Use of Regional Mechanical Properties of Abdominal Aortic Aneurysms to Advance Finite Element Modeling of Rupture Risk

2012 ◽  
Author(s):  
Áine P. Tierney ◽  
Anthony Callanan ◽  
Timothy M. McGloughlin
Keyword(s):  
Mechanical Properties ◽  
Stress Distribution ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Aortic Tissue ◽  
Structural Problems ◽  
Aneurysm Wall ◽  
Abdominal Aortic ◽  
Computer Based ◽  
Complex Structural

AAA rupture represents a catastrophic failure of the degenerated aortic tissue when the aneurysm wall can no longer withstand the stresses on it. Understanding the stress distribution in the aneurysm, along with its material properties, is an essential step toward predicting the rupture of an AAA. FE analysis is a computer-based method of solving complex structural problems for which the stress distribution can be easily studied. In analyzing AAA behavior with FE models, realistic aortic anatomies with patient-specific physiological and mechanical properties have been used in recent years. Data for these anatomies have typically come from computed tomography (CT) scans.

scholarly journals On the Relative Impact of Intraluminal Thrombus Heterogeneity on Abdominal Aortic Aneurysm Mechanics

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Joseph R. Leach ◽  
Evan Kao ◽  
Chengcheng Zhu ◽  
David Saloner ◽  
Michael D. Hope
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Aneurysm Rupture ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Rupture Risk ◽  
Intraluminal Thrombus ◽  
Element Analysis ◽  
Aneurysm Wall ◽  
Abdominal Aortic

Intraluminal thrombus (ILT) is present in the majority of abdominal aortic aneurysms (AAA) of a size warranting consideration for surgical or endovascular intervention. The rupture risk of AAAs is thought to be related to the balance of vessel wall strength and the mechanical stress caused by systemic blood pressure. Previous finite element analyses of AAAs have shown that ILT can reduce and homogenize aneurysm wall stress. These works have largely considered ILT to be homogeneous in mechanical character or have idealized a stiffness distribution through the thrombus thickness. In this work, we use magnetic resonance imaging (MRI) to delineate the heterogeneous composition of ILT in 7 AAAs and perform patient–specific finite element analysis under multiple conditions of ILT layer stiffness disparity. We find that explicit incorporation of ILT heterogeneity in the finite element analysis is unlikely to substantially alter major stress analysis predictions regarding aneurysm rupture risk in comparison to models assuming a homogenous thrombus, provided that the maximal ILT stiffness is the same between models. Our results also show that under a homogeneous ILT assumption, the choice of ILT stiffness from values common in the literature can result in significantly larger variations in stress predictions compared to the effects of thrombus heterogeneity.

Local Mechanical Properties of Abdominal Aortic Aneurysms

2008 ◽  
Author(s):  
Evelyne van Dam ◽  
Marcel Rutten ◽  
Frans van de Vosse
Keyword(s):  
Mechanical Properties ◽  
Stress Analysis ◽  
Vessel Wall ◽  
Computational Models ◽  
Wall Stress ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Rupture Risk ◽  
Abdominal Aortic

Rupture risk of abdominal aortic aneurysms (AAA) based on wall stress analysis may be superior to the currently used diameter-based rupture risk prediction [4; 5; 6; 7]. In patient specific computational models for wall stress analysis, the geometry of the aneurysm is obtained from CT or MR images. The wall thickness and mechanical properties are mostly assumed to be homogeneous. The pathological AAA vessel wall may contain collageneous areas, but also calcifications, cholesterol crystals and large amounts of fat cells. No research has yet focused yet on the differences in mechanical properties of the components present within the degrading AAA vessel wall.

