Method and device for removing EEG artifacts
View Patent ↗Systems and methods for automatically identifying segments of EEG signals or other brain electrical activity signals that contain artifacts, and/or editing the signals to remove segments that include artifacts.
1. A method for automatically editing brain electrical activity data, comprising:
positioning at least two frontal EEG electrodes on a patient, wherein the at least two electrodes are positioned at any two of FP 1 , FP 2 , F 7 , F 8 , and AFz positions based on the expanded international 10/20 placement system;
obtaining a signal representing brain electrical activity in each of the electrodes; and
using an analysis unit:
analyzing the signal to determine if temporal segments of the signal include artifacts due to at least one of eye movements, cable or electrode movements, impulse artifacts, and muscle activity, and if at least one segment does include artifacts identifying the segment as including artifacts; and
editing the signal to remove segments that include artifacts;
wherein determining if temporal segments of this signal include artifacts due to eye movements comprises filtering signals obtained from electrodes positioned at the FP 1 and FP 2 positions, comparing each signal to an average signal from the same Electrode, determining if the signals exceed a threshold, and if either signal exceeds a threshold, determining if changes in the FP 1 and FP 2 signals occur concurrently, and if the changes do occur concurrently, identifying the segment as including artifacts;
wherein determining if temporal segments of the signal include impulse artifacts comprises high pass filtering a signal from at least one electrode to remove the alpha component of the signal and determining if successive 100ms segments include signal variations greater than a predetermined threshold, and if successive 100ms segments include signal variations of greater than the threshold, identifying the segments as containing impulse artifacts; and
wherein determining if temporal segments of the signal include muscle movement artifacts comprises band pass filtering a signal from at least one electrode in a range of an EEG β1 band to produce signal E 1 and band pass filtering the same signal in the range of a β2 band to produce signal E 2 , and if a relative energy of E 2 relative to E 1 exceeds a threshold, identifying the segment as containing muscle movement artifacts.
2. The method of claim 1 , wherein the at least two frontal EEG electrodes are positioned at FP 1 and FP 2 positions based on the expanded international 10/20 placement system.
3. The method of claim 1 , wherein the at least two frontal EEG electrodes are positioned at F 7 and F 8 positions based on the expanded international 10/20 placement system.
4. The method of claim 1 , wherein the electrodes include at least five electrodes positioned at FP 1 , FP 2 , F 7 , F 8 , and AFz positions based on the expanded international 10/20 placement system.
5. The method of claim 1 , further including analyzing the signal to determine if temporal segments of the signal include artifacts due to at least one of significantly low amplitude signal and atypical electrical activity.
6. The method of claim 5 , wherein the electrodes include at least five electrodes positioned at FP 1 , FP 2 , F 7 , F 8 , and AFz positions based on the expanded international 10/20 placement system.
7. The method of claim 6 , wherein determining if temporal segments of the signal include significantly low amplitude signal includes determining if a mean square energy of a segment is below a threshold, and if the mean square energy is below a threshold, identifying the segment as including significantly low amplitude signal.
8. The method of claim 1 , wherein determining if temporal segments of the signal include artifacts due to eye movements includes filtering signals obtained from electrodes positioned at F 7 and F 8 positions and determining if the difference between the filtered signals exceeds a threshold.
9. The method of claim 1 , wherein determining if temporal segments of the signal include artifacts due to cable or electrode movement includes identifying a signal amplitude greater than a predetermined threshold, and if any segment includes an amplitude greater than the threshold identifying that segment as including cable or electrode movement artifacts.
10. The method of claim 9 , wherein the predetermined threshold is between 50 and 250 μV.
11. The method of claim 1 , wherein the threshold in the high pass filtering step is between 25 and 250 μV.
12. A device for automatically editing brain electrical activity data signals, comprising:
at least two electrodes;
a circuit for measuring electrical potential signals from the electrodes;
a memory unit configured to store data related to the electrical potential;
an analysis unit configured to analyze the signal to determine if temporal segments of the signal include artifacts due to at least one of eye movements, cable or electrode movements, impulse artifacts, and muscle activity, and if any segment does include artifacts identifying the segment as including artifacts, editing the data in the analysis unit to remove segments that include artifacts:
wherein determining if temporal segments of the signal include artifacts due to eye movements comprises the at least two electrodes being positioned on the device such that when the device is placed on a person, the electrodes are at FP 1 and FP 2 positions based on the expanded international 10/20 placement system, and filtering signals obtained from electrodes positioned at FP 1 and FP 2 positions, comparing each signal to an average signal from the same electrode, determining if the signal exceeds a threshold, and if either signal exceeds a threshold, determining if changes in the FP 1 and FP 2 signals occur concurrently, and if the changes do occur concurrently, identifying the segment as including artifacts;
wherein determining if temporal segments of the signal include impulse artifacts comprises high pass filtering a signal from at least one electrode to remove the alpha component of the signal and determining if successive 100ms segments include signal variations greater than a predetermined threshold, and if successive 100ms segments include signal variations of greater than the threshold, identifying the segments as containing impulse artifacts; and
wherein determining if temporal segments of the signal include muscle movement artifacts comprises band pass filtering a signal from at least one electrode in the range of an EEG β1 band to produce signal E 1 and band pass filtering the same signal in a range of a β2 band to produce signal E 2 ,and if a relative energy of E 2 relative to E 1 exceeds a threshold, identifying the segment as containing muscle movement artifacts.
13. The device of claim 12 , wherein the at least two EEG electrodes are positioned on the device such that when the device is placed on a person, the electrodes are at FP 1 and FP 2 positions based on the expanded international 10/20 placement system.
14. The device of claim 12 , wherein the at least two EEG electrodes are positioned on the device such that when the device is placed on a person, the electrodes are at F 7 and F 8 positions based on the expanded international 10/20 placement system.
15. The device of claim 12 , wherein the electrodes include at least five electrodes positioned on the device such that when the device is placed on a person, the electrodes are at FP 1 , FP 2 , F 7 , F 8 , and AFz positions based on the expanded international 10/20 placement system.
16. The device of claim 12 , wherein the analysis unit is configured to analyze the signal to determine if temporal segments of the signal include artifacts due to of any significantly low amplitude signal and atypical electrical activity.
17. The device of claim 16 , wherein the electrodes include at least five electrodes positioned on the device such that when the device is placed on a person, the electrodes are at FP 1 , FP 2 , F 7 , F 8 , and AFz positions based on the expanded international 10/20 placement system.
18. The device of claim 17 , wherein determining if temporal segments of the signal include artifacts due to eye movements includes filtering signals obtained from electrodes positioned at F 7 and F 8 positions and determining if the difference between the filtered signals exceeds a threshold.
19. The device of claim 17 , wherein determining if temporal segments of the signal include significantly low amplitude signal includes determining if a mean square energy of a segment is below a threshold, and if the mean square energy is below a threshold, identifying the segment as including significantly low amplitude signal.
20. The device of claim 12 , wherein determining if temporal segments of the signal include artifacts due to cable or electrode movement includes identifying a signal amplitude greater than a predetermined threshold, and if any segment includes an amplitude greater than the threshold, identifying that segment as including cable or electrode movement artifacts.