JP3525873B2 - Initial value estimation method in magnetic field source analysis method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly sensitive quantum interference device (SQUID: superconducting quanta) for a biomagnetic field generated by nerve activity of the brain of the living body, myocardial activity of the heart, and the like.
The present invention relates to a biomagnetic field measuring method and a biomagnetic field measuring apparatus for measuring using a plurality of magnetometers each including an um interference device). Especially for the initial value estimation method in the magnetic field source analysis method
Concerned.

[0002]

BACKGROUND OF THE INVENTION The present invention is a highly sensitive quantum interference device (SQUID: superconducting) for a biomagnetic field generated by a nerve activity of the brain of a living body, a myocardial activity of the heart, and the like.
quantum interference devi
The present invention relates to a biomagnetic field measuring method and a biomagnetic field measuring apparatus for measuring using a plurality of magnetometers composed of (c.

The biological magnetic field includes a magnetic field produced by a current dipole and a magnetic field caused by a volume current flowing in the living body. It is considered that the measurement of the normal component of the biomagnetic field (B _z (Z component in the Cartesian coordinate system) or B _r (radial component in the polar coordinate system)) is not easily affected by the volume current. In the conventional technique, the surface of the detection coil connected to the SQUID is arranged parallel to the surface of the living body, and B _z or B _r , which is a normal component perpendicular to the surface of the living body, is measured. The result of the biomagnetic field measurement was displayed by a waveform representing the time change of the measured magnetic field component and an contour diagram (contour map) connecting points of the measured magnetic field component having the same intensity at arbitrary times.
In addition, various analysis methods have been proposed to analyze the magnetic field source that generates the biomagnetic field from the obtained isomagnetic field maps. In typical analysis methods, the magnetic field source is replaced with a current dipole. I was doing.

The normal component of the magnetic field created by the current dipole (B
_z or B _r ) is the magnetic field map (magnetic dipole)
The pattern has a magnetic field evacuation pole and a magnetic field suction pole at positions separated from each other. The size, position, direction, etc. of the magnetic field source (current dipole) are analyzed based on the magnetic field strengths at the two poles and the distance between the two poles.

The first prior art (H. Hosaka an
d D. Cohen, J .; Electrocardio
l. , 9 (4), 426-432 (1976)),
In order to make it easier to see the direction and strength of the electric current in the myocardium, it is defined by (Equation 1) as a method for displaying the current source distributed in the myocardium using the contour map of the measured normal component B _z . Arrow maps have been devised in which the current vector <J (x, y)> is represented by an arrow on each measurement point. In the following description, parentheses <> indicate that the symbol in <> is a vector, and, for example, <J> indicates that J is a vector.

[0006]

[Equation 1] <J (x, y)> = (∂B _z (x, y) / ∂y) <e _x >-(∂B _z (x, y) / ∂ x) <e _y > ... ( (Equation 1) In (Equation 1), <e _x > is a unit vector in the x direction,
<E _y > is a unit vector in the y direction. However, when there are a plurality of current sources, there is a problem that it is difficult to distinguish the individual current sources from the isomagnetic field diagram of the normal component B _z .

The second prior art (K. Tukada et.
al. , Reveiw of the Scient
if Instruments, 66 (10) 50
85-5091 (1995)), in order to visualize a plurality of distributed current sources, instead of measuring the normal component (B _z or B _r ), the plane of the detection coil is made perpendicular to the surface of the living body. It is arranged and the tangential components B _x and B _y are measured.
The measured tangential line components B _x and B _y are displayed as an isomagnetic field diagram for each component. Tangent component B measured by Conventional Technique 2
_x, although B _y is considered the influence of the volume current, (Equation 2)
Therefore, in the isomagnetic field diagram of the two-dimensional vector intensity B _{xy that combines} B _x and B _y measured at time t, a peak is always obtained immediately above the current dipole, so that there are multiple current dipoles. In this case, each current dipole can be separated and visualized.

[0008]

[Number 2] _{│B xy (x, y, t} ) │ = √ {(B x (x, y, t)) 2 + (B y (x, y, t)) 2} ... ( Equation 2) The 3 of the prior art (Y. Yoshida et al.,
Tenth International Conf
Rence on Biomagnism, San
tana Fe, New Mexico, Feb. 20
(1996)), the planes of the coil are orthogonal to each other 3
A vector magnetic field sensor consisting of two detection coils is used to detect the normal line component and two tangential line components of the biomagnetic field, and the detection result of the magnetic field component is converted into a rectangular coordinate system, and the components B _x and B _{y of the} rectangular coordinate system are detected. , B _z are obtained, and the contour lines of the normal component B _z and the two-dimensional vector intensity B _xy are displayed.

A fourth conventional technique (K. Tsukada, e.
t. al. , Tenth International
Conference on Biomagneti
sm, Santana Fe, New Mexico,
Feb. 20 (1996)), the two tangential components B _x biomagnetic field to detect _{B y, | B xy | =} | B x + B y | in based like magnetic field diagrams and the like magnetic field based on the normal component B _z We are making a comparison with the diagram.

An electroencephalogram obtained by measuring with an electroencephalograph (ME) as a diagram showing the measurement result of the electrophysiological phenomenon in the living body.
G, magnetoencephalogram), and an electrocardiogram (ECG) obtained by measuring with an electrocardiograph. Body surface potential map for mapping electrocardiogram using multiple electrodes in electrocardiogram measurement
Is a well-known technique. These electroencephalograms or body surface electrocardiograms were displayed as equipotential maps connecting equal potential points.

Fifth prior art (TJ Montagu
e et al. , Circulation 63, N
o. 5, pp1166-1172 (1981)),
An isointegral map that integrates the waveform representing the time change of each electrode output of multiple electrodes in an arbitrary time interval
Is displayed as a body surface electrocardiogram.

[0012]

In the following description, "biomagnetic field" means "magnetic field emitted from biomagnetic field", "cardiac magnetic field measurement" means "measurement of magnetic field emitted from heart", and The “magnetocardiographic waveform” means “a waveform represented by a magnetocardiogram (MCG, Magnetocardiogram) obtained by measurement of magnetocardiographic field”. Further, "measurement of magnetic field in brain" means "measurement of magnetic field emitted from brain", and "magnetoencephalographic waveform" means "waveform represented by magnetoencephalogram (MEG, Magnetoencephalogram) obtained by measurement of magnetic field in brain".

The isomagnetic field diagram for each component in the prior art has its own characteristics. When a single current dipole is present, the isomagnetic field diagram for the normal component B _z indicates the position of the current source,
The size and direction can be easily analyzed. On the other hand, the tangent component B
_x, in isomagnetic field of a two-dimensional vector magnitude B _xy obtained from the measurement results of B _y, even when the plurality of current dipoles are present, is characterized readily determine each current dipole.
However, since the number of coils for detecting the magnetic field is necessary in each of the x and y directions, the number of coils is doubled as compared with the detection of only the normal component B _z . Also, B _x, B _y, the vector measurement for measuring all the components B _z, it is necessary to 3 times the number of coils in comparison to the detection of the normal component B _z only. Therefore, there is a problem that the number of magnetic field sensors including the detection coil and the SQUID is increased, the number of signal processing circuits is increased, and the biomagnetic field measurement system becomes an expensive system. Further, the first conventional technique has a problem in that it is difficult to identify the detailed distribution state of the current source because only the arrow is displayed on each measurement point.

The position, size, direction, etc. of the current source in the living body at any time can be analyzed from the isomagnetic field diagram represented by the biomagnetic field component, and detailed information on the position, size, direction, etc. of the current source can be analyzed. You can know the changes. In the prior art, a large number of figures displayed or output on the device are used to detect a dynamic change in various information and diagnose a disease or the like. However, in the related art, a large number of figures showing various information are required for diagnosis, and an abnormality in the change of various information is empirically performed. As described above, according to the conventional technique, comprehensive information indicating which amount of current has flowed in which part of the living body, where the abnormal biological current is flowing, and the like is displayed as one diagram. The processing for was not executed. Moreover, in the body surface electrocardiogram, an arbitrary time interval (Q,
In the isointegral diagram showing the points where the integrated values are the same during the period in which each wave of R and S is generated, the period in which the S wave is generated from the S wave, etc.), it is necessary to have a plurality of equipotential diagrams at each successive time. Instead, information on the heart can be obtained with a single electrocardiogram. However, if the current source in the heart is assumed to be one current dipole in the equipotential diagram, a figure in which the peak of the anode and the peak of the cathode exist at a position apart from just above the current dipole There is a problem that becomes. Furthermore, if the position of the current dipole does not change and the direction of the current dipole changes, the peak positions of the anode and cathode change, and there is the problem that the current source and the peak of the integrated value do not correspond when integrating the potential. It was Further, even if the components of the biomagnetic field obtained by the biomagnetic field measurement are simply integrated, there is a problem that the peak position of the biomagnetic field component does not correspond to the position of the current source, as in the case of the electrocardiogram. In addition, there is a problem that it is difficult to accurately determine an abnormality such as a disease simply from the isometric chart because there are individual differences such as the position and size of organs only with the isometric chart obtained from the electrocardiogram.

