Blood velocity estimation by Doppler ultrasound: Problems and issues

Abstract

Modern methods of estimating blood flow have advanced considerably since Dr. Satamura and his colleagues at Osaka University reported the first measurements in 1959 using CW ultrasound. Most current methods involve the use of linear or phased arrays, which make possible 2-D color flow mapping, measurements from a single sample volume, and simultaneous B-mode imaging. However, along with this technology, troubling reports have been published (including our own) concerning the accuracy with which the velocity can be estimated and this has serious potential consequences in the quantitative assessment of vascular disease. The cause has not yet been completely identified, but appears to be partially associated with the wide range of Doppler angles within the sample volume, the complexity of the ultrasound propagation process, and the stochastic nature of the red blood cells flowing in the blood vessels. These causes will provide a focus for our review of the current status of Doppler ultrasound for vascular disease assessment and suggestions for future research. Specifically, a complete model of the entire measurement system is needed, and this includes the beamforming architecture, signal processing, possible nonlinear effects, scattering process, and nature of the 3-D vector flow field being measured.