Use of the Photoelastic Method to Determine the Wall Stress in Realistic Abdominal Aortic Aneurysm Models

2011 ◽  
Author(s):  
Barry J. Doyle ◽  
Anthony Callanan ◽  
John Killion ◽  
Timothy M. McGloughlin
Keyword(s):  
Wall Stress ◽  
Aortic Aneurysms ◽  
Maximum Diameter ◽  
Patient Specific ◽  
Western World ◽  
Photoelastic Method ◽  
Element Analysis ◽  
Abdominal Aortic ◽  
The Us ◽  
Numerical Tools

Abdominal aortic aneurysms (AAAs) remain a significant cause of death in the Western world with over 15,000 deaths per year in the US linked to AAA rupture. Recent research [1] has questioned the use of maximum diameter as a definitive risk parameter as it is now believed that alternative factors may be important in rupture-prediction. Wall stress was shown to be a better predictor than diameter of rupture [1], with biomechanics-based rupture indices [2,3] and asymmetry also reported to have potential clinical applicability [4]. However, the majority of numerical methods used to form these alternative rupture parameters are without rigorous experimental validation, and therefore may not be as accurate as believed. Validated experiments are required in order to convince the clinical community of the worth of numerical tools such as finite element analysis (FEA) in AAA risk-prediction. Strain gauges have been used in the past to determine the strain on an AAA [5], however, the photoelastic method has also proved to be a useful tool in AAA biomechanics [6]. This paper examines the approach using three medium-sized patient-specific AAA cases at realistic pressure loadings.

Porohyperelastic Simulation of Abdominal Aortic Aneurysms

2008 ◽  
Author(s):  
Avinash Ayyalasomayajula ◽  
Bruce R. Simon ◽  
Jonathan P. Vande Geest
Keyword(s):  
Wall Stress ◽  
Aortic Aneurysms ◽  
Maximum Diameter ◽  
Patient Specific ◽  
Infrarenal Aorta ◽  
Stress Studies ◽  
Abdominal Aortic ◽  
Peak Wall Stress ◽  
Work Done

Abdominal aortic aneurysm (AAA) is a progressive dilation of the infrarenal aorta and results in a significant alteration in local hemodynamic environment [1]. While an aneurysmal diameter of 5.5cm is typically classified as being of high risk, recent studies have demonstrated that maximum wall stress could be a better indicator of an AAA rupture than maximum diameter [2]. The wall stress is greatly influenced by the blood pressure, aneurysm diameter, shape, wall thickness and the presence of thrombus. The work done by Finol et al. suggested that hemodynamic pressure variations have an insignificant effect on AAA wall stress and that primarily the shape of the aneurysm determines the stress distribution. They noted that for peak wall stress studies the static pressure conditions would suffice as the in vivo conditions. Wang et al have developed an isotropic hyperelastic constitutive model for the intraluminal thrombus (ILT). Such models have been used to study the stress distributions in patient specific AAAs [3, 4].

3D Reconstruction of Patient-Specific Abdominal Aortic Aneurysms: From CT Scan to Silicone Model

2007 ◽  
Author(s):  
Barry J. Doyle ◽  
Liam G. Morris ◽  
Anthony Callanan ◽  
Eamon Kavanagh ◽  
Pat Kelly ◽  
...  
Keyword(s):  
Clinical Importance ◽  
Aortic Aneurysms ◽  
Maximum Diameter ◽  
Patient Specific ◽  
Abdominal Aortic ◽  
The Us ◽  
Normal Diameter ◽  
The Uk ◽  
Silicone Model ◽  
Small Aneurysms

Abdominal aortic aneurysm (AAA) is a local, permanent, irreversible dilation of the infrarenal section of the aorta that risks rupture until treated. AAA is defined as an infrarenal diameter 1.5 times the normal diameter. Currently, surgeons intervene when the aneurysm reaches a maximum diameter of 50mm [1]. 200,000 new cases are diagnosed each year in the US, with 500,000 new cases diagnosed worldwide [2]. This results in 15,000 deaths each year from AAA rupture in the US alone [3], with 8,000 deaths per year in the UK [4]. Literature supports the theory that small aneurysms may be as likely to rupture as larger aneurysms [5–7], and therefore, the need for a more reliable predictor of AAA rupture may have clinical importance.

