Objetivo: Evaluar el grosor dentinario en el tercio cervical, medio y apical de primeros molares deciduos a nivel de las paredes de los conductos radiculares mediante el uso de tomografía computarizada de haz cónico. Materiales y métodos: La muestra estuvo conformada por 30 tomografías de haz cónico. La unidad de análisis estuvo compuesta por primeros molares deciduos, los cuales fueron divididos en dos grupos (n=15), el grupo de primeros molares deciduos superiores e inferiores. Para la toma de las medidas del grosor dentinario de las paredes de cada conducto, se realizó 3 cortes de vista axial en la tomografía en el tercio cervical, medio y apical. Luego, cada tercio fue dividido en 4 superficies (distal, mesial, lingual/palatino y vestibular), lo cual sirvió para tomar las medidas y realizar la sumatoria de las 4 superficies del grosor dentinario en milímetros para obtener el promedio final del tercio. Los datos fueron analizados mediante estadística descriptiva (media, mediana, desviación estándar y rango intercuartílico). Resultado: Se obtuvieron las medias para el grupo del primer molar deciduo superior e inferior, en los cuales se observó medidas diferentes a nivel de los tres tercios y superficies evaluadas. Conclusión: Es importante tener mayor conocimiento sobre la anatomía del primer molar deciduo, debido a las diversas características que esta presenta en comparación a los molares de la dentición permanente. / Objective: To evaluate the dentin thickness in cervical, middle and apical third of deciduous first molars at the level of the root canal walls by using cone beam computed tomography. Materials and Methods: The sample consisted of 30 Cone Beam tomography. The analysis unit was made up of deciduous first molars, which were divided into two groups (n=15), the group of upper and lower deciduous first molars. To take the measurements of the dentin thickness of the walls of each canal, 3 axial views were made on the tomography in the cervical, middle and apical third. Then each third was divided into 4 surfaces (distal, mesial, lingual / palatal and vestibular), which served to take the measurements and make the sum of the 4 surfaces of the dentin thickness in millimeters to obtain the final average of the third. Data were analyzed using descriptive statistics (mean, median, standard deviation and interquartile range). Results: The means for the upper and lower deciduous first molar group were obtained, in which different measures were observed at the level of the three-thirds and evaluated surfaces. Conclusion: It is important know more about anatomy of the first deciduous molar, due to the various characteristics that it presents compared to the molars of the permanent dentition. / Tesis

