MRI-Based Inflow Boundary Conditions for Patient Specific Fluid Structure Interaction Modeling of Abdominal Aortic Aneurysms

2012 ◽  
Author(s):  
Santanu Chandra ◽  
Samarth Raut ◽  
Anirban Jana ◽  
Robert W. Biederman ◽  
Mark Doyle ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Wall Thickness ◽  
Wall Stress ◽  
Patient Specific ◽  
Structure Interaction ◽  
Outflow Boundary Conditions ◽  
Abdominal Aortic ◽  
Outflow Boundary ◽  
Fully Coupled

Rupture of abdominal aortic aneurysm (AAA) is the 10th leading cause of death for men over age of 50 in US. The decision for surgical intervention is currently based on aneurysm diameter or its expansion rate. However, the use of these criteria for all patients is debatable. For example, small aneurysms do rupture or become symptomatic before reaching the critical diameter. Computationally predicted mechanical wall stress is considered a viable alternative criterion for rupture risk assessment. Hence, it is important to evaluate the effect of different modeling approaches on the accuracy of the predicated AAA wall stress. For computational solid stress (CSS) analysis or finite element analysis (FEA), a uniform static or transient intraluminal pressure is generally applied on the wall-lumen surface whereas in fluid-structure interaction (FSI) modeling the wall-lumen surface experiences transient and non-uniform fluid stress. An earlier comparison on idealized AAA models [1] revealed that static and transient CSS underestimate the peak wall stress (PWS) by an average 20–30% for variable wall thickness and 10% for uniform wall thickness when compared to fully coupled FSI. However, FSI-predicted stresses and strains were observed to be sensitive to inflow and outflow boundary conditions, warranting further study on a more accurate approach for FSI modeling. Though significant work has been performed on modeling outflow boundary conditions [2], studies on the sensitivity of computed stress or strain to the type of FSI inflow boundary condition is scarce [2–4]. We hypothesize that a FSI framework with a patient specific velocity boundary condition derived from magnetic resonance imaging (MRI) data applied to patient specific AAA geometry would provide better accuracy of PWS calculations compared to a FEA model. In this work, we present a framework where the AAA geometry is reconstructed from computed tomography (CT) images, on which FSI simulations were performed with inlet velocity components extracted from patient MR images of the abdominal aorta. Fully coupled FSI simulations were performed and results were compared with CSS simulations with uniform transient pressure boundary conditions.

Tuning a Multiscale Model of Abdominal Aortic Hemodynamics to Incorporate Patient-Specific Features of Flow and Pressure Waveforms

2009 ◽  
Author(s):  
Ryan L. Spilker ◽  
Charles A. Taylor
Keyword(s):  
Boundary Conditions ◽  
Computational Models ◽  
Multiscale Model ◽  
Patient Specific ◽  
Vascular Walls ◽  
Outflow Boundary Conditions ◽  
Abdominal Aortic ◽  
Cardiovascular Models ◽  
Outflow Boundary ◽  
Aortic Hemodynamics

Computational models enable the calculation of quantities that are impractical or impossible to measure and the prediction of physiological changes due to interventions. In order to be useful, cardiovascular models must be both rooted in physical principles and designed such that measured or otherwise desired features of the cardiovascular system are reproduced. The former requirement has motivated the development of image-based anatomic models, patient-specific inflow boundary conditions, deformable vascular walls, outflow boundary conditions that represent the influence of the downstream circulation, and multiscale models. The development of approaches to address the latter requirement, reproducing desired features of the circulation, is a critical area of modeling research that has received comparatively little attention.

