In vivo chemistry has become a major focus of nuclear medicine. By means of positron- and γ-emittingradioactive tracers, the regional chemistry of body organs can now be measured with the same sensitivity as hormones in body fluids by radioimmunoassay. Nuclear medicine focuses on molecules, as well as cells, as a basic unit of study.
Many new nuclear medicine procedures are still at the interface between research and clinical practice, but it is becoming increasingly clear that positron emission tomography (PET) examinations can help care for patients with epilepsy, cancer, dementia, and heart disease. It is somewhat unfortunate that technological advances such as PET and single photon emission computed tomography (SPECT), have occurred when cost containment is a major focus of medical practice. However, knowledge about a patient can help decrease the overall cost of medical care. For example, detection of occult coronary heart disease in a patient being considered for