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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This PhD thesis, addresses the issue of evaluation of cone beam computed tomography, CBCT, scanning protocols, was introduced in dental radiology at the end of the 1990s, and it quickly became a fundamental examination for various procedures. Its main characteristic, the difference of medical CT is the beam shape. This study aimed to calculate the absorbed dose in eight tissues / organs of the head and neck, and to estimate the effective dose in 13 protocols and two techniques (stitched FOV e single FOV) of 5 equipment of different manufacturers of cone beam CT. For that purpose, a female anthropomorphic phantom was used, representing a default woman, in which were inserted thermoluminescent dosimeters at several points, representing organs / tissues with weighting values presented in the standard ICRP 103. The results were evaluated by comparing the dose according to the purpose of the tomographic image. Among the results, there is a difference up to 325% in the effective dose in relation to protocols with the same image goal. In relation to the image acquisition technique, the stitched FOV technique resulted in an effective dose of 5.3 times greater than the single FOV technique for protocols with the same image goal. In the individual contribution, the salivary glands are responsible for 31% of the effective dose in CT exams. The remaining tissues have also a significant contribution, 36%. The results drew attention to the need of estimating the effective dose in different equipment and protocols of the market, besides the knowledge of the radiation parameters and equipment manufacturing engineering to obtain the image. / Na presente tese de doutoramento foi abordada a temática da avaliação de protocolos de exame de tomografia computadorizada de feixe cônico - TCFC, que foi iniciada na radiologia odontológica no fim da década de 1990 e rapidamente tornou-se um exame fundamental para diversos procedimentos. Sua principal característica, que a diferencia da tomografia computadorizada médica, é a forma do feixe. Assim, este estudo objetivou calcular a dose absorvida em 8 tecidos/órgãos da cabeça e pescoço e estimar a dose efetiva em 13 protocolos e duas técnicas (stitched FOV e single FOV) de 5 equipamentos diferentes fabricantes de tomografia computadorizada de feixe cônico. Para isto, foi utilizado um simulador antropomórfico feminino, representando uma mulher padrão, onde foram inseridos dosímetros termoluminescentes em diversos pontos, representando órgãos e tecidos com valores de ponderação apresentados na norma ICRP 103. Os resultados foram avaliados, comparando-se a dose de acordo com o objetivo da imagem tomográfica. Dentre os resultados, observou-se uma diferença de até 325 % de dose efetiva em relação a protocolos com o mesmo objetivo de imagem. Em relação à técnica de obtenção de imagem, a técnica stitched FOV resultou em uma dose efetiva até 5,3 vezes maior que a single FOV para protocolos com o mesmo objetivo de imagem. Na contribuição individual, as glândulas salivares são responsáveis por 31% da dose efetiva, nos exames tomográficos. Os tecidos restantes também apresentaram uma contribuição significativa, 36 %. Os resultados apontam a necessidade de se estimar a dose efetiva nos diversos equipamentos e protocolos presentes no mercado, além de conhecer os parâmetros de radiação e a engenharia de fabricação dos equipamentos para a obtenção da imagem.

This thesis addresses three problems related to image registration, prediction and tracking, applied to Angiography and Oncology. For image analysis, various probabilistic models have been employed to characterize the image deformations, target motions and state estimations. (i) In Digital Subtraction Angiography (DSA), having a high quality visualization of the blood motion in the vessels is essential both in diagnostic and interventional applications. In order to reduce the inherent movement artifacts in DSA, non-rigid image registration is used before subtracting the mask from the contrast image. DSA image registration is a challenging problem, as it requires non-rigid matching across spatially non-uniform control points, at high speed. We model the problem of sub-pixel matching, as a labeling problem on a non-uniform Markov Random Field (MRF). We use quad-trees in a novel way to generate the non uniform grid structure and optimize the registration cost using graph-cuts technique. The MRF formulation produces a smooth displacement field which results in better artifact reduction than with the conventional approach of independently registering the control points. The above approach is further improved using two models. First, we introduce the concept of pivotal and non-pivotal control points. `Pivotal control points' are nodes in the Markov network that are close to the edges in the mask image, while 'non-pivotal control points' are identified in soft tissue regions. This model leads to a novel MRF framework and energy formulation. Next, we propose a Gaussian MRF model and solve the energy minimization problem for sub-pixel DSA registration using Random Walker (RW). An incremental registration approach is developed using quad-tree based MRF structure and RW, wherein the density of control points is hierarchically increased at each level M depending of the