JP3196771B2 - 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 quant
The present invention relates to a method of measuring a biomagnetic field using a plurality of magnetometers including a um interference device and a method of analyzing a magnetic field source in a biomagnetic measurement apparatus.

[0002]

2. Description of the Related Art The present invention relates to a highly sensitive quantum interference device (SQUID: superconducting device) that converts a biomagnetic field generated by neural activity of the brain of a living body, cardiac muscle activity of the heart, and the like.
quantum interference devi
The present invention relates to a biomagnetic field measurement method and a biomagnetic field measurement apparatus for performing measurement using a plurality of magnetometers comprising ce).

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 the time change of the measured magnetic field component and an isomagnetic field map (contour map) connecting points of the measured magnetic field component having the same intensity at an arbitrary point in time.
In addition, various analysis methods have been proposed to analyze the magnetic field source that is generating 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 normal component (B) of the magnetic field created by the current dipole
_z or _Br ) is a magnetic field source (current dipole)
Is a pattern having a magnetic field starting pole and a magnetic field suction pole at positions separated from the center. The size, position, direction, and the like of the magnetic field source (current dipole) are analyzed based on the magnetic field strength at the two poles and the distance between the two poles.

[0005] The first prior art (H. Hosaka an
d D. Cohen, J .; Electrocardio
l. , 9 (4), 426-432 (1976))
For clarity the direction and intensity of the current in the myocardium, with the isomagnetic field of the measured normal component B _z, as a method for displaying a current source distributed in the myocardium, is defined by (Equation 1) An arrow map has been devised in which a current vector <J (x, y)> is expressed on each measurement point by an arrow. In the following description, parentheses <> indicate that the symbol in <> is a vector, for example, <J> indicates that J is a vector.

[0006]

[Number 1] <J (x, y)> = (∂B z (x, y) / ∂y) <e x> - (∂B z (x, y) / ∂x) <e y> ... ( number 1) (in Equation 1), <e _x> is the x-direction of the 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.

A second prior art (K. Tukada et. Al.)
al. , Revive of the Scient
ific Instruments, 66 (10) 50
In 85-5091 (1995)), in order to visualize a plurality of current sources distributed, rather than measure the normal component (B _z or B _r), perpendicular surfaces of the detection coil with respect to the living body surface arranged to, measures the tangential components B _x and B _y.
It measured tangential components B _x, and a B _y displayed as isomagnetic field for each component. Tangent component B measured in prior art 2
_x, although B _y is considered the influence of the volume current, (Equation 2)
Accordingly the isomagnetic field of a two-dimensional vector magnitude B _xy obtained by combining the measured B _x and B _y at time t, always from a peak immediately above the current dipole can be obtained, there are a plurality of current dipoles In this case, each current dipole can be separated and visualized.

[0008]

| B _xy (x, y, t) | = ((B _x (x, y, t)) ² + (B _y (x, y, t)) ² } (Equation 2) 3 prior art (Y. Yoshida et al.,
Tenth International Confes
rence on Biomagnetism, San
tana Fe, New Mexico, Feb. 20
(1996)), the three planes of the coil were orthogonal to each other.
One of using vector magnetic field sensor comprising a detecting coil to detect the normal component and two tangential components of the biomagnetic field, converts the detection result of the magnetic field components in orthogonal coordinate system, an orthogonal coordinate system of the component B _x, B _y , _Bz are obtained, and isomagnetic field diagrams of the normal component _Bz and the two-dimensional vector intensity _Bxy are displayed.

A fourth prior art (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 Comparison with the diagram is performed.

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

A fifth prior art (TJ Montagu)
e et al. , Circulation 63, N
o. 5, pp1166-1172 (1981))
Isointegral map that integrates the waveform representing the time change of the output of each electrode 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 generated from biomagnetic field", "cardiac magnetic field measurement" means "measurement of magnetic field generated from heart", and " The “magnetocardiogram waveform” means “a waveform represented by a magnetocardiogram (MCG, Magnetocardiogram) obtained by measuring a magnetocardiogram”. “Measurement of brain magnetic field” means “measurement of magnetic field generated from the brain”, and “magnetoencephalogram waveform” means “waveform represented by MEG (Magnetoencephalogram) obtained by brain magnetic field measurement”.

[0013] isomagnetic field for each in the prior art component is characterized respectively, when a single current dipole exists, the isomagnetic field of the normal component B _z, of the current source position,
Size, direction, etc. 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, 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. Further, in the first conventional technique, there is a problem that only an arrow is displayed on each measurement point, and it is difficult to identify a detailed distribution state of the current source.

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 change. In the related art, a diagnosis of a disease or the like is performed by capturing a dynamic change of various information using a large number of figures displayed or output on an apparatus. However, in the related art, a large number of diagrams representing various information are required for diagnosis, and abnormal changes in various information are empirically performed. As described above, in the related art, comprehensive information indicating which magnitude of current flows in which part of the living body, or where an abnormal biocurrent is flowing is displayed as one diagram. Has not been executed. In the body surface electrocardiogram, arbitrary time intervals (Q,
In the isointegral diagram showing the points where the integral values are equal in the period in which the R and S waves are generated, the period in which the S wave is generated in the T wave, etc., it is necessary to have a plurality of equipotential diagrams at each successive time. Instead, heart information can be obtained with one electrocardiogram. 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 on 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 there is a problem that the peak of the current source does not correspond to the peak of the integrated value when integrating the potential. 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 position of the peak 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 due to individual differences in the position, size, and the like of an organ only with the isointegral diagram obtained from the electrocardiogram.

