Doppler and Hemodynamics
Color Doppler is a form of pulsed Doppler that displays returning echoes as color superimposed on a 2D image. Frequency shift (or Doppler shift) between successive transmitted and returned sample points is processed using “autocorrelation.”
Color is assigned based on the direction of flow and mean velocity in the sampled area, so unlike spectral Doppler, alignment with flow is not required.
By convention, the color displayed depends on blood flow direction relative to the transducer: Blue is flow Away, and Red is flow Towards (BART). The zero velocity baseline in the center is black as there is no frequency shift (no flow).
Color Doppler is displayed using different color maps. The enhanced velocity color map shows higher velocity flows as brighter colors. The variance color map uses additional colors (yellow and green) to indicate turbulent flow, thus displaying a mosaic of colors. Variance expresses the degree to which velocities within a given sample volume differ from the mean velocity within that sample.