What artifact occurs when the PRF is set too low during Doppler interrogation?

What artifact occurs when the PRF is set too low during Doppler interrogation?

• A. Aliasing
• B. Spectral broadening
• C. Clutter
• D. Noise

Answer: (A)

The main idea here is sampling and the Nyquist limit in Doppler ultrasound. The pulse repetition frequency (PRF) sets how often the Doppler signal is sampled, which in turn defines the maximum Doppler frequency (unambiguous velocity) you can measure—the Nyquist velocity, equal to half the PRF. If the blood flow velocity yields a Doppler shift higher than this limit, the measurements wrap around and appear as lower velocities on the opposite side of the baseline. This wrap-around artifact is called aliasing. On the spectral display, you'll see high-velocity components suddenly reappear near the bottom (or top) of the spectrum, creating a misrepresented velocity pattern. To reduce or avoid aliasing, you can increase the PRF (raising the Nyquist velocity) or use continuous-wave Doppler, which isn’t subject to this sampling limitation. The other issues—spectral broadening, clutter, or noise—stem from different causes and aren’t specifically a result of a too-low PRF.

The main idea here is sampling and the Nyquist limit in Doppler ultrasound. The pulse repetition frequency (PRF) sets how often the Doppler signal is sampled, which in turn defines the maximum Doppler frequency (unambiguous velocity) you can measure—the Nyquist velocity, equal to half the PRF. If the blood flow velocity yields a Doppler shift higher than this limit, the measurements wrap around and appear as lower velocities on the opposite side of the baseline. This wrap-around artifact is called aliasing. On the spectral display, you'll see high-velocity components suddenly reappear near the bottom (or top) of the spectrum, creating a misrepresented velocity pattern. To reduce or avoid aliasing, you can increase the PRF (raising the Nyquist velocity) or use continuous-wave Doppler, which isn’t subject to this sampling limitation. The other issues—spectral broadening, clutter, or noise—stem from different causes and aren’t specifically a result of a too-low PRF.