circuit 56B.

The digital data D1 and D2 'correspond to the first
After being latched via the latch circuit 56A and the second latch circuit 56B, respectively, they are sent to the first DAC 57A and the second DAC 57B. These first DACs
The DC voltage signals V1 and V2 obtained via 57A and the second DAC 57B are sent to respective feedback circuits 14A of the first SQUID magnetometer 30a1 and the second SQUID magnetometer 30a2.

The DC voltage signals V1 and V2 sent to each feedback circuit 14A are connected to the resistor 12 (impedance Z
f0), and converted as a feedback current into the first SQUID magnetometer 30a1 and the second SQUID.
It is supplied to each feedback coil 13 of the ID magnetometer 30a2. As a result, the feedback magnetic flux is applied to each SQUID element 5, and the change in the measured magnetic signal is canceled.

On the other hand, the sample and hold circuit 52
The amplified voltage signals Vout1 and Vout2 are held (held) in response to the rising edge of the subsequently sent sample clock (n + 1), and A / A in response to the falling edge.
The signal is output to the D converter 53. Then, the sent voltage signal Vout1 and voltage signal Vout2 are converted into digital data D1 and D2 via an A / D converter 53 and sent to the control operation unit 54.

At this time, the control operation unit 54 monitors the transmitted digital data D1 and D2 via the monitor 55, amplifies the digital data D2 of the digital data D1 and D2 (D2 → D2a '). , The ratio of the data values (D2a '/ D1) is equal to the focal length = X in equation (6) above.
2 (for example, 4 cm).

Then, the first and second latch circuits 56A, 56A,
The magnetic flux feedback processing described above is performed via the 56B, the first and second DACs 57A and 57B, and the respective feedback circuits 14A.

Hereinafter, the data processing device 51 performs the above-described arithmetic processing while sequentially changing the focal length from X1: 3 cm to X5: 7 cm in accordance with the sequentially transmitted sampling clocks (nth to n + 4th). , It is possible to estimate current sources having different focal lengths X1: 3 cm to X5: 7 cm in the depth direction (see FIG. 11, sampling clock groups from nth to n + 4th, and this sampling clock The digital data D1 group and the digital data D2 group corresponding to the group are referred to as a data group 1).

Then, the data processing device 51 sends the n + 5th, n + 6th,..., N + 10,.
In accordance with the sampling clock, the focal length is returned to X1: 3 cm again and the above-described processing is repeated to repeatedly obtain a current source having a focal length X1: 3 cm to X5: 7 cm in the depth direction. be able to.

That is, according to this configuration, by amplifying the signal detected by the second pickup coil every sampling time using the first and second pickup coils, the number of pickup coils (2) Can be estimated in the depth direction of the current source having a large number of focal lengths beyond the range. Therefore, for example, since it is not necessary to use a large number of pickup coils as shown in FIGS. 3 and 4 of the first embodiment, the position of the current source having the multiple focal lengths in the depth direction can be efficiently and simply configured. It can be estimated by the configuration.

According to the first and second embodiments and the respective modifications, the dewar accommodating the pickup coil, the input coil, the SQUID element, and the feedback coil of the SQUID magnetometer and the living body are separated from each other by the magnetic shield room R. Although it is disposed inside to shield the environmental magnetic field noise, the present invention is not limited to this. For example,
A method of disposing a reverse magnetic field generating coil (for example, a Helmholtz coil) constituting an active shield in a predetermined space portion including a pickup coil and feeding back a signal based on an environmental magnetic field to the reverse magnetic field generating coil to cancel the environmental magnetic field (Active shield) or a method for removing environmental magnetic field noise by subtracting an environmental magnetic field signal received by an SQUID magnetometer for canceling an environmental magnetic field (for a reference signal) from a magnetic field signal received by a SQUID magnetometer for detecting a biological magnetic field signal. Etc. can also be applied.

For example, as shown in FIG. 12, signal detecting coil groups 6c1... 6cn and compensating coil groups 6d1.
pickup coil groups 6a1... 6an
60an and a reference signal coil group 60a1... 60an of an SQUID magnetometer for detecting an environmental magnetic field (not shown) are installed in the dewar D, and the environmental magnetic field obtained based on the magnetic flux detected by the pickup coil groups 6a1. 60a1... 60 from the biomagnetic signal including
By subtracting the environmental magnetic field signal (reference signal) obtained based on the magnetic flux detected by an, the position estimation process of the current source in the depth direction can be performed without being affected by the environmental magnetic field noise. .

The above-described environmental magnetic field noise elimination system using the active shield and the reference signal can be used in combination with the magnetic shield room. Can do it.

