Foetal ultrasound. Three-dimensional (3-D) ultrasound scan of the face of a human foetus. The image was produced by a third generation 3-D ultrasound scanner called Voluson 730. 3-D scanning enables physiological disorders such as harelip and spina bifida to be diagnosed before birth. Once detected, it may be possible to perform corrective surgery while the foetus is still in the uterus. Ultrasound is a diagnostic technique which sends high-frequency sound waves into the body via a transducer. The returning echoes are recorded and used to build an image of an internal structure.