scholarly journals A Methodology for the Derivation of Unloaded Abdominal Aortic Aneurysm Geometry With Experimental Validation

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Santanu Chandra ◽  
Vimalatharmaiyah Gnanaruban ◽  
Fabian Riveros ◽  
Jose F. Rodriguez ◽  
Ender A. Finol
Keyword(s):  
Finite Element ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Stress Component ◽  
Wall Stress ◽  
Patient Specific ◽  
Element Analysis ◽  
Nodal Surface ◽  
Abdominal Aortic ◽  
Peak Wall Stress

In this work, we present a novel method for the derivation of the unloaded geometry of an abdominal aortic aneurysm (AAA) from a pressurized geometry in turn obtained by 3D reconstruction of computed tomography (CT) images. The approach was experimentally validated with an aneurysm phantom loaded with gauge pressures of 80, 120, and 140 mm Hg. The unloaded phantom geometries estimated from these pressurized states were compared to the actual unloaded phantom geometry, resulting in mean nodal surface distances of up to 3.9% of the maximum aneurysm diameter. An in-silico verification was also performed using a patient-specific AAA mesh, resulting in maximum nodal surface distances of 8 μm after running the algorithm for eight iterations. The methodology was then applied to 12 patient-specific AAA for which their corresponding unloaded geometries were generated in 5–8 iterations. The wall mechanics resulting from finite element analysis of the pressurized (CT image-based) and unloaded geometries were compared to quantify the relative importance of using an unloaded geometry for AAA biomechanics. The pressurized AAA models underestimate peak wall stress (quantified by the first principal stress component) on average by 15% compared to the unloaded AAA models. The validation and application of the method, readily compatible with any finite element solver, underscores the importance of generating the unloaded AAA volume mesh prior to using wall stress as a biomechanical marker for rupture risk assessment.

Automated Methodology for Determination of Stress Distribution in Human Abdominal Aortic Aneurysm

2005 ◽  
Vol 127 (5) ◽  
pp. 868-871 ◽  
Author(s):  
Madhavan L. Raghavan ◽  
Mark F. Fillinger ◽  
Steven P. Marra ◽  
Bernhard P. Naegelein ◽  
Francis E. Kennedy
Keyword(s):  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Peak Stress ◽  
Wall Stress ◽  
Patient Specific ◽  
Element Analysis ◽  
Biomechanical Stress ◽  
Abdominal Aortic ◽  
Study Population ◽  
Peak Wall Stress

Knowledge of impending abdominal aortic aneurysm (AAA) rupture can help in surgical planning. Typically, aneurysm diameter is used as the indicator of rupture, but recent studies have hypothesized that pressure-induced biomechanical stress may be a better predictor. Verification of this hypothesis on a large study population with ruptured and unruptured AAA is vital if stress is to be reliably used as a clinical prognosticator for AAA rupture risk. We have developed an automated algorithm to calculate the peak stress in patient-specific AAA models. The algorithm contains a mesh refinement module, finite element analysis module, and a postprocessing visualization module. Several aspects of the methodology used are an improvement over past reported approaches. The entire analysis may be run from a single command and is completed in less than 1h with the peak wall stress recorded for statistical analysis. We have used our algorithm for stress analysis of numerous ruptured and unruptured AAA models and report some of our results here. By current estimates, peak stress in the aortic wall appears to be a better predictor of rupture than AAA diameter. Further use of our algorithm is ongoing on larger study populations to convincingly verify these findings.

