Ultrasound scanning/ultrasonography A method of investigation which uses high frequency, low intensity, ultrasonic waves to produce a picture on a television monitor. Tissues and organs vary in the way they transmit and reflect ultrasound and it is this that gives contrast to the images. It can be used to examine the fetus in the pregnant uterus in order to detect anatomical abnormalities or to monitor growth. It can show meningomyelocoele, anencephaly and an increasing number of other defects in time for termination of pregnancy (abortion). It can also be used to examine the head and brain of an infant up to 6 months of age and, although it does not produce such detailed pictures as a CT scan, it is safe, rapid and can be carried out at the bedside. It is particularly useful to show an abnormal collection of fluid or blood in the brain (echoencephalogram).