C-arm Cone Beam CT (CBCT) systems – due to compact size, flexible geometry and low radiation exposure – inaugurated the era of on-board 3D image guidance in therapeutic and surgical procedures. Leksell Gamma Knife Icon by Elekta introduced an integrated CBCT system to determine patient position prior to surgical session, thus advancing to a paradigm shift in facilitating frameless stereotactic radiosurgeries. While CBCT offers a quick imaging facility with high spatial accuracy, the quantitative values tend to be distorted due to various physics based artifacts such as scatter, beam hardening and cone beam effect. Several 3D reconstruction algorithms targeting these artifacts involve an accurate and fast segmentation of craniofacial CBCT images into air, tissue and bone. The objective of the thesis is to investigate the performance of deep learning based convolutional neural networks (CNN) in relation to conventional image processing and machine learning algorithms in segmenting CBCT images. CBCT data for training and testing procedures was provided by Elekta. A framework of segmentation algorithms including multilevel automatic thresholding, fuzzy clustering, multilayer perceptron and CNN is developed and tested against pre-defined evaluation metrics carrying pixel-wise prediction accuracy, statistical tests and execution times among others. CNN has proven its ability to outperform other segmentation algorithms throughout the evaluation metrics except for execution times. Mean segmentation error for CNN is found to be 0.4% with a standard deviation of 0.07%, followed by fuzzy clustering with mean segmentation error of 0.8% and a standard deviation of 0.12%. CNN based segmentation takes 500s compared to multilevel thresholding which requires ~1s on similar sized CBCT image. The present work demonstrates the ability of CNN in handling artifacts and noise in CBCT images and maintaining a high semantic segmentation performance. However, further efforts targeting CNN execution speed are required to utilize the segmentation framework within real-time 3D reconstruction algorithms. / C-arm Cone Beam CT (CBCT) system har tack vare sitt kompakta format, flexibla geometri och låga strålningsdos startat en era av inbyggda 3D bildtagningssystem för styrning av terapeutiska och kirurgiska ingripanden. Elektas Leksell Gamma Knife Icon introducerade ett integrerat CBCT-system för att bestämma patientens position för operationer och på så sätt gå in i en paradigm av ramlös stereotaktisk strålkirurgi. Även om CBCT erbjuder snabb bildtagning med hög spatiel noggrannhet så tenderar de kvantitativa värdena att störas av olika artefakter som spridning, beam hardening och cone beam effekten. Ett flertal 3D rekonstruktionsalgorithmer som försöker reducera dessa artefakter kräver en noggrann och snabb segmentering av kraniofaciala CBCT-bilder i luft, mjukvävnad och ben. Målet med den här avhandlingen är att undersöka hur djupa neurala nätverk baserade på faltning (convolutional neural networks, CNN) presterar i jämförelse med konventionella bildbehandlings- och maskininlärningalgorithmer för segmentering av CBCT-bilder. CBCT-data för träning och testning tillhandahölls av Elekta. Ett ramverk för segmenteringsalgorithmer inklusive flernivåströskling (multilevel automatic thresholding), suddig klustring (fuzzy clustering), flerlagersperceptroner (multilayer perceptron) och CNN utvecklas och testas mot fördefinerade utvärderingskriterier som pixelvis noggrannhet, statistiska tester och körtid. CNN presterade bäst i alla metriker förutom körtid. Det genomsnittliga segmenteringsfelet för CNN var 0.4% med en standardavvikelse på 0.07%, följt av suddig klustring med ett medelfel på 0.8% och en standardavvikelse på 0.12%. CNN kräver 500 sekunder jämfört med ungefär 1 sekund för den snabbaste algorithmen, flernivåströskling på lika stora CBCT-volymer. Arbetet visar CNNs förmåga att handera artefakter och brus i CBCT-bilder och bibehålla en högkvalitativ semantisk segmentering. Vidare arbete behövs dock för att förbättra presetandan hos algorithmen för att metoden ska vara applicerbar i realtidsrekonstruktionsalgorithmer.

After over a decade of its discovery, the Electroretinogram (ERG) still remains the objective tool that is conventionally used in assessment of retinal function in health and disease. Although there is ongoing research in developing ERG- recording techniques, interpretation and clinical applications, there is still a limited understanding on how each photoreceptor class contribute to the ERG waveform and their role and/or susceptibilities in various retinal diseases still remains unclear. Another limitation with currently used conventional testing protocols in a clinical setting is the requirement of an adaptation period which is time-consuming. Furthermore, the ERG responses derived in this manner are recorded under different stimulus conditions, thus, making comparison of these signals difficult. To address these issues and develop a new testing method, we employed silent substitution paradigm in obtaining cone- and rod- isolating ERGs using sine- and square- wave temporal profiles. The ERGs achieved in this manner were shown to be photoreceptor-selective. Furthermore, these responses did not only provide the functional index of photoreceptors but their contributions to their successive postreceptoral pathways. We believe that the substitution stimuli used in this thesis could be a valuable tool in functional assessment of individual photoreceptor classes in normal and pathological conditions. Furthermore, we speculate that this method of cone/rod activity isolation could possibly be used in developing faster and efficient photoreceptor-selective testing protocols without the need of adaptation. / Bradford School of Optometry and Vision Sciences

