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Image-Based Computational Modeling of the Human Circulatory and Pulmonary Systems provides an overview of the current modeling methods and applications enhancing interventional treatments and computer-aided surgery. A detailed description of the techniques behind image acquisition, processing and three-dimensional reconstruction are included. Techniques for the computational simulation of solid and fluid mechanics and structure interaction are also discussed, in addition to various cardiovascular and pulmonary applications. Engineers and researchers involved with image processing and computational modeling of human organ systems will find this a valuable reference.

Inhaltsverzeichnis

Frontmatter

Cardiac and Pulmonary Imaging,Image Processing,and Three-Dimensional Reconstruction in Cardiovascular and Pulmonary Systems

Chapter 1. Image Acquisition for Cardiovascular and Pulmonary Applications

Abstract
Medical imaging hardware can provide detailed images of the cardiac and pulmonary anatomy. High-speed imaging can be used to acquire time sequences showing tissue dynamics or can capture a snapshot of the changing anatomy at an instant in time. Some imaging modalities can also provide functional information, such as perfusion, ventilation, and metabolic activity, or mechanical information, such as tissue deformation and strain. With the appropriate acquisition protocol, some of these imaging devices can acquire 3D (volumetric) and even 4D (volume data plus time) data with excellent anatomic detail. This image data can be visualized using computer graphics techniques to show geometric information, and the data can be processed to provide realistic anatomic models for subsequent computer simulations that explore physiologic function. This chapter describes the most commonly used imaging modalities for cardiovascular and pulmonary applications and describes some of the advantages and disadvantages of the different modalities. New, emerging modalities that may be important imaging tools in the future are introduced.
Daniel R. Thedens

Chapter 2. Three-dimensional and Four-dimensional Cardiopulmonary Image Analysis

Abstract
Modern medical imaging equipment can provide data that describe the anatomy and function of structures in the body. Image segmentation techniques are needed to take this raw data and identify and delineate the relevant cardiovascular and pulmonary anatomy to put it into a form suitable for 3D and 4D modeling and simulation. These methods must be able to handle large multi-dimensional data sets, possibly limited in resolution, corrupted by noise and motion blur, and sometimes depicting unusual anatomy due to natural shape variation across the population or due to disease processes. This chapter describes modern techniques for robust, automatic image segmentation. Several applications in cardiovascular and pulmonary imaging are presented.
Andreas Wahle, Honghai Zhang, Fei Zhao, Kyungmoo Lee, Richard W. Downe, Mark E. Olszewski, Soumik Ukil, Juerg Tschirren, Hidenori Shikata, Milan Sonka

Computational Techniques for Fluid and Soft Tissue Mechanics,Fluid-structure Interaction,and Development of Multi-scale Simulations

Chapter 3. Computational Techniques for Biological Fluids: From Blood Vessel Scale to Blood Cells

Abstract
Simulation of flows in the cardiovascular system faces many challenges. Chief among these is the issue of treatment of blood flow at disparate scales. For blood flows through large vessels a Newtonian homogeneous fluid model can be adequate, while in the capillaries and in orifices and constrictions individual blood cells and interactions among blood cells assume importance. Another important feature of flows in the cardiovascular system or in the presence of cardiovascular prostheses is the interaction of blood with moving boundaries (e.g. arterial walls, heart, heart valves, and ventricular assist devices). Computational fluid dynamics has made significant progress in tackling these challenges to the extent that it is now feasible to calculate flows through parts of the cardiovascular system with a great degree of fidelity and physiological realism. This chapter presents fundamental aspects of the demands on and capabilities of numerical solution techniques for solving a variety of blood flow phenomena. Large scale flows with significant fluid inertia and small scale flows with individual blood cells are covered. Applications of the methods and sample results are shown to illustrate the state-of-the-art of computations in cardiovascular biofluid dynamics.
Fotis Sotiropoulos, Cyrus Aidun, Iman Borazjani, Robert MacMeccan

Chapter 4. Formulation and Computational Implementation of Constitutive Models for Cardiovascular Soft Tissue Simulations

Abstract
Predictive computational modeling of the cardiovascular system has often been utilized as a powerful investigative tool. Motivated by the need for a deeper understanding of the underlying physiology, the identification of pathological initiators, as well as the development of bioprosthetic devices, a broad variety of modeling approaches have been introduced into the literature. Central to system- and organ-level functional simulations is the need for robust and physiologically meaningful constitutive models of the underlying soft tissue structures. While studied for many decades, Y.C. Fung popularized the field of soft tissue mechanics through a set of influential books which demonstrated the unique challenges involved in the mathematical characterization of living tissue mechanical behaviors. Overall, his main contribution was to establish constitutive relationships for the purpose of examining biological tissues in a continuum mechanics framework. Particular challenges in soft tissue constitutive modeling are encountered due to their complex mechanical behavior. For example, because of their oriented fibrous structures, they often exhibit pronounced mechanical anisotropy, nonlinear stress–strain relationships, large deformations, viscoelasticity, poroelasticity, and strong mechanical coupling. Taken as a whole, soft biological tissues defy simple material models. The focus of this chapter is the description and computational application of relevant biomechanical constitutive theories. Throughout this chapter, we will utilize the assumption of hyperelastic behavior as fundamental to soft tissue biomechanics, utilizing the concept of pseudo-elasticity, so that the loading response is modeled only.
Michael S. Sacks, Jia Lu

