Towards Predicting Patient-Specific Flow-Diverter Treatment Outcomes for Bifurcation Aneurysms: From Implantation Rehearsal to Virtual Angiograms

Abstract

Despite accounting for the majority of all cerebral aneurysm cases, bifurcation aneurysms present many challenges to standard endovascular treatment techniques. This study examines the treatment of bifurcation aneurysms endovascularly with flow-diverting stents and presents an integrative computational modeling suite allowing for rehearsing all aspects of the treatment. Six bifurcation aneurysms are virtually treated with 70% porosity flow-diverters. Substantial reduction (>50%) in aneurysm inflow due to device deployment is predicted in addition to reductions in peak and average aneurysm wall shear stress to values considered physiologically normal. The subsequent impact of flow-diverter deployment on daughter vessels that are jailed by the device is investigated further, with a number of simulations conducted with increased outlet pressure conditions at jailed vessels. Increased outlet pressures at jailed daughter vessels are found to have little effect on device-induced aneurysm inflow reduction, but large variation (13-86%) is seen in the resulting reduction in daughter vessel flow rate. Finally, we propose a potentially powerful approach for validation of such models, by introducing an angiographic contrast model, with contrast transport modeled both before and after virtual treatment. Virtual angiograms and contrast residence curves are created, which offer unique clinical relevance and the potential for future in vivo verification of simulated results.

Keywords: Bifurcation aneurysm; Computational fluid dynamics; Flow-diverter; Stent; Virtual contrast; Virtual deployment.

Figure 1

Bifurcation aneurysm geometries selected for virtual flow-diverter deployment. Major arterial segments: (A) basilar artery (BA); (B) internal carotid artery (ICA); (C) posterior cerebral artery (PCA); (D) superior cerebellar artery (SCA); (E) anterior cerebral artery (ACA); (F) middle cerebral artery (MCA). Geometry inlets are located at the BA or ICA respectively (parent vessels) with all remaining arteries (the daughter vessels) corresponding to geometry outlets.

Figure 2

Detail of the centerline vertex representation of the device (blue) and circular cross-section strut thickness added in Blender after deployment (black).

Figure 3

Virtual deployment of a flow-diverter device in the ICA_02 geometry from crimped configuration (a) to deployed position (d).

Figure 4

Mesh independence graphs for both the BA_02 and ICA_02 geometries at salient points in the cardiac cycle and mean flow rate. The mesh fineness level at which independence (<1% variation) is reached is indicated in the green box.

Figure 5

Mean aneurysm inflow reduction due to device deployment. The range in flow reduction seen over the cardiac cycle is indicated in black.

Figure 6

WSS at peak parent vessel flow rate both before and after device deployment.

Figure 7

Lines tangent to instantaneous velocity vectors, at mean parent vessel flow rate, for all six aneurysm geometries with and without a device deployed. Larger variation in aneurysm flow pattern (jet location, number and location of areas of circulation etc.) after device deployment appears to correspond to greater WSS variation, shown in Fig. 6.

Figure 8

The effect of jailed daughter vessel outlet pressure conditions (+0 to 300 Pa) on aneurysm inflow reduction due to the device (a) and stented daughter vessel outflow distributions (b).

Figure 9

Simulated aneurysm contrast residence curves and virtual angiography generated for the ICA_02 geometry both with and without a flow-diverter device deployed.