CW envelope selection and Doppler gain
Quick reference:↑ LVOT and general Doppler hemodynamics↑ Aortic stenosis↑ Aortic regurgitation↑ Mitral regurgitation↑ Mitral stenosis↑ Tricuspid and pulmonic valves↑ Prosthetic aortic valves↑ Prosthetic mitral and tricuspid valves
| View | Any spectral Doppler recording (PW or CW), beam as parallel to flow as possible. |
|---|---|
| Timing | Measure the representative beats of the rhythm; edit out poor-quality, lower-velocity signals. |
| Caliper / trace | Measurements at the modal (densest) margin of the signal; peak at the dense edge, not at weak signals beyond it. |
Example
Correct example
Gain adjusted so the full spectrum of velocities is shown without noise filling the envelope; the smooth modal curve is traced; when a jet is acquired from several sites, the highest-quality and highest-velocity signal is used.
Common error
Overgaining and then tracing the noise, measuring weak ill-defined signals beyond the modal velocity, or reporting a signal of marginal quality.
Effect on interpretation
Overgained or noisy envelopes overestimate peak velocity and gradients; underestimated or poor-quality signals should be withheld rather than reported as a low gradient.
Why
The modal velocity is the velocity of most of the blood cells in the sample; the faint edges are the tails of the spectrum and transit-time effects, not flow.