Apparatus and method for reconstructing subsurface electrophysiological patterns

• US 4,416,288 A
• Filed: 08/14/1980
• Issued: 11/22/1983
• Est. Priority Date: 08/14/1980
• Status: Expired due to Term

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Freeman, Walter J.
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): Jaworski, Francis J.
• Application Number:
  US06/178,170
• Time in Patent Office: 1,195 Days
• Field of Search: 128/639-640, 128/644, 128/653, 128/696, 128/709-710, 128/731-732, 128/734, 364/415, 364/417, 364/728, 364/819-824
• US Class Current: 600/544
• CPC Class Codes: A61B 5/369 Electroencephalography [EEG] devices for psychotechnics A61B5/16
• CPC Class Codes: A61B 5/372 Analysis of electroencephalograms

Abstract

Signals representative of electric potentials generated by cells of a given depth in the cerebral cortex or in other organs of a living body are detected at the surface thereof by an array of electrodes. These signals are amplified, digitized, and then spatially deconvoluted, to remove distortions introduced by the physical properties of the organ, to recover the desired pattern of electric potential within the living body.

Claims

1. An apparatus for recovering a pattern of cell generated electrical field potential U occurring at a specific time t and at a selected depth within a living organ from an associated pattern of electrical potential V at said specific time and at the surface of said living organ, said cell generated electrical field potential U having coordinates x'"'"', y'"'"' and being describable as U=U(x'"'"', y'"'"', y'"'"', t), said electrical potential V having coordinates x, y and being describable as V=V(x, y, t), said apparatus comprising:

an electrode array for detecting values of V(x, y, t) at a plurality of points on the surface of said living organ, said points being spaced from each other by a distance determined by the expected spatial frequency of said electrical potential V(x, y, t);

means for digitizing the detected values of V(x, y, t); and

means for spatially deconvolving the digitized values of V(x, y, t) to recover the desired pattern of electrical field potential U(x'"'"', y'"'"', t) within said living organ, said deconvolving means including computing a transform function f_z =f_z (x-x'"'"', y-y'"'"'), said transform function having the value determined by an equation which describes the field potential at each of a plurality of subsurface points with respect to the field potential of each of a plurality of other selected sets of subsurface electric field potential generators, such that the potential at any one point is the sum of potentials from such surrounding generator sets, with each potential having a value determined by the laws of conduction in the volume of said organ, and means for computing the product of said surface field potential V(x, y, t) and the inverse of said transform function to generate values of the electric field potential U(x'"'"', y'"'"', t).

2. The apparatus of claim 1 wherein said means for spatially deconvolving the digitized values of V(x,y,t) comprises:

means for computing a matrix relationship between the fields of potential of each of a plurality of selected sets of subsurface electric field potential generators, such that the potential at any one point approximates the sum of potentials from an indefinite number of surrounding generator sets weighted as a function of their distance from said point; and

means for computing the martrix product of V(x,y,t) and the inverse of said matrix to generate values of U(x'"'"', y'"'"', t).

3. The apparatus of claim 1 wherein said electrode array includes a plurality of electrodes spaced such that they are separated by a distance that is less than one half the shortest spatial wavelength of the detected values of V(x, y, t).

4. An apparatus for recovering a pattern of cell generated electrical field potential U occurring at a specific time t and at a selected depth within a living organ from an associated pattern of electrical potential V at said specific time and at the surface of said living organ, said cell generated electrical field potential u having coordinates x'"'"', y'"'"' and being describable as U=U(x'"'"', y'"'"', t), said electrical potential V having coordinates x, y and being describable as V=V(x, y, t), said apparatus comprising:

an array of electrodes, said array detecting an electric field potential signal at a plurality of points on the surface of said living organ, generating thereby said V(x, y, t) pattern, said points being spaced from each other by a distance determined by the expected spatial frequency of said electrical potential V(x, y, t);

amplifier means attached to each said electrode in said electrode array for amplifying said detected signal;

multiplexer means for sampling the output level of each said amplifier means and for outputting a time division multiplexed signal made up of such signal levels, said multiplexing being performed at a fast rate as compared with the rate of change of said electric field potential signals;

analog to digital converter means for digitizing said multiplexer means output;

means for controlling the operation of said multiplexer means and said analog to digital converter means, such that the output of said converter means is a plurality of digital words, each digital word reflecting the present analog level of electric field potential detected by a given electrode in said electode array; and

processor means for storing said digital words until the signal outputs of each electrode in said array have been sampled and digitized, and for generating from this V(x, y, t) pattern of signals, by spatial deconvolution, a pattern of electrical potential U(x'"'"', y'"'"', t) occurring within said living organ, said spatial deconvolution being performed by computing a transform function f_z =f_z (x-x'"'"', y-y'"'"'), said transform function having the value determined by an equation which describes the field potential at each of a plurality of subsurface points with respect to the field potential of each of a plurality of other selected sets of subsurface electric field potential generators, such that the potential at any one point is the sum of potentials from such surrounding generator sets, with each potential having a value determined by the laws of conduction in the volume of said organ, and means for computing the product of said surface field potential V(x, y, t) and the inverse of said transform function to generate values of the electric field potential U(x'"'"', y'"'"', t).

5. The apparatus of claim 4 further comprising means for displaying said recovered pattern of electrical potential U(x'"'"', y'"'"', t).

