PIV investigation of the flow fields in subject-specific vertebro-basilar (VA-BA) junction

Abstract

Background: As the only arterial structure of which two main arteries merged into one, the vertebro-basilar (VA-BA) system is one of the favorite sites of cerebral atherosclerotic plaques. The aim of this study was to investigate the detailed hemodynamics characteristics in the VA-BA system.

Methods: A scale-up subject-specific flow phantom of VA-BA system was fabricated based on the computed tomography angiography (CTA) scanning images of a healthy adult. Flow fields in eight axial planes and six radial planes were measured and analyzed by using particle image velocimetry (PIV) under steady flow conditions of [Formula: see text], [Formula: see text]. A water-glycerin mixture was used as the working fluid.

Results: The flow in the current model exhibited highly three-dimensional characteristics. The confluence of VAs flow formed bimodal velocity distribution near the confluence apex. Due to the asymmetrical structural configuration, the bimodal velocity profile skewed towards left, and sharper peaks were observed under higher Reynolds condition. Secondary flow characterized by two vortices formed in the radial planes where 10 mm downstream the confluence apex and persists along the BA under both Reynolds numbers. The strength of secondary flow under [Formula: see text] is around 8% higher than that under [Formula: see text], and decayed nonlinearly along the flow direction. In addition, a low momentum recirculation region induced by boundary layer separation was observed near the confluence apex. The wall shear stress (WSS) in the recirculation area was found to be lower than 0.4 Pa. This region coincides well with the preferential site of vascular lesions in the VA-BA system.

Conclusions: This preliminary study verified that the subject-specific in-vitro experiment is capable of reflecting the detailed flow features in the VA-BA system. The findings from this study may help to expand the understanding of the hemodynamics in the VA-BA system, and further clarifying the mechanism that underlying the localization of vascular lesions.

Keywords: Hemodynamics; In-vitro; PIV; VA-BA.

Fig. 1

CTA image set of cerebral scanning

Fig. 2

Reconstructed digital model of the VA-BA junction

Fig. 3

Physical phantom fabrication for experiment

Fig. 4

Experimental setup

Fig. 5

Image distortion after refractive matching

Fig. 6

Schematic diagram of velocity fields in axial planes under $\mathit{Re}=300$ (a) and $\mathit{Re}=500$ (b)

Fig. 7

Velocity fields and velocity profiles in axial planes under $\mathit{Re}=300$ (left) and $\mathit{Re}=500$ (right)

Fig. 8

Schematic diagram of streamlines in axial planes under $\mathit{Re}=300$ (a) and $\mathit{Re}=500$ (b)

Fig. 9

Velocity fields and velocity profiles in axial planes under $\mathit{Re}=300$ (left) and $\mathit{Re}=500$ (right)

Fig. 10

Schematic diagram of shear stress in axial planes under $\mathit{Re}=300$ (a) and $\mathit{Re}=500$ (b)

Fig. 11

Shear stress in axial planes under $\mathit{Re}=300$ (left) and $\mathit{Re}=500$ (right)

Fig. 12

Schematic diagram of velocity fields in radial planes under $\mathit{Re}=300$ (a) and $\mathit{Re}=500$ (b)

Fig. 13

Velocity fields in radial planes under $\mathit{Re}=300$ (left) and $\mathit{Re}=500$ (right)

Fig. 14

Schematic diagram of velocity vectors in radial planes under $\mathit{Re}=300$ (a) and $\mathit{Re}=500$ (b)

Fig. 15

Velocity vectors in radial planes under $\mathit{Re}=300$ (left) and $\mathit{Re}=500$ (right)

Fig. 16

Impacts of Reynolds number and distance from confluence apex on mean secondary velocity

Fig. 17

Schematic diagram of shear stress in radial planes under $\mathit{Re}=300$ (a) and $\mathit{Re}=500$ (b)

Fig. 18

Shear stress in radial planes under $\mathit{Re}=300$ (left) and $\mathit{Re}=500$ (right)