Doppler Ultrasonography

Abstract

Doppler ultrasound (US) is used to measure blood flow. This technology exploits the Doppler effect to measure blood flow in the vessels based on backscatter from red blood cells. Color, spectral, and power Doppler techniques are used to characterize different aspects of blood flow.

What is the Doppler effect?	Objects moving toward a detector reflect sound at higher frequencies. Conversely, objects moving away from a detector reflect sound at lower frequencies [1].
What is frequency shift?	Doppler US measures the frequency shift or the change in sound wave frequency as it reflects off a moving object [1].
What is color Doppler US?	Color Doppler US assigns a color spectrum to blood flowing toward and away from the US transducer. It can assess flow direction and velocity, though velocity measurements are more qualitative [1, 2].
What is spectral Doppler US?	Spectral Doppler US is used to quantify blood flow velocity [2].
How does spectral Doppler US work?	Spectral Doppler US evaluates the intensity of the frequency shift of sound waves at a specific region of interest as a function of time. The intensity is used to calculate flow velocity [2].
What is power Doppler US?	Power Doppler uses the amplitude of Doppler signal to detect flow. Unlike color Doppler, it ignores blood flow direction and velocity [1].
What is the benefit of power Doppler US?	Higher sensitivity for blood flow [2]