Analysis of Intracranial Aneurysm Wall Motion and its Effects on Hemodynamic Patterns Estanislao Oubel a , Mathieu De Craene a , Christopher M. Putman b , Juan R. Cebral c and Alejandro F. Frangi a a Computational Imaging Laboratory, Pompeu Fabra University, Barcelona, Spain; b Interventional Neuroradiology, Inova Fairfax Hospital, Falls Church (VA), USA c School of Computational Sciences, George Mason University, Fairfax (VA), USA ABSTRACT Hemodynamics, and in particular Wall Shear Stress (WSS), is thought to play a critical role in the progression and rupture of intracranial aneurysms. Wall motion is related to local biomechanical properties of the aneurysm, which in turn are associated with the amount of damage undergone by the tissue. The underlying hypothesis in this work is that injured regions show differential motion with respect to normal ones, allowing a connection between local wall biomechanics and a potential mechanism of wall injury such as elevated WSS. In a previous work, 1 a novel method was presented combining wall motion estimation using image registration techniques with Computational Fluid Dynamics (CFD) simulations in order to provide realistic intra-aneurysmal flow patterns. It was shown that, when compared to compliant vessels, rigid models tend to overestimate WSS and produce smaller areas of elevated WSS and force concentration, being the observed differences related to the magnitude of the displacements. This work aims to further study the relationships between wall motion, flow patterns and risk of rupture in aneurysms. To this end, four studies containing both 3DRA and DSA studies were analyzed, and an improved version of the method developed previously was applied to cases showing wall motion. A quantification and analysis of the displacement fields and their relationships to flow patterns are presented. This relationship may play an important role in understanding interaction mechanisms between hemodynamics, wall biomechanics, and the effect on aneurysm evolution mechanisms. Keywords: Image Registration, Wall Motion Estimation, Computational Fluid Dynamics, Aneurysm Rupture, Compliant Models 1. INTRODUCTION Intracranial aneurysms are pathological dilatations of cerebral arteries, which tend to occur at or near arterial bifurcations, mostly in the circle of Willis. The optimal management of unruptured aneurysms is controversial and current decision-making is mainly based on considering their size and location, as derived from the Inter- national Study of Unruptured Intracranial Aneurysms (ISUIA). 2 Although there is little doubt that arterial and aneurysmal walls do move under physiologic pulsatile flow conditions, 3 there is no accurate information on the magnitude and other motion characteristics required to understand the interaction between hemodynamics and wall biomechanics. Although the visualization of aneurysmal pulsation seems to be possible with the ad- vent of 4DCTA gated imaging techniques, 4, 5 there are a number of imaging artifacts related to motion of bony structures 4 which bring questions about the accuracy and reliability of this method. It is thought that the inter- action between hemodynamics and wall mechanics plays a critical role in the formation, growth and rupture of aneurysms. However, since there are no reliable techniques for measuring flow patterns in vivo, various modeling approaches were considered in the past. 6, 7 Hitherto, most CFD methods assume rigid walls due to a lack of information regarding both wall elasticity and thickness. Moreover, in order to perform simulations that account for the fluid-structure interaction, it is also necessary to prescribe the intra-arterial pressure waveform, which is not normally acquired during routine clinical exams. In this paper, wall motion is quantified by applying image registration techniques to sequences of Digital Substraction Angiography (DSA). To study the effects of wall Further author information: E-mail: estanislao.oubel@upf.edu; phone: +34 93 542 1350; fax: +34 93 542 2517; web: http://www.cilab.upf.edu