It is an object of the present invention that the number of maps is much smaller than that required in the prior art.
An object of the present invention is to provide a biomagnetic field measuring method and a biomagnetic field measuring apparatus capable of grasping the entire state of a living body part using.

Another object of the present invention is to provide an initial value estimation method in a magnetic field source analysis method by measuring the vertical component Bz of a biomagnetic field without increasing the number of detection coils .
It is an object of the present invention to provide a biomagnetic field measuring method and a biomagnetic field measuring apparatus capable of analyzing a magnetic field source.

[0017]

The biomagnetic field measuring method of the present invention comprises (1) a quantum interference device (SQUID),
A first step of measuring a temporal change of a magnetic field component of a biomagnetic field emitted from the living body in a first direction perpendicular to the surface of the living body, using a plurality of magnetometers arranged outside the living body, and a crossing with the first direction. The second step of obtaining a waveform representing the time change of the value proportional to the square root of the sum of squares of the rate of change of the magnetic field component in the first direction in the second direction and the third direction, and in the second step A third step of integrating the obtained waveform in a predetermined period to obtain an integrated value, and a fourth step of displaying the integrated value obtained in the step of the third step.
And (2) using a plurality of magnetometers, which are composed of quantum interference devices (SQUIDs) and are arranged outside the living body, and The first step of measuring the time change of the magnetic field components in the parallel first and second directions and the waveform representing the time change of the value proportional to the square root of the sum of squares of the magnetic field components in the first and second directions are obtained. The second step, the third step of integrating the waveform obtained in the second step for a predetermined period to obtain an integrated value, and the third step
It is characterized by having a fourth step of displaying the integrated value obtained in the step of step. Further, in the biomagnetic field measuring method having the above-mentioned features (1) and (2), the points having the same integral value in the fourth step are connected by interpolation and extrapolation using the integral value. Displaying an equal-integral diagram and, in the above-mentioned third step, integrating the above-mentioned waveform obtained in the above-mentioned second step in a predetermined period to obtain an integrated value are performed in a plurality of predetermined periods. It is also characterized in that a plurality of integrated values are obtained, and an operation is performed to obtain either a sum or a difference between the plurality of integrated values including ratio, equal weighting. In the orthogonal coordinate system (x, y, z), the direction perpendicular to the surface of the living body is the z axis, the first direction is the z direction, the second direction is the x direction, and the third direction is the y direction. In the polar coordinate system (r, θ, φ), the direction perpendicular to the surface of the living body is the r axis, the first direction is the r direction, the second direction is the θ direction, and the third direction is the φ direction.

In the biomagnetic field measuring apparatus of the present invention, (1) a plurality of magnetic flux meters arranged outside the living body, which are composed of quantum interference elements (SQUIDs) and detect the biomagnetic field emitted from the living body as a signal, and signal calculation In a biomagnetic field measuring apparatus for measuring a biomagnetic field distribution, which has an arithmetic processing means for performing processing and a display means for displaying a result of the arithmetic processing, the magnetometer is a first magnetic field perpendicular to the surface of the living body of the biomagnetic field. The time change of the magnetic field component in the direction is detected, and the arithmetic processing means is proportional to the square root of the sum of squares of the rate of change of the magnetic field component in the first direction in the second direction and the third direction intersecting with the first direction. It is characterized in that a calculation for obtaining a waveform showing a time change of a value and a calculation for obtaining an integrated value by integrating this waveform for a predetermined period are performed and the integrated value is displayed on the display means. In the biological magnetic field measuring device of The meter detects the time change of the magnetic field components of the biomagnetic field in the first and second directions parallel to the surface of the living body, and the arithmetic processing means is proportional to the square root of the sum of squares of the magnetic field components of the first and second directions. It is characterized in that a calculation for obtaining a waveform representing a time change of a value to be performed and a calculation for obtaining an integrated value by integrating this waveform for a predetermined period are performed and the integrated value is displayed on the display means. Further, in the biomagnetic field measuring apparatus having the features (1) and (2), the display means displays an isointegral diagram connecting points having the same integral value by interpolation and extrapolation, and an arithmetic process. The means integrates the waveform in a predetermined period to obtain an integrated value, obtains a plurality of integrated values in a plurality of predetermined periods, and includes a ratio and equal weighting among the plurality of integrated values. It is also characterized by performing an operation for obtaining either the sum or the difference, and arranging a plurality of magnetometers at equal intervals on the surface of the living body. In the biomagnetic field measuring apparatus of the present invention, the normal (vertical) component and the tangent (parallel) of the magnetic field emitted from the heart to the chest surface.
Simultaneous display of ingredients is possible. The Cartesian coordinate system (x,
In y, z), the direction perpendicular to the surface of the living body is the z axis,
The first direction is the z direction, the second direction is the x direction, and the third direction is the y direction. In the polar coordinate system (r, θ, φ), the direction perpendicular to the surface of the living body is the r axis, the first direction is the r direction, the second direction is the θ direction, and the third direction is the φ direction.

The essential feature of the present invention is that when the direction perpendicular to the living body surface is the z-axis of the Cartesian coordinates (x, y, z) and the plane parallel to the living body surface is the (x, y) plane, perpendicular normal component to the living body surface of the biomagnetic field B _z (x, y) is detected and tangential component parallel to the biological surface of the biomagnetic field B _x, B _y, respectively, x-direction of the normal component B _z, y It is characterized by estimating from the rate of change in direction.

According to the invention, obtained tangential components B _x, without the need for a detection coil for measuring the B _y, the magnetic field distribution of the living body 2D (x, y) the isomagnetic field projected on a plane Therefore, the current source in the living body can be discriminated from the peak pattern of the isomagnetic field diagram, and the positions of the plurality of current dipoles at (x, y) coordinates can be known.

Hereinafter, the arithmetic processing means in the present invention (a computer such as a personal computer which collects signals measured by a plurality of magnetometers and performs the following arithmetic processing on the signals, or a dedicated hardware is used. The contents of the arithmetic processing performed by the electronic circuit for performing the arithmetic processing) will be described.

Using a plurality of magnetometers composed of quantum interference devices (SQUIDs), the tangential component (component parallel to the surface of the living body) B _x (of the living body) at the position (x, y) on the surface of the living body B _x ( x, y, t), B _y (x, y, t) is measured (however, in the Cartesian coordinate system (x, y, z), the plane parallel to the plane of the living body is the xy plane, , Where z is the axis perpendicular to the plane of, and tangent components B _x (x, y, t) and B _y (x, y,
t) 2D vector strength | B
_xy (x, y) | (hereinafter, || represents an absolute value) is calculated by (Equation 3).

[0023]

Equation 3] _{│B xy (x, y, t} ) │ = √ {(B x (x, y, t)) 2 + (B y (x, y, t)) 2} ... ( Equation 3) then , Waveform in arbitrary period for each point (x, y) |
_{B xy (x, y, t} ) │ integrated value I ₁ (x, y) and calculated by equation (4), the interpolation, the integral value I ₁ at each point by extrapolation (x, y) (x, y) Obtain an isointegral diagram connecting points having the same value, and display the isointegral diagram on the display screen.

[0024]

[Equation 4] I ₁ (x, y) = ∫│B _xy (x, y, t) │dt (Equation 4) Hereinafter, a magnetic field component B _z (x, x, which is perpendicular to the measured surface of the living body).
Estimating the tangential components B _x and B _y from y, t) (normal components) will be described.

Taking advantage of the fact that the tangential component parallel to the body surface of the biomagnetic field best reflects the current flowing directly under the body surface, from the relationship between the direction of the current flowing and the direction of the magnetic field,
Tangent vector (B _x, B _y) of the measured magnetic field by 90 ° rotation to counterclockwise, the current distribution in the living body can overview by projecting a two-dimensional plane parallel to the surface of the living body. That is, tangent component B _{x at} each measurement point, where <e _x >, <e _y > are unit vectors in the x-axis direction and the y-axis direction, respectively.
From B _y , the current vector <J> shown in (Equation 5) is obtained,
It can be expressed as a distribution (arrow map) of the current vector field at each measurement point (x, y).

[0026]

<J> = − B _y <ex _x > + B _x <e _y > (Equation 5) On the other hand, when measuring the normal component B _z of the magnetic field perpendicular to the living body surface, An arrow map using the expressed current vector is defined (first conventional technique: H,
Hosaka and D.M. Cohen (197
6)).

The inventors of the present invention compare the equations (1) and (5) with the possibility that the equations (6) and (7) are established, that is, the normal component of the measured magnetic field. It was found that tangential components B _x and B _y could be derived from B _z , and various studies were conducted. The results of the examination will be described in detail below.

[0028]

[Equation 6] B _x = − (∂B _z / ∂x) (Equation 6)

[0029]

[Equation 7] B _y =-(∂B _z / ∂y) (Equation 7) FIG. 1 shows that the magnetic field (cardiac magnetic field) generated by the activity of the heart is generated by the current dipole in the infinite plane conductor. It is a figure for modeling and analyzing. In Figure 1,
P is an infinite plane conductor having a surface on the xy plane of the Cartesian coordinate system (x, y, z), and <Q> is a position vector <r ₀ (x ₀ , y ₀ ,
z ₀ )〉 the moment of the current dipole present at the position, <r (x, y, z)> is the magnetic flux density (magnetic field)
The position vector of the measurement point for measuring <B (r)> is shown.
In the model shown in FIG. 1, the magnetic field <B (r)> generated outside the infinite plane conductor P is Sarvas (reference: Phy).
s. Med. Biol. , Vol. 32, No. 1,1
1-22 (1987)) and is expressed by (Equation 8).

