Modern medical imaging devices are able to generate highly detailed three-dimensional (3D) images of the skeleton. Computerized image processing and analysis methods, combined with real-time volume visualization techniques, can greatly facilitate the interpretation of such images and are increasingly used in surgical planning to aid reconstruction of the skeleton after trauma or disease. Two key challenges are to accurately separate (segment) bone structures or cavities of interest from the rest of the image and to interact with the 3D data in an efficient way. This thesis presents efficient and precise interactive methods for segmenting, visualizing, and analysing 3D computed tomography (CT) images of the skeleton. The methods are validated on real CT datasets and are primarily intended to support planning and evaluation of cranio-maxillofacial (CMF) and orthopedic surgery. Two interactive methods for segmenting the orbit (eye-socket) are introduced. The first method implements a deformable model that is guided and fitted to the orbit via haptic 3D interaction, whereas the second method implements a user-steered volumetric brush that uses distance and gradient information to find exact object boundaries. The thesis also presents a semi-automatic method for measuring 3D angulation changes in wrist fractures. The fractured bone is extracted with interactive mesh segmentation, and the angulation is determined with a technique based on surface registration and RANSAC. Lastly, the thesis presents an interactive and intuitive tool for segmenting individual bones and bone fragments. This type of segmentation is essential for virtual surgery planning, but takes several hours to perform with conventional manual methods. The presented tool combines GPU-accelerated random walks segmentation with direct volume rendering and interactive 3D texture painting to enable quick marking and separation of bone structures. It enables the user to produce an accurate segmentation within a few minutes, thereby removing a major bottleneck in the planning procedure.

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AIM: Extraction of a tooth can lead to alveolar ridge resorption which can be minimized by socket preservation. The aim of this study is to analyze vertical and horizontal alveolar ridge dimensions clinically and by CBCT immediately following extraction and 3-4 months following socket preservation. METHODS: The preserved group (P) consisted of 20 patients with1-2 non-molar teeth requiring extraction with socket preservation, while the control group (C) consisted of 5 patients requiring extraction alone. An acrylic stent was fabricated presurgically in order to measure vertical and horizontal ridge dimensions clinically and radiographically immediately following extraction and 3-4 months following socket preservation. RESULTS: Overall, P sites gained ridge height and lost minimal ridge width over 3-4 months, while C sites lost both ridge height and width. Preserved sites in which the teeth were extracted due to caries had the most significant gain in the radiographic vertical occlusal dimension (RVO). Overall, high correlations were found between the clinical and radiographic measurements at the initial surgery and at the 3-4 month follow up. CONCLUSIONS: The preserved group had minimal ridge resorption and more socket bony fill when compared to the non-preserved group 3-4 months following tooth extraction, especially when the tooth was extracted due to caries. Additionally, the CBCT can be a useful diagnostic tool to evaluate socket preservation healing, as it compares well to clinical assessments of socket healing.

BACKGROUND: The use of three-dimensional imaging has shown to provide advantages to the clinician in assessing bone morphology. The aim of this study will be to compare the diagnostic efficacy of cone beam computed tomography (CBCT) versus diagnostic clinical measurements in patients presenting with furcation involved maxillary first molars. METHODS: The study population included 20 patients with 34 maxillary first molar teeth with furcation involvement. Clinical horizontal and vertical probing measurements were compared to CBCT measurements taken by two calibrated examiners. RESULTS: Horizontal measurements showed a significant difference between Glickman class II and class III. There were no statistical significant differences with the horizontal measurements between clinical probing, bone sounding and CBCT measurements. CBCT vertical measurements were statistically greater than clinical probing measurements. CONCLUSION: The CBCT can provide similar horizontal measurements to standard clinical horizontal probing measurements and will provide a greater vertical dimension of a furcation defect to standard vertical probing measurements.

