In the past nuclear medicine has tended to develop in cycles governed by the development of new radiopharmaceuticals followed or preceded by advances in instrumentation. The development of alternative techniques, such as X-Ray Computer Tomography, NMR Imaging and Ultrasound have also had a stimulating effect and pointed the way to new developments. The development of Positron Emission Tomography, while in itself of limited application because of high costs involved, provided a great deal of information which led to the development of new organ or disease specific, single photon emitting...