[0030]

<B (r)> = {μ ₀ / (4πK ² )} {<Q> × <a> · <e _z > ∇K−K <e _z > × <Q>} (Equation 8) In (Equation 8), μ ₀ is the magnetic permeability of the vacuum, < _ez > is the unit vector in the z-axis direction, × is the vector product, · is the scalar product,
∇ represents grad = (∂ / ∂x, ∂ / ∂y, ∂ / ∂z), where <a> is (Equation 9), a is (Equation 10), and K is (Equation 1
1) and ∇K are represented by (Equation 12). | | Indicates an absolute value.

[0031]

<a> = <r (x, y, z)>-<r ₀ (x ₀ , y ₀ , z ₀ )> (Equation 9)

[0032]

[Equation 10] a = | <a> | ... (Equation 10)

[0033]

[Equation 11] K = a (a + <a> · <e _z >) (Equation 11)

[0034]

[Equation 12] ∇K = (2 + a ⁻¹ <a> · <e _z >) <a> + a <e _z > (Equation 12) Infinite plane conductor of <B> (r) represented by (Equation 8) P
The tangential components B _x and B _y parallel to and the normal component B _z perpendicular to the infinite plane conductor P are (Equation 13) and (Equation 1), respectively.
4) and (Equation 15) are given.

[0035]

B _x = {μ ₀ / (4πK ² )} × [{Q _x (y−y ₀ ) −Q _y (x−x ₀ )} (∇K) _x + KQ _y ] ... (Equation 13)

[0036]

B _y = {μ ₀ / (4πK ² )} × [{Q _y (y−y ₀ ) −Q _x (x−x ₀ )} (∇K) _y + KQ _x ] ... (Equation 14)

[0037]

B _Z = {μ ₀ / (4πK ² )} × [{Q _x (y−y ₀ ) −Q _y (x−x ₀ )} (∇K) _z ] ... (Equation 15) On the other hand, The differential in the x direction of the normal component B _Z expressed by (Equation 13) is expressed by (Equation 16).

[0038]

∂B _Z / ∂x = {μ ₀ / (4πK ² )} × [{Q _x (y−y ₀ ) −Q _y (x−x ₀ )} {−2 (∇K) _z ( ∇K) _x / K−a ⁻³ (x−x ₀ ) (z−z ₀ ) ² + a ⁻¹ (x−x ₀ )} − (∇K) _z Q _y ] ... (Equation 16) Similarly, The derivative of the normal component B _{Z in} the y direction is (Equation 1)
7).

[0039]

∂B _Z / ∂y = − {μ ₀ / (4πK ² )} × [{Q _x (y−y ₀ ) −Q _y (x−x ₀ )} {2 (∇K) _z ( ∇K) _y / K + a ^-3 (y-y ₀ ) (z-z ₀ ) ^2- a ^-1 (y-y ₀ )} + (∇K) _z Q _x ] ... (Equation 17) (Equation 16) ), (Equation 17)

[0040]

[Equation 18] α = (∇K) _z / K (Equation 18)

[0041]

Β _x = −a ⁻³ (x−x ₀ ) (z−z ₀ ) ² + a ⁻¹ (x−x ₀ ) ... (Formula 19)

[0042]

[Formula 20] β _y = −a ⁻³ (y−y ₀ ) (z−z ₀ ) ² + a ⁻¹ (y−y ₀ ) ... (Formula 20) When (Formula 16), (Formula 17) ) Are each (number 2)
1) and (Equation 22).

[0043]

∂B _Z / ∂x = − {μ ₀ / (4πK ² )} × [{Q _x (y−y ₀ ) −Q _y (x−x ₀ )} {2α (∇K) _x − β _x } + αKQ _y ] (Equation 21)

[0044]

∂B _Z / ∂y = − {μ ₀ / (4πK ² )} × [{Q _x (y−y ₀ ) −Q _y (x−x ₀ )} {2α (∇K) _y − β _y } + αKQ _x ] (Equation 22) For simplicity, (Equation 13), (Equation 21), (Equation 14),
(Equation 22) is standardized by {μ ₀ / (4πK ² )} which is a common factor to perform transformation, (Equation 23), (Equation 24),
(Equation 25) and (Equation 26) are obtained.

[0045]

B _x = (∇K) _x {Q _x (y−y ₀ ) −Q _y (x−x ₀ )} + KQ _y (Equation 23)

[0046]

Equation 24] _{∂B Z / ∂x = -2α (∇K} ) x {Q x (y-y 0) -Q y (x-x 0)} - αKQ y + β x {Q x (y-y 0 _{) -Q y (x-x 0} )} = -2αB x + αKQ y + β x {Q x (y-y 0) -Q y (x-x 0)} ... ( number 24)

[0047]

B _y = (∇K) _y {Q _y (y−y ₀ ) −Q _x (x−x ₀ )} + KQ _x (Equation 25)

[0048]

∂B _Z / ∂y = −2α (∇K) _y {Q _x (y−y ₀ ) −Q _y (x−x ₀ )} − αKQ _x ] + β _y {Q _x (y−y _{0) -Q y (x-x} 0)} = -2αB y + αKQ x + β y {Q x (y-y 0) -Q y (x-x 0)} ... ( Expression 26) and (Equation 23) ( As is clear from (24), ∂B _Z
The value of / ∂x is a term equal to -2α times the tangential component B _x ,
Equal to the value obtained by adding two additional sections (number 25) and as apparent from the equation (26), the value of .differential.B _Z / ∂y is a term equal to -2α times the tangential component B _y, It is equal to the value obtained by adding the two additional terms.

Here, as shown in the schematic position in FIG. 2, points <r ₀ (0, 0, −z ₀ )>, z inside the infinite plane conductor P are shown.
_{At 0} = 0.05 [m], the moment of the current dipole <Q> = (Q _x , Q _y , 0), Q _x = Q _y = 50 [nAm]
, Then B _x ((Equation 13)) and −∂B _Z / ∂x
((Equation 16)) is compared. x ₀ = y ₀ = y = 0, Q _z =
Substituting 0 into (Equation 13) and (Equation 16), (Equation 27),
(Equation 28) is obtained.

[0050]

B _x (x, 0) = {μ ₀ / (4πK ² )} {− (∇K) _x Q _y x + KQ _y } (Equation 27)

[0051]

∂B _Z (x, 0) / ∂x = {μ ₀ / (4πK ² )} {2α (∇K) _x Q _y x−αKQ _y −β _x Q _y x} (Equation 28) FIG. 3 shows a relative magnetic field strength curve C _{1 obtained} by normalizing B _x ((Equation 27)) and −∂B _Z / ∂x ((Equation 28)) on the infinite plane conductor P with their respective maximum values. This is indicated by C ₂ .

That is, the curve C ₁ is B _x (x, 0) / max |
B _x (x, 0) | and the curve C ₂ is {−∂B _Z (x, 0) /
Represents ∂x} / max | ∂B _Z (x, 0) / ∂x |.
As is clear from FIG. 3, the distributions of B _x and −∂B _Z / ∂x are just above the origin (x =
Both have peaks in 0), and both show that the maximum signal can be detected when the measurement point is directly above the point where the current dipole exists. Further, the curve C ₂ is the curve C ₁
Gives a sharper peak than -∂B _Z / ∂x ((Equation 1
It is shown that the magnetic field distribution according to 6)) has a higher spatial resolution than the magnetic field distribution according to B _x ((Equation 13)).

The magnetic field strength curves C ₃ , C ₄ and C ₅ shown in FIG. 4 are the first and second terms of −∂B _Z (x, 0) / ∂x, respectively.
The term and the third term are shown. From the results shown in FIG. 4, the third term is the first
Negative for terms and second terms, −∂B _Z (x, 0) /
It can be regarded that the shape of ∂x is determined by the first and second terms, and (Equation 28) can be approximated to (Equation 29).

[0054]

∂B _Z (x, 0) / ∂x = {μ ₀ / (4πK ² )} {2α (∇K) _x Q _y x−αKQ _y } (Equation 29) FIG. FIG. 13 is a diagram showing a relative magnetic field strength curve obtained by comparing the first and second terms of 13) and (Equation 16) after normalization. In FIG. 5, {first term of B _{x (x,} 0)} curve C ₆ in _{/ max | B x (x,} 0) |, i.e., {- (∇
K) _x Q _y x} / max | B _x (x, 0) |, and the curve C ₇ is {−∂B _Z (x, 0) / first term of ∂x} / max.
| ∂B _Z (x, 0) / ∂x |, that is, {−2α (∇K) _x
Q _y x} / max | ∂B _Z (x, 0) / ∂x |
The curve C ₈ is {B _x (x, 0) second term} / max | B
_x (x, 0) |, that is, {KQ _y } / max | B _x (x,
0) |, and the curve C ₉ is {−∂B _Z (x, 0) / ∂x
The second term of {circumflex over}} / max | ∂B _Z (x, 0) / ∂x |, that is, {αKQ _y } / max | ∂B _Z (x, 0) / ∂x |.

