JP2004073894A - Calculation method of isomagnetic field map of biomagnetic field - Google Patents

Abstract

A without increasing the number of detection coils, to measure the vertical component B _z of the biomagnetic field to provide a biomagnetic field measurement method that enables analysis of the magnetic field source.
SOLUTION: A plurality of SQUID magnetometers arranged at equal intervals in two directions detect a time change of magnetic field components of a biomagnetic field emitted from the living body 2 in first and second directions parallel to a surface of the living body. , A calculation for obtaining a waveform representing a time change of a value proportional to the square root of the sum of squares of the magnetic field components in the first and second directions, and a calculation for integrating the waveform over a predetermined period to obtain an integrated value. And a step of displaying an isointegral diagram connecting points having the same integral value.
[Effect] Since the quantitative biomagnetic field distribution is displayed using a small number of figures, it is possible to objectively and quantitatively grasp diseases and abnormalities for each individual.
[Selection diagram] FIG.

Description

The present invention relates to a biomagnetic field for measuring a biomagnetic field generated by a brain activity of a living body, a myocardial activity of a heart, and the like using a plurality of magnetometers including a SQUID (superconducting quantum interference device). The present invention relates to a measurement method and a calculation method of a biomagnetic field distribution in a biomagnetic field measurement device.

The present invention relates to a biomagnetic field that measures a biomagnetic field generated by a neural activity of a living body's brain, a myocardial activity of a heart, and the like using a plurality of magnetometers including a high-sensitivity quantum interference device (SQUID: superconducting quantum device). The present invention relates to a measurement method and a biomagnetic field measurement device.

The biomagnetic field includes a magnetic field generated by a current dipole and a magnetic field caused by a volume current flowing in a living body. It is considered that the measurement of the normal component (B _z (Z component in the orthogonal coordinate system) or _Br (radial component in the polar coordinate system)) of the biomagnetic field is hardly affected by the volume current. In the prior art, the surface of the detection coil connected to the SQUID to a living body surface is disposed in parallel, was measured B _z or B _r is a perpendicular normal component to the surface of the living body. The result of the biomagnetic field measurement was displayed as a waveform representing a time change of the measured magnetic field component, and an isomagnetic field map (contour map) connecting points having the same intensity at any time of the measured magnetic field component. In addition, various analysis methods have been proposed to analyze the magnetic field source that generates the biomagnetic field from the obtained isomagnetic field map. In a typical analysis method, the analysis is performed by replacing the magnetic field source with a current dipole. I was doing.

The isomagnetic field map of the normal component (B _z or _Br ) of the magnetic field created by the current dipole is a pattern with a magnetic field extruding pole and a magnetic field suction pole at positions separated from the magnetic field source (current dipole). Become. The size, position, direction, and the like of the magnetic field source (current dipole) are analyzed based on the magnetic field strength at these two poles and the distance between the two poles.

In the first prior art (H. Hosaka and D. Cohen, J. Electrocardiol., 9 (4), 426-432 (1976)), measurement was performed to make it easier to see the direction and intensity of the current in the myocardium. with isomagnetic field of the normal component B _z, as a method for displaying a current source distributed in the myocardium, the current vector defined by equation (1) <J (x, y )> a on each measurement point Arrow maps expressed by arrows have been devised. In the following description, parentheses <> indicate that the symbol in <> is a vector, for example, <J> indicates that J is a vector.

<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 the x direction unit vector, <e _y> is a unit vector in the y-direction. However, when a plurality of current sources are present, there is a problem that the isomagnetic field of the normal component B _z difficult to determine the individual current sources.

In the second prior art (K. Tukada et al., Review of the Scientific Instruments, 66 (10) 5085-5091 (1995)), in order to visualize a plurality of distributed current sources, a normal component (B _{z) is used.} or B _r) does not measure the, place vertically face of the detection coil with respect to the living body surface, and measure the tangential component B _x and B _y. It measured tangential components B _x, and a B _y displayed as isomagnetic field for each component. Measured by the prior art 2 tangential component B _x, although B _y is considered the influence of the volume current, two-dimensional vector magnitude obtained by combining the B _x and B _y, which is measured at according to the time t (Equation 2) the isomagnetic field of B _xy, always from a peak immediately above the current dipole can be obtained, even when a plurality of current dipoles are present, can be visualized by separating each current dipole.

| B _xy (x, y, t) |
= {(B _x (x, y, t)) ² + (B _y (x, y, t)) ² }
... (Equation 2)
In the third related art (Y. Yoshida et al., Tenth International Conference on Biomagnetism, Santana Fe, New Mexico, Feb. 20 (1996)), a vector magnetic field sensor composed of three detection coils whose coils are orthogonal to each other. detecting a normal component and two tangential components of the biomagnetic field with, converts the detection result of the magnetic field components in orthogonal coordinate system, an orthogonal coordinate system of the component B _x, B _y, and B _z calculated, normal The _isomagnetic field diagram of the component B _z and the two-dimensional vector intensity B _xy is displayed.

Fourth prior art (K.Tsukada, et.al., Tenth International Conference on Biomagnetism, Santana Fe, New Mexico, Feb.20 (1996)) in two tangential components B _x biomagnetic field, B _y detected and, | B _xy | = | is performed a comparison between such magnetic field lines based on the diagram and the like field diagram based on the normal component _{B z | B x + B y} .

図 As a figure showing the measurement result of the electrophysiological phenomenon in the living body, there are an electroencephalogram (MEG, magnetoencephalogram) obtained by measuring with an electroencephalograph, and an electrocardiogram (ECG, electrocardiogram) obtained by measuring with an electrocardiograph. 2. Description of the Related Art In measurement of an electrocardiogram, a body surface potential map for mapping an electrocardiogram using a plurality of electrodes is a well-known technique. These electroencephalograms or body surface electrocardiograms were displayed as equipotential maps connecting equal potential points.

In the fifth related art (TJ Montaguet et al., Circulation 63, No. 5, pp 1166-1172 (1981)), a waveform representing the time change of the output of each of a plurality of electrodes is represented by an arbitrary time interval. The isointegral map integrated by is displayed as a body surface electrocardiogram.

H. Hosaka @ and @ D. Cohen, J .; Electrocardiol. , 9 (4), 426-432 (1976).

K. Tukada et al. , Reveiw of the Scientific Instruments, 66 (10) 5085-5091 (1995). Y. Yoshida et al. , Tenth International Conference on Biomagnetism, Santana Fe, New Mexico, Feb. 20 (1996) K. Tsukada, et. al. , Tenth International Conference on Biomagnetism, Santana Fe, New Mexico, Feb. 20 (1996) T. J. Montague et al. , Circulation # 63, No. 5, pp1166-1172 (1981)

In the following description, “biomagnetic field” means “magnetic field generated from biomagnetic field”, “cardiac magnetic field measurement” means “measurement of magnetic field generated from heart”, and “cardiac magnetic waveform” means “cardiac magnetic field” A waveform represented by a magnetocardiogram (MCG, Magnetocardiogram) obtained by measurement ". “Measurement of brain magnetic field” means “measurement of a magnetic field generated from the brain”, and “magnetoencephalogram waveform” means “waveform represented by MEG (Magnetoencephalogram) obtained by brain magnetic field measurement”.