Fully Coupled vs. Partially Coupled Fluid-Structure Interaction Methods for Patient-Specific Abdominal Aortic Aneurysm Biomechanics

2007 ◽  
Author(s):  
Christine M. Scotti ◽  
Ender A. Finol
Keyword(s):  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Fluid Structure Interaction ◽  
Wall Stress ◽  
Patient Specific ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Abdominal Aortic ◽  
Mechanical Factors ◽  
Fully Coupled

Primary among the mechanical factors linked with abdominal aortic aneurysm (AAA) rupture is peak wall stress, frequently quantified as either the maximum principal or Von Mises stress exerted along the diseased arterial wall. Intraluminal pressure, as an impinging normal force on the wall, has been hypothesized as the dominant influence on this stress and thus the majority of numerical modeling studies of AAA mechanics have focused on static computational solid stress (CSS) predictions [1,2]. Unfortunately, retrospective studies comparing the magnitude of wall stress with the failure strength of the aneurysmal wall have yet to consistently predict the outcome for patient-specific AAAs [3,4]. Previous studies have shown that hemodynamics also plays a significant role in both the biological and mechanical factors that exist within AAAs. In the present investigation, partially and fully coupled fluid-structure interaction (p-FSI and f-FSI, respectively) computations of patient-specific AAA models are presented and compared to identify the effect of fluid flow in the biomechanical environment of these aneurysms.

scholarly journals Fluid-Structure Interaction Modeling of Abdominal Aortic Aneurysms: The Impact of Patient-Specific Inflow Conditions and Fluid/Solid Coupling

2013 ◽  
Vol 135 (8) ◽  
Author(s):  
Santanu Chandra ◽  
Samarth S. Raut ◽  
Anirban Jana ◽  
Robert W. Biederman ◽  
Mark Doyle ◽  
...  
Keyword(s):  
Velocity Profile ◽  
Boundary Conditions ◽  
Fluid Structure Interaction ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Fluid Structure ◽  
Inlet Velocity ◽  
Structure Interaction ◽  
Biomechanical Assessment ◽  
Fully Coupled

Rupture risk assessment of abdominal aortic aneurysms (AAA) by means of biomechanical analysis is a viable alternative to the traditional clinical practice of using a critical diameter for recommending elective repair. However, an accurate prediction of biomechanical parameters, such as mechanical stress, strain, and shear stress, is possible if the AAA models and boundary conditions are truly patient specific. In this work, we present a complete fluid-structure interaction (FSI) framework for patient-specific AAA passive mechanics assessment that utilizes individualized inflow and outflow boundary conditions. The purpose of the study is two-fold: (1) to develop a novel semiautomated methodology that derives velocity components from phase-contrast magnetic resonance images (PC-MRI) in the infrarenal aorta and successfully apply it as an inflow boundary condition for a patient-specific fully coupled FSI analysis and (2) to apply a one-way–coupled FSI analysis and test its efficiency compared to transient computational solid stress and fully coupled FSI analyses for the estimation of AAA biomechanical parameters. For a fully coupled FSI simulation, our results indicate that an inlet velocity profile modeled with three patient-specific velocity components and a velocity profile modeled with only the axial velocity component yield nearly identical maximum principal stress (σ1), maximum principal strain (ε1), and wall shear stress (WSS) distributions. An inlet Womersley velocity profile leads to a 5% difference in peak σ1, 3% in peak ε1, and 14% in peak WSS compared to the three-component inlet velocity profile in the fully coupled FSI analysis. The peak wall stress and strain were found to be in phase with the systolic inlet flow rate, therefore indicating the necessity to capture the patient-specific hemodynamics by means of FSI modeling. The proposed one-way–coupled FSI approach showed potential for reasonably accurate biomechanical assessment with less computational effort, leading to differences in peak σ1, ε1, and WSS of 14%, 4%, and 18%, respectively, compared to the axial component inlet velocity profile in the fully coupled FSI analysis. The transient computational solid stress approach yielded significantly higher differences in these parameters and is not recommended for accurate assessment of AAA wall passive mechanics. This work demonstrates the influence of the flow dynamics resulting from patient-specific inflow boundary conditions on AAA biomechanical assessment and describes methods to evaluate it through fully coupled and one-way–coupled fluid-structure interaction analysis.