From the results shown in FIG. 5, −∂B _Z (x, 0)
The distributions of the first and second terms of / ∂x are both B
_x (x, 0) is sharper than the distributions of the first and second terms, and the sharpness of the distribution is defined by (Equation 18) α = (∇K) _z
/ K.

In FIG. 6, the magnetic field curve C ₁₀ is α = (∇
K) _z / K, the magnetic field curve C ₁₁ is-{(Equation 28)
Term} / {first term of (Equation 27)}, that is, 2α (∇K) _x
Q _y x / (∇K) _x Q _y x = 2α, and the magnetic field curve C ₁₂ is −
{{2nd term of (Equation 28)} / {2nd term of (Equation 27)}, that is, αKQ _y / KQ _y = α, respectively. As shown in FIG. 6, α = (∇K) _z / K (curve C ₁₀ ) has a peak point at the origin where the current dipole exists, and the peak value is 2 /
(Z−z ₀ ). The magnitude of −∂B _Z (x, 0) / ∂x is 2 / (z− at the peak of B _x (x, 0).
only z ₀ ). (Z−z ₀ ) is the depth at which the current dipole exists. It is difficult to determine (z−z ₀ ) from actual magnetic field measurement. (Equation 30) is obtained from the comparison between (Equation 27) and (Equation 29).

[0057]

[Expression 30] −∂B _Z (x, 0) / ∂x = {μ ₀ / (4πK ² )} {− 2α (∇K) _x Q _y x + αKQ _y } = 2αB _x (x, 0) − {μ ₀ / (4πK)} αQ _y (Equation 30) That is, when the second term of (Equation 30) is smaller than the first term, it can be considered that (Equation 31) approximately holds.

[0058]

[Expression 31] −∂B _Z (x, 0) / ∂x = 2αB _x (x, 0) (Expression 31) In generalization (Expression 24), two additional terms other than −2αB _x are If it is smaller than −2αB _x , it can be considered that (Equation 32) approximately holds.

[0059]

[Expression 32] ∂B _Z / ∂x = −2αB _x (Expression 32) The above is the result of examining the relationship between −∂B _Z / ∂x and B _x , but the same thing can be applied to −∂B _Z. / well established relationship between ∂y and B _y, approximately from (Expression 26) (number 33)
It can be regarded as established.

[0060]

Equation 33] _{∂B Z / ∂y = -2αB y ...} ( number 33) or less, (number 32), respectively, from the equation (33), B _x is -
.Differential.B _Z / ∂x, B _y is assumed to be proportional to -∂B _Z / ∂y, tangential components B _x from the measured normal component B _z, obtains the isomagnetic field by estimating a B _y The procedure will be described in detail.

Magnetic field component B _z (x, y, perpendicular to the plane of the living body)
When t) is measured, the rate of change of B _z (x, y, t) in the x direction ∂B _z (x, y, t) / ∂x and B _z (x, y, t)
Change rate ∂B _z (x, y, t) / ∂y
As shown in (Equation 34), the square root of the sum of squares S _t (x, y,
Find t).

[0062]

S _t (x, y, t) = √ [{∂B _z (x, y, t) / ∂x} ² + {∂B _z (x, y, t) / ∂y} ² ] (Equation 34) Next, for each point (x, y), the waveform S in an arbitrary period
_t (t, x, y) integrated value I ₂ of (x, y) and determined by (number 35), the interpolation, the points by extrapolation (x, y) integrated value I ₂ at (x, y) Find an isointegral diagram connecting points with the same value of
Display the isometric diagram on the display screen.

[0063]

[Equation 35] I ₂ (x, y) = ∫│S _t (x, y, t) | dt (Equation 35) The integration range of (Equation 4) and (Equation 35) is, for example, the heart. When the target of measurement is, the QRS wave (QRS wave generated from the Q wave to the S wave)
complex), T wave generation period, etc. Furthermore, a sum or difference including equal weights (weights are w ₁ and w ₂ ) among a plurality of integration values obtained by taking a plurality of integration ranges as the integration ranges of (Equation 4) and (Equation 35). , Calculation of ratio, etc. is performed, and by interpolation and extrapolation, an isointegral diagram connecting the points with the same value of the arithmetic result is obtained, and the isointegral diagram is displayed on the display screen. For example, a period T ₁ in which a QRS wave is generated as a _first integration range, and a period T _{2 in which} a T wave is generated as a second integration range.
Is set, and according to (Equation 4) or (Equation 35), the period T
Integral values for _{1 I 1, T1 (x,} y), I 2, T1 (x,
y), the integration value with respect to a period _{T 2 I 1, T2 (x} , y), I 2,
Each of _T2 (x, y) is calculated, and integrated values I ₁ , _T1 (x,
y) and the integrated value I ₁ , _T2 (x, y), or the integrated value I ₂ ,
A sum I _sum (x, y) including equal weights or a difference I _dif (x, y) between _T1 (x, y) and the integrated values I ₂ and _T2 (x, y).
The ratio r (x, y) is calculated from (Equation 36) to (Equation 37), (Equation 3)
8) to (Equation 39) and (Equation 40) to (Equation 41).

[0064]

I _sum (x, y) = w ₁ × I ₁ , _T1 (x, y) + w ₂ × I ₁ , _T2 (x, y) (Equation 36)

[0065]

I _sum (x, y) = w ₁ × I ₂ , _T1 (x, y) + w ₂ × I ₂ , _T2 (x, y) (Equation 37)

[0066]

I _dif (x, y) = w ₂ × I ₁ , _T2 (x, y) −w ₁ × I ₁ , _T1 (x, y) (Equation 38)

[0067]

I _dif (x, y) = w ₂ × I ₂ , _T2 (x, y) −w ₁ × I ₂ , _T1 (x, y) (Equation 39)

[0068]

R (x, y) = I ₁ , _T1 (x, y) / I ₁ , _T2 (x, y) (Equation 40)

[0069]

R (x, y) = I ₂ , _T1 (x, y) / I ₂ , _T2 (x, y) (Equation 41) (Equation 36)-(Equation 37), (Equation 38)- (Equation 39),
As a result of the computations of (Equation 40) to (Equation 41), the variation of the equal integration diagram due to the individual difference is improved, and the abnormality of the biological function due to the disease or the like can be detected.

According to the isointegral diagram obtained by the present invention, it is possible to analyze the biological phenomenon by using a large number of maps (maps) representing the state of the body part at each time, which is required in the prior art, without analyzing the biological phenomenon. It is possible to grasp the overall state of the living body part using a much smaller number of maps (maps) than the number of maps (maps) required for the technology. In addition, since the peak position of the isointegral diagram obtained by using the tangential component or the normal component of the biomagnetic field matches the part where a large amount of current flows in the living body,
It is possible to determine in which part of the living body a large amount of current has flowed in an arbitrary time zone from the isometric diagram. Although the biomagnetic field distribution varies greatly among individuals, in the present invention, since an integral value at an arbitrary time (period) obtained from a waveform representing the temporal change of each direction component of the biomagnetic field is used, a more quantitative biomagnetic field distribution can be obtained. It can be displayed using a small number of maps (maps), so that individual diseases and abnormalities can be grasped objectively and quantitatively.

In the present invention, the magnetic field component B perpendicular to the plane of the living body is used.
_z (x, y, t) is measured and B _x is B _z (x, y, t)
Change rate in the x direction ∂B _z (x, y, t) / ∂x, B _y
Is the rate of change in the direction of B _z (x, y, t) ∂ B _z (x, y,
t) / ∂y, the background magnetic field (interference magnetic field) existing in common at each adjacent measurement point (x, y) must be canceled in the x and y directions. Becomes

[0072]

DETAILED DESCRIPTION OF THE INVENTION biomagnetic field orthogonal coordinate system as in the coordinate system for measurement (x, y, z) (the magnetic field components B _x, B _y, B
_z ) and a polar orthogonal coordinate system (r, θ, φ) are used. When the measurement target is the heart or the like, an orthogonal coordinate system (x, y, z) having the chest wall as the xy plane is used. When the measurement target is the brain or the like, since the head has a shape close to a sphere, the polar coordinate system (r, θ, φ) (the magnetic field components are B _r , B _θ ,
B _φ ) is used. In this embodiment, magnetic field component perpendicular to the biological surface (normal component) is represented by B _z, B _r, parallel component (tangential component) in a surface of the living _{body, B x, B y, B} θ,
It is represented by B _φ . Hereinafter, in the present embodiment, the orthogonal coordinate system (x, y, z) will be described, but the polar coordinate system (r,
θ, φ), B _z is B _r and B _x is B
_It may be read as _θ and B _y as B _φ .

