Radiopharmaceuticals for positron emission tomography. Development of new, innovative tracers for measuring the rates of physiologic and biochemical processes.

Positron emission tomography (PET) can give quantitative local information about many processes in the intact human body, which may be useful both for basic studies of metabolic processes in health and disease, and also for diagnostic purposes in individual patients. PET is absolutely limited by the availability of suitable radiotracers. Natural substrates for metabolic processes, e.g. 11C glucose, are not generally useful; compounds with a restricted range of metabolic transformations, all of which can be distinguished kinetically, are better. Radiotracer behavior may then be describable by a fairly simple set of linear first-order rate constants (kinetic model) which can each be determined from PET scan sequences and which can be combined to give physiologically meaningful data. Three 18F compounds, which form a hierarchy of pharmacologic complexity, are briefly described: fluoromethane, for blood flow, 2-deoxy-2-fluoro-D-glucose, for glucose metabolic rates, and 16-fluoropalmitic acid, a candidate tracer for rates of long-chain fatty acid metabolism.