Determining the peak velocity in a blood flow from its Doppler spectrum

The signal backscattered by blood cells crossing a sample volume produces a Doppler power spectrum determined by the scatterers´ velocity distribution. Several methods have been proposed for estimating the maximum velocity component - an important clinical parameter - but these methods are approximate solutions based on heuristic thresholds applied to the Doppler power spectrum. Reported here is a modeling of the Doppler power spectrum by the distribution of scatterer velocities; the resulting model provides the location of the peak velocity in terms of a threshold applied to the descending slope of the power spectrum. In particular it is shown that, for a parabolic velocity distribution, the peak velocity corresponds to the half-power point. This result is verified experimentally using Doppler spectra obtained from a sample volume intercepting laminar flows of peak velocity from ~ 7 - 20 cm/s. Peak velocities obtained from the half-slope frequency of the measured Doppler spectra show an error with + 0.3% bias and 1.5% standard deviation, suggesting this is an accurate model.