La quantification de la perfusion tissulaire à partir de données dynamiques d’échographie de contraste repose sur une modélisation appropriée de la cinétique de la concentration en agent de contraste dans le tissu étudié. De nombreux facteurs, expérimentaux ou physiologiques, rendent la comparaison inter ou intra-individu de ces paramètres de perfusion difficile. Dans cette thèse, la reproductibilité et la comparaison de différentes méthodes de quantification ont été étudiées dans le cadre d’une étude préclinique de test-retest et sur des simulations numériques. Les méthodes étudiées ont été : le modèle log-normal, le modèle compartimental avec fonction d’entrée et le modèle compartimental avec tissu de référence. Les études précliniques ont montré la difficulté d’estimation d’une fonction d’entrée artérielle et la nécessité de corriger localement le temps d’arrivée de l’agent de contraste dans le tissu pour que l’approximation des cinétiques expérimentales par le modèle soit de qualité suffisante. Une estimation linéaire sous contrainte des paramètres du modèle compartimental avec tissu de référence tirant profit de différentes zones d’intérêt dans l’image a été ensuite proposée pour obtenir à l’échelle régionale et/ou locale des valeurs relatives cohérentes de débit sanguin tissulaire et de volume sanguin tissulaire, exprimées par rapport aux valeurs dans le tissu de référence. Il a été montré que cette approche est la plus robuste et la plus reproductible. L’influence des facteurs tels que la durée d’acquisition, la fréquence d’échantillonnage, le nombre de régions utilisées et l’amplitude du bruit a été étudiée sur des simulations et a permis de formuler des recommandations pour l’acquisition et le traitement des études en échographie de contraste. / Quantification of tissue perfusion from dynamic contrast-enhanced ultrasound data relies on appropriate modeling of the curve representing the evolution of the contrast-agent concentration inside the studied tissue. Many factors, experimental or physiological, make inter-subject or intra-subject comparison of these perfusion parameters difficult. In this thesis, the reproducibility and the comparison of various quantification methods was investigated through preclinical test-retest experiments and through simulations. The investigated methods were: the log-normal model, the one-compartment model using an arterial input function, and the one-compartment model using a reference tissue. The preclinical experiments revealed the difficulty to estimate an arterial input function directly from the image, as well as the necessity to locally correct for the time of arrival of the contrast agent in the tissue in order to ensure the model accurately fits the experimental enhancement curves. A regularized linear estimation of the parameters of the one-compartment model using a reference tissue taking advantage of multiple tissue regions was then proposed to obtain homogeneous relative values of the tissue blood flow and tissue blood volume, expressed relatively to the parameter value inside the reference tissue. The improved robustness and reproducibility of the method was demonstrated. The influence of factors such as the exam duration, the sampling frequency, the number of tissue regions in the analysis, and the noise amplitude were investigated through simulations, and allowed us to formulate recommendations regarding the acquisition and the analysis of contrast-enhanced ultrasound studies.

L'objectif de cette thèse est d'explorer plusieurs approches pour l'étude des données censurées multivariées, à savoir l'estimation non paramétrique de la fonction de répartition jointe, la modélisation de dépendance par les modèles de copules et l'étude exploratoire par des méthodes de clustering. Le Chapitre 1 introduit le contexte général de cette thèse ainsi que ses contributions. Le Chapitre 2 est consacré à l'estimation de la distribution jointe des deux variables censurées dans le cadre d'un modèle de durée simplifié où la différence entre deux variables de censure est observée. Un nouvel estimateur non paramétrique de la fonction de répartition jointe y est introduit. La normalité asymptotique a été démontrée, pour les intégrales par rapport à la mesure définie par cet estimateur. Le Chapitre 3 est dédié à la problématique de l'estimation non paramétrique de la copule bivariée, à partir d'un échantillon de données censurées. La copule est d'abord estimée par une fonction discrète qui peut être interprétée comme une extension de la copule empirique en présence de censure, puis par ses versions lisses. Les propriétés asymptotiques et des applications de des estimateurs ont été considérées. Le Chapitre 4 présente une approche exploratoire pour l'étude de données censurées. Plus précisément, une configuration multivariée est considérée où une variable est une durée sujette à la censure, et toutes les autres variables sont observées. Sous ces conditions, une nouvelle méthode de quantification de la loi jointe est introduite. La méthode est étudiée théoriquement et appliquée à la construction d'un algorithme de clustering pour des observations censurées. / The main purpose of this thesis is to explore several approaches for studying multivariate censored data: nonparametric estimation of the joint distribution function, modeling dependence with copulas and k-clustering for the exploratory analysis. Chapter 1 presents the general framework and the contributions of this thesis. Chapter 2 deals with the estimation of the joint distribution function of two censored variables in a simplified survival model in which the difference between two censoring variables is observed. We provide a new nonparametric estimator of the joint distribution function and we establish the asymptotic normality of the integrals with respect to its associated measure. Chapter 3 is devoted to nonparametric copula estimation under bivariate censoring. We provide a discrete and two smooth copula estimators along with two estimators of its density. The discrete estimator can be seen as an extension of the empirical copula under censoring. Chapter 4 provides a new exploratory approach for censored data analysis. We consider a multivariate configuration with one variable subjected to censoring and the others completely observed. We extend the probabilistic k-quantization method in the case of random vector with one censored component. The definitions of the empirical distortion and of empirically optimal quantizer are generalized in presence of one-dimensional censoring. We study the asymptotic properties of the distortion of the empirically optimal quantizer and we provide a non-asymptotic exponential bound for the rate of convergence. Our results are then applied to construct a new two-step clustering algorithm for censored data.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第22363号 / 医博第4604号 / 新制||医||1043(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 川口 義弥, 教授 富樫 かおり, 教授 上本 伸二 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