FIG. 7 shows a schematic configuration of a biomagnetic field measuring apparatus in which the present invention is implemented. A biomagnetic field measuring apparatus that measures a cardiac magnetic field uses a plurality of magnetic field sensors including quantum interference devices (SQUIDs). In order to remove the influence of environmental magnetic field noise, the magnetic field measurement of the heart is performed inside the magnetic field shield room 1. The subject 2 lies on the bed 3 and measures (FIG. 11).
The orthogonal coordinate system (x, y, z) is set so that the xy plane becomes the bed plane, as shown in FIG. A plurality of magnetic field sensors in which the SQUID and the detection coil connected to the SQUID are integrated are housed above the chest of the subject 2 and the liquid H
The dewar 4 that satisfies e is arranged. The liquid He is continuously replenished with the liquid He by an automatic replenishing device 5 outside the magnetic field shield room 1.

The output from the magnetic field sensor is a FLL (Flux) which outputs a voltage proportional to the magnetic field strength detected by the detection coil.
Locked Loop) circuit 6 is input. This FFL circuit cancels the change in the biomagnetic field input to the SQUID via the feedback coil so as to keep the output of the SQUID constant. By converting the current flowing in the feedback coil into a voltage, a voltage output proportional to the change of the biomagnetic field signal can be obtained. This voltage output is amplified by an amplifier (not shown), a frequency band is selected by a filter circuit 7, AD-converted by an AD converter (not shown), and a computer 8
Is taken into. In the computer 8, various arithmetic processing is executed, the arithmetic processing result is displayed on the display, and further,
It is output by the printer.

As the detection coil for detecting the tangential component of the magnetic field, two coils whose coil surfaces are oriented in the x direction and the y direction are used, and the detection coil for detecting the tangential component of the magnetic field is used. As a coil for detecting the normal component of the magnetic field, z
Use oriented coils. These magnetic field sensors (2
0-1, 20-2, ~, 20-8, 21-1, ~, 21
-8, 22-1, ~, 22-8, 23-2, ~, 23-
8, 24-1, ~, 24-8, 25-1, ~, 25-
8, 26-1, ~, 26-8, 27-1, ~, 27-
The layout of 8) is shown in FIG. The magnetic field sensor 9 is installed vertically from the bottom inside the dewar, and the distance between the sensors is set at equal intervals in the x and y directions so as to accurately capture the amount of change of the magnetic field in the x and y directions. did. Here, the distance between the sensors was set to 25 mm, and the number of sensors was set to 64 channels of 8 × 8.

A schematic view of one magnetic field sensor installed according to this arrangement method is shown in FIGS. The magnetic field sensor shown in FIG. 9 is a sensor for measuring a component B _z perpendicular to the surface of a living body, and the surface of a coil made of a superconducting wire (Nb-Ti wire) faces the z direction. This coil is a combination of two coils in opposite directions. One closer to the living body is used as the detection coil 10, and the farther coil is used as a reference coil 11 for removing external magnetic field noise to form a first-order differential coil. ing. Here, the coil diameter was 20 mm and the baseline between the coils was 50 mm. External magnetic field noise originates from a signal source farther than the living body, and these are similarly detected by the detection coil and the reference coil. On the other hand, since the signal from the living body is close to the coil, it is detected more strongly by the detection coil 10. Therefore, the detection coil 10 detects a signal and noise, and the reference coil 11 detects only noise. Therefore, a high S / N can be measured by taking the difference between the magnetic fields captured by both coils.

The primary differential coil is connected to the SQUID input coil via the superconducting wiring of the mounting board on which SQUID12 is mounted, and the biomagnetic field detected by the coil is SQUID.
Communicate to ID. Tangential component B _x biomagnetic field components, a schematic diagram of a magnetic field sensor for detecting the B _y shown in FIG. 10. This magnetic field sensor uses a flat coil,
0 ′, 10 ″ and reference coils 11 ′, 11 ″ are arranged on one plane, the coil diameter is 20 mm × 20 mm, and the baseline is 50 mm. The coil is SQ as for the normal component
It is connected to a mounting board of UID 12 ', 12 ". By attaching the magnetic field sensor 13 for detecting the x component and the magnetic field sensor 14 for detecting the y component to two surfaces of the support of the quadrangular prism which are orthogonal to each other, x And a magnetic field sensor capable of measuring the y component are formed, and the rectangular prisms are arranged in an array as shown in FIG.

The Dewar with a built-in magnetic field sensor is arranged above the chest of the subject lying on the bed and measures the magnetic field generated from the heart. Here, the horizontal direction of the body is the x-axis, and the vertical direction of the body is the y-axis. Magnetic field sensor (20-1, ~, 2
0-8, 21-1, ~, 21-8, 22-1, ~, 22
-8, 23-2, ~, 23-8, 24-1, ~, 24-
8, 25-1, ~, 25-8, 26-1, ~, 26-
8, 27-1, ..., 27-8) and the positional relationship between the chest 30 are shown in FIG. The biomagnetic field signals measured in this positional relationship are shown in FIGS. 12 (a), 12 (b) and 12 (c).

FIGS. 12A, 12B and 12C are waveforms showing the time change of the magnetic field emitted from the heart of a healthy person by each magnetic field sensor (magnetic field sensors arranged in an 8 × 8 array). The horizontal axis of the 64 waveforms in each figure represents the time axis, and the vertical axis represents the detected magnetic field strength. 12
(A) the tangential components B _x, FIG. 12 (b) tangential component B _y, a change in FIG. 12 (c) normal component B _z, each component of the time (horizontal axis), for each magnetic field component The maximum absolute value of the channel with the highest signal strength is standardized and displayed.

The dotted and solid lines shown in FIG. 13 are the tangent components (B
_The waveforms representing the changes over time in ( _x ) are shown by the solid and dotted lines. The time points at which the peaks (extreme values) of the Q wave, the R wave, and the S wave in the time zone T _{1 in} which the QRS wave in which the ventricle of the heart is depolarized appear appear in FIG. 13 are t _Q , t _R , and t _s , respectively. Indicated by.
In addition, the time period T in which the T wave appears, which is the repolarization process of the heart, appears.
_2, and the time point at which the peak (extreme value) is given is indicated by t _T.

In FIG. 13, the P wave indicates atrial excitation (depolarization), the QRS wave composed of the Q wave, R wave, and S wave indicates ventricular excitation (depolarization), and T The wave is a gentle runout that appears after the QRS wave and indicates myocardial repolarization. Depolarization is the process by which excitement first spreads in muscles, and repolarization is the process by which excited muscles return to rest.

FIGS. 14A, 14B and 14C show t _Q ,
t _R, indicating the like field diagram connecting by lines the points of equal intensity of the cardiac magnetic field at the time of t _s. 14 (a), (b), (c)
Is represented by | B _xy (x, y, t) | of (Equation 4), and 64
Tangential component B _x which is measured at the point, shows a two-dimensional vector intensity distribution obtained by combining the B _y. Furthermore, as shown in FIG.
The arrows in (b) and (c) indicate the two-dimensional current vector when it is assumed that the current sources at the 64 measurement points make the magnetic fields at the measurement points. The current direction and distribution in the heart can be estimated from this current vector. In each of FIGS. 14A, 14B, and 14C, the horizontal axis x and the vertical axis y indicate the coordinates where the magnetic field sensor is arranged. 14
As shown in (a), at the peak of the Q wave, the current flowing in the heart flows in the lower right direction in the interventricular septum, and as shown in FIG. 14 (b), at the peak of the R wave, the left ventricle. A large current flows diagonally downward as a whole, and as shown in FIG.
It can be seen that at the peak of the S wave, a current flows diagonally upward to the left in the direction of the base of the ventricle, ending the ventricular depolarization process. Thus, it can be seen from the isomagnetic field diagrams of FIGS. 14A, 14B, and 14C that the active site and current direction in the heart at each time can be visualized.

FIG. 15 shows a two-dimensional vector intensity | obtained from the two tangential components B _x and B _y detected in the time zone T _{1 in} which the QRS wave from the Q wave to the S wave of the magnetocardiogram appears. B _xy
(X, y, t) | for each point (x, y), (Equation 4)
Is an isointegral diagram in which points of the same integrated value are connected by performing the integration of. The x-axis and the y-axis of FIG. 15 represent the coordinates of the magnetic field sensor arranged on the surface of the living body, and the numerical values shown in the vicinity of the black circles of each curve in the isointegral diagram indicate the integral value of that curve. It can be seen from FIG. 15 that most of the current flowing in the myocardium during the QRS time period flowed in the left ventricle where the thickness of the myocardium is large, and the peak position in the isometric chart and the region where the amount of current flowing to the heart are large It turned out to correspond well.

FIG. 16 shows FIGS. 12 (a), 12 (b) and 12 (c).
The normal line segment B _z was measured at each point (x, y) for the same healthy person who obtained the data of FIG.
34 is an equal integration diagram in which S _t (x, y, t) is obtained by (Equation 34), the integration of (Equation 35) is performed for the time zone T ₁ of the QRS wave, and the points of the same integral value are connected. Hereinafter, in FIGS. 16 to 21, the x-axis and the y-axis represent the position coordinates (unit is m) of the magnetic field sensor arranged on the surface of the living body. Figure 1
Numerical values 6 to 6 shown in the vicinity of the black circle of the curve show the integral value of the curve.

It was found that the pattern of the isointegral diagram obtained from the tangential components B _x and B _{y of the} magnetic field shown in FIG. 15 and the pattern of the isointegral diagram obtained from the normal component B _{z of the} magnetic field shown in FIG. . This agreement is expressed by (Equation 6) and (Equation 7), or (Equation 3)
It means that 2) and (Equation 33) are almost established in the actual experimental data.

