Where along a vessel is aliasing more likely to occur and why?

• A. Center due to higher velocities
• B. Edges due to lower velocities
• C. Uniform along vessel
• D. Only near stenosis

Answer: (A)

Aliasing in Doppler imaging happens when the Doppler shift exceeds the Nyquist limit set by the PRF. In a typical vessel with laminar flow, the velocity profile is parabolic: the fastest speed is at the center and it slows toward the walls. Because the center harbors the highest velocities, the Doppler shift there is most likely to exceed the Nyquist limit, making aliasing show up first or most prominently there. The edges experience lower velocities due to the no-slip condition, so aliasing is less likely there. A uniform velocity along the vessel isn’t realistic for laminar flow, and while a stenosis can create a high-velocity jet that can alias locally, the center of a normal vessel represents the region where aliasing is most likely across the length of the vessel.