6. The apparatus of claim 4 further comprising means for storing said patterns of electrical potential U(x'"'"', y'"'"', t) as a function of the time t of occurrence of each such pattern.

7. The apparatus of claim 4 wherein said array of electrodes comprises a rectangular array of electrodes wherein the inter-electrode spacing between adjacent electrodes is equal, and the number of electrodes in each column of said array is equal and the number of electrodes in each row of said array is equal.

8. The apparatus of claim 4 further comprising filter means for band pass filtering each said detected electric field potential signal.

9. The apparatus of claim 4 wherein said array of electrodes is arranged such that each electrode in said array is spaced such that it is separated by a distance from adjacent electrodes in said array that is less than one-half the shortest expected spatial wavelength of said detected electric field potential signal.

10. An apparatus for recovering a pattern of cell generated electrical field potential U occurring at a specific time t and at a selected depth within a living organ from an associated pattern of electrical potential V at said specific time and the surface of said living organ, said cell generated electrical field potential u having coordinates x'"'"', y'"'"' and being describable as U=U(x'"'"', y'"'"', t), said electrical potential V having coordinates x, y and being describable as V=V(x, y, t), said apparatus comprising:

a plurality of electrode arrays each detecting a separate pattern of electric field potential V(x, y, t) at a plurality of points on the surface of said living organ, said points being spaced from each other by a distance determined by the expected spatial frequency of said electrical potential V(x, y, t);

amplifier means for amplifying the signal output of each electrode in each said electrode array;

means for filtering said electric field potential signals, to eliminate frequency components therein outside of a selected band of frequency;

means for digitizing the signals output from each said electrode array;

means for spatially deconvolving the digitized signals, representing the pattern V(x, y, t) for each said electrode array, to recover the desired respective pattern of electrical potential U(x'"'"', y'"'"', t) within said living organ beneath such electrode array, said deconvolving means including computing a transform function f_z =f_z (x-x'"'"', y-y'"'"'), said transform function having the value determined by an equation which describes the field potential at each of a plurality of subsurface points with respect to the field potential of each of a plurality of other selected sets of subsurface electric field potential generators, such that the potential at any one point is the sum of potentials from such surrounding generator sets, with each potential having a value determined by the laws of conduction in the volume of said organ, and means for computing the product of said surface field potential V(x, y, t) and the inverse of said transform function to generate values of the electric field potential U(x'"'"', y'"'"', t).

11. An apparatus for recovering a pattern of electrical potential U(t) appearing within a living body from an associated pattern of electrical potential V(t) at the surface of said living body, comprising:

an electrode array of N insulated electrodes for detecting V(t) at a plurality of points, each corresponding to a given electrode, on the surface of said living body;

means for digitizing the detected values of V(t); and

means for spatially deconvolving the digitized values of V(t) to recover the desired pattern of electrical potential U(t) within said living body, said means for spatially deconvolving comprising;

means for computing an N×

N matrix having values determined by linear simultaneous equations which describe the field potential at each of a plurality of subsurface points with respect to the field potential of each of a plurality of other selected sets of subsurface electric field potential generators, such that the potential at any one point is the sum of potentials from such surrounding generator sets, with each potential having a value inversely related to its distance from such point; and

means for computing the matrix product of V(t) as an N×

1 column vector and the inverse of said N×

N matrix to generate values of U(t) as an N×

1 column vector.

12. A machine implemented method for digitally enhancing electrical signals detected by an array of electrodes attached to the surface of the brain or other organ of a living subject, such that the effects of volume conduction distortion of electric field potentials generated at a depth z below the surface of the subject is corrected, comprising the steps of:

digitizing the detected electrical signal from each of said electrodes;

defining a matrix of coupling coefficients wherein each coupling coefficient is derived for a given set of electric field potential generators according to the distance of that set to an indefinite number of other sets of generators in the organ;

obtaining the inverse of said matrix;

computing the matrix product of said inverse matrix and said digitized electrical signals in the form of a column vector; and

reassembling the resultant column vector as an array of spatially deconvolved signals to obtain the desired enhanced pattern of electrical signals.

13. The method of claim 12 wherein the coupling coefficients comprise linear simultaneous equations and wherein the amplitude of potential at a given point contributed by each of the other electric field potential generator sets falls off as a function of the inverse of the distance of each such other set from said given point.

14. A machine implemented method for digitally recovering a pattern of enhanced all generated electric field potential U having coordinates x'"'"', y'"'"' as describable as U=U(x'"'"', y'"'"', t) and being detected by an array of N electrodes attached to the surface of the brain or other organ of a living subject, said electrodes detecting electrical signal V having coordinates x'"'"', y'"'"' and describable as V=V(x, y, t), such that said enhanced signals U(x'"'"', y'"'"', t) correspond to electric field potentials generated by cell generators acting as dipoles at a depth z₀ below the surface of the organ, where the positive and negative point charges in said dipoles are separated by the distance 2, with the effects of volume conduction distortion caused by the organ tissue being eliminated, comprising the steps of:

digitizing the detected electrical signal from each of said electrods;

computing an N×

N matrix F_z of coupling coefficients wherein;

##EQU3## obtaining the inverse of said matrix, F_z^-1 ;

assembling the values V(x, y, t) as an N×

1 column vector;

computing U(N×

1)=F_z^- V(N×

1); and

reassembling the resultant column vector U(N×

1) as an array of spatially deconvolved signals to obtain the desired enhanced pattern of electrical signals U(x'"'"', y'"'"', t).