FIG. 17 shows the two-dimensional vector intensity obtained from the two tangential components B _x and B _y detected in the time zone T ₂ of the T wave for the same healthy person as in FIG. B _xy
(X, y) | is an isointegral diagram in which points of the same integrated value are obtained by performing integration of (Equation 4) for each point (x, y). In FIG. 17, 1e + 003 indicates 1000.

FIG. 18 shows (Formula 4) for the time zone T _2.
FIG. 33 is a contour diagram showing a difference (Equation 37) between the integral value of (Equation 4) and the integral value of (Equation 4) for the period T ₁ in which the QRS wave is generated. That is, FIG. 18 is obtained by comparing FIG.
It is the figure which deducted the isometric diagram shown in FIG. T wave time zone T
₂ is longer than the time zone T ₁ of the QRS wave. In addition,
The pattern 7 is similar to the pattern shown in FIG. Therefore, the contour map shown in FIG. 18 has a positive value as a whole.
The numerical values shown in the vicinity of the black circles in the curves in FIGS. 17 and 18 indicate the values of the difference between the integrated values of the curves.

Next, FIG. 19, FIG. 20 and FIG. 21 show the results regarding the measurement of the magnetic field of the myocardial infarction patient. FIG. 19
Is an isointegral diagram obtained in the same manner as in FIG. 15 for the QRS wave time zone T ₁ , FIG. 20 is an isointegral diagram obtained in the same manner as in FIG. 17 for the T wave time zone T ₂ , and FIG. The difference (Equation 38) between the integrated value (Equation 4) for the time zone T ₂ of the T wave and the integral value (Equation 4) for the time zone T ₁ of the QRS wave is represented and calculated in the same manner as in FIG. It is a contour map. That is, FIG. 21 is a diagram obtained by subtracting the isometric diagram shown in FIG. 19 from the isometric diagram shown in FIG. The numerical values shown in the vicinity of the black circles of the curves in FIGS. 19 and 20 indicate the integrated values of the curves, and the numerical values shown in the vicinity of the black circles of the curves of FIG. 21 are the difference values of the above integrated values of the curves. Indicates.

The isointegral diagram in the time zone T ₁ shown in FIG.
It is a pattern that does not differ much from the equal integration diagrams shown in FIGS. 15 and 16, and it can be seen that a large amount of current has flowed into the left ventricle.
However, the isointegral diagram in the time zone T ₂ shown in FIG.
The pattern is different from the isointegral diagram in the time zone T ₁ shown in FIG. 9, and it is clearly seen that the pattern of the amount of current flowing through the heart greatly differs between the time zone T ₁ and the time zone T ₂ due to myocardial infarction. Further, the contour map shown in FIG. 21 has a negative value as a whole and is largely different from the contour map of a healthy person shown in FIG. 18, which has a positive value as a whole.
_It can be clearly seen in ₂ that the current flowing in the heart is impaired.

As described above, by imaging the magnetic field intensities in the time zones T ₁ and T ₂ of the heart, it is non-invasive and non-invasive in a short period of 1 minute or less without causing pain to the patient. A healthy state and an abnormal state (for example, myocardial infarction state, ischemic state, etc.) can be easily discriminated from time. That is,
It enables early detection and estimation of disease sites without solving the inverse problem.

FIG. 22 shows an example of a processed image on the screen of the computer of the biomagnetic field measuring apparatus. It has a multi-window format, and each processed image can be displayed on each window. In addition, in FIGS. 15 to 21 described above, numerical values are entered in each curve so that the strength of the magnetic field and the height of the integrated value can be seen, but on the display, color coding is performed according to the height of the contour lines and three-dimensional color display is performed. . At the same time, it is possible to display a waveform (magnetocardiogram) showing a temporal change of the magnetic field component as shown in FIG. 13 and also an electrocardiogram so that a comprehensive analysis of a heart disease can be performed.

FIG. 23 is a view showing an example of a processed image displayed on the display of the biomagnetic field measuring apparatus of the present invention. In FIG. 23, MCG is an example of a magnetocardiogram, QRS is the first equal integration diagram obtained by (Equation 35), where the integration range is the period T _{1 in} which the QRS wave is generated, and T is the integration range of the T wave. The second equal-integral diagram, (T-QRS), obtained by (Equation 35) with the period T ₂ occurring, shows each example of the difference between the first and second equal-integral diagrams. In the display examples on the display shown in FIGS. 22 and 23, three-dimensional color display is performed by color-coding by the height of the contour lines.

In (Equation 4) and (Equation 35), I ₁ (x, y), I
It is also possible to obtain ₂ (x, y). That is, from the following (Equation 42) to (Equation 45), I ₁ (x, y), I ₂ (x, y)
Then, (Equation 36) to (Equation 41) are applied.
When _measuring tangential components (components parallel to the surface of the living body) B _x (x, y, t) and B _y (x, y, t) of the magnetic field emitted from the living body (however, the Cartesian coordinate system (x, In y, z), the plane parallel to the plane of the living body is the xy plane, and the axis perpendicular to the plane of the living body is z), and the two-dimensional vector strength from the square root of the sum of squares of the tangential components B _x and B _y | B _xy (x, y) | (|| represents an absolute value) is calculated by (Equation 42).

[0094]

│B _xy (x, y, t ₀ ) │ = √ {(B _x (x, y, t ₀ )) ² + (B _y (x, y, t ₀ )) ² } ... 42) Next, for each point (x, y), the waveform at an arbitrary time point |
The value I ₁ (x, y) of B _xy (x, y, t ₀ ) |
I ₁ at each point (x, y) by interpolation and extrapolation
An isomagnetic field map connecting points having the same value of (x, y) is obtained, and the isomagnetic field map is displayed on the display screen.

[0095]

[Expression 43] I ₁ (x, y) = │B _xy (x, y, t ₀ ) │ (Expression 43) When measuring the magnetic field component B _z (x, y, t) perpendicular to the surface of the living body , The change rate ∂B _z (x, y, t ₀ ) / ∂x of the perpendicular magnetic field component B _z (x, y, t ₀ ) in the x direction and B _z (x, x
y, t ₀ ) change rate ∂B _z (x, y, t ₀ ) / ∂y
And the square root S of the sum of squares S
_{Find t0} (x, y, t).

[0096]

S _t0 (x, y, t ₀ ) = √ [{∂B _z (x, y, t ₀ ) / ∂x} ² + {∂B _z (x, y, t ₀ ) / ∂y } ² ] (Equation 44) Next, for each point (x, y), the waveform S at an arbitrary time point
_t0 (x, y, t ₀₎ the value I ₂ (x, y) of the determined by (number 45), the value at each point interpolation, by extrapolation (x, y) I
₂ Obtain an isomagnetic field map connecting points with the same value of (x, y),
Display the contour plots on the display screen.

[0097]

[Expression 45] I ₂ (x, y) = | S _t0 (x, y, t ₀ ) | (Expression 45) Note that in Expressions 42 to 45, t ₀ is, for example, the heart. When is the target of measurement, the time when the maximum value of each wave of Q, R, and S when the ventricle contracts is given. Further, in (Equation 42) to (Equation 45), as t ₀ , an operation such as obtaining a sum or difference including equal weighting or a ratio between a plurality of values obtained by obtaining a plurality of t ₀ is performed. , The contour diagram of the magnetic field connecting the points having the same value is calculated by the interpolation and the extrapolation, and the contour map is displayed on the display screen. With such a method as well, it is possible to obtain almost the same result as the method using (Equation 4) and (Equation 35) described above.

FIG. 24 (a) is an isomagnetic field diagram at the time when the extreme values of the Q wave, R wave, and S wave of the magnetocardiogram of the patient X obtained by measuring the normal component B _z by the conventional method appear. ), (B), (c)
Shown in. In FIGS. 24 (a), (b), and (c), the dotted line shows the isomagnetic field map of the magnetic field absorbed, the solid line shows the isomagnetic field map of the boiling magnetic field, and the white arrow shows the current dipole. The size and direction are shown. FIG. 24 (a),
In the isomagnetic field diagrams shown in (b) and (c), the position of the current dipole, assuming that there is one current source existing in the heart, is indicated by a white arrow and is superimposed and displayed. Figure 24
As shown in (a), when the extreme value of the Q wave appears,
A current flows in the lower right direction in the ventricular septum, and as shown in FIG. 24B, at the time when the extreme value of the R wave appears, a large current flows in the lower left direction in the entire left ventricle. Also, FIG. 24 (c)
As shown in FIG. 5, it is understood that at the time when the extreme value of the S wave appears, a current flows diagonally upward to the base of the ventricle and the depolarization process of the ventricle ends.

The tangential components B _x and B _y of the magnetic field emitted from the heart of the patient X are measured, and the tangential components are calculated at the time when the extreme values of the Q wave, R wave, and S wave appear (Equation 42). , (Equation 43)
FIG. 25 (a) shows an isomagnetic field diagram synthesized based on FIG.
Shown in (b) and (c).