Fluid-Solid Interaction Simulation of Flow and Stress Pattern in Thoracoabdominal Aneurysms: A Patient Specific Study

2006 ◽  
Author(s):  
Alessandro Borghi ◽  
Nigel B. Wood ◽  
Raad H. Mohiaddin ◽  
X. Yun Xu
Keyword(s):  
Wall Stress ◽  
Aortic Aneurysms ◽  
Maximum Diameter ◽  
Patient Specific ◽  
Specific Flow ◽  
Hyperelastic Materials ◽  
Abdominal Aortic ◽  
Magnetic Resonance Imaging Mri ◽  
Fluid Solid Interaction

Thoracoabdominal aneurysm (TA) is a pathology that involves the enlargement of the aortic diameter in the inferior descending thoracic aorta and has risk factors including aortic dissection, aortitis or connective tissue disorders (Webb, T. H. and Williams, G. M. 1999). Abnormal flow patterns and stress on the diseased aortic wall are thought to play an important role in the development of this pathology and the internal wall stress has proved to be more reliable as a predictor of rupture than the maximum diameter for abdominal aortic aneurysms (Fillinger, M. F., et al. 2003). In the present study, two patients with TAs of different maximum diameters were scanned using magnetic resonance imaging (MRI) techniques. Realistic models of the aneurysms were reconstructed from the in vivo MRI data acquired from the patients, and subject-specific flow conditions were applied as boundary conditions. The wall and thrombus were modeled as hyperelastic materials and their properties were derived from the literature. Fully coupled fluid-solid interaction simulations were performed for both cases using ADINA 8.2. Results were obtained for both the flow and wall stress patterns within the aneurysms. The results show that the wall stress distribution and its magnitude are strongly dependent on the 3-D shape of the aneurysm and the distribution of thrombus.

The Relationship Between Wall Stress and 3D Asymmetry in Repaired and Ruptured Abdominal Aortic Aneurysms

2010 ◽  
Author(s):  
Barry J. Doyle ◽  
Tim M. McGloughlin
Keyword(s):  
Risk Factors ◽  
Wall Stress ◽  
Posterior Wall ◽  
Aortic Aneurysms ◽  
Three Dimensions ◽  
Maximum Diameter ◽  
Patient Specific ◽  
Infrarenal Aorta ◽  
Abdominal Aortic ◽  
The Relationship

Abdominal aortic aneurysm (AAA) is a permanent dilation of the infrarenal aorta and is defined as having a diameter 50% greater than the original diameter. If left untreated, an AAA will continue to expand until rupture. The maximum diameter is currently the primary indicator of rupture-risk with AAAs > 5.5 cm deemed a likely to rupture. There have, however, been many reports identifying the inadequacies of the maximum diameter criterion to accurately determine the threat of rupture. It is believed by many researchers that there is a need to review the decision of surgical intervention based solely on aneurysm diameter, and rather include other relevant risk factors. These additional risk factors could, for example, include, AAA wall stress, AAA expansion rate, degree of asymmetry, presence of intraluminal thrombus (ILT), and hypertension. The addition of these parameters may aid the surgical decision-making process. A previous report by our group identified the relationship between asymmetry and posterior wall stress in patient-specific cases [1,2] and as over 80% of ruptures occur on the posterior wall [3] this finding may have significant clinical relevance. In this previous report, the study group was limited to 15 cases and asymmetry was only measured in the anterior-posterior plane. This current paper furthers this previous work by increasing the cohort to 40 cases of electively repaired AAAs and also examines 8 cases of ruptured AAAs. The methodology has been improved to now measure asymmetry in all three dimensions (3D).

On the Uptake of Ultrasmall Superparamagnetic Particles of Iron Oxide and Biomechanical Wall Stress in Abdominal Aortic Aneurysms

2012 ◽  
Author(s):  
Barry Doyle ◽  
Jennifer Richards ◽  
Scott Semple ◽  
Tom MacGillivray ◽  
Calum Gray ◽  
...  
Keyword(s):  
Wall Stress ◽  
Inflammatory Cells ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Western World ◽  
Important Work ◽  
General Belief ◽  
Abdominal Aortic ◽  
The Us ◽  
Improved Methods

Abdominal aortic aneurysms (AAAs) remain a significant cause of death in the Western world with over 15,000 deaths per year in the US linked to AAA rupture. There is a general belief among the clinical and engineering community that improved methods of risk prediction are needed. The growth and expansion of AAAs over time is thought to be associated with the mechanobiological interactions within the diseased AAA wall. The stresses and strains induced in the wall by the internal blood pressure trigger increased protease activity and turnover of the extracellular matrix (ECM), thus enabling degradation and expansion of the wall. Inflammatory cells also control collagen synthesis and inflammation can reduce the tensile strength of the wall, thus contributing to the likelihood of rupture. Recently, important work by Richards et al. [1] showed that AAAs with specific sites of focal inflammation have threefold higher growth rates than AAAs with non-specific inflammation.

