Validation of Immersed Boundary Simulations of Heart Valve Hemodynamics against In Vitro 4D Flow MRI Data

The immersed boundary (IB) method is a mathematical framework for fluid-structure interaction problems (FSI) that was originally developed to simulate flows around heart valves. Validation of FSI simulations around heart valves against experimental data is challenging, however, due to the difficulty of performing robust and effective simulations, the complications of modeling a specific physical experiment, and the need to acquire experimental data that is directly comparable to simulation data. In this work, we performed physical experiments of flow through a pulmonary valve in an in vitro pulse duplicator, and measured the corresponding velocity field using 4D flow MRI (4-dimensional flow magnetic resonance imaging). We constructed a computer model of this pulmonary artery setup, including modeling valve geometry and material properties via a technique called design-based elasticity, and simulated flow through it with the IB method. The simulated flow fields showed excellent qualitative agreement with experiments, excellent agreement on integral metrics, and reasonable relative error in the entire flow domain and on slices of interest. These results validate our design-based valve model construction, the IB solvers used and the immersed boundary method for flows around heart valves

Towards a 3D printed patient clone: Application to the effect of aortic regurgitation on the flow in the left ventricle

Heart disease is the leading cause of death in the world. Amongst the many cardiovascular diseases, heart valve failure is a common reoccurrence. Patient safety has risen to being a top priority focus for every field of medicine therefore heart simulators are implemented and expected to contribute immensely to the medical training of physicians, medical device testing and the study of cardiovascular fluid dynamics. Common methods to studying cardiovascular fluid dynamics have been the use of Doppler echocardiography or 2D plane analysis using particle image velocimetry. The objective of this thesis is to design an innovated 3D printed heart simulator which is completely mobile and M.R.I. (magnetic resonance imaging)-compatible which can obtain results that are not possible with present methods. The 3D printed heart simulator created for this dissertation was named the MaxTron system. Among the many heart diseases that could be modeled with the system, aortic regurgitation was chosen to demonstrate one of its many capabilities. Simulation was controlled through guided wires entering the 3D printed representation of the left side of a male patient’s heart. Each leaflet of the aortic heart valve could be independently controlled to represent different severities of the disease. Results demonstrate the accuracy of 4D flow readings and the versatility of the MaxTron system. Vortex formation and particle pathlines formed by aortic regurgitation and mitral inflow interaction can be observed from any angle or plane during both diastolic and systolic phases. Lifelike heart valves perform better for M.R.I. experiments when compared to both mechanical and bio-prosthetic heart valves that contain metal components which are less M.R.I.-compatible

Virtual and Augmented Reality Techniques for Minimally Invasive Cardiac Interventions: Concept, Design, Evaluation and Pre-clinical Implementation

While less invasive techniques have been employed for some procedures, most intracardiac interventions are still performed under cardiopulmonary bypass, on the drained, arrested heart. The progress toward off-pump intracardiac interventions has been hampered by the lack of adequate visualization inside the beating heart. This thesis describes the development, assessment, and pre-clinical implementation of a mixed reality environment that integrates pre-operative imaging and modeling with surgical tracking technologies and real-time ultrasound imaging. The intra-operative echo images are augmented with pre-operative representations of the cardiac anatomy and virtual models of the delivery instruments tracked in real time using magnetic tracking technologies. As a result, the otherwise context-less images can now be interpreted within the anatomical context provided by the anatomical models. The virtual models assist the user with the tool-to-target navigation, while real-time ultrasound ensures accurate positioning of the tool on target, providing the surgeon with sufficient information to ``see\u27\u27 and manipulate instruments in absence of direct vision. Several pre-clinical acute evaluation studies have been conducted in vivo on swine models to assess the feasibility of the proposed environment in a clinical context. Following direct access inside the beating heart using the UCI, the proposed mixed reality environment was used to provide the necessary visualization and navigation to position a prosthetic mitral valve on the the native annulus, or to place a repair patch on a created septal defect in vivo in porcine models. Following further development and seamless integration into the clinical workflow, we hope that the proposed mixed reality guidance environment may become a significant milestone toward enabling minimally invasive therapy on the beating heart

Computed Tomography-Derived 3D Modeling to Guide Sizing and Planning of Transcatheter Mitral Valve Interventions

A plethora of catheter-based strategies have been developed to treat mitral valve disease. Evolving 3-dimensional (3D) multidetector computed tomography (MDCT) technology can accurately reconstruct the mitral valve by means of 3-dimensional computational modeling (3DCM) to allow virtual implantation of catheter-based devices. 3D printing complements computational modeling and offers implanting physician teams the opportunity to evaluate devices in life-size replicas of patient-specific cardiac anatomy. MDCT-derived 3D computational and 3D-printed modeling provides unprecedented insights to facilitate hands-on procedural planning, device training, and retrospective procedural evaluation. This overview summarizes current concepts and provides insight into the application of MDCT-derived 3DCM and 3D printing for the planning of transcatheter mitral valve replacement and closure of paravalvular leaks. Additionally, future directions in the development of 3DCM will be discussed

The Role of Visualization, Force Feedback, and Augmented Reality in Minimally Invasive Heart Valve Repair