The pattern of FIG. 25 (a) and the pattern of FIG. 24 (a), the pattern of FIG. 25 (b) and the pattern of FIG. 24 (b), the pattern of FIG. 25 (c) and the pattern of FIG. 24 (c). , And are almost the same. However, FIG. 25 (b)
In the pattern at the time when the R-wave extreme value appears, the myocardium is active in a wide area, and a plurality of currents that are not clear in the pattern at the time when the R-wave extreme value appears in FIG. The sources can be easily discerned, one current source is to the left and the other current source is below.

Q shown in FIGS. 24 (a), 24 (b) and 24 (c)
Normal component B at the time when each extreme value of the wave, R wave, and S wave appears
Using each _z- field data, (Equation 44),
FIG. 26 (a) shows an isomagnetic field diagram obtained at the time when the extreme values of the Q wave, the R wave, and the S wave, which are obtained based on (Equation 45), appear.
Shown in (b) and (c). 26 (a), (b), (c)
From the results shown in Fig. 24, it is found that a plurality of current sources that are difficult to discriminate in the isomagnetic field diagram of the normal component B _z shown in Figs. 24 (a), 24 (b) and 24 (c) and the arrow map based on (Equation 1). Can be determined. The patterns of FIGS. 26A, 26B, and 26C are shown in FIG.
5 (a), (b), (c) shown in the pattern (tangential component B
It can be seen that this is equivalent to the _isomagnetic field diagram of B _xy obtained from _x and B _{y combination} ). This means that (Equation 6) and (Equation 7)
Alternatively, it means that (Equation 32) and (Equation 33) are substantially established in the actual experimental data.

In each of FIGS. 24 (a) to 26 (c), the horizontal axis x and the vertical axis y represent the position coordinates of the magnetic field sensor arranged on the surface of the living body.

In the above description, the present invention has been described by taking an example relating to the measurement of the magnetocardiographic field, but it goes without saying that the present invention can also be applied to the case of measuring the brain magnetic field to obtain a magnetoencephalogram (MEG).

FIG. 27 is a sectional view showing a part of the internal structure of the dewar for measuring a brain magnetic field of the brain magnetic field measuring system for measuring a brain magnetic field. As shown in FIG. 27, when measuring a brain magnetic field, the head is spherical unlike the chest, so that the SQUID
The head bottom 100 of the head measurement dewar 102 having the built-in magnetometers 103-1, 103-2, ..., 103-N is a hemisphere to cover the head 100. SQUID magnetometer 103
-1, 103-2, ..., 103-N are arranged radially along the inner surface of the head measurement dewar 102, and each SQU
The front end surface (magnetic field measurement surface) of the ID magnetometer is arranged so as to be substantially parallel to the tangential surface of the hemisphere. The radius of the hemisphere was set assuming that the center of the hemisphere is almost the center of the brain of the head, and the radius of the hemisphere was set to about 10 cm so that even adults can measure it. A thermal radiation shield member 104 is arranged inside the head measuring dewar 102, and the upper part of the head measuring dewar is sealed by an upper plate 105. SQ
The signals detected by the UID magnetometers 103-1, ..., 103-N are taken out of the head measurement dewar through the signal lines 106-1 ,.

FIG. 28 is a diagram for explaining the relationship between the magnetic field component measurable by the brain magnetic field measurement system shown in FIG. 27 and the head. The component of the cerebral magnetic field B that can be measured by the QUID magnetometer radially arranged at one of a plurality of positions above the head is the direction of r in polar coordinates (r, θ, φ) with O as the origin. Component B _r (normal component) of. In FIG. 28, components B _θ and B _φ represent tangential components parallel to the head surface, and the origin O is the center of the sphere when the brain is assumed to be a sphere. An electrical stimulus is applied to the right middle finger as a somatic sensation, the normal component B _r is detected by the brain magnetic field measurement system shown in FIG. 27, and about 100 msec after the electrical stimulus is applied, the electroencephalogram appears at the maximum, Obtain the magnetic field diagram. 29 (a), 29 (b)
29A is a diagram showing an example of an isomagnetic field diagram obtained by the brain magnetic field measurement system shown in FIG. 27, FIG. 29A is an isomagnetic field diagram of a normal component B _r by the conventional method, and FIG. ) Is an isomagnetic field diagram obtained by using (Equation 46) of the present invention shown below (indicates the intensity distribution of the brain magnetic field displayed on a spherical surface that approximates the brain like the map shown on the globe). ) Is shown.

[0106]

[Formula 46] S _t (θ, φ, t) = √ {(∂B _r (t) / ∂θ) ² + (∂B _r (t) / ∂φ) ² } (Formula 46) FIG. In the isomagnetic field diagram shown in a), the position of the current dipole when assuming that there is one current source existing in the brain is indicated by an outline arrow and is superimposed and displayed. FIG. 29 (a)
In, the dotted line shows the isomagnetic field map of the magnetic field drawn in, the solid line shows the isomagnetic field map of the boiling magnetic field, and the white arrows show the size and direction of the current dipole. Figure 2
The current source (current dipole shown by white arrow), which was conventionally estimated from the isomagnetic field diagram of the normal component B _r shown in 9 (a),
In the isomagnetic field diagram shown in FIG. 29 (b), it is easy to directly see that the peak position A appears. Figure 2
Other configurations of the brain magnetic field measurement system not shown in FIG. 7 are basically the same as the configurations of the biomagnetic field measurement apparatus shown in FIG.

Various algorithms for solving the inverse problem are conceivable as a method of analyzing the magnetic field source by using the contour magnetic field diagrams regarding the cardiac magnetic field and the brain magnetic field obtained by the various methods according to the present invention described above. A simple algorithm that is often used in practice assumes a single or two current dipoles as a magnetic field source, and arbitrarily assumes position coordinates where these current dipoles exist as initial conditions,
The magnetic field at the measurement point (x, y) of the measured magnetic field is calculated assuming that the current dipole existing at each position coordinate creates the magnetic field represented by the Biot-Savart equation. Calculated magnetic field <B _c (x, y)> and measured magnetic field <V _m (x, y)>
(M = 1, 2, ..., M: M is the total number of measured magnetic field measurement points) and the evaluation function shown in the following (Equation 47) is calculated, and the position coordinates of each current dipole are calculated. By changing
The minimum value of the evaluation function L is analytically obtained. (Formula 47)
, G is a constant, <n _s > is a unit vector in the normal line or the z direction, and the addition symbol Σ indicates addition with respect to m = 1, 2, ..., M.

[0108]

L = Σ {<V _m (x, y)> − G ([<B _c (x, y)>] · n _s )} ² (Equation 47) However, based on (Equation 47) In the method, when analyzing a wide measurement area of a magnetic field, there are cases where it does not converge to the minimum value. In the present invention, the position of the dipole and the initial condition of the number of dipoles at the time of calculating the evaluation function L are the dipole as the peak position in the contour diagram based on (Equation 3), (Equation 34) or (Equation 46). Position, and the number of peaks in the isomagnetic field diagram is determined in advance as the number of dipoles. By thus giving the initial conditions and solving the evaluation function L, the magnetic field source analysis always converges. Displayed on the display,
Coordinates of each peak position and its number are automatically specified by specifying each peak position on the contour magnetic field map regarding the cardiac magnetic field and the brain magnetic field based on (Equation 3), (Equation 34), or (Equation 46). Is automatically input to the device as the above initial value, the evaluation function L is solved, and a convergent magnetic field source analysis result is obtained.

Therefore, it is possible to set the initial value almost uniquely and easily based on the data of the isomagnetic field diagram obtained as a result of the measurement, instead of setting the initial value by trial and error as in the prior art. This makes it possible to solve the inverse problem efficiently and more accurately.

In each of the diagrams showing the isomagnetic field diagrams used in the above description, the right side of the human body is displayed on the left side of each figure and the left side of the human body is shown according to the usual practice in the medical field. It is displayed on the right side of each figure.

[0111]

According to the present invention, based on B _xy in the prior art shown in (Equation 2), only the normal component B _z is measured without measuring the tangential components B _x and B _y by vector measurement. An equivalent magnetic field diagram that is equivalent to the equivalent magnetic field diagram is obtained. In the isomagnetic field diagram obtained directly from the normal component B _{z in the} prior art, it was difficult to distinguish a plurality of current sources, but in the isomagnetic field diagram of the present invention, in the prior art shown in (Equation 2). Similar to the _isomagnetic field diagram based on B _xy , a peak pattern appears just above the current source, so multiple current sources in the living body can be read directly, and the inverse problem of analyzing the positions, sizes, etc. of multiple current sources Can be easily solved. According to the device of the present invention, discovery of myocardial infarction, ischemia, etc., discovery of position causing arrhythmia, discovery of myocardial hypertrophy, discovery of heart-related diseases such as evaluation of pre- and postoperative changes in myocardial state, You can easily check the status.

[Brief description of drawings]

FIG. 1 is a diagram for modeling generation of a magnetocardiographic field in the present invention by using a magnetic field generated from a current dipole in an infinite plane conductor for analysis.

FIG. 2 is a diagram showing a schematic position of a moment of a current dipole existing inside an infinite plane conductor in the present invention.

