Stereoscopically Observed Deformations of a Compliant Abdominal Aortic Aneurysm Model

Abstract

A new experimental setup has been implemented to precisely measure the deformations of an entire model abdominal aortic aneurysm (AAA). This setup addresses a gap between the computational and experimental models of AAA that have aimed at improving the limited understanding of aneurysm development and rupture. The experimental validation of the deformations from computational approaches has been limited by a lack of consideration of the large and varied deformations that AAAs undergo in response to physiologic flow and pressure. To address the issue of experimentally validating these calculated deformations, a stereoscopic imaging system utilizing two cameras was constructed to measure model aneurysm displacement in response to pressurization. The three model shapes, consisting of a healthy aorta, an AAA with bifurcation, and an AAA without bifurcation, were also evaluated with computational solid mechanical modeling using finite elements to assess the impact of differences between material properties and for comparison against the experimental inflations. The device demonstrated adequate accuracy (surface points were located to within 0.07 mm) for capturing local variation while allowing the full length of the aneurysm sac to be observed at once. The experimental model AAA demonstrated realistic aneurysm behavior by having cyclic strains consistent with reported clinical observations between pressures 80 and 120 mm Hg. These strains are 1-2%, and the local spatial variations in experimental strain were less than predicted by the computational models. The three different models demonstrated that the asymmetric bifurcation creates displacement differences but not cyclic strain differences within the aneurysm sac. The technique and device captured regional variations of strain that are unobservable with diameter measures alone. It also allowed the calculation of local strain and removed rigid body motion effects on the strain calculation. The results of the computations show that an asymmetric aortic bifurcation created displacement differences but not cyclic strain differences within the aneurysm sac.

Minimal Preconditioning Effects Observed for Inflation Tests of Planar Tissues

“…Digital image correlation has become widely used to measure displacements and strains of soft tissues, and a number of authors have calculated the accuracy and resolution of 3D-DIC displacements [37][38][39][40][41] and strains [40,42,43] using methods similar to those described here. For example, Sutton et al [42] reported a standard deviation of 0.03%-0.08% strain for a 3D translation of a cylinder.…”

A simple, effective and clinically applicable method to compute abdominal aortic aneurysm wall stress

“…Then the "rubber aneurysm" can be pressure-loaded and its deformed configuration measured precisely, together with the surface strain field (e.g. by stereoscopic techniques (Meyer et al, 2011) or the photoelastic method (Doyle et al, 2012)). The load can be increased until the "rubber aneurysm" ruptures and the rupture site can then be located.…”

Influence of compliance on flow rate waveforms in hydraulic circuits for in vitro modeling the human circulatory system

“…Abdominal Aortic Aneurysms (AAA) pose a serious health risk due to their potential for thrombus formation, dissection, and, more importantly, rupture [1,2]. In vitro studies on AAA have been performed since the end of the last century [3].…”