To reduce aliasing in Doppler ultrasound, which strategy increases the pulsed repetition frequency (PRF)?

• A. Increase depth to reduce aliasing.
• B. Increase PRF by reducing depth.
• C. Use lower line rate.
• D. Use slower acquisition.

Answer: (B)

Aliasing in Doppler ultrasound occurs when the Doppler frequency shift exceeds half of the PRF, so increasing PRF raises the Nyquist limit and reduces aliasing. PRF is set by how quickly you can emit pulses and listen for echoes, which depends on the time it takes for echoes to travel to the depth being imaged and back. Deeper imaging requires longer round-trip times, meaning pulses are sent less often and PRF drops. By reducing the imaging depth, echoes return faster, allowing more pulses per second and increasing PRF, which lowers the chance of aliasing. The other options either deepen the depth (which lowers PRF) or involve slower acquisition or line-rate changes (which don’t raise PRF and can worsen sampling).