The Radiopharmaceutical Chemistry of Carbon-11: Basic Principles

Abstract

Carbon-11 is an accelerator-produced, positron-emitting radionuclide. Its physical half-life of 20.4 min is sufficiently long to allow for multistep syntheses while short enough to enable multiple PET scans of the same individual on the same day. Carbon-11‘s short half-life is also advantageous with respect to the radiation dose to the subject undergoing investigation; indeed, for most carbon-11 PET tracers, up to four administrations to healthy volunteers can be accepted. The radionuclide decays almost exclusively via positron emission (β+), and the emitted particle has a maximum energy of 0.960 MeV. Carbon-11 is produced using a cyclotron in high molar activity, a prerequisite for the tracer principle which underlies the very concept for PET. From the precursor [11C]carbon dioxide, a large number of secondary precursors can be synthesized, thus creating a wide range of opportunities for labeling biologically relevant compounds. Undoubtedly, the most useful of all these secondary precursors is [11C]methyl iodide due to the presence of methylated heteroatoms in many drugs and naturally occurring biomolecules.