A Comparative Study of Biomechanical and Geometrical Attributes of Abdominal Aortic Aneurysms in the Asian and Caucasian Populations

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Tejas Canchi ◽  
Sourav S. Patnaik ◽  
Hong N. Nguyen ◽  
E. Y. K. Ng ◽  
Sriram Narayanan ◽  
...  
Keyword(s):  
Wall Thickness ◽  
Gaussian Curvature ◽  
Wall Stress ◽  
Aneurysm Rupture ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Backward Elimination ◽  
Abdominal Aortic ◽  
Highly Correlated ◽  
Peak Wall Stress

Abstract In this work, we provide a quantitative assessment of the biomechanical and geometric features that characterize abdominal aortic aneurysm (AAA) models generated from 19 Asian and 19 Caucasian diameter-matched AAA patients. 3D patient-specific finite element models were generated and used to compute peak wall stress (PWS), 99th percentile wall stress (99th WS), and spatially averaged wall stress (AWS) for each AAA. In addition, 51 global geometric indices were calculated, which quantify the wall thickness, shape, and curvature of each AAA. The indices were correlated with 99th WS (the only biomechanical metric that exhibited significant association with geometric indices) using Spearman's correlation and subsequently with multivariate linear regression using backward elimination. For the Asian AAA group, 99th WS was highly correlated (R2 = 0.77) with three geometric indices, namely tortuosity, intraluminal thrombus volume, and area-averaged Gaussian curvature. Similarly, 99th WS in the Caucasian AAA group was highly correlated (R2 = 0.87) with six geometric indices, namely maximum AAA diameter, distal neck diameter, diameter–height ratio, minimum wall thickness variance, mode of the wall thickness variance, and area-averaged Gaussian curvature. Significant differences were found between the two groups for ten geometric indices; however, no differences were found for any of their respective biomechanical attributes. Assuming maximum AAA diameter as the most predictive metric for wall stress was found to be imprecise: 24% and 28% accuracy for the Asian and Caucasian groups, respectively. This investigation reveals that geometric indices other than maximum AAA diameter can serve as predictors of wall stress, and potentially for assessment of aneurysm rupture risk, in the Asian and Caucasian AAA populations.

scholarly journals The impact of scaled boundary conditions on wall shear stress computations in atherosclerotic human coronary bifurcations

2016 ◽  
Vol 310 (10) ◽  
pp. H1304-H1312 ◽  
Author(s):  
Jelle T. C. Schrauwen ◽  
Janina C. V. Schwarz ◽  
Jolanda J. Wentzel ◽  
Antonius F. W. van der Steen ◽  
Maria Siebes ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Boundary Conditions ◽  
Scaling Laws ◽  
Coronary Intervention ◽  
Patient Specific ◽  
Outflow Boundary Conditions ◽  
Wall Shear ◽  
Outflow Boundary ◽  
The Impact

The aim of this study was to determine if reliable patient-specific wall shear stress (WSS) can be computed when diameter-based scaling laws are used to impose the boundary conditions for computational fluid dynamics. This study focused on mildly diseased human coronary bifurcations since they are predilection sites for atherosclerosis. Eight patients scheduled for percutaneous coronary intervention were imaged with angiography. The velocity proximal and distal of a bifurcation was acquired with intravascular Doppler measurements. These measurements were used for inflow and outflow boundary conditions for the first set of WSS computations. For the second set of computations, absolute inflow and outflow ratios were derived from geometry-based scaling laws based on angiography data. Normalized WSS maps per segment were obtained by dividing the absolute WSS by the mean WSS value. Absolute and normalized WSS maps from the measured-approach and the scaled-approach were compared. A reasonable agreement was found between the measured and scaled inflows, with a median difference of 0.08 ml/s [−0.01; 0.20]. The measured and the scaled outflow ratios showed a good agreement: 1.5 percentage points [−19.0; 4.5]. Absolute WSS maps were sensitive to the inflow and outflow variations, and relatively large differences between the two approaches were observed. For normalized WSS maps, the results for the two approaches were equivalent. This study showed that normalized WSS can be obtained from angiography data alone by applying diameter-based scaling laws to define the boundary conditions. Caution should be taken when absolute WSS is assessed from computations using scaled boundary conditions.

