JPH01126949A - Intracorporeal equivalent current dipole tracing apparatus and display apparatus thereof - Google Patents

Abstract

PURPOSE:To calculate the position and vector component of an equivalent dipole with high accuracy, by operating the square error between the actual measured value and calculated value of the potential of each electrode to calculate the position of a current dipole where the operated value becomes min. and setting the current dipole at this position to the equivalent dipole. CONSTITUTION:A current dipole is supposed at a certain position in the skull and the potential generated at the position of each electrode from said current dipole is calculated using formula [wherein p is the vector component of the current dipole, r is the position of the current dipole and A(r) is a transmission matrix of M-line 3-row when the number of electrodes are set to M (the function of the position r of the dipole)]. Then, the square error So of the potential Vm actually measured at each electrode and the potential Vc calculated from the current dipole is calculated and, next, the position of the current dipole is slightly shifted to measure a square error in the same way as mentioned above. By this method, the position where the square error becomes min. is found out while the position of the current dipole is changed little by little and determined as the position of the current dipole. The dipole degree showing the approximate degree of the potential calculated from the current dipole is calculated with respect to the actually measured potential to display the current dipole on a CRT so as to be capable of tracing a nerve activity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an in-vivo equivalent current dipole tracking device, and in particular, it replaces the neural activity of the living body with a current dipole, and by this replacement, the current dipole is projected onto the body surface. The present invention relates to an in-vivo equivalent current dipole tracking device (Summary of the Invention). Using multiple electrodes attached to the body surface of a living body, we simultaneously measure the potential generated at each electrode based on the living body's neural activity, and then assume a current dipole at a predetermined position within the living body, which is a heterogeneous medium. , calculate the potential at each electrode position created by this current dipole, then calculate the square error between the measured value and the calculated value obtained for each electrode, and find the current dipole that minimizes this square error. The position and vector component of the current are determined and used as a quadrivalent current twin winding, so that the flow of electrical information within the living body can be tracked.

[Conventional technology]

2. Description of the Related Art Conventionally, electroencephalographs, electromyographs, evoked potential addition devices, and the like have been used as devices for measuring potentials appearing on the body surface due to neural activity of living organisms. Recently, the iso-oil-water method has been proposed, which measures the potential generated on the body surface due to neural activity in the living body and estimates the active site within the living body. In this method, for example, when cells in each active region of the brain are stimulated, an electromotive force is generated, resulting in a potential distribution on the scalp. From this potential distribution, each region is associated with an electrical dipole, and the position of this dipole and vector component are calculated from the above potential distribution to estimate the location of active brain cells. It is designed to track activity status. In the iso-oil-hydropole method for estimating such dipoles, because the potential distribution generated by the dipole is repeatedly calculated, conventionally, in order to calculate the potential distribution, for example, the head is assumed to be a perfect sphere. At the same time, calculations were performed on the assumption that the skull was inside a --like infinite conductor. Furthermore, methods have been proposed in which the potential distribution is calculated assuming a homogeneous conductive sphere or concentric or eccentric spherical shells, assuming that a homogeneous brain exists within the head.

In addition, X-ray CT (computed tomography), M
Rl (nuclear magnetic resonance computer tomography), PE”
r (positron emission tomograph), etc. are used. These X-ray CT and MHI are used to view the state of brain organs, while PE'I' is used to view the metabolic results of active tissues, and the flow of electrical information within the living body is tracked moment by moment. could not be displayed.

