What term describes substances used to visualize biological processes in PET?

• A. Tracers
• B. Radiopharmaceuticals
• C. Contrast media
• D. Reagents

Answer: (B)

In PET imaging, visualization of biological processes is achieved with radiopharmaceuticals—radioactively labeled compounds that act like normal drugs in the body while emitting radiation that the PET scanner detects. These substances are designed to participate in specific metabolic pathways, so their distribution reflects underlying physiology. A familiar example is a glucose analog labeled with a radioactive isotope, which highlights areas of high metabolic activity. While people sometimes talk about tracers in a general sense, radiopharmaceuticals is the precise term because it conveys both the pharmacologic nature of the agent and its radioactive labeling. Contrast media used in CT or MRI, or generic reagents used in labs, do not serve this purpose in PET imaging.