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• Study of angulations of visceral abdominals arteries in their abdominal aorta emergency

  C. Vaquero, G. Vilalta, J. Vilalta, F. Nieto, M. Pérez, E. , E. Soudah, L. Lipsa, L. Río, E. Norberto, N. Cenizo, J. Brizuela, M. Martín, J. Montes

  Revista Iberoaméricana de Cirugía Vascular (2016). Vol. 4 (4), pp. 184-189 (Preprint)

  
  

  Abstract

  Recently, fenestrated, branched and stent grafts have been developed in order to treat endovascular aneurysmal pathology at the level of the aorta in the emergence of the visceral arteries. For the implantation of stents, it is necessary to have a precise planimetry of the origin and orientation of the visceral branches in order firstly to perform the correct manufacture of the endoprosthesis and secondly the placement with precision of the same. The knowledge of the emergency of the vessels of the aortic wall and its orientation knowing the angle of emergency. The data obtained for the planning of the endovascular treatment of 37 patients in order to obtain data from the descriptive point of view of this sector.

  Abstract
  Recently, fenestrated, branched and stent grafts have been developed in order to treat endovascular aneurysmal pathology at the level of the aorta in the emergence of the [...]

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• Estimation of wall shear stress using 4D flow cardiovascular MRI and computational fluid dynamics

  E. Soudah, J. Casacuberta, P. Gámez-Montero, G. Raush, R. Castilla

  Journal of Mechanics in Medicine and Biology (2016). Vol. 17 (3), pp. 1-16 (Preprint)

  
  

  Abstract

  Company In the last few years, wall shear stress (WSS) has arisen as a new diagnostic indicator in patients with arterial disease. There is a substantial evidence that the WSS plays a significant role, together with hemodynamic indicators, in initiation and progression of the vascular diseases. Estimation of WSS values, therefore, may be of clinical significance and the methods employed for its measurement are crucial for clinical community. Recently, four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has been widely used in a number of applications for visualization and quantification of blood flow, and although the sensitivity to blood flow measurement has increased, it is not yet able to provide an accurate three-dimensional (3D) WSS distribution. The aim of this work is to evaluate the aortic blood flow features and the associated WSS by the combination of 4D flow cardiovascular magnetic resonance (4D CMR) and computational fluid dynamics technique. In particular, in this work, we used the 4D CMR to obtain the spatial domain and the boundary conditions needed to estimate the WSS within the entire thoracic aorta using computational fluid dynamics. Similar WSS distributions were found for cases simulated. A sensitivity analysis was done to check the accuracy of the method. 4D CMR begins to be a reliable tool to estimate the WSS within the entire thoracic aorta using computational fluid dynamics. The combination of both techniques may provide the ideal tool to help tackle these and other problems related to wall shear estimation

  Abstract
  Company In the last few years, wall shear stress (WSS) has arisen as a new diagnostic indicator in patients with arterial disease. There is a substantial evidence that the [...]

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• Mechanical stress in abdominal aortic aneurysms using artificial neural networks

  E. Soudah, J. Rodríguez, R. López

  Journal of Mechanics in Medicine and Biology (2015). Vol. 15 (3), p. 1550029

  
  

  Abstract

  Combination of numerical modeling and artificial intelligence (AI) in bioengineering processes are a promising pathway for the further development of bioengineering sciences. The objective of this work is to use Artificial Neural Networks (ANN) to reduce the long computational times needed in the analysis of shear stress in the Abdominal Aortic Aneurysm (AAA) by finite element methods (FEM). For that purpose two different neural networks are created. The first neural network (Mesh Neural Network, MNN) creates the aneurysm geometry in terms of four geometrical factors (asymmetry factor, aneurism diameter, aneurism thickness, aneurism length). The second neural network (Tension Neural Network, TNN) combines the results of the first neural network with the arterial pressure (new factor) to obtain the maximum stress distribution (output variable) in the aneurysm wall. The use of FEM for the analysis and design of bioengineering processes often requires high computational costs, but if this technique is combined with artificial intelligence, such as neural networks, the simulation time is significantly reduced. The shear stress obtained by the artificial neural models developed in this work achieved 95% of accuracy respect to the wall stress obtained by the FEM. On the other hand, the computational time is significantly reduced compared to the FEM.