[Problems to be Solved by the Invention] According to the iso-oil-hydropole method with the conventional configuration described above, it is assumed that the living body, for example, the head, is a pseudo-spherical body or a spherical shell, and the infinite -
similar medium, i.e. the same conduction as the brain? 1! Suppose that a conductor with a constant rate exists outside the head in a similar manner, or suppose that the head is a spherical body or a spherical shell, and that there is a medium in a similar manner, that is, the brain, inside the sphere. Two problems arise in calculating the potential distribution. The first problem is that because the inside of the head is a homogeneous medium, the precision of the specified dipole position and vector component is not sufficient.The reason for this is explained with Figure @4. In Fig. 4, a skull is considered as a living body +1), and cavities (2) for eye holes and ear holes are considered within this skull. For the equi-immersed water pole specified just now, if the vector component direction of the equi-immersed water pole's true value (3a) is toward the cavity (2) as shown in Figure 4, then this equi-immersed water pole's The calculated value (3b) is influenced by the cavity (2) and becomes farther from the cavity (2) than the true position, and its vector component becomes smaller than the true value. On the other hand, the true value of the equi-immersed water pole (3a'
) is parallel to the cavity (2), this equivalent dipole (3b') will be influenced by the cavity (2) and will move closer to the cavity (2) than its true position. The vector component becomes larger than the true value (3b'). However, in the conventional iso-oil-water pole method, these points are not taken into account, so there is a problem that the accuracy of the position of the aiff pole and the accuracy of the vector component deteriorates.

The second problem is that the head is not originally a spherical body, but since the skull is approximated by a sphere and the equidispersed water pole is specified, it is difficult to determine where in the brain the estimated equidistant water pole is located. It is impossible to specify.

The present invention has been made in view of the above-mentioned drawbacks, and the main purpose of the present invention is to estimate the position and vector components of oil water poles when transcutaneously tracing the flow of electrical information in a living body. The goal is to obtain an in-vivo equivalent current dipole tracking device that requires high accuracy.

Another object of the present invention is to provide an in-vivo equivalent current dipole tracking display device that can momentarily display biological activity sites from iso-oil water poles when transcutaneously tracing the flow of electrical information in a living body. It is on offer.

(Means for Solving the Problems) As shown in one example in FIG. A calculation means (9b) assumes a current dipole at an arbitrary position in the living body where the current dipole is non-uniform, and manipulates the potential corresponding to each of the plurality of electrodes (5) created by the current dipole.
), the actual measured value of the potential measuring means (1o), and the calculating means (9
Find the position and vector component of the current dipole that minimizes the squared error value obtained from the squared error calculation means (9b) and the squared it/4 difference calculation means for calculating the squared error between the calculated value in b). An equivalent current dipole setting means (
9b).

(Function) Measure the potential of multiple electrodes attached to the living body to obtain the actual value, assume a current dipole at an arbitrary position within the living body, calculate the potential created by this current dipole, and use it as the calculated value. , calculate the square iI4 difference between the measured value and the calculated value of the potential of each electrode, and find the position of the current dipole where the value is the minimum,
The current dipole at this position is an iso-oil water pole.

〔Example〕

Hereinafter, an embodiment of the in-vivo 1th electric current tracking device of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 shows a system diagram for tracking the activity state of brain cells in a living body 11) as a brain in the head.

Figure 1 will be described in detail below.

First of all, in order to accurately grasp the shape and size of the measurement site on the body surface of the living body (1), for example, the head, approximately 15 CT tomograms (16) are taken using X-ray CT, and then this CT tomogram is taken. The two-dimensional dimensions of the image (16) are measured one by one using a digitizer (1
Using the pickup (17) of 8), pick up the human-powered boat (14)
) to the computer (9), and the three-dimensional head shape is determined from the signal. Further, each electrode position corresponding to the three-dimensional head shape is manually entered as three-dimensional coordinates XI'I'' from an electrode position signal input device (19) such as a keyboard.

Next, a group of about 21 electrodes (5), for example, is attached to the head (1), and the potential based on the neural activity in the brain is measured by the potential measuring means (1).
0). The measured potential from the electrode (51) is measured by the amplifier (
6) and a multiplexer (7) to an analog-to-digital converter (A/D) (8), and the digitized measured potential is sent to a computer (9) via an input capo-1-(14). Supplied. The computer (9) has a control section (9a) and a calculation section (9b), and an address bus (
lla) and data bus (llb) are ROM (12)
, RAM (13), input port (14), and output port-1-(15). Above ROM (12)
and RAM (13) stores programs necessary for signal processing, as well as a digitizer (1B), an electrode position signal input device (19), ? It is a storage means for storing data from the ti position measuring means (10). Computer(
Is the arithmetic unit (9a) in 9) equivalent to the arithmetic means? first-stream dipole setting means. The input port (14) is connected to an external storage device (2
0) is connected to the output board (14), and a display means (22) such as a CRT for displaying the calculation results of the computer (9).
) and a printer (20) for recording the data and waveforms displayed on the display means (22) are connected.