The isomagnetic field for each component in the prior art are characterized, respectively, when a single current dipole exists, the isomagnetic field of the normal component B _z, the position of the current source, size, direction, etc. Can be easily analyzed. On the other hand, the tangential 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, the number of coils for detecting a magnetic field x, because it is required in the y-direction, respectively, the number of coils is doubled as compared with the detection of the normal component B _z only. 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. For this reason, the number of magnetic field sensors including the detection coil and the SQUID increases, and further, the number of signal processing circuits and the like increases, and there is a problem that the biomagnetic field measurement system becomes an expensive system. In the first prior art, there is a problem that an arrow is simply displayed on each measurement point, and it is difficult to identify a detailed distribution state of a current source.

By using the isomagnetic field map represented by the biomagnetic field component, the position, size, direction, etc. of the current source in the living body at any time can be analyzed, and detailed changes in information such as the position, size, direction, etc. of the current source can be analyzed. You can know. In the related art, diagnosis of a disease or the like is performed by capturing dynamic changes in various types of information using a large number of figures displayed or output on an apparatus. However, in the prior art, a large number of diagrams representing various types of information are required for diagnosis, and abnormal changes in various types of information are empirically performed. As described above, according to the conventional technology, comprehensive information indicating which magnitude of current flows in which part of a living body, the location of an area where an abnormal biocurrent is flowing, and the like are displayed as one diagram. Has not been executed. In addition, in the body surface electrocardiogram, in the isointegral diagram showing points where the integral values are equal at arbitrary time intervals (a period during which each wave of Q, R, and S is generated, a period during which a T wave is generated from an S wave, etc.), The heart information can be obtained by one electrocardiogram without requiring a plurality of equipotential diagrams at each successive time. However, assuming that the current source in the heart is a single current dipole in the equipotential diagram, a diagram in which the anode peak and the cathode peak exist not directly above the current dipole but at a position distant from the current dipole. There is a problem that it 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 the cathode change, and when integrating the potential, the current source and the peak of the integrated value do not correspond. Was. Further, even if the component of the biomagnetic field obtained by the biomagnetic field measurement is 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 isointegral diagram because there are individual differences in the position and size of an organ only with the isointegral diagram obtained from the electrocardiogram.

An object of the present invention is to provide a biomagnetic field measuring method and a biomagnetic field measuring apparatus capable of grasping the whole state of a living body part by using a much smaller number of maps (maps) than required in the prior art. Is to provide.

It is another object of the present invention to provide a biomagnetic field measuring method and a biomagnetic field measuring apparatus which can measure a vertical component _Bz of a biomagnetic field and analyze a magnetic field source without increasing the number of detection coils. It is in.

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

In the biomagnetic field measuring apparatus according to the present invention, (1) a plurality of magnetometers, which are composed of quantum interference devices (SQUIDs) and detect a biomagnetic field emitted from a living body as a signal, are arranged outside the living body, and perform signal arithmetic processing. In a biomagnetic field measuring apparatus for measuring a biomagnetic field distribution, which has an arithmetic processing means and a display means for displaying a result of the arithmetic processing, the magnetometer is provided with a magnetic field in a first direction perpendicular to the surface of the living body of the biomagnetic field. The time change of the component is detected, and the arithmetic processing means calculates a time proportional to the square root of the sum of squares of the change rate of the magnetic field component in the first direction in the second direction and the third direction crossing the first direction. It is characterized in that a calculation for obtaining a waveform representing a change and a calculation for integrating the waveform over a predetermined period to obtain an integrated value are performed, and the integrated value is displayed on a display means. In the measuring device, the magnetometer The time change of the magnetic field component in the first and second directions parallel to the surface of the living body of the magnetic field is detected, and the arithmetic processing means determines the time of the value proportional to the square root of the sum of squares of the magnetic field components in the first and second directions. It is characterized in that a calculation for obtaining a waveform representing a change and a calculation for integrating the waveform over a predetermined period to obtain an integrated value are performed, and the integrated value is displayed on the display means. Further, in the biomagnetic field measuring apparatus having the features of the above (1) and (2), the display means displays an isointegral diagram connecting points having equal integral values by interpolation and extrapolation, The means integrates the waveform over a predetermined period to determine an integral value over a plurality of predetermined periods to determine a plurality of integral values, and includes a ratio and an equal weight among the plurality of integral values. It is also characterized in that the calculation for obtaining either the sum or the difference is performed, and a plurality of magnetometers are arranged at equal intervals on the surface of the living body. The biomagnetic field measuring apparatus of the present invention can simultaneously display the normal (vertical) component and the tangential (parallel) component of the magnetic field generated from the heart with respect to the chest surface. In the orthogonal coordinate system (x, y, z), the direction perpendicular to the surface of the living body is set as the z-axis, the first direction is set as the z direction, the second direction is set as the x direction, and the third direction is set as the y direction. In the polar coordinate system (r, θ, φ), a direction perpendicular to the surface of the living body is defined as an r axis, a first direction is defined as an r direction, a second direction is defined as a θ direction, and a third direction is defined as a φ direction.

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

According to the present invention, the tangential component 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) can be obtained isomagnetic field projected on a plane , The current source in the living body can be determined from the peak pattern of the isomagnetic field map, and the positions of a plurality of current dipoles at (x, y) coordinates can be known.

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

Using a plurality of magnetometers composed of quantum interference devices (SQUIDs), a tangential component (a component parallel to the surface of the living body) B _x (x, y) of a magnetic field emitted from the living body at the position (x, y) on the surface of the living body , T), B _y (x, y, t) (where the plane parallel to the plane of the living body is defined as the xy plane and the plane of the living body in the rectangular coordinate system (x, y, z)). an axis perpendicular to the z), tangential components _{B x (x, y, t} ) and B _y (x, _y, 2-dimensional vector magnitude from the square root of the square sum of _{t) │B xy (x, y} ) │ (Hereinafter, | | represents an absolute value) is obtained by (Equation 3).

│B _xy (x, y, t) │ = √ ｛(B _x (x, y, t)) ²
+ (B _y (x, y, t)) ² ｝
… (Equation 3)
Next, for each point (x, y), the integral I ₁ (x, y) of the waveform | B _xy (x, y, t) | To obtain an isointegral diagram connecting points having the same value of the integral value I ₁ (x, y) at each point (x, y), and display the isointegral diagram on the display screen.

I ₁ (x, y) = ∫ | B _xy (x, y, t) | dt
… (Equation 4)
Hereinafter, from the measured magnetic field component perpendicular to the plane of the living body _{B z (x, y, t} ) ( normal component), it is described that estimate the tangential component B _x, the B _y.

Taking advantage of the fact that the tangential component parallel to the body surface of the biomagnetic field reflects the current flowing directly below the body surface best, the tangent vector of the measured magnetic field (from the relationship between the current flowing direction and the magnetic field direction) By rotating B _x , B _y ) counterclockwise by 90 °, the current distribution in the living body can be projected onto a two-dimensional plane parallel to the surface of the living body to give an overview. _{That, <e x>, <e} y> each x-axis direction, a unit vector in the y-axis direction, in the tangential component B _x in each measurement point, the B _y, Bekutoku current shown in equation (5) <J > Can be obtained and expressed as a distribution (arrow map) of a current vector field at each measurement point (x, y).

_{<J> = - B y <} e x> + B x <e y>
… (Equation 5)
On the other hand, when measuring the perpendicular normal component B _z to a biological surface of a magnetic field, which is defined arrow map using the current vector represented by equation (1) (first prior art: H, Hosaka and D. Cohen (1976)).

