In color Doppler color mapping, the color green represents which concept?

• A. Aliasing
• B. Laminar flow
• C. Variance
• D. Negative Doppler shift

Answer: (C)

Color Doppler color mapping can show not only flow direction and speed but also how uniform the flow is within the sampled area. In variance-based color Doppler, the green color flags turbulence—the high variability of velocities within a single voxel. When flow is laminar and velocities are consistent, there’s little variance and little or no green appearance. But when flow is disturbed—such as at a stenosis, around bifurcations, or in jets—velocity values spread out more, and green appears to indicate that increased variance. This helps clinicians spot areas of disturbed flow. The other concepts aren’t represented by green: aliasing is a sampling artifact from too-low PRF causing wrap-around in the velocity display, and negative Doppler shift relates to flow direction toward the transducer, shown by direction color, not by variance.