Surveys in the U.K. have identified the patterns of patient exposure from diagnostic medical radiological procedures and have led to the development of structured advice to promote optimisation of patient protection, including diagnostic reference levels for some common conventional X-ray examinations. Trends for reductions in individual patient and collective doses from these particular procedures have been offset by increasing application of computed tomography. Practice in diagnostic nuclear medicine is conducted by authorized physicians on the basis of recommended maximum usual activities of radiopharmaceutical for specific procedures.