PET radiotracers for molecular imaging in the brain: past, present and future.

Neuroimaging of brain receptors began in the early 1980s. Now, some thirty-five years later, PET imaging is still an expanding field of preclinical and clinical investigations. In addition to improvements in PET cameras and image analysis, the availability of suitable radiotracers is a crucial factor leading this expansion. Radiotracers have been developed to visualize and quantify a growing numbers of brain receptors, transporters, enzymes and other molecular targets. The development of adequate PET radiotracers represents an exciting challenge, given the large number of targets and neurochemical functions that have yet to be explored. In this article, we review the main evolutions led by preclinical radiotracers and clinical radiopharmaceuticals. The current main contributions of PET radiotracers are described in terms of imaging of neuronal metabolism, receptor and transporter quantification and neurodegenerative, neuroinflammatory and neurooncologic process imaging. In the last part, we highlight some applications presenting a potential for novel functional explorations of the brain.