JPH08140953A - Apparatus for estimating three-dimensional electrode position and head model - Google Patents

Abstract

PURPOSE: To provide an apparatus for estimating three-dimensional electrode position and head model by which the burden on an experimenting person is lightened and the time required to measure the position of an electrode is significantly shortened. CONSTITUTION: An operation plane containing a great circle passing two points on a head skin is specified with a head skin upper operation surface section 11, and positions at arbitrary two points within an operation plane are measured with a position parameter electronic conversion section 12 to calculate a linear distance between these arbitrary two points with a linear distance computing section 13 by electronic application thereof. An output of a signal pertaining to the linear distance is controlled with a linear distance measurement control section 14 to calculate a three-dimensional position of an electrode with a three- dimensional electrode position estimating section 15 based on a linear distance data pertaining to the electrode and a reference point. A head model is estimated with a head model estimating section 17 from a data of the three dimensional position and the three-dimensional position of the electrode and the head model are displayed at an estimation result display section 17. The control of the linear distance measurement control section 14, the three-dimensional electrode position estimating section 15, the head model estimating section 16 and the estimation result display section 17 is performed with a three-dimensional electrode position/head model estimation control section 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-dimensional electrode position / head model estimating apparatus which greatly reduces the time required for electrode position measurement and reduces the burden on the experimenter.
The present invention relates to a head model estimation device.

[0002]

2. Description of the Related Art As a conventional three-dimensional electrode position / head model estimating apparatus, for example, "Electroenceph"
allography and clinical Ne
urophysiology, Vol. 78, 85-87
1991, "J. C. DeMunkck, P .; C.
M. Vijn, H .; Spekreijse "A pr
actual method for death
ining electrode positions
A device described in a paper entitled "on the head" is known. FIG. 7 shows the basic configuration of this device.

[0003] The three-dimensional electrode position estimating section 22 has three different
The three-dimensional coordinate value of the electrode position is calculated based on the principle of triangulation using the linear distance from two reference points to the electrode. The three reference points are the left pinna, the right pinna, and the inion, as shown in FIG. The linear distance from the reference point to the electrode is determined by the linear distance measuring unit 21 using the calipers shown in FIG. Note that in order to determine the three-dimensional position coordinate values of the three reference points, the linear distance (2
b), linear distance between left pinna and inion (c), right pinna
The linear distance (c) between the inions must also be measured by the linear distance calculation unit 21.

The head model estimating section 23 estimates the head model using the three-dimensional coordinate values of each electrode position obtained by the three-dimensional electrode position estimating section 22. The head is approximated by a multilayered concentric sphere, taking into account the differences in the electrical conductivity of the scalp, skull, cerebrospinal fluid, and brain. The parameters of the sphere model representing the outermost part of the head model (radius and center position of the sphere) are parameters that minimize the error function defined by the sum of squares of the distance between each electrode and the surface of the sphere. Desired.

In this three-dimensional electrode position / head model estimating apparatus, a linear distance measuring unit 21 and a three-dimensional electrode position estimating unit 22
Is not directly connected physically. Therefore, the straight-line distance data obtained by the straight-line distance measurement unit 21 must be re-input to the three-dimensional electrode position estimation unit 22. The straight-line distance measurement unit 21 must measure each straight-line distance using calipers. Therefore, for example, when the number of electrodes is 31, 96 times (= 31 × 3 + 3), and when the number of electrodes is 62, 189 times (= 62 × 3 + 3), the linear distance must be measured with a vernier caliper. Would have to do very complicated work. In addition, since the inion is one of the reference points, it may be difficult to measure the linear distance with a normal caliper when the electrode is mounted on the forehead.

[0006]

In the above-described conventional three-dimensional electrode position / head model estimating apparatus, the operation for the linear distance measurement is complicated and the linear distance data is re-input.
There was a problem that the experimenter was forced to perform a very complicated work.

It is an object of the present invention to significantly reduce the burden on the experimenter by digitizing the linear distance measuring unit and physically connecting it to the three-dimensional electrode position estimating unit in order to solve the above problems. It is to provide a three-dimensional electrode position / head model estimation device.

