Increasing PRF to eliminate aliasing in Doppler ultrasound could introduce which artifact?

• A. Multipath reflections
• B. Range ambiguity
• C. Spectrum mirror image
• D. Propagation speed error

Answer: (B)

The main idea is how PRF controls sampling in Doppler ultrasound and the trade-off it creates. When you increase the pulse repetition frequency, you raise the Nyquist limit, so Doppler shifts that would previously alias into other frequencies are now captured properly. That’s why higher PRF helps eliminate aliasing.

But pushing PRF higher shortens the time between pulses. Echoes coming from deeper depths may not have finished returning before the next pulse is emitted, so the system can’t unambiguously assign a given echo to the correct depth. This creates range ambiguity—the depth information can wrap around or be misinterpreted because the echoes from deeper tissue overlap with echoes from shallower regions in time.

So, eliminating aliasing by increasing PRF introduces range ambiguity as the trade-off. Multipath reflections, spectrum mirror image, and propagation speed error are not the artifacts directly caused by increasing PRF in this context.