Measurement of Global Brain Metabolism to differentiate MCI Patients and Controls

Objectives: Studying regional differences in brain metabolism in mild cognitive impairment (MCI) has been extensively studied but the global brain metabolism is less explored. This study aims to determine differences in global cerebral glucose metabolism between patients with MCI and healthy controls utilizing 18F-fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) method. We predicted vulnerable patients would exhibit lower global brain glucose metabolism indicating deteriorated brain function in comparison to healthy subjects. Methods: FDG-PET/CT scans were collected from 25 controls and 39 patients with MCI in the Penn Memory Center (PMC) cohort for this study. Diagnosis of MCI was determined by National Institute for Aging - Alzheimer's Association (NIA-AA) guidelines. Images were collected on hybrid PET/CT scanners (Philips Gemini TF). Patients fasted for at least 4 hours before scan acquisition; all had blood-glucose levels under 180 mg/dl. Patients were injected with 5.0 ± 0.5 mCi of FDG 30 minutes prior to scanning. Low dose CT was collected for attenuation correction. Regions of interest (ROI) were drawn for global assessment of the supratentorium and cerebellum by manually delineating around the cortical regions on each axial slice from the superior most aspect of the brain to the inferior-most aspect of the cerebellum. Global SUVmean (aSUVmean) was obtained by averaging all SUVmeans across the brain to obtain a score for total brain metabolism. Unpaired, 2-sample t-tests and linear regressions were used for statistical analysis.

Results: Patients with MCI had decreased global aSUVmean and Mini-mental state examination (MMSE) scores compared to healthy controls (aSUVmean: 5.32 vs 6.09, p=0.005; MMSE: 27.18 vs 28.96, p<0.001). Age was negatively correlated with aSUVmean in the total cohort (r= -0.35, p<0.001). aSUVmean was a significant predictor of MCI (aSUVmean: β=0.80, p<0.01). Conclusion: The global brain methodology to quantify metabolism proves effective for the diagnosis of and monitoring of MCI as the condition continues.