An object of the present invention is to reduce the number of diagrams (maps) much more than required in the prior art.
It is an object of the present invention to provide a biomagnetic field measuring method and a biomagnetic field measuring apparatus which can grasp the entire state of a living body part using the method.

Another object of the present invention is 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. To provide.

[0017]

According to the biomagnetic field measuring method of the present invention, (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 disposed outside the living body, and intersecting the first direction. 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 change rate of the magnetic field component in the first direction in the second direction and the third direction; 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) a quantum interferometer (SQUID), and a plurality of magnetometers arranged outside the living body are used to apply a biomagnetic field generated from the living body to the surface of the living body. A first step of measuring the time change of the magnetic field components in the parallel first and second directions, and 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; A second step, a third step of integrating the waveform obtained in the second step for a predetermined period to obtain an integrated value, and a third step of
And a fourth step of displaying an integrated value obtained in the step of the above step. Further, in the biomagnetic field measuring method having the features of the above (1) and (2), the points where the integral values are equal in the fourth step are connected by interpolation and extrapolation using the above integral values. 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 are performed 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, equal weight, and the like among the plurality of integrated values is performed. 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.

According to the biomagnetic field measuring apparatus of 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, and are arranged outside the living body, In a biomagnetic field measuring apparatus for measuring a biomagnetic field distribution, the magnetometer includes a calculation processing means for performing a process and a display means for displaying a calculation processing result. 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 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 by performing a calculation for obtaining a waveform representing a time change of a value and a calculation for integrating the waveform over a predetermined period to obtain an integrated value, and displaying the integrated value on a display means. Magnetic field measurement device The meter detects the time change of the magnetic field components in the first and second directions parallel to the surface of the living body of the biomagnetic field, and the arithmetic processing means is 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 time change of the value to be performed 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 the same integral value by interpolation and extrapolation. The means integrates the waveform over a predetermined period to obtain an integrated value over a plurality of predetermined periods, obtains a plurality of integrated values, and includes a ratio and an equal weight among the plurality of integrated 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. In the biomagnetic field measurement apparatus of the present invention, the normal (vertical) component and the tangent (parallel) of the magnetic field generated from the heart with respect to the chest surface
Simultaneous display of components is possible. Note that a rectangular coordinate system (x,
y, z), the direction perpendicular to the living body surface 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), 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.

An essential feature of the present invention is that when a direction perpendicular to the surface of a living body is set as the z-axis of rectangular coordinates (x, y, z) and a plane parallel to the surface of the living body is set as an (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 The feature is that it is estimated from the rate of change in the 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 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 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), a tangential component (a component parallel to the surface of the living body) of a magnetic field emitted from the living body at a position (x, y) on the surface of the living body, B _x ( x, y, t), B y (x, y, in the case of measuring the t) (where the orthogonal coordinate system (x, y, z) xy plane parallel to the plane of the living body at the biological of the z axis perpendicular to the plane), the tangential component _{B x (x, y, t} ) and B _y (x, y,
t) From the square root of the sum of squares of two-dimensional vector intensity | B
_xy (x, y) | (hereinafter, | │ represents an absolute value) is obtained by (Equation 3).

[0023]

| B _xy (x, y, t) | = {(B _x (x, y, t)) ² + (B _y (x, y, t)) ² } (Equation 3) , Waveform at an 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) obtains an isointegral diagram connecting points having the same value, and displays the isointegral diagram on the display screen.

[0024]

I ₁ (x, y) = ∫ | B _xy (x, y, t) | dt (Equation 4) Hereinafter, the measured magnetic field component B _z (x,
The estimation of the tangent components B _x and B _y from (y, t) (normal component) will be described.

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 relationship between the current flowing direction and the magnetic field direction is given by
By rotating the tangent vector (B _x , B _y ) of the measured magnetic field by 90 ° in a counterclockwise direction, the current distribution in the living body can be projected on a two-dimensional plane parallel to the surface of the living body to give an overview. _{That, <e x>, <e} y> the x-axis direction, a unit vector in the y-axis direction, in the tangential component B _x in the respective measurement points,
From B _y, seek Bekutoku <J> current shown in (5),
It can be expressed as a distribution (arrow map) of a current vector field at each measurement point (x, y).

[0026]

Equation 5] _{<J> = - B y <} e x> + B x <e y> ... ( 5) On the other hand, when measuring the perpendicular normal component B _z to a biological surface of the magnetic field, by (Equation 1) An arrow map using the expressed current vector is defined (first conventional technique: H,
Hosaka and D.S. Cohen (197
6)).

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

[0028]

B _x = − (∂B _z / ∂x) (Equation 6)

[0029]

Equation 7] _{B y = - (∂B z /} ∂y) ... ( 7) 1, the generation of the magnetic field (cardiac magnetic field) by activity of the heart, the magnetic field generated from a current dipole in the infinite plane conductor It is a figure for modeling and analyzing. In FIG.
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 position indicated by <r (x, y, z)> is the magnetic flux density (magnetic field)
It shows the position vector of the measurement point for measuring <B (r)>.
In the model shown in FIG. 1, the magnetic field <B (r)> generated outside the infinite planar conductor P is Sarvas (reference: Phy).
s. Med. Biol. , Vol. 32, no. 1,1
1-22 (1987)) and is expressed by (Equation 8).

[0030]

Equation 8] <B (r)> = { μ 0 / (4πK 2)} {<Q> × <a> · <e z> ∇K -K <e z> × <Q>} ... ( number 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,
∇ represents grad = (∂ / ∂x, ∂ / ∂y, ∂ / ∂z), <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]

A = | <a> | (Equation 10)

[0033]

[Number 11] K = a (a + <a> · <e z>) ... ( number 11)

[0034]

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

[0035]

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

[0036]

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

[0037]

B _z = {μ ₀ / (4πK ² )} × [{Q _x (y−y ₀ ) −Q _y (x−x ₀ )} (∇K) _z ] (Equation 15) in differentiation in the x direction of the normal component B _Z represented by (Expression 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 )} − (ΔK) _z Q _y ] (Equation 16) The derivative of the normal component B _{Z in} the y direction is (Equation 1)
7).