[0008]

A three-dimensional electrode position / head model estimating apparatus of the present invention comprises an on-scalp operation surface specifying means for specifying an operation plane including a great circle passing through any two points on the scalp.
Position parameter electronic means for measuring and digitizing two position parameters representing the position of an arbitrary point in the operation plane specified by the above-scalp operation surface specifying means, and output from the position parameter electronic means Any 2 on the scalp
A three-dimensional position of the electrode is calculated based on the linear distance calculation means for calculating the linear distance between the two points from the position parameter regarding the point and the linear distance data regarding the electrode and the reference point output from the linear distance measurement control means. Three-dimensional electrode position estimating means, head model estimating means for estimating a head model from the three-dimensional electrode position data output from the three-dimensional electrode position estimating means, and three output from the three-dimensional electrode position estimating means. Dimensional electrode position data and estimation result display means for displaying the head model output from the head model estimation means.

[0009]

According to the present invention, the linear distance measuring means for generating digitized linear distance data and the three-dimensional electrode position estimating means are physically connected. As a result, the time required for measuring the linear distance data can be significantly reduced, and the burden on the experimenter can be significantly reduced.

[0010]

FIG. 1 shows an embodiment of a three-dimensional electrode position / head model estimation device of the present invention. This three-dimensional electrode position / head model estimation device is specified by an on-scalp operation surface specifying unit 11 that specifies an operation plane including a great circle that passes through any two points on the scalp, and an on-scalp operation surface specifying unit 11. The position parameter computer 12 that measures and computerizes two position parameters that represent the position of an arbitrary point in the operation plane, and the positions of any two points on the scalp output from the position parameter computer 12 A straight line distance calculation unit 13 that calculates a straight line distance between the two points from parameters, a straight line distance measurement control unit 14 that controls the output of a signal related to the straight line distance calculated by the straight line distance calculation unit 13, and a straight line distance measurement control unit. A three-dimensional electrode position estimation unit 15 for calculating the three-dimensional position of the electrode based on the straight line distance data regarding the electrode and the reference point output from 14;
Head model estimation unit 1 that estimates a head model from the three-dimensional electrode position data output from the three-dimensional electrode position estimation unit 15.
6, to the estimation result display unit 17 that displays the three-dimensional electrode position data output from the three-dimensional electrode position estimation unit 15 and the head model output from the head model estimation unit 16, and to the linear distance measurement control unit 14. A signal related to the start / end of measurement and a signal related to the number of electrodes 181 are output to control the linear distance measurement, and a signal 182 related to the start of electrode position estimation is output to the three-dimensional electrode position estimation unit 15 to control the electrode position estimation. And outputs a signal 183 regarding the start of head model estimation to the head model estimation unit 16 to control the head model estimation, and outputs a signal 184 regarding the start of result display to the estimation result display unit 17 and outputs the result. It has a three-dimensional electrode position / head model estimation control unit 18 that controls display.

The measurement of the linear distance between any two points on the scalp is performed by the operation surface specifying unit 11 on the scalp, two position parameter digitizing units 12, the linear distance calculating unit 13, and the linear distance measuring control unit 14. You.

Assuming that the scalp surface can be approximated by a sphere,
Any two points on the scalp may be approximately on a great circle passing through these two points. Therefore, two points on the scalp exist in the plane including this great circle, and only two of some parameters representing the position in the plane, for example, the coordinate value of the orthogonal coordinate system or the coordinate value of the polar coordinate system, The position can be specified. That is, the on-scalp operation surface specifying unit 11 is a means for limiting the operation on the scalp to the great circle, and the position parameter computerization unit 12 determines any two points on the scalp in the plane including the great circle. It is a means for digitizing two parameters representing a position.

The linear distance calculator 13 calculates a linear distance between any two points on the scalp digitized by the position parameter digitizer 12 from the position parameters for the two points.
Since the operation plane is specified by the on-scalp operation surface specifying unit 11, it is possible to easily obtain the linear distance according to the coordinate system that defines the operation plane, for example, the orthogonal coordinate system or the polar coordinate system.

The linear distance measurement control unit 14 outputs a signal regarding the start / end of linear distance measurement and a signal regarding the number of electrodes 1 output from the three-dimensional electrode position / head model estimation control unit 18.
Based on 81, the output of a signal related to the linear distance output from the linear distance calculation unit 13 is controlled.