The inventors of the present invention, from comparison of equation (1) and (5), (6) and possibly (7) is satisfied, i.e., the normal component B _z of the measured magnetic field It found that there is a possibility of deriving the tangential components B _x and B _y, conducted various studies. Hereinafter, the results of the study will be described in detail.

B _x = − (∂B _z / ∂x)
… (Equation 6)

B _y = − (∂B _z / ∂y)
… (Equation 7)
FIG. 1 is a diagram for modeling and analyzing the generation of a magnetic field (cardiac magnetic field) due to the activity of the heart using a magnetic field generated from a current dipole in an infinite planar conductor. In FIG. 1, P is an infinite plane conductor having a surface on the xy plane of a rectangular 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 existing at the indicated position, <r (x, y, z)>, indicates the position vector of the measurement point for measuring the magnetic flux density (magnetic field) <B (r)>. In the model shown in FIG. 1, the magnetic field <B (r)> generated outside the infinite planar conductor P is determined by Sarvas (Literature: Phys. Med. Biol., Vol. 32, No. 1, 11-22 (1987). )) And is represented by (Equation 8).

<B (r)> = { μ 0 / (4πK 2)} {<Q> × <a> · <e z> ∇K
−K < _ez > × <Q>｝
… (Equation 8)
In (Equation 8), μ ₀ is the magnetic permeability of vacuum, <e _z > is a unit vector in the z-axis direction, × is a vector product, · is a scalar product, and ∇ is grad = (∂ / ∂x, ∂ / Ａy, ∂ / ∂z), where <a> is represented by (Equation 9), a is represented by (Equation 10), K is represented by (Equation 11), and ∇K is represented by (Equation 12). || indicates an absolute value.

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

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

K = a (a + <a> · <e z>)
... (Equation 11)

^{∇K = (2 + a -1 <a>} · <e z>) <a> + a <e z>
... (Equation 12)
<B> represented by the equation (8) and the infinite plane conductor P tangential components B _x and B _y are parallel to the (r), infinite plane conductor perpendicular Do normal component B _z to P, respectively (equation 13) , (Equation 14) and (Equation 15).

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

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

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

_{∂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 differentiation of the normal component _{BZ in} the y direction is represented by (Equation 17).

{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)
In (Equation 16) and (Equation 17),

α = (∇K) _z / K
… (Equation 18)

β _x = −a ⁻³ (x−x ₀ ) (z−z ₀ ) ² + a ⁻¹ (x−x ₀ )
... (Equation 19)

β _y = −a ⁻³ (y−y ₀ ) (z−z ₀ ) ² + a ⁻¹ (y−y ₀ )
... (Equation 20)
(Equation 16) and (Equation 17) are represented by (Equation 21) and (Equation 22), respectively.

∂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)

{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), and (Equation 22) are normalized by {μ ₀ / (4πK ² )}, which is a common factor, and transformed. , (Equation 24), (Equation 25), and (Equation 26) are obtained.

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

∂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 )}
… (Equation 24)

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

∂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 )}
… (Equation 26)
As is clear from (Equation 23) and (Equation 24), the value of ∂B _Z / ∂x is equal to a value equal to −2α times the tangential component B _x and two additional terms, and (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, equal to a value obtained by adding the two additional terms.

Here, as shown schematically in FIG. 2, the moment of the current dipole is set at a point <r ₀ (0,0, −z ₀ )>, z ₀ = 0.05 [m] inside the infinite planar conductor P. When <Q> = (Q _x , Q _y , 0) and Q _x = Q _y = 50 [nAm], B _x ((Equation 13)) and −∂B _Z / ∂x ((Equation 16) )). By substituting x ₀ = y ₀ = y = 0 and Q _z = 0 into (Equation 13) and (Equation 16), (Equation 27) and (Equation 28) are obtained.

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

∂B _Z (x, 0) / ∂x =
｛Μ ₀ / (4πK ² )｝ ｛2α (∇K) _x Q _y x -α KQ _y -β _x Q _y x｝
… (Equation 28)
FIG. 3 shows a relative magnetic field strength curve C ₁ , in which B _x ((Equation 27)) and −∂B _Z / ∂x ((Equation 28)) on the infinite planar conductor P are normalized by their maximum values. It is shown by C _2.
That is, the curve C ₁ represents B _x (x, 0) / max | B _x (x, 0) |, and the curve C ₂ represents ｛− {B _Z (x, 0) / {x} / max | ∂B _Z (X, 0) / ∂x |. As is clear from FIG. 3, the distributions of B _x and −∂B _Z / ∂x both have a peak at the origin (x = 0) immediately above the current dipole, and both have the current dipole. This indicates that the maximum signal can be detected when there is a measurement point right above the point. Moreover, given the sharp peak than it is the curve C ₁ in the curve _{C 2, -∂B Z / ∂x (} ( number 16)) magnetic field distribution by the spatial resolution than the magnetic field distribution by B _x ((number 13)) Is high.

Magnetic field strength curves C ₃ , C ₄ , and C ₅ shown in FIG. 4 indicate the first, second, and third terms of −∂B _Z (x, 0) / ∂x, respectively. From the results shown in FIG. 4, the third term is negligible with respect to the first and second terms, and the shape of −∂B _Z (x, 0) / ∂x is determined by the first and second terms. (Equation 28) can be approximated to (Equation 29).

∂B _Z (x, 0) / ∂x =
｛Μ ₀ / (4πK ² )｝ ｛2α (∇K) _x Q _y x-αKQ _y ｝
… (Equation 29)
FIG. 5 is a diagram showing a relative magnetic field strength curve in which the first and second terms of (Equation 13) and (Equation 16) are compared after normalization. In FIG. 5, curve C ₆ is the first term of {B _x (x, 0)} / max | B _x (x, 0) |, that is, ｛− (∇K) _x Q _y x} / max. _{| B x (x, 0)} | a represents the curve C ₇ is _{{-∂B Z (x, 0)} / the first term of _{∂x} / max | ∂B Z (} x, 0) / ∂x |, _{That, {- 2α (∇K) x} Q y x} / max | ∂B Z (x, 0) / ∂x | a represents {second term of B _{x (x,} 0)} curve C ₈ is / max | B _x (x, 0) |, that is, {KQ _y } / max | B _x (x, 0) |, and the curve C ₉ is the first curve of ｛−∂B _Z (x, 0) / ∂x. 2 _{Section} / max | ∂B Z (x} , 0) / ∂x |, i.e., {αKQ _y} / max | represent _{| ∂B Z (x, 0)} / ∂x.

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

In FIG. 6, the magnetic field curve C ₁₀ is _{α = (∇K) z / K} , the magnetic field curve C ₁₁ is - {first term of equation (28)} / {the first term of equation (27)}, That is, the _{2α (∇K) x Q y x} / (∇K) x Q y x = 2α, magnetic field curve C ₁₂ is - the second term in {second term of equation (28)} / {(number 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 differs from the magnitude of B _x (x, 0) by 2 / (z−z ₀ ) at the peak point. (Z-z ₀₎ is the depth of the presence of current dipole. It is difficult to determine (z-z ₀ ) from actual magnetic field measurements. (Equation 30) is obtained from a comparison between (Equation 27) and (Equation 29).

−∂B _Z (x, 0) / ∂x =
{Μ ₀ / (4πK ² )} − 2α (ΔK) _x Q _y x + α KQ _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) is approximately established.

−∂B _Z (x, 0) / ∂x = 2αB _x (x, 0)
… (Equation 31)
To generalize In equation (24), if two additional terms other than -2ArufaB _x is small relative -2ArufaB _x is approximately (number 32)做thereby expected to satisfied.

