Spatial variation of perfusion MRI reflects cognitive decline in mild cognitive impairment and early dementia

Abstract

Cerebral blood flow (CBF) measured with arterial spin labelling (ASL) magnetic resonance imaging (MRI) reflects cerebral perfusion, related to metabolism, and arterial transit time (ATT), related to vascular health. Our aim was to investigate the spatial coefficient of variation (sCoV) of CBF maps as a surrogate for ATT, in volunteers meeting criteria for subjective cognitive decline (SCD), amnestic mild cognitive impairment (MCI) and probable Alzheimer's dementia (AD). Whole-brain pseudo continuous ASL MRI was performed at 3 T in 122 participants (controls = 20, SCD = 44, MCI = 45 and AD = 13) across three sites in New Zealand. From CBF maps that included all grey matter, sCoV progressively increased across each group with increased cognitive deficit. A similar overall trend was found when examining sCoV solely in the temporal lobe. We conclude that sCoV, a simple to compute imaging metric derived from ASL MRI, is sensitive to varying degrees of cognitive changes and supports the view that vascular health contributes to cognitive decline associated with Alzheimer's disease.

Figure 1

Illustrative figure depicting the appearance of CBF maps with low versus high sCoV in sagittal (left) coronal (middle) and axial (right) orientations. Top row, average non-PVC CBF maps for 10 participants with the lowest sCoV in GM ROI from the total cohort studied. This averaged CBF map representing low sCoV appears as expected, with high grey-white matter contrast, and increased perfusion in the region of the posterior cingulate cortex (PCC) and precuneus (see filled arrow). Bottom row, average non-PVC CBF maps for 10 participants with the highest sCoV in GM. The averaged CBF map for highest sCoV shows lower cortical perfusion overall, most notably in the posterior vascular territory (see open arrow), suggesting too short post labelling delay (PLD)/prolonged ATT.

Figure 2

Spatial CoV group results (a) total grey matter (GM) and (b) temporal lobe ROIs in control group, subjective cognitive decline (SCD), mild cognitive impairment (MCI) and probable Alzheimer’s disease (AD). All data plotted are residual values after accounting for age, sex and site.

Figure 3

Spatial CoV (sCoV) and partial volume corrected cerebral blood flow (PVC CBF) in grey matter (GM) for each participant. Correlation between sCoV and CBF evaluated using Pearson’s correlation coefficient, with regression line and 95% confidence interval.