scholarly journals Structured Tree Impedance Outflow Boundary Conditions for 3D Lung Simulations

2010 ◽  
Vol 132 (8) ◽  
Author(s):  
Andrew Comerford ◽  
Christiane Förster ◽  
Wolfgang A. Wall
Keyword(s):  
Boundary Conditions ◽  
Flow Distribution ◽  
Left Lobe ◽  
Patient Specific ◽  
Outflow Boundary Conditions ◽  
Human Lungs ◽  
Clinical Scenarios ◽  
Mean Pressure ◽  
Acceleration And Deceleration ◽  
Outflow Boundary

In this paper, we develop structured tree outflow boundary conditions for modeling the airflow in patient specific human lungs. The utilized structured tree is used to represent the nonimageable vessels beyond the 3D domain. The coupling of the two different scales (1D and 3D) employs a Dirichlet–Neumann approach. The simulations are performed under a variety of conditions such as light breathing and constant flow ventilation (which is characterized by very rapid acceleration and deceleration). All results show that the peripheral vessels significantly impact the pressure, however, the flow is relatively unaffected, reinforcing the fact that the majority of the lung impedance is due to the lower generations rather than the peripheral vessels. Furthermore, simulations of a hypothetical diseased lung (restricted flow in the superior left lobe) under mechanical ventilation show that the mean pressure at the outlets of the 3D domain is about 28% higher. This hypothetical model illustrates potential causes of volutrauma in the human lung and furthermore demonstrates how different clinical scenarios can be studied without the need to assume the unknown flow distribution into the downstream region.

Fluid-structure interaction in abdominal aortic aneurysms: Structural and geometrical considerations

2015 ◽  
Vol 26 (04) ◽  
pp. 1550038 ◽  
Author(s):  
Yaser Mesri ◽  
Hamid Niazmand ◽  
Amin Deyranlou ◽  
Mahmood Reza Sadeghi
Keyword(s):  
Wall Thickness ◽  
Arterial Wall ◽  
Fluid Structure Interaction ◽  
Wall Stress ◽  
Aortic Aneurysms ◽  
Material Behavior ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Abdominal Aortic ◽  
Iliac Bifurcation

Rupture of the abdominal aortic aneurysm (AAA) is the result of the relatively complex interaction of blood hemodynamics and material behavior of arterial walls. In the present study, the cumulative effects of physiological parameters such as the directional growth, arterial wall properties (isotropy and anisotropy), iliac bifurcation and arterial wall thickness on prediction of wall stress in fully coupled fluid-structure interaction (FSI) analysis of five idealized AAA models have been investigated. In particular, the numerical model considers the heterogeneity of arterial wall and the iliac bifurcation, which allows the study of the geometric asymmetry due to the growth of the aneurysm into different directions. Results demonstrate that the blood pulsatile nature is responsible for emerging a time-dependent recirculation zone inside the aneurysm, which directly affects the stress distribution in aneurismal wall. Therefore, aneurysm deviation from the arterial axis, especially, in the lateral direction increases the wall stress in a relatively nonlinear fashion. Among the models analyzed in this investigation, the anisotropic material model that considers the wall thickness variations, greatly affects the wall stress values, while the stress distributions are less affected as compared to the uniform wall thickness models. In this regard, it is confirmed that wall stress predictions are more influenced by the appropriate structural model than the geometrical considerations such as the level of asymmetry and its curvature, growth direction and its extent.

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