. 2019 Jul 26;13:775. doi: 10.3389/fnins.2019.00775

TABLE 1.

Main findings of functional connectivity analyses using PET and fMRI.

Authors (year)	Participants	Method of analysis and main findings
Savio et al., 2017	A total of 22 healthy, right-handed participants (15 men, 7 women; mean age: 54.5 ± 10.0 years)	Acquisition: Simultaneous PET/MRI with static ¹⁸F-FDG-PET. Analysis: ICA (20 components). Results: Similar RSNs were detected via fMRI and ¹⁸F-FDG PET when resting-state fMRI and ¹⁸F-FDG-PET data were acquired simultaneously.
Marchitelli et al., 2018	A total of 23 patients with aMCI/AD and 23 healthy older adults	Acquisition: Simultaneous PET/MRI with static ¹⁸F-FDG-PET. Analysis: Uptake on ¹⁸F-FDG-PET and resting-state fMRI metrics were compared between patients with aMCI/AD and controls and expressed as Z scores. Results: For within-subject PET/fMRI comparisons, correlations were high overall in healthy controls but 17% lower in patients with aMCI/AD (significant at p < 0.05). For between-subject comparisons, FDG/gICA-DR exhibited the greatest overlap around the posterior DMN nodes.
Yokoi et al., 2018	Amyloid-positive patients with early AD (n = 23) and amyloid-negative control participants (n = 24)	Acquisition: Separate PET (¹⁸F-THK5351, static) and MRI (3T). Analysis: Seed-based connectivity analysis was performed by generating seed ROIs based on regions exhibiting the most significant differences in ¹⁸F-THK5351 retention between patients with AD and controls. Results: Patients with AD exhibited significant decreases in connectivity between the PCC and widespread brain regions.
Kim et al., 2019	A total of 16 patients with MDD without comorbidities and 15 healthy controls	Acquisition: Separate PET [(¹¹C)ABP688, dynamic] and MRI (3T). Analysis: The BP_ND of [¹¹C]ABP688 was quantified using the SRTM for mGluR5 availability. Seed-based functional connectivity analysis was performed using resting-state fMRI data with regions derived from quantitative [¹¹C]ABP688 PET as seeds. Results: Patterns of correlation between [¹¹C]ABP688 BP_ND and the strength of functional connectivity involving the superior prefrontal cortex were opposite in the depression and control groups.
Hamilton et al., 2018	A total of 16 patients with MDD and 14 controls	Acquisition: Simultaneous fMRI and ¹¹C-raclopride PET targeting the dopamine D₂ receptor. Analysis: BP_ND was estimated via the MRTM, using the cerebellum as the reference tissue. Functional connectivity analysis was performed using striatal regions exhibiting significant between-group BP_ND differences as seeds. Results: Increased BP_ND and decreased connectivity were observed in the striatum. The BP_ND was increased in both the left ventral striatum and right dorsal striatum in patients with MDD. Connectivity between these regions and cortical targets was also decreased in the MDD group.

ICA, independent component analysis; aMCI/AD, amnestic mild cognitive impairment/mild-to-moderate Alzheimer’s disease; gICA- DR, group independent component analysis with dual regression; PCC, posterior cingulate cortex; BP_ND, non-displaceable binding potential; SRTM, simplified reference tissue model; mGluR5, metabotropic glutamate receptor-5; MRTM, multi-linear reference tissue model; MDD, major depressive disorder.