There is accumulating evidence suggesting that inflammatory processes, through microglial activation, would play a key role in the neurodegenerative process of Parkinson's disease (PD). It is considered that microglial activation would be part of self-propelling cycle of neuroinflammation that fuels the progressive dopaminergic neurodegeneration. It is however hard to evidence microglial activation in vivo, especially in the substantia nigra: first, the investigators need very high resolution imaging tools and then, the only ligand available to date, 11C-PK11195, has a low sensitivity and specificity and provided heterogeneous results.