JP3977725B2 - Phantom of the magnetoencephalograph - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a phantom in which a simulated current dipole is fixedly arranged in a spherical conductor model with uniform conductivity, which is used for evaluation and experiments of a magnetoencephalograph.
[0002]
[Prior art]
[0003]
[Non-Patent Document 1]
Proceedings of the 7th Annual Meeting of the Biomagnetic Society of Japan Vol.5, No.1,1992.6 p.218-p.219
"Signal source estimation accuracy of multi-channel SQUID system"
[Non-Patent Document 2]
Special issue of Japanese Society for Biomagnetics
Vol.9, No.1,1996 Proceedings of the 11th Annual Meeting of the Biomagnetic Society of Japan p.62-p.63
"Evaluation of dipole estimation accuracy using spherical phantom"
[0004]
FIG. 2 is a schematic diagram for explaining the concept of magnetoencephalogram measurement. When nerve cells 1 in the cerebral cortex are stimulated to be electrically activated, an intracellular current 2 flows. Reference numeral 3 denotes magnetic lines generated through the head surface 4 by the current 2, and a magnetic field 5 is generated on the head surface 4 by the magnetic lines 3. When this magnetic field distribution is measured in the vicinity of the head surface 4 with a high-sensitivity magnetometer such as a SQUID (Superconducting Quantum Interference Device), the active site of the nerve cell 1 can be estimated conversely.
[0005]
Intracellular current 2 is a state in which a pair of current source and sink is close to each other. Actually, in addition to this current 2, what is called extracellular current 6 is the return of intracellular current 2. Current (distributed current, secondary current) flows widely distributed throughout the cerebrum. FIG. 3 is a schematic diagram showing the distribution of extracellular current 6 flowing in the brain.
[0006]
The intracellular current 2 is often compared to a current dipole. An infinitely small positive electrode and an infinitely small negative electrode are arranged at an infinitely small distance, and an infinitely large current flows between the positive and negative electrodes as a current dipole. I'm calling. That is, it is a state in which a pair of spring and suction touches at a distance close to innocence.
[0007]
A device in which a current dipole is arranged in a spherical conductor with uniform conductivity is called a spherical model. Since it cannot physically exist only by current source and sink, a return current widely distributed in the spherical conductor flows. This situation is similar to the relationship between the intracellular current and the extracellular current.
[0008]
When estimating the source of the magnetic field from the measurement result of the magnetoencephalograph, it is often estimated assuming this spherical model. Therefore, if there is an accurately processed sphere model (called phantom), it is possible to check whether the magnetic field source estimation method is correct, or to evaluate whether the magnetoencephalograph itself is measuring correctly. .
[0009]
FIG. 4 is a schematic diagram showing a conventional phantom structure. Reference numeral 7 denotes a spherical container formed of a transparent resin material having a diameter of 100 mm to 150 mm, which imitates the brain, and 8 is a physiological saline filled in the spherical container 7.
[0010]
A pair of electrodes 9 a and 9 b having a distance of about 1 cm are a spring electrode and a suction electrode forming a pseudo current dipole, and are fixedly arranged at a predetermined predetermined position in the spherical container 7. A finite current, for example, an alternating current of about 20 μA flows between the electrodes.
[0011]
Reference numeral 10 denotes a two-core stranded lead wire that supplies a sinusoidal alternating current to the electrodes 9a and 9b from a power source (not shown) provided outside the spherical container 7. The reason for using a stranded wire is to minimize the magnetic field emitted from the lead wire. Considering the same effect, a parallel proximity wire or a coaxial cable may be used as the two-core stranded wire.
[0012]
In order to accurately fix and arrange the electrodes 9a and 9b and the lead wire 10 at predetermined positions in the spherical container 7 filled with the physiological saline 8, some support means is necessary. Usually, a columnar support member that guides the lead wire to the electrode is installed in the spherical container 7.
[0013]
[Problems to be solved by the invention]
If the spring electrode 9a and the suction electrode 9b are supported by a support member having a large volume, the distribution of the return current (distributed current, secondary current) is disturbed. As a result, there is a problem that the position of the electrode is dull and accurate measurement cannot be performed, or the position accuracy of the electrode is not accurate.
[0014]
If the strength of the support member is restricted, the type and weight of the lead wire are also restricted, which becomes an obstacle to design for minimizing the magnetic field emitted from the lead wire.
[0015]
Furthermore, in a phantom having a conventional structure, the return current (distributed current, secondary current) flows through an electrolyte such as physiological saline, so electrolysis occurs according to the total amount of the flowed electric charge, and the resistance of the electrolyte is high. As a result, there is a problem that the current distribution changes and the magnetic field distribution is disturbed.
