In color Doppler, if the internal carotid artery (ICA) is directed upward toward the transducer and appears blue while the external carotid and common carotid deeper appear red, is there reversal flow in the ICA?

• A. Yes
• B. The color always indicates reversal in the ICA
• C. The color indicates forward flow regardless of direction
• D. Not determinable from color alone

Answer: (D)

Color Doppler conveys flow direction only relative to the transducer, and the meaning of red versus blue can vary with machine settings and color maps. In this scenario, you cannot infer reversal of flow in the internal carotid just from the colors seen. The ICA is oriented toward the transducer, so forward flow would be expected, but the blue color on this vessel does not reliably indicate retrograde flow because color coding is not universal and can be inverted or misinterpreted depending on baseline and settings. The fact that deeper arteries show the opposite color reinforces that color alone is not enough to determine direction of flow. To determine if there is reversal, rely on spectral (pulsed-wave) Doppler at the ICA to measure the actual velocity and its direction, rather than relying on color alone.