The operation of this example in the above configuration will be explained with reference to the flowchart of FIG.

In FIG. 2, although not shown, the in-vivo equivalent current dipole tracking device (23) of this example is set in the initial state as shown in the first step S by turning on the current. In the 0th-order second step ST2, programs for various calculations and signal processing programs, etc., which will be described later, are stored in an external storage device (20
) and stores it in the RAM (13) in the computer (9).
). Such a program can be run on a computer (9
), the second step ST2 becomes unnecessary.

In the next third step S'l'3, for example, input the head shape and size of a living body (11). Approximately 15 CT tomograms (16) are created.These CT tomograms (16) are made by measuring several parameters such as the circumference, width, length, and anteroposterior direction of the cranium for each individual.
If the method is applied to a standard model that has been neglected, the measurement becomes easier because the trouble of taking C'r tomographic images to measure each person's cranium can be saved. Of course - one person's cranium may be measured. 15 pieces of CT sliced like this
Two-dimensional tomographic image (16) ii! Each tomographic image (16
) is taken out by the pickup (17), inputted into the computer (9) from the input board (14) using the digitizer (18), and stored in the RAM (13). In this case, when stacking slices three-dimensionally and moving them through the air,
The intersection points of three straight lines perpendicular to the slice cross section may be placed at a fixed location in each slice to prevent "misalignment" from occurring.

In the fourth step ST4, the computer (9) performs interpolation calculations based on the head shape and dimensions manually inputted in this way and converts it into three-dimensional data of the cranium.

In the next fifth step ST5, the positions of the 21 electrodes (5) placed on the head of the living body +1) are changed to the fourth step S'1.
' In order to correspond to the three-dimensional head shape obtained in 4.
Electrode position signal input device (19) such as a keyboard shown in the figure
are input as three-dimensional coordinates of the x, y, and z axes and stored in the RAM (13) in the computer (9).

In the sixth step S'rε, as shown in Figure 1, the living body (1)
Approximately 21 electrode groups (5) are placed on the head, and electrical potentials are measured based on neural activity in the brain. The neural activity potential measured in this way may be an evoked potential in response to various stimuli such as electrical stimulation, optical stimulation, or sound stimulation, or a neural activity potential in a state where no stimulation is applied, and the measured value is amplifier(
6) - Multiplexer (7) - A/D (Supplied as digital data from the human powered boat (14) to the computer (9) via A/D (81) and stored on the RAM (13).

In the seventh step S'rt, one sample clock potential is extracted from the neural activity potentials and the computer (
9).

In the next eighth step STs, the calculation means (9b) of the combiator (9) calculates the transfer matrix of the specified electrode (5) position assuming that the current dipole is placed at a predetermined position in the skull, and Calculate the potential at each electrode location where the child occurs. Generally, when the source of a nerve action potential is assumed to be a current dipole, the potential VC generated on the scalp by the current dipole is expressed by equation (11).

Vc = A (r) ・p ... (1 round, p
: vector component of current dipole, r: fli-flow twin current ladder arrangement, A(r): where M is the number of electrodes, transfer matrix with M rows and 3 columns (
function of dipole position γ).

Here, if we consider the intracranial brain as an infinite-like medium, the potential generated from the current dipole is φ.

From this potential, as shown in Figure 3, a living body (11) has cavities such as eye holes and ear holes (2) in the skull, and the brain (24).
) to the potential of a heterogeneous medium.