Abdominal Aortic Aneurysm Rupture Risk Assessment Exploiting Dynamic (4D) CT Based Wall Motion Data and Finite Element Analysis

2013 ◽  
Author(s):  
Eleni Metaxa ◽  
Vasileios Vavourakis ◽  
Nikolaos Kontopodis ◽  
Konstantinos Pagonidis ◽  
Christos V. Ioannou ◽  
...  
Keyword(s):  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Risk Estimation ◽  
Wall Stress ◽  
Aneurysm Rupture ◽  
Patient Specific ◽  
Rupture Risk ◽  
Element Analysis ◽  
Motion Data ◽  
Abdominal Aortic

Abdominal aortic aneurysm (AAA) disease is primarily a degenerative process, where rupture occurs when stress exerted on the aortic wall exceeds its failure strength. Therefore, knowledge of both the wall stress distribution and the mechanical properties of the AAA wall is required for patient specific rupture risk estimation.

scholarly journals The Association of Wall Mechanics and Morphology: A Case Study of Abdominal Aortic Aneurysm Growth

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
Christopher B. Washington ◽  
Judy Shum ◽  
Satish C. Muluk ◽  
Ender A. Finol
Keyword(s):  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Stress ◽  
Aneurysm Rupture ◽  
Maximum Diameter ◽  
Least Squares Regression ◽  
Surveillance Period ◽  
Element Analysis ◽  
Abdominal Aortic ◽  
Peak Wall Stress

The purpose of this study is to evaluate the potential correlation between peak wall stress (PWS) and abdominal aortic aneurysm (AAA) morphology and how it relates to aneurysm rupture potential. Using in-house segmentation and meshing software, six 3-dimensional (3D) AAA models from a single patient followed for 28 months were generated for finite element analysis. For the AAA wall, both isotropic and anisotropic materials were used, while an isotropic material was used for the intraluminal thrombus (ILT). These models were also used to calculate 36 geometric indices characteristic of the aneurysm morphology. Using least squares regression, seven significant geometric features (p < 0.05) were found to characterize the AAA morphology during the surveillance period. By means of nonlinear regression, PWS estimated with the anisotropic material was found to be highly correlated with three of these features: maximum diameter (r = 0.992, p = 0.002), sac volume (r = 0.989, p = 0.003) and diameter to diameter ratio (r = 0.947, p = 0.033). The correlation of wall mechanics with geometry is nonlinear and reveals that PWS does not increase concomitantly with aneurysm diameter. This suggests that a quantitative characterization of AAA morphology may be advantageous in assessing rupture risk.

scholarly journals Predictors of Abdominal Aortic Aneurysm Risks

2020 ◽  
Vol 7 (3) ◽  
pp. 79
Author(s):  
Stephen J. Haller ◽  
Amir F. Azarbal ◽  
Sandra Rugonyi
Keyword(s):  
Risk Assessment ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Stress ◽  
Patient Specific ◽  
Rupture Risk ◽  
Element Analysis ◽  
Computational Biomechanics ◽  
Wall Strength ◽  
Abdominal Aortic

Computational biomechanics via finite element analysis (FEA) has long promised a means of assessing patient-specific abdominal aortic aneurysm (AAA) rupture risk with greater efficacy than current clinically used size-based criteria. The pursuit stems from the notion that AAA rupture occurs when wall stress exceeds wall strength. Quantification of peak (maximum) wall stress (PWS) has been at the cornerstone of this research, with numerous studies having demonstrated that PWS better differentiates ruptured AAAs from non-ruptured AAAs. In contrast to wall stress models, which have become progressively more sophisticated, there has been relatively little progress in estimating patient-specific wall strength. This is because wall strength cannot be inferred non-invasively, and measurements from excised patient tissues show a large spectrum of wall strength values. In this review, we highlight studies that investigated the relationship between biomechanics and AAA rupture risk. We conclude that combining wall stress and wall strength approximations should provide better estimations of AAA rupture risk. However, before personalized biomechanical AAA risk assessment can become a reality, better methods for estimating patient-specific wall properties or surrogate markers of aortic wall degradation are needed. Artificial intelligence methods can be key in stratifying patients, leading to personalized AAA risk assessment.

scholarly journals NUMERICAL ANALYSIS OF THE WALL STRESS IN ABDOMINAL AORTIC ANEURYSM: INFLUENCE OF THE MATERIAL MODEL NEAR-INCOMPRESSIBILITY