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This dissertation examines the role of nongovernmental public action (NGPA) in the controversial field of adolescent fertility in Buenos Aires (Argentina), Santiago (Chile) and Montevideo (Uruguay). Embracing a comparative perspective the study investigates the modes in which national policy and institutional environments shape the role of civil society organizations and their margins of autonomy vis a vis other powerful actors such as the State and the Catholic church. Forty one organizations whose mission includes the prevention of teenage pregnancy or the support of teenage parents were studied using a multi-method approach to explore cross national similarities and differences. An exhaustive account of national and subnational policies and programs in this field demonstrates the existence of isomorphic trends in the treatment and framing of adolescent reproductive behavior as a critical issue of public policy in each country. Similarly in all three countries women’s rights organizations play a critical role in the legal recognition and enforcement of adolescents’ sexual and reproductive rights while pro-poor organizations are fundamental actors in addressing the specific needs of teenage mothers and their children. However, important cross national differences were found regarding the modes in which NGPA engages with governmental agencies. As distinctive national marks, the study reveals a strong presence of NGOs in the role of rights watchdogs and monitors in Argentina, a strong alliance between central government structures and technical NGOs to confront resistances to reforms in Chile, and the utilization of NGOs as service providers in detriment of their participation in phases of policy design in Uruguay. Although the language of rights has colonized most of the surveyed organizations, adult-centric practices and discourses are still defining the interaction with adolescents. Adolescent’s demands are rarely voiced and only a few organizations favor their engagement in contentious politics and community activism. Nongovernmental autonomy is severely curtailed as a result of the influence of religion, and the lack of state modernization or financial opportunities, in the three countries. On theoretical grounds, the study highlights the importance of public policy as the arena where the potential of civil society can be maximized. / text

The objective of this work is to develop an on-line planning and delivery technique for palliative radiotherapy of spinal metastases using a linear accelerator capable of cone-beam CT (CBCT) imaging. This technique integrates all preparation and delivery steps into a single session equivalent to an initial treatment session. The key technical challenges pertaining to the development and implementation of this novel treatment technique are related to CBCT image performance, efficient system integration, development of on-line planning tools and design of novel quality assurance (QA) phantoms and processes. Hardware and software image corrections were first implemented to make CBCT images suitable for target definition and planning. These corrections reduced CBCT non-uniformity and improved CBCT-number accuracy. The on-line treatment technique workflow and the integration of all the subsystems involved in the process were assessed on a customized spine phantom constructed for the study. The challenges related to the routine QA of the highly integrated on-line treatment technique were addressed with the construction and validation of an integral test phantom. This phantom, which contains point detectors (diodes) allows for real-time QA of the entire image guidance, planning and treatment process in terms of dose delivery accuracy. The integral test phantom was also effective for the QA of high-dose, high-precision spinal radiosurgery. Simulation of the on-line treatment technique on patient data showed that the planning step was the one of the most time consuming tasks due predominantly to manual target definition. A semi-automatic method for detection and identification of vertebrae on CBCT images was developed and validated to streamline vertebra segmentation and improve the on-line treatment efficiency. With a single patient setup at the treatment unit, patient motion during the on-line process represents the main source of geometric uncertainty for dose delivery. Spine intra-fraction motion was assessed on CBCT for a group of 49 patients treated with a palliative intent. The use of surface marker tracking as a surrogate for spine motion was also evaluated. Finally, the complete on-line planning and delivery technique was implemented in a research ethics board (REB) approved clinical study at the Princess Margaret Hospital and 7 patients have been successfully treated at the time of this report with this novel treatment approach.

The design and optimisation of a modern gasoline direct injection (GDI) engine requires a thorough understanding of the fuel sprays characteristics and atomisation process.Therefore this thesis presents a detailed optical analysis of atomisation, penetration and interaction of multi-stream GDI sprays under engine relevant pressures and temperatures. The characteristics of the fuel spray in a GDI engine have a great influence on the fuel-air mixing and combustion processes as fuel injectors must provide adequate atomisation for vaporisation of the fuel to take place before combustion is initiated, whilst also avoiding spray impingement on the cylinder walls or piston crown. In this study multi-stream injectors, to be used within GDI engines, are quantified using Laser Doppler Anemometry (LDA) on an atmospheric bench. This process allowed for highly detailed spray analysis of droplet velocities and diameter at precise locations, using a three dimensional traverse, within the injector spray. The aim of the study was to analyse plume interaction between separate plumes of multi-stream injectors. Three multi-stream injectors were subjected to testing; two six-hole injectors and one three-hole injector. The injectors differed by having different distances between the plumes. The effect of fuel type on the liquid break-up and atomisation was investigated using Phase Doppler Anemometry (PDA) and Mie imaging. Mie imaging was also performed to capture images of fuel from a multi-stream injector as it was sprayed into a pressure chamber which was used to recreate the conditions found in an engine likely to cause flash boiling. In total, five variables were investigated: fuel pressure, ambient pressure, ambient temperature, fuel composition and injector geometry. Once processed, the recorded images allowed measurement of spray tip penetration and cone angle. Qualitative data on the change in shape of the spray was also available. The results showed that flash boiling has potential to reduce droplet diameters and improve fuel vaporisation, however, the associated change in spray shape must be taken into account to avoid problems with spray impingement. Keywords: Gasoline Direct Injection, multi-stream injector, atomisation, penetration, cone angle, Mie imaging, Phase Doppler Anemometry, flash boiling.

