Heterogeneous, Variable Wall-Thickness Modeling of a Ruptured Abdominal Aortic Aneurysm

2004 ◽  
Author(s):  
Madhavan Raghavan ◽  
Jarin Kratzberg ◽  
Erasmo Sima˜o da Silva
Keyword(s):  
Finite Element ◽  
Wall Thickness ◽  
Regional Distribution ◽  
Uniaxial Extension ◽  
Aortic Aneurysms ◽  
Surface Model ◽  
Thin Wall ◽  
Material Parameters ◽  
Abdominal Aortic ◽  
Rupture Site

Pressure-induced mechanical stress in ruptured abdominal aortic aneurysms (AAA) was investigated using a finite element model with measured variations in wall thickness and material properties. We harvested an 8-cm ruptured AAA from a cadaver and recorded its geometry on bi-plane photographs and three-dimensionally reconstructed. The wall thickness was measured at over 100 sites on the aneurysm surface using digital calipers. Regional mechanical property variation (failure strengths and hyperelastic material parameters) was determined using data from uniaxial extension tests of 19 test strips cut from various regions of the AAA surface. The measured data for wall thickness and mechanical properties were transferred to the 3D AAA surface model and nonlinearly interpolated on the surface to obtain the point-to-point regional distribution for thickness and material parameters. Modeling the AAA as a thick shell, finite element stress analysis was performed. The peak stress was found to be exactly at the rupture site and was substantially higher than population averages. The measured low wall thickness at the rupture site appeared to play a major role in elevating stresses indicating that localized thin wall may be an important risk factor for AAA rupture.

Abstract 236: Local Wall Thickness in Finite Element Models Improves Prediction of Abdominal Aortic Aneurysm Growth

2013 ◽  
Vol 33 (suppl_1) ◽  
Author(s):  
Eric K Shang ◽  
Derek P Nathan ◽  
Ronald M Fairman ◽  
Edward Y Woo ◽  
Grace J Wang ◽  
...  
Keyword(s):  
Growth Rate ◽  
Finite Element ◽  
Clinical Outcomes ◽  
Wall Thickness ◽  
Aortic Aneurysms ◽  
Element Analysis ◽  
Abdominal Aortic ◽  
Variable Wall Thickness ◽  
Aneurysm Growth ◽  
Variable Wall

Objective Growing evidence suggests that peak wall stress (PWS) derived from finite element analysis (FEA) of abdominal aortic aneurysms (AAAs) predicts clinical outcomes better than diameter alone. Prior models assume uniform wall thickness (UWT). We hypothesize that inclusion of locally variable wall thickness (VWT) into FEA of AAAs will improve the ability to predict clinical outcomes. Methods Patients with AAAs (n=26) undergoing radiologic surveillance were identified. Custom MATLAB algorithms generated UWT and VWT aortic geometries from CTA images, which were subsequently loaded with systolic blood pressure using FEA. PWS and aneurysm growth (as a proxy for rupture risk and the need for repair) were examined. Results The average radiologic follow-up time was 22.0±13.6 months and the average aneurysm growth rate was 2.8±1.7 mm/year. PWS in VWT models significantly differed from PWS in UWT models (238±68 vs 212±73 kPa, P=0.025). In our sample, initial aortic diameter was not found to be correlated with aneurysm growth (r=0.26, P=0.19). A stronger correlation was found between aneurysm growth and PWS derived from VWT models as compared to PWS from UWT models (r=0.86 vs r=0.58, P=0.032 by Fisher’s r to Z transformation). The three panels in the figure demonstrate the correlation between aneurysm growth rate and (1) initial diameter, (2) PWS using UWT model, and (3) PWS using VWT model, respectively. Conclusion The inclusion of locally variable wall thickness significantly improved the correlation between PWS and aneurysm growth. Aortic wall thickness should be incorporated into future FEA models to accurately predict clinical outcomes.