[0039]

１７B _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]

Α = (∇K) _z / K (Equation 18)

[0041]

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

[0042]

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

[0043]

２１B _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]

２２B _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 normalized by {μ ₀ / (4πK ² )}, which is a common factor, and transformed, and (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]

２４B _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)

[0047]

Equation 25] _{B y = (∇K) y {} Q y (y-y 0) -Q x (x-x 0)} + KQ x ... ( number 25)

[0048]

２６B _Z / ∂y = −2α (∇K) _y ｛Q _x (y−y ₀ ) −Q _y (x−x ₀ )｝ − α KQ _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 24), ∂B _Z
/ Value of ∂x is the term equal to -2α times the tangential components 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 sum of two additional terms.

Here, as shown schematically in FIG. 2, a point <r ₀ (0,0, −z ₀ )>, z inside the infinite planar conductor P
_{At 0} = 0.05 [m], the moment of the current dipole <Q> = (Q _x , Q _y , 0), Q _x = Q _y = 50 [nAm]
Exist, B _x ((Equation 13)) and −∂B _Z / ∂x
((Equation 16)) is compared. x ₀ = y ₀ = y = 0, Q _z =
By 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 … (Formula 27)

[0051]

∂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 is represented by B _x (x, 0) / max |
B _x (x, 0) | and curve C ₂ is ｛−∂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 are both the origin (x =
0) has a peak, and both indicate that the maximum signal can be detected when the measurement point is located immediately above the point where the current dipole exists. Curve C ₂ is better than curve C ₁
Giving a sharper peak than -∂B _Z / ∂x ((Equation 1
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 term and the second term of −∂B _Z (x, 0) / ∂x, respectively.
Item and Item 3 are shown. From the results shown in FIG. 4, the third term is the first
Term and the second term, negligible, −∂B _Z (x, 0) /
It can be considered that the shape of に よ り x is determined by the first and second terms, and (Expression 28) can be approximated to (Expression 29).

[0054]

２９B _Z (x, 0) / ∂x = ｛μ ₀ / (4πK ² )｝ ｛2α (∇K) _x Q _y x−α KQ _y ｝ (Formula 29) FIG. It is a figure which shows the relative magnetic field strength curve which compared the 1st term and the 2nd term of each of (13) and (Equation 16) 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) |, and curve C ₇ is the first term of {− {B _Z (x, 0) / {x}} / max
| ∂B _Z (x, 0) / ∂x |, that is, ｛-2α (∇K) _x
Q _y x} / max | ∂B _Z (x, 0) / ∂x |
Curve C ₈ is the second term of {B _x (x, 0)} / max | B
_x (x, 0) |, that is, {KQ _y } / max | B _x (x,
0) |, and the curve C ₉ is represented by ｛−∂B _Z (x, 0) / ∂x
｝ / 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 distribution of the first and second terms of / ∂x is B
_x (x, 0) is sharper than the distribution of the first and second terms, and the sharpness of the distribution is α = (∇K) _z defined by (Equation 18)
/ K.

[0056] In FIG. 6, the magnetic field curve C ₁₀ is alpha = (∇
The K) _z / K, the magnetic field curve C ₁₁ is - first {(number 28)
The first term の of the term｝ / ｛(Equation 27), that is, 2α (∇K) _x
Q _y x / (∇K) _x Q _y x = 2α, and the magnetic field curve C ₁₂ is −
The second term of {(Equation 28)} / the second 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 ). -∂B _Z (x, 0) / size of ∂x is 2 / in size and the peak point of _{B x (x, 0) (} z-
z ₀ ). (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).

[0057]

-{B _Z (x, 0) / ∂x = ｛μ ₀ / (4πK ² )｝ ｛-2α (∇K) _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.

[0058]

∂B _Z (x, 0) / ∂x = 2αB _x (x, 0) (Equation 31) In general, in (Equation 24), two additional terms other than -2αB _x are obtained. If it is smaller than −2αB _x , it can be considered that Equation 32 is approximately established.

[0059]

Equation 32] .differential.B _Z / ∂x = in -2αB _x ... (number 32) above is a result of studying the relationship between -∂B _Z / ∂x and B _x, the same is -∂B _Z / well established relationship between ∂y and B _y, approximately from (Expression 26) (number 33)
It can be considered that it holds.

[0060]

３３B _Z / ∂y = −2αB _y (Equation 33) From the following (Equation 32) and (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.

A magnetic field component B _z (x, y,
When t) is measured, the rate of change zB _z (x, y, t) / ∂x of B _z (x, y, t) in the x direction and B _z (x, y, t)
方向 B _z (x, y, t) / ∂y
As shown in (Equation 34), the square root 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 3
4) 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) Finds an isointegral diagram connecting points with the same value, and
Display the equal integral diagram on the display screen.

