Introduction: Root resorption is an undesired but frequent side effect of orthodontic treatment. Several studies have already aimed to evaluate the performance of CBCT on this topic. However, none have addressed the peculiarities of the most common daily orthodontic scenario. The aim of the study was to evaluate the influence of CBCT scans on the diagnosis of artificial external root resorption in the apical third of anterior teeth. Materials and methods: One hundred extracted human anterior teeth were randomly assigned to 2 uneven groups (51 as the control and 49 as the experimental group). A limited area of the apical third of the root of the teeth of the experimental group was selected and a buffer solution was used to induce tooth subsurface demineralization. Before CBCT image acquisition, each tooth was coated with an approximately 0.3 mm thick layer of utility wax to simulate the radiographic appearance of the periodontal space and placed into an empty mandibular anterior socket of a partially edentulous dry human mandible. The mandible was placed into a polystyrene box filled with water prior to the CBCT examination to simulate soft-tissue attenuation and scattering. The CBCT images were obtained on an i-CAT unit (i-CAT Next Generation, Imaging Sciences International, Hatfield, PA) according to three protocols: (I) half scan (180°), 0.40 mm voxel size; (II) full scan (360°), 0.40 mm voxel size; and (III) full scan (360°), 0.125 mm voxel size. The 300 resultant CBCT DICOM volumes were imported into InVivo software (InVivo5, Anatomage, San Jose, CA) for evaluation by three blinded, previously calibrated observers using a five-point confidence rating scale. Cohen’s kappa was used to calculate observers’ agreement. The diagnostic values of sensitivity (Sn), specificity (Sp) and accuracy (Ac) were performed by pooling observer responses for every image modality. Receiver operating characteristic (ROC) were built and the areas under the curve (AUC) were calculated. The Sn, Sp and Ac values were compared by Cochran’s Q test. The AUC values were compared by Mann-Whitney U test. Results: The observers’ agreement ranged from 0.63 to 0.71, which was interpreted as a substantial agreement. Protocol III (0.125 mm voxel size) displayed the highest Sn (81.63 %), Ac (80.67%) and AUC (0.807). There were statistically significant differences between protocol III and the other two protocols (p < 0.001). The specificity of protocol I (84.97 %) was greater than that of protocols II (69.93 %) and III (79.74 %); however statistically significant difference was only found between protocols I and II (p = 0.005). Conclusion: Although there was no difference in accuracy between the degrees of rotation (half and full scan) within the same voxel size (0.4 mm), there was a considerable difference between those and the smallest voxel size (0.125 mm). In fact, it may be suggested that a more dedicated, high resolution scan should be acquired when one intends to investigate the early stage of external root resorption during orthodontic treatment.

Les protocoles de traitement du cancer par Radiothérapie Conformationnelle par Modulation d'Intensité (RCMI) ciblent avec une précision de plus en plus grande la tumeur. Pour cela, ils nécessitent des informations anatomiques précises du patient juste avant le traitement, qui peuvent d'être obtenues à l'aide de systèmes d'imagerie embarqués sur l'accélérateur linéaire médical délivrant le faisceau de traitement. Ces systèmes, composés d'un tube à rayons X et d'un détecteur 2D planaire, sont appelés kV-Cone Beam CT (kV-CBCT). Aujourd'hui, leur usage est très fortement répandu dans le cadre des traitements par RCMI. Cependant, ces examens kV-CBCT sont responsables d'une dose de rayonnements ionisants additionnelle qui est loin d'être négligeable et pouvant d'être à l'origine de l'apparition d'effets secondaires, tels que des cancers radio-induits chez les patients traités. Au cours de cette thèse, un simulateur basé sur la méthode de Monte-Carlo a été développé permettant ainsi d'estimer avec précision les doses délivrées aux organes lors des examens d'imagerie kV-CBCT. Cet outil a ensuite été utilisé afin d'étudier différentes stratégies de prise en compte clinique de ces doses additionnelles. L'étude présentée dans ce manuscrit propose notamment une méthode rapide d'estimation des niveaux de doses délivrés aux organes prenant en compte la morphologie de chaque patient. Cette stratégie a été développée à partir d'une cohorte de 50 patients incluant 40 enfants et 10 adultes. Ces travaux ont été réalisés en collaboration avec l'unité de physique médicale du Centre Eugène Marquis à Rennes qui a fourni les données cliniques nécessaires à l'étude. / Protocols for cancer treatment using intensity-modulated radiation therapy (IMRT) allow to target the tumor with an increased precision. They require accurate anatomical information of the patient just before the treatment, which can be obtained using on-board imaging systems mounted on the medical linear accelerator delivering the treatment beam. These systems, composed of an X-ray tube and a 2D planar detector, are called kV-Cone Beam CT (kV-CBCT). Nowadays, they are widely used in the context of IMRT treatments. However, these kV-CBCT examinations are also responsible for an additional dose of ionizing radiations which is far to be negligible and could be the cause for secondary effects, such as radiation-induced second cancers for treated patients. During this PhD work, a simulator based on the Monte Carlo method was developed in order to calculate accurately the doses delivered to organs during kV-CBCT examinations. Then, this tool was used to study several strategies to take in account for the imaging additional doses in clinical environment. The study reported here includes, in particular, a fast and personalized method to estimate the doses delivered to organs. This strategy was developed using a cohort of 50 patients including 40 children and 10 adults. This work has been done in collaboration with the medical physics unit of the Eugène Marquis medical center in Rennes, which has collected the clinical data used for this study.