Discrimination of Vessel Wall Components of Abdominal Aortic Aneurysms by Multi-Contrast MRI

2008 ◽  
Author(s):  
Evelyne van Dam ◽  
Marcel Rutten ◽  
Frans van de Vosse
Keyword(s):  
Vessel Wall ◽  
Computational Models ◽  
Wall Stress ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Western World ◽  
Atherosclerotic Plaques ◽  
Abdominal Aortic ◽  
Wall Components

Rupture of an abdominal aortic aneurysm (AAA) is a major cause of death in the Western world. When the AAA is diagnosed timely, rupture can be prevented by conventional surgical or by endovascular repair. To date, the decision to operate is based on geometry alone, but it has already been suggested that wall stress would be a better predictor [2]. Patient specific computational models have been developed to calculate wall stress [2; 5; 9; 8; 10]. In these models, the AAA wall is assumed to be homogeneous. Patient-specific inhomogeneities such as atherosclerotic plaques and calcifications have large effects on the maximum wall stress and wall stress distribution [6; 7]. Histological examination is not feasible for determining wall composition of patients.

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 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.

scholarly journals The Effect of Pentagalloyl Glucose on the Wall Mechanics and Inflammatory Activity of Rat Abdominal Aortic Aneurysms

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Mirunalini Thirugnanasambandam ◽  
Dan T. Simionescu ◽  
Patricia G. Escobar ◽  
Eugene Sprague ◽  
Beth Goins ◽  
...  
Keyword(s):  
Biological Markers ◽  
Wall Stress ◽  
Treated Group ◽  
Untreated Group ◽  
Aortic Aneurysms ◽  
Inflammatory Activity ◽  
Element Analysis ◽  
Abdominal Aortic ◽  
Pentagalloyl Glucose ◽  
And Biological Markers

An abdominal aortic aneurysm (AAA) is a permanent localized expansion of the abdominal aorta with mortality rate of up to 90% after rupture. AAA growth is a process of vascular degeneration accompanied by a reduction in wall strength and an increase in inflammatory activity. It is unclear whether this process can be intervened to attenuate AAA growth, and hence, it is of great clinical interest to develop a technique that can stabilize the AAA. The objective of this work is to develop a protocol for future studies to evaluate the effects of drug-based therapies on the mechanics and inflammation in rodent models of AAA. The scope of the study is limited to the use of pentagalloyl glucose (PGG) for aneurysm treatment in the calcium chloride rat AAA model. Peak wall stress (PWS) and matrix metalloproteinase (MMP) activity, which are the biomechanical and biological markers of AAA growth and rupture, were evaluated over 4 weeks in untreated and treated (with PGG) groups. The AAA specimens were mechanically characterized by planar biaxial tensile testing and the data fitted to a five-parameter nonlinear, hyperelastic, anisotropic Holzapfel–Gasser–Ogden (HGO) material model, which was used to perform finite element analysis (FEA) to evaluate PWS. Our results demonstrated that there was a reduction in PWS between pre- and post-AAA induction FEA models in the treatment group compared to the untreated group using either animal-specific or average material properties. However, this reduction was not statistically significant. Conversely, there was a statistically significant reduction in MMP-activated fluorescent signal between pre- and post-AAA induction models in the treated group compared to the untreated group. Therefore, the primary contribution of this work is the quantification of the stabilizing effects of PGG using biomechanical and biological markers of AAA, thus indicating that PGG could be part of a new clinical treatment strategy that will require further investigation.

Abdominal Aortic Aneurysm Growth: The Association of Aortic Wall Mechanics and Geometry

2011 ◽  
Author(s):  
Christopher B. Washington ◽  
Judy Shum ◽  
Satish C. Muluk ◽  
Ender A. Finol
Keyword(s):  
Wall Stress ◽  
Abdominal Ultrasound ◽  
Aneurysm Rupture ◽  
Computational Method ◽  
Maximum Diameter ◽  
Patient Specific ◽  
Element Analysis ◽  
Wall Strength ◽  
Aneurysm Growth ◽  
Peak Wall Stress

In an effort to prevent rupture, patients with known AAA undergo periodic abdominal ultrasound or CT scan surveillance. When the aneurysm grows to a diameter of 5.0–5.5 cm or is shown to expand at a rate greater than 1 cm/yr, elective operative repair is undertaken. While this strategy certainly prevents a number of potentially catastrophic ruptures, AAA rupture can occur at sizes less than 5 cm. From a biomechanical standpoint, aneurysm rupture occurs when wall stress exceeds wall strength. By using non-invasive techniques, such as finite element analysis (FEA), wall stress can be estimated for patient specific AAA models, which can perhaps more carefully predict the rupture potential of a given aneurysm, regardless of size. FEA is a computational method that can be used to evaluate complicated structures such as aneurysms. To this end, it was reported earlier that AAA peak wall stress provides a better assessment of rupture risk than the commonly used maximum diameter criterion [1]. What has yet to be examined, however, is the relationship between wall stress and AAA geometry during aneurysm growth. Such finding has the potential for providing individualized predictions of AAA rupture potential during patient surveillance. The purpose of this study is to estimate peak wall stress for an AAA under surveillance and evaluate its potential correlation with geometric features characteristic of the aneurysm’s morphology.

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