[0063]

I ₂ (x, y) = ∫ | S _t (x, y, t) | dt (Equation 35) The integration range of (Equation 4) and (Equation 35) is, for example, heart Is the object of measurement, the QRS wave (QRS) in which the S wave is generated from the Q wave during the period when the Q, R, and S waves are generated
complex), the period during which a T-wave is generated, and the like. Further, a sum or difference including equal weights (weights are w ₁ and w ₂ ) between a plurality of integrated values obtained by taking a plurality of integration ranges as the integration ranges of (Equation 4) and (Equation 35). , A ratio, and the like, and an isointegral diagram connecting points having the same value of the operation result 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.
Is set, and the period T is calculated according to (Equation 4) or (Equation 35).
_1, I ₁ , _{T 1} (x, y), I ₂ , _{T 1} (x, y
y), the integration value with respect to a period _{T 2 I 1, T2 (x} , y), I 2,
_T2 (x, y) are obtained, and the integrated values I ₁ , _T1 (x, y) are obtained.
y) and the integral values I ₁ , _T2 (x, y) or the integral values I ₂ ,
_The sum I _sum (x, y) including equal weights or the difference I _dif (x, y) between _T1 (x, y) and the integral values I ₂ , _T2 (x, y),
The ratio r (x, y) is expressed by (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 , _{T 1} (x, y) + w ₂ × I ₁ , _{T 2} (x, y) (Expression 36)

[0065]

I _sum (x, y) = w ₁ × I ₂ , _{T 1} (x, y) + w ₂ × I ₂ , _{T 2} (x, y) (Expression 37)

[0066]

I _dif (x, y) = w ₂ × I ₁ , _{T 2} (x, y) −w ₁ × I ₁ , _{T 1} (x, y) (Expression 38)

[0067]

I _dif (x, y) = w ₂ × I ₂ , _{T 2} (x, y) −w ₁ × I ₂ , _{T 1} (x, y) (Expression 39)

[0068]

R (x, y) = I ₁ , _{T 1} (x, y) / I ₁ , _{T 2} (x, y) (Expression 40)

[0069]

R (x, y) = I ₂ , _{T 1} (x, y) / I ₂ , _{T 2} (x, y) (Formula 41) (Formula 36) to (Formula 37), (Formula 38) (Equation 39),
As a result of the calculations of (Equation 40) to (Equation 41), variations in the isointegral diagram due to individual differences are improved, and abnormalities in biological functions due to diseases and the like can be detected.

According to the isointegral diagram obtained in the present invention, the biological phenomena can be analyzed without analyzing the biological phenomena using a large number of maps (maps) representing the state at each time of the living body part required in the prior art. The entire state of the living body part can be grasped by using a much smaller number of maps (maps) than the number of maps (maps) required by the technology. In addition, since the peak position of the isointegral diagram obtained using the tangential component or normal component of the biomagnetic field matches the site where a large amount of current flows in the living body,
From the isointegral diagram, it is possible to determine at which part in the living body a large amount of current flows in an arbitrary time zone. Although the biomagnetic field distribution has a large individual difference, in the present invention, an integrated value at an arbitrary time (period) obtained from a waveform representing a time change of each direction component of the biomagnetic field is used. 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 perpendicular to the surface of the living body
_z (x, y, t) by measuring the, B _x and _{B z (x, y, t} )
In the x direction of the change rate _{∂B z (x, y, t} ) / from ∂x, B _y
The _{B z (x, y, t} ) the direction of the change rate .differential.B _z (x in, y,
t) / ∂y, the background magnetic field (disturbing magnetic field) common to each adjacent measurement point (x, y) is canceled in the x and y directions, respectively. Becomes

[0072]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An orthogonal coordinate system (x, y, z) (magnetic field components are represented by B _x , B _y , B
_z ) and a polar 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) using the chest wall as an 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) (magnetic field components are _Br , _Bθ ,
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, the present embodiment will be described using the rectangular coordinate system (x, y, z), but the polar coordinate system (r,
θ, φ), B _z is B _r and B _x is 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 (FIG. 11)
(X, y, z) is set such that the xy plane is the bed plane as shown in FIG. Above the chest of the subject 2, a plurality of magnetic field sensors in which a SQUID and a detection coil connected to the SQUID are integrated are stored.
The dewar 4 satisfying e is arranged. The liquid He is continuously replenished with the liquid He by the automatic replenishing device 5 outside the magnetic field shield room 1.

The output from the magnetic field sensor is FLL (Flux) which outputs a voltage proportional to the magnetic field intensity detected by the detection coil.
Locked Loop) circuit 6. 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, and AD converted (not shown) by an AD converter (not shown).
It is taken in. In the computer 8, various calculation processes are executed, the calculation process results are displayed on a display, and furthermore,
Output by 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 to detect the tangent component of the magnetic field. 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-
FIG. 8 shows the layout of 8). The magnetic field sensors 9 are installed in the direction perpendicular to the bottom of the Dewar, and the distance between the sensors is set so as to be equally spaced in the x and y directions so as to accurately capture the amount of 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 magnetic field sensors installed 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) is oriented in the z direction. This coil is a combination of two oppositely-oriented coils. The coil closer to the living body is used as the detection coil 10, and the coil 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, a high S / N measurement can be performed by taking the difference between the magnetic fields captured by the two coils.

The primary differential coil is connected to the input coil of the SQUID via the superconducting wiring of the mounting board on which the SQUID 12 is mounted, and the biomagnetic field detected by the coil is connected to the SQUID.
Notify 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 planar coil, and the detection coil 1
0 ′, 10 ″ and reference coils 11 ′, 11 ″ were arranged in one plane, the coil diameter was 20 mm × 20 mm, and the baseline was 50 mm. The coil is SQ like the normal component
UIDs 12 ′ and 12 ″ are connected to the mounting substrate. The x-component detecting magnetic field sensor 13 and the y-component detecting magnetic field sensor 14 are attached to two mutually orthogonal surfaces of a quadrangular prism support, so that x And a magnetic field sensor capable of measuring the y component.The quadrangular 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 defined as the x-axis, and the vertical direction of the body is defined as 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 with the chest 30 are shown in FIG. 12 (a), 12 (b) and 12 (c) show the biomagnetic signal measured in this positional relationship.

