AAPM/RSNA physics tutorial for residents: Topics in US - Doppler US techniques: Concepts of blood flow detection and flow dynamics

Techniques of Doppler ultrasonography (US) have been available to clinicians for nearly 40 years. The Doppler effect as developed by sound propagation in human tissues and with the velocities observed for the human vasculature produces shifts in the frequencies of returning echo signals. These signals can be processed in a manner that allows the observer to determine the condition of the blood flow. The instrumentation for Doppler US has evolved to accommodate the expanding clinical use of US. Each development (eg, pulsed-wave Doppler US, color flow imaging) has been motivated by a desire to provide more clinical information about flow in the body. The algorithms used are complex, but increasingly powerful microelectronics have made these methods a reality at a reasonable cost. Users of Doppler US techniques must be aware of the complicated aspects of flow in the body, especially with regard to detection of disease in the human vasculature. The continuing development of US equipment aims to provide a greater understanding of hemodynamics and the relationship between blood flow and various disease processes. (C)RSNA, 2003.