∂B _Z / ∂x = -2αB _x
… (Equation 32)
In is a result of studying the relationship between -∂B _Z / ∂x and B _x, the same is also true for the relationship -∂B _Z / ∂y and B _y, approximating the equation (26) above It can be considered that (Equation 33) holds.

∂B _Z / ∂y = -2αB _y
… (Equation 33)
Hereinafter, (number 32), respectively, from the equation (33), B _x is -∂B _Z / ∂x, B _y is assumed to be proportional to -∂B _Z / ∂y, measured normal component B _z procedure will be described in detail for determining the isomagnetic field estimated tangential components B _x, the B _y from.

When the magnetic field component B _z (x, y, t) perpendicular to the surface of the living body is measured, the rate of change of B _z (x, y, t) in the x direction ∂B _z (x, y, t) / ∂x When, B _z (x, y, t) the direction of the change rate .differential.B _z of (x, y, t) / ∂y and determined, the sum of squares, as shown in equation (34) the square root S _t (x, y, t).

_{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 integrated value I ₂ (x, y) of the waveform _St (t, x, y) in an arbitrary period is obtained by (Equation 35), and each value is obtained by interpolation and extrapolation. An isointegral diagram connecting points having the same value of the integral value I ₂ (x, y) at the point (x, y) is obtained, and the isointegral diagram is displayed on the display screen.

_{I 2 (x, y) =} ∫│S t (x, y, t) │dt
… (Equation 35)
The integration ranges of (Equation 4) and (Equation 35) include, for example, when the heart is to be measured, the periods in which the Q, R, and S waves are generated, and the QRS in which the S wave is generated from the Q wave. The period of the wave (QRS complex), the period when the T wave is generated, and the like are taken. Further, the sum or difference including equal weights (weights are w ₁ and w ₂ ) between a plurality of integral values obtained by taking a plurality of integral ranges as the integral ranges of (Equation 4) and (Equation 35). , A ratio, etc., are calculated, an isointegral diagram connecting the points having the same value is obtained by interpolation and extrapolation, and the isointegral diagram is displayed on the display screen. For example, a period T ₁ during which a QRS wave is generated as a _first integration range, and a period T ₂ during which a T wave is generated as a second integration range, and the period T ₁ according to (Equation 4) or (Equation 35). integral value _{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, T2 (x, y) , respectively about Is calculated, and between the integral values I ₁ , _T1 (x, y) and the integral values I ₁ , _T2 (x, y), or the integral values I ₂ , _T1 (x, y) and the integral values I ₂ , _T2 ( x, y), the sum I _sum (x, y) including the equal weight, or the difference I _dif (x, y), and the ratio r (x, y) are expressed by ( _Equation 36) to (Equation 37). , (Equation 38) to (Equation 39), and (Equation 40) to (Equation 41).

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

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

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

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

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

r (x, y) = I ₂ , _{T 1} (x, y) / I ₂ , _{T 2} (x, y)
... (Equation 41)
As a result of the calculations of (Equation 36) to (Equation 37), (Equation 38) to (Equation 39), and (Equation 40) to (Equation 41), the variation of the isointegral diagram due to individual differences is improved, Function abnormality can be detected.

According to the isointegral diagram obtained by the present invention, it is necessary to use the conventional technique without analyzing the biological phenomena using a large number of maps (maps) representing the state of the living body part at each time, which is required by the conventional technique. The entire state of the living body part can be grasped using a much smaller number of figures (maps) than the number of figures (maps) that were set. In addition, since the peak position of the isointegral chart obtained using the tangent component or normal component of the biomagnetic field matches the portion where a large amount of current flows in the living body, the in vivo It can be determined at which part of the current a large amount of current flows. Although the biomagnetic field distribution has a large individual difference, the present invention uses an integral value at an arbitrary time (period) obtained from a waveform representing a time change of each direction component of the biomagnetic field. It can be displayed using a small number of figures (maps), and can objectively and quantitatively grasp diseases and abnormalities for each individual.

In the present invention, the magnetic field component B _z (x, y, t) perpendicular to the surface of the living body is measured, and B _x is changed in the x direction of B _z (x, y, t) ∂B _z (x, x). y, t) / from ∂x, B _y and B _z (x, y, the direction of the change rate .differential.B _z (x of t), y, since obtaining estimated from t) / ∂y, adjacent each measurement The background magnetic field (disturbing magnetic field) commonly existing at the point (x, y) is canceled in the x direction and the y direction, respectively.

In the present invention, without measuring tangential components B _x, the B _y by vector measurement, only the measurement of the normal component B _z, and the like magnetic field diagrams based in B _xy in the prior art shown in equation (2) An equivalent isomagnetic field diagram is obtained. The isomagnetic field obtained directly from in normal component B _z of the prior art, a plurality of current sources is was difficult to determine, in isomagnetic field of the present invention, in the prior art shown in equation (2) Similar to the _isomagnetic field map based on Bxy, a peak pattern appears immediately above the current source, so that multiple current sources in the living body can be read directly, and the inverse problem of analyzing the position, size, etc. of multiple current sources Can be easily solved. According to the device of the present invention, discovery of heart-related diseases such as discovery of myocardial infarction, ischemia, etc., location of arrhythmia, discovery of myocardial hypertrophy, evaluation of changes in myocardial condition before and after surgery, The state can be easily checked.

Biomagnetic field orthogonal coordinate system as in the coordinate system for measurement (x, y, z) (the magnetic field components B _x, B _y, and B _z) and pole orthogonal coordinate system (r, θ, φ) are used. When the measurement target is a heart or the like, an orthogonal coordinate system (x, y, z) in which the chest wall is an xy plane is used. When the measurement target is a brain or the like, since the head has a shape close to a sphere, a polar coordinate system (r, θ, φ) (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, represented by B _φ. Hereinafter, in the present embodiment, an orthogonal coordinate system (x, y, z) will be described with reference to, polar coordinate system (r, theta, phi) in the case of using the a B _z in B _r and B _x B to _theta, it may be read as respectively B _y in B _phi.

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

出力 The output from the magnetic field sensor is input to a FLL (Flux Locked Loop) circuit 6 that outputs a voltage proportional to the magnetic field strength detected by the detection coil. This FFL circuit cancels the change of 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 through the feedback coil into a voltage, a voltage output proportional to a change in 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, A / D converted by an A / D converter (not shown), and taken into a computer 8. In the computer 8, various calculation processes are executed, the calculation process results are displayed on a display, and further output by a printer.

(2) As a 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 detects the tangential component of the magnetic field. As a coil for detecting the normal component of the magnetic field, a coil oriented in the z direction is used. These magnetic field sensors (20-1, 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, ~, 27-8) are shown in Fig. 8. The magnetic field sensors 9 are installed in a direction perpendicular to the bottom of the Dewar, and the distance between the sensors is set to be equal in the x and y directions so as to accurately capture the change in the magnetic field in the x and y directions. did. Here, the distance between the sensors was 25 mm, and the number of sensors was 64 channels of 8 × 8.

FIGS. 9 and 10 show schematic views of one of the installed magnetic field sensors according to this arrangement method. The magnetic field sensor shown in FIG. 9 is a sensor for measuring a component _Bz 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 opposite coils. The one closer to the living body is used as the detection coil 10, and the one farther away is used as a reference coil 11 for removing external magnetic field noise to form a primary differential coil. ing. Here, the coil diameter was 20 mm, and the baseline between the coils was 50 mm. External magnetic field noise comes from signal sources that are 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, by taking the difference between the magnetic fields captured by the two coils, a high S / N measurement can be performed.

