Figure 1.

Denser materials reflect more ultrasound waves. Accordingly, fluid (like ascites) is black (anechoic), soft tissue (like the liver) is gray, fibrous tissue (like the diaphragm) is white without a shadow, and stones are white (hyperechoic) with a shadow. The air is very hyperechoic having reverberation artifacts. (This figure was reproduced from the study of Abu-Zidan and Cevik[42]), which is distributed under the terms of the Creative Commons Attribution 4.0 International License