FIG. 3 is a diagram showing relative magnetic field strength curves C ₁ and C _{2 obtained} by normalizing B _x and −∂B _Z / ∂x on the infinite plane conductor with their respective maximum values in the present invention.

FIG. 4 shows the magnetic field strength curves C ₃ , C ₄ , showing the first, second and third terms of −∂B _Z (x, 0) / ∂x in the present invention.
Shows the C _5.

FIG. 5 shows relative magnetic field strength curves C ₆ , C ₇ , C ₈ and C obtained by comparing the first and second terms of B _x and ∂B _Z / ∂x after normalization in the present invention. shows a _9.

[FIG. 6] In the present invention, α = (∇K) _z / K, {−∂
B _Z (x, 0) / ∂x first term} / {B _x (x, 0) first term}, {−∂B _Z (x, 0) / ∂x second term} / { B _x
(X, 0) second term} each magnetic field strength curve C ₁₀ ,
Shows the C _11, C _12.

FIG. 7 is a diagram showing a schematic configuration of a biomagnetic field measuring apparatus for performing a cardiac magnetic field measurement according to the present invention.

FIG. 8 is a diagram showing an arrangement configuration of magnetic field sensors in a biomagnetic field measuring apparatus for performing a cardiac magnetic field measurement according to the present invention.

FIG. 9 is a diagram showing a configuration of a single magnetic field sensor for detecting a normal component of a magnetic field in a biomagnetic field measuring apparatus for performing a cardiac magnetic field measurement according to the present invention.

FIG. 10 is a diagram showing a configuration of a single magnetic field sensor for detecting a tangential component of a magnetic field in a biomagnetic field measuring apparatus for performing a cardiac magnetic field measurement according to the present invention.

FIG. 11 is a diagram showing the positional relationship between the placement of magnetic field sensors and the chest of a human body in the biomagnetic field measuring apparatus for performing a cardiac magnetic field measurement according to the present invention.

FIG. 12 is a diagram showing a waveform representing a temporal change of a component in each direction of a magnetic field emitted from a heart of a healthy person measured at each magnetic field sensor position in the embodiment of the invention.

FIG. 13 is a tangential component (B _x ) for two specific channels measured in a healthy person in the example of the present invention.
The figure which shows the waveform showing the time change of.

FIG. 14 shows the tangential component B of the magnetic field in the example of the present invention.
_x, to obtain a B _y from healthy subjects of the magnetocardiogram waveform measured, Q wave, R
Isomagnetic field line diagram at the peak of each wave of S wave and S wave.

FIG. 15 is an isointegral diagram obtained from two tangential components detected in a time zone in which a QRS wave of a magnetocardiogram waveform of a healthy person appears in the example of the present invention.

FIG. 16 is an isointegral diagram obtained from a normal line segment detected in a time zone in which a QRS wave of a magnetocardiogram waveform of a healthy person appears in the example of the present invention.

FIG. 17 is an isointegral diagram obtained from two tangential components detected in a time zone in which a T wave of a magnetocardiogram waveform of a healthy person appears in the example of the present invention.

FIG. 18 is a diagram obtained by subtracting the isometric diagram shown in FIG. 15 from the isometric diagram shown in FIG.

FIG. 19 is an isointegral diagram obtained from two tangential components detected in a time zone in which a QRS wave of a magnetocardiogram waveform of a patient with myocardial infarction appears in the example of the present invention.

FIG. 20 is a graph showing a case where a T wave of a magnetocardiographic waveform of a patient with myocardial infarction is detected in a time zone in which the T wave appears in Example 2 of the present invention.
Isometric diagram obtained from two tangent components.

21 is a diagram obtained by subtracting the isometric diagram shown in FIG. 19 from the isometric diagram shown in FIG. 20.

FIG. 22 is a diagram showing an example of an output screen on a personal computer of the biomagnetic field measuring apparatus for performing a cardiac magnetic field measurement according to the present invention.

FIG. 23 is a diagram showing an example of a processed image displayed on the display of the biomagnetic field measuring apparatus of the present invention.

FIG. 24 is a diagram showing an isomagnetic field map at the time when the extreme values of the Q wave, R wave, and S wave of the magnetocardiogram (MCG) are obtained by measuring the normal component B _z by the conventional method.

FIG. 25 shows tangential components B _x and B _y of the magnetic field from the heart, respectively, measured at the time when the extreme values of the Q wave, the R wave, and the S wave appear in the embodiment of the present invention. B which synthesized the ingredients
_The figure which shows the _isomagnetic field diagram of _xy .

FIG. 26 shows the Q shown in FIG. 24 in the embodiment of the present invention.
Normal component B _z at the time when the extreme values of the R wave, R wave, and S wave appear
Using each of the isomagnetic field map data of (Equation 43),
The figure which shows the isomagnetic field diagram at each time point calculated | required based on (Equation 44).

FIG. 27 is a cross-sectional view showing a part of the internal configuration of the dewar for cerebral magnetic field measurement of the cerebral magnetic field measurement system for measuring the cerebral magnetic field in the example of the present invention.

28 is a diagram for explaining the relationship between a magnetic field component measurable by the brain magnetic field measurement system shown in FIG. 27 and the head.

29 is a diagram showing an example of an isomagnetic field diagram obtained by the brain magnetic field measurement system shown in FIG. 27. FIG.

[Explanation of symbols]

1 ... Magnetic field shield room, 2 ... Subject, 3 ... Bed, 4
... Dewar, 5 ... Automatic replenishing device, 6 ... FFL circuit, 7 ... Filter circuit, 8 ... Calculator, 10, 10 ', 10 "... Detection coil, 11, 11', 11" ... Reference coil, 12,
12 ', 12 "... SQUID, 13 ... Magnetic field sensor for detecting x component, 14 ... Magnetic field sensor for detecting y component, 20-1, 2
0-2, ~, 20-8, 21-1, ~, 21-8, 22
-1, ~, 22-8, 23-2, ~, 23-8, 24-
1, ~, 24-8, 25-1, ~, 25-8, 26-
1, ..., 26-8, 27-1, ..., 27-8 ... Magnetic field sensor, 30 ... Chest, 103-1, 103-2, ..., 103
-N ... SQUID magnetometer, 100 ... Head, 102 ... Head dewar, 104 ... Thermal radiation shield member, 105 ...
Upper plate, 106-1, ..., 106-N ... Signal lines.

Front page continued (72) Inventor Hiroyuki Suzuki, 882 Ichimo, Hitachinaka City, Ibaraki Prefecture, Hitachi Instruments Co., Ltd., Measuring Instruments Division (72) Inventor, Shoji Kondo, 882, Ichige, Hitachinaka City, Ibaraki Hitachi, Ltd., Measuring Instruments Division, Ltd. (72) Inventor Yasuaki Omiyama, 882 Ichimo, Hitachinaka City, Ibaraki Hitachi Instrument Co., Ltd. (72) Kenichi Okajima 1-280, Higashi Renegakubo, Kokubunji, Tokyo (56) Documents JP-A-9-66038 (JP, A) JP-A-9-56688 (JP, A) JP-A-8-299295 (JP, A) JP-A-2-249530 (JP, A) JP-A-10- 248821 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) A61B 5/05

Claims (2)

(57) [Claims] 1. A plane parallel to the surface of a living body is represented by Cartesian coordinates of x and y planes.
Plane, the direction perpendicular to the surface of the living body is defined as the z-axis of the Cartesian coordinates.
And a quantum interference element for detecting a biomagnetic field emitted from the living body
Magnetic field consisting of a child (SQUID) and perpendicular to the surface of the living body
componentB _z With multiple magnetometers that detect (x, y, t)
The measured magnetic field componentB _z X direction of (x, y, t)
And sum of squares of change rate in y direction S (x, y, t) = {(∂B _z (X, y, t) / ∂x) ^Two + (∂B
_z (X, y, t) / ∂y) ^Two } Find a value proportional to the square root of
Of the equal magnetic field lines connecting points of
The number of peaks and the position data of the peaks are recorded in the living body.
Before solving the inverse problem of estimating the position and strength of the magnetic field source in
The number of magnetic field sources and the initial value of the position of the magnetic field sources
Of initial value in magnetic field source analysis method characterized by
Law. 2. Assuming that the head of a living body is a sphere, the center of the sphere
Magnet in the r direction in polar coordinates (r, θ, φ) with the origin as
A biomagnetic field that is a field component and is generated from the brain part of the living body.
Of the normal line perpendicular to the tangential surface of the hemisphere with the radius of the sphere
MinuteB _r (Θ, φ, t) is almost parallel to the tangent plane
Multiple SQUID magnetometers with their tips arranged like
Detected normal componentB _r Θ direction of (θ, φ, t)
And sum of squares of change rate in φ direction S (θ, φ, t) = {(∂B _r (Θ, φ, t) / ∂θ) ^Two + (∂B
_r (Θ, φ, t) / ∂φ) ^Two } Find a value proportional to the square root of
Of the equal magnetic field lines connecting points of
The number of peaks and the position data of the peaks are recorded in the living body.
Before solving the inverse problem of estimating the position and strength of the magnetic field source in
The number of magnetic field sources and the initial value of the position of the magnetic field sources
Of initial value in magnetic field source analysis method characterized by
Law.