Operation of PET Cyclotrons for Medical Imaging

The attendees of this conference have their own views of the operation of a cyclotron. In the context of this paper it is viewed primarily as a source of positron emitting radioisotopes which are used for molecular imaging based on positron emitting tracers and positron emission tomography (PET). This form of imaging is the most sensitive and specific method for measuring, in life, molecular interactions and molecular pathways. It represents a fundamental bridge between basic molecular, cellular and experimental animal studies to those of measurements of diseased tissue function in the living patient. The specificity of PET arises from the use of Carbon11, Oxygen-15 and Fluorine 18 which can be used to label biochemicals and pharmaceuticals without disturbing their biological function. The sensitivity of PET arises from the fact that imaging is based on the coincidence counting of the annihilation photons emitted following positron capture. As a result of this electronic coincidence counting, high solid angle for detection is offered unlike the case where lead collimation is necessary for example in single photon detection. Within the scope of this sensitivity and specificity it is possible to identify the role of PET within the spectrum of medical imaging (1). Here it is unrivalled by other methods in the detection of molecular pathways and specific binding and receptor sites where high sensitivity is necessary in order not to disturb the function of those sites with blocking doses of chemical. Within the long term, the role of PET is assured for studying neurotransmitter pathways, receptors, drug binding and general pharmacology. As a research tool it is destined to be used to obtain new information on human disease, to assess the efficacy and mechanisms of therapies and for drug development and discovery.