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Foetus skeleton. Coloured 3-D ultrasound scan of part of the skeleton of a foetus. The spine is seen from top to bottom, with ribs on either side. Ultrasound scanning is a diagnostic technique that 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. Foetal ultrasound scanning is routine during pregnancy. 3-D ultrasound uses computer technology to return more detailed images than conventional 2-D scans. (KEYSTONE/SCIENCE PHOTO LIBRARY/DR NAJEEB LAYYOUS)