[0016]
FIG. 5 is a transition diagram for explaining disturbance of the magnetic field distribution due to electrolysis. The transition shows how the magnetic field distribution changes over time. The current flowing through the electrode is a sine wave, and five times (t1, t2, t3, t4, t5) when the phase becomes (−π / 4, −π / 8, 0, π / 8, π / 4) The magnetic field distribution is shown. The upper row (A) shows the phantom measurement results according to the prior art, and the lower row (B) shows the ideal magnetic field distribution.
[0017]
Focusing on the position of the maximum and minimum centers of the magnetic field, in the ideal case, the two centers should not move because the position and orientation of the electrodes do not change. You can see that they rotate clockwise to each other. This is because the return current distribution (distributed current, secondary current) varies due to electrolysis.
A first object of the present invention is to provide a phantom that solves the problems caused by the conventional phantom structure, such as unstable electrode position or inaccurate position of electrode installation.
[0019]
A second object of the present invention is to provide a phantom that solves the problem that the return current distribution (distributed current, secondary current) changes due to electrolysis, which has occurred in the conventional phantom structure.
[0020]
[Means for Solving the Problems]
The configuration of the present invention for achieving such an object is as follows.
(1) In a phantom of a magnetoencephalography device in which a simulated current dipole is fixedly arranged in a spherical conductor with uniform conductivity,
A portion of the simulated current dipole that transmits a return current is formed of a conductive solid.
(2) The phantom of the magnetoencephalogram measuring apparatus according to claim 1, wherein the conductive solid is formed of a member containing carbon in a foamable resin.
(3) The phantom of the magnetoencephalogram measuring apparatus according to claim 1, wherein the conductive solid is formed of a member in which a metal powder is included in a paste.
(4) The phantom of the magnetoencephalogram measuring apparatus according to claim 1, wherein the conductive solid is formed of a member obtained by solidifying conductive fine particles.
(5) The phantom of the magnetoencephalogram measuring apparatus according to any one of claims 1 to 4, wherein the conductive solid is formed by dividing a spherical conductive member into a plurality of pieces and sandwiching the simulated current dipole. .
(6) The conductive solid is formed by solidifying a hollow spherical mold material in which the simulated current dipole is installed at a predetermined position inside by filling a fluid conductive member. The phantom of the magnetoencephalogram measuring apparatus in any one of.
(7) The phantom of the magnetoencephalogram measuring apparatus according to any one of claims 1 to 6, wherein a lead wire for supplying a current to the simulated current dipole is formed of a two-core stranded wire.
(8) The phantom of the magnetoencephalogram measuring apparatus according to any one of claims 1 to 6, wherein a lead wire for supplying a current to the simulated current dipole is formed by a parallel proximity wire.
(9) The phantom of the magnetoencephalogram measuring apparatus according to any one of claims 1 to 6, wherein a lead wire for supplying current to the simulated current dipole is formed of a coaxial cable.
(10) The phantom of the magnetoencephalogram measuring apparatus according to any one of claims 1 to 6, wherein a lead wire for supplying a current to the simulated current dipole is formed of a printed board or a flexible printed board.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a phantom of a magnetoencephalography measuring apparatus to which the present invention is applied. The same elements as those described in the conventional structure of FIG.
[0022]
The feature of the present invention is that, in a phantom in which a simulated current dipole is fixedly arranged in a spherical conductor having a uniform conductivity , a portion that transmits a return current of the simulated current dipole , which corresponds to a conventional physiological saline portion, is made conductive. It is in the point formed with a solid.
[0023]
A specific configuration example will be described with reference to FIG. (A) is the figure which looked at the spring electrode 9a and the suction electrode 9b which comprise the pseudo-current dipole fixed in the spherical conductor from the front, (B) is the side view seen from the X direction.
[0024]
Reference numeral 11 denotes a spherical conductive solid, which is made of hemispherical conductive solids 11a and 11b as shown in (B), and includes a spring electrode 9a, a suction electrode 9b, and a lead wire 10 arranged at predetermined positions. Is sandwiched and fixed as shown by arrows P and P ′.
[0025]
Reference numerals 12a and 12b are guide grooves formed on the adhesively facing surfaces of the hemispherical conductive solids 11a and 11b, and the shape of the grooves matches the shape of the source electrode 9a, the suction electrode 9b, and the lead wire 10. Is formed.
[0026]
The spring electrode 9a and the suction electrode 9b have a distance of about 1 cm, as in the conventional phantom, and a finite current, for example, an AC current of about 20 μA flows between the electrodes via the lead wire 10. . As for the lead wire 10, similarly to the conventional phantom, a two-core stranded wire, a parallel proximity wire, a coaxial cable, or the like can be used.
