Effects of Foreshortening and Oversizing of Flow Diverting Stents for Intracranial Aneurysms

Abstract

Understanding the effects of flow diverting stents is important to evaluate and plan treatments, identify possible failure modes and limitations, and improve the design of flow diverting devices. The purpose of this work was to develop methods for precise deployment of flow diverting stent models into patient-specific vascular geometries reconstructed from three-dimensional (3D) anatomical images of brain aneurysms. The stent is modeled as a series of interconnected wire segments that is released inside the vascular model under the influence of angular and stretching forces that try to recover the reference (un-deformed) configuration and contact forces with the vascular wall that constrain the stent to the vessel interior. This methodology attempts to properly capture the foreshortening characteristics of these devices, which is extremely important because in the majority of treatments the stents are oversized in order to achieve a good wall apposition against the parent artery. The methodology was tested against theoretical results of a series of stents released into straight tubes of varying diameters. The results indicate that the numerical models were able to reproduce the stent foreshortening characteristics in these situations to within a 1% error. Subsequently, the hemodynamic effects of the geometric deformation of the stent cells due to the foreshortening of oversized stents were studied using the patient-specific geometry of a giant internal carotid artery aneurysm with a wide neck. The results show that for an oversized stent, i.e. when it is deployed in an artery of smaller diameter, the changes in the geometry of the stent cells have a significant impact on its flow diverting characteristics. Specifically, the stent cells widen allowing a larger inflow into the aneurysm, thus reducing its hemodynamic performance. In conclusion, these effects must be considered when designing new devices or conducting clinical studies of stent efficacy.