2012 ◽  
Vol 12 (01) ◽  
pp. 1250005 ◽  
Author(s):  
MAMADOU TOUNGARA ◽  
GREGORY CHAGNON ◽  
CHRISTIAN GEINDREAU
Keyword(s):  
Finite Element ◽  
Abdominal Aortic Aneurysm ◽  
Numerical Analysis ◽  
Aortic Aneurysm ◽  
Maximum Stress ◽  
Mechanical Response ◽  
Wall Stress ◽  
Model Complexity ◽  
Anisotropic Models ◽  
Abdominal Aortic

Recently, hyperelastic mechanical models were proposed to well capture the aneurismal arterial wall anisotropic and nonlinear features experimentally observed. These models were formulated assuming the material incompressibility. However in numerical analysis, a nearly incompressible approach, i.e., a mixed formulation pressure-displacement, is usually adopted to perform finite element stress analysis of abdominal aortic aneurysm (AAA). Therefore, volume variations of the material are controlled through the volumetric energy which depends on the initial bulk modulus κ. In this paper, an analytical analysis of the influence of κ on the mechanical response of two invariant-based anisotropic models is first performed in the case of an equibiaxial tensile test. This analysis shows that for the strongly nonlinear anisotropic model, even in a restricted range of deformations, large values of κ are necessary to ensure the incompressibility condition, in order to estimate the wall stress with a reasonable precision. Finite element simulations on idealized AAA geometries are then performed. Results from these simulations show that the maximum stress in the AAA wall is underestimated in previous works, committed errors vary from 26% to 58% depending on the geometrical model complexity. In addition to affect the magnitude of the maximum stress in the aneurysm, we found that too small value of κ may also affect the location of this stress.

Computational Modeling of the Effects of Transient Blood Flow Characteristics and Wall Thickness on the Rupture of Abdominal Aortic Aneurysm

2014 ◽  
Author(s):  
Pinaki Pal
Keyword(s):  
Blood Flow ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Wall Thickness ◽  
Flow Model ◽  
Wall Stress ◽  
Flow Transition ◽  
Abdominal Aortic ◽  
Sst Model ◽  
Peak Wall Stress

Precise estimation of wall stress distribution within an abdominal aortic aneurysm (AAA) is clinically useful for prediction of its rupture. In this paper a computational fluid dynamic model incorporating two-way coupled fluid-structure interaction is employed to investigate the role of laminar-turbulent flow transition and wall thickness in altering the distribution and magnitude of wall stress in an AAA. Blood flow in axially symmetric aneurysm models governed by a compliant wall mechanics was simulated. Menter’s hybrid k-epsilon/k-omega shear stress transport (SST) model with a correlation-based transition model was used to capture laminar-turbulent transition in the blood flow. Realistic physiological transient boundary conditions were prescribed. The numerical model was validated against experimental data available from the literature. Fluid flow analysis showed the formation of recirculating vortices at the proximal end of the aneurysm after the peak systole which then, moved towards the distal end of the aneurysm along with the bulk flow and were dissipated eventually due to viscous effects. These vortices interacted with the aortic wall and led to local pressure rise. Von Mises stress distribution on the aneurysm wall and location of its peak value were computed and compared with those of a separate numerical simulation performed using a laminar viscous flow model. The predicted peak wall stress was found to be significantly higher for the SST model as compared to the laminar flow model. The location of maximum stress shifted more towards the posterior end of the aneurysm when laminar-turbulent flow transition was considered. In addition, a small reduction of 0.4 mm in wall thickness resulted in the elevation of peak wall stress by a factor of 1.4. The present study showed that capturing flow transition in an AAA is essential to accurate prediction of its rupture. The proposed numerical model provides a robust computational framework to gain more insight into AAA biomechanics and to accurately estimate wall stresses in realistic aneurysm configurations.

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