CFD simulations are valuable tools in evaluating and deploying oxy-fuel and other carbon capture technologies either as retrofit technologies or for new construction. However, accurate predictive simulations require physically realistic submodels with low computational requirements. In particular, comprehensive char oxidation and gasification models have been developed that describe multiple reaction and diffusion processes. This work extends a comprehensive char conversion code (the Carbon Conversion Kinetics or CCK model), which treats surface oxidation and gasification reactions as well as processes such as film diffusion, pore diffusion, ash encapsulation, and annealing. In this work, the CCK model was thoroughly investigated with a global sensitivity analysis. The sensitivity analysis highlighted several submodels in the CCK code, which were updated with more realistic physics or otherwise extended to function in oxy-coal conditions. Improved submodels include a greatly extended annealing model, the swelling model, the mode of burning parameter, and the kinetic model, as well as the addition of the Chemical Percolation Devolatilization (CPD) model. The resultant Carbon Conversion Kinetics for oxy-coal combustion (CCK/oxy) model predictions were compared to oxy-coal data, and further compared to parallel data sets obtained at near conventional conditions.

This work focuses on the construction of functional representations in high-dimensional spaces.Attention is focused on the modeling of ignition phenomena using detailed kinetics, and on the ignition delay time as the primary quantity of interest (QoI). An iso-octane air mixture is first considered, using a detailed chemical mechanism with 3,811 elementary reactions. Uncertainty in all reaction rates is directly accounted for using associated uncertainty factors, assuming independent log-uniform priors. A Latin hypercube sample (LHS) of the ignition delay times was first generated, and the resulting database was then exploited to assess the possibility of constructing polynomial chaos (PC) representations in terms of the canonical random variables parametrizing the uncertain rates. We explored two avenues, namely sparse regression (SR) using LASSO, and a coordinate transform (CT) approach. Preconditioned variants of both approaches were also considered, namely using the logarithm of the ignition delay time as QoI. A global sensitivity analysis is performed using the representations constructed by SR and CT. Next, the tangent linear approximation is developed to estimate the sensitivity of the ignition delay time with respect to individual rate parameters in a detailed chemical mechanism. Attention is focused on a gas mixture reacting under adiabatic, constant-volume conditions. The approach is based on integrating the linearized system of equations governing the evolution of the partial derivatives of the state vector with respect to individual random variables, and a linearized approximation is developed to relate the ignition delay sensitivity to the scaled partial derivatives of temperature. In particular, the computations indicate that for detailed reaction mechanisms the TLA leads to robust local sensitivity predictions at a computational cost that is order-of-magnitude smaller than that incurred by finite-difference approaches based on one-at-a-time rate parameters perturbations. In the last part, we explore the potential of utilizing TLA-based sensitivities to identify active subspace and to construct suitable representations. Performance is assessed based contrasting experiences with CT-based machinery developed earlier.

No description available.

This thesis focuses on cardiac imaging and quantification of T1 relaxation time in rat hearts. Its main focus is to investigate available methods for such quantification and their application in the development of quantification tools. The large impact is given to methods of acquisition synchronization, mainly with respect to cardiac motion and breathing using retrospective gating, where the navigator signal is obtained solely from the acquired data, so without any external equipment such as the ECG or respiratory sensors. This paper takes into account situations where steady-state has been reached and also those where it has not, by means of contrast agent injection or by inversion pulses.

No description available.

Due to the goals made by the European Union as well as the country of Sweden regarding the desired decrease of the ongoing greenhouse gas emissions, electrical alternatives have increased enormously in the industry and the automotive areas in recent years. By going from petrol-powered vehicles to electrical vehicles, the transport sector has the potential to produce zero direct emissions. To be able to develop electrical vehicles with the highest efficiency possible, it is of great importance to understand what losses occurs in the vehicle. By lowering these losses, we create a vehicle which both become cheaper and better for the climate. The aim of his thesis is to study the performance of the motors with different combinations of angular velocity and torque, analyse what losses occur with the combinations and also how the result is affected by the resolution of the drive cycles. Produced drive cycles, with a purpose to represent the velocity and acceleration of a vehicle in a realistic way, was used during the study to obtain a drive pattern. MATLAB was used during the whole thesis for analysis, simulation and plotting. Firstly, a method to obtain the probability of certain combinations of torques and angular velocities for a specific drive cycle was created. With this probability, a method to be able to adjust and choose the resolution of the torques and angular velocities was created. It was later concluded that these two methods functioned as desired. With the obtained combinations, the mechanical power as well as the most common losses in the electrical motor could be calculated. With this, an efficiency could be calculated and analysed. The energy demand of the different combinations was also obtained. One conclusion that could be made with this thesis was that the average efficiency did not depend on the resolution of the torque and angular velocity much at all. With a resolution going from 0.5 Nm to 20 Nm, the average efficiency only changed by below 0.3 percent units. At the end of the thesis, a continued work is proposed to implement different magnetic properties that are not accounted for in this thesis. Another suggestion made is to include scenarios where the battery is charged when a negative torque is applied to the motor shaft.

This diploma thesis deals with analysing of modern methods for cell detection, visualization and quantification in 3D space. The first section deals with optical methods for cells detection. There is detailed discussion about cell labeling and detection on confocal microscopy. There is also description about developed algorithm for whole cell volume quantification from microscopy images. This could made a comparsion of fluorescence signal according to time of cell labeling and according to cell shapes. There was also optimalization of handmade tissue phantoms visualization. It could be compared a possibilities of cell detections in these phantoms by confocal microscopy and OCT. It was also implemented algorithm for quantification of cells from OCT images. Besides confocal microscopy and OCT cells are also analyzed by other methods. The last part is the Conclusion of results and comparison of used methods.