Key result
S-transform de-noising reduces 60 Hz ECG interference and preserves signal spectrum better than notch filtering.
Why the study?
Most existing methods to reduce powerline interference in biomedical signals also attenuate the 60 Hz power of the signals themselves.
Does the S-transform improve the removal of powerline interference from biomedical signals compared to a notch filter?
Does the S-transform improve the removal of powerline interference from biomedical signals compared to a notch filter?
The S-transform is a novel and superior method for removing 60 Hz powerline interference from ECG signals compared to traditional notch filters.
S-transform may preserve 60 Hz signal power during interference removal; leaves open clinical validation before routine use.
Powerline interference always disturbs recordings of biomedical signals. Numerous methods have been developed to reduce powerline interference. However, most of these techniques not only reduce the interference but also attenuate the 60 Hz power of the biomedical signals themselves. In the present study, we applied the S-transform, which provides an absolute phase of each frequency in a multi-resolution time-frequency analysis, to reduce 60 Hz interference. According to results from an electrocardiogram (ECG) to which a simulated 60 Hz noise was added, the S-transform de-noising process restored a power spectrum identical to that of the original ECG coincident with a significant reduction in the 60 Hz interference. Moreover, the S-transform de-noised the signal in an intensity-independent manner when reducing the 60 Hz interference. In both a real ECG signal from the MIT database and natural brain activity contaminated with 60 Hz interference, the S-transform also displayed superior merit to a notch filter in the aspect of reducing noise and preserving the signal. Based on these data, a novel application of the S-transform for removing powerline interference is established.
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Huang et al. (2008) studied Biomedical signals with powerline interference. S-transform vs. Notch filter was evaluated on Reduction of 60 Hz interference and preservation of signal power spectrum. The S-transform successfully reduced 60 Hz powerline interference in ECG and brain activity signals while preserving the original signal power spectrum better than a notch filter.
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