What should be done to improve the Doppler waveform?

• A. Change the Doppler angle
• B. Decrease the Doppler gain
• C. Increase the PRF
• D. Reposition the sample volume

Answer: (A)

Improving a Doppler waveform hinges on aligning the ultrasound beam with the direction of blood flow. The Doppler frequency shift depends on the cosine of the angle between the beam and the flow: fD = 2 f0 v cos(theta) / c. When the beam is more parallel to the flow (a smaller theta), cos(theta) is larger, so the Doppler shift increases. That makes the spectral trace clearer and reduces spectral broadening, giving a sharper, more reliable waveform. In practice, aiming for an angle around 45–60 degrees often yields the best balance between accurate velocity measurement and a strong signal; angles steeper than about 60 degrees reduce the shift and degrade the waveform.

Lowering the gain can make the waveform look weaker and more fragmented, and increasing the PRF mainly affects aliasing and sample rate rather than improving the waveform shape itself. Repositioning the sample volume can help if you’re sampling in a region with complex or turbulent flow, but the primary, most effective fix when the waveform is suboptimal is changing the Doppler angle to better align with the flow.