Estimation of the blood Doppler frequency shift by a time-varying parametric approach

Doppler ultrasound is widely used in medical applications to extract the bl ood Doppler flow velocity in the arteries via spectral analysis. The spectral analysis of non-stationary signals and particularly Doppler si gnals requires adequate tools that should present both good time and freque ncy resolutions. It is well-known that the most commonly used time-windowed Fourier transform, which provides a time-frequency representation, is limi ted by the intrinsic trade-off between time and frequency resolutions. Para metric methods have then been introduced as an alternative to overcome this resolution problem. However, the performance of those methods deteriorates when high non-stationarities are present in the Doppler signal. For the pu rpose of accurately estimating the Doppler frequency shift, even when the t emporal flow velocity is rapid thigh non-stationarity), we propose to combi ne the use of the time-varying autoregressive (AR) method and the (dominant ) pole frequency. This proposed method performs well in the context where n on-stationarities are very high. A comparative evaluation has been made bet ween classical (FFT based) and AR (both block and recursive) algorithms. Am ong recursive algorithms we test an adaptive recursive method as well as a time-varying recursive method. Finally, the superiority of the time-varying parametric approach in terms o f frequency tracking and delay in the frequency estimate is illustrated for both simulated and in vivo Doppler signals. (C) 2000 Elsevier Science B.V. All rights reserved.