Electrode configuration for central nervous system monitoring

• US 20070255164A1
• Filed: 12/22/2005
• Published: 11/01/2007
• Est. Priority Date: 12/22/2005
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Sampson, Timothy, Viertio-Oja, Hanna
• Granted Patent: US 7,599,735 B2
• Time in Patent Office: Days
• US Class Current: 600/558
• CPC Class Codes: A61B 5/291 for electroencephalography [EEG]
• CPC Class Codes: A61B 5/297 for electrooculography [EOG]: for electroretinography [ERG]
• CPC Class Codes: A61B 5/398 Electrooculography [EOG], e.g. detecting nystagmus; Electroretinography [ERG]
• CPC Class Codes: A61B 5/6814 Head

Abstract

The invention relates to a method for positioning electrodes in an electrode array comprising a plurality of electrodes for central nervous system (CNS) monitoring from the forehead of a subject. In order to enable efficient detection of eye movement artifacts with a minimum number of electrodes, first and second electrodes are positioned so that eye movement in one of the horizontal or vertical directions causes a negligible overall voltage change between the first and second electrodes and at least a third electrode is positioned so that eye movement in the other of said horizontal and vertical directions causes a high potential difference between the third electrode and an auxiliary electrode, wherein the auxiliary electrode is one of the electrodes in a set comprising one of the first and second electrodes and a fourth electrode. The first and second electrodes are arranged to record an EEG signal and the third electrode and the auxiliary electrode are arranged to record an EOG signal indicative of eye movements of the subject.

Claims

1. A method for positioning electrodes in an electrode array comprising a plurality of electrodes for central nervous system (CNS) monitoring from the forehead of a subject, the method comprising the steps of:

positioning first and second electrodes so that eye movement in one of the horizontal or vertical directions causes a negligible overall voltage change between the first and second electrodes; and

positioning at least a third electrode so that eye movement in the other of said horizontal and vertical directions causes a high potential difference between the third electrode and an auxiliary electrode, the auxiliary electrode being one of the electrodes in a set comprising the first electrode, the second electrode, and an optional fourth electrode, p1 wherein the first and second electrodes are arranged to record an EEG signal and the third electrode and the auxiliary electrode are arranged to record an EOG signal indicative of eye movements of the subject.

2. A method according to claim 1, wherein the positioning steps include

positioning the first electrode on the front-lateral area of the frontal lobe of the subject;

positioning the second electrode on the front-lateral area of the frontal lobe of the subject at the opposite hemhisphere when compared to the first electrode so that the first and second electrodes locate substantially symmetrically with respect to the eyes of the subject; and

positioning the third electrode to the temple of the subject.

3. A method according to claim 2, wherein the auxiliary electrode is one of the first and second electrodes.

4. A method according to claim 2, wherein the auxiliary electrode is the fourth electrode and the positioning steps further include positioning the fourth electrode above the eyebrow at the same hemisphere as the third electrode and beyond the vertical axis of the respective eye with respect to the third electrode.

5. A method according to claim 1, wherein the positioning steps include positioning the third electrode to the temple of the subject, in which the temple is the area between an eye and an ear, the area being substantially at eye level anterior of the ear.

6. A method according to claim 1, wherein the positioning steps include:

positioning the first electrode symmetrically with respect to the eyes to the forehead of the subject;

positioning the second electrode on the mastoid of the subject; and

positioning the third electrode above one of the eyebrows of the subject.

7. A method according to claim 6, wherein the auxiliary electrode is one of the first and second electrodes.

8. A method according to claim 6, wherein the auxiliary electrode is the fourth electrode and the positioning steps further include positioning the fourth electrode below the eye at the same hemisphere as the third electrode.

9. A method according to claim 1, further comprising the steps of:

comparing the EEG and EOG signals with each other; and

defining artifact-contaminated time periods of the EEG signal based on the comparing step.

10. A method according to claim 9, wherein

the comparing step includes the sub-steps of dividing the EEG and EOG signals into successive epochs, each epoch comprising a certain number of signal values, determining differences of simultaneous absolute signal values within each epoch, and examining the differences within each epoch;

and

the defining step includes a sub-step of flagging the respective epoch as contaminated by eye movement, when at least a predetermined number of the differences in the epoch fulfills a predetermined criterion.

11. A method according to claim 10, wherein the examining sub-step includes a sub-step of comparing the differences with a predetermined threshold value.

12. A method according to claim 10, wherein the flagging sub-step includes flagging the respective epoch as contaminated by eye movement, when at least the predetermined number of the differences in the epoch fulfills the predetermined criterion, in which the predetermined number is one.

13. An electrode array for acquiring electrical biopotential signals from the skin surface of a subject, the electrode array comprising:

a single substrate attachable onto the skin of a subject, the substrate forming a strip-like structure comprising a first end and a second end;

a first EOG electrode positioned on the substrate at the first end of the strip-like structure;

a first EEG electrode positioned on the substrate at the second end of the strip-like structure; and

a second EEG electrode positioned on the substrate so that the distance between the first EEG electrode and the second EEG electrode is at least as long as the distance between the first EOG electrode and the second EEG electrode,

wherein the first EEG electrode and the second EEG electrode are arranged for recording an EEG signal and the first EOG electrode and the first EEG electrode are arranged for recording an EOG signal indicative of eye movements of the subject.

14. An electrode array according to claim 13, wherein the second EEG electrode is positioned substantially as far from the first EOG electrode as from the first EEG electrode.

15. An electrode array according to claim 13, wherein the strip-like structure comprises a first strip portion between the first EOG electrode and the second EEG electrode and a second strip portion between the second EEG electrode and the first EEG electrode, the first strip portion being set at an angle relative to the second strip portion.

16. An electrode array according to claim 13, further comprising an indicator element indicating a central line between the first EEG electrode and the second EEG electrode.

17. An electrode array according to claim 16, wherein the indicator element is a ground electrode.