  Abstract
  Combination of numerical modeling and artificial intelligence (AI) in bioengineering processes are a promising pathway for the further development of bioengineering [...]

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• Modeling human tissues : an efficient integrated methodology

  G. Gavidia, E. Soudah, M. Cerrolaza, M. Martín

  Biomedical engineering: applications, basis and communications (2014). Vol. 26 (1), pp. 1-21

  
  

  Abstract

  Geometric models of human body organs are obtained from imaging techniques like computed tomography (CT) and magnetic resonance image (MRI) that oallow an accurate visualization of the inner body, thus providing relevant information about their its structure and pathologies. Next, these models are used to generate surface and volumetric meshes, which can be used further for visualization, measurement, biomechanical simulation, rapid prototyping and prosthesis design. However, going from geometric models to numerical models is not an easy task, being necessary to apply image-processing techniques to solve the complexity of human tissues and to get more simplified geometric models, thus reducing the complexity of the subsequent numerical analysis. In this work, an integrated and efficient methodology to obtain models of soft tissues like gray and white matter of brain and hard tissues like jaw and spine bones is proposed. The methodology is based on image-processing algorithms chosen according to some characteristics of the tissue: type, intensity profiles and boundaries quality. First, low-quality images are improved by using enhancement algorithms to reduce image noise and to increase structures contrast. Then, hybrid segmentation for tissue identification is applied through a multi-stage approach. Finally, the obtained models are resampled and exported in formats readable by computer aided design (CAD) tools. In CAD environments, this data is used to generate discrete models using finite element methed (FEM) or other numerical methods like the boundary element method (BEM). Results have shown that the proposed methodology is useful and versatile to obtain accurate geometric models that can be used in several clinical cases to obtain relevant quantitative and qualitative information.

  Abstract
  Geometric models of human body organs are obtained from imaging techniques like computed tomography (CT) and magnetic resonance image (MRI) that oallow an accurate visualization [...]

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• CFD modelling of abdominal aortic aneurysm on hemodynamic loads using a realistic geometry with CT

  E. Soudah, E. Kwee, T. Loong, M. Bordone, U. Pua, S. Narayanan

  Computational and Mathematical Methods in Medicine (2013). Vol. 2013 (472564), pp. 1-9

  
  

  Abstract

  The objective of this study is to find a correlation between the abdominal aortic aneurysm (AAA) geometric parameters, wall stress shear (WSS), abdominal flow patterns, intraluminal thrombus (ILT), and AAA arterial wall rupture using computational fluid dynamics (CFD). Real AAA 3D models were created by three-dimensional (3D) reconstruction of in vivo acquired computed tomography (CT) images from 5 patients. Based on 3D AAA models, high quality volume meshes were created using an optimal tetrahedral aspect ratio for the whole domain. In order to quantify the WSS and the recirculation inside the AAA, a 3D CFD using finite elements analysis was used. The CFD computation was performed assuming that the arterial wall is rigid and the blood is considered a homogeneous Newtonian fluid with a density of 1050¿kg/m3 and a kinematic viscosity of Pa·s. Parallelization procedures were used in order to increase the performance of the CFD calculations. A relation between AAA geometric parameters (asymmetry index (ß), saccular index (¿), deformation diameter ratio (¿), and tortuosity index (e)) and hemodynamic loads was observed, and it could be used as a potential predictor of AAA arterial wall rupture and potential ILT formation.

  Abstract
  The objective of this study is to find a correlation between the abdominal aortic aneurysm (AAA) geometric parameters, wall stress shear (WSS), abdominal flow patterns, [...]

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• Hemodynamic features associated with abdominal aortic aneurysm (AAA) geometry

  G. Vilalta, E. Soudah, J. Vilalta, F. Nieto, M. Bordone, M. Pérez, C. Vaquero

  Journal of Biomechanics (2012). Vol. 45 (S1), p.S37

  
  

  Abstract

  Recent findings have shown that maximum diameter of abdominal aortic aneurysm (AAA) and its growth rate are not entirely reliable indicators of rupture potential. The AAA geometrical shape and size may be related to the rupture risk which is a clinical manifestation of the balance between the forces generated by blood flow within the AAA and its strength. This study aims at assessing the hemodynamic features associated with the geometry of AAAs.

  Abstract
  Recent findings have shown that maximum diameter of abdominal aortic aneurysm (AAA) and its growth rate are not entirely reliable indicators of rupture potential. The [...]

