Method and system for the denoising of large-amplitude artifacts in electrograms using time-frequency transforms
First Claim
1. A system for removing artifacts from an observed electrogram of a subject in order to produce a denoised electrogram, given a time-frequency transform, and given a database of reference electrograms, each said reference electrogram being free of said artifacts, and each said reference electrogram having been acquired from individuals other than said subject, said system comprising:
- a. a sensor for acquiring the electrogram of said subject to complement said database of reference electrograms, and for producing said observed electrogram; and
b. a digital signal processor for;
i. applying said time-frequency transform to said reference electrograms to produce a plurality of reference coefficient sets, each said reference coefficient set corresponding to a respective time-frequency span;
ii. calculating a threshold for each said time-frequency span based on a corresponding reference coefficient set;
iii. applying said time-frequency transform to said observed electrogram to produce a plurality of observed coefficient sets, each said observed coefficient set corresponding to a respective time-frequency span;
iv. comparing each coefficient of each said observed coefficient set with the corresponding threshold for a respective time-frequency span;
v. replacing every large coefficient of each said observed coefficient set which is above the respective threshold for the corresponding time-frequency span with a replacement value in order to produce denoised observed coefficient sets; and
vi. applying the inverse transform of said time-frequency transform to said denoised observed coefficient sets to reconstruct the denoised electrogram.
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Abstract
The present invention relates to a method of signal processing of electrograms for use in medical devices, preferably by time-frequency transforms. The present invention additionally relates to a system for receiving and analyzing such signals. The present invention preferably is a method utilizing the time-frequency transforms, such as wavelet transforms, for the purpose of artifact removal from EGs. These transforms decompose a signal in both time and frequency domains, and therefore, are well suited for non-stationary signal analysis. As a result, dissimilar signal features are well localized both in time and frequency, which potentially provides a good separation between the signal of interest and artifacts. This particularly applies to large-amplitude artifacts corrupting EGs.
66 Citations
23 Claims
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1. A system for removing artifacts from an observed electrogram of a subject in order to produce a denoised electrogram, given a time-frequency transform, and given a database of reference electrograms, each said reference electrogram being free of said artifacts, and each said reference electrogram having been acquired from individuals other than said subject, said system comprising:
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a. a sensor for acquiring the electrogram of said subject to complement said database of reference electrograms, and for producing said observed electrogram; and b. a digital signal processor for; i. applying said time-frequency transform to said reference electrograms to produce a plurality of reference coefficient sets, each said reference coefficient set corresponding to a respective time-frequency span; ii. calculating a threshold for each said time-frequency span based on a corresponding reference coefficient set; iii. applying said time-frequency transform to said observed electrogram to produce a plurality of observed coefficient sets, each said observed coefficient set corresponding to a respective time-frequency span; iv. comparing each coefficient of each said observed coefficient set with the corresponding threshold for a respective time-frequency span; v. replacing every large coefficient of each said observed coefficient set which is above the respective threshold for the corresponding time-frequency span with a replacement value in order to produce denoised observed coefficient sets; and vi. applying the inverse transform of said time-frequency transform to said denoised observed coefficient sets to reconstruct the denoised electrogram. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for removing artifacts from an observed electrogram of a subject in order to provide a denoised electrogram, said method comprising:
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a. acquiring a plurality of reference electrograms, each said reference electrogram being free of said artifacts; b. selecting a time-frequency transform which, when applied to said reference electrograms yields a plurality of reference coefficient sets, each said reference coefficient set corresponding to a respective time-frequency span; c. selecting a threshold for each time-frequency span; d. acquiring an electrogram from said subject to produce said observed electrogram; e. applying said time-frequency transform to said observed electrogram to produce a plurality of observed coefficient sets, each said observed coefficient set corresponding to a respective time-frequency span; f. comparing each coefficient of each said observed coefficient set with the corresponding threshold for a respective time-frequency span; and g. replacing every large coefficient of each said observed coefficient set which is above exceeds the respective threshold for the corresponding time-frequency span with a replacement value in order to produce denoised observed coefficient sets. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method for extracting artifacts from an observed electrogram of a subject in order to provide an artifactual electrogram, said method comprising:
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a. acquiring a plurality of reference electrograms, each said reference electrogram being free of said artifacts; b. selecting a time-frequency transform which, when applied to said reference electrograms yields a plurality of reference coefficient sets, each said reference coefficient set corresponding to a respective time-frequency span; c. selecting a threshold for each time-frequency span; d. acquiring an electrogram from said subject to produce said observed electrogram; e. applying said time-frequency transform to said observed electrogram to produce a plurality of observed coefficient sets, each said observed coefficient set corresponding to a respective time-frequency span; f. comparing each coefficient of each said observed coefficient set with the corresponding threshold for a respective time-frequency span; g. replacing every small coefficient of each said observed coefficient set which is less than the respective threshold for the corresponding time-frequency span with a replacement value in order to produce artifactual observed coefficient sets; and h. applying the inverse transform of said selected time-frequency transform to said artifactual observed coefficient sets to reconstruct the artifactual electrogram. - View Dependent Claims (18, 19, 20, 21, 22, 23)
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Specification