Trans-Thrombus Blood Pressure Effects in Abdominal Aortic Aneurysms

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Clark A. Meyer ◽  
Carine Guivier-Curien ◽  
James E. Moore
Keyword(s):  
Wall Stress ◽  
Aortic Aneurysms ◽  
Pressure Effects ◽  
Von Mises Stress ◽  
Patient Specific ◽  
Aneurysm Wall ◽  
Abdominal Aortic ◽  
Histopathological Studies ◽  
Von Mises ◽  
Von Mises Stresses

How much and how the thrombus supports the wall of an abdominal aortic aneurysm (AAA) is unclear. While some previous studies have indicated that thrombus lacks the mechanical integrity to support much load compared with the aneurysm wall, others have shown that removing thrombus in computational AAA models drastically changes aneurysm wall stress. Histopathological studies have shown that thrombus properties vary through the thickness and it can be porous. The goal of this study is to explore the variations in thrombus properties, including the ability to isolate pressure from the aneurysm wall, incomplete attachment, and their effects on aneurysm wall stress, an important parameter in determining risk for rupture. An analytical model comprised of cylinders and two patient specific models were constructed with pressurization boundary conditions applied at the lumen or the thrombus/aneurysm wall interface (to simulate complete transmission of pressure through porous thrombus). Aneurysm wall stress was also calculated in the absence of thrombus. The potential importance of partial thrombus attachment was also analyzed. Pressurizing at either surface (lumen versus interface) made little difference to mean von Mises aneurysm wall stress values with thrombus completely attached (3.1% analytic, 1.2% patient specific) while thrombus presence reduced mean von Mises stress considerably (79% analytic, 40–46% patient specific) in comparison to models without it. Peak von Mises stresses were similarly influenced with pressurization surface differing slightly (3.1% analytic, 1.4% patient specific) and reductions in stress by thrombus presence (80% analytic, 28–37% patient specific). The case of partial thrombus attachment was investigated using a cylindrical model in which there was no attachment between the thrombus and aneurysm wall in a small area (10 deg). Applying pressure at the lumen resulted in a similar stress field to fully attached thrombus, whereas applying pressure at the interface resulted in a 42% increase in peak aneurysm wall stress. Taken together, these results show that the thrombus can have a wall stress reducing role even if it does not shield the aneurysm wall from direct pressurization—as long as the thrombus is fully attached to the aneurysm wall. Furthermore, the potential for porous thrombus to transmit pressure to the interface can result in a considerable increase in aneurysm wall stress in cases of partial attachment. In the search for models capable of accurately assessing the risk for rupture, the nature of the thrombus and its attachment to the aneurysm wall must be carefully assessed.

scholarly journals Does the Intraluminal Thrombus Provoke the Rupture of the Abdominal Aortic Aneurysm Wall?

2021 ◽  
Vol 11 (21) ◽  
pp. 9941
Author(s):  
Mohammed Almijalli
Keyword(s):  
Computer Modelling ◽  
Aortic Aneurysms ◽  
Oxygen Flow ◽  
Patient Specific ◽  
Aortic Blood Flow ◽  
Intraluminal Thrombus ◽  
Volume Percentage ◽  
Aneurysm Wall ◽  
Abdominal Aortic ◽  
Risk Of Rupture

The role of intraluminal thrombus (ILT) in the rupture of abdominal aortic aneurysms (AAA) is controversial, and it is unclear whether it increases or decreases the risk of rupture. This research aims to find a clear answer to this question. Previous computer modelling suggests that an ILT lowers oxygen dissemination to the AAA wall, contributing to wall thinning. The methodology used in this study determines the amount of oxygen reaching the aneurysm wall after passing through the ILT by using the porous nature of the ILT to recreate the condition as closely as feasible. Using computed tomographic images, patient-specific three-dimensional (3D) AAA geometries were recreated. Modelling blood and oxygen flow in AAA was obtained using a computational fluid dynamics (CFD) approach. Our findings indicated that the oxygen volume percentage had completely reached the aneurysm wall. Only at the inlet and outflow did the greatest wall shear stress (WSS) occur, with a significant drop in the central region of the aneurysm wall. CFD was used to calculate the velocity, pressure, and WSS of aortic blood flow. ILT had no effect on oxygen flow to the aneurysm wall, disproving the theory that it produces local hypoxia.

