Color Doppler color significantly overwriting the vessel wall. Which explanation best accounts for this?

• A. The color Doppler threshold is set too low
• B. The color Doppler scale is set too low
• C. Axial resolution is lower with color Doppler compared to B-mode
• D. Color Doppler uses a higher frequency transmitted pulse than B-mode

Answer: (C)

Color Doppler trades spatial detail for velocity information, so its axial resolution is lower than that of B-mode. Because color Doppler relies on sampling over a larger voxel and uses ensemble averaging to estimate flow, the edge between lumen and vessel wall becomes less sharp. This reduced edge resolution allows the color information to spill onto or overwrite the wall boundary, making it look like color is extending beyond the true wall. The issue isn’t mainly about the color threshold or scale, and the transmitted frequency isn’t higher for color Doppler; the fundamental factor is the inherently lower spatial (axial) resolution of color overlaid on the grayscale image.