Nuclear imaging in Parkinson's disease: The past, the present, and the future

The current review analyzed Parkinson's disease-related (PD) literature published from 1817 to 2021 and specifically concentrated on imaging-related works published from the 1960s to 2021. We analyzed the history of PD-related imaging development, its current condition, and pointed out some understudied aspects to be investigated in the future. The present review is specifically concentrated on nuclear imaging techniques. The available imaging armamentarium for PD investigation is very broad, variable, and diversified and includes structural, diffusion-weighted and diffusion tensor, resting-state, and task-based functional MRI, proton magnetic resonance spectroscopy, transcranial B-mode sonography, single-photon emission CT (SPECT), and positron emission tomography (PET). Specifically, PET is a reliable tool for quantifying nigrostriatal functions, glucose metabolism, amyloid, tau, and α-synuclein molecular imaging, as well as neuroinflammation. Besides ¹⁸F-DOPA and ¹⁸F-FDG, PET and SPECT use various other radiopharmaceuticals. Also, some studies have demonstrated that myocardial ¹²³I-MIBG scintigraphy can be useful for the early differential diagnosis of patients with PD from other atypical PD. However, in addition to further perfecting of differential diagnosis imaging tools, some aspects of etiology (PD genetics), pathology (the pons and medulla), pathophysiology (neuroinflammation), and early diagnosis of PD remain understudied. The currently available set of neuroimaging tools can provide adequate imaging data for early diagnosis, differential diagnosis, progression assessment, and treatment assessment of PD. To adjust this armamentarium to routine clinical needs, there is an urgent need for the generally accepted protocol for PD-related imaging investigations. Closer cooperation and data exchange between radiologists and pathologists are desirable.