Correlations between the specific brain nuclei and GI organs
Pairwise comparisons within the digestive and cerebral regions of the HC and PD group were separately summarized (Figure 4-5 ). For the inter-nigrostriatal region correlations, strong positive correlation for R1, DVR, SUVREP and SUVRLP were found among nearly all the four nigrostriatal nuclei within the HC group (all P <0.05). Conversely, these correlations were notably diminished in the PD cohort.
For the “brain-GI” correlations within the HC group, the significant negative correlations were revealed between the stomach and putamen for both the early perfusion parameters R1 (r =-0.833, P <0.05) and SUVREP (r =-0.821, P <0.05). Meanwhile, the significant positive correlation relationships of the tracer density parameters DVR and SUVRLP were identified between pancreas and all the four brain nuclei including caudate (r =0.918, P <0.05 for DVR; r =0.899,P <0.05 for SUVRLP), putamen (r =0.977, P <0.001 for DVR; r =0.993,P <0.001 for SUVRLP), pallidum (r =0.909, P <0.05 for DVR; r =0.828,P <0.05 for SUVRLP) and substantial nigra (r =0.894, P <0.05 for DVR; r =0.964,P <0.01 for SUVRLP). In contrast, among PD patients, significant correlations between most of the brain nuclei and digestive organ targets were absent, except for a positive correlation was observed between the pancreas and pallidum (r=0.912, P <0.05 for DVR; r =0.904,P <0.05 for SUVRLP), and substantia nigra (r =0.912, P <0.05 for SUVRLP). Additionally, the VT of pancreas and putamen estimated using the VOI-based 1T2K were also significantly correlated in the HC group rather than PD group (Supplemental Figure 1C ).