Accurate and automatic segmentation techniques that do not require any explicit prior model have been of high interest in the medical community. We propose a fully-automatic method for segmenting the femur from 3D Computed Tomography scans, based on the graph-cut segmentation framework and the bone boundary enhancement filter analyzing second-order local structures. The presented algorithm is evaluated in large-scale experiments, conducted on 197 CT volumes, and compared to other three automatic bone segmentation methods. Out of the four tested approaches, the proposed algorithm achieved most accurate results and segmented the femur correctly in 81% of the cases.

<p>X-ray computed tomography (CT) is a non-invasive medical imaging technique that generates cross-sectional images by acquiring attenuation-based projection measurements at multiple angles. Since its first introduction in the 1970s, substantial technical improvements have led to the expanding use of CT in clinical examinations. CT has become an indispensable imaging modality for the diagnosis of a wide array of diseases in both pediatric and adult populations [1, 2]. Currently, approximately 272 million CT examinations are performed annually worldwide, with nearly 85 million of these in the United States alone [3]. Although this trend has decelerated in recent years, CT usage is still expected to increase mainly due to advanced technologies such as multi-energy [4], photon counting [5], and cone-beam CT [6].</p><p>Despite the significant clinical benefits, concerns have been raised regarding the population-based radiation dose associated with CT examinations [7]. From 1980 to 2006, the effective dose from medical diagnostic procedures rose six-fold, with CT contributing to almost half of the total dose from medical exposure [8]. For each patient, the risk associated with a single CT examination is likely to be minimal. However, the relatively large population-based radiation level has led to enormous efforts among the community to manage and optimize the CT dose.</p><p>As promoted by the international campaigns Image Gently and Image Wisely, exposure to CT radiation should be appropriate and safe [9, 10]. It is thus a responsibility to optimize the amount of radiation dose for CT examinations. The key for dose optimization is to determine the minimum amount of radiation dose that achieves the targeted image quality [11]. Based on such principle, dose optimization would significantly benefit from effective metrics to characterize radiation dose and image quality for a CT exam. Moreover, if accurate predictions of the radiation dose and image quality were possible before the initiation of the exam, it would be feasible to personalize it by adjusting the scanning parameters to achieve a desired level of image quality. The purpose of this thesis is to design and validate models to quantify patient-specific radiation dose prospectively and task-based image quality. The dual aim of the study is to implement the theoretical models into clinical practice by developing an organ-based dose monitoring system and an image-based noise addition software for protocol optimization. </p><p>More specifically, Chapter 3 aims to develop an organ dose-prediction method for CT examinations of the body under constant tube current condition. The study effectively modeled the anatomical diversity and complexity using a large number of patient models with representative age, size, and gender distribution. The dependence of organ dose coefficients on patient size and scanner models was further evaluated. Distinct from prior work, these studies use the largest number of patient models to date with representative age, weight percentile, and body mass index (BMI) range.</p><p>With effective quantification of organ dose under constant tube current condition, Chapter 4 aims to extend the organ dose prediction system to tube current modulated (TCM) CT examinations. The prediction, applied to chest and abdominopelvic exams, was achieved by combining a convolution-based estimation technique that quantifies the radiation field, a TCM scheme that emulates modulation profiles from major CT vendors, and a library of computational phantoms with representative sizes, ages, and genders. The prospective quantification model is validated by comparing the predicted organ dose with the dose estimated based on Monte Carlo simulations with TCM function explicitly modeled. </p><p>Chapter 5 aims to implement the organ dose-estimation framework in clinical practice to develop an organ dose-monitoring program based on a commercial software (Dose Watch, GE Healthcare, Waukesha, WI). In the first phase of the study we focused on body CT examinations, and so the patient’s major