Technical limitations of the present color coded US-Doppler systems in analyzing flow anomalies in arteries

The pulsatile nature of blood flow, compliance and tapering of arteries, and arterial bifurcations and curves affect the flow distribution within an artery as function of time. Temporarily and spatially secondary flow phenomena may occur. The presence of secondary flow phenomena causes the flow velocity vector to deviate from the axial direction. In general ultrasound Doppler systems only register the velocity component along the line of observation. For color coded Doppler systems the accuracy to assess this velocity component highly depends on the number of subsequent pulses issued along the same line. A high number of repetitive pulses will improve the accuracy, but only at the expense of a reduced frame rate in the Doppler mode, a reduced width of the region of interest, or both. To appreciate properly the time dependent nature of the velocity distribution quite a high frame rate is required. This paper discusses the flow phenomena of interest and the basic factors affecting the accuracy in velocity assessment that can be obtained. Computer generated Doppler signals are analyzed to obtain quantitative information about the standard deviation of the estimate for the velocity in a given sample volume.