Which radiotracer is used to measure glucose metabolism?

• A. 18F-FDG
• B. 15O-water
• C. 11C-methionine
• D. 13N-ammonia

Answer: (A)

Measuring glucose metabolism with a radiotracer depends on using a glucose analog that cells take up and trap, so the imaging signal reflects how actively cells are using glucose. 18F-FDG behaves like glucose: it enters cells via glucose transporters and is phosphorylated by hexokinase to FDG-6-phosphate, but it isn’t further metabolized, so it gets trapped. This accumulates in proportion to local glycolytic activity, making it ideal for PET imaging of metabolic rate in tissues such as brain, heart, and especially tumors.

Other tracers serve different purposes. 15O-water measures blood flow (perfusion) rather than metabolism. 11C-methionine tracks amino acid transport and protein synthesis, useful in tumor characterization but not a direct measure of glucose use. 13N-ammonia is used mainly for myocardial perfusion imaging and provides perfusion information rather than glycolytic activity.

Therefore, the radiotracer used to measure glucose metabolism is 18F-FDG.