features to be used and the required accuracy. A novel numbering scheme of the control points allows us to reuse the computations done at level M in M + 1. Both the models result in an accelerated performance without compromising on the artifact reduction. We have also provided a CUDA based design of the algorithm, and shown performance acceleration on a GPU. We have tested the approach using 25 clinical data sets, and have presented the results of quantitative analysis and clinical assessment. (ii) In External Beam Radiation Therapy (EBRT), in order to monitor the intra fraction motion of thoracic and abdominal tumors, the lung diaphragm apex can be used as an internal marker. However, tracking the position of the apex from image based observations is a challenging problem, as it undergoes both position and shape variation. We propose a novel approach for tracking the ipsilateral hemidiaphragm apex (IHDA) position on CBCT projection images. We model the diaphragm state as a spatiotemporal MRF, and obtain the trace of the apex by solving an energy minimization problem through graph-cuts. We have tested the approach using 15 clinical data sets and found that this approach outperforms the conventional full search method in terms of accuracy. We have provided a GPU based heterogeneous implementation of the algorithm using CUDA to increase the viability of the approach for clinical use. (iii) In an adaptive radiotherapy system, irrespective of the methods used for target observations there is an inherent latency in the beam control as they involve mechanical movement and processing delays. Hence predicting the target position during `beam on target' is essential to increase the control precision. We propose a novel prediction model (called o set sine model) for the breathing pattern. We use IHDA positions (from CBCT images) as measurements and an Unscented Kalman Filter (UKF) for state estimation. The results based on 15 clinical datasets show that, o set sine model outperforms the state of the art LCM model in terms of prediction accuracy.

Syfte: Att granska hur väl indikatorbilden och rotfyllningsbilden överensstämmer utifrån mätningar med elektronisk apexlokalisator. Dessutom granskas om rotfyllningskvalitet är beroende av tandtyp och antal besök samt om det förekommer någon skillnad på behandlingsproceduren före eller under COVID-19 pandemin. Vidare granskas tecken på läkning i de fall där läkningsbild finns.  Material och metod: Totalt har 635 patienter fått endodontisk behandling på studentklinik för endodonti på Malmö Tandvårdshögskola under perioden 2016–2021. Av dessa uppfyllde 350 journaler inklusionskriterierna. Journaldata tillsammans med röntgenbilder granskades av två oberoende observatörer. Resultat: Av 350 tänder överensstämde 262 tänders indikatorbild och rotfyllningsbild med EAL-mätningar. Underkäksmolarer till följd av överkäksmolarer och överkäkpresmolarer som hade inadekvat rotfyllningskvalitet.  Cirka 70% av tänderna som behandlades färdigt krävde mellan 2–6 besök. Tecken på läkning kunde observeras hos 78 patienter (ca. 92 %) som följts med klinisk undersökning och läkningsbilder. Inga märkbara skillnader noterades i behandlingsproceduren före eller under Covid-19 pandemin. Slutsats: Rotfyllningarna uppvisade god kvalitet baserat på kliniskt och röntgenologiskt underlag. Studenterna behöver relativt många besök för att genomföra en endodontisk behandling. Behandlingen resulterar ofta i en rotfyllning som bedöms ha god kvalitet och så många fall läker. Det behövs ges tydligare rekommendationer till studenter gällande bestämning av arbetslängden och information om att EAL är mer pålitlig att fastställa arbetslängd. / Aim: To evaluate how well the working length radiograph and obturation radiograph corresponded with the working length (WL) measured initially by electronic apex locator (EAL). Furthermore, the aim of this study was to evaluate if the quality of root canal fillings was dependent on tooth type, number of dental visits and if there was any different in treatment procedure before and during the Covid-19 pandemic. Additionally, signs of healing were evaluated if radiographs were available.  Material and method: Patient journal and intraoral radiographs of 635 patients who had undergone endodontic treatment by students at the Faculty of Odontology at University of Malmö during 2016–2021 were evaluated. A total number of 350 patients fulfilled the inclusion’s criteria. Patient’s journal and radiographs were reviewed by two independent observers.  Results: Of 350 teeth, in 262 teeth working length radiograph and obturation radiograph was consistent with the working length determined by EAL. Mandibular morals followed by maxillary molars and premolars were tooth types that failed to keep WL measured by EAL. Approximately 70% teeth were treated between 2-6 visits. In 84 cases radiographs were available and signs of healing were observed in 78 cases (approx. 92%). No significant differences were observed in treatment procedure before and under the Covid-19 pandemic.   Conclusion: The root canal fillings were of good quality based on clinical and radiographic evidence. Students need more time to carry out endodontic treatment but, in most cases, root canal fillings were of good quality and periapical healing was obtained. Furthermore, the students need clearer recommendations regarding determination of WL.