Registered Physician in Vascular Interpretation (RPVI) Practice Exam

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.