Fetal heart rate signal denoising by processing the wavelet transform modulus maxima

The Wavelet Transform Analysis offers the possibility to decompose time series into both time and scale components. The paper applies the Wavelet Transform to analyse the Fetal Heart Rate (FHR) signal. A noise reduction technique that detects noise components by analysing the evolution of the Wavelet Transform modulus maxima across scales is adapted to improve the quality of FHR recording. The denoising scheme relies on the elimination of those multiscale maxima that correspond to noise components. The denoised FHR signal is reconstructed from the processed maxima by the inverse Wavelet Transform. The algorithm effectively removes transient spikes and reduces noise (both Gaussian and coloured) without destroying the frequency information content of the signal (as traditional low pass filtering does).