Spectral Doppler artifacts: mirroring, double envelope, tiger stripes
| View | PW and CW recordings, especially near the pleura or pericardium, across prosthetic or calcified valves, and over oscillating structures. |
|---|---|
| Timing | Mirrored signals are simultaneous with the true signal; tiger stripes are horizontal bands on both sides of the baseline. |
| Caliper / trace | Measure only the dense true envelope: the mirrored copy is less dense on the opposite side; the double envelope is a faint outer copy at exactly twice the modal velocity. |
Correct example
A faint symmetric signal below the baseline of pulmonary venous or mitral flow is a spectral mirror; a faint outer envelope at twice the velocity of the dense CW jet is a double envelope; evenly spaced bands across the baseline are tiger stripes from an oscillating leaflet, lead or mass.
Common error
Tracing the outer duplicated envelope (doubling the gradient), reading a mirror signal as reversed flow, or interpreting tiger stripes as a flow signal.
Effect on interpretation
A doubled envelope overestimates velocity and gradient across a prosthetic or calcified valve; mirroring suggests non-existent bidirectional flow. Lowering Doppler gain and improving alignment reduce both.
Why
Mirroring arises from near-perpendicular interrogation or system misinterpretation; the double envelope is a reverberation/duplication from a strong reflector in high flow with high gain; tiger stripes are the fundamental and harmonic frequencies of a vibrating structure.