Cerebral biopotential analysis system and method

• US 4,907,597 A
• Filed: 10/09/1987
• Issued: 03/13/1990
• Est. Priority Date: 10/09/1987
• Status: Expired due to Term

• Current Assignee: Imperial Bank (Imperial Bancorp)
• Original Assignee: Aspect Medical Systems, Inc. (Medtronic Plc)
• Inventors: Chamoun, Nassib G.
• Primary Examiner(s): Jaworski, Francis
• Assistant Examiner(s): MANUEL, GEORGE C
• Application Number:
  US07/107,357
• Time in Patent Office: 886 Days
• Field of Search: 128/731, 128/733, 128/734, 364/726, 364/413.05
• US Class Current: 600/544
• CPC Class Codes: A61B 2505/05 Surgical care
• CPC Class Codes: A61B 5/1106 to assess neuromuscular blockade, e.g. to estimate depth of anaesthesia
• CPC Class Codes: A61B 5/374 Detecting the frequency distribution of signals, e.g. detecting delta, theta, alpha, beta or gamma waves
• CPC Class Codes: A61B 5/4821 Determining level or depth of anaesthesia A61B5/1106 takes precedence
• CPC Class Codes: A61B 5/6814 Head
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

Disclosed is a biopotential analysis system and method of the present invention for determining, in a noninvasive manner, cerebral electrical properties. A suitable electrode and amplifier system is used to obtain biopotentials from the region of interest. Surface electroencephalographic signals are then digitized and transmitted over a serial RS232C line to a host computer where a two minute long signal is divided into 30 consecutive four second intervals. A fast Fourier transform (FFT) is then performed on every interval, and the resulting fast Fourier transforms are then used to produce bispectral complex triple product and bispectral real triple product arrays for that interval. The complex triple product arrays of all intervals are added together, and the real triple product arrays of all intervals are also added together. Each element in the final complex array and final real array is then divided by 30 (the number of intervals) to produce an average complex triple product array and an average real triple product array. The magnitude squared of each element in the complex triple product array is divided by the corresponding element in the real triple product array to form the bicoherence array. The bicoherence array is displayed on a video terminal or plotted, and is used as a figure of merit for the assessment of cerebral electrical function.

Claims

1. A method of noninvasively detecting cerebral irregularities that effect cerebral electrical activity, said method comprising the steps of:

acquiring electroencephalographic signals from a surface of a region of the head of a subject being analyzed through a surface electrode;

dividing said acquired signals into segments and representing said segments as data records;

computing bispectral values for all data records of said acquired signals;

utilizing said bispectral values to generate single number indices to quantify a contribution to overall cerebral electrophysiologic stability provided by the region to which said surface electrode is connected.

2. The method of noninvasively detecting cerebral irregularities of claim 1 wherein said step of acquiring electroencephalographic signals comprises the step of:

placing a surface electrode on a region of the head of said subject being analyzed and detecting signals relating to cerebral activity in the region where the electrode is placed;

amplifying signals detected by said surface electrodes;

digitizing said amplified signals;

transmitting said digitized signals in a serial stream to a processing system.

3. The method of noninvasively detecting cerebral irregularities of claim 1 wherein said step of computing bispectral values comprises:

computing a fast Fourier transform for each of said records of said acquired signals;

computing a power spectrum for each of said data records;

computing individual complex triple product arrays for each of said records of said acquired signals and then computing an average complex triple product array of all of said individual complex triple product arrays;

computing individual real triple product arrays for each of said records of acquired signals and then computing an average real triple product array of all said individual real triple arrays;

computing a bispectral density array.

4. The method of noninvasively detecting cerebral irregularities of claim 3 wherein said complex triple product array, represented by bc_i (f₁,f₂), for each data record, represented by x_i (t), where 0≦

i≦

y is computed as follows;

space="preserve" listing-type="equation">bc.sub.i (f.sub.1,f.sub.2)=X.sub.i (f.sub.1)*X.sub.i (f.sub.2)*Xi(f.sub.1 +f.sub.2)

space="preserve" listing-type="equation">f.sub.1 +f.sub.2 ≦

N/2

space="preserve" listing-type="equation">0≦

f.sub.2 ≦

f.sub.1

where X_i (f) is the fast Fourier transform of a record.

