Method and apparatus for reducing contamination of an electrical signal

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 digitizing is performed at a sampling rate below the Nyquist rate for the contaminating signal.

A method of reducing contamination of electrical signals recorded in the presence of repeated interference contamination comprising:

• (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.

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;
• (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.