CFD and PTV Steady Flow Investigation in an Anatomically Accurate Abdominal Aortic Aneurysm

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Evangelos Boutsianis ◽  
Michele Guala ◽  
Ufuk Olgac ◽  
Simon Wildermuth ◽  
Klaus Hoyer ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Three Dimensional ◽  
Numerical Data ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Velocity Measurements ◽  
Cfd Simulations ◽  
Aneurysm Neck ◽  
Hexahedral Elements ◽  
Abdominal Aortic

There is considerable interest in computational and experimental flow investigations within abdominal aortic aneurysms (AAAs). This task stipulates advanced grid generation techniques and cross-validation because of the anatomical complexity. The purpose of this study is to examine the feasibility of velocity measurements by particle tracking velocimetry (PTV) in realistic AAA models. Computed tomography and rapid prototyping were combined to digitize and construct a silicone replica of a patient-specific AAA. Three-dimensional velocity measurements were acquired using PTV under steady averaged resting boundary conditions. Computational fluid dynamics (CFD) simulations were subsequently carried out with identical boundary conditions. The computational grid was created by splitting the luminal volume into manifold and nonmanifold subsections. They were filled with tetrahedral and hexahedral elements, respectively. Grid independency was tested on three successively refined meshes. Velocity differences of about 1% in all three directions existed mainly within the AAA sack. Pressure revealed similar variations, with the sparser mesh predicting larger values. PTV velocity measurements were taken along the abdominal aorta and showed good agreement with the numerical data. The results within the aneurysm neck and sack showed average velocity variations of about 5% of the mean inlet velocity. The corresponding average differences increased for all velocity components downstream the iliac bifurcation to as much as 15%. The two domains differed slightly due to flow-induced forces acting on the silicone model. Velocity quantification through narrow branches was problematic due to decreased signal to noise ratio at the larger local velocities. Computational wall pressure and shear fields are also presented. The agreement between CFD simulations and the PTV experimental data was confirmed by three-dimensional velocity comparisons at several locations within the investigated AAA anatomy indicating the feasibility of this approach.

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.

Anatomically Accurate Haemodynamic Simulations of Abdominal Aortic Aneurysms

2003 ◽  
Author(s):  
Evangelos Boutsianis ◽  
Thomas Frauenfelder ◽  
Simon Wildermuth ◽  
Dimos Poulikakos ◽  
Yiannis Ventikos
Keyword(s):  
Interventional Procedure ◽  
Imaging Techniques ◽  
Objective Assessment ◽  
Three Dimensional ◽  
Quantitative Information ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Significant Information ◽  
Comprehensive Collection ◽  
Abdominal Aortic

The pulsatile blood flow field in a patient-specific pathology of a large Abdominal Aortic Aneurysm (AAA) is being simulated, both pre and post interventionally. The anatomies of the aortic wall and blood lumen have been derived by digitized Computerized Tomography (CT) scans. Three dimensional unsteady computational fluid dynamics simulations have provided a comprehensive collection of quantitative information on the haemodynamics and the flow features that present themselves in both the temporal and spatial spaces. The focus lies on alterations in the haemodynamics triggered by the interventional procedure itself, which consists of the endoluminal introduction of a stent-graft. Significant information may also be deduced concerning the hydrodynamic loading of such implants. Computational tools of this nature, along with the non-invasive CT or Magnetic Resonance (MR) aortic imaging techniques, could enable an objective assessment of the possible effects of any interventional scenario in a virtual noninvasive environment both proximally and distally to the diseased region.

Three-Dimensional Geometrical Characterization of Abdominal Aortic Aneurysms: Image-Based Wall Thickness Distribution

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Giampaolo Martufi ◽  
Elena S. Di Martino ◽  
Cristina H. Amon ◽  
Satish C. Muluk ◽  
Ender A. Finol
Keyword(s):  
Wall Thickness ◽  
Three Dimensional ◽  
Aortic Aneurysms ◽  
Maximum Diameter ◽  
Patient Specific ◽  
Future Research ◽  
Geometrical Shape ◽  
Rupture Risk ◽  
Abdominal Aortic ◽  
Elective Repair

