Which statement best describes carotid bulb color flow?

• A. Boundary layer separation with flow reversal and aliasing is typical
• B. Frequent aliasing
• C. No flow
• D. Boundary layer separation with flow reversal and no aliasing

Answer: (D)

The carotid bulb naturally creates a disturbance in flow as the jet expands into a wider region, causing boundary layer separation. This separation forms a small recirculation zone where the flow can reverse direction locally, even though the overall forward flow remains. On color Doppler, this appears as a retrograde component within the bulb, consistent with flow reversal.

Alias-free reverse flow is typical here because the velocities in the bulb are usually not high enough to exceed the Doppler Nyquist limit. Alias occurs when the velocity exceeds the scale, which is more common with high-velocity stenotic jets. So you can have visible flow reversal due to the separation without aliasing.

Other statements imply either no flow, persistent forward flow, or aliasing from the bulb, which doesn’t match the expected patterns: there is some reversed flow from the separation, but the velocities don’t usually produce aliasing in a normal bulb.