What system control should be adjusted to optimize a Doppler waveform's display?

• A. Velocity range
• B. Flow rate
• C. PRF
• D. Velocity scale

Answer: (D)

The key idea is that the display of a Doppler waveform is driven by the vertical velocity scale. The spectral Doppler plot uses velocity on the vertical axis, so the velocity scale determines how many meters per second (or cm/s) are represented per vertical division. Setting this scale correctly makes the waveform fit the display: high-velocity components stay within the top and bottom without clipping, and low-velocity components rise above the noise floor so they’re visible. If the scale is too small, fast flow clips at the top or bottom and you lose information; if it’s too large, slow velocities can become indistinguishable from background noise. Flow rate isn’t a direct display control, and PRF affects sampling and potential aliasing rather than the actual vertical display range. So adjusting the velocity scale is the most direct way to optimize how a Doppler waveform appears.