5. The method of noninvasively detecting cerebral irregularities of claim 3 wherein the average complex triple product array, represented by BC (f₁, f₂), of the individual triple product arrays, represented by bc_i (f₁, f₂), is computed as follows:

##EQU3##

6. The method of noninvasively detecting cerebral irregularities of claim 3 wherein said real triple product array, represented by bc_i (f₁,f₂), for each data record, represented by x_i (t), where 0≦

i≦

y is computed as follows;

space="preserve" listing-type="equation">br.sub.i (f.sub.1,f.sub.2)=X.sub.i (f.sub.1)*X.sub.i (f.sub.2)*X.sub.i (f.sub.1 +f.sub.2)

space="preserve" listing-type="equation">f.sub.1 +f.sub.2 ≦

N/2

space="preserve" listing-type="equation">0≦

f.sub.2 ≦

f.sub.1

where X_i (f) is the fast Fourier transform of a record.

7. The method of noninvasively detecting cerebral irregularities of claim 3 wherein the average real triple product array, represented by BR (f₁,f₂), of the individual triple product arrays, represented by br_i (f₁, f₂), is computed as follows:

##EQU4##

8. The method of noninvasively detecting cerebral irregularities of claim 3 wherein said bispectral density array, represented by BD (f₁, f₂), is computed as follows:

space="preserve" listing-type="equation">BD(f.sub.1,f.sub.2)=|BC(f.sub.1,f.sub.2)|.sup.2

Where BC (f₁, f₂) represents said average complex triple array.

9. The method of noninvasively detecting cerebral irregularities of claim 3 further comprising the step of computing a bicoherence array.

10. The method of noninvasively detecting cerebral irregularities of claim 9 wherein said step of computing the bicoherence array represented by R² (f₁,f₂) comprises the step of calculating:

space="preserve" listing-type="equation">R.sup.2 (f.sub.1,f.sub.2)=BD(f.sub.1,f.sub.2)/BR(f.sub.1,f.sub.2)

space="preserve" listing-type="equation">0≦

R.sup.2 ≦

1

where

BD(f₁,f₂) represents said bispectral density array, and

BR(f₁,f₂) represents said average real triple product array.

11. The method of noninvasively detecting cerebral irregularities of claim 1 wherein said step of utilizing said bispectral values to quantify the contribution to overall cerebral electrophysiologic activity provided by the region probed by said surface electrode comprises the step of:

determining the depth of anesthesia by producing indexes representing the sum of all absolute values of the changes in each element in an array of bispectral values, said indexes gradually increasing during the induction of anesthesia until a maximum is reached when the anesthesia takes full effect.

12. The method of noninvasively detecting cerebral irregularities of claim 1 wherein said step of utilizing said bispectral values to quantify the contribution to overall cerebral electrophysiologic activity provided by the region probed by said surface electrode comprises the step of determining the depth of anesthesia and said step of determining the depth of anesthesia, comprises the steps of:

producing a bispectral density array and a bicoherence array from the signals received through each of said electrodes;

subtracting said bispectral density array of each electrode from a preanesthesia control bispectral array of that electrode;

computing a bispectral density index for each lead representing the sum of all of the absolute values of the changes in each element in said bispectral density array;

subtracting said bicoherence array of each electrode from a preanesthesia control bicoherence array of that electrode;

computing a bicoherence index for each lead representing the sum of all the absolute values of the changes in each element in said bicoherence array;

said indexes gradually increasing during the induction of anesthesia until a maximum is reached when the anesthesia takes full effect.

13. The method of noninvasively detecting cerebral irregularities of claim 12 further comprising the step of:

displaying said bispectral density index and said bicoherence index on a grid, said grid having an area representing a location of each electrode on the surface of the skull with each area containing both the bispectral density index and the bicoherence index.

14. The method of noninvasively detecting cerebral irregularities of claim 1 wherein said step of utilizing said bispectral values to quantify the contribution to overall cerebral electrophysiologic activity provided by the region probed by said surface electrode comprises the step of determining the depth of anesthesia, said step of determining the depth of anesthesia comprises the steps of:

producing a bispectral density array of the signals received through each of said electrodes;

correlating said bispectral density array with a control spectral density array in order to produce a cross-correlation coefficient, said cross-correlation coefficient gradually decreasing during the induction of anesthesia until a minimum is reached when the anesthesia takes full effect.