Chapter 5. Algorithms for Fluid–Structure Interaction

Abstract
The human body presents several fluid–structure interaction (FSI) problems, such as the operation of the heart and its valves, motion of blood cells in the circulation, peristaltic contractions in the gut, vibration of vocal cords, operation of the lungs during breathing, contraction of the urinary bladder, and a host of others. Modeling such problems and devising computational techniques to solve the governing equations is an increasingly popular and powerful way to understand the behavior of these systems in the healthy and pathological states. Fluid–structure interaction problems in different organ systems can present different challenges. In the presence of blood (i.e., in the cardiovascular system), FSI problems are plagued by numerical stiffness arising from added mass effects, while such constraints are absent in the presence of air (as in the respiratory and voice systems). In addition, at large scales, fluid inertia can play a significant role, leading to unsteady, transitional, and weakly turbulent flows. At small scales (as in blood cells), viscous effects assume importance. This chapter provides a survey of some of the important issues that arise in the cardiovascular system when FSI problems are tackled. Three primary techniques are discussed, viz., the immersed boundary approach, the immersed interface approach, and the sharp interface approach. The suitability of these approaches to specific problems is addressed and example calculations are shown to illustrate the state of the art of FSI in the cardiovascular system.
Sarah C. Vigmostad, H.S. Udaykumar

Chapter 6. Mesoscale Analysis of Blood Flow

Abstract
Blood flow in the cardiovascular system and its interaction with the vessel walls plays a crucial role in health and disease. Individual blood cells play varied and vital roles in the circulation, including transport of nutrients and dissolved gases (red blood cells), fighting infections and disease (white blood cells), and healing of wounds (platelets). Malfunctioning of blood cells can result in pathologies such as sickle cell disease (red blood cells), ischemia (white blood cells), atherosclerosis (white blood cells and platelets) and thrombosis (platelets and red blood cells). To better understand the behavior of blood cells and their role in health and disease, microscale models that capture the dynamics of individual cells and their interactions with other cells/vessel walls can be very useful. However, since even micro-volumes of blood contain extremely large numbers of cells, connecting blood flow phenomena to cell dynamics and cell–cell/cell–wall interactions limits the usefulness of micro-scale models. Mesoscale models that do not model individual cells in detail, but allow for the treatment of large numbers of cells can provide important insights into the impact of the particulate nature of blood; such mesoscale models can represent transport phenomena, aggregation/disaggregation of cell clusters, collisional interactions of cells with each other and with walls and other phenomena important to healthy and pathological states in the circulation. This chapter describes the important features of such mesoscale models of blood; the treatment of the particulate nature of blood and the modeling and simulation of cell–cell and cell–surface interactions are covered. The examples presented illustrate the state of the art in mesoscale modeling of blood flow.
Jeffrey S. Marshall, Jennifer K.W. Chesnutt, H.S. Udaykumar

Applications of Computational Simulations in the Cardiovascular and Pulmonary Systems

Frontmatter

Chapter 7. Arterial Circulation and Disease Processes

Abstract
Atherosclerosis is an arterial disease resulting in thickening of the arterial wall and occlusion of the vessels in advanced stages. In addition to hereditary and environmental factors, the effect of fluid-induced stresses on the arterial wall has also been implicated on the etiology of the disease due to the fact that the lesions are found in arterial curvature and branching sites with complex flow dynamics. In this chapter, the computational modeling of the fluid dynamics in the coronary arteries and the aorta is discussed in order to determine the relationship between wall shear stress and its temporal and spatial gradients with the disease progression. The importance of the use of three-dimensional geometry of the region of interest from imaged data, the effect of boundary conditions as well as the unsteady flow analysis on the results are discussed. The modeling of the flow dynamics in the abdominal aortic aneurysm (AAA) geometrical models, as well as models of vascular graft anastomotic regions is also discussed.
Tim McGloughlin, Michael T. Walsh