In Figure 3, A0: Potential in tissues other than the brain and cavity v1: Potential in the brain A2: Potential in the cavity Kout: Potential outside the skull Ω0: Region of tissues other than the brain and air conditioning Ω1: Brain region Ω2: Cavity region out: Extracranial region σG = Electrical conductivity of tissues other than the brain and cavity σ1: Brain conductivity σ2: Cavity conductivity σout: Extracranial conductivity Say St+ S2: Each If we take the current dipole as the boundary with the region, then the current dipole is the region Ω! Let φ be the potential generated from this current dipole when I assumes that this region is an infinite-like medium, then φ. is given by the formula ■where σ1 is the brain conductor 1 which is an infinite-like medium! For the ratio ra+, if the electrode attachment position region is Ω and there is a current source in the region, the potential can be described by Poisson's equation. That is, within the region Ω, lφ−−□ ... (3) σ where σ is the electrical conductivity ■ is the strength of the current outflow φ is the electric potential This Poisson's equation is difficult to solve using the boundary element method, so the following equation Define.

φ0yoK0−φoo1 Using this equation (4), Poisson's equation becomes the following Laplace's equation, which can be solved using the boundary element method.

Since the potential and current density are equal on SL and S2, the following equation holds true.

φ0 + φ661 so = φ shout + φoo13゜here n
represents the outward normal line. By solving equations (5) and (6) above using the boundary element method, the potential in the heterogeneous medium can be found.

In the next ninth step STs, it is difficult to directly determine the current dipole from the measured potential of the nerve activity measured in the sixth step STs (assumed to be -), so the current dipole is determined by the method described below.

Letting S be the square error between the above-mentioned measured potential vIII and the potential Vc in the heterogeneous medium determined by equation (1), S is (7+I equation % equation %) where t is a transposed matrix.

The position r of the current dipole that minimizes this squared error S
and find the vector component p. When the position r of the current dipole is arbitrarily fixed, the vector p that minimizes equation (7) is (1
It can be found from equation 1 as follows.

p= (AtA)-1・A''-VIl
...(81 When the vector component p is selected in this way,
The squared error S is So as a function of only the position r of the current dipole
=Vmt ・(EX −A (A” A)−”
・A')VIl...(91 Here, EM is found as an M-th order unit matrix.

In the next tenth step S'r1o, the position r of the current dipole that minimizes the square error 9So is determined, and the computer (9) determines whether the square error is less than a reference value.

If this squared error is greater than the standard, the position of the current dipole is determined by the simplex method in the 11th step S T I
The simplex method described above, which moves as shown in L, returns to the 8th step STa, and repeats this operation until the value of the squared error converges, is one of the nonlinear salmonization methods, and is an iterative method. An approximate solution is obtained by performing calculations. When performing this iterative calculation, for example, set a regular tetrahedron in the gB lid, and set the four vertices of the regular tetrahedron at ¥, -
Assuming valence dual oil and water, calculate the square error between the potential at the electrode position on the scalp where the equihydroptic pole occurs and the actual potential for each equivalent dipole, and calculate the value of the largest square error among them. Move the vertex with , in the direction where the squared error becomes smaller. The algorithm for determining where to move at this time is (l
O) It is carried out according to the formula.

Here, X is the vertex position xh of the tetrahedron, and the vertex position XIII is the center of gravity at all vertices except for Xh. While calculating the three equations for each calculated value, each vertex of the tetrahedron is moved in the direction where the squared error becomes smaller, and the process is stopped when the stopping condition is satisfied. The position when the robot stops is determined as the final position.

In this way, when the value of the squared 8% difference converges and becomes "YES" and becomes less than the reference value, the current dipole at that position is set as an iso-oil water pole and the position is stored in the RAM ( 13) etc.

Next, the vector component p given to the equation 8 of the equal 11III dipole at the position determined in the 12th step S 'T' 12 is calculated by the computer (9) as shown in the 13th step ST13.
) is calculated by the calculation unit (9b).

In the next 14th step S'r' 14, a bipolar preshock d is calculated, which indicates how close the potential obtained from the current dipole is to the actually measured potential.

This bipolar preshock d is obtained by equation (11).

Here M is the number of electrodes.

Next, the value of this bipolar preshock d is determined in advance, and it is determined in a 15th step STzs whether or not it is greater than a limit value.

