11c

Carbon-11 (11C) is a radioactive isotope of carbon with mass number 11. It decays by positron emission to boron-11, with a half-life of about 20.3 minutes. The emitted positrons annihilate with electrons to produce two 511 keV gamma photons, which are detected in positron emission tomography (PET).

11C is produced in medical cyclotrons by irradiating natural nitrogen targets with protons via the 14N(p, α)11C reaction, typically yielding [11C]CO2. This activity is then chemically transformed into other radiolabeled forms such as [11C]methyl iodide, [11C]methyl triflate, or [11C]carbon monoxide, enabling the incorporation of the 11C label into a wide range of organic tracers for PET.

In PET imaging, 11C-labeled compounds are used to visualize and measure biochemical processes in vivo. Common tracers include [11C]raclopride for dopamine D2 receptors, [11C]PiB for amyloid plaques in Alzheimer's disease, [11C]choline for tumor imaging, and [11C]methionine for amino acid metabolism. The short half-life provides high specific activity and limits radiation exposure, but it also requires on-site production and rapid synthesis, restricting use to facilities with a cyclotron and radiochemistry capabilities.

Safety and regulatory considerations include standard radiopharmaceutical handling procedures to protect staff and patients. The rapid decay reduces long-term radiation burden, but the production, labeling, and administration of 11C tracers demand specialized facilities and trained personnel.