Bias in mean frequency estimation of Doppler signals due to wall clutter filters.
Wall clutter filters used in Doppler ultrasound systems give rise to a bias in the mean frequency estimation. This effect has been explored for two second order filters: the initialised infinite impulse response (IIR)-type filter, and the finite impulse response (FIR) echo-canceller filter. These are used in conjunction with two mean frequency estimation algorithms: the FFT-based intensity-weighted-mean algorithm, and the autocorrelation algorithm. The bias is shown to be caused by the finite settling times of the filters. The IIR filter, although having a much better frequency response than the FIR filter, has a greater bias associated with it. A compromise between bias and frequency response is suggested and a simple method of bias correction is described.
Division of Medical Physics, Faculty of Medicine, Leicester University, UK.
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Tysoe
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Evans
D000465:Algorithms; D015982:Bias; D001808:Blood Vessels / Q000000981:diagnostic imaging*; D003198:Computer Simulation; D006801:Humans; D008961:Models, Structural; D018608:Ultrasonography, Doppler / Q000379:methods*