Supplementary Material for: Relation between cerebral small vessel function at 7T MRI and small vessel disease burden in a general ageing population

Introduction
There is a need for measures of early stages of cerebral small vessel diseases (cSVDs). Recently, using 7T MRI, abnormalities of small vessel function were reported in patients with clinically manifest cSVD. The question is if such abnormalities are also present in early, covert stages of cSVD. We therefore studied the relation between cerebral small vessel function measures on 7T MRI and the burden of covert cSVD in the general ageing population.
Methods
Two hundred participants (mean age (years) ± SD: 71 ± 5, 43% women) without a history of stroke or dementia from the Rotterdam Study were included. Small vessel measures at 7T MRI, including perforating artery blood flow velocity and pulsatility and cerebrovascular reactivity (CVR) to carbon dioxide, were related to markers of cSVD burden at 1.5T MRI, including white matter hyperintensity volume and microbleed, enlarged perivascular spaces, and lacune presence, using linear and logistic regression analyses. We also included cognitive performance as a clinical indicator of covert cSVD.
Results
Across the population, neither perforating artery flow measures nor CVR were significantly associated with cSVD lesion burden or cognition, with small point estimates and no consistent direction of effects. Yet, within individuals, CVR was lower inside white matter hyperintensities compared to normal-appearing white matter (CVR_NAWM=0.54±0.48%; CVR_WMH=0.24±0.94%; p = 0.006).
Conclusion
Although these data confirm that vascular function is affected within WMH, we did not observe relations between small vessel function measures at 7T MRI and the burden of covert cSVD in this population-based sample. Apparently, these measures have limited sensitivity to early stages of cSVD.