The concept of Microbiota-gut-brain axis has long been elucidated. However, only few microbiota-related radionuclide imaging studies have been published. The etiology of physiologic bowel FDG uptake is not fully understood. Some previous studies suggested that bacteria play a role in accumulating FDG and the variability of intestinal FDG activity may rely on a specific type of bacteria in the lumen. It is unclear if FDG transfer from the blood to the bowel lumen through a transcellular or paracellular pathways. The GLUT transporters are known to export glucose from mucosal cells to the blood, but it is doubtful they can also transport in the opposite direction. Therefore, some research speculated the focal or intense FDG uptake might be caused by an increase in intestinal permeability and reflects intestinal barrier impairment. Gut microbiota compositional changes may affect pathogenesis in patients with Parkinson's disease (PD). A previous hypothesis of PD pointed disease originates in the enteric nervous system and spreads via autonomic neurons to the brain, eventually causing PD. Besides, several studies support the clinical use of Tc-99m TRODAT-1 SPECT in assessing the neurodegenerative status of PD. To date, the correlation between physiologic bowel FDG uptake and dopamine transporter degeneration, as evaluated by either semiquantitative or visual analyses, has never been elucidated. The objective of this study is to investigate the relationship between the pattern of intestinal FDG activity and Tc-99m TRODAT-1 SPECT images based on the theory of Microbiota-gut-brain axis.