Development of carbon-11 labelled PET tracers-radiochemical and technological challenges in a historic perspective.

The development of positron emission tomography (PET) from being an exclusive and expensive research tool at major research institutes to a clinically useful modality found at most major hospitals around the world is largely dependent on radiochemistry and synthesis technology achievements by a few pioneer researchers starting their PET careers 40 to 50 years ago. Especially, the introduction of [(11) C]methyl iodide resulted in a quantum jump in the history of PET tracer development enabling the smooth labelling of a multitude of useful tracers. A more recent and still challenging methodological improvement is transition metal mediated (11) C-carbonylations, having a large synthetic potential that has, however, not yet been realized in the clinical setting. This mini-review focuses on the history of carbon-11 radiochemistry and related technology developments and the role this played in PET tracer developments, especially emphasizing radiolabelling of endogenous compounds. A few examples will be presented of how the use of radiolabelled endogenous substances have provided fundamental information of in vivo biochemistry using the concept of position-specific labelling in different positions in the same molecule.