De nombreux descripteurs sont utilisés pour décrire les composites tissés. Cela est dû en partie aux différents usages que l’on peut en faire. Par exemple, le descripteur le plus approprié pour une simulation mécanique (par exemple, un maillage d’éléments finis), n’est pas nécessairement le même que pour un algorithme de contrôle non destructif (par exemple, des descripteurs statistiques issus d’images tomographiques). Cette recherche propose de reconnaître que, malgré les nombreuses formes que peuvent prendre ces descripteurs textiles, le composite tissé 3D qui nous intéresse est intrinsèquement structuré. En fait, il est principalement défini par son motif de tissage 3D (arrangement des torons). Cette caractéristique commune à tous les descripteurs peut être exploitée pour “construire des liens” entre les nombreuses analyses différentes. Ceux-ci peuvent être obtenus à travers de la Corrélation d’Images Volumiques (DVC), qui fournit le champ de déplacement reliant toute paire de descripteurs. Les avantages de la DVC sont démultipliés en permettant la “relaxation” de l’hypothèse fondamentale de la conservation des coefficients d’absorption (le contraste tomographique), et l’utilisation d’une technique de régularisation mécanique “complète”. Cela se traduit par un algorithme de recalage robuste et rapide. Il permet de mesurer les “différences métriques” (déformations et distorsions du toron) et d’identifier les “différences topologiques” possibles (par exemple, les anomalies de tissage) qu’un textile peut connaitre. En somme, ce nouvel “cadre de corrélation” permets l’unification des descripteurs textiles dans un seul descripteur topologique. Divers échantillons tissés observés à l’échelle méso ont été étudiés dans ce contexte. / Many descriptors are employed for describing the woven composites. This is, in part, due to the different uses one may give them. For example, the most appropriate descriptor for a mechanical simulation (e.g., a finite element mesh), may not necessarily be the same as for a nondestructive testing algorithm (e.g., statistical descriptors issued from tomographic images). This research proposes to acknowledge that, despite the many forms that these textile descriptors may take, the 3D woven composite tat interests us is intrinsically structured. In fact, it is mainly defined by its 3D weaving pattern (arrangement of yarns). This common characteristic to all descriptors can be exploited to “construct bridges” between the many different analyses. These can be obtained by means of Digital Volume Correlation (DVC), which provides the displacement field relating any pair of descriptors. It should be noted that the advantages of DVC are multiplied by allowing for the “relaxation” of the fundamental assumption of conservation of absorption coefficients (i.e., the tomographic contrast), and the use of a “complete” mechanical regularization technique. This results in a robust and fast registration algorithm. It allows measuring the “metric differences” (yarn deformations and distortions) as well as identifying the possible “topological differences” (e.g., weaving anomalies) that a textile may undergo. In short, this new “correlation framework” allows the unification of the textile descriptors into a single topological descriptor. Various woven samples observed at the meso-scale were studied in this context.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第22316号 / 医博第4557号 / 新制||医||1040(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 溝脇 尚志, 教授 松田 秀一, 教授 安達 泰治 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第22328号 / 医博第4569号 / 新制||医||1041(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 大森 孝一, 教授 椛島 健治, 教授 松田 秀一 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

