Computational methods in cardiovascular mechanics

The introduction of computational models in cardiovascular sciences has been progressively bringing new and unique tools for the investigation of the physiopathology. Together with the dramatic improvement of imaging and measuring devices on one side, and of computational architectures on the other one, mathematical and numerical models have provided a new, clearly noninvasive, approach for understanding not only basic mechanisms but also patient-specific conditions, and for supporting the design and the development of new therapeutic options. The terminology in silico is, nowadays, commonly accepted for indicating this new source of knowledge added to traditional in vitro and in vivo investigations. The advantages of in silico methodologies are basically the low cost in terms of infrastructures and facilities, the reduced invasiveness and, in general, the intrinsic predictive capabilities based on the use of mathematical models. The disadvantages are generally identified in the distance between the real cases and their virtual counterpart required by the conceptual modeling that can be detrimental for the reliability of numerical simulations.Comment: 54 pages, Book Chapte

In Vitro and Computational Analyses of Blood Flow at Aortoiliac Bifurcation for Patients with Atherosclerotic Plaque Treated with Endovascular Procedures

This research has developed an appropriate approach allowing for more accurate assessment of haemodynamic changes following implantation of endovascular stent graft to treat patients with occlusive aortoiliac disease. Two different endovascular techniques involving the use of different types of stent grafts were analysed and compared with regard to haemodynamics associated with these techniques. Results improved understanding of the flow characteristics of these endovascular techniques

The LifeV library: engineering mathematics beyond the proof of concept

LifeV is a library for the finite element (FE) solution of partial differential equations in one, two, and three dimensions. It is written in C++ and designed to run on diverse parallel architectures, including cloud and high performance computing facilities. In spite of its academic research nature, meaning a library for the development and testing of new methods, one distinguishing feature of LifeV is its use on real world problems and it is intended to provide a tool for many engineering applications. It has been actually used in computational hemodynamics, including cardiac mechanics and fluid-structure interaction problems, in porous media, ice sheets dynamics for both forward and inverse problems. In this paper we give a short overview of the features of LifeV and its coding paradigms on simple problems. The main focus is on the parallel environment which is mainly driven by domain decomposition methods and based on external libraries such as MPI, the Trilinos project, HDF5 and ParMetis. Dedicated to the memory of Fausto Saleri.Comment: Review of the LifeV Finite Element librar

A (Near) Real-Time Simulation Method of Aneurysm Coil Embolization

International audienceA (Near) Real-Time Simulation Method of Aneurysm Coil Embolizatio

Interactive Blood-Coil Simulation in Real-time during Aneurysm Embolization

International audienceOver the last decade, remarkable progress has been made in the field of endovascular treatment of aneurysms. Technological advances continue to make it possible for a growing number of patients with cerebral aneurysms to be treated with a variety of endovascular strategies, essentially using detachable platinum coils. Yet, coil embolization remains a very complex medical procedure for which careful planning must be combined with advanced technical skills in order to be successful. In this paper, we describe a complete process for patient-specific simulations of coil embolization, from mesh generation with medical datasets to computation of coil-flow bilateral influence. We propose a new method for simulating the complex blood flow patterns that take place within the aneurysm, and for simulating the interaction of coils with this flow. This interaction is twofold, first involving the impact of the flow on the coil during the initial stages of its deployment, and second concerning the decrease of blood velocity within the aneurysm, as a consequence of coil packing. We also propose an approach to achieve real-time computation of coil-flow bilateral influence, necessary for interactive simulation. This in turns allows to dynamically plan coil embolization for two key steps of the procedure: choice and placement of the first coils, and assessment of the number of coils necessary to reduce aneurysmal blood velocity and wall pressure. Finally, we provide the blood flow simulation results on several aneurysms with interesting clinical characteristics both in 2D and 3D, as well as comparisons with a commercial package for validation. The coil embolization procesure is simulated within an aneurysm, and pre- and post-operative status is reported

Computational analysis of the hemodynamic performance of novel endovascular and surgical procedures for complex aortic diseases

Novel branched stent-grafts (BSG) have been developed for endovascular repair of complex thoracic aortic aneurysms (TAA) involving the aortic arch or thoracoabdominal aorta, but their haemodynamic performance has not been adequately studied. In addition, surgical replacement of the ascending aorta with a Dacron graft remains the gold standard for type A aortic dissection (TAAD), although 12% of patients are at risk of aortic rupture due to further dilatation of the residual dissected aorta. The underlying mechanisms for progressive aortic dilatation following TAAD repair are poorly understood, but haemodynamic and biomechanical factors are believed to play an important role. Therefore, the present study aims to provide more insights into the haemodynamics in novel BSGs developed for treating complex aortic diseases, and a comprehensive evaluation of flow and biomechanical conditions in post-surgery TAADs by means of state-of-the-art computational methods. The first part of this thesis focuses on evaluating the haemodynamic performance of novel BSG designs, including thoracoabdominal branch endoprosthesis (TAMBE) and dual-branched thoracic endograft. Haemodynamics in idealised and patient-specific BSG models has been analysed by examining side branch outflow waveforms, wall shear stress related indices, and displacement forces, in order to assess their long-term durability. The numerical results show that all the stent-graft models examined in this study are capable of providing normal blood perfusion to side vessels, and are at low risk of in-stent thrombosis and device migration. Furthermore, it has been shown that geometric variations in TAMBE do not affect the key haemodynamic results, indicating its potential suitability for a variety of visceral artery anatomies. Comparisons of dual-branched thoracic endograft models with different inner tunnel diameters suggest that BSGs with larger inner tunnel diameters than the respective vessels would be preferred. Comparisons between the pre- and post-intervention models show that insertion of a dual-branched stent-graft significantly alters the flow pattern in the aortic arch, some of which may have a detrimental effect in the long term, thus requiring follow-up studies. The second part of the thesis provides a comprehensive analysis of the haemodynamic and biomechanical conditions in surgically repaired TAAD. Geometric and haemodynamic parameters have been analyzed and compared between the group of patients with stable aortic diameter and another group with progressive aortic dilatation. The number of re-entry tears (6±5 vs 2±1;P= 0.02) and luminal pressure difference (1.3 ±1 vs 11.7 ±14.6 mmHg;P= 0.001) have been identified as potential predictors of progressive aortic dilatation in TAAD patients following surgical repair. This is an important finding and can potentially assist clinicians to make the most appropriate choice or surgical plan for individual patients. Based on the finite element analysis of four patient-specific cases, there are no clear differences in biomechanical parameters between the stable and unstable groups. Furthermore, a preliminary fluid-solid interaction (FSI) simulation performed on a single TAAD model has demonstrated the important influence of wall compliance on pressures in the true and false lumen. Compared to a rigid wall model, the FSI simulation results show a reduction in systolic pressure by up to 10 mmHg and a slight increase in diastolic pressure. However, pressures in the true and false lumen are affected in the same way, so that the luminal pressure difference remains the same between the rigid and FSI models.Open Acces