Which Doppler control has the greatest impact on accuracy of pulsatility or resistive index measurements?

• A. Wall Filters
• B. PRF
• C. Gain
• D. Doppler angle

Answer: (A)

Accurate pulsatility and resistive indices depend on reliable measurement of both peak systolic and end-diastolic velocities. Wall filters remove low-frequency signals from tissue motion and slow flow. If the filter is set too aggressively, the end-diastolic velocity, which is often very small, can be attenuated or lost. That directly skews the RI and PI calculations because the end-diastolic component is in the denominator for RI and in the numerator for PI. Even modest loss or distortion of diastolic velocity can markedly alter these indices, making wall filter settings the most influential factor for their accuracy.

In comparison, PRF mainly governs the risk of aliasing and how well high velocities are sampled, which matters for peak velocities but doesn’t inherently bias the relationship between systolic and diastolic velocities. Gain affects overall signal brightness but not the actual velocity values used in the indices. Doppler angle alters measured velocity via the cos theta term, but RI and PI are ratios that partly cancel angle effects, so angle errors tend to have a smaller impact on these indices than the diastolic signal loss caused by an improper wall filter.