The three-dimensional electrode position estimating unit 15 uses the signals related to the linear distance data from the three different reference points to the electrode output from the linear distance measurement control unit 14 based on the principle of triangulation, and Calculate the three-dimensional coordinate value of the electrode position. The three reference points are the left pinna, the right pinna, and the inion, as shown in FIG. However, there is no necessity for these three points. For example, a point G as shown in FIG. 3 may be used instead of the inion. In order to determine the three-dimensional position coordinate values of the three reference points, the linear distance between the two pinnaes (2b), the linear distance between the left pinna and the point G (d' ₃ ), and the right pinna and the point G The linear distance (d ′ ₂ ) between them is also measured in advance by the on-scalp operation surface specifying unit 11, the position parameter digitizing unit 12, and the linear distance calculating unit 13.

The head model estimating unit 16 estimates a head model by using the three-dimensional coordinate values of each electrode position obtained by the three-dimensional electrode position estimating unit 15. The head is approximated by a multilayered concentric sphere, taking into account the differences in the electrical conductivity of the scalp, skull, cerebrospinal fluid, and brain. The parameters of the sphere model representing the outermost part of the head model (radius and center position of the sphere) are parameters that minimize the error function defined by the sum of squares of the distance between each electrode and the surface of the sphere. Desired. Optimization techniques can be used to minimize this error function.

As a method of estimating the head model,
In addition to the method of approximation using a multilayer concentric sphere, for example, MRI (M
acoustic Resonance Imagin
g: nuclear magnetic resonance image), from each layer of the head (scalp, skull,
It is also possible to extract the boundaries of the cerebrospinal fluid and the brain) and use a real head shape model created by three-dimensionally reconstructing them.

The estimation result display unit 17 displays the three-dimensional position of the electrode obtained by the three-dimensional electrode position estimation unit 15 and the head model obtained by the head model estimation unit 16 on the same coordinate system. (See FIG. 6).

3D electrode position / head model estimation control unit 1
8 outputs a signal regarding the start / end of the measurement and a signal 181 regarding the number of electrodes to the linear distance measurement control unit 14 to control the distance measurement, and sends a signal 182 regarding the start of the electrode position estimation to the three-dimensional electrode position estimation unit 15. To control the electrode position estimation, output a signal 183 relating to the start of the head model estimation to the head model estimation device 16 to control the head model estimation, and display the result display on the estimation result display unit 17. The start signal 184 is output to control the result display.

Next, an example of estimating the three-dimensional position of 31 electrodes mounted on the scalp and the head model using the present invention will be described.

For example, as the operation surface identification unit 11 on the scalp,
An arm type device as shown in FIG. 4 is used. The two axes F51 and M52 have the same center of rotation O, and the surface including the circumference around which these two axes can move is the operation surface 1 on the scalp.
11 (see FIG. 2). This operation surface 111
Is represented by a Cartesian coordinate system (x, y) with the center of rotation O as the origin. At this time, the arbitrary two points P _F 112 and P _M 113 (see FIG. 2) on the scalp positioned by the fixed-side measurement pin 53 attached to the shaft F51 and the movable-side measurement pin 54 attached to the shaft M52. The coordinate values are given by P _F : (A, 0) (1) P _M : ((A−Δr) cos Δθ, (A−Δr) sin Δθ) (2) Where A is the distance between the origin O and the point P _F 112, Δθ is the angle between the axis _F 51 and the axis M 52, Δr is the difference in the radial distance between the point P _F 112 and the point P _M 113,
And Therefore, the straight-line distance between the points P _F 112 and P _M 113 is

[0022]

[Equation 1]

Is given by

As for the value of A, the measuring pin 53 on the fixed side has an axis F51.
, And may be known. Δθ can be measured as a potential signal by, for example, the rotary encoder 55 attached to the origin O as the position parameter digitizing unit 12. Δr can be measured as a potential signal by the position parameter computerization section 12, for example, by a potentiometer 56 attached to the movable side measurement pin 54. In this way, the linear distance calculation unit 13 can execute the calculation of the expression (3).

