Ring down artifact
The artifact is only associated with gas bubbles, and occurs when an ultrasound pulse encounters a "horn" or "bugle" shaped fluid collection that is trapped between an inverted tetrahedron of 4 bubbles (3 on top and 1 nestled deep to them) The trapped fluid resonates, emitting a continuous signal back to the transducer. Whereas the transducer pulse is broad spectrum, the returning signal consists of one or more discrete (resonant) frequencies. "Beats" between these frequencies produce the variable appearance of the ring down. There is no "reverberation" ( i.e. multiple reflectances).
- 1. Avruch L, Cooperberg PL. The ring-down artifact. J Ultrasound Med. 1985;4 (1): 21-8. Pubmed citation