Assessment of brain oxygen extraction fraction between normal cognition and mild cognitive impairment in an elderly cohort using quantitative BOLD

Abstract

AbstractBackgroundThis study is to quantify oxygen extraction fraction (OEF), an important physiological biomarker for brain hemodynamic impairment, in the elderly cohort using non‐invasive quantitative BOLD (qBOLD) modeling, which is an MRI method for assessment of hemodynamic and metabolic properties.Method56 participants (75.4±7.0yo, 37F), including 46 cognitively normal (CN) individuals (75.2±7.3yo, 29F) and 10 mild‐cognitive‐impairment (MCI) patients (76.0±6.1yo, 7F), were recruited from UC Davis Alzheimer’s Disease Research Center cohort. MRI scans were acquired on a 3T scanner (Siemens Tim Trio) with a 32‐channel head coil, including an Asymmetric Spin Echo (ASE) scan (TR/TE, 2800/66ms; 2.3×2.3.x1.3mm3 resolution; FOV, 224mm; 13 values of the spin echo displacement time, from 0 to 52ms) and a T1‐weighted MPRAGE. T1‐weighted images were segmented into regions of interest (ROI), including gray matter (GM), white matter (WM), and cortical lobes (frontal, parietal, occipital, temporal) using FSL FAST. ASE signal curves were preprocessed and fit to two‐compartment qBOLD model with Variational Bayesian framework to estimate deoxygenated blood volume (DBV) and transverse relaxation rate (R2’), which are used to quantify OEF with known physiological constants (Cherukara et al., NeuroImage 2019). Average OEF values were calculated and compared for each ROI between CN and MCI groups using pairwise t‐tests with Bonferroni correction. The correlation between OEF and age were assessed using a linear mixed effects model that accounted for subject clustering.ResultCompared to CN, reduced DBV and increased OEF were observed throughout most of the brain on the group average level in MCI (Figure 1). In regional analysis, we observed a trend of increased OEF in MCI compared to CN in several ROIs, which was significant in the occipital lobe (p = 0.007) (Figure 2). In Figure 3, OEF was inversely correlated with age in the parietal lobe for CN (p = 0.026). In contrast, there was a positive trend of association between OEF and age for MCI across all regions.ConclusionThis study showed that age has an association with brain oxygen extraction that are differently affected by normal aging and MCI. Higher brain OEF in MCI individuals may reflect changes in oxygen metabolism because of underlying pathology, including vascular injury and compensation for hypoperfusion.