The primary differentiating coil is connected to the SQUID input coil via the superconducting wiring of the mounting board on which the SQUID 12 is mounted, and transmits the biomagnetic field detected by the coil to the SQUID. 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 planar coil, in which the detection coils 10 ′ and 10 ″ and the reference coils 11 ′ and 11 ″ are arranged on one plane, the coil diameter is 20 mm × 20 mm, and the baseline is 50 mm. The coils are connected to the mounting boards of SQUIDs 12 'and 12 "in the same manner as for the normal component. On the two orthogonal surfaces of the support of the quadrangular prism, the magnetic field sensor 13 for detecting the x component and the magnetic field for detecting the y component are provided. A magnetic field sensor capable of measuring x and y components is formed by attaching the sensor 14. The quadrangular prisms are arranged in an array as shown in FIG.

デ ュ The Dewar with a built-in magnetic field sensor is placed 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 defined as the x-axis, and the vertical direction of the body is defined as the y-axis. Magnetic field sensors (20-1, ~, 20-8, 21-1, ~, 21-8, 22-1, ~, 22-8, 23-2, ~, 23-8, 24-1, ~, 24 -8, 25-1, to 25-8, 26-1, to 26-8, 27-1, to 27-8) and the positional relationship with the chest 30 are shown in FIG. 12 (a), 12 (b) and 12 (c) show biomagnetic field signals measured in this positional relationship.

12 (a), (b), and (c) show waveforms representing the time change of a magnetic field emitted from a certain healthy person's heart by each magnetic field sensor (magnetic field sensors arranged in an 8 × 8 array). The horizontal axis of the 64 waveforms in each figure is the time axis, and the vertical axis is the detected magnetic field strength. FIG. 12A shows the change in time (horizontal axis) of each component of the tangential component B _x , FIG. 12B shows the tangential component B _y , and FIG. 12C shows the normal component B _z . Each channel is standardized by the maximum value of the absolute value of the channel having the highest signal strength and displayed.

The dotted line and the solid line shown in FIG. 13 show the waveform representing the time change of the tangential component (B _x ) for two specific channels measured for a healthy person by the solid line and the dotted line. The time points at which the peaks (extreme values) of the Q wave, R wave, and S wave are given in the time zone T _{1 in} which the QRS wave in which the ventricle of the heart is depolarized appear are shown as t _Q , t _R , and t _{s in} FIG. Indicated by. Further, the time period T ₂ to the appearance of T-wave is repolarization of the heart, showing a point that gives a peak (extreme value) at t _T.

In FIG. 13, the P wave indicates atrial excitation (depolarization), the QRS wave composed of Q, R, and S waves indicates ventricular excitation (depolarization), and the T wave indicates QRS. This is a gentle run following the wave, indicating myocardial repolarization. Depolarization is the process by which the excitement initially spreads through the muscle, and repolarization is the process by which the excited muscle returns to a resting state.

Figure 14 (a), (b) , (c) shows t _Q, t _R, etc. field diagram connecting by lines the points of equal intensity of the cardiac magnetic field at the time of t _s. Figure 14 (a), (b), (c) is indicated by _{│B xy (x, y, t} ) │ (Equation 4), measured at 64 points tangential component B _x, synthesize B _y 2 shows a two-dimensional vector intensity distribution obtained. Further, arrows in FIGS. 14 (a), (b) and (c) indicate two-dimensional directions on the assumption that the current source at each of the 64 measurement points creates a magnetic field at each of the measurement points. 4 shows a current vector. The current direction and distribution in the heart can be estimated from the 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. As shown in FIG. 14 (a), at the time of the peak of the Q wave, the current flowing in the heart flows downward and to the right in the interventricular septum. As shown in FIG. 14 (b), at the time of the peak of the R wave, A large current flows obliquely downward in the entire left ventricle. As shown in FIG. 14 (c), at the peak of the S-wave, a current flows obliquely upward and leftward in the direction of the base of the ventricle, and the depolarization process of the ventricle occurs. It turns out that it ends. Thus, it can be seen that the active site and the current direction in the heart at each time can be visualized by the isomagnetic field diagrams of FIGS. 14 (a), (b) and (c).

15, the two tangential components detected at a time zone T ₁ which QRS wave from the Q wave of the magnetocardiogram waveforms until S wave appears B _x, 2-dimensional vector magnitude ￨B _xy obtained from B _y ( (x, y, t) | is integrated for each point (x, y) by (Equation 4), and is an isointegral diagram connecting points of the same integral value. The x-axis and y-axis in FIG. 15 represent the coordinates of the magnetic field sensor arranged on the surface of the living body, and the numerical values shown near the black circles of the respective curves in the isometric diagram indicate the integral values of the curves. From FIG. 15, it can be seen that most of the current flowing to the myocardium during the time period of the QRS wave flows in the left ventricle where the thickness of the myocardium is large. It turns out that it corresponds well.

FIG. 16 shows a normal line segment _Bz at each point (x, y) for the same healthy person who obtained the data of FIG. 15 from FIGS. 12 (a), (b) and (c). measured, calculated (number 34) by S _t (x, y, t), the time period T ₁ of the QRS wave, it is like integration diagram connecting points of the same integral value performs the integration of equation (35) . Hereinafter, in FIGS. 16 to 21, the x-axis and the y-axis represent the position coordinates (the unit is m) of the magnetic field sensor disposed on the surface of the living body. Numerical values shown near the black circles on the curves in FIGS. 16 to 21 indicate the integral values of the curves.

Tangential component B _x of a magnetic field shown in FIG. 15, the isointegral obtained from B _y, the pattern of isointegral obtained from normal component B _z of the magnetic field shown in FIG. 16 were found to match. This agreement means that (Equation 6) and (Equation 7), or (Equation 32) and (Equation 33) are almost satisfied in actual experimental data.

FIG. 17 shows two-dimensional vector intensities | B _xy (B _xy (B _xy) obtained from two tangent components B _x and B _y detected in the time zone T ₂ of the T wave for the same healthy person as obtained in FIG. (x, y) | for each point (x, y), is an integral diagram obtained by integrating (Equation 4) and connecting points having the same integral value. In FIG. 17, 1e + 003 indicates 1000.

Figure 18 is a contour diagram showing the integrated value of (number 4) for the time period T _2, the period zone T ₁ which QRS wave occurs in the difference (number 37) of the integrated value of (number 4) . That is, FIG. 18 is a diagram obtained by subtracting the isometric diagram shown in FIG. 15 from the isometric diagram shown in FIG. If the time period T ₂ of the T wave is longer than the time period T ₁ of the QRS wave. The pattern in FIG. 17 is similar to the pattern shown in FIG. For this reason, 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 difference between the above-mentioned integral values of the curves.

Next, FIG. 19, FIG. 20, and FIG. 21 show the results regarding the measurement of the cardiac magnetic field of patients with myocardial infarction. 19, isointegral obtained in the same manner as in FIG. 15 for the time period T ₁ of the QRS wave, FIG. 20, isointegral was determined in the same manner as in FIG. 17 for the time period T ₂ of the T-wave, Fig. 21 the integrated value of the time period T ₂ of the T-wave and (Equation 4), represents the difference (number 38) of the integral value for the time period T ₁ of the QRS wave (Equation 4), in the same way as in FIG. 18 FIG. 9 is a contour map obtained. 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 integral values of the curves, and the numerical values shown in the vicinity of the black circles of the curves in FIG. 21 are the values of the above-mentioned integral values of the curves. Is shown.

