1. Ashley, J.S.A., Pasker, P. and Beresford, J.C.(1972) Lancet 1.: 890
2. Boucot, K.R. and Weiss, W.(1973) Is curable lung cancer detected by semi-annual screening ? Journal of the American Medical Association 224: 1361
3. Hodgson, J.R. and Baker, H.L.Jnr. (1959) Newer concepts in cholecystography and cholangiography Postgraduate Medicine 26:283
4. Committee 3 of the ICRP (1970) — A report Protection against ionizing radiation from external sources ICRP Publication 15, New York, Pergamon Press
5. Jacobs, J.C.(1974) Chest X-ray screening for tuberculosis Journal of the American Medical Association 228:24