Acoustic shadow is produced by the following except-

Ultrasound waves are reflected at the surfaces between the tissues of different density The reflection being propoional to the difference in If the difference in density is increased, the propoion of reflected sound is increased, and the propoion of transmitted sound is propoionately decreased. If the difference in tissue density is very different, then the sound is completely reflected, resulting in total Acoustic shadowing is present behind bones, calculi (stones in kidneys, gallbladder, etc.) and air (intestinal gas) Ref : Physical principles of ultrasound (Dr Daniel J Bell and Ass. Pr. Mirjan M. Nadrljanski et al.)