Differentiation of acoustic shadowing due to calculi and gas collections.

In abdominal sonography, acoustic shadowing may be seen distal either to calculi or gas collections. This in vitro study suggests that acoustic shadows distal to calculi contain significantly fewer echoes, and are therefore more sharply defined than those distal to gas collections. Artifactual reverberation echoes within acoustic shadows distal to gas collections result from virtually total sound reflection at tissue-air interfaces, whereas shadows distal to calculi are primarily due to sound absorption. The appearances of shadowing distal to calculi or gas collections may be of value in clinical sonography.