body landmark information was extracted from the patient scout image in order to match clinical patients against a computational phantom in the library. The organ dose coefficients were estimated based on CT protocol and patient size as reported in Chapter 3. The exam CTDIvol, DLP, and TCM profiles were extracted and used to quantify the radiation field using the convolution technique proposed in Chapter 4. </p><p>With effective methods to predict and monitor organ dose, Chapters 6 aims to develop and validate improved measurement techniques for image quality assessment. Chapter 6 outlines the method that was developed to assess and predict quantum noise in clinical body CT images. Compared with previous phantom-based studies, this study accurately assessed the quantum noise in clinical images and further validated the correspondence between phantom-based measurements and the expected clinical image quality as a function of patient size and scanner attributes. </p><p>Chapter 7 aims to develop a practical strategy to generate hybrid CT images and assess the impact of dose reduction on diagnostic confidence for the diagnosis of acute pancreatitis. The general strategy is (1) to simulate synthetic CT images at multiple reduced-dose levels from clinical datasets using an image-based noise addition technique; (2) to develop quantitative and observer-based methods to validate the realism of simulated low-dose images; (3) to perform multi-reader observer studies on the low-dose image series to assess the impact of dose reduction on the diagnostic confidence for multiple diagnostic tasks; and (4) to determine the dose operating point for clinical CT examinations based on the minimum diagnostic performance to achieve protocol optimization. </p><p>Chapter 8 concludes the thesis with a summary of accomplished work and a discussion about future research.</p> / Dissertation

A short report submitted to the Faculty of Medicine, University of the Witwatersrand in partial fulfilment of the requirements for the degree of Master of Medicine in Nuclear Medicine / 19 patients were selected, from the patients screened, for investigation within 48 hours of the onset of an ischaemic cerebrovascular accident. Clinical neurulogical scoring, computerized tomography lCT) scans and single photon emission computed tomography (SPECT) scans were performed on day 1, day 10 and day 30. SPECT scan data was analysed by 5 semi-quantitative methods, and findings were compared with neuroloyical clinical scores on each respective day. It was found that day 1 SPECT scans are of value for early localization of the acute ischaemic infarction. A multiple regression model was developed using both the day 30 Defect Volume index and segmental analysis score which related to the day 30 clinical scores. The day 1 model was unsatisfactory and no such model was found relating day 10 SPECT semi-quantitative methods to day 10 clinical scoring. Changes in semi-quantitative scores from day 1 to day 30 did not correlate with clinical changes. Longer follow up may be required for there to be value in performing SPECT scans in stroke trials. A prognostic equation was derived by multiple regression analysis of day 1 SPECT scan scores and day 30 clinical scores. / Andrew Chakane 2019

M.Med. (Radiology), Faculty of Health Sciences, University of the Witwatersrand, 2011 / Lymphobronchial tuberculosis (LBTB) is tuberculous lymphadenopathy involving the airways, which is particularly common in children. AIM: To describe the CT findings of LBTB in children, the parenchymal complications and associated abnormalities. METHOD: CT scans of 98 children with LBTB were retrospectively reviewed. Lymphadenopathy, bronchial narrowing, parenchymal complications and associations were documented. RESULTS: Infants comprised 51% of patients. The commonest lymphadenopathy was subcarinal (97% of patients). Bronchial compressions (259 in total) were present in all patients, of which 23% were severe / complete stenoses and 28% affected bronchus intermedius. Parenchymal complications were present in 94% of patients, including consolidation (88%), breakdown (42%), air trapping (38%), expansile pneumonia (28%), collapse (17%) and bronchiectasis (9%), all predominantly right-sided (63%). Associations included oval focal bodies, miliary nodules, pleural disease and intracavitory bodies. CONCLUSIONS: The most important CT finding of children with LBTB is visible airway compression as a result of lymphadenopathy. CT of children with LBTB showed that airway compressions were more severe in infants and most commonly involved bronchus intermedius. Numerous parenchymal complications were documented, all showing rightsided predominance. Several associations were identified.

