Posterior acoustic enhancement is seen with

Posterior acoustic enhancement is seen with cystic lesions, gall bladder and urinary bladder. Posterior acoustic shadowing is seen with air, bone, calcification. Acoustic shadowing on an ultrasound image is characterized by a signal void behind structures that strongly absorb or reflect ultrasonic waves. This happens most frequently with solid structures, as sound conducts most rapidly in areas where molecules are closely packed such as in bone and stone.