X-ray computed tomography presents and ultimate for non-destructive investigation of objects. Under normal circumstances is the object placed on stage and the temperature of the object is defined by ambient air. However there are also cases when observation at freezing or high temperatures is needed to reveal thermal stability of observed object. Naturally the size of used tomography equipment and the object just like form of cooling or heating are subjected to final design. This work provides a summary of used methods for temperature controlled tomography. Furthermore handles about design of cooling chamber capable to reach -40°C by preserving relative high X-ray transparency. As an addition that showed up as a response to additional requirements is here presented a heating chamber, in which the object can be maintained at 80°C . All test and scans were carried out on GE phoenix v|tome|x L240 industrial computed tomography scanner.

Articular cartilage is a highly organized, anisotropic tissue lining the ends of bones within synovial joints. Composed primarily of water, collagens, proteoglycans and chondrocytes which synergistically give rise to the tissue's mechanical and tribological properties. Fluid pressurization and resistance to fluid flow within the porous extracellular matrix of cartilage, coupled with the low hydraulic permeability of the tissue endow the tissue with a viscoelastic response to loading and aid to reduce the coefficient of friction between articulating surfaces, with the pressurized fluid supporting 95% of applied loads. Experiencing millions of articulations throughout an average lifetime, articular cartilage possesses distinct biotribological properties. These require effective lubrication, mediated by the synergistic interaction between fluid and boundary lubricants, to provide a low coefficient of friction and prevent wear at the cartilage surface. Osteoarthritis is the progressive deterioration of articular cartilage and synovial joint structure and function, leading to softer and wear prone tissue on account of altered biochemical composition of the extracellular matrix. Plain radiography remains the most accessible tool and the current standard of care to visualize musculoskeletal diseases and injuries (e.g., osteoarthritis), but cannot directly visualize soft tissues or cartilage, and diagnoses are based solely on boney changes, which occur in the later stages of the disease. Coupled with no way to quantitatively assess tissue health prior to irreversible deterioration, there remains no cure for osteoarthritis. Integral to OA pathology are concomitant changes in the biochemical composition of synovial fluid that result in deterioration of rheological properties, contributing to increased cartilage wear. To address both the lack of quantitative diagnosis methods and lack of chondroprotective therapies, this dissertation presents a dual faceted approach to quantitatively image articular cartilage health, coupled with lubrication strategies to improve cartilage lubrication, and preserve cartilage tissue. This dissertation describes the synthesis of tantalum oxide nanoparticles of varying surface charges for use as contrast agents for rapid, minimally invasive, non-destructive, and quantitative contrast-enhanced computed tomography to assess both the biochemical content and biomechanical integrity of articular cartilage. Ex vivo contrast enhanced computed tomography attenuation using the nanoparticle contrast agent reveals correlations between attenuation and the mechanical and biochemical properties of the tissue. The lubrication strategy described within this dissertation involves introducing a rolling ball element between two surfaces to reduce friction. In this strategy, either single, globular macromolecules or nanoparticles are employed as ball bearings between articulating surfaces to reduce friction when asperities on the surfaces are in direct contact. Rheological characterization and construction of classical Stribeck curves using the lubricant formulations reveal that introducing the rolling element reduces the coefficient of friction during boundary lubrication, while leaving the rheological properties of the base fluid intact. Ex vivo cartilage mechanical testing involving shear deformation under varying speeds and loads reveal improved biotribological performance compared to pure synovial fluid or saline.

