ultrasound

ultrasound or sonography, in medicine, technique that uses sound waves to study and treat hard-to-reach body areas. In scanning with ultrasound, high-frequency sound waves are transmitted to the area of interest and the returning echoes recorded (for more detail, see ultrasonics ). First developed in World War II to locate submerged objects, the technique is now widely used in virtually every branch of medicine . In obstetrics it is used to study the age, sex, and level of development of the fetus and to determine the presence of birth defects or other potential problems. Its use to determine fetal sex has led to the widespread abortion of female fetuses in some countries, such as China and India, where male offspring are more highly valued. Ultrasound is used in cardiology to detect heart damage and in ophthalmology to detect retinal problems. It is also used to heat joints, relieving arthritic joint pain, and for such procedures as lithotripsy, in which shock waves break up kidney stones, eliminating the need for surgery. Ultrasound is noninvasive, involves no radiation, and avoids the possible hazards—such as bleeding, infection, or reactions to chemicals—of other diagnostic methods.

ultrasound Waves of higher frequency than audible sound waves. Reflection of ultrasound waves was applied to underwater detection during World War II, and subsequently to imaging the body. The harmless waves (>100 Mhz) are aimed at the part to be examined, and reflections are detected from tissue components in proportion to their acoustic impedance. These signals can be processed to create two- or three-dimensional images. The most common use is for viewing the fetus in early pregnancy, but there are also many other diagnostic applications.

Treatment by ultrasound (ultrasonics) is widely used by physiotherapists, particularly for soft tissue injuries but also for a variety of more chronic conditions, with a view to promoting healing and relieving pain. Most commonly frequencies of 1–3 MHz are used. There are differences of opinion and practice, related to whether the intended action should be primarily thermal or non-thermal, but there is a lack of controlled trials on the efficacy of the different methods used.

J. K. Davidson, and Stuart Judge

ultrasound (ultrasonic waves) (ul-tră-sownd) n. sound waves of high frequency (above 20 kHz), inaudible to the human ear. Ultrasound in the range 2–20 MHz can be used to produce images of the interior of the body as the waves reflect off structures back to the probe (see ultrasonography). The vibratory effect of ultrasound can also be used to break up stones (see lithotripsy) and cataracts (see phacoemulsification), to remove calculus from the teeth, to destroy tumours (high-intensity focused u.; HIFU), and in the treatment of rheumatic conditions.