Vortex Phenomena in Sidewall Aneurysm Hemodynamics: Experiment and Numerical Simulation

Abstract

We carry out high-resolution laboratory experiments and numerical simulations to investigate the dynamics of unsteady vortex formation across the neck of an anatomic in vitro model of an intracranial aneurysm. A transparent acrylic replica of the aneurysm is manufactured and attached to a pulse duplicator system in the laboratory. Time-resolved three-dimensional three-component velocity measurements are obtained inside the aneurysm sac under physiologic pulsatile conditions. High-resolution numerical simulations are also carried out under conditions replicating as closely as possible those of the laboratory experiment. Comparison of the measured and computed flow fields shows very good agreement in terms of instantaneous velocity fields and three-dimensional coherent structures. Both experiments and numerical simulations show that a well-defined vortical structure is formed near the proximal neck at early systole. This vortical structure is advected by the flow across the aneurysm neck and impinges on the distal wall. The results underscore the complexity of aneurysm hemodynamics and point to the need for integrating high-resolution, time-resolved three-dimensional experimental and computational techniques. The current work emphasizes the importance of vortex formation phenomena at aneurysmal necks and reinforces the findings of previous computational work and recent clinical studies pointing to links between flow pulsatility and aneurysm growth and rupture.

A review of solid–fluid selection options for optical-based measurements in single-phase liquid, two-phase liquid–liquid and multiphase solid–liquid flows

“…Le et al (2013) matched urethane rubber with a RI of 1.490 to an aqueous solution of sodium iodide (NaI) and glycerol to study a model of an aneurysm. The different liquids identified as having been used in RIM experiments featuring rubbers are shown in Table 2.…”

“…They have been used as Aq. Le et al (2013) * Temperature for viscosity is provided when stated; otherwise, it is assumed that this is at ambient laboratory conditions between 20 and 25 °C Table 3 List of hydrogel, custom-polymer, and resin-based RIM systems * Temperature for viscosity is provided when stated; otherwise, it is assumed that this is at ambient laboratory conditions between 20 and 25 °C Solid Aq. Bai and Katz (2014) Forecast3D UOPTIC 2 Butscher et al (2012) particles in flows but are less likely to be suitable for use as rigid walls as they possess a degree of flexibility.…”

Identification of vortex structures in a cohort of 204 intracranial aneurysms

“…To perform pulsatile CFD simulations for our IA cases, we adopted the standard practice of scaling a generic waveform based on the inlet diameter. This corresponds to a constant pulsatility index [53], while previous studies have suggested that pulsatility index with geometry could influence vortex formation in the aneurysm [23,24,54]. Although our study indicates that the vVF and the sVF may be minimally influenced by the transient waveform (figure 6d ), future studies should examine the impact of different pulsatility indices on these metrics.…”

“…Since it is straightforward to calculate, it has been frequently used for visualizing and quantifying vortical coherent structures. Recently, the Q-criterion has been used to examine the formation and evolution of vortex structures in a rabbit aneurysm model [23,24] and a few patient IA models, to demonstrate the feasibility and potential value of vortex visualization [25,26].…”

Multi-time-lag PIV analysis of steady and pulsatile flows in a sidewall aneurysm

“…During the last decade, several PIV measurements have been performed on IA models to evaluate, on one hand, the influence of different geometry parameters on flow dynamics (Liou and Liao 1997;Yu and Zhao 1999;Tateshima et al 2003Tateshima et al , 2007Tateshima et al , 2008Liou et al 2007;Ford et al 2008a;Yamaguchi et al 2008;Morino et al 2010;Tanoue et al 2011;Raschi et al 2012), and on the other hand, to validate computational fluid dynamics (CFD) predictions (Hoi et al 2006;Ford et al 2008b;Mulder et al 2009;Ugron et al 2012;Le et al 2013). Idealized IA models, made of a spherical aneurysm connected to a cylindrical pipe, were essentially used to study the influence of several factors: (a) the curvature of the parent artery (Liou and Liao 1997), (b) the angular orientation of IA with respect to parent vessel (in basilar tip (Ford et al 2008a) and sidewall IAs (Liou et al 2007)) and (c) IA aspect ratio (Yamaguchi et al 2008) (i.e.…”