An Adaptive Wavelet Method for Clutter Rejection of Doppler Signal: A Simulation Study

An adaptive method combining wavelet transform (WT) with the bivariate shrinkage function (BSF) with local variance estimation is presented for rejecting the strong clutter from Doppler ultrasound signal. The raw Doppler signal is decomposed by the undecimated WT in which the fast algorithm of translation invariant discrete wavelet transform (TIDWT) is adopted, and then the scale and wavelet coefficients selected in terms of clutter frequency range are shrunk by BSF. The clutter is first reconstructed by updated coefficients. This new method was validated by simulated carotid Doppler signal, and compared to static high pass filter (HPF). The improvements including spectrogram and signal-to-clutter (S/C) ratio by the new method over HPF was noticeable. For the simulated signal with S/C ratio -20 dB, the improvement in S/C ratio was 22.66 by the new method, but 22.05 by HPF. The mean spectrum further indicated that the new method effectively reject clutter and simultaneously possess nicer retention of blood components.