Nuclear medicine is the branch of medicine that involves the application of small amounts of radioactive substances to assess bodily functions and for diagnostic and treatment purposes. It is also called “endoradiology” because it records radiation energy emitted from within the body. Positron emission tomography (PET) and single photon emission computed tomography (SPECT) are the most common imaging modalities in nuclear medicine.
PET scans use small amounts of radioactive materials, also called radiotracers, to show differences between healthy tissue and diseased tissue, allowing in vivo imaging of metabolic, physiologic and pathologic processes. The most commonly used radiotracer is fluorodeoxyglucose (FDG) which is injected into the patient. Cancer cells grow at a faster rate than healthy tissue and thereby absorb more of the FDG. The PET scanner detects the radiation emitted by the FDG, producing color-coded images of the body showing normal and cancerous tissue. PET scans are also used to view, monitor and diagnose diseases of the heart, especially related to blood flow to the heart, and brain.
A PET scan is mostly harmless as the amount of radiation is low and short-lived and insufficient to affect normal body processes. However, the radioactive substance may expose radiation to the fetus of a pregnant woman or the baby of a woman who is breastfeeding. There is also a rare risk of a major allergic reaction to the tracer.