Studies on radiofrequency (RF) ablation are often aimed at accurately predicting tissue temperature distributions by numerical solution of the bioheat equation. This thesis describes the development of an analytical solution to serve as a benchmark for subsequent numerical solutions. The solution, which was obtained using integral transforms, has the form of a surface integral nested within another surface integral. An integration routine capable of evaluating such integrals was developed and a C program was written to implement this routine. The surface integration routine was validated using a surface integral with a known analytical solution. The routine was, then, used to generate temperature profiles at various times and for different convection coefficients. To further validate the numerical methods used to obtain temperature profiles, a numerical model was developed with the same approximations used in obtaining the analytical solution. Results of the analytical and numerical solutions match very closely. In addition, three numerical models were developed to assess the validity of some of the assumptions used in obtaining the analytical solution. For each numerical model, one or two of the assumptions used in the analytical model were relaxed to better assess the degree to which they influence results. The results indicate that (1) conduction of heat into the electrode significantly affects lesion size, (2) temperature distributions can be assumed to be axisymmetric, and (3) lesion size and maximum temperature are strongly influenced by the temperature-dependence of electrical conductivity. These conclusions are consistent with results from previous studies on radiofrequency cardiac ablation.

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Traditional 1H lung imaging using MRI faces numerous challenges and difficulties due to low proton density and air-tissue susceptibility artifacts. New imaging techniques using inhaled xenon gas can overcome these challenges at the cost of lower signal to noise ratio. The signal to noise ratio determines reconstructed image quality and is an essential parameter in ensuring reliable results in MR imaging. The traditional RF surface coils used in MR imaging exhibit an inhomogeneous field, leading to reduced image quality. For the last few decades, fractal-shaped antennas have been used to optimize the performance of antennas for radiofrequency systems. Although widely used in radiofrequency identification systems, mobile phones, and other applications, fractal designs have yet to be fully researched in the MRI application space. The use of fractal geometries for RF coils may prove to be fruitful and thus prompts an investiga- tion as the main goal of this thesis. Preliminary simulation results and experimental validation results show that RF coils created using the Gosper and pentaflake offer improved signal to noise ratio and exhibit a more homogeneous field than that of a traditional circular surface coil. / Thesis / Master of Applied Science (MASc)

Axially symmetric rf ion traps consists of a mass analyser having three electrodes, one of which is a central ring electrode and the other two are endcap electrodes. In the ideal Paul trap mass spectrometer, the electrodes have hyperboloidal shape (March and Hughes, 1989) and in mass analyser with simplified geometry, such as the cylindrical ion trap (Wu et al.,2005) the central electrode is a cylinder and the two endcap electrode and flat plates. rf-only or rf/dc potential is applied across the ring electrode and the grounded endcap electrodes for conducting the basic experiments of the mass spectrometer. In recent times, the miniaturisation of ion trap is one of the research interests in the field of mass spectrometry. The miniaturisation has the advantages of compactness, low power consumption and portability. However, this is achieved at the cost of the overall performance of the mass spectrometer with its deleterious effect on resolution. Research groups study the field distribution in the trap for better understanding of ion dynamics in the direction of achieving improved performance with the miniaturised traps. One aspect which has not received any attention in research associated with quadrupole ion traps is the possible role of the magnetic field in improving performance of these traps. Since in the quadrupole ion trap mass analyser ion is confined by an oscillating (rf) field, magnetic fields have been considered superfluous. The motivation of the thesis is to understand the dynamics of ions in axially symmetric rf ion traps, in the presence of the magnetic field. The axially symmetric rf ion trap geometries considered in this thesis are the Paul trap and the cylindrical ion trap (CIT). The changes incurred to the ion motion and Mathieu stability diagram in the presence of magnetic field is observed in this work. Also, the relation between the magnetic field and the Mathieu parameter is shown. The thesis contains 4 chapters: Chapter 1 provides the basic back ground of mass spectrometry and the operating principles. The equations of ion motion in the Paul trap is derived and also the solution to Mathieu equation is provided. The solution to the Mathieu equation are the Mathieu parameters and , when plotted with on the x-axis and on the y-axis, results in the Mathieu stability plot, the explanation of which is also given in the chapter. A brief description of the secular frequency associated with the ion dynamics is given in this chapter. The popular experiments conducted (i.e. the mass selective boundary ejection and resonance ejection) with a mass spectrometer is described here. Finally at the end of the chapter is the scope of the thesis. Chapter 2 facilitates with the preliminary study required fort he accomplishment of the task. The Paul trap and the CIT are the rf ion traps considered in this work. The geometries of these two traps are described in this chapter. The computational methods used for the analysis of various aspects of mass spectrometer is introduced. The computational methods used involve the methods used for calculating the charge distribution on the electrodes, potentials, multipole co-efficients and trajectory calculations. The boundary element method(BEM), calculation for Potentials and the Runge-Kutta method used for the trajectory calculations are introduced in this chapter. The expressions for calculating the multipole co-efficients are also specified. Chapter 3 presents the results obtained. The equations of ion motion in a quadrupole ion trap in the presence of magnetic field is derived here. Verification of numerical results with and without the magnetic field are presented at the end of this chapter. The chapter also presents various graphs showing the impact of magnetic field on the ion dynamics in the Paul trap and the CIT. The impact of the presence of magnetic field on the micro motion in -, -and -directions of the rf ion traps are shown in this chapter. Also the figures showing the variation in the Mathieu stability plots, with varying magnetic field intensity are presented in the chapter. At the end of this chapter the relation between the magnetic field and the Mathieu parameter is derived and plotted. Chapter 4 explains the various observations made from the results obtained. This chapter also highlights the future scope of the work for making this a more applicable one. References in the text have been given by quoting the author’s name and year of publication. Full references have been provide, in an alphabetic order, at the end of the thesis.