Further, according to the first embodiment, two coils located on two different (separated) planes along the depth direction are wound in opposite phases and connected by placing the baseline BL.
Although the SQUID magnetometer having the secondary differential pickup coil is used, the present invention is not limited to this. For example, a SQUID magnetometer having a secondary differential or higher-order differential pickup coil may be used. Good.

For example, the second-order differential pickup coil 6A shown in FIG. 13 is a signal detection coil 6M1 located on three different (separated) planes in the depth direction.
And 6M2 and a compensating coil (double coil) 6M3 are wound in opposite phases to form a second-order differential structure in which they are connected at intervals (base lines) BL1 and BL2, respectively. The magnetic field in the normal direction (radial direction) is detected.

Then, the pickup coil 6A is the first coil disposed closest to the living body in the coil 6A.
The coil area of the signal detection coil 6M1 is S1, and the second signal detection coil 6M2 disposed farthest from the living body is
Is S2, and the coil area of the compensating coil 6M3 interposed between the signal detecting coil 6M1 and the second signal detecting coil 6M2 is S3.

S3 = S1 + S2 (14)

By using the second-order differential pickup coil configured as described above, the first signal detecting coil 6M1
The detection sensitivity to the environmental magnetic field caused by the difference in the area (unbalance) between the second signal detection coil 6M3 and the compensation coil 6M3 can be canceled by the second signal detection coil 6M3. In other words, by balancing between the first signal detecting coil 6M1 and the second signal detecting coil 6M2 and the compensating coil 6M3, the detection sensitivity to the environmental magnetic field can be greatly reduced. The processing of estimating the position of the current source in the depth direction can be performed with almost no influence of the environmental magnetic field noise.

Further, according to the first embodiment, the second embodiment and the modifications thereof, the signal detecting coil and the compensating coil having different detection sensitivities are located on two different planes along the depth direction. However, it is also possible to arrange a pickup coil including such a signal detecting coil and a compensating coil in two stages along two different planes in the depth direction to perform biomagnetic field measurement. In addition, the position of the current source in the body in the depth direction can be more accurately estimated.

Further, according to the first and second embodiments and the modifications thereof, the current source estimating apparatus using the SQUID magnetometer of the magnetic flux transfer type with the pickup coil is shown. Without limitation, other types of SQUID magnetometers, for example, Dire
A current source estimating device using a SQUID magnetometer of the ct Coupling method may be used, or a digital SQUID may be used.
A current source estimation device using an ID magnetometer may be used.

[0114]

As described above, according to the current source estimating apparatus of the present invention, a plurality of coils (signal detecting coils,
A weak magnetic signal emitted from the object to be measured via the compensation coil) is detected as an electric signal with different magnetic field sensitivities, and the position of the current source in the depth direction is directly estimated based on the detected electric signal. For example, the position of the current source at a deep position along the depth direction in the measurement target, such as the deep part of the heart or brain of a living body, can be estimated with high accuracy without causing local and global minimums. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a current source estimating apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration in which a pickup coil for detecting a tangential magnetic field is used as a pickup coil of the SQUID magnetometer in FIG. 1;

FIGS. 3A and 3B are diagrams illustrating an example of the arrangement of a plurality of pickup coils having different sensitivities. FIGS.

FIG. 4 is a diagram showing an arrangement example of a plurality of pickup coils having different sensitivities.

FIG. 5 is a block diagram showing a schematic configuration of a current source estimating device according to a second embodiment of the present invention.

FIG. 6 is a schematic flowchart showing an example of a process of the data processing device of FIG. 5;

FIG. 7 is a block diagram showing a schematic configuration of a modified example of the current source estimating device according to the second embodiment.

FIG. 8 is a block diagram showing a schematic configuration of a modified example of the current source estimation device according to the second embodiment.

FIG. 9 is a schematic flowchart illustrating an example of a process of a control calculation unit in FIG. 8;

FIG. 10 is a block diagram showing a schematic configuration of a modified example of the current source estimating device according to the second embodiment.

FIG. 11 is a timing chart showing data of each SQUID element according to each sampling clock in the processing of the data processing device of FIG. 8;

FIG. 12 is a diagram showing a reference signal coil group and a biomagnetic signal detection pickup coil group of a reference signal SQUID magnetometer for canceling an environmental magnetic field installed in a dewar.

FIG. 13 is a diagram showing a schematic configuration of a second-order differential type pickup coil according to the present invention.

FIG. 14 is a view for explaining measurement of a magnetic signal from a living body using a conventional gradiometer.

FIG. 15 is a diagram schematically showing a configuration in which two pickup coil groups of a conventional SQUID magnetometer are arranged in two stages along two different planes in the depth direction to perform biomagnetic field measurement.

FIG. 16 is a diagram showing a relationship between a baseline length of a conventional primary differential pickup coil for a tangential direction component and a sensitivity distribution in a depth direction. FIG. Figure when set to (b)
7 is a diagram when the base line length of the pickup coil is changed to 7 cm.

