Vascular Tree Structure: Fast Curvature Regularization and Validation

This work addresses the challenging problem of accurate vessel structure analysis in high resolution 3D biomedical images. Typical segmentation methods fail on recent micro-CT data sets resolving near-capillary vessels due to limitations of standard first-order regularization models. While regularization is needed to address noise and partial volume issues in the data, we argue that extraction of thin tubular structures requires higher-order curvature-based regularization. There are no standard segmentation methods regularizing surface curvature in 3D that could be applied to large 3D volumes. However, we observe that standard measures for vessels structure are more concerned with topology, bifurcation angles, and other parameters that can be directly addressed without segmentation. We propose a novel methodology reconstructing tree structure of the vessels using a new centerline curvature regularization technique. Our high-order regularization model is based on a recent curvature estimation method. We developed a Levenberg-Marquardt optimization scheme and an efficient GPU-based implementation of our algorithm. We also propose a validation mechanism based on synthetic vessel images. Our preliminary results on real ultra-resolution micro CT volumes are promising

Robust real-time control of an adaptive optics system

This research contributes to the understanding of the limitations when designing a robust control real-time system for Adaptive Optics (AO). One part of the research is a new method regarding the evaluation of a Shack-Hartmann wavefront sensor (SHWFS) to enhance the overall performance. The method is presented based on the application of a Field Programmable Gate Array (FPGA) using Connected Component Labeling (CCL) for blob detection. The FPGA has been utilized since the resulting delay is crucial for the general AO performance. In this regard, the FPGA may accelerate the evaluation largely by its parallelism. The developed algorithm does not rely on a fixed assignment of the camera sensor area to the lenslet array to maximize the dynamic range. In extension to the SHWFS evaluation, a new rapid control prototyping (RCP) system based on hard real-time RTAI-patched Linux kernel has been developed. This system includes the required hardware e.g.~the analog output cards and FPGA based frame-grabber. Based upon a Simulink model, accelerated C/C++ code is automatically generated which uses the available parallel features of the processor. A continuative contribution is the application of a robust control scheme using H-infinity methods for designing a controller while considering uncertainty of the identified model. For synthesizing the controller, a special optimization technique called non-smooth mu-synthesis is utilized which minimizes the H-infinity norm while coping with pre-specified controller schemes. Depending on the pre-specified controller scheme, the resulting controller can be computationally costly but the RCP approach is designed to cope with the problem. Based on simulations and according to experiments, the validity of the identified models of the AO setup is assured. At the same time, the enhanced performance of the new RCP setup is demonstrated.Die wissenschaftliche Arbeit trägt maßgeblich zum Verständnis der gängigen Limitierungen bei robusten echtzeit-fähigen Regelungssystemen für Adaptiv Optische (AO) Systeme bei. Ein wesentlicher Teil der Arbeit befasst sich mit einer neuartigen Methode der Auswertung eines Shack-Hartmann Wellenfrontsensors (SHWFS). Die Methode basiert auf der Anwendung eines Field Programmable Gate Arrays (FPGA) zur Auswertung des SHWFS. Die zu Grunde liegende Methode ist ein Resultat der Graphentheorie zur Erkennung zusammenhängender Bildbereiche. Der Einsatz eines FPGA ermöglicht hierbei, dass die resultierende Verzögerung durch die Auswertung des SHWFS auf ein Minimum reduziert wird. Hinzu kommt, dass die neuartige Auswertungsmethode den dynamischen Bereich des Wellenfrontsensors gegenüber dem üblichen Verfahren erweitert, da für die Methode keine feste Zuordnung der Spots zu dem Linsenarray notwendig ist. Zusätzlich zu dem neuartigen Verfahren für die Auswertung wurde ein Rapid Control Prototyping (RCP) System entworfen, welches auf einem echtzeitfähigen Linux Kernel basiert. Die Echtzeitfähigkeit wird durch die Verwendung des Real-Time Application Interface for Linux (RTAI) erreicht. Der Entwurf des RCP Systems umfasst die Entwicklung spezieller Hardware wie beispielsweise eine analoge Ausgangskarte und der PCIe FPGA Framegrabber. Aus einem Simulink Modell wird automatisch C/C++ Quellcode generiert. Dieser generierte Code nutzt die vorhandenen parallelen Erweiterungen des Prozessors zur Beschleunigung der vorkommenden Berechnungen. Basierend auf diesem System wurde ein robustes Regelungsverfahren angewendet, welches auf der H_infty Entwurfsmethodik basiert. Das Entwurfverfahren des Reglers (non-smooth mu Synthese) berücksichtigt die vorhandene Unsicherheit der identifizierten Modelle bereits während der Synthese. Das Verfahren ermöglicht die H_infty Norm des geschlossenen Regelkreises zu minimieren, wobei die Regler-Struktur vorgegeben werden kann. Basierend auf verschiedenen Simulationen und experimentellen Versuchen wurde die Gültigkeit der identifizierten Modelle des AO Systems nachgewiesen. Zudem wird gezeigt, dass das entworfene RCP System deutlich leistungsfähiger als vergleichbare Systeme ist und somit eine deutlich verbesserte Performance aufweist