The clinical assessment of abdominal aortic aneurysm (AAA) rupture risk is based on the quantification of AAA size by measuring its maximum diameter from computed tomography (CT) images and estimating the expansion rate of the aneurysm sac over time. Recent findings have shown that geometrical shape and size, as well as local wall thickness may be related to this risk; thus, reliable noninvasive image-based methods to evaluate AAA geometry have a potential to become valuable clinical tools. Utilizing existing CT data, the three-dimensional geometry of nine unruptured human AAAs was reconstructed and characterized quantitatively. We propose and evaluate a series of 1D size, 2D shape, 3D size, 3D shape, and second-order curvature-based indices to quantify AAA geometry, as well as the geometry of a size-matched idealized fusiform aneurysm and a patient-specific normal abdominal aorta used as controls. The wall thickness estimation algorithm, validated in our previous work, is tested against discrete point measurements taken from a cadaver tissue model, yielding an average relative difference in AAA wall thickness of 7.8%. It is unlikely that any one of the proposed geometrical indices alone would be a reliable index of rupture risk or a threshold for elective repair. Rather, the complete geometry and a positive correlation of a set of indices should be considered to assess the potential for rupture. With this quantitative parameter assessment, future research can be directed toward statistical analyses correlating the numerical values of these parameters with the risk of aneurysm rupture or intervention (surgical or endovascular). While this work does not provide direct insight into the possible clinical use of the geometric parameters, we believe it provides the foundation necessary for future efforts in that direction.

Development of an Abdominal Aortic Aneurysm Ruptures Mechanism Using a Geometric Analytical Technique

2014 ◽  
Author(s):  
A. H. Embong ◽  
A. M. Al-Jumaily ◽  
G. Mahadevan ◽  
A. Lowe ◽  
S. Sugita
Keyword(s):  
Imaging Techniques ◽  
Three Dimensional ◽  
Aneurysm Rupture ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Analytical Technique ◽  
Abdominal Aortic ◽  
Risk Of Rupture ◽  
Wall Deformation ◽  
Rupture Mechanism

Current ultrasound approaches practice probe for diagnosing instantaneous abdominal aortic aneurysms (AAA) based on arterial tissue deformation. However, tracking the progression of potential aneurysms, and predicting the risk of rupture is based on the diameter of the aneurysm and is still an insufficient method: Larger diameter aneurysms do not always lead to ruptures, and smaller diameter aneurysms unexpectedly rupture. In order to improve diagnostic accuracy of ultrasound imaging techniques, this paper presents geometric analyses of patient-specific instant deformations as a means to develop an aneurysm rupture mechanism. Segmented AAA images were used to analyze dependent elements that contribute to a three-dimensional (3-D) aneurysm reconstructive model using proposed Patient-Specific Aneurysm Rupture Predictor (P-SARP) method. The outcomes indicate that the proposed technique has the ability to associate the distortion of wall deformation with geometric analyses. This method can positively be integrated with established ultrasound techniques for improvements in the accuracy of future diagnoses of potential AAA ruptures.

Cyclic Breathing Simulations in Large Scale Models of the Lung Airway From the Oronasal Opening to the Terminal Bronchioles

2012 ◽  
Author(s):  
D. Keith Walters ◽  
Greg W. Burgreen ◽  
Robert L. Hester ◽  
David S. Thompson ◽  
David M. Lavallee ◽  
...  
Keyword(s):  
Steady State ◽  
Boundary Conditions ◽  
Large Scale ◽  
Whole Body ◽  
Patient Specific ◽  
Cfd Simulations ◽  
Reduced Order ◽  
Scale Models ◽  
Steady State Simulation ◽  
Conducting Zone

Computational fluid dynamics (CFD) simulations were performed for unsteady periodic breathing conditions, using large-scale models of the human lung airway. The computational domain included fully coupled representations of the orotracheal region and large conducting zone up to generation four (G4) obtained from patient-specific CT data, and the small conducting zone (to G16) obtained from a stochastically generated airway tree with statistically realistic geometrical characteristics. A reduced-order geometry was used, in which several airway branches in each generation were truncated, and only select flow paths were retained to G16. The inlet and outlet flow boundaries corresponded to the oronasal opening (superior), the inlet/outlet planes in terminal bronchioles (distal), and the unresolved airway boundaries arising from the truncation procedure (intermediate). The cyclic flow was specified according to the predicted ventilation patterns for a healthy adult male at three different activity levels, supplied by the whole-body modeling software HumMod. The CFD simulations were performed using Ansys FLUENT. The mass flow distribution at the distal boundaries was prescribed using a previously documented methodology, in which the percentage of the total flow for each boundary was first determined from a steady-state simulation with an applied flow rate equal to the average during the inhalation phase of the breathing cycle. The distal pressure boundary conditions for the steady-state simulation were set using a stochastic coupling procedure to ensure physiologically realistic flow conditions. The results show that: 1) physiologically realistic flow is obtained in the model, in terms of cyclic mass conservation and approximately uniform pressure distribution in the distal airways; 2) the predicted alveolar pressure is in good agreement with previously documented values; and 3) the use of reduced-order geometry modeling allows accurate and efficient simulation of large-scale breathing lung flow, provided care is taken to use a physiologically realistic geometry and to properly address the unsteady boundary conditions.

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.

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].

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