New cardiovascular techniques have been developed to address the unique requirements of high risk, elderly, surgical patients with heart valve disease by avoiding both sternotomy and cardiopulmonary bypass. However, these technologies pose new challenges in visualization, force application, and intracardiac navigation. Force feedback and augmented reality (AR) can be applied to minimally invasive mitral valve repair and transcatheter aortic valve implantation (TAVI) techniques to potentially surmount these challenges. Our study demonstrated shorter operative times with three dimensional (3D) visualization compared to two dimensional (2D) visualization; however, both experts and novices applied significantly more force to cardiac tissue during 3D robotics-assisted mitral valve annuloplasty than during conventional open mitral valve annuloplasty. This finding suggests that 3D visualization does not fully compensate for the absence of haptic feedback in robotics-assisted cardiac surgery. Subsequently, using an innovative robotics-assisted surgical system design, we determined that direct haptic feedback may improve both expert and trainee performance using robotics-assisted techniques. We determined that during robotics-assisted mitral valve annuloplasty the use of either visual or direct force feedback resulted in a significant decrease in forces applied to cardiac tissue when compared to robotics-assisted mitral valve annuloplasty without force feedback. We presented NeoNav, an AR-enhanced echocardiograpy intracardiac guidance system for NeoChord off-pump mitral valve repair. Our study demonstrated superior tool navigation accuracy, significantly shorter navigation times, and reduced potential for injury with AR enhanced intracardiac navigation for off-pump transapical mitral valve repair with neochordae implantation. In addition, we applied the NeoNav system as a safe and inexpensive alternative imaging modality for TAVI guidance. We found that our proposed AR guidance system may achieve similar or better results than the current standard of care, contrast enhanced fluoroscopy, while eliminating the use of nephrotoxic contrast and ionizing radiation. These results suggest that the addition of both force feedback and augmented reality image guidance can improve both surgical performance and safety during minimally invasive robotics assisted and beating heart valve surgery, respectively

Platelet Activation in Artificial Heart Valves

A numerical framework is developed to perform multi-scale (hinge-to valve-scale) flow simulation and quantify the thrombogenic performance of prosthetic heart valves. This aim is achieved by 1) developing a parallel dynamic overset grid and combining it with the curvilinear immersed boundary (overset-CURVIB) method to reduce the computational cost; and 2) developing a framework for evaluating the thrombogenic performance of heart valves in terms of platelet activation. The dynamic overset grids are used to locally increase the grid resolution near immersed bodies, which are handled using a sharp interface immersed boundary method, undergoing large movements as well as arbitrary relative motions. The new framework extends the previous overset-CURVIB method with fixed overset grids and a sequential grid assembly to moving overset grids with an efficient parallel grid assembly. In addition, a new method for the interpolation of variables at the grid boundaries is developed which can drastically decrease the execution time and increase the parallel efficiency. This overset grid framework is integrated with a framework to quantify the platelet activation which is developed using a Eulerian frame of reference which calculates the activation over the whole computational domain (contrary to Largrangian methods which use limited number of particles). The new framework is verified and validated against experimental data, and analytical/benchmark solutions. This framework is used to compare the role of systole phase in the poor performance of bileaflet mechanical heart (BMHV) valve by using the bioprothtetic heart valve as a control. The results show that the activation in the bulk flow during the systole phase might play an essential role in poor hemodynamic performance of BMHVs. In addition, the contribution of bulk and hinge flows to the activation of platelets in BMHVs is quantified for the first time by performing simulations of the flow through a BMHV and resolving the hinge by overset grids. The total activation by the bulk flow is found to be several folds higher than that by the hinge/leakage flow. This is mainly due to the higher flow rate of the bulk flow which exposes much more platelets to shear stress than the leakage flow. For the future work, this framework is going to be applied for thrombogenic optimization of new designs of mechanical heart valves including trileaflet ones as well as patient-specific hemodynamic analysis of heart valves using fluid-structure interaction in more realistic geometries extracted from the medical images such as echocardiography

3-DIMENSIONAL NUMERICAL AND EXPERIMENTAL STUDIES TO MODEL ARTIFICIAL HEART VALVES HEMODYNAMICS

Ph.DDOCTOR OF PHILOSOPH

SGABU computational platform for multiscale modeling:Bridging the gap between education and research

BACKGROUND AND OBJECTIVE: In accordance with the latest aspirations in the field of bioengineering, there is a need to create a web accessible, but powerful cloud computational platform that combines datasets and multiscale models related to bone modeling, cancer, cardiovascular diseases and tissue engineering. The SGABU platform may become a powerful information system for research and education that can integrate data, extract information, and facilitate knowledge exchange with the goal of creating and developing appropriate computing pipelines to provide accurate and comprehensive biological information from the molecular to organ level. METHODS: The datasets integrated into the platform are obtained from experimental and/or clinical studies and are mainly in tabular or image file format, including metadata. The implementation of multiscale models, is an ambitious effort of the platform to capture phenomena at different length scales, described using partial and ordinary differential equations, which are solved numerically on complex geometries with the use of the finite element method. The majority of the SGABU platform's simulation pipelines are provided as Common Workflow Language (CWL) workflows. Each of them requires creating a CWL implementation on the backend and a user-friendly interface using standard web technologies. Platform is available at https://sgabu-test.unic.kg.ac.rs/login. RESULTS: The main dashboard of the SGABU platform is divided into sections for each field of research, each one of which includes a subsection of datasets and multiscale models. The datasets can be presented in a simple form as tabular data, or using technologies such as Plotly.js for 2D plot interactivity, Kitware Paraview Glance for 3D view. Regarding the models, the usage of Docker containerization for packing the individual tools and CWL orchestration for describing inputs with validation forms and outputs with tabular views for output visualization, interactive diagrams, 3D views and animations. CONCLUSIONS: In practice, the structure of SGABU platform means that any of the integrated workflows can work equally well on any other bioengineering platform. The key advantage of the SGABU platform over similar efforts is its versatility offered with the use of modern, modular, and extensible technology for various levels of architecture.</p