Virtual flow-diverter treatment planning: The effect of device placement on bifurcation aneurysm haemodynamics

Abstract

Bifurcation aneurysms account for a large fraction of cerebral aneurysms and often present morphologies that render traditional endovascular treatments, such as coiling, challenging and problematic. Flow-diverter stents offer a potentially elegant treatment option for such aneurysms, but clinical use of these devices remains controversial. Specifically, the deployment of a flow-diverter device in a bifurcation entails jailing one or more potentially vital vessels with a low-porosity mesh designed to restrict the flow. When multiple device placement configurations exist, the most appropriate clinical decision becomes increasingly opaque. In this study, three bifurcation aneurysm geometries were virtually treated by flow-diverter device. Each aneurysm was selected to offer two possible device deployment positions. Flow-diverters similar to commercially available designs were deployed with a fast-deployment algorithm before transient and steady state computational fluid dynamics simulations were performed. Reductions in aneurysm inflow, mean wall shear stress and maximum wall shear stress, all factors often linked with aneurysm treatment outcome, were compared for different device configurations in each aneurysm. In each of the three aneurysms modelled, a particular preferential device placement was shown to offer superior performance with the greatest reduction in the flow metrics considered. In all the three aneurysm geometries, substantial variations in inflow reduction (up to 25.3%), mean wall shear stress reduction (up to 14.6%) and maximum wall shear stress reduction (up to 12.1%) were seen, which were all attributed to device placement alone. Optimal device placement was found to be non-trivial and highly aneurysm specific; in only one-third of the simulated geometries, the best overall performance was achieved by deploying a device in the daughter vessel with the highest flow rate. Good correspondence was seen between transient results and steady state computations that offered a significant reduction in simulation run time. If accurate steady state computations are combined with the fast-deployment algorithm used, the modest run time and corresponding hardware make a virtual treatment pipeline in the clinical setting a meaningful possibility.

A Virtual Comparison of the eCLIPs Device and Conventional Flow-Diverters as Treatment for Cerebral Bifurcation Aneurysms

“…A mesh density greater than 5000 cells/mm 3 was sufficient to capture the inflow reduction with less than 1% uncertainty. This finding is consistent with previous studies and devices 21,23. The corresponding reduction in mean and maximum wall shear stress (WSS) with increasing mesh fineness was also considered.…”

Computational Fluid Dynamics of a Fatal Ruptured Anterior Communicating Artery Aneurysm

“…Some recent studies show that CFD analysis may be performed in a significantly shorter time period. 28 Such evaluation time may already be applicable in the clinical decision-making process for unruptured brain aneurysms, especially if we can expect further time shortening due to technological advances. It is therefore not the computer simulation time but rather the limitations of the CFD methodology that still prevent its use in everyday clinical practice.…”

Hemodynamic Differences Between Recurrent and Nonrecurrent Intracranial Aneurysms: Fluid Dynamics Simulations Based on MR Angiography

“…The meshing of each geometry was completed with a Projected Single Domain mesh, an Omnitree Cartesian tree type, and three near‐wall Cartesian layers to give a smooth and well‐resolved boundary definition. All the simulations were run on meshes with a minimum mesh density of 8,000 elements/mm 3 , resulting in mesh sizes between 1.9 and 4.0 million elements and assuming mesh independence as per previous studies . To reduce the computation time, a steady‐state, radially symmetric parabolic velocity profile was prescribed at the inlet of each aneurysm geometry as steady‐state flow simulations of the cerebral vasculature have been reported to be just as effective as pulsatile flow simulations for estimating most key indices .…”