Desde a invenção da tomografia computadorizada (CT) nos anos 70, toda década trouxe novas tecnologias para esta modalidade. Com estes avanços, também surgiu a necessidade de novas e melhores técnicas de avaliação de desempenho e segurança dos equipamentos de CT. Hoje, o controle de qualidade de equipamentos de CT é, em grande parte, feito manualmente. Portanto, é lento e, em parte, subjetivo. Neste trabalho, um software foi escrito em MatLab® para processar imagens do phantom de CT Catphan500®, aperfeiçoando a rotina do programa de controle de qualidade de CT. Com pouca interferência do usuário, o software mede a espessura de corte, incremento entre cortes e tamanho de pixel, avalia a linearidade do número CT, estima a Função Transferência de Modulação (MTF), o ruído e o Espectro de Potência do Ruído (NPS). Para a validação do software, conjuntos de imagens do phantom foram obtidas em 10 equipamentos de CT diferentes, com 27 protocolos diferentes. Cada conjunto foi analisado pelo software, e os resultados obtidos foram comparados aos resultados previamente obtidos pela rotina normal do programa controle de qualidade. Para essa comparação, dois testes de hipótese foram empregados: o teste t de Student (para os valores de espessura de corte, incremento entre cortes, tamanho de pixel e os coeficientes da avaliação de linearidade do número CT, adotando um valor-p de 0,01) e o teste F de Fisher (para o ruído, valor-p de 0,05). As funções MTF e NPS atualmente não são medidas na rotina do controle de qualidade, portanto não há resultado prévio para fazer esta comparação. Ao invés disso, o NPS foi ajustado em função da MTF (através da relação teórica que há entre os dois) e a qualidade do ajuste foi avaliada pelo teste de qui-quadrado. Dos 101 valores de t e 25 valores de F calculados, 2 e 1 respectivamente estavam fora do intervalo de aceitação. Este resultado está de acordo com os valores-p escolhidos e, portanto, os resultados obtidos pelo software estão de acordo com os resultados da rotina de controle de qualidade convencional. Os ajustes de NPS e MTF obtiveram incertezas grandes nos parâmetros de ajuste (incertezas da mesma ordem de grandeza dos próprios parâmetros). Porém, a avaliação do qui-quadrado reduzido indica que os ajustes foram aceitáveis (com exceção de um, que mostrou uma anomalia no NPS medido e foi desconsiderado). Portanto, o NPS e MTF obtidos estão de acordo com a expectativa teórica. / Since the introduction of the CT scanner as a diagnostic imaging modality, the scientific community has seen new and more complex CT technologies. These improvements brought the need for new and improved techniques to evaluate the safety and performance of these scanners. Nowadays, the interpretation of images generated during the implementation of CT quality control procedures are done visually in much of the cases. Therefore, it is slow and partially subjective. In this work, a software was written in MatLab to process images of the Catphan500 CT phantom, in order to improve the CT quality control workflow and its accuracy. The software evaluate the slice thickness, slice increment, and pixel size, calculates the CT number linearity, and assesses the Modulation Transfer Function (MTF), the noise and the Noise Power Spectrum (NPS). Image sets of the phantom were obtained from 10 different scanners using 27 different protocols in order to validate the software. Comparative results correlating the software output and corresponding data previously obtained by the current quality control program routine were used to conduct this validation. For this comparison, two statistical tests were employed: the Students t-test (for slice thickness, slice increment, pixel size, and the coefficients of the CT number linearity evaluation, with a chosen p-value of 0.01) and the Fisher F-test (for the noise, with chosen p-value of 0.05).The functions MTF and NPS are not currently measured by the quality control routine, so there was no previous result for comparison. Instead, the NPS was fitted as a function of the MTF (using the theoretical relationship between both functions) and the quality of the fit was evaluated using the reduced chi-square. From 101 t values and 25 F values calculated, 2 and 1 were outside the acceptance interval, respectively. This result agrees with the chosen p-values, and therefore the software results are in good agreement with the traditional quality control routine results. The fits of NPS and MTF presented large uncertainties in the fitting parameters (uncertainties of the same order of magnitude as the parameters themselves). However, the reduced chi-square evaluation indicates a good fit (with the exception of one fit, which showed an anomaly on the measured NPS and was unconsidered). Therefore, the obtained MTF and NPS were in agreement with the theoretical expectations.