Feasibility of Determination of Mechanical Properties of Abdominal Aortic Aneurysms by Simultaneous Pressure and Volume Measurements In-Vivo

2008 ◽  
Author(s):  
Marcel van ’t Veer ◽  
Marcel C. M. Rutten ◽  
Jaap Buth ◽  
Nico H. J. Pijls ◽  
Frans N. van de Vosse
Keyword(s):  
Mechanical Properties ◽  
Wall Stress ◽  
Tensile Tests ◽  
Aortic Aneurysms ◽  
Wall Material ◽  
Patient Specific ◽  
Abdominal Aortic ◽  
Risk Of Rupture

In an effort to better predict the risk of rupture of an abdominal aortic aneurysm (AAA), methods have been developed that comprise more than diameter information alone. Wall stress calculations demonstrated superior results compared to the diameter criterion [1]. Accurate wall stress calculations require patient specific geometry, load, and wall properties of the aneurysm [2]. Usually, values for mechanical properties obtained from in-vitro tensile tests of excised aneurysmal wall material are used for wall stress calculations [3]. For obvious reasons such experiments to obtain vessel properties are impossible to perform in patient specific cases for risk assessment.

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.

Inflation Testing as a Means of Measuring Failure Strength of Aortic Tissue

2003 ◽  
Author(s):  
Jeffrey N. Kinkaid ◽  
Steven P. Marra ◽  
Francis E. Kennedy ◽  
Mark F. Fillinger
Keyword(s):  
United States ◽  
Abdominal Aortic Aneurysms ◽  
The United States ◽  
Aortic Aneurysms ◽  
Aortic Tissue ◽  
Failure Strength ◽  
Health Statistics ◽  
Mortality Risks ◽  
Abdominal Aortic ◽  
Risk Of Rupture

Abdominal Aortic Aneurysms (AAAs) are localized enlargements of the aorta. If untreated, AAAs will grow irreversibly until rupture occurs. Ruptured AAAs are usually fatal and are a leading cause of death in the United States, killing 15,000 per year (National Center for Health Statistics, 2001). Surgery to repair AAAs also carries mortality risks, so surgeons desire a reliable tool to evaluate the risk of rupture versus the risk of surgery.

Transport and Mixing in Patient Specific Abdominal Aortic Aneurysms With Lagrangian Coherent Structures

2012 ◽  
Author(s):  
Amirhossein Arzani ◽  
Shawn C. Shadden
Keyword(s):  
Coherent Structures ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Lagrangian Coherent Structures ◽  
Patient Specific ◽  
Complex Flow ◽  
Flow Topology ◽  
Finite Time Lyapunov Exponent ◽  
Abdominal Aortic ◽  
High Gradients

Abdominal aortic aneurysms (AAA) are characterized by disturbed flow patterns, low and oscillatory wall shear stress with high gradients, increased particle residence time, and mild turbulence. Diameter is the most common metric for rupture prediction, although this metric can be unreliable. We hypothesize that understanding the flow topology and mixing inside AAA could provide useful insight into mechanisms of aneurysm growth. AAA morphology has high variability, as with AAA hemodynamics, and therefore we consider patient-specific analyses over several small to medium sized AAAs. Vortical patterns dominate AAA hemodynamics and traditional analyses based on the Eulerian fields (e.g. velocity) fail to convey the complex flow structures. The computation of finite-time Lyapunov exponent (FTLE) fields and underlying Lagrangian coherent structures (LCS) help reveal a Lagrangian template for quantifying the flow [1].

Method for Incorporating Three-Dimensional Residual Stresses Into Patient-Specific Simulations of Arteries

2013 ◽  
Author(s):  
David M. Pierce ◽  
Thomas E. Fastl ◽  
Hannah Weisbecker ◽  
Gerhard A. Holzapfel ◽  
Borja Rodriguez-Vila ◽  
...  
Keyword(s):  
Medical Imaging ◽  
Three Dimensional ◽  
Constitutive Models ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Abdominal Aortic ◽  
Model Geometry ◽  
Reconstructed Model

Through progress in medical imaging, image analysis and finite element (FE) meshing tools it is now possible to extract patient-specific geometries from medical images of, e.g., abdominal aortic aneurysms (AAAs), and thus to study clinically relevant problems via FE simulations. Medical imaging is most often performed in vivo, and hence the reconstructed model geometry in the problem of interest will represent the in vivo state, e.g., the AAA at physiological blood pressure. However, classical continuum mechanics and FE methods assume that constitutive models and the corresponding simulations start from an unloaded, stress-free reference condition.

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