Fig. 4

Hippocampal FDG uptake is higher in human AD and MCI. A As a human study, FDG uptake in the hippocampus was analyzed and compared with soluble TREM2 (sTREM2) obtained by CSF, a biomarker for evaluating microglia-mediated inflammation. FDG PET images and three-dimensional T1 MRI were coregistered with each other. Patient-wise volume of interest was automatically generated, and FDG uptake in the hippocampus was calculated with the correction of partial volume effect. B CSF sTREM2 of AD, MCI, and controls (CN) was not significantly different (2.63 ± 1.03 × 10³ vs. 2.35 ± 0.88 × 10³ vs. 2.30 ± 0.79 × 10³; p = 0.45). However, the hippocampal FDG uptake of different groups was different. C For the right hippocampus, FDG uptake of different groups, AD, MCI, and CN, showed a marginal difference. AD showed marginally higher FDG uptake in the right hippocampus than CN (1.36 ± 0.14 vs. 1.34 ± 0.16 vs. 1.28 ± 0.12; p = 0.03). D FDG uptake in the left hippocampus was significantly different between the groups (1.46 ± 0.17 vs. 1.42 ± 0.20 vs. 1.34 ± 0.12; p = 0.02). AD and MCI showed higher FDG uptake in the left hippocampus compared with CN (p = 0.007 for AD vs. CN; p = 0.02 for MCI vs. CN). E We also measured FDG uptake using a volume-of-interest including both hippocampi. FDG uptake in both hippocampi was also significantly different between the groups (1.41 ± 0.15 vs. 1.38 ± 0.17 vs. 1.31 ± 0.11; p = 0.023). AD and MCI showed higher FDG uptake in both hippocampi compared with CN (p = 0.008 for AD vs CN; p = 0.04 for MCI vs CN). F CSF sTREM2 of MCI-C was higher than that of MCI-NC, although it showed borderline significance (2.49 ± 0.98 × 10³ vs. 2.13 ± 0.72 × 10³; p = 0.065). G For the right hippocampus, FDG uptake of MCI-C and MCI-NC was significantly different (1.39 ± 0.16 vs. 1.29 ± 0.14; p = 0.046). H For the left hippocampus, FDG uptake of MCI-C and MCI-NC was also significantly different (1.50 ± 0.16 vs. 1.35 ± 0.22; p = 0.046). I For both hippocampi, FDG uptake of MCI-C and MCI-NC was also significantly different (1.45 ± 0.16 vs. 1.32 ± 0.18; p = 0.035)