The effect of noise and high-pass filtering on the estimation of mean blood velocity using wide and narrow ultrasound beams

Recently, a new method of analysis has been proposed for the calculation of a Doppler frequency proportional to mean blood velocity for the case where the Doppler beam is assumed to be of negligible thickness compared to the vessel diameter, and the velocity profile is axisymmetric and monotonic increasing from the vessel wall to the vessel center. Such analysis of the Doppler signal is an alternative to that commonly performed under the assumption that the beam insonates the vessel uniformly. Errors in each method are found and compared for the case where the Doppler signal is contaminated by noise, and for the case where the signal is subjected to an ideal high-pass filter. The frequency resulting from the new method of analysis is affected by low-frequency perturbations approximately twice as much as that resulting from the standard method. However, the new method is much more immune to high frequency perturbations. If each method is used with the beam shape for which it is appropriate then, for a given velocity profile, each method is equally affected by the use of the same ideal high-pass filter.