Fig. 2

Molecular imaging in Parkinson’s disease (PD). Selected biological targets that have been harnessed for positron emission tomography (PET) and single photon-emission tomography (SPECT) imaging in PD. These targets have been used to allow diagnostic imaging as well as to facilitate drug discovery & development and include the translocator protein 18 kDa (TSPO), which is upregulated in activated microglia, mitochondrial complex I (MC-I) to assess mitochondrial function, various α-synuclein and amyloid-β (Aβ)-targeted probes, radiolabeled dopamine & serotonin transporter substrates & ligands of dopamine receptors, probes targeting the vesicular monoamine transporter 2 (VMAT2) and attempts to visualize autophagy as well as cytokines such as the tumor necrosis factor α (TNF-α). Given that these molecular variables are critical to the pathophysiology of PD, most of them have been suggested as therapeutic targets