15. The method of noninvasively detecting cerebral irregularities of claim 14 further comprising the step of:

displaying the cross-correlation coefficient of the bispectral density array on a grid, said grid having an area representing a location of each electrode on the surface of the skull with each area displaying a numerical representation of the cross-correlation coefficient of the bispectral density array.

16. The method of noninvasively detecting cerebral irregularities of claim 1 wherein said step of utilizing said bispectral values to quantify the contribution to overall cerebral electrophysiologic activity provided by the region probed by said surface electrode comprises the step of determining the depth of anesthesia, said step of determining the depth of anesthesia comprises the steps of:

producing a bicoherence array of the signals received through each of said electrodes;

correlating a bicoherence array with a control bicoherence array in order to produce a cross-correlation coefficient, said cross-correlation coefficient gradually decreasing during the induction of anesthesia until a minimum is reached when the anesthesia takes full effect.

17. The method of noninvasively detecting cerebral irregularities of claim 16 further comprising the step of:

displaying the cross-correlation coefficient of the bicoherence array on a grid, said grid having an area representing a location of each electrode on the surface of the skull with each area displaying a numerical representation of the cross-correlation coefficient of the bicoherence array.

18. The method of noninvasively detecting cerebral irregularities of claim 1 wherein said step of utilizing said bispectral values to quantify the contribution to overall cerebral electrophysiologic activity provided by the region probed by said surface electrode determines a degree of intoxication due to the use of alcohol or drugs.

19. The method of noninvasively detecting cerebral irregularities of claim 1 wherein said step of utilizing said bispectral values to quantify the contribution to overall cerebral electrophysiologic activity provided by the region probed by said surface electrode determines adequacy of oxygenation of a cortical region probed by a particular electrode.

20. The method of noninvasively detecting cerebral irregularities of claim 1 wherein said step of utilizing said bispectral values to quantify the contribution to overall cerebral electrophysiologic activity provided by the region probed by said surface electrode determines a cortical area affected by ischemia.

21. A system for noninvasively detecting cerebral irregularities that affect cerebral electrical acitvity, said system comprising:

means for acquiring electroencephalographic signals from a surface of the head of a subject being analyzed;

means for dividing said acquired electroencephalographic signals into a plurality of data records;

means for computing at least one array of bispectral values from said data records of electroencephalographic signals;

means for utilizing said at least one array of bispectral values to generate single number indices to quantify a contribution to overall cerebral electrophysiologic stability provided by a region to which said means for acquiring electroencephalographic signals is connected.

22. The system for noninvasively detecting cerebral irregularities of claim 21 wherein said means for acquiring electroencephalographic signals is a plurality of electrodes adapted to be attached to said surface of the head of the subject being analyzed.

23. The system for noninvasively detecting cerebral irregularities of claim 21 wherein said means for acquiring electroencephalographic signals comprises a surface electrode adapted to be attached to the head of the subject being analyzed.

24. The system for noninvasively detecting cerebral irregularities of claim 21 wherein said means for acquiring electroencephalographic signals comprises:

a plurality of surface electrodes mounted on said surface of the head of the subject being analyzed;

means for providing electrosurgery protection including a radio frequency filter for limiting radio frequency current to said electrodes;

means for providing defibrillator protection for limiting the current through said electrodes during a defibrillator discharge;

means for amplifying signals acquired by said electrodes;

means for multiplexing said amplified signals so as to provide one signal at a time in a serial stream, said signal being fed to a means for converting analog signals into digital signals in order to convert said amplified signals into digital signals.

25. The system for noninvasively detecting cerebral irregularities of claim 21 wherein said means for computing at least one array of bispectral values comprises a computer system including:

means for receiving data in a serial stream from said means for acquiring electroencephalographic signals;

an array processor for performing arithmetic calculations on an entire array of data simultaneously;

a math coprocessor for calculating graphic modalities;

means for controlling receipt of input data or other signals from peripheral devices connected to said means for computing and means for controlling output of data or other signals to peripheral devices connected to said means for computing.

26. The system for noninvasively detecting cerebral irregularities of claim 21 wherein said cerebral irregularities being detected is a depth of anesthesia.

27. The system for noninvasively detecting cerebral irregularities of claim 21 wherein said cerebral irregularities is a degree of intoxication due to alcohol or drugs.

28. The system for noninvasively detecting cerebral irregularities of claim 21 wherein said system determines a cortical area effected by ischemia.