A large proportion of dogs undergoing computed tomography are anaesthetised and receive concurrent supplementary oxygen. Both factors promote the development of pulmonary atelectasis, which may mask or mimic lung pathology and compromise image quality, which is of concern to the radiologist. The aim of the study was firstly to determine whether significant atelectasis would develop using a commonly employed anaesthetic protocol in a typical hospital setting, especially where dogs may have been anaesthetised in lateral recumbency prior to scanning. Secondly, to determine whether a change in body position to sternal recumbency would be sufficient to resolve atelectasis. Six healthy adult Beagles were anaesthetised in sternal recumbency and using a breath-hold technique, baseline helical transverse thoracic images were acquired. Dogs were then placed in either right or left lateral recumbency for 30 minutes, with scans performed at predetermined lung lobe locations and time intervals. Dogs were then repositioned in sternal recumbency for a further 20 minutes, with similar scans performed. The study was repeated two weeks later in the opposite lateral recumbency. Changes in Hounsfield units and cross-sectional area of all lung lobes were measured. Lateral recumbency did not result in true atelectasis in healthy Beagles of normal body condition. Infrequently, patchy increased attenuation, which failed to resolve completely during sternal recumbency, was visualised in the left cranial lobe during left lateral recumbency. The degree of attenuation changes in healthy Beagles was minimal, and thus if dogs were anaesthetised in lateral recumbency prior to computed tomography, this should not preclude scanning. / Dissertation (MMedVet)--University of Pretoria, 2016. / Companion Animal Clinical Studies / MMedVet / Unrestricted

Thesis (MSc (Radiography))--Cape Peninsula University of Technology, 2019 / Introduction: Traumatic brain injury (TBI) is frequently associated with mortality and morbidity in low-income countries. Computed Tomography Brain (CTB) imaging aid in the management of patients by accurately exploring primary and secondary brain injuries following trauma. However, there is controversy among researchers on the benefits of follow-up CTB imaging (FCTBI) amongst patients presenting with TBI showing a normal baseline scan. As such, in an attempt to address the contention, the primary focus of this research study was to explore the role of FCTBI with regards to the clinical status of such patients. The secondary focus was to determine the timing of performing FCTBI post TBI. Method: A retrospective cross sectional quantitative design was conducted for this research study. A total sampling strategy was employed on medical records of 85 patients treated at the research site in Zimbabwe. Data were collected over a two year period. Adult patients between the ages of 18 and 75, with TBI and who had a normal first CTBI1 (primary scan done upon hospital admission) were included in this research study. The evolution of different types of brain pathology diagnosed on FCTBI in affected patients were recorded on data collection sheets. An analysis then followed to establish whether the sample patients had developed any neurological complications. Results: The study showed that in 85 patients with TBI, 36% recorded abnormal radiological findings on FCTBI with subdural haematoma (19%) being the most common intracranial lesion followed by intracerebral haemorrhage (8%), subarachnoid haemorrhage (6%) and lastly, pneumocephalus and epidural haematoma (1% respectively). The most frequent causal mechanism of trauma was road traffic accidents (RTAs) at 58%. Males with TBI comprised a higher proportion (53%) than did females (47%). The performance of CTBI1 at 8 hours post trauma occurrence, within a recommended hospital observation period of 20 hours post trauma occurrence, may provide sufficient time for lesions to evolve and thus determine the appropriate patient management. The young adult age group of 26-35 years was found to be more susceptible to TBI. Conclusion: FCTBI was found to be of value in timely detection of evolving intracranial lesions which enabled appropriate management of patients. The current study recommends that patients who exhibit a declining Glasgow Coma Scale (GCS) score and deteriorating neurological status undergo a FCTBI.

Introduction: Magnetic resonance (MR) represents still the gold standard in myocardial imaging. There are some studies suggesting that the computed tomography (CT) might be a valid alternative for some patients (especially the ones who are unable to undergo MR). Aims: We had two aims. Aim number 1: To evaluate the ability of CT in the evaluation of delayed contrast enhancement (DCE) in patients with dilated cardiomyopathy. Aim number 2: To assess the possibilities of CT originally performed for a different indication in myocardial tissue characterization. Methods: Part 1: We prospectively enrolled 17 patients with dilated cardiomyopathy. All the patients underwent both cardiac CT and cardiac MR. We compared the findings of DCE on CT with the findings of DCE on MR. Part 2: We retrospectively evaluated 96 patients who underwent both CT for any indication and cardiac MR. We compared the findings of a hypodense area in the myocardium with the findings of DCE on MR. Results: Part 1: CT detected DCE in 3 patients and MR detected DCE in 6 patients. The agreement between both modalities was in v 82% cases (kappa 0.56). The sensitivity and specificity of CT were 50% and 100%, respectively and the positive predictive value was 100%. In patients with positive findings on CT, the localization of DCE was almost...