Sonographic artifacts and their origins.

Artifacts are encountered daily in clinical sonography. They may be observed in B-mode gray-scale imaging, spectral pulsed Doppler imaging, and color Doppler imaging. Most of these distortions can be understood at a basic level by an appreciation of the form of the focused sound beam, the interaction of sound with tissue, and assumptions made about the spatial assignment of reflected echoes. Sonographic systems assign depth based on the time interval of round-trip echo travel and assume a straight line and singular path from transducer to reflector and reflector to transducer. The same speed of sound is assumed in all tissues for the purposes of spatial assignment. Some inherent acoustic artifacts are used reflexively to characterize tissue. Strong acoustic enhancement behind an anechoic structure confirms the diagnosis of a cyst. Clean acoustic shadowing distal to an echogenic focus in the gallbladder leads us to the diagnosis of gallstones. If unrecognized, acoustic artifacts can cause serious misdiagnoses. Several commonly encountered artifacts are illustrated, with a basic physical explanation of their occurrence.