Computer-aided detection of polyps in CT colonography

Master'sMASTER OF ENGINEERIN

Drainage control and diffusion resistance in dropwise condensation in a compact heat exchanger

Condensation of a vapor in the presence of non-condensable gas occurs frequently in process industry. For example in compact condensers for heat recovery, in extraction of toxic components from exhaust gases, in cooling systems of nuclear power plants, seawater desalination systems, air conditioning and petrochemical industry. It is well known that even small concentrations of non-condensable gas have a detrimental effect on condensation heat transfer rates. The key difference between the condensation of pure vapor and vapor in the presence of non-condensable gas compounds is that mass diffusion in the gas phase instead of heat diffusion in the condensate layer dominates heat transfer in the heat exchanger in the latter case. In condensation heat transfer with non-condensable gases, vapor-sided heat and mass transfer are essential. If possible, the diffusion resistance in the gas-liquid boundary layer should be reduced in order to enhance heat and mass transfer. A way to augment heat transfer is by introducing dropwise condensation instead of filmwise condensation. Heat transfer by dropwise condensation is possibly a factor 8 to 10 higher than filmwise condensation [115]. The exact reasons for this difference are still not fully understood. Where filmwise condensation is characteristic of metal heat exchangers with clean uncontaminated surfaces, dropwise condensation is, for example, achieved by applying a fluoropolymer heat exchanging surface. This study aims to elucidate the importance of the initial phase of dropwise condensation after drainage on heat transfer, when diffusion is not yet limiting. The effects of growth, coalescence and drainage of droplets with surface refreshing on airsteam condensation heat transfer enhancement are quantified. For this reason, a new small scale condenser setup is designed and applied. To supply a gas flow at well defined conditions, existing infrastructure is combined with an acoustic relative humidity sensor tailored to the required flow conditions. Also other measures are taken to increase accuracy of the heat exchanger test rig. An apparatus with controlled removal of condensate droplets from the condenser plates is designed and applied. The dropwise condensation process is frequently interrupted upon which nucleation restarts upon each sweep. Condensate growth and surface temperatures are assessed by simultaneous video and infrared recordings. Software is developed to automatically extract the positions and radii of condensate droplets from images quickly and reliably. Cold wakes downstream of big drops on the condenser plate were observed. A single controlled droplet removal action enables a ’reset’ of the condenser surface. This allows measurement of droplet growth histories. It is found that droplet growth follows a power law with the exponent increasing with increasing inlet vapor mass fraction. Direct contact condensation on drops at condenser plate dominates drop growth. The main finding is that that the total heat transfer resistance decreases with increasing droplet removal frequency, while two measures for mass transfer simultaneously increase. Increasing diffusion limitation is one explanation for the observed decreasing mass transfer rate with time. After initial fast growth of drops, the slight increase in interfacial temperature observed offers another explanation. Furthermore, the effect of a structured heterogeneous plate surface on droplet drainage and heat transfer in dropwise condensation is investigated. A structured coating of the condenser plates is applied to create two coexisting dropwise condensation patterns. The structured coating constrains drainage and introduces directed surface energy gradients. The condenser with the structured coating is compared with two equally sized condensers: a non-coated pvdf and a fully coated pvdf condenser. It is found that drop drainage is promoted by oriented Ti-coated tracks to such a degree that the maximum obtainable heat transfer performance is practically reached. Design recommendations are given

