A heterogeneous model of endovascular devices for the treatment of intracranial aneurysms

Abstract

Numerical computations of hemodynamics inside intracranial aneurysms treated by endovascular braided devices such as flow‐diverters contribute to understanding and improving such treatment procedures. Nevertheless, these simulations yield high computational and meshing costs due to the heterogeneity of length scales between the dense weave of the fine struts of the device and the arterial volume. Homogeneous strategies developed over the last decade to circumvent this issue substitute local dissipations due to the wires with a global effect in the form of a pressure‐drop across the device surface. However, these methods cannot accurately reproduce the flow‐patterns encountered near the struts, the latter strongly dictating the intra‐saccular flow environment. In this work, a versatile theoretical framework which aims at correctly reproducing the local flow heterogeneities due to the wires while keeping memory consumption, meshing and computational times as low as possible is introduced. This model reproduces the drag forces exerted by the device struts onto the fluid, thus producing local and heterogeneous effects on the flow. Extensive validation for various flow and geometric configurations using an idealized device is performed. To further illustrate the method capabilities, a real patient‐specific aneurysm endovascularly treated with a flow‐diverter is used, enabling quantitative comparisons with classical approaches for both intra‐saccular velocities and computational costs reduction. The proposed heterogeneous model endeavors to bridge the gap between computational fluid dynamics and clinical applications and ushers in a new era of numerical treatment planning with minimally costing computational tools.

Assessing a heterogeneous model for accounting for endovascular devices in hemodynamic simulations of cerebral aneurysms

“…The heterogeneous model 22 reproduces all the trends observed in the wire‐resolved simulations, 14,15 for all the flow diverter and WEB cases considered. The model performances are even more noteworthy that the range of reduction of both macroscopic quantities is rather large, from approximately 10% (case e35) to 60% (case eweb35) for the averaged velocity (see Figure 6C,D) and from 15% (case eweb38acom) to 65% (case eweb35) for the inflow rate entering the sac (see Figure 7C,D).…”

“…This was precisely measured in Reference 22 for a typical flow diverter for which the memory usage was reduced by a 22 factor, while the computational cost was divided by 5766. The latter reduction is partly explained by the time‐step reduction (factor 300) induced by the mesh coarsening in the explicit solver used in Reference 22. A more conservative reduction factor of can be inferred for a flow solver with implicit time‐stepping.…”

“…This study takes advantage of existing results obtained with the CFD solver FEFLO from George Mason University authors (J. R. Cebral and F. Mut), using a wire‐resolved type of approach, namely the embedded modeling (EM) of devices 27 (see section 2.2.1). Then, a second CFD solver called YALES2BIO and developed at the University of Montpellier was used to predict the same cases with a heterogeneous immersed method 22 (HIM); whenever relevant, results from an homogeneous porous method 17 (PM) implemented in the same flow solver as HIM were also included for comparison (see section 2.2.2). Of course, the pretreatment cases were computed by using the two flow solvers independently to make sure that the numerical results before the device implementation were in good agreement—see Table 2.…”

“…Another limitation is the modeling of the forces induced by each wire and which relies on two main assumptions 22 : the curvature of the device can be neglected and the flow regime is inertial. Both assumptions are valid in most of the cases, thus the successful comparison obtained in this study.…”

“…The following correlations are used to assess the force in the same three directions, which depend on the incident velocity and wire characteristics. The interested readers should refer to Berod et al 22 for the most technical details relevant to the practical computation of the forces induced by the network of struts.…”