The calculated value of equation (3) is used as a three-dimensional electrode position estimating unit 15 by, for example, EWS manufactured by NEC Corporation.
Whether to transmit to a workstation such as 4800 via RS232C is determined by the linear distance measurement control unit 14, for example, ON / OFF of the push button switch 57.
Control with. It should be noted that the device driver of the position parameter digitizing unit 12, communication of the potential signal relating to the position parameter, and processing of the potential signal necessary for calculating the linear distance can be realized by an existing electronic circuit.

The three-dimensional electrode position estimating unit 15 has different three
Using the linear distance from one reference point to the electrode, the three-dimensional coordinate value of the electrode position is calculated based on the principle of triangulation.
As shown in FIG. 3, the three reference points are the left auricle, the right auricle, and the point G. Linear distance from each reference point to each of the 31 electrodes (d ₃ : linear distance between left pinna and point P, d ₂ : linear distance between right pinna and point P, d ₄ : point G-point P Linear distance between)
Is obtained by the on-scalp operation surface identification unit 11, the position parameter digitizing unit 12, the linear distance calculation unit 13, and the linear distance measurement control unit 14. The position of the point G is considered to be desirable on the median line, at the top of the head or at the frontal region.

Further, in order to determine the three-dimensional position coordinate values of the three reference points, a straight line distance between the two auricles (2b), a left auricle-inion straight line (c), and a right auricle-in advance. Straight line distance between inion (c), straight line distance between point G and inion (d' ₁ ), straight line distance between left auricle and point G (d' ₃ ), straight line distance between right auricle and inion (d). ′ ₂ ) is also measured by the on-scalp operation surface identification unit 11, the position parameter computerization unit 12, the linear distance calculation unit 13, and the linear distance measurement control unit 14.

The specific calculation in the three-dimensional electrode position estimating unit 15 is as follows. The coordinates (x,
y, z) is

[0029]

[Equation 2]

It is assumed that

As the head model estimating unit 16, for example, a workstation such as EWS4800 manufactured by NEC Corporation is used. The head model estimating unit 16 fits the three-dimensional position data of the electrodes estimated by the three-dimensional electrode position estimating unit 15

[0032]

[Outside 1]

Find out However,

[0034]

[Outside 2]

Is the center of the sphere, and R is the radius of the sphere.

[0036]

[Outside 3]

Is a vector representing the i-th electrode position estimated by the three-dimensional electrode position estimating unit 15. this

[0038]

[Outside 4]

And

[0040]

[Outside 5]

If both are given in the coordinate system shown in FIG.

[0042]

(Equation 3)

Is a vector directed from the center of the sphere to the i-th electrode position. Therefore, with respect to the center of the sphere, an error function H defined as the sum of squares of the distance between each electrode position and the sphere

[0044]

[Equation 4]

Parameter to minimize

[0046]

[Outside 6]

Should be obtained. Here, I is the number of electrodes (31 in this embodiment). The above principle is illustrated in FIG.
The minimum value of H is determined by an optimization method such as Simpl
If the ex method is used, it can be easily obtained. Incidentally, Si
Specific programming of the plex method is, for example,
"Byte, May, pages 340-362, 1984".
To M. S. Caseci, W.C. P. Chacheris
Is "Fitting curves to data"
Details of the paper published under the title.

As the estimation result display section 17, for example, a workstation such as EWS4800 manufactured by NEC Corporation is used. FIG. 6 is a diagram exemplifying the display of the estimation result of the three-dimensional electrode position estimation unit 15 and the estimation result of the head model estimation unit 16, which is an example of the display screen of the CRT display connected to the workstation. . Three-dimensional electrode position estimator 1 relating to the sphere estimated by head model estimator 16
The electrode position estimated in 5 is the center of the estimated sphere

[0049]

[Outside 7]

Is given by equation (16) using the value of

In FIG. 6, each of the three circles is a projection of a sphere, which is a head model estimated by the head model estimating unit 16, and includes a top view, an upper right, and a lower right in order from the side view and the back of the head. It shows a view seen from above and a view seen from above. Also, diameter 2
The point of about mm is the electrode position converted according to the equation (16) projected on each circle.

