Longitudinal changes in blood flow, vessel pulsatility, and trans‐capillary pulse wave delay in small vessel disease and amyloid biomarker positive

Abstract

AbstractBackgroundThis work characterized longitudinal changes in cerebrovascular health in humans with and without presence of small vessel disease (SVD) and amyloid‐β using different neuroimaging techniques.MethodParticipants (n = 41) were biomarker characterized into three groups: amyloid and SVD negative (A‐V‐; “control”), SVD positive (A‐V+), and amyloid positive (A+V‐). All were cognitively unimpaired except two participants clinically diagnosed with MCI (A‐V+) and dementia (A+V‐) (Table 1). MRI: Vascular imaging: Whole‐brain 4D‐Flow data were acquired to characterize cerebrovascular health. Two MRI time‐points were used to establish 4D‐Flow‐based longitudinal changes. Measurements were extracted from intracranial arteries and veins and included blood flow, vessel pulsatility index, and trans‐capillary pulse wave delay (TPWD). TPWD was defined as the time shift between arterial and venous cardiac waveforms. Structural imaging: TIV‐normalized WMH volumes were segmented from T2‐FLAIR images and used as surrogate for SVD. V+/‐ thresholds were determined from Gaussian Mixture Model on 930 participants. PET: Amyloid‐β burden was assessed using 11C‐PiB PET imaging. Amyloid positivity was established as mean cortical PiB DVR >1.16. Vascular changes were assessed using Kruskal‐Wallis followed by multiple comparisons (P<0.05 significance).ResultAfter ∼4.5 years, middle cerebral arteries (MCAs) blood flow decreased significantly more in amyloid than SVD groups, while vessel pulsatility increased significantly more in amyloid compared to SVD (Fig.1). TPWD shortened significantly in SVD compared to amyloid and control groups. All groups showed a decreased in blood flow, increased in vessel pulsatility and shortening of TPWD with time. At the time of the last MRI visit, MCAs blood flow was somewhat higher in SVD compared to amyloid and control groups, but not significantly (Fig.2). Vessel pulsatility was similar between groups, yet slightly higher in SVD and amyloid groups. TPWD was significantly shorter in SVD compared to the amyloid group.ConclusionThis work demonstrates the feasibility to measure longitudinal cerebrovascular changes using 4D‐Flow MRI in the context of SVD and AD biomarker positive groups. Preliminary results indicate 4D‐Flow‐based vascular markers can detect differences between SVD and amyloid groups both longitudinally and cross‐sectionally. Cerebrovascular changes in A+ suggest decreased metabolism and increased macro‐vessel stiffness, while findings in SVD positive supports stiffness of the micro‐circulation and capillaries.