L'objet de cette thèse est l'étude de la structure symplectique des orbites coadjointes holomorphes, et de leurs projections.Une orbite coadjointe holomorphe O est une orbite coadjointe elliptique d'un groupe de Lie G réel semi-simple connexe non compact à centre fini provenant d'un espace symétrique hermitien G/K, telle que O puisse être naturellement munie d'une structure kählérienne G-invariante. Ces orbites coadjointes sont une généralisation de l'espace symétrique hermitien G/K.Dans cette thèse, nous prouvons que le symplectomorphisme de McDuff se généralise aux orbites coadjointes holomorphes, décrivant la structure symplectique de l'orbite O par le produit direct d'une orbite coadjointe compacte et d'un espace vectoriel symplectique. Ce symplectomorphisme est ensuite utilisé pour déterminer les équations de la projection de l'orbite O relative au sous-groupe compact maximal K de G, en faisant intervenir des résultats récents de Ressayre en Théorie Géométrique des Invariants. / This thesis studies the symplectic structure of holomorphic coadjoint orbits and the projection of such orbits.A holomorphic coadjoint orbit O is an elliptic coadjoint orbit which is endowed with a natural invariant Kählerian structure. These coadjoint orbits are defined for real semi-simple connected non compact Lie group G with finite center such that G/K is a Hermitian symmetric space, where K is a maximal compact subgroup of G. Holomorphic coadjoint orbits are a generalization of the Hermitian symmetric space G/K.In this thesis, we prove that the McDuff's symplectomorphism, available for Hermitian symmetric spaces, has an analogous for holomorphic coadjoint orbits. Then, using this symplectomorphism and recent GIT arguments from Ressayre, we compute the equations of the projection of the orbit O, relatively to the maximal compact subgroup K.

This dissertation describes the application of two principled variance reduction strategies to increase the efficiency for two applications within medical physics. The first, called correlated Monte Carlo (CMC) applies to patient-specific, permanent-seed brachytherapy (PSB) dose calculations. The second, called adjoint-biased forward Monte Carlo (ABFMC), is used to compute cone-beam computed tomography (CBCT) scatter projections. CMC was applied for two PSB cases: a clinical post-implant prostate, and a breast with a simulated lumpectomy cavity. CMC computes the dose difference between the highly correlated dose computing homogeneous and heterogeneous geometries. The particle transport in the heterogeneous geometry assumed a purely homogeneous environment, and altered particle weights accounted for bias. Average gains of 37 to 60 are reported from using CMC, relative to un-correlated Monte Carlo (UMC) calculations, for the prostate and breast CTV’s, respectively. To further increase the efficiency up to 1500 fold above UMC, an approximation called interpolated correlated Monte Carlo (ICMC) was applied. ICMC computes using CMC on a low-resolution (LR) spatial grid followed by interpolation to a high-resolution (HR) voxel grid followed. The interpolated, HR is then summed with a HR, pre-computed, homogeneous dose map. ICMC computes an approximate, but accurate, HR heterogeneous dose distribution from LR MC calculations achieving an average 2% standard deviation within the prostate and breast CTV’s in 1.1 sec and 0.39 sec, respectively. Accuracy for 80% of the voxels using ICMC is within 3% for anatomically realistic geometries. Second, for CBCT scatter projections, ABFMC was implemented via weight windowing using a solution to the adjoint Boltzmann transport equation computed either via the discrete ordinates method (DOM), or a MC implemented forward-adjoint importance generator (FAIG). ABFMC, implemented via DOM or FAIG, was tested for a single elliptical water cylinder using a primary point source (PPS) and a phase-space source (PSS). The best gains were found by using the PSS yielding average efficiency gains of 250 relative to non-weight windowed MC utilizing the PPS. Furthermore, computing 360 projections on a 40 by 30 pixel grid requires only 48 min on a single CPU core allowing clinical use via parallel processing techniques.