11Clabeled

11C-labeled, commonly written as 11C-labeled, refers to chemical compounds in which the radioactive isotope carbon-11 is incorporated. Carbon-11 is a positron-emitting radioisotope with a half-life of about 20.3 minutes, making it suitable for positron emission tomography (PET) imaging. Because of its short half-life, 11C-labeled tracers must be produced in close proximity to the imaging facility and used quickly after synthesis.

Production and labeling strategies

Carbon-11 is typically produced in a medical cyclotron by irradiating nitrogen-14 targets with protons via the 14N(p,α)11C reaction, yielding radioactive carbon species such as [11C]CO2. From there, the radioactive carbon can be converted into a variety of labeling agents, enabling different chemical incorporation pathways. Common labeling strategies include incorporation of [11C]methyl groups (as [11C]methyl iodide or [11C]methyl triflate) to form 11C-labeled methyl ethers or amines, and carboxylation with [11C]CO2 or [11C]CO to introduce carbonyl or carboxyl groups. Other methods use [11C]cyanide or other transient intermediates to attach the label to diverse molecular frameworks. The choice of method depends on the target molecule and the desired site of labeling, with an emphasis on rapid, high-yield radiochemical reactions compatible with the short half-life.

Applications and examples

11C-labeled radiotracers are widely used in PET imaging to study brain function, oncology, and cardiology. Notable examples include [11C]raclopride for dopamine receptor imaging, [11C]PIB for amyloid plaque imaging in Alzheimer's disease, and [11C]methionine for tumor metabolism. The short half-life enables high-contrast, dynamic imaging but requires on-site synthesis and stringent regulatory controls for radiopharmaceutical production and clinical use.

Safety and regulatory considerations

Production and use of 11C-labeled tracers are governed by radiation safety guidelines and pharmaceutical regulations. Facilities require appropriate shielding, monitoring, and validated synthesis procedures, with rapid quality control and strict timing due to the isotope’s rapid decay.