Isointegral in the time zone T ₁ shown in FIG. 19 is a pattern isointegral no little difference shown in FIGS. 15 and 16, it can be seen that flow much current in the left ventricle. However, isointegral in the time zone T ₂ shown in FIG. 20 becomes a pattern different from the isointegral in the time zone T ₁ shown in FIG. 19, for myocardial infarction, the time zone T ₁ and the time period T ₂ clearly shows that the pattern of the amount of current flowing to the heart is greatly different. Further, contour plot shown in FIG. 21 is a whole have a negative value, the whole is quite different from the contour plot of the healthy person shown in FIG. 18 having a positive value in patients with myocardial infarction, cardiac time zone T ₂ It can be clearly seen that the current flowing through the device has been damaged.

As described above, by imaging the magnetic field strength in the time zone T ₁ and the time zone T ₂ of the heart, the patient can be invasively non-invasively without causing pain and in a short time of 1 minute or less. A healthy state and an abnormal state (for example, a state of myocardial infarction, an ischemic state, etc.) can be easily distinguished. That is, early detection and estimation of a disease site that does not solve the inverse problem can be performed.

FIG. 22 shows an example of a processed image on the screen of the computer of the biomagnetic field measuring apparatus. The multi-window format allows each processed image to be displayed on its own window. In FIG. 15 to FIG. 21 described above, numerical values are entered in each curve so that the level of the magnetic field strength and the integrated value can be understood. However, on the display, color is classified according to the level of the contour lines, and three-dimensional color display is performed. . At the same time, a waveform (magnetocardiogram) representing a time change of the magnetic field component as shown in FIG. 13 and an electrocardiogram can be displayed, so that a comprehensive analysis relating to a heart disease can be performed.

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. In FIG. 23, MCG is an example of a magnetocardiogram, QRS is a first isointegral diagram obtained by (Equation 35) assuming that an integration range is a period T ₁ during which a QRS wave is generated, and T is an integration range of a T wave. second isointegral of obtained by a period T ₂ for generating (number 35), (T-QRS) indicate each example of the difference between the first and second isointegral. In the display examples on the display shown in FIGS. 22 and 23, three-dimensional color display is performed by color-coding according to the level of contour lines.

In Equations (4) and (35), I ₁ (x, y) and I ₂ (x, y) can be obtained by a simple method without performing integration. That is, I ₁ (x, y) and I ₂ (x, y) are obtained from the following (Formula 42) to (Formula 45), and further, (Formula 36) to (Formula 41) are applied. Tangential component of the magnetic field emanating from the living body (a component parallel to the plane of the living _{body) B x (x, y,} t), B y (x, y, t) in the case of measuring the can (provided that the orthogonal coordinate system (x, y, xy plane parallel to the plane of the living body at a z), and z axis perpendicular to the plane of the living body), 2-dimensional vector magnitude from the square root of the square sum of tangential components B _x and B _y │ B _xy (x, y) | (|| represents an absolute value) is obtained by (Equation 42).

| B _xy (x, y, t ₀ ) | =
{(B _x (x, y, t ₀ )) ² + (B _y (x, y, t ₀ )) ² }
... (Equation 42)
Next, a waveform | B _xy (x, y, t ₀ ) at each point (x, y) at an arbitrary time point
| I ₁ (x, y) is obtained by (Equation 43), and each point (x, y) is obtained by interpolation and extrapolation.
), An isomagnetic field diagram connecting points having the same value of I ₁ (x, y) is obtained, and the isomagnetic field diagram is displayed on the display screen.

I ₁ (x, y) = | B _xy (x, y, t ₀ ) |
… (Equation 43)
When measuring the magnetic field component B _z (x, y, t) perpendicular to the surface of the living body, the rate of change ∂B _z (x, x) of the magnetic field component B _z (x, y, t ₀ ) perpendicular to the x direction is measured. y, t ₀ ) / ∂x and the rate of change ∂B _z (x, y, t ₀ ) / ∂y in the direction of B _z (x, y, t ₀ ) are obtained as shown in (Expression 44). The square root S _t0 (x, y, t) of the sum of squares is obtained.

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 value I ₂ (x, y) of the waveform S _t0 (x, y, t ₀ ) at an arbitrary time is obtained by (Equation 45), and each value is obtained by interpolation and extrapolation. An isomagnetic field diagram connecting points having the same value I ₂ (x, y) at the point (x, y) is obtained, and the isomagnetic field map is displayed on the display screen.

_{I 2 (x, y) =} │S t0 (x, y, t 0) │
… (Equation 45)
In Equations (42) to (45), for example, when the heart is to be measured, the time when the maximum value of each of the Q, R, and S waves when the ventricle contracts is given as t _0. Take. Further, as (t ₀ ) in (Equation 42) to (Equation 45), calculations such as finding a sum or difference including equal weights and a ratio between a plurality of values obtained by taking a plurality of t ₀ are performed. , Interpolation and extrapolation to obtain an isomagnetic field diagram connecting points having the same value of the operation result, and display the isomagnetic field map on the display screen. Even with such a method, it is possible to obtain substantially the same results as the methods using (Equation 4) and (Equation 35) described above.

Q waves MCG patient X obtained by measuring the normal component B _z in a conventional manner, R-wave, the isomagnetic field at the time the extreme values of the S wave appears, FIG. 24 (a), ( These are shown in b) and (c). In FIGS. 24 (a), (b) and (c), the dotted line shows the isomagnetic field map of the magnetic field to be absorbed, the solid line shows the isomagnetic field map of the boiling magnetic field, and the white arrow shows the current dipole of the current dipole. The size and direction are shown. In the isomagnetic field diagrams shown in FIGS. 24A, 24B, and 24C, the position of the current dipole when the current source existing in the heart is assumed to be one is indicated by a white arrow and is superimposed and displayed. are doing. At the time when the extreme value of the Q wave appears as shown in FIG. 24A, a current flows in the lower right direction in the interventricular septum, and the extreme value of the R wave appears as shown in FIG. At this point, a large current flows diagonally downward to the left in the entire left ventricle. Further, as shown in FIG. 24 (c), at the time when the extreme value of the S-wave appears, it can be seen that a current flows diagonally upward and rightward in the direction of the ventricle base, and the depolarization process of the ventricle ends.

Tangential component B _x of a magnetic field generated from the heart of the patient X, the B _y is measured, Q-wave, in the time when the R-wave, each extremum of S-wave occurrence, the tangential component (number 42), (the number FIGS. 25 (a), (b) and (c) show isomagnetic field diagrams synthesized based on 43).

The pattern of FIG. 25A and the pattern of FIG. 24A, the pattern of FIG. 25B and the pattern of FIG. 24B, the pattern of FIG. 25C and the pattern of FIG. Almost match. However, in the pattern at the time when the extreme value of the R wave shown in FIG. 25B appears, the myocardium is active in a wide area, and in the pattern at the time when the extreme value of the R wave shown in FIG. A plurality of unclear current sources can be easily identified, and it can be seen that one of the current sources is located to the left and the other is located below.

