Abstract
The vertebrobasilar system (VBS) is unique in human anatomy in that two arteries merge into a single vessel, and it is especially important because it supplies the posterior circulation of the brain. Atherosclerosis develops in this region, and atherosclerotic plaques in the vertebrobasilar confluence can progress with catastrophic consequences, including artery occlusion. Quantitative assessments of the flow characteristics in the VBS could elucidate the factors that influence flow patterns in this confluence, and deviations from normal patterns might then be used to predict locations to monitor for potential pathological changes, to detect early signs of disease, and to evaluate treatment options and efficacy. In this study, high-field MRI was used in conjunction with computational fluid dynamics (CFD) modeling to investigate the hemodynamics of subject-specific confluence models (n = 5) and to identify different geometrical classes of vertebrobasilar systems (n = 12) of healthy adult subjects. The curvature of the vessels and their mutual orientation significantly affected flow parameters in the VBS. The basilar artery geometry strongly influenced both skewing of the velocity profiles and the wall shear stress distributions in the VBS. All five subjects modeled possessed varying degrees of vertebral asymmetry, and helical flow was observed in four cases, suggesting that factors other than vertebral asymmetry influence mixing of the vertebral artery flow contributions. These preliminary studies verify that quantitative, MR imaging techniques in conjunction with subject-specific CFD models of healthy adult subjects may be used to characterize VBS hemodynamics and to predict flow features that have been related to the initiation and development of atherosclerosis in large arteries. This work represents an important first step towards applying this approach to study disease initiation and progression in the VBS.
Highlights
The vertebrobasilar system is unique in humans in that it is the sole instance where two large arteries merge into another vessel
When one vertebral artery was larger than the other, the plaque thickness on the lateral wall of the basilar artery was greater on the same side as the dominant vertebral
Based on the TOF images, we found vertebrobasilar system (VBS) geometries can be qualitatively classified into three basic geometric configurations: Walking, Tuning Fork, and Lambda (Figure 3)
Summary
The vertebrobasilar system is unique in humans in that it is the sole instance where two large arteries (the vertebral arteries) merge into another vessel (the basilar artery). Manifestations of disease in this confluence, including vertebrobasilar dissection and occlusion, can have significant consequences It accounts for only approximately 1% of all ischemic strokes, acute basilar artery occlusion (ABAO) occurs in younger patients (mean age 60 vs 71 years in all-cause ischemic stroke) and results in greater risk for in-hospital death than all other causes of ischemic stroke (30% vs 8% inhospital mortality) and generally poorer functional outcomes (in nearly 80% of surviving patients) upon release [1,2]. When one vertebral artery was larger than the other, the plaque thickness on the lateral wall of the basilar artery was greater on the same side as the dominant vertebral. This statistically significant difference in the circumferential localization of basilar artery plaque implicates a role for hemodynamics in the development of atherosclerosis at this location. In other vasculature, local flow characteristics such as areas of low and oscillating wall shear stress (WSS) and recirculation regions correlate strongly with atherosclerosis initiation, development, and vulnerability [4,5,6,7]
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