Radioactive Tracers

Regular chemical reactions attach the radionuclide to the rest of the tracer molecule. Technetium-99m (99mTc) is commonly used. This emits gamma rays of optimal energy for detection, with no damaging beta particles. It has a short half-life (six hours) which leads to fast elimination from the body by decay. It can be generated when needed from a more stable isotope, molybdenum-99.

Tracers are introduced into the body by injection, orally, or by breathing gases. Some scans are obtained immediately after administration, but others are taken Figure 1. Schematic diagram of an anger scintillation camera. Illustration by Hans & Cassidy. Courtesy of Gale Group. hours or even days later. Scans themselves usually take 30 minutes to three hours. Patients receive about the same dose of radiation from a radioactive tracer scan as from a chest x ray.