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• An explicit/implicit Runge–Kutta-based PFEM model for the simulation of thermally coupled incompressible flows

  J. Marti, P. Ryzhakov

  Computational Particle Mechanics (2020). Vol. 7 (1), pp. 57-69

  
  

  Abstract

  A semi-explicit Lagrangian scheme for the simulation of thermally coupled incompressible flow problems is presented. The model relies on combining an explicit multi-step solver for the momentum equation with an implicit heat equation solver. Computational cost of the model is reduced via application of an efficient strategy adopted for the solution of momentum/continuity system by the authors in their previous work. The applicability of the method to solving thermo-mechanical problems is studied via various numerical examples.

  Abstract
  A semi-explicit Lagrangian scheme for the simulation of thermally coupled incompressible flow problems is presented. The model relies on combining an explicit multi-step solver [...]

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• Computational modeling of the fluid flow and the flexible intimal flap in type B aortic dissection via a monolithic arbitrary Lagrangian/Eulerian fluid-structure interaction model

  P. Ryzhakov, E. Soudah, N. Dialami

  International journal for numerical methods in biomedical engineering (2019). Vol. 35 (11), pp. e3239;1-e3239:21

  
  

  Abstract

  In the present work, we perform numerical simulations of the fluid flow in type B aortic dissection (AD), accounting for the flexibility of the intimal flap. The interaction of the flow with the intimal flap is modeled using a monolithic arbitrary Lagrangian/Eulerian fluid-structure interaction model. The model relies on choosing velocity as the kinematic variable in both domains (fluid and solid) facilitating the coupling. The fluid flow velocity and pressure evolution at different locations is studied and compared against the experimental evidence and the formerly published numerical simulation results. Several tear configurations are analyzed. Details of the fluid flow in the vicinity of the tears are highlighted. Influence of the tear size upon the fluid flow and the flap deformation is discussed.

  Abstract
  In the present work, we perform numerical simulations of the fluid flow in type B aortic dissection (AD), accounting for the flexibility of the intimal flap. The interaction [...]

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• An explicit–implicit finite element model for the numerical solution of incompressible Navier–Stokes equations on moving grids

  P. Ryzhakov, J. Marti

  Computer Methods in Applied Mechanics and Engineering (2019). Vol. 350, pp. 750-765

  
  

  Abstract

  In this paper an efficient mesh-moving Finite Element model for the simulation of the incompressible flow problems is proposed. The model is based on a combination of the explicit multi-step scheme (Runge–Kutta) with an implicit treatment of the pressure. The pressure is decoupled from the velocity and is solved for only once per time step minimizing the computational cost of the implicit step. Novel solution algorithm alleviating time step restrictions faced by the majority of the former Lagrangian approaches is presented. The method is examined with respect to its space and time accuracy as well as the computational cost. Two numerical examples are solved: one involving a problem on a domain with fixed boundaries and the other one dealing with a free surface flow. It is shown that the method can be easily parallelized.

  Abstract
  In this paper an efficient mesh-moving Finite Element model for the simulation of the incompressible flow problems is proposed. The model is based on a combination of the [...]

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• A semi-explicit multi-step method for solving incompressible navier-stokes equations

  P. Ryzhakov, J. Marti

  Applied Sciences (2018). Vol. 8, pp. 1-14

  
  

  Abstract

  The fractional step method is a technique that results in a computationally-efficient implementation of Navier–Stokes solvers. In the finite element-based models, it is often applied in conjunction with implicit time integration schemes. On the other hand, in the framework of finite difference and finite volume methods, the fractional step method had been successfully applied to obtain predictor-corrector semi-explicit methods. In the present work, we derive a scheme based on using the fractional step technique in conjunction with explicit multi-step time integration within the framework of Galerkin-type stabilized finite element methods. We show that under certain assumptions, a Runge–Kutta scheme equipped with the fractional step leads to an efficient semi-explicit method, where the pressure Poisson equation is solved only once per time step. Thus, the computational cost of the implicit step of the scheme is minimized. The numerical example solved validates the resulting scheme and provides the insights regarding its accuracy and computational efficiency

  Abstract
  The fractional step method is a technique that results in a computationally-efficient implementation of Navier–Stokes solvers. In the finite element-based models, it [...]

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