Computational Fluid Dynamics Simulation of a-v Fistulas: From MRI and Ultrasound Scans to Numeric Evaluation of Hemodynamics

Abstract

A-v anastomosis entails dramatic changes in hemodynamic conditions, which may lead to major alterations to the vessels involved; primarily dilatations and devastating stenoses. Wall shear stress is thought to play a key role in the remodeling of the vessels exposed to abnormal levels and oscillating wall shear stress. In this study we sought to develop a framework suitable for thorough in vivo analyses of wall shear stress and vessel morphology of a-v fistulas in patients. Using ultrasound and magnetic resonance imaging (MRI) transverse image stacks from six patient a-v fistulas were obtained. From the image stacks three-dimensional geometries of the patient fistulas were created using dedicated segmentation software. Geometries of three a-v fistulas were imported into finite element software in order to perform fluid flow simulations of blood flows and frictional forces on the vessel walls in the a-v fistulas. Boundary conditions for the simulations were obtained using both a MRI phase contrast and an ultrasound Doppler technique. The segmentation of the six fistulas of very different age and morphology (two end-to-side and four side-to-side) showed the ability of the approach to create geometries of various fistula morphologies. Simulations of the three fistulas showed an instant picture of the present status of the exposure to different levels of wall shear stress and the morphological status in the vessel remodeling process. The study demonstrated the capability of the CFD framework to analyze patient a-v fistulas on a regular basis using both MRI and ultrasound-based approaches.