Removing mains interference from the mfERG by applying a post-processing digital notch filter: for the good or the
1Eye Center, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Killianstr. 5, 79106, Freiburg, Germany. sven.heinrich@uni-freiburg.de.
Documenta Ophthalmologica. Advances in Ophthalmology
|November 30, 2021
Summary
Digital notch filters can remove mains interference from multifocal electroretinography (mfERG) recordings. A 50-Hz filter caused mild amplitude reduction, while a 60-Hz filter had minimal impact, ensuring clinical interpretation remains valid.
Area of Science:
- Ophthalmology
- Neuroscience
- Signal Processing
Background:
- Mains interference can contaminate electroretinogram (ERG) recordings, potentially affecting diagnostic accuracy.
- Digital notch filters offer a post-processing solution to mitigate mains interference in electrophysiological data.
- The impact of filtering on signal amplitude and timing in multifocal electroretinography (mfERG) requires careful evaluation.
Purpose of the Study:
- To assess the effects of 50-Hz and 60-Hz digital notch filters on mfERG amplitude and peak time.
- To evaluate the filter's performance on both clean and mains-interference-contaminated mfERG traces.
- To investigate potential artifacts arising from nonlinear superposition of signals.
Main Methods:
- Analysis of 24 routine mfERG recordings without perceivable mains interference.
- Application of non-causal digital notch filters at 50 Hz and 60 Hz.
- Simulation of mains interference to demonstrate nonlinear superposition effects.
Main Results:
- The 50-Hz filter reduced mfERG amplitudes by 0%-15% (median 6%).
- The 60-Hz filter showed virtually no effect on mfERG amplitude.
- Simulations highlighted potential spurious high-frequency components in severely clipped signals.
Conclusions:
- A 50-Hz digital notch filter causes a mild amplitude reduction in mfERG, generally not impacting clinical interpretation.
- A 60-Hz digital notch filter is even more favorable, with minimal effects on mfERG data.
- Caution is advised when mains interference violates the assumption of linear additivity with the retinal signal.
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