For example, the limit value of bipolar preshock d is set to (capital)% or more, and 90%
If the above is valid, if it is 90% or less, the 7th step S
Return to T↑ and specify the sampling value at the next point in time. If the bipolar preshock d is more than (capital)%, the 16th step 5TLG
As shown in , the position and vector component of the current dipole are displayed in a three-dimensional head shape on the CRT (22) of the display means.

In this example, the control operations described above are performed, but to summarize these control operations, a current dipole is assumed at a certain position within the skull, and the potential generated from the current dipole at each electrode position is 1) Calculate using the formula. Then, a square error So between the potential V■ actually measured at each electrode and the potential Vc calculated from the current dipole is calculated. Next, the position of the current dipole is slightly shifted and the square error is determined in the same manner as above. In this way, while changing the position of the current dipole little by little, find the position where the squared error is minimized, and decide that position as the position of the current dipole. In addition, the bipolar preshock that indicates the degree of approximation of the potential obtained from the current dipole to the actual measured potential is determined, and the current dipole is CR
The neural activity state can be tracked by displaying it on the T.

In the above example, the case where the position and vector component of the iso-oil water pole at a specific time is found, but it is also possible to find the iso-oil water pole at several points in time and store them in memory, and display them on the same screen. By displaying them simultaneously, it is possible to track changes in the iso-oil water pole over time, and various modifications can be made without being limited to the above-described embodiments without departing from the gist of the present invention.

〔Effect of the invention〕

Since the present invention is configured like a ridge, it is possible to accurately track the rapid movement and position of current dipoles within a living body. Furthermore, in addition to abnormal areas within the body that are thought to be the source of body surface potential, stimulation from the outside world (light, sound,
For example, information processing processes in the brain can be elucidated by tracking information about areas that are particularly excited by electricity, specific questions, or medications. Furthermore, when inputting the head dimensions, if a standard model pattern is used, in-vivo measurements can be safely and non-invasively performed on the subject H. That is, it has the advantage that it is not necessary to irradiate X-rays like X-ray C'r or P E'r, or to administer radioactive materials.

[Brief explanation of the drawing]

11121 is a system diagram showing an example of the in-vivo equivalent current dipole tracking device of the present invention, FIG. 2 is an example of the flowchart of FIG. 1, and FIG. 3 is a schematic diagram of the head explaining a heterogeneous medium, ff14
The figure is a schematic diagram of the head for explaining the influence of a heterogeneous medium. (1) is a living body, (2) is a cavity, (5) is an electrode, (9)
is a computer, (10) is a potential measuring means, (18) is a digitizer, (19) is an electrode position signal input device, (22)
) is a display means, (23) is an in-vivo equivalent current dipole tracking device, and (24) is a brain.

Claims (1)

[Claims] 1. Potential measuring means for simultaneously measuring the potentials of a plurality of electrodes attached to a living body; Assuming a current dipole at an arbitrary position in the living body where the medium is non-uniform, a calculation means for calculating a potential corresponding to each of the plurality of electrodes created by the above; a square error calculation means for calculating a square error between an actual measurement value of the potential measurement means and a calculated value of the calculation means; An in-vivo equivalent current dipole characterized by having an equivalent current dipole setting means for determining the position and vector component of the current dipole that minimizes the square error value obtained from the square error calculation means and setting it as an equivalent current dipole. Child tracking device. 2. Potential measuring means for simultaneously measuring the potentials of a plurality of electrodes attached to a living body, and assuming a current dipole at an arbitrary position within the living body, each corresponding to the plurality of electrodes created by the current dipole. a calculation means for calculating the electric potential; an actual value measured by the electric potential measurement means;
a square error calculation means for calculating the square error between the calculated value of the calculation means; and an equivalent current dipole for determining the position and vector component of the current dipole that minimizes the square error value obtained from the square error calculation means an equivalent current dipole setting means as a child, and an approximation degree calculating means for calculating a degree of approximation of a predetermined value or more by calculating a residual from the actual measurement value of the potential measuring means and the equivalent current dipole setting means, A display device for tracking an equivalent current dipole in a living body, characterized in that the position and vector component of the equivalent current dipole obtained by the approximation degree calculating means are displayed on a display means.