Objective: The primary aim of this study was to assess patients’ preferences between radiofrequency ablation (RFA) versus hepatic resection (HR) for the treatment of small hepatocellular carcinomas (HCC). Methods: Decision analysis was performed by using probability trade-off (PTO) technique to elicit patients’ preferences and the strength of their decisions. Results: The vast majority of the study population preferred RFA over HR (70% vs. 30%, p=0.001). Their initial choice changed if 5-year survival benefit after surgery was at least 14% superior to RFA and if the 3-year disease-free survival advantage was at least 13% better than ablation. Conclusions: The results of this study suggest that fully informed cirrhotic patients would prefer RFA if diagnosed with early stage HCC even if able to undergo surgery.

En IRM haute résolution du petit animal, un rapport signal sur bruit (RSB) convenable demande habituellement l'utilisation d'un champ magnétique statique beaucoup plus élevé, (jusqu'à 20 T) que pour les applications cliniques quotidiennes (1,5 et 3 T). Une alternative est offerte avec le développement récent d’antennes miniatures en matériau supraconducteur à haute température critique (HTS). Cependant de nombreux problèmes liés à ce type d'antennes subsistent et limitent leur diffusion à grande échelle. Le présent manuscrit présente le développement théorique et expérimental d'une antenne de surface HTS de très petite dimension destinée à l’imagerie du cerveau de souris in vivo à 4,7 T.La première partie traite de la modélisation électromagnétique 3D, à l’aide d’un logiciel commercial (CST-Microwave Studio), de structures monolithiques auto-résonantes adaptées à l'obtention de facteurs de qualité extrêmement élevés (105). Le modèle numérique permet, par rapport à un modèle analytique approché, une meilleure prise en compte de la complexité géométrique de l’antenne et de son environnement cryogénique proche, dont les effets sur les caractéristiques radiofréquences de l’antenne sont considérables.Une deuxième partie présente l'étude des effets du champ statique (de 0 à 4,7 T) et de la température (de 65 à 83 K) sur les caractéristiques électriques d’une antenne HTS, dans le domaine de fréquences de l'IRM pour lequel les propriétés des supraconducteurs ont été peu étudiées jusqu'ici. L'étude montre que les effets délétères du champ sur la sensibilité de l’antenne sont partiellement compensés par une diminution modérée de sa température de fonctionnement. Cette diminution est accessible avec un dispositif original de contrôle de température qui évite de faire appel à un système cryogénique complexe limitant le domaine d’application des antennes HTS.La troisième partie présente les résultats obtenus en imagerie à 4,7 T avec une antenne de surface en matériau HTS dont la taille (diamètre de 6 mm) a été optimisée pour obtenir les meilleures performances en RSB, en vue d'une intégration dans un réseau de 4 antennes. Un RSB 4,5 fois supérieur à celui obtenu avec une antenne en cuivre de même géométrie a été démontré sur fantôme. Ce travail aboutit à la réalisation de la première image de cerveau de souris in-vivo à une valeur de champ supérieure à 3 T avec une antenne HTS. La mise en réseau d'antennes de ce type devrait permettre de couvrir le cerveau de souris complet en imagerie très haute résolution à 4,7 T, avec un RSB comparable à celui qui est accessible aujourd'hui à la limite supérieure de champ magnétique. / High resolution magnetic resonance imaging (MRI) of small animals requires generally higher static magnetic field (up to 20 T) than those used for clinical applications (1,5 and 3 T) in order to reach a satisfactory signal to noise ratio (SNR). An alternative can be the use of miniature surface coils made of high temperature superconducting (HTS) material. However, several issues remain with such coils and limit their use at a large scale. In this work we present the theoretical and experimental development of a miniature HTS surface coil dedicated to mouse brain imaging at 4.7 T.The first chapter presents 3D electromagnetic simulations to design monolithic self-resonant structures with very high quality factors (≈105) using a commercial software (CST-Microwave Studio). In contrast to an analytical model, a numerical model allows to handle the complex geometry of the coil and its cryogenic environment, which may influence notably the radiofrequency characteristics of the coil.The second chapter presents a study of the coupled effects of the static magnetic field B0 (from 0 to 4,7 T) and temperature (from 66 to 80 K) on the electrical properties of a HTS coil in the frequency range involved in MRI, for which HTS properties have been poorly studied. This study shows that deleterious effects of B0 on coil sensitivity can be partially compensated by a moderate decrease of its working temperature. An original cryogenic system was designed to enable temperature regulation avoiding the use of more complex systems that limit the use of HTS coils for MRI experiments.The third chapter presents MRI results obtained at 4.7 T using a small HTS surface coil. The 6 mm coil has been optimized for best SNR performances and in order to be integrated in a 4-element coil array in a future refinement. A 4.5 fold SNR enhancement as compared to the one achieved using a copper coil with the same geometry was demonstrated. This work provides the first in-vivo imaging of a mouse brain using a HTS coil at a B0 value higher than 3 T. Arrays made of such coils will allow to perform very high resolution imaging of the complete mouse brain at 4.7 T with SNR values that are comparable to those achieved at the highest B0 fields accessible today.

