Reverberation

A circumferential, “napkin ring” calcification is seen in this image with three arcs of reverberation artifacts (arrowheads).
Reverberation artifacts are repetitive false echo images due to high acoustic impedance mismatch such as the presence of heavily calcified lesions.
When ultrasound passes into calcium (or stent struts), it can strongly and repeatedly reflect before it returns to the transducer producing these reverberations.