Figure 24 (a), (b) , shown in (c), Q waves, using R-wave, the isomagnetic field data of the normal component B _z at the time the extreme values of the S wave appears respectively, FIGS. 26 (a), (b), and (c) show the isomagnetic field diagrams at the time when the extreme values of the Q wave, the R wave, and the S wave appear based on (Equation 44) and (Equation 45). ). Figure 26 (a), (b) , from the results (c), the FIG. 24 (a), the (b), the or isomagnetic field of normal component B _z of (c), the (number 1) A plurality of current sources that are difficult to determine can be identified by the arrow map based on the arrow map. FIG. 26 (a), the pattern of (b), (c), as shown in FIG. 25 (a), (b) , the pattern shown in (c) (tangential components B _x, equal magnetic field B _xy obtained from B _y synthesis (Diagram). This means that (Equation 6) and (Equation 7), or (Equation 32) and (Equation 33) are almost satisfied with actual experimental data.

In FIGS. 24A to 26C, 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 magnetocardiographic measurement, but it goes without saying that the present invention can also be applied to cerebral magnetic field measurement for obtaining a magnetoencephalogram (MEG).

FIG. 27 is a cross-sectional view showing a part of the internal configuration of a dewar for brain magnetic field measurement of a brain magnetic field measurement system for measuring a brain magnetic field. As shown in FIG. 27, when the brain magnetic field is measured, since the head is spherical unlike the chest, the head measurement for incorporating a SQUID magnetometer 103-1, 103-2,. The dewar 102 has a hemispherical bottom surface so as to cover the head 100. The SQUID magnetometers 103-1, 103-2, ..., 103-N are radially arranged along the inner surface of the head measurement dewar 102, and the tip surface (magnetic field measurement surface) of each SQUID magnetometer is a hemispherical surface. Are arranged so as to be substantially parallel to the tangential plane of the. The radius of the hemisphere was set assuming that the brain is a sphere so that the center of the hemisphere substantially coincides with the center of the brain of the head, and this radius was set to about 10 cm so that an adult could measure it. A heat radiation shield member 104 is arranged inside the head measurement dewar 102, and the upper part of the head measurement dewar is sealed by an upper plate 105. The signals detected by the SQUID magnetometers 103-1,..., 103-N are taken out of the head measuring dewar through the signal lines 106-1,.

FIG. 28 is a diagram illustrating the relationship between a magnetic field component and the head that can be measured by the brain magnetic field measurement system illustrated in FIG. 27. The component of the cerebral magnetic field B that can be measured by a QUID magnetometer radially arranged at one of a plurality of positions O ′ above the head is the r direction in polar coordinates (r, θ, φ) with O as the origin. Is the component _Br (normal component) of In FIG. 28, components B _θ and B _φ indicate 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, a normal component _Br is detected by the brain magnetic field measurement system shown in FIG. 27, and a point at which the electroencephalogram which appears approximately 100 msec after the electrical stimulus is maximized is obtained. Find the magnetic field diagram. Figure 29 (a), (b) is a diagram showing an example of such a magnetic field diagram obtained by cerebral magnetic field measurement system shown in FIG. 27, FIG. 29 (a) is a normal component B _r by conventional methods The isomagnetic field map, FIG. 29 (b), is an isomagnetic field map obtained by using the following (Equation 46) of the present invention (displayed on a spherical surface approximating the brain as in a map shown on a globe). 2 shows the intensity distribution of the brain magnetic field.

_St (θ, φ, t) =
_{√ {(∂B r (t)} / ∂θ) 2 + (∂B r (t) / ∂φ) 2}
... (Equation 46)
In the isomagnetic field diagram shown in FIG. 29 (a), the position of the current dipole when the number of current sources existing in the brain is assumed to be one is superimposed and indicated by a white arrow. In FIG. 29 (a), a dotted line shows an isomagnetic field diagram of a magnetic field to be sucked, a solid line shows an isomagnetic field diagram of a magnetic field to be boiled, and outline arrows show the size and direction of a current dipole. Current source was estimated conventionally isomagnetic field of normal component B _r shown in FIG. 29 (a) (current dipole shown by outline arrows), the peak position in isomagnetic field shown in FIG. 29 (b) It can be easily seen directly that it appears corresponding to A. The other configuration of the brain magnetic field measurement system not shown in FIG. 27 is basically the same as the configuration of the biomagnetic field measurement device shown in FIG.

Various algorithms for solving the inverse problem can be considered as a method of analyzing the magnetic field source using the isomagnetic maps relating to 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 is to assume one or two current dipoles as the magnetic field source, and arbitrarily assume the position coordinates where these current dipoles exist as initial conditions. The magnetic field at the measurement point (x, y) of the actually measured magnetic field is calculated on the assumption that the existing current dipole creates a magnetic field represented by the Biot-Savart equation. Calculated magnetic field <B _c (x, y)
> And the actually measured magnetic field <V _m (x, y)> (m = 1, 2,..., M: M is the total number of actually measured magnetic field measurement points). ) Is calculated, the position coordinates of each current dipole are changed, and the minimum value of the evaluation function L is analytically obtained. In (Equation 47), G is a constant, < _ns > is a normal vector or a unit vector in the z direction, and the addition symbol Σ indicates addition for m = 1, 2,..., M.

L = {< _Vm (x, y)>-G ([< _Bc (x, y)>]. _Ns )} ²
… (Equation 47)
However, in the method based on (Equation 47), when analyzing a measurement region with a wide magnetic field, there are cases where the measurement value does not converge to the minimum value. In the present invention, the initial condition of the position and the number of dipoles when calculating the evaluation function L is defined as the peak position in the isomagnetic field map based on (Equation 3), (Equation 34), or (Equation 46). 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. By specifying each peak position on the isomagnetic field map for the magnetocardiogram and brain magnetic field based on (Equation 3), (Equation 34), or (Equation 46) displayed on the display, each The coordinates of the peak position and the number thereof are automatically input to the apparatus as the initial values, the evaluation function L is solved, and a converged magnetic field source analysis result is obtained.

Therefore, the initial value can be set almost unambiguously 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 unlike the prior art. It is possible to efficiently and more accurately solve the inverse problem.

In each figure representing the isomagnetic field map 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 in each figure in accordance with the usual practice in the medical field. It is displayed on the right.

