In 1985 and 1986 nuclear medicine became more and more oriented toward in vivo chemistry, chiefly as a result of advances in positron emission tomography (PET).1,2 The most important trend was the extension of PET technology into the care of patients with brain tumors, epilepsy, and heart disease. A second trend was the increasing use of single-photon emission computed tomography (SPECT).
Positron tomography has made possible for the first time accurate measurement of absolute quantities of radioactive tracers of biologically important molecules within the living human body. With mathematical models, PET images can be transformed by computers into measurement of specific biochemical reaction rates or molecular concentrations within organs or parts of organs. Just as carbon 14 and tritium have been the backbone of the tracer principle in basic research, tracer studies with carbon 11, fluorine 18, and oxygen 15 are the backbone of tracer studies in living human