FIG. 17 is a diagram showing a sensitivity distribution in a depth direction when the sensitivities of the signal detection coil and the compensation coil in the pickup coil for the tangential component are changed;
(A) is a diagram in which the sensitivity of the compensation coil is adjusted so that the focal length is 5 cm, and (b) is a diagram in which the focal length is 7c.
FIG. 9 is a diagram when the sensitivity of the compensation coil is adjusted to be m.

[Explanation of symbols]

1, 25, 50 Current source estimating device 2a1 to 2a3, 30a1, 30a2 SQUID magnetometer 5 SQUID element 6a1 to 6a3, 6A, 20a1 to 20a12, 32a1
, 32a2 Pickup coil Coil 6c1-6c3, 6M1, 6M2, 20c1-20c3
Signal detection coils 6d1 to 6d3, 6M3, 20d1 to 20d3 Compensation coils 7 Input coils 8 Current sources 11 Drive circuits 12 Resistors 13 Feedback coils 14 Feedback circuits 15 SQUID drive circuits 16, 31, 31A, 51 Data processing devices 21A1 to 21Am Pickup coil group 33 gain control unit 33a first gain controller 33b second gain controller 34, 34A, 53 A / D converter 35, 35A, 54 control operation unit 40 difference circuit 52 sample and hold circuit 55 monitor 56A first Latch circuit 56B Second latch circuit 57A First DAC 57B Second DAC

Claims (15)

