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.
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.
It is also used for such procedures as lithotripsy, in which shock waves break up kidney stones, eliminating the need for surgery. Ultrasound is noninvasive and involves no radiation.