Esta pesquisa foi realizada para verificar se o padrão morfogenético da base craniana é determinante das dimensões transversais da maxila e mandíbula e se tal influência também se estende à porção alveolar das bases apicais. Complementarmente buscou-se avaliar as inclinações vestíbulo-linguais dos dentes posteriores com intuito de verificar se tais inclinações são padronizadas, independente das larguras das bases alveolares, ou se existem variações significativas. A amostra foi composta por 30 indivíduos adultos jovens, brasileiros, leucodermas com perfis faciais equilibrados e neutro-oclusão. Dividiu-se em dois grupos de acordo com a dimensão transversal da base anterior do crânio, definida pela distância entre os pontos esfenóide direito e esquerdo, sendo o grupo G1 composto pelos indivíduos apresentando valores menores que a mediana, e o grupo G2 com indivíduos apresentando valores maiores ou iguais a mediana. Foi realizada correlação intraclasse para avaliar o erro do método; média, mediana e desvio padrão para descrever o grupo amostral; teste t-Student para comparar os grupos G1 e G2; teste exato de Fischer para avaliar associação entre base do crânio e gêneros e Teste de Correlação Linear de Pearson. As medidas apresentaram alta reprodutibilidade. Indivíduos do grupo G2 apresentaram maior largura de mandíbula e maior espessura alveolar dos primeiros molares e primeiros pré-molares superiores. Não houve associação entre largura de base do crânio e gêneros. A largura basal da mandíbula apresentou correlação estatisticamente significante com a largura da base do crânio, assim como a largura alveolar maxilar na região de prémolares e molares superiores em relação à largura basal da maxila. As conclusões foram: a largura da base craniana apresenta correlação com a largura da mandíbula; a largura da maxila varia em consonância com a largura da mandíbula; a largura alveolar da maxila na região de primeiros pré-molares e molares superiores apresenta correlação com largura basal da maxila; a largura basal mandibular apresenta correlação com a largura alveolar da mandíbula na região dos primeiros pré-molares; as inclinações vestíbulo-linguais dos primeiros molares e primeiros prémolares são constantes, independentes das larguras basais e alveolares de suas respectivas bases ósseas. / This research intended to check if the morphogenetic pattern of cranial base determines transverse dimensions of upper and lower face and if it extends to alveolar portion basis. In addition evaluated buccal-lingual inclinations of posterior teeth to examine if they are standardized, regardless of the widths of the alveolar bases, or whether there are significant variations. The sample comprised 30 young adults, Caucasian Brazilian facial profiles with balanced and neutral occlusion. Divided into two groups according to the transverse dimension of the anterior skull base, defined by the distance between right and left sphenoid´s points, the G1 made of individuals with lower values than the median, and G2 with individuals with values greater or equal to median. Intraclass correlation was performed to evaluate the method error, mean, median and standard deviation to describe the sample group, Student t test to compare the groups G1 and G2, Fisher exact test to access the relation between skull base and genres and Test Linear correlation of Pearson. Measurements showed high reproducibility. G2 individuals showed greater mandible width and greater thickness of alveolar bone on upper first molars and first premolars. There was no association between width of skull base and genres. The width of the mandible showed a statistically significant correlation with the width of the skull base and maxillary alveolar width in premolars and molars in relation to basal width of jaw. Conclusions: the width of cranial base is correlated with width of jaw; jaw width varies in line with jaw width and width of maxillary alveolar region of first premolars and molars is correlated with basal width jaw, the basal mandibular width correlates with width of jaw in alveolar region first premolars; the buccolingual inclinations of the first molars and first premolars are constant, independent of basal width and alveolar bone of their respective bases.