For example, gallbladder stones and bile duct stones inside and outside the liver are accompanied by acoustic shadowing. In contrast, gallbladder polyps and bile duct tumors are not accompanied by acoustic shadowing. In addition, intrahepatic calcified foci may also have acoustic shadows, which can be used clinically to make a preliminary judgment of the disease based on the presence of acoustic shadows. It is currently believed that acoustic shadowing is caused by the high acoustic impedance of ultrasound when it encounters denser media such as stones, calcifications or bone, and the ultrasound is completely reflected back to the deeper layers because of the absence of acoustic energy and the appearance of an echo-free flat striped area. However, it is also clinically possible to have a stone lesion without acoustic shadowing, which depends not only on the composition and structure of the stone itself, but also on the contrast conditions of the media surrounding the stone.