Method and system for limiting interference in electroencephalographic signals
First Claim
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1. A method for processing a composite physiological signal having at least one physiological signal of interest and at least one unwanted spurious signal, the composite physiological signal having a first duration, the method comprising:
- determining a variable spurious signal threshold, said spurious signal threshold being determined as a function of signal spectral energy;
or eliminating at least one narrow-band spurious signal in said physiological signal throughout said signal first duration that meets or exceeds said spurious signal threshold by performing a plurality of Fourier transforms, each of said Fourier transforms being performed on at least one of a plurality of overlapping temporal windows of said physiological signal, and filtering Fourier coefficients by reducing said Fourier coefficients in narrow bands of frequencies, whereby a window-to-window temporal variation of said Fourier coefficients to be filtered is distinguishably less than a window-to-window temporal variation of non-filtered Fourier coefficients;
recreating an intermediate signal throughout substantially all of said physiological signal first duration by inverse Fourier transforming said filtered Fourier coefficients;
eliminating at least one intermittently-occurring spurious signal in said intermediate signal by performing at least one wavelet analysis on said intermediate signal, said intermittently-occurring spurious signal including a plurality of intermittently-occurring wavelet coefficients, and filtering said intermittently-occurring wavelet coefficients by reducing or zeroing intermittently-occurring wavelet coefficients that are distinguishably greater than the remaining intermittently-occurring wavelet coefficients in said intermittently-occurring spurious signal; and
recreating a second physiological signal in filtered form by performing a plurality or inverse wavelet analyses on said filtered intermittently-occurring wavelet coefficients.
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Abstract
This invention provides methods and systems for removing or limiting interference and artifacts often found in EEG signals and/or EOG signals and/or other physiological signals, and produces output signals that can be of greater use for analytic or diagnostic purposes, such as sleep studies. Interference and artifacts are removed by applying a plurality of filtering methods targeted to the particular time-frequency characteristics of the anticipated interference.
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Citations
28 Claims
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1. A method for processing a composite physiological signal having at least one physiological signal of interest and at least one unwanted spurious signal, the composite physiological signal having a first duration, the method comprising:
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determining a variable spurious signal threshold, said spurious signal threshold being determined as a function of signal spectral energy; or eliminating at least one narrow-band spurious signal in said physiological signal throughout said signal first duration that meets or exceeds said spurious signal threshold by performing a plurality of Fourier transforms, each of said Fourier transforms being performed on at least one of a plurality of overlapping temporal windows of said physiological signal, and filtering Fourier coefficients by reducing said Fourier coefficients in narrow bands of frequencies, whereby a window-to-window temporal variation of said Fourier coefficients to be filtered is distinguishably less than a window-to-window temporal variation of non-filtered Fourier coefficients; recreating an intermediate signal throughout substantially all of said physiological signal first duration by inverse Fourier transforming said filtered Fourier coefficients; eliminating at least one intermittently-occurring spurious signal in said intermediate signal by performing at least one wavelet analysis on said intermediate signal, said intermittently-occurring spurious signal including a plurality of intermittently-occurring wavelet coefficients, and filtering said intermittently-occurring wavelet coefficients by reducing or zeroing intermittently-occurring wavelet coefficients that are distinguishably greater than the remaining intermittently-occurring wavelet coefficients in said intermittently-occurring spurious signal; and recreating a second physiological signal in filtered form by performing a plurality or inverse wavelet analyses on said filtered intermittently-occurring wavelet coefficients. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 27)
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18. A method for processing a physiological signal of interest having a certain duration and comprising unwanted spurious signals, the method comprising:
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applying to said physiological signal one or more filters for producing a plurality of transform coefficients that are responsive to signal components present in sub-domains of a time/frequency domain plane having a plurality of different shapes, said filters comprising one or more windowed Fourier transformations responsive to signal components in sub-domains having a shape with a relative temporal duration substantially greater than a relative frequency bandwidth, and also comprising one or more wavelet transformations responsive to signal components in sub-domains having a limited relative temporal duration, and performing a first filtering operation that reduces or eliminates spurious signals by reducing or zeroing first Fourier transform coefficients in one or more narrow bands with a substantially constant frequency that have temporal variations distinguishably less than the temporal variations of second Fourier transform coefficients, and a second filtering operation that reduces or eliminates spurious signals by reducing or zeroing third wavelet transform coefficients with a limited relative temporal duration and with amplitudes that are distinguishably greater than the amplitudes of fourth wavelet transform coefficients; and performing a plurality of inverse transformations to recreate a signal of interest in filtered form. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 28)
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Specification