Chapter 8. Biomechanical Modeling of Aneurysms

Abstract
Aneurysms are abnormal dilations in the arterial wall and predominantly occur in the aorta and in the cerebral vasculature. The aortic aneurysm is predominantly found in the infrarenal abdominal region and the cerebral aneurysms generally occur in or near the circle of Willis. There is considerable interest in understanding the mechanism underlying aneurysm growth, diagnosing their severity or propensity to rupture, and developing endovascular implants to treat the same. Biomechanical simulations are being employed to improve our understanding of factors that trigger aneurysms and mechanisms for growth/rupture of the lesions. In this chapter, studies on reconstruction of the three-dimensional geometry of the aneurysms, material modeling of the arterial wall and aneurysm components, and biomechanical analyses toward prediction of potential rupture are discussed.
Madhavan L. Raghavan, David A. Vorp

Chapter 9. Advances in Computational Simulations for Interventional Treatments and Surgical Planning

Abstract
Computational analyses of blood flow through the vascular system have the potential to improve medical care by identifying and quantifying hemodynamics relevant to the protection from and initiation and progression of vascular disease. In addition to identifying relevant mechanics, computational analyses coupled with advanced simulation environments could also be used to predict the hemodynamics associated with alternate anatomic or hemodynamic scenarios and to predict the overall performance of each scenario. Such simulations can be used by clinicians to design optimized interventional treatments and by engineers to design optimal vascular devices. In this chapter, the application of computational simulations for the prediction of vulnerable atherosclerotic plaques, improved understanding of the mechanics of balloon angioplasty, design of endovascular stents, and patient-specific surgical planning is discussed.
Diane A. de Zélicourt, Brooke N. Steele, Ajit P. Yoganathan

Chapter 10. Computational Analyses of Airway Flow and Lung Tissue Dynamics

Abstract
The function of the mammalian respiratory system is the facilitation the transfer of gas exchange between the organism’s environment and its internal transport medium, the blood. Evolutionary processes have optimized the anatomic structure of the lung as a tree-like branching network of airways terminating in thin-walled elastic ducts and alveoli, where this gas exchange occurs. Both dissipative and elastic properties of the respiratory system contribute to its unique static and dynamic mechanical behavior. In this chapter, we will explore the various structural and functional relationships of the respiratory system, and review several computational and modeling analyses that provide insight into the pathophysiology of common respiratory diseases. Particular emphasis is placed on studies that utilize imaging to help understand and/or validate the distributed regional nature of lung function.
David W. Kaczka, Ashley A. Colletti, Merryn H. Tawhai, Brett A. Simon

Chapter 11. Native Human and Bioprosthetic Heart Valve Dynamics

Abstract
Native human heart valves undergo complex deformation during a cardiac cycle and the tissue leaflets are subjected to regions of stress concentrations particularly during the opening and closing phases. Diseases of the heart valves include stenosis and valvular incompetence and the valves in the left heart (aortic and mitral valves) subjected to higher pressure loads are more prone to these diseases. A correlation has been established between regions of high stress concentration on the leaflets and regions of calcification and tissue failure. Computational simulations play a significant role in the determination of stress distribution on the leaflets during a cardiac cycle. In this chapter, the development of state-of-the-art structural analysis of the biological leaflet valves as well as fluid–structure interaction algorithms for the analysis of biological tissue valve dynamics are described. The potential application of the computational analyses on improving the design of biological heart valve prostheses is discussed. The need for further advancements in multiscale simulation for increasing our understanding of the effect of mechanical stresses on the leaflet microstructure is also pointed out.
Hyunggun Kim, Jia Lu, K.B. Chandran

Chapter 12. Mechanical Valve Fluid Dynamics and Thrombus Initiation

Abstract
Heart valve, and subsequently cardiac function, may be seriously compromised as a result of stenosis or regurgitation. If necessary, the native heart valve is surgically replaced with an artificial substitute, which is in about 40% of the cases a bileaflet mechanical heart valve (BMHV). While generally showing excellent hemodynamic performance in the short term, current BMHVs are not free of clinical complications, which are induced by thrombus formation and hemolysis. Computational fluid dynamic (CFD) modeling is now considered a powerful and extremely useful tool to investigate blood flow in existing BMHVs and to reduce the costs associated with the development of new prototypes. A prerequisite for performing realistic heart valve simulations is the implementation of a fluid–structure interaction (FSI) algorithm that accounts for the mechanical interaction between the valve leaflets and the ambient blood. Provided the numerical resolution is sufficiently high, three-dimensional CFD-FSI models are able to compute the complex flow structures that exist in the vicinity of a BMHV. In order to get information about the valve’s potential for platelet activation and blood hemolysis, these CFD models must be accompanied by appropriate mathematical models that describe the relation between fluid dynamic variables and the damage to blood corpuscles. This chapter provides an overview on the state of the art in computational flow simulations in BMHV and discusses various approaches taken to integrate blood damage accumulation models into flow simulations.
Tom Claessens, Joris Degroote, Jan Vierendeels, Peter Van Ransbeeck, Patrick Segers, Pascal Verdonck

Backmatter

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