Doctor of Philosophy

dissertationTreatment and management of heart disease is challenging due to the heart's limited ability to self-repair. Although current approaches to manage heart disease, such as pharmacotherapy, medical devices, lifestyle changes, and heart transplantation, have improved and extended the quality of life for millions of individuals, they have inherent shortcomings. Future strategies to manage heart disease will likely be based upon a combination of biological and engineering approaches through cell therapy and tissue engineering strategies, both of which have the potential to regenerate the myocardium and improve cardiac function. However, a key hurdle in applying biological approaches is our limited ability to produce reliable tissue to study disease progression and tissue development, therapeutic intervention, drug discovery, or tissue replacement. Establishing hallmarks of the native myocardium in engineered cardiac tissue is a central goal and appears to be required for creating functional tissue that can serve as a surrogate for in vitro testing or the eventual replacement of diseased or injured myocardium. The objective of this research was to apply an engineering approach to develop tools and methods to produce engineered cardiac tissue and characterize both native and engineered cardiac tissue. Three phases of research included: 1) the development and utilization of a framework to characterize microstructure in living cardiac tissue using confocal microscopy and local dye delivery, 2) the development a next-generation bioreactor capable of continuously monitoring force-displacement in engineered tissue, and 3) the application of confocal imaging and image analysis to quantitatively describe features of the native myocardium, focusing on myocyte geometry and spatial distribution of a major gap junction protein connexin-43, in both engineered tissue and native tissue

Real-Time Statistics for Padel Tennis Using Artificial Intelligence

O Padel, desporto conhecido pelo seu crescimento explosivo e jogabilidade emocionante, está à beira de uma revolução tecnológica. Com o objetivo de transformar o jogo de Padel através do uso criativo de técnicas de deteção de objetos e Deep Learning, esta dissertação de mestrado investiga a junção da Inteligência Arti cial (IA) e do Padel. O principal objetivo é usar a IA para produzir estatísticas em tempo real que darão aos jogadores, treinadores e fãs um melhor conhecimento das complexidades do Padel e dos meios para levar o jogo a novos patamares. Esta dissertação explora a monitorização e localização em tempo real dos jogadores e da bola dentro do campo, através de algoritmos de visão computacional. As Redes Neu ronais de Convolução (RNC), um tipo de modelo de Deep Learning, são essenciais para o reconhecimento preciso de eventos e ações importantes durante o jogo. A criação de um sistema baseado em IA que produz dados instantâneos para partidas de Padel é a inovação central desta dissertação. Estas estatísticas oferecem uma visão analítica e detalhada de cada jogo, tendo em consideração os movimentos dos jogadores, as trajetórias da bola e a dinâmica do jogo. Esta dissertação não promove apenas o Padel, mas também cria novas oportunidades para a utilização de IA em outros desportos.The sport of Padel, known for its explosive growth and exciting gameplay, is on the verge of a technological revolution. With the goal of transforming the game of Padel through the creative use of object detection and deep learning techniques, this master's thesis investi gates the junction of Arti cial Intelligence (AI) and Padel. The main goal is to use AI to produce real-time statistics that will give players, coaches and fans a better knowledge of the complexities of Padel and the means to take the game to new heights. This dissertation explores the real-time tracking and localization of players and the ball within the court by utilizing cutting-edge computer vision algorithms. Convolution Neural Networks (CNN), one type of deep learning model, are essential for the precise recognition of important gaming events and actions. The creation of an AI-driven system that produces in-the-moment data for Padel matches is the central innovation of this dissertation. These statistics o er a detailed and analytical view of each game by taking into account player movements, ball trajectories, and game dynamics. This dissertation not only advances the sport of Padel but also creates new op portunities for the use of AI in other sports analytics

Computational processing and analysis of ear images

Tese de mestrado. Engenharia Biomédica. Faculdade de Engenharia. Universidade do Porto. 201