Abdominal Aortic Aneurysm: From Clinical Imaging to Realistic Replicas

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Sergio Ruiz de Galarreta ◽  
Aitor Cazón ◽  
Raúl Antón ◽  
Ender A. Finol
Keyword(s):  
Wall Thickness ◽  
Physiological Stress ◽  
Ex Vivo ◽  
Casting Process ◽  
Aortic Aneurysms ◽  
Optical Methods ◽  
Patient Specific ◽  
Uniaxial Tensile ◽  
Element Analysis ◽  
Abdominal Aortic

The goal of this work is to develop a framework for manufacturing nonuniform wall thickness replicas of abdominal aortic aneurysms (AAAs). The methodology was based on the use of computed tomography (CT) images for virtual modeling, additive manufacturing for the initial physical replica, and a vacuum casting process and range of polyurethane resins for the final rubberlike phantom. The average wall thickness of the resulting AAA phantom was compared with the average thickness of the corresponding patient-specific virtual model, obtaining an average dimensional mismatch of 180 μm (11.14%). The material characterization of the artery was determined from uniaxial tensile tests as various combinations of polyurethane resins were chosen due to their similarity with ex vivo AAA mechanical behavior in the physiological stress configuration. The proposed methodology yields AAA phantoms with nonuniform wall thickness using a fast and low-cost process. These replicas may be used in benchtop experiments to validate deformations obtained with numerical simulations using finite element analysis, or to validate optical methods developed to image ex vivo arterial deformations during pressure-inflation testing.

scholarly journals Local Wall Thickness in Finite Element Models Improves Prediction of Abdominal Aortic Aneurysm Growth

2013 ◽  
Vol 57 (5) ◽  
pp. 78S-79S
Author(s):  
Eric K. Shang ◽  
Derek P. Nathan ◽  
Ronald M. Fairman ◽  
Edward Y. Woo ◽  
Grace J. Wang ◽  
...  
Keyword(s):  
Finite Element ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Thickness ◽  
Finite Element Models ◽  
Abdominal Aortic ◽  
Aneurysm Growth

Flexibility Factors and Stress Indices for Piping Components With D/T ≧ 100 Subjected to In-Plane or Out-of-Plane Moment

1988 ◽  
Vol 110 (4) ◽  
pp. 374-386 ◽  
Author(s):  
T. Fujimoto ◽  
T. Soh
Keyword(s):  
Finite Element ◽  
Wall Thickness ◽  
Large Diameter ◽  
Thin Wall ◽  
Finite Element Analyses ◽  
Empirical Formulas ◽  
Stress Evaluation ◽  
Stress Indices ◽  
Piping Systems ◽  
Out Of Plane

The finite element analyses are carried out for the several piping components (D/T ≧ 100) subjected to in-plane or out-of-plane moment. For the stress evaluation of the chemical plant piping systems, ANSI B31.3 is usually applied. But the stress intensification factors and flexibility factors in this code are mainly for a heavy-wall-thickness pipe, so it is necessary to reconsider these factors for a thin-wall-thickness pipe with a large diameter. In our study, several finite element analyses using MSC/NASTRAN program were performed on the pipe bends (elbow or miter bend, 0.01 ≦ h ≦ 0.2) and the unreinforced fabricated tees (50 ≦ D/Tr ≦ 300, 0.5 ≦ d/D ≦ 0.95, 0.25 ≦ Tb/Tr ≦ 0.95), and the empirical formulas for the flexibility factors and the stress indices, due to out-of-plane or in-plane moment, were proposed. Experimental stress analyses for the piping components with D/Tr = 127 were also carried out, and it was confirmed that the results agreed well with the numerical ones.

scholarly journals Finite Element Analysis of Abdominal Aortic Aneurysms: Predicted Rupture Risk Correlates With Aortic Wall Histology in Individual Patients

2014 ◽  
Vol 21 (4) ◽  
pp. 556-564 ◽  
Author(s):  
Philipp Erhart ◽  
Caspar Grond-Ginsbach ◽  
Maani Hakimi ◽  
Felix Lasitschka ◽  
Susanne Dihlmann ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Aortic Wall ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Rupture Risk ◽  
Element Analysis ◽  
Abdominal Aortic

scholarly journals Dynamic geometry and wall thickness of the aortic neck of abdominal aortic aneurysms with intravascular ultrasonography

2007 ◽  
Vol 46 (5) ◽  
pp. 891-897 ◽  
Author(s):  
Frank R. Arko ◽  
Erin H. Murphy ◽  
Chad M. Davis ◽  
Eric D. Johnson ◽  
Stephen T. Smith ◽  
...  
Keyword(s):  
Wall Thickness ◽  
Dynamic Geometry ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Intravascular Ultrasonography ◽  
Aortic Neck ◽  
Abdominal Aortic
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