Recent advances in PET imaging for evaluation of Parkinson's disease.

Parkinson's disease (PD) consists of loss of pigmented dopamine-secreting neurons in the pars compacta of the midbrain substantia nigra. These neurons project to the striatum (putamen and caudate nucleus) and their loss leads to alterations in the activity of the neural circuits that regulate movement. In a simplified model, two dopamine pathways are involved: the direct pathway, which is mediated through facilitation of the D(1) receptors, and the indirect pathway through D(2) receptors (inhibitory). Positron emission tomography (PET) tracers to image the presynaptic sites of the dopaminergic system include 6-[(18)F]FDOPA and 6-[(18)F]FMT, [(11)C]dihydrotetrabenazine, [(11)C]nomifensine and various radiolabelled cocaine derivatives. Postsynaptically, for the dopamine D(1) subtype the most commonly used ligands are [(11)C]SCH 23390 or [(11)C]NNC 112 and for the D(2) subtype [(11)C]raclopride, [(11)C]MNPA and [(18)F]DMFP. PET is a sensitive and specific non-invasive molecular imaging technique that may be helpful for evaluation of PD and its differential diagnosis from other parkinsonian syndromes.