The specialty of nuclear medicine is relatively recent compared with the use of X-rays in diagnosis and therapy and of radium in therapy, in that it effectively dates from the Manhattan Project in World War II, which led in peacetime to the production of artificially produced radioactive isotopes in sufficient quantity for medical applications h Previously, attempts to use radioactivity for diagnostic purposes had proved a failure as early as 1904^ as seen in Figures [3.7] and [3.8] when only radium and radon were available for imaging purposes, although in 1927 Blumgart and Weiss^ successfully injected aqueous solutions of radon intravenously and monitored the velocity of blood flow between one arm and the other with a cloud chamber. The description 'nuclear medicine’ was introduced only gradually and departments of medical physics were originally divided into radiotherapy and isotope sections with the latter including both therapy and diagnosis using radionuclides such as iodine-131. This was largely due to the early medical uses being the responsibility of radiotherapy physicians.