La pénétration importante d’objets communicants dans notre vie quotidienne révèle des défis important quant à leur développement. Notamment l’explosion d'applications multimédia sans fil pour l'électronique grand public fait de la consommation électrique une métrique clef dans la conception des dispositifs portables multimodes sans fil. Les émetteurs-récepteurs conventionnels proposent des performances fixes et sont conçus pour respecter ces hautes performances dans toutes les conditions de communication sans fil. Cependant, la plupart du temps, le canal n'est pas dans le pire cas de communication et ces émetteurs-récepteurs sont donc surdimensionnés. En connaissant l’état du canal en temps réel, de tels dispositifs pourraient s'adapter aux besoins et réduire significativement leur consommation électrique. Le défi consiste à respecter la Qualité de Service , ou Quality of Service (QoS) en anglais, imposée par les différents standards de communication. Afin de rester compétitifs, les émetteurs-récepteurs adaptatifs doivent donc proposer une même QoS que ceux déjà disponibles sur le marché. Ainsi, ni la portée de communication ni le temps de réponse ne peuvent être dégradés.Basé sur ces exigences, cette thèse propose une technique d'adaptation pour la conception d'un récepteur reconfigurable qui fonctionne à la limite des performances nécessaires pour recevoir le signal utile. Ainsi, le récepteur proposé est toujours au minimum de consommation électrique tout en garantissant la bonne QoS. Ceci permet alors de multiplier la durée de vie de sa batterie par un facteur 5.Cette adaptabilité est démontrée ensuite côté circuit par la conception d'un LNA (Amplificateur Faible Bruit) dont les performances sont reconfigurables. En effet, en tant que premier élément de la chaîne de réception, le LNA limite le récepteur en termes de sensibilité. Ces travaux exploitent la technologie FD-SOI (Fully Depleted Silicon-On-Insulator) pour d’une part, réduire la consommation du LNA et d’autre part, ajouter de la reconfigurabilité à ce même circuit. / Communicating objects are inviting themselves into daily life leading to digitization of the physical world. This explosion of multimedia wireless applications for consumer electronics makes the power consumption a key metric in the design of multi-mode wireless portable devices. Conventional transceivers have fixed performances and are designed to meet high performances in all wireless link conditions. However, most of the time, the channel of communication is not at worst case and these transceivers are therefore over specified. Being aware of the channel link conditions would allow such devices to adapt themselves and to reduce significantly their power consumption. Therefore, the challenge is to propose a QoS (Quality of Service) in terms of communication range, response time as instance, equivalent to industrial modules with a reduced overall power consumption.To address this purpose, this thesis proposes a design strategy for the implementation of adaptive radio-frequency receiver (Rx) modules. Hence the Rx front end achieves the correct QoS for various scenarii of communications with a minimum of power consumption.As a proof of concept, the adaptive approach is demonstrated with the design of a tunable LNA (Low Noise Amplifier). As the first element of the receiver chain, the LNA limits the receiver in terms of sensitivity and is therefore a good candidate to perform reconfiguration. The body biasing of the FD-SOI (Fully Depleted Silicon-On-Insulator) technology is first exploited to reduce the power consumption of a circuit and then as an opportunity to perform circuit tunability.