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SUMMARY:MECHANICAL STRESS IN ABDOMINAL ANEURYSM: INFLUENCE OF MATERIAL ANI
 SOTROPY AND UNLOAD CONFIGURATION - Dr. Jose F. Rodriguez\, Mechanical Engi
 neering Department. Aragon Institute of Engineering Research (I3A). Univer
 sity of Zaragoza (Spain).
DTSTART:20110513T100000Z
DTEND:20110513T110000Z
UID:TALK31361@talks.cam.ac.uk
CONTACT:Dr. Teng
DESCRIPTION:Biomechanical studies suggest that risk for rupture of an abdo
 minal aortic aneurysm (AAA) is more precisely related to mechanical wall s
 tress. In this regard\, a reliable and accurate stress analysis of an in v
 ivo AAA requires the use of suitable constitutive\nmodels. To date\, all s
 tress analysis conducted on AAA have considered the tissue as isotropic. H
 owever\, recent biaxial tensile tests conducted on AAA tissue samples demo
 nstrate the anisotropic nature of this tissue. In addition\, the standard 
 procedure for\ncalculating wall stress is by means of the finite element a
 nalysis (FEA) on patientspecific AAA models generated from computed tomogr
 aphy (CT) images. However\, these models presents the vasculature in press
 urized form\, so assuming it as unloaded\nmodel and applying a real physio
 logical pressure might overestimate the maximum stress in the AAA. To solv
 e this problem\, we propose a methodology to derive the unloaded geometrie
 s of structural and fluid domain\, ready to be used for subsequent FEA\, C
 FD or fluid-structure interaction (FSI) studies. The purpose of this work 
 is to study the influence of geometry and material anisotropy and the zero
  pressure configuration on the magnitude and distribution of the peak wall
  stress in AAAs. CT\nscans were obtained retrospectively from 6 AAA subjec
 ts (3 ruptured and 3 unruptured aneurysms) treated at Allegheny General Ho
 spital in Pittsburgh\, Pennsylvania. The corresponding DICOM images were i
 mported into an in-house Matlab based image\nsegmentation code (VESSEG v.1
 .0.1\, Carnegie Mellon University)\, for the lumen\, inner wall\, and oute
 r wall segmentations. Three-node shell elements (quadratic\, with 5 integr
 ation points through the thickness) were used for meshing the arterial wal
 l\, while ten-node tetrahedral elements (quadratic\, with 4 integration po
 ints) were used to mesh the thrombus. A comparison between ruptured and un
 ruptured wall mechanics on the basis of the anisotropic material model yie
 lds mean peak wall stresses (in kPa) of 977.9\n± 179.6 and 702.6 ± 166.2
 \, for the ruptured and unruptured geometries\, respectively. The anisotro
 pic characteristics of the AAA wall\, previously verified by means of biax
 ial tensile testing of AAA tissue specimens\, also play a role in the dist
 ribution of wall stress yielding higher peak wall stresses that likely inf
 luence the assessment of rupture potential in individual AAAs. We finally 
 compare the stress results obtained from CT image based geometry and unloa
 ded geometry to understand the effect of the modeling assumption.
LOCATION:Venue to be confirmed
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