Assessing imaging biomarker in the prodromal and early phases of Parkinson's disease (PD) is of great importance to ensure an early and safe diagnosis. In the last decades, imaging modalities advanced and are now able to assess many different aspects of neurodegeneration in PD. MRI sequences can measure iron content or neuromelanin. Apart from SPECT imaging with Ioflupane, more specific PET tracers to assess degeneration of the dopaminergic system are available. Furthermore, metabolic PET patterns can be used to anticipate a phenoconversion from prodromal PD to manifest PD. In this regard, it is worth mentioning that PET imaging of inflammation will gain significance. Molecular imaging of neurotransmitters like serotonin, noradrenaline and acetylcholine shed more light on non-motor symptoms. Outside of the brain, molecular imaging of the heart and gut is used to measure PD-related degeneration of the autonomous nervous system. Moreover, optical coherence tomography can noninvasively detect degeneration of retinal fibers as a potential biomarker in PD. In this review, we describe these state-of-the-art imaging modalities in early and prodromal PD and point out in how far these techniques can and will be used in the future to pave the way towards a biomarker-based staging of PD.

Aarhus University Institute of Clinical Medicine Department of Nuclear Medicine and PET Aarhus N Denmark

Masaryk University Applied Neuroscience Research Group Central European Institute of Technology CEITEC Brno Czech Republic

Masaryk University Faculty of Medicine and St Anne's University Hospital 1st Department of Neurology Brno Czech Republic

Masaryk University Faculty of Medicine and St Anne's University Hospital International Clinical Research Center ICRC Brno Czech Republic

Newcastle University Translational and Clinical Research Institute Newcastle upon Tyne United Kingdom

University of Cologne Faculty of Medicine and University Hospital Cologne Department of Neurology Cologne Germany

University of Cologne Faculty of Medicine and University Hospital Cologne Department of Nuclear Medicine Multimodal Neuroimaging Group Cologne Germany

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Early Changes in the Locus Coeruleus in Mild Cognitive Impairment with Lewy Bodies