Use of ultrasonic waves to produce images of body structures. The waves travel through tissues and are reflected back where density differs (e.g., the border between a hollow organ's wall and its inside). The reflected echoes are received by an electronic apparatus that measures their intensity level and the position of the tissue reflecting them. The results can be displayed as still images or as a moving picture of the inside of the body. Unlike X-rays or other ionizing radiation, ultrasound carries minimal, if any, risk. Most often used during pregnancy to examine the fetus, ultrasound imaging is also used on internal organs and on the eye, breast, and major blood vessels. It can often show whether a growth is benign or malignant. Seealso diagnostic imaging.

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