FIGS. 12 (a), 12 (b) and 12 (c) show waveforms representing 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 is the time axis, and the vertical axis is the detected magnetic field strength. FIG.
(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 signal is normalized and displayed with the maximum value of the absolute value of the channel having the highest signal strength.

The dashed line and the solid line shown in FIG. 13 indicate the tangent components (B
_The waveform representing the time change of _x ) is shown by a solid line and a dotted line. The time points at which the peaks (extreme values) of the Q wave, R wave, and S wave in the time zone T ₁ during which the QRS wave in which the ventricle of the heart is depolarized appears are shown in FIG. 13 as t _Q , t _R , and t _s , respectively. Indicated by
Also, the time zone T in which the T wave, which is the process of repolarization of the heart, appears
_2, and shows the time at which gives a peak (extreme value) at t _T.

In FIG. 13, a P wave indicates atrial excitation (depolarization), a QRS wave composed of Q, R and S waves indicates ventricular excitation (depolarization). The wave is a gradual shake that appears following the QRS wave, indicating cardiac 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.

FIGS. 14A, 14B and 14C show t _Q ,
FIG. 4 shows an isomagnetic field diagram in which points having equal strengths of the magnetocardiograms at times t _R and t _s are connected by lines. FIG. 14 (a), (b), (c)
Is represented by | B _xy (x, y, t) | in (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. Further, FIG.
Arrows in (b) and (c) indicate two-dimensional current vectors when it is assumed that current sources at 64 measurement points generate a magnetic field at each measurement point. With this current vector, the current direction and distribution in the heart can be estimated. In each of FIGS. 14A, 14B, and 14C, the horizontal axis x and the vertical axis y indicate coordinates where the magnetic field sensor is arranged. FIG.
As shown in (a), at the time of the peak of the Q wave, the current flowing in the heart flows in the lower right direction in the septum of the ventricle, and as shown in FIG. As a whole, a large current flows obliquely downward, and as shown in FIG.
It can be seen that at the peak of the S-wave, a current flows in a diagonally upper left direction in the direction of the base of the ventricle, and the depolarization process of the ventricle ends. Thus, it can be seen that the active site and current direction in the heart at each time can be visualized by the isomagnetic field diagrams of FIGS. 14 (a), (b) and (c).

[0083] Figure 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 obtained from B _y │ B _xy
(X, y, t) | for each point (x, y), (Equation 4)
Is an integral diagram obtained by integrating the points and connecting points having the same integral value. The x-axis and the 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 isointegral diagram indicate the integrated values of the curves. From FIG. 15, it can be seen that most of the current flowing to the myocardium during the time zone 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 the state shown in FIGS. 12 (a), (b) and (c).
For the same healthy subjects and were determined the data of FIG. 15, at the normal line B _z at each point (x, y) measured from,
Seeking S _t (x, y, t) by equation (34), the time period T ₁ of the QRS wave, a like integral 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 arranged on the surface of the living body. FIG.
Numerals shown in the vicinity of the black circles of the curves in FIGS. 6 to 21 indicate the integral values of the curves.

[0085] the tangential component of the magnetic field shown in FIG. 15 B _x, and isointegral obtained from B _y, the pattern of isointegral obtained from normal component B _z of the magnetic field shown in FIG. 16 to be consistent found . This match is expressed by (Equation 6) and (Equation 7), or (Equation 3)
It means that 2) and (Equation 33) are almost satisfied with actual experimental data.

[0086] Figure 17, the same healthy subjects and were determined to 15, the two tangential components B _x detected at the time slot T ₂ of the T-wave, two-dimensional vector magnitude │ obtained from B _y B _xy
(X, y) | is an integral diagram obtained by integrating (Equation 4) for each point (x, y) and connecting points having the same integral value. In FIG. 17, 1e + 003 indicates 1000.

FIG. 18 shows (Equation 4) for the time zone T _2.
And integral value of a contour plot representative of the difference (number 37) of the integrated value of (number 4) for the period zone T ₁ which QRS wave occurs. That is, FIG. 18 is based on the isometric diagram shown in FIG.
3 is a diagram obtained by subtracting an equal integral diagram shown in FIG. Time zone T of T wave
_2/5 is longer than the time period T ₁ of the QRS wave. Also, FIG.
The pattern 7 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.
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 related to the measurement of the cardiac magnetic field in patients with myocardial infarction. FIG.
Is isointegral obtained in the same manner as in FIG. 15 for the time period T ₁ of the QRS wave, FIG. 20, isointegral obtained in the same manner as in FIG. 17 for the time period T ₂ of the T-wave, Fig. 21, integral values for the time slot 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), was obtained in the same manner as FIG. 18 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 integral values of the curves, and the numerical values shown in the vicinity of the black circles of the curves in FIG. Is shown.

The equal integral diagram in the time zone T ₁ shown in FIG.
The pattern is not so different from the equal integration diagrams shown in FIGS. 15 and 16, and it can be seen that a large amount of current flows in the left ventricle.
However, isointegral in the time zone T ₂ shown in FIG. 20, FIG. 1
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 to the heart is significantly different 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 significantly different from the contour map of a healthy person shown in FIG. 18 having a positive value as a whole.
_In Figure ₂ , it can be clearly seen that the current flowing to the heart is 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 discomfort within 1 minute or less. With time, a healthy state and an abnormal state (for example, a state of myocardial infarction, an ischemic state, etc.) can be easily distinguished. That is,
This enables early detection and estimation of disease sites that do not solve the inverse problem.

