Method and apparatus for reducing contamination of an electrical signal
First Claim
1. A method of reducing contamination of electrical signals recorded in the presence of repeated interference contamination comprising:
- (a) obtaining an electrical signal, wherein the electrical signal was recorded in the presence of a contaminating signal;
(b) detecting a timing signal that occurs at a fixed time point during the electrical signal relative to the onset of the contaminating signal;
(c) digitizing the electrical signal, wherein the digitizing begins with the timing signal;
(d) analyzing a plurality of digitized electrical signals, wherein the electrical signals are synchronized with respect to the timing signal, to obtain an estimated contaminating signal; and
(e) subtracting the estimated contaminating signal from the digitized electrical signal, thereby reducing contamination of the electrical signal;
wherein the analyzing to obtain the estimate of the contaminating signal comprises calculating a weighted average of the contaminating signals; and
wherein the estimate of the contaminating signal is biased towards recent events, and comprises a first sum consisting of the nth electrical signal added to a scalar multiple, w, of a prior estimate of the contaminating signal, divided by a second sum obtained by adding a series 1+w2+w3+w4 . . . + . . . wn.
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Abstract
The method of reducing contamination of electrical signals recorded in the presence of repeated interference contamination comprises obtaining an electrical signal recorded in the presence of a contaminating signal, and detecting a timing signal that occurs at a fixed time point during the electrical signal relative to the onset of the contaminating signal. The electrical signal is digitized, wherein the digitizing begins with the timing signal. A plurality of digitized electrical signals is analyzed, wherein the electrical signals are synchronized with respect to the timing signal, to obtain an estimated contaminating signal that is subtracted from the digitized electrical signal. This method can be used with electrophysiological signals, such as EEG, ECG, EMG and galvanic skin response, and for elimination of noise associated with concurrently used methods such as MRI. The method of noise reduction is applicable to recordings of other electrical signals, including audio recordings.
203 Citations
34 Claims
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1. A method of reducing contamination of electrical signals recorded in the presence of repeated interference contamination comprising:
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(a) obtaining an electrical signal, wherein the electrical signal was recorded in the presence of a contaminating signal; (b) detecting a timing signal that occurs at a fixed time point during the electrical signal relative to the onset of the contaminating signal; (c) digitizing the electrical signal, wherein the digitizing begins with the timing signal; (d) analyzing a plurality of digitized electrical signals, wherein the electrical signals are synchronized with respect to the timing signal, to obtain an estimated contaminating signal; and (e) subtracting the estimated contaminating signal from the digitized electrical signal, thereby reducing contamination of the electrical signal; wherein the analyzing to obtain the estimate of the contaminating signal comprises calculating a weighted average of the contaminating signals; and
wherein the estimate of the contaminating signal is biased towards recent events, and comprises a first sum consisting of the nth electrical signal added to a scalar multiple, w, of a prior estimate of the contaminating signal, divided by a second sum obtained by adding a series 1+w2+w3+w4 . . . + . . . wn.- View Dependent Claims (2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 18, 19, 26, 27, 28)
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7. A method of reducing contamination of electrical signals recorded in the presence of repeated interference contamination comprising:
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(a) obtaining an electrical signal, wherein the electrical signal was recorded in the presence of a contaminating signal; (b) detecting a timing signal that occurs at a fixed time point during the electrical signal relative to the onset of the contaminating signal; (c) digitizing the electrical signal, wherein the digitizing begins with the timing signal; (d) analyzing a plurality of digitized electrical signals, wherein the electrical signals are synchronized with respect to the timing signal, to obtain an estimated contaminating signal; and (e) subtracting the estimated contaminating signal from the digitized electrical signal, thereby reducing contamination of the electrical signal, wherein the digitizing is performed at a sampling rate below the Nyquist rate for the contaminating signal. - View Dependent Claims (29, 30, 31)
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14. A method of reducing contamination of electrical signals recorded in the presence of repeated interference contamination comprising:
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(a) obtaining an electrical signal and removing a DC offset from the electrical signal by analog subtraction using a differential amplifier, wherein the electrical signal was recorded in the presence of a contaminating signal; (b) detecting a timing signal that occurs at a fixed time point during the electrical signal relative to the onset of the contaminating signal; (c) digitizing the electrical signal, wherein the digitizing begins with the timing signal; (d) analyzing a plurality of digitized electrical signals, wherein the electrical signals are synchronized with respect to the timing signal, to obtain an estimated contaminating signal; and (e) subtracting the estimated contaminating signal from the digitized electrical signal. thereby reducing contamination of the electrical signal, wherein the DC offset is measured; (i) by analog to digital conversion, and averaged over a time period long compared to lowest frequencies of interest in the electrical signal;
or(ii) in an analog integrator having a time constant long compared with lowest freguencies of interest in the signal. - View Dependent Claims (15, 16, 17, 32, 33, 34)
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20. A method of reducing contamination of electrical signals recorded in the presence of repeated interference contamination comprising:
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(a) obtaining an electrical signal, wherein the electrical signal was recorded in the presence of a contaminating signal; (b) detecting a timing signal that occurs at a fixed time point during the electrical signal relative to the onset of the contaminating signal; (c) digitizing the electrical signal, wherein the digitizing begins with the timing signal; (d) analyzing a plurality of digitized electrical signals, wherein the electrical signals are synchronized with respect to the timing signal, to obtain an estimated contaminating signal; (e) subtracting the estimated contaminating signal from the digitized electrical signal, thereby reducing contamination of the electrical signal; wherein the estimate of the contaminating signal is multiplied by a scalar prior to the subtracting of step (e);
wherein the electrical recording comprises an electrophysiological signal and wherein the electrophysiological recordings comprise an electroencephalogram, are recorded concurrently with magnetic resonance image acquisition, and are used in a statistical analysis of change in intensity of the magnetic resonance signal.- View Dependent Claims (21, 22, 23, 24, 25)
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Specification