Foetal ultrasound. Three-dimensional (3-D) ultrasound scan of a human foetus. Its head is at centre right, its body at bottom centre, and its legs at far left. The umbilical cord is seen at centre left. 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. 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.