[0027]
When the phantom of the present invention is energized, a finite current flows out from the spring electrode 9a, which flows and distributes in the spherical conductive solid 11 sphere, and returns to the suction electrode 9b. That is, both a portion simulating a current dipole and a portion simulating a return current (distributed current, secondary current) can be generated.
[0028]
The embodiment of FIG. 1 has a structure in which an electrode is sandwiched between two conductive solid hemispheres. However, when making a phantom having a plurality of simulated current dipoles, an arbitrary number of blocks of conductive solid can be formed. It is also possible to divide the electrodes into pieces and support them so that they form a sphere in an assembled form.
[0029]
The conductive solid 11 is formed by processing a solid conductive member, filling a hollow spherical mold material with a simulated current dipole at a predetermined position inside, and solidifying by filling the fluid conductive member. You may make it do.
[0030]
The conductive solid 11 may be any member as long as it has conductivity, such as carbon containing foamable resin, metal powder contained in paste, or conductive fine particles solidified. Is available.
[0031]
According to the configuration of the present invention, there is essentially no support member that holds the electrode and guides the lead wire as in the prior art, so there is no restriction on the shape and weight of the lead wire, and the lead of the two-core stranded wire Since any wire, parallel proximity wire, coaxial cable, printed circuit board, flexible printed circuit board or the like can be selected, the design for minimizing the magnetic field emitted from the lead wire becomes easy.
[0032]
According to the configuration of the present invention, since the spherical conductor simulating the brain is not a physiological saline like a phantom but a conductive solid, distribution of return current by electrolysis (distributed current, secondary current) There is essentially no disturbance.
[0033]
【The invention's effect】
As is apparent from the above description, according to the present invention, since the electrode forming the simulated current dipole is fixed in the conductive solid, the electrode position is not stable or the position accuracy of the electrode installation is not The problems of conventional phantoms can be solved.
[0034]
In addition, since no electrolyte is used for the portion that transmits the return current, the problem of the conventional phantom that the distribution of the return current (distributed current, secondary current) changes can be solved.
[0035]
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration example of a phantom of a magnetoencephalogram measuring apparatus to which the present invention is applied.
FIG. 2 is a schematic diagram for explaining the concept of magnetoencephalogram measurement.
FIG. 3 is a schematic diagram showing the distribution of extracellular current flowing in the brain.
FIG. 4 is a schematic diagram showing a conventional phantom structure.
FIG. 5 is a transition diagram for explaining disturbance of a magnetic field distribution due to electrolysis.
[Explanation of symbols]
9a Spring electrode 9b Suction electrode 10 Lead wire 11 Conductive solid 11a Conductive solid (hemisphere)
11b Conductive solid (hemisphere)
12a guide groove 12b guide groove

Claims (10)

In the phantom of a magnetoencephalograph that has a simulated current dipole fixedly placed in a spherical conductor with uniform conductivity,
A portion of the simulated current dipole that transmits a return current is formed of a conductive solid.   The phantom of the magnetoencephalogram measuring apparatus according to claim 1, wherein the conductive solid is formed of a member containing carbon and a foamable resin.   The phantom of the magnetoencephalogram measuring apparatus according to claim 1, wherein the conductive solid is formed of a member in which a metal powder is included in a paste.   The phantom of the magnetoencephalogram measurement apparatus according to claim 1, wherein the conductive solid is formed of a member obtained by solidifying conductive fine particles.   5. The phantom of the magnetoencephalogram measuring apparatus according to claim 1, wherein the conductive solid is formed by dividing a spherical conductive member into a plurality of parts and sandwiching the simulated current dipole.   5. The conductive solid according to claim 1, wherein the conductive solid is solidified by filling a hollow spherical mold having the simulated current dipole in a predetermined position inside with a fluid conductive member. A phantom of the magnetoencephalography measuring device described in 1.   The phantom of the magnetoencephalogram measuring apparatus according to any one of claims 1 to 6, wherein a lead wire for supplying current to the simulated current dipole is formed of a two-core stranded wire.   The phantom of the magnetoencephalogram measuring apparatus according to any one of claims 1 to 6, wherein a lead wire for supplying a current to the simulated current dipole is formed by a parallel proximity wire.   The phantom of the magnetoencephalogram measuring apparatus according to any one of claims 1 to 6, wherein a lead wire for supplying a current to the simulated current dipole is formed of a coaxial cable.   The phantom of the magnetoencephalogram measuring apparatus according to any one of claims 1 to 6, wherein a lead wire for supplying a current to the simulated current dipole is formed of a printed board or a flexible printed board.

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