We focus on the PET radiotracers that are currently available on the market and have a role in clinical practice in the evaluation of patients with cognitive impairment and/or parkinsonism, and the parameters that these radiotracers show: Protein aggregation (amyloid and tau PET imaging), neuronal activity, and neurodegeneration (2-[18F]fluoro-2-deoxy-d-glucose [18F]FDG) and presynaptic dopaminergic activity (L-6-[18F]fluorodopa PET, DAT SPECT, and PET). Here, MAPT is linked to Cognitive impairment.