FIG. 22 shows an example of a processed image on a computer screen 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. On the display, the 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 on 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 Figure 23, the MCG is MCG example, the first isointegral obtained by QRS is set to a period T ₁ of occurrence of QRS wave integration range (number 35), T is the integration range of the 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 example 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), I ₁ (x, y)
₂ (x, y) can also be obtained. That is, from the following (Equation 42) to (Equation 45), I ₁ (x, y) and I ₂ (x, y)
And (Equation 36) to (Equation 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).

[0094]

│B _xy (x, y, t ₀ ) │ = √ ｛(B _x (x, y, t ₀ )) ² + (B _y (x, y, t ₀ )) ² … (number 42) Then, for each point (x, y), the waveform at any time |
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 diagram connecting points having the same value of (x, y) is obtained, and the isomagnetic field diagram is displayed on the display screen.

[0095]

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 Include the rate of change ∂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,
y, t ₀ ) direction change rate ∂B _z (x, y, t ₀ ) / ∂y
And the square root S of the sum of squares as shown in (Equation 44)
_{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, the waveform S at each point (x, y) 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 Find an isomagnetic field map connecting points where (x, y) have the same value.
The isomagnetic field map is displayed on the display screen.

[0097]

I ₂ (x, y) = | S _t0 (x, y, t ₀ ) | (Expression 45) Note that, in Expressions 42 to 45, as t ₀ , for example, heart Is taken as a measurement target, a time point at which the maximum value of each of the Q, R, and S waves when the ventricle contracts is taken. Further, as (t ₀ ) in (Equation 42) to (Equation 45), an operation 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 is performed. , Interpolation and extrapolation to obtain an isomagnetic field map 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.

[0098] Q-wave of MCG conventional methods patients obtained by measuring the normal component B _z by X, R-wave, the isomagnetic field at the time the extreme values of the S wave appears, FIG. 24 (a ), (B), (c)
Shown in 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. 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 when the number of current sources existing in the heart is assumed to be one is superimposed and indicated by a white arrow. FIG.
As shown in (a), when the extreme value of the Q wave appears,
A current flows in the lower right direction in the interventricular 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 entire left ventricle in a diagonally lower left direction. FIG. 24 (c)
As shown in FIG. 7, at the time when the extreme value of the S-wave appears, a current flows obliquely to the upper right in the direction of the ventricle base, and the depolarization process of the ventricle ends.

[0099] the tangential component of the magnetic field generated from the heart of the patient X B _x, the B _y is measured, Q wave, R wave, at the time of the extreme value of the S wave appears, the tangential component (number 42) , (Equation 43)
Fig. 25 (a),
(B) and (c) show.

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. , Are almost the same. However, FIG.
In the pattern at the time when the extreme value of the R-wave appears as shown in FIG. 24, the myocardium is active in a wide area, and a plurality of currents that were not clear in the pattern at the time when the extreme value of the R-wave in FIG. The sources can be easily identified, and it can be seen that one of the current sources is to the left and the other is below.

The Q shown in FIGS. 24 (a), (b) and (c)
Normal component B at the time when each extreme value of wave, R wave and S wave appears
_{Using the isomagnetic} field map data of _z ,
The isomagnetic field diagram at the time when the extreme values of the Q wave, R wave, and S wave appear based on (Equation 45) is shown in FIG.
(B) and (c) show. FIGS. 26 (a), (b), (c)
From the results shown in FIG. 24 (a), (b), and isomagnetic field of normal component B _z of (c), the plurality of current source which was difficult to determine the arrow map that is based on equation (1) Can be determined. The patterns of FIGS. 26 (a), (b) and (c) are shown in FIG.
5 (a), (b) and (c) show patterns (tangent component B
_x, it is found that equivalent to isomagnetic field) of the resulting B _xy from B _y synthesis. This means that (Equation 6) and (Equation 7),
Or, it means that (Equation 32) and (Equation 33) are almost satisfied with 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 magnetocardiogram, but it is needless to say that the present invention can be applied to the measurement of the magnetoencephalogram (MEG).

FIG. 27 is a 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 SQUID
.., 103-N, the bottom surface of the head measurement dewar 102 is formed as a hemisphere so as to cover the head 100. SQUID magnetometer 103
, 103-N are radially arranged along the inner surface of the head measurement dewar 102, and
The tip surface (magnetic field measurement surface) of the ID magnetometer is disposed so as to be substantially parallel to the tangent surface of the hemisphere. The radius of the hemisphere was set on the assumption 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 even adults could measure it. A heat radiation shield member 104 is disposed inside the head measurement dewar 102, and an upper portion of the head measurement 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 measuring dewar through the signal lines 106-1,.

FIG. 28 is a view for explaining the relationship between the magnetic field component and the head which can be measured by the brain magnetic field measurement system shown in FIG. The component of the cerebral magnetic field B measurable by the QUID magnetometer radially arranged at one of a plurality of positions O ′ above the head is the r direction in the polar coordinates (r, θ, φ) with O as the origin. Is a 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 cerebral magnetic field measurement system shown in FIG. Find the magnetic field diagram. FIG. 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 isomagnetic field of normal component B _r by conventional methods, FIG. 29 (b ) Shows the intensity distribution of the brain magnetic field displayed on a spherical surface approximating the brain, such as a map shown on a globe, obtained by using the following (Equation 46) of the present invention. ).

