What explains color speckling on Doppler color flow imaging?

• A. Vibration of surrounding soft tissue due to turbulence in the fistula channel; relatively low velocities show up darker red and blue
• B. Color aliasing due to high velocity
• C. Motion artifact from patient movement
• D. Color bleed due to angle

Answer: (A)

Color speckling comes from the motion of tissue caused by turbulent flow in a high-flow channel, such as a fistula. The turbulence creates rapid, small velocity components within the Doppler sample volume, so the color Doppler algorithm sees a mix of forward and backward velocities in a single area. This random mix produces a speckled, mosaic appearance rather than a uniform color. The low-velocity components tend to appear as darker red or blue tones because their Doppler shifts are smaller and register as weaker on the color map.

Aliasing would cause a distinct color wrap when velocities exceed the Nyquist limit, rather than a speckled pattern. Motion artifact from patient movement generally looks like overall image smear, not localized speckle tied to turbulent flow. Color bleed from an unfavorable angle would extend color along a vessel boundary, not create a speckled patch around turbulent flow.