ultrasound
n. sound whose frequency exceeds the human audibility range, often used to measure and record structures and structural change within the body in the imaging technique called ultrasonography (or sonography). Echoes from ultrasound waves reflected from tissue surfaces are recorded to form structural images for diagnostic purposes, such as to examine a growing fetus during pregnancy or to examine internal organs, such as the heart, liver, kidneys, and gallbladder, for signs of health or disease. Compare infrasound.