[0106]

S _t (θ, φ, t) = √ ｛(∂B _r (t) / ∂θ) ² + (∂B _r (t) / ∂φ) ² … (Formula 46) In the isomagnetic field diagram shown in 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. FIG. 29 (a)
In, 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 arrows show the size and direction of the current dipole. FIG.
9 the current source has been estimated conventionally isomagnetic field of normal component B _r shown in (a) (current dipole shown by a white arrow) is,
In the isomagnetic field diagram shown in FIG. 29 (b), it can be easily seen directly that it appears corresponding to the peak position A. Note that FIG.
The other configuration of the brain magnetic field measurement system not shown in FIG. 7 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 often used in practice is to assume one or two current dipoles as magnetic field sources, and arbitrarily assuming 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 current dipole existing at each position coordinate generates a magnetic field represented by the Biot-Savart equation. The calculated magnetic field <B _c (x, y)> and the actually measured magnetic field <V _m (x, y)>
(M = 1, 2,..., M: where M is the total number of measurement points of the actually measured magnetic field) 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 obtained analytically. (Equation 47)
, G is a constant, < _ns > is a unit vector in the normal direction or z direction, and the addition symbol Σ indicates addition for m = 1, 2,..., M.

[0108]

L = {<V _m (x, y)> − G ([<B _c (x, y)>] · _ns )} ² (Equation 47) However, based on (Equation 47) In the method, when analyzing a wide measurement region of a 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 at the time of 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 condition and solving the evaluation function L, the magnetic field source analysis always converges. Displayed on the display,
The coordinates of each peak position and the number of the peak positions are automatically specified by designating each peak position on the isomagnetic field map for the cardiac magnetic field and brain magnetic field based on (Expression 3), (Expression 34), or (Expression 46). Is automatically input to the apparatus as the above initial value, 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 as in the prior art. It is possible to solve the inverse problem efficiently and more accurately.

In each of the figures 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 displayed in accordance with the usual practice in the medical field. It is displayed on the right side of each figure.

[0111]

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, based in B _xy in the prior art shown in equation (2) An isomagnetic field diagram equivalent to the isomagnetic 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 diseases related to the heart, such as discovery of myocardial infarction, ischemia, etc., discovery of arrhythmic locations, discovery of myocardial hypertrophy, evaluation of changes in myocardial condition before and after surgery, It is easy to check the status.

[Brief description of the drawings]

FIG. 1 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. 2 is a diagram showing a schematic position of a moment of a current dipole existing inside an infinite planar conductor in the present invention.

FIG. 3 is a diagram showing relative magnetic field strength curves C ₁ and C _{2 in} which B _x and −ΔB _Z / Δx on an infinite planar conductor are normalized by respective maximum values in the present invention.

[4] In the present _{invention, -∂B Z (x, 0)} / first term of ∂x, paragraph 2, the magnetic field intensity curve C ₃ showing a third term, C _4,
Shows the C _5.

FIG. 5 shows relative magnetic field strength curves C ₆ , C ₇ , C ₈ , C ₈ in which the first and second terms of B _x , ∂B _Z / ∂x are compared after normalization. shows a _9.

FIG. 6 is a graph showing a relation between α = (∇K) _z / K and ｛−∂ in the present invention.
B _Z (x, 0) / the first term of ∂x} / {first term of _{B x (x, 0)}} , {- ∂B Z (x, 0) / second term of ∂x} / { B _x
The magnetic field strength curves 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 a magnetic field sensor in a biomagnetic field measuring apparatus that performs a cardiac magnetic field measurement according to the present invention.

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

FIG. 11 is a diagram showing a positional relationship between an arrangement of a magnetic field sensor and a chest of a human body in a 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 healthy person's heart measured at each magnetic field sensor position in the embodiment of the present invention.

FIG. 13 is a diagram illustrating a tangential component (B _x ) of two specific channels measured for a healthy person in the embodiment of the present invention.
FIG. 3 is a diagram showing a waveform representing a time change of the waveform.

FIG. 14 shows a tangential component B of a magnetic field in the embodiment of the present invention.
_x, to obtain a B _y from healthy subjects of the magnetocardiogram waveform measured, Q wave, R
FIG. 3 is an isomagnetic field diagram at the peak of each of the wave and the S wave.

FIG. 15 is an isointegral 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 the embodiment of the present invention.

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

FIG. 17 is an isointegral graph 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. 19 is an isometric diagram obtained from two tangent components detected in a time zone in which a QRS wave of a magnetocardiographic waveform of a patient with myocardial infarction appears in an embodiment of the present invention.

FIG. 20 is a graph showing the detection of a T-wave of a magnetocardiographic waveform of a patient with a myocardial infarction in a time period when the T-wave appears in an embodiment of the present invention.
Isointegral diagram obtained from two tangent components.

FIG. 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 a biomagnetic field measurement apparatus for performing cardiac magnetic field measurement according to the present invention.

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.

FIG. 24 is a diagram showing an isomagnetic field diagram 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 according} to the conventional method.

[Figure 25], 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, at the time of the Q wave, R wave, the extreme values of the S-wave occurrence, tangent B that synthesized components
_The figure which shows the _isomagnetic field map of _xy .

FIG. 26 is a diagram showing an embodiment of the present invention;
Component B _z at the time when the extreme values of the wave, R wave and S wave appear
(Equation 43)
The figure which shows the iso-magnetic-field map in each time calculated | required based on (Equation 44).

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 in an embodiment of the present invention.

28 is a view for explaining the relationship between a magnetic field component and the head which can be measured by the brain magnetic field measurement system shown in FIG. 27.