[Claims] 1. A current source estimating apparatus for estimating a position of a current source based on a weak magnetic signal emitted from the current source in the measurement target, wherein the current source estimating device is arranged at different positions along a depth direction of the measurement target. Magnetic signal detecting means having a plurality of coils provided, detecting weak magnetic signals emitted from the object to be measured through the plurality of coils with different magnetic field sensitivities, and outputting an electric signal; An estimating means for estimating the position of the current source in the depth direction based on the electric signal output from the detecting means. 2. The pickup device according to claim 1, wherein the magnetic signal detection unit includes a pickup coil in which the signal detection coil and the compensation coil constituting the plurality of coils are wound in opposite phases and coupled with each other at a baseline, and A magnetic field measuring means having a SQUID element for outputting an electric signal in accordance with a magnetic flux based on the detected weak magnetic signal;
The electric signal output from the UID element is used as
SQ which makes the electric signal an output signal proportional to the weak magnetic signal by feeding back to a QUID element
2. The current source estimating apparatus according to claim 1, further comprising a UID driving unit, wherein the magnetic field sensitivity of the signal detection coil itself and the magnetic field sensitivity of the compensation coil itself are set to be different from each other. 3. The magnetic field sensitivity of the signal detecting coil itself and the magnetic field sensitivity of the compensating coil itself are set so that the magnetic field sensitivity of the compensating coil is higher than the magnetic field sensitivity of the signal detecting coil. Item 2. The current source estimating device according to Item 2. 4. The pickup coil according to claim 1, wherein the pickup coil is a first-order differential pickup coil in which one signal detecting coil and one compensating coil are wound in opposite phases and coupled with each other with a baseline placed therebetween. 4. The current source estimating device according to claim 3, wherein the coil is arranged closer to the current source in the measurement object than the compensation coil. 5. The distance (baseline) between the signal detection coil and the compensation coil of the pickup coil is represented by B
L, the distance (focal length) along the depth direction between the signal detection coil and the measurement object, F, the magnetic field sensitivity of the signal detection coil of the pickup coil, Z1, and the magnetic field of the compensation coil. when the sensitivity was Z2, the magnetic field sensitivity Z1 and field sensitivity Z2 following equation ## EQU1 ## Z2 / Z1 = (BL + F ) 2 / F 2 ...... (1) according to claim 4, wherein the set to satisfy the Current source estimation device. 6. A plurality of said pickup coils, said magnetic field measuring means and said SQUID driving means, and at least a part of said plurality of pickup coils is measured in a direction normal to a coil surface of said pickup coils. The current source estimating device according to any one of claims 2 to 5, wherein the current source estimating device is arranged so as to coincide with a normal direction of the surface of the current source. 7. A plurality of said pickup coils, said magnetic field measuring means and said SQUID driving means, and at least a part of said plurality of pickup coils is measured with a normal direction of a coil surface of the pickup coil being measured. The current source estimating device according to any one of claims 2 to 5, wherein the current source estimating device is arranged so as to coincide with a tangential direction of a surface of the current source. 8. The current source estimating apparatus according to claim 7, wherein a plurality of sets of said plurality of pickup coils, a plurality of magnetic field measuring means and a plurality of SQUID driving means are provided. 9. The current source estimating apparatus according to claim 8, wherein the plurality of pickup coils of each set are arranged in a fine-point-weighted structure. 10. The current source estimating apparatus according to claim 8, wherein the plurality of pickup coils of each set are arranged in a grid pattern. 11. A method according to claim 1, wherein the plurality of coils are a first pickup coil disposed in close proximity to a current source in the object to be measured, and a predetermined length of the first pickup coil along the depth direction with respect to the first pickup coil. It has a second pickup coil arranged at intervals, and the magnetic signal detecting means,
A plurality of magnetic field measuring means provided for each of the first pickup coil and the second pickup coil, each having a SQUID element for outputting an electric signal in accordance with a magnetic flux based on each weak magnetic signal detected by each pickup coil; A plurality of SQUIDs which output the electric signals as output signals in proportion to the respective weak magnetic signals by feeding back the respective electric signals output from the plurality of SQUID elements as magnetic flux to the respective SQUID elements.
ID driving means, and the estimating means includes:
Gain adjusting means for adjusting the gain of at least one of the electric signals output from the QUID driving means to change the magnetic field sensitivity relating to the electric signals; and adjusting the gain of each electric signal gain-adjusted by the gain adjusting means. 2. The current source estimating device according to claim 1, further comprising: an arithmetic processing unit that obtains a position in a depth direction of the current source by an arithmetic process based on a gain value. 12. The arithmetic processing means includes means for converting each of the electric signals gain-adjusted by the gain adjusting means into digital data, and obtaining a difference value between the converted digital data, and based on the difference value. Means for obtaining a magnetic field distribution (magnetic field mapping) in the measurement object, a means for extracting a peak on the magnetic field mapping, and judging whether or not a difference value at the peak is zero; Means for controlling the gain adjusting means when the difference is not zero to change a set gain value for at least one of the electric signals, wherein the gain adjustment is performed when the difference value at the peak as a result of the determination is zero. Means for performing arithmetic processing based on the gain value of each electric signal set by the means to determine the position of the current source in the depth direction. The current source estimating device according to claim 11, wherein 13. A first pickup coil disposed in close proximity to a current source in the object to be measured and a predetermined distance from the first pickup coil along the depth direction with respect to the first pickup coil. And a second pickup coil disposed with the magnetic signal detection means,
A plurality of magnetic field measuring means provided for each of the first pickup coil and the second pickup coil, each having a SQUID element for outputting an electric signal in accordance with a magnetic flux based on each weak magnetic signal detected by each pickup coil; A plurality of SQUIDs which output the electric signals as output signals in proportion to the respective weak magnetic signals by feeding back the respective electric signals output from the plurality of SQUID elements as magnetic flux to the respective SQUID elements.
ID driving means, wherein the estimating means converts the electric signals into digital data, and performs the measurement based on the first digital data related to the first pickup coil in the converted digital data. Means for determining a magnetic field distribution (magnetic field mapping) in the object;
Means for extracting a peak value on the magnetic field mapping to obtain a difference value between the value of the second digital data relating to the second pickup coil and the peak value, and the obtained difference value becomes zero Means for adjusting the gain of the second digital data as described above, and arithmetic processing based on the gain value of the first digital data and the gain value of the second digital data when the difference value becomes zero. 2. A current source estimating apparatus according to claim 1, further comprising: an arithmetic processing unit for performing a step of calculating a depth direction position of the current source. 14. A plurality of coils, a first pickup coil disposed close to a current source in the object to be measured, and a predetermined distance from the first pickup coil along the depth direction with respect to the first pickup coil. And a second pickup coil disposed with the magnetic signal detection means,
A plurality of magnetic field measuring means provided for each of the first pickup coil and the second pickup coil, each having a SQUID element for outputting an electric signal in accordance with a magnetic flux based on each weak magnetic signal detected by each pickup coil; And the estimating means comprises:
Sample and hold means for sampling and holding each electric signal output from the ID driving means, conversion means for converting each electric signal output from the sample and hold means into digital data, Arithmetic processing means for amplifying the second digital data related to the pickup coil and calculating the ratio of the first digital data to the first digital data related to the first pickup coil to obtain the position of the current source in the depth direction; Converting means for converting the first and second digital data output through the arithmetic processing means into electric signals, and feeding back the electric signals converted by the converting means as magnetic flux to the respective SQUID elements. The electric signal converted by the conversion means can be Current source estimating apparatus according to claim 1, further comprising a plurality of SQUID drive means for the output signal proportional to the electrical signal. 15. The arithmetic processing means changes an amount of amplification of the second digital data according to a sampling clock of the sample-and-hold circuit, and uses the plurality of second digital data having different amounts of amplification to calculate the second digital data. 15. The current source estimating device according to claim 14, wherein the position of each of the plurality of current sources in the depth direction is obtained by performing arithmetic processing on a ratio with respect to one digital data.