FIG. 4 is a diagram for modeling and analyzing generation of a cardiac magnetic field by a magnetic field generated from a current dipole in an infinite planar conductor in the present invention. FIG. 4 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. ₄ is a diagram showing relative magnetic field strength curves C ₁ and C _{2 in} which B _x and −∂B _Z / ∂x on an infinite plane conductor are normalized by their respective maximum values in the present invention. FIG. ₆ is a diagram showing magnetic field strength curves C ₃ , C ₄ , and C ₅ showing the first, second, and third terms of −∂B _Z (x, 0) / ∂x in the present invention. FIG. ₆ is a diagram showing relative magnetic field strength curves C ₆ , C ₇ , C ₈ , and C _{9 in} which the first and second terms of B _x and ∂B _Z / ∂x are compared after normalization in the present invention. . In the present invention, α = (∇K) _z / K, the first term of ｛−∂B _Z (x, 0) / ∂x｝ / the first term of B _x (x, 0)｝, ｛ -∂B _Z (x, 0) / second term of _{∂x} / {B x (x} , 0) shows each of the magnetic field strength curve C _10, C _11, C ₁₂ of the second term of}. FIG. 1 is a diagram illustrating a schematic configuration of a biomagnetic field measurement apparatus that performs a cardiac magnetic field measurement according to an embodiment of the present invention. FIG. 1 is a diagram illustrating an arrangement configuration of a magnetic field sensor in a biomagnetic field measurement apparatus that performs a cardiac magnetic field measurement according to an embodiment of the present invention. FIG. 1 is a diagram showing a configuration of a magnetic field sensor alone for detecting a normal component of a magnetic field in a biomagnetic field measuring apparatus for performing a cardiac magnetic field measurement according to an embodiment of the present invention. FIG. 1 is a diagram showing a configuration of a magnetic field sensor alone that detects a tangential component of a magnetic field in a biomagnetic field measuring apparatus that performs a cardiac magnetic field measurement according to an embodiment of the present invention. The figure which shows the positional relationship of the arrangement | positioning of the magnetic field sensor in the biomagnetic field measuring apparatus which performs the cardiac magnetic field measurement which implements this invention, and a chest of a human body. FIG. 4 is a diagram showing a waveform representing a time change of a component in each direction of a magnetic field emitted from a healthy person's heart measured at each magnetic field sensor position in the embodiment of the present invention. FIG. 7 is a diagram showing a waveform representing a temporal change of a tangent component (B _x ) regarding two specific channels measured for a healthy person in the embodiment of the present invention. In the embodiment of the present invention, the tangential component B _x of a magnetic field, the B _y were obtained from healthy subjects of the magnetocardiogram waveform measured, Q wave, R wave, in such magnetic field lines at the peak of each wave of the S-wave FIG. FIG. 5 is an isometric diagram obtained from two tangent components detected in a time zone in which a QRS wave of a magnetocardiogram of a healthy person appears in an embodiment of the present invention. FIG. 3 is an isointegral diagram obtained from a normal line segment detected in a time zone when a QRS wave of a magnetocardiogram of a healthy person appears in an embodiment of the present invention. FIG. 4 is an isointegral diagram obtained from two tangent components detected in a time zone in which a T wave of a magnetocardiogram of a healthy person appears in the embodiment 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. 17. FIG. 3 is an isointegral diagram obtained from two tangent components detected in a time zone when a QRS wave of a magnetocardiographic waveform of a patient with myocardial infarction appears in an embodiment of the present invention. FIG. 6 is an isointegral diagram obtained from two tangent components detected in a time zone in which a T wave of a magnetocardiographic waveform of a patient with myocardial infarction appears in the embodiment of the present invention. FIG. 21 is a diagram obtained by subtracting the isometric diagram shown in FIG. 19 from the isometric diagram shown in FIG. 20. The figure which shows the example of the output screen in the personal computer of the biomagnetic field measuring apparatus which performs the cardiac magnetic field measurement which implements this invention. The figure which shows an example of the processed image displayed on the display of the biomagnetic field measuring apparatus of this invention. By a conventional method was obtained by measuring the normal component B _z, Q wave MCG (MCG), R-wave, shows the isomagnetic field at the time the extreme values of the S wave appears. Respectively In the embodiment of the present invention, the tangential component B _x of a magnetic field from the heart, the B _y is measured, Q wave, R wave, at the time when the extreme value of the S wave appears, was synthesized tangential component The figure which shows the _isomagnetic field map of _Bxy . In the embodiment of the present invention, shown in FIG. 24, by using Q-wave, R-wave, the isomagnetic field data of the normal component B _z at the time the extreme values of the S wave appears respectively, (the number of 43 FIG. 47 is a diagram showing isomagnetic field diagrams at each time point, which are obtained based on (Equation 44). FIG. 4 is a cross-sectional view showing a part of the internal configuration of a brain magnetic field measurement dewar of a brain magnetic field measurement system that measures a brain magnetic field in an embodiment of the present invention. FIG. 28 is a diagram illustrating a relationship between a magnetic field component and a head that can be measured by the brain magnetic field measurement system illustrated in FIG. 27. FIG. 28 is a diagram showing an example of an isomagnetic field diagram obtained by the brain magnetic field measurement system shown in FIG. 27.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Magnetic field shield room, 2 ... Examinee, 3 ... Bed, 4 ... Dewa, 5 ... Automatic replenishing device, 6 ... FFL circuit, 7 ... Filter circuit, 8 ... Computer, 10, 10 ', 10 "... Detection coil , 11, 11 ', 11 "... Reference coil, 12, 12', 12"... SQUID, 13... X-component detecting magnetic field sensor, 14... Y-component detecting magnetic field sensor, 20-1, 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, ..., 27-8 ... magnetic field sensor, 30 ... chest, 103-1, 103-2, ..., 103-N ... SQUID magnetometer, 100 ... Head, 102 ... Head measurement dewar, 104 ... Heat radiation shield member, 105 ... Top plate, 106-1, ..., 06-N ... signal line.

Claims (8)

Detecting, with a plurality of SQUID magnetometers arranged at equal intervals in two directions, a temporal change in a magnetic field component of a biomagnetic field emitted from the living body in first and second directions parallel to the surface of the living body; Performing a calculation for obtaining a waveform representing a time change of a value proportional to the square root of the sum of squares of the magnetic field component in the second direction and a calculation for integrating the waveform over a predetermined period to obtain an integrated value; Displaying an isointegral diagram connecting points having the same integral value. 2. The biomagnetic field measurement method according to claim 1, wherein the calculation of the integral value is performed in a plurality of the predetermined periods to determine a plurality of the integral values, and a plurality of the integral values are calculated between the plurality of the integral values. A method for measuring a biomagnetic field, comprising a step of calculating one of a sum and a difference including a ratio and an equal weight. Detecting, with a plurality of SQUID magnetometers arranged at equal intervals in the x and y directions, a time change of a magnetic field component in the x and y directions parallel to the surface of the living body, of the biomagnetic field emitted from the living body; Performing a calculation for obtaining a waveform representing a time change of a value proportional to the square root of the sum of squares of the magnetic field component in the direction and a calculation for integrating the waveform over a predetermined period to obtain an integrated value; Displaying an isointegral diagram connecting the biometrics. 4. The biomagnetic field measurement method according to claim 3, wherein the calculation of the integrated value is performed in a plurality of the predetermined periods to obtain a plurality of the integrated values, and a plurality of the integrated values are calculated between the plurality of the integrated values. A method for measuring a biomagnetic field, comprising a step of calculating one of a sum and a difference including a ratio and an equal weight. Detecting a normal component perpendicular to the surface of the living body of a biomagnetic field emitted from the living body using a plurality of SQUID magnetometers arranged in two directions at equal intervals, and estimating a tangential component in two directions from the normal component A step of calculating an isomagnetic field map at an arbitrary point in time obtained from the tangential components in the two directions, and a step of displaying the isomagnetic field map. Biomagnetic field measurement method. Detecting a normal component perpendicular to the surface of the living body of a biomagnetic field emitted from the living body using a plurality of SQUID magnetometers arranged in two directions at equal intervals, and estimating a tangential component in two directions from the normal component Performing a calculation to perform the biomagnetic field measurement. Equal intervals x, a plurality of SQUID magnetometers disposed in the y direction, and detecting a vertical normal component B _z in the plane of the body of the biomagnetic field generated from a living body, x from the normal component B _z a step of performing a step of performing an operation of estimating the tangential components B _x, B _y of the y-direction, the tangential component B _x, the calculation for obtaining the isomagnetic field at any point in time determined from B _y, wherein like Displaying a magnetic field diagram. Equal intervals x, a plurality of SQUID magnetometers disposed in the y direction, and detecting a vertical normal component B _z in the plane of the body of the biomagnetic field generated from a living body, x from the normal component B _z biomagnetic field measuring method characterized by a step of performing an operation of estimating the tangential components B _x, B _y in the y direction.

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