FIG. 29 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 symbols]

1: magnetic field shield room, 2: subject, 3: bed, 4
... Dua, 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 ... Magnetic field sensor for detecting x component, 14 ... Magnetic field sensor for detecting y component, 20-1 and 20-1
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: heat radiation shield member, 105:
.., 106-N... Signal lines.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hiroyuki Suzuki 882 Ma, Hitachinaka-shi, Ibaraki Pref.Hitachi, Ltd.Measurement Equipment Division (72) Inventor Shoji Kondo 882-Homo, Hitachinaka-shi, Ibaraki Pref. (72) Inventor Yasuaki Omiyama 882 Ma, Hitachinaka-shi, Ibaraki Pref.Hitachi, Ltd.Measurement Instruments Division (72) Inventor Kenichi Okajima 1-280, Higashi-Koikekubo, Kokubunji-shi, Tokyo Within Central Research Laboratory, Hitachi, Ltd. 56) References JP-A-8-266499 (JP, A) JP-A-6-121776 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 5/05

Claims (4)

(57) [Claims] 1. A plane parallel to a living body surface is defined as an x, y plane of rectangular coordinates, and a direction perpendicular to the biological surface is defined as az axis of the rectangular coordinates, and is detected by a plurality of magnetometers comprising a quantum interference device (SQUID). And the sum of squares of the rate of change in the x and y directions of the magnetic field component B _z (x, y, t) of the biomagnetic field emitted from the living body perpendicular to the surface of the living body S (x, y, t) = ｛ (∂B _z (x, y, t) / ∂x) ²
+ (∂B _z (x, y, t) / ∂y) ²を a value proportional to the square root of ² ，, and an isomagnetic field diagram connecting points having the same value at any time t, A step of displaying an isomagnetic field map on a display, wherein the number of peaks and the position data of the peaks in the isomagnetic field map are used to solve an inverse problem for estimating the position and intensity of a magnetic field source in the living body. A method of inputting the number of sources and an initial value of the position of the magnetic field source. 2. A plane parallel to the living body surface is defined as an x, y plane of rectangular coordinates, and a direction perpendicular to the biological surface is defined as az axis of the rectangular coordinates, and is detected by a plurality of magnetometers comprising a quantum interference device (SQUID). And the sum of squares of the rate of change in the x and y directions of the magnetic field component B _z (x, y, t) of the biomagnetic field emitted from the living body perpendicular to the surface of the living body S (x, y, t) = ｛ (∂B _z (x, y, t) / ∂x) ²
+ ({B _z (x, y, t) / {y) ² } A step of obtaining a value proportional to the square root of ² ｝ and obtaining an isomagnetic field map connecting points having the same value at an arbitrary time t Displaying the isomagnetic field map on a display;
Automatically inputting the coordinates and the number of each peak position of the isomagnetic field map specified on the isomagnetic field map displayed on the display as initial conditions; Assuming the position coordinates where the dipoles are present, assuming that the current dipoles present at the respective position coordinates generate a magnetic field represented by the Biot-Savart equation, a plurality of measured biomagnetic fields (m = 1, 2) ,…,
M), the magnetic field <B _c (x, y) at the position (x, y)
y)>, and the measured biomagnetic field <V _m (x,
y)> and the calculated coordinates of the magnetic field <B _c (x, y)> are used to change the position coordinates where each of the current dipoles are present to analyze the minimum value of the evaluation function. Analyzing the magnetic field source in a predetermined manner, and displaying the analysis result of the magnetic field source on the display. 3. Assuming that the head of the living body is a sphere, the head is detected by a plurality of SQUID magnetometers whose tips are arranged so as to be substantially parallel to a tangent surface of a hemisphere having a radius of the sphere. A magnetic field component in the r direction in polar coordinates (r, θ, φ) with the center of the sphere as the origin, and a normal component B _r (θ perpendicular to the tangent plane of the biomagnetic field generated from the brain of the living body , Φ,
t) the sum of squares of the rate of change in the θ and φ directions S (θ, φ, t) = ｛(∂B _r (θ, φ, t) / ∂θ) ²
+ (∂B _r (θ, φ, t) / ∂φ) ²求 め to obtain a value proportional to the square root of ² ，, and at any time t to obtain an isomagnetic field map connecting points having the same value, A step of displaying an isomagnetic field map on a display, wherein the number of peaks and the position data of the peaks in the isomagnetic field map are used to solve an inverse problem for estimating the position and intensity of a magnetic field source in the living body. A method of inputting the number of sources and an initial value of the position of the magnetic field source. 4. Assuming that the head of the living body is a sphere, the head is detected by a plurality of SQUID magnetometers whose tips are arranged substantially parallel to a tangent surface of a hemisphere having a radius of the sphere. A magnetic field component in the r direction in polar coordinates (r, θ, φ) with the center of the sphere as the origin, and a normal component B _r (θ perpendicular to the tangent plane of the biomagnetic field generated from the brain of the living body , Φ,
t) the sum of squares of the rate of change in the θ and φ directions S (θ, φ, t) = ｛(∂B _r (θ, φ, t) / ∂θ) ²
+ (∂B _r (θ, φ, t) / ∂φ) ²求 め to obtain a value proportional to the square root of ² ，, and at any time t to obtain an isomagnetic field map connecting points having the same value, Displaying the isomagnetic field map on a display, and automatically inputting the coordinates and the number of each peak position of the isomagnetic field map specified on the isomagnetic field map displayed on the display as initial conditions And the current dipole present at each of the position coordinates is assumed to generate a magnetic field represented by the Biot-Savart equation, assuming the position coordinates of the current dipole assumed as the magnetic field source. The magnetic field <B _c (θ, φ)> at the position (θ, φ) at a plurality of (m = 1, 2,..., M) where the magnetic field was measured,
Using the evaluation function represented by the difference between the measured biomagnetic field <V _m (θ, φ)> and the calculated magnetic field <B _c (θ, φ)>, the position coordinates where each of the current dipoles are present And analyzing the magnetic field source by analytically obtaining the minimum value of the evaluation function, and displaying the analysis result of the magnetic field source on the display.