Spectral mirroring artifact is most commonly associated with what Doppler angle?

• A. Doppler angle near 0 degrees
• B. Doppler angle near 90 degrees
• C. Wall filter high
• D. PRF low

Answer: (B)

Spectral mirroring shows up as a duplicate of the Doppler spectrum on the opposite side of the baseline. It occurs most often when the Doppler angle is near 90 degrees because the velocity component along the beam becomes almost zero, so the true signal is very small and easily overwhelmed by noise. That tiny, ambiguous signal can be misinterpreted by the display or processing as a mirrored version of the flow, producing a phantom spectrum on both sides of the baseline. By angling the probe to obtain a Doppler angle well away from 90 degrees (around 45–60 degrees), the true velocity component along the beam increases, the spectrum becomes clearer, and the mirroring artifact diminishes. Other factors like wall filter settings or PRF target different artifacts and aren’t the primary cause of spectral mirroring.