Spectrogram enhancement algorithm: a soft thresholding-based approach.
Enhancing the spectrogram by denoising the Doppler ultrasound signal is a preliminary step, and important for further processing. Because the spectrogram may be based on the short-time fast Fourier transform (FFT) of the Doppler ultrasound signal, whose power spectrum density is time-varying, traditional denoising algorithms that simply optimize the mean-squared error are not appropriate, and they may exhibit considerable undesirable, noise-induced frequency components. A soft thresholding-based denoising algorithm is put forward in this paper, that achieves almost the minimax mean square error (MSE) over a wide range of function classes having norms measuring smoothness (i.e., it meets both the requirement of smoothness and MSE). Due to the importance of noise level estimation while applying this method, several robust L-estimators are compared and the median absolute deviation (MAD) method is chosen to estimate the noise level. The simulation study shows better performance of the later algorithm under various quantification measures, compared to the FFT thresholding and the hard thresholding wavelet method, and the results of clinical data also confirm it.
Liu
B
B
Electrical Engineering Department, Fudan University, Shanghai, China.
Wang
Y
Y
Wang
W
W
D000465:Algorithms; D016477:Artifacts; D002648:Child; D002675:Child, Preschool; D003198:Computer Simulation; D005583:Fourier Analysis; D006801:Humans; D007223:Infant; D013997:Time Factors; D018608:Ultrasonography, Doppler / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data