/ul"treuh sownd'/, n.1. Physics. sound with a frequency greater than 20,000 Hz, approximately the upper limit of human hearing.2. Med. the application of ultrasonic waves to therapy or diagnostics, as in deep-heat treatment of a joint or imaging of internal structures. Cf. ultrasonography.[1920-25; ULTRA- + SOUND1]
* * *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, the eye, breast, and major blood vessels. It can often show whether a growth is benign or malignant. See also diagnostic imaging.
* * *also called ultrasonographyin medicine, the use of high-frequency sound (ultrasonic) waves to produce images of structures within the human body. Ultrasonic waves are sound waves that are above the range of sound audible to humans. The ultrasonic waves are produced by the electrical stimulation of a piezoelectric crystal and can be aimed at a specific area of the body. As the waves travel through bodily tissues, they are reflected back at any point where there is a change in tissue density, as, for instance, in the border between two different organs of the body. The reflected echoes are received by an electronic apparatus that determines the intensity level of the echoes and the position of the tissue giving rise to the echoes. The images thus formed can be displayed in static form, or, through the use of rapid multiple sound scans, they can in effect provide a moving picture of the inside of the body.Part of ultrasound's usefulness derives from the fact that the sound waves are less potentially harmful to human tissues than are X rays (X-ray) or other ionizing radiations. Because it is an invasive procedure, theoretical risks to the tissues do exist; however, there are no known examples of tissue damage from conventional ultrasound imaging. Ultrasound is most commonly used to examine fetuses in utero in order to ascertain size, position, or abnormalities. Ultrasound is also used to provide images of the heart, liver, kidneys, gallbladder, breast, eye, and major blood vessels.
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