Noise reduction for Doppler ultrasound signal based on cycle-spinning and thresholding methods

The spectrogram of Doppler ultrasound signal has been widely used in the clinical diagnosis. The additional frequency component arising from noise will produce an adverse effect on the subjective analysis of the spectrogram and its quantitative analysis. The methods combining cycle-spinning with thresholding methods using orthogonal wavelet transform and cosine packet decomposition are proposed to remove noise from Doppler ultrasound signal. At first, a specified transform method is performed on the signal of interest. Then the soft or hard thresholding method is used to shrink the coefficients, from which the denoised signal is reconstructed. In the simulation study, the improvements of the mean frequency waveform and the SNR before and after denoising are studied. Simulation results have shown that the methods incorporating with cycle-spinning are superior to those traditional denoising methods. In view of computational complexity and performance improvements, the orthogonal wavelet transform combined with cycle-spinning is a practical approach for denoising Doppler ultrasound signal.