Compensation of the bias caused by the wall filter on the meanDoppler frequency

摘要

In the presence of noise, any wall filter induces a bias on thenmean Doppler frequency estimated by the algorithm based on thencalculation of the phase of the autocorrelation function at lag 1. Innthis paper, it is shown that the bias results from the nonzero value ofnthe autocorrelation function of the filtered noise at lag 1. A generalnmethod for compensating the bias was then deduced. It consists of anpreliminary estimation of the filtered noise contribution and itsnsubtraction from the autocorrelation function of the Doppler signal. Thenmethod is independent of the nature of the noise and wall filter. Annevaluation of this method on simulated Doppler signals and onnmeasurements from a moving-string phantom showed that effectivencompensation of the bias was obtained, but at the expense of a highernvariance. Taking into account both the bias and the variance, however,nit was shown that this method offers an improvement over thennoncompensated method. Finally, the performance of this method wasndemonstrated using in vivo measurements taken from a human aorta