Modeling, Simulation, And Visualization Of 3d Lung Dynamics

Medical simulation has facilitated the understanding of complex biological phenomenon through its inherent explanatory power. It is a critical component for planning clinical interventions and analyzing its effect on a human subject. The success of medical simulation is evidenced by the fact that over one third of all medical schools in the United States augment their teaching curricula using patient simulators. Medical simulators present combat medics and emergency providers with video-based descriptions of patient symptoms along with step-by-step instructions on clinical procedures that alleviate the patient\u27s condition. Recent advances in clinical imaging technology have led to an effective medical visualization by coupling medical simulations with patient-specific anatomical models and their physically and physiologically realistic organ deformation. 3D physically-based deformable lung models obtained from a human subject are tools for representing regional lung structure and function analysis. Static imaging techniques such as Magnetic Resonance Imaging (MRI), Chest x-rays, and Computed Tomography (CT) are conventionally used to estimate the extent of pulmonary disease and to establish available courses for clinical intervention. The predictive accuracy and evaluative strength of the static imaging techniques may be augmented by improved computer technologies and graphical rendering techniques that can transform these static images into dynamic representations of subject specific organ deformations. By creating physically based 3D simulation and visualization, 3D deformable models obtained from subject-specific lung images will better represent lung structure and function. Variations in overall lung deformations may indicate tissue pathologies, thus 3D visualization of functioning lungs may also provide a visual tool to current diagnostic methods. The feasibility of medical visualization using static 3D lungs as an effective tool for endotracheal intubation was previously shown using Augmented Reality (AR) based techniques in one of the several research efforts at the Optical Diagnostics and Applications Laboratory (ODALAB). This research effort also shed light on the potential usage of coupling such medical visualization with dynamic 3D lungs. The purpose of this dissertation is to develop 3D deformable lung models, which are developed from subject-specific high resolution CT data and can be visualized using the AR based environment. A review of the literature illustrates that the techniques for modeling real-time 3D lung dynamics can be roughly grouped into two categories: Geometrically-based and Physically-based. Additional classifications would include considering a 3D lung model as either a volumetric or surface model, modeling the lungs as either a single-compartment or a multi-compartment, modeling either the air-blood interaction or the air-blood-tissue interaction, and considering either a normal or pathophysical behavior of lungs. Validating the simulated lung dynamics is a complex problem and has been previously approached by tracking a set of landmarks on the CT images. An area that needs to be explored is the relationship between the choice of the deformation method for the 3D lung dynamics and its visualization framework. Constraints on the choice of the deformation method and the 3D model resolution arise from the visualization framework. Such constraints of our interest are the real-time requirement and the level of interaction required with the 3D lung models. The work presented here discusses a framework that facilitates a physics-based and physiology-based deformation of a single-compartment surface lung model that maintains the frame-rate requirements of the visualization system. The framework presented here is part of several research efforts at ODALab for developing an AR based medical visualization framework. The framework consists of 3 components, (i) modeling the Pressure-Volume (PV) relation, (ii) modeling the lung deformation using a Green\u27s function based deformation operator, and (iii) optimizing the deformation using state-of-art Graphics Processing Units (GPU). The validation of the results obtained in the first two modeling steps is also discussed for normal human subjects. Disease states such as Pneumothorax and lung tumors are modeled using the proposed deformation method. Additionally, a method to synchronize the instantiations of the deformation across a network is also discussed

Actores sintéticos en tiempo real: Nuevas estructuras de datos y métodos para su integración en aplicaciones de simulación.

RESUMEN La forma más extendida de implementar una aplicación de simulación es mediante la utilización de un grafo de escena. Este tipo de estructura resulta muy adecuado para definir escenas estáticas, pero presenta serias carencias a la hora de representar estructuras articuladas, u objetos con comportamientos complejos. Ambas circunstancias se dan en el caso de los actores virtuales. Este trabajo define nuevas estructuras de datos y métodos que permiten integrar de una forma adecuada actores virtuales en una aplicación de simulación: 1-Se presentan dos nuevos tipos de nodos (Actor y Skeleton), que actúan como elemento modular para la definición y gestión de cualquier tipo de actor virtual. En el diseño de estos nodos se ha prestado especial atención a la estandarización, y la eficiencia computacional. 2-Se proponen técnicas que permiten solventar algunas carencias de los grafos de escena actuales a la hora de ser empleados con actores virtuales. Se actúa sobre el cuello de botella existente en relación con aplicación de matrices de transformación. Se define un nuevo método de gestión de culling específico para actores, es compatible con el tradicional, y actúa sobre los costes asociados a la gestión del comportamiento. Se define un método de gestión de nivel de detalle específico, que actúa simultáneamente sobre la geometría, la topología y el comportamiento, y se realiza un análisis sobre la forma en que los actores han de ser integrados en un sistema multiprocesador 3-Se describe una estructura de nombre ActorClass, que es independiente del grafo de escena y que se encarga de almacenar todas las informaciones de alto nivel que son compartidas por varios actores de la misma especie. Esta estructura es capaz de absorber futuras ampliaciones y permite realizar simulaciones macroscópicas. Con el objeto de demostrar la utilidad práctica de los resultados de este trabajo, se ha implementado una librería de programación y una arquitectura modular que actúan sobre la base de las estructuras y métodos descritos, y se ha desarrollado un ejemplo de su utilización que muestra en detalle todos los aspectos de la integración de actores virtuales en una aplicación de simulación ya existente. ____________________________________________________________________________________________________The Scene Graph is the most widespread method of implementation simulation applications. This kind of structure is a very convenient way to define static scenes, but it has serious drawbacks in representing articulated structures or objects with complex behaviours. Both circumstances are inherent in virtual actors. This thesis defines new data structures and methods permiting the adequate integratión of virtual actors in a simulatión application: 1. Two new kinds of nodes are presented (Actor and Skeleton). These nodes function as modular elements to define and manage all kinds of virtual actor. During the dessing process of this nodes a great attention was paid to standarization and computational efficience. 2. Special techniques are presented in order to solve problems in the current scene graphs: Working on the bottleneck that exists in relation to the transformation matrix process; Defining a new method of culling, specific to actors, that is compatible with the traditional, and considers the costs associated with the behaviour management; Defining a specific Level of Detail method, that works simultaneously with the geometry, the topology and the behaviour; Making an analisis of the technique to ingrate actors in a multiprocessor system. 3. A new structure, named ActorClass, is defined. This structure is independent of the scene graph and is responsible for storing all the high level information that is shared by several actors of the same species. This structure has the capability of assimilating future expansions, and supporting the definition of macroscopic simulations. In order to show the practical utility of the results of this work, a programming library and a modular architecture have been implemented on the basis of these proposed structures and methods. In addition, a practical sample sample has been developed, showing in detail all the aspects of the integratión of virtual actors in an existing simulation application