Three-dimensional electrode position / head model estimation control unit 1
For example, a workstation such as EWS4800 manufactured by NEC Corporation is used as 8. The three-dimensional electrode position / head model estimation control unit 18 sends a signal regarding the start / end of the measurement and a signal 1 regarding the number of electrodes to the linear distance measurement control unit 14.
A signal 18 relating to the start of electrode position estimation is output to the three-dimensional electrode position estimation unit 15 by outputting 81 to control the linear distance measurement.
2 is output to estimate the electrode position, a signal 183 relating to the start of head model estimation is output to the head model estimation unit 16 to control the head model estimation, and the estimation result display unit 17
A signal 184 relating to the start of the result display is output to control the result display. The transmission of these control signals 181 to 184 is performed by setting a menu screen for each control content on a CRT display connected to the workstation, excluding the input of the number of electrodes, and easily executing / stopping by operating the mouse. Control can be realized. Also, the number of electrodes can be set by keyboard input or the like.

[0053]

According to the present invention, the time required for electrode position measurement can be greatly reduced.

The measurement of the position of 31 electrodes described in the embodiment is taken as an example. In the conventional apparatus, each straight-line distance must be measured 96 times with a vernier caliper, and each numerical value must be written on paper or the like, so that it took 2-3 hours to measure the straight-line distance alone.
In the present invention, since the linear distance measurement is digitized and the linear distance measurement can be controlled with a single push button, each distance measurement takes only a few seconds. For example, even if it takes 10 seconds, 960 seconds = 16 minutes, and the process ends in less than 20 minutes.
This effect becomes more remarkable as the number of electrodes increases. Furthermore, the linear distance measuring unit is physically connected to the three-dimensional electrode position estimating unit and the head model estimating unit, and all these functions can be realized and automated by one workstation. Therefore, the burden on the experimenter can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating an operation surface on the scalp of the present invention.

FIG. 3 is a diagram illustrating a coordinate system defining a head;

FIG. 4 is a diagram illustrating a linear distance measuring unit of the present invention.

FIG. 5 is a diagram illustrating the principle of a head model estimating unit according to the present invention.

FIG. 6 is a diagram illustrating a display result of an estimation result display unit according to the present invention.

FIG. 7 is a block diagram showing a conventional example.

FIG. 8 is a diagram exemplifying a conventional linear distance measuring unit (calipers).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 On-scalp operation surface identification part 12 Position parameter digitization part 13 Linear distance calculation part 14 Linear distance measurement control part 15 Three-dimensional electrode position estimation part 16 Head model estimation part 17 Estimation result display part 18 Three-dimensional electrode position / head Model estimation unit 21 Linear distance measurement unit 22 Three-dimensional electrode position estimation unit 23 Head model estimation unit 51 Axis F 52 Axis M 53 Fixed measurement pin 54 Movable measurement pin 55 Rotary encoder 56 Potentiometer 57 Push button switch 111 On scalp operation surface 112 points P _F 113 point P _M 181 measuring start / stop and signal 200 left auricle 201 on starting the start signal 184 results regarding the start to signal 183 head model estimation signals 182 electrode position estimate for the number of electrodes Right auricle 202 Inion

Claims (1)

[Claims] 1. A three-dimensional electrode position / head model estimation device for generating electrode position data and a head model required for the equivalent current dipole localization method for estimating an intracerebral activity source from multi-channel EEG data. On the scalp operation surface specifying means for specifying an operation plane including a great circle passing through any two points of, and two position parameters representing the position of any point on the operation plane specified by the above-mentioned scalp operation surface specifying means. Position parameter computerization means for measuring and digitizing, and linear distance calculation means for calculating the linear distance between the two points from the position parameters relating to any two points on the scalp output from the position parameter computerization means. A three-dimensional electrode position estimating means for calculating a three-dimensional position of the electrode based on the linear distance data regarding the electrode and the reference point output from the linear distance measurement control means; Head model estimating means for estimating a head model from the three-dimensional electrode position data output by the pole position estimating means, three-dimensional electrode position data output by the three-dimensional electrode position estimating means and the head model estimating means Estimation result display means for displaying the head model output from the three-dimensional electrode position / head model estimation device.