Accounting for respiration motion during imaging helps improve targeting precision in radiation therapy. Respiratory motion can be a major source of error in determining the position of thoracic and upper abdominal tumor targets during radiotherapy. Thus, extracting respiratory motion is a key task in radiation therapy planning. Respiration-correlated or four-dimensional CT (4DCT) imaging techniques have been recently integrated into imaging systems for verifying tumor position during treatment and managing respiration-induced tissue motion. The quality of the 4D reconstructed volumes is highly affected by the respiratory signal extracted and the phase sorting method used. This thesis is divided into two parts. In the first part, two image-based respiratory signal extraction methods are proposed and evaluated. Those methods are able to extract the respiratory signals from CBCT images without using external sources, implanted markers or even dependence on any structure in the images such as the diaphragm. The first method, called Local Intensity Feature Tracking (LIFT), extracts the respiratory signal depending on feature points extracted and tracked through the sequence of projections. The second method, called Intensity Flow Dimensionality Reduction (IFDR), detects the respiration signal by computing the optical flow motion of every pixel in each pair of adjacent projections. Then, the motion variance in the optical flow dataset is extracted using linear and non-linear dimensionality reduction techniques to represent a respiratory signal. Experiments conducted on clinical datasets showed that the respiratory signal was successfully extracted using both proposed methods and it correlates well with standard respiratory signals such as diaphragm position and the internal markers’ signal. In the second part of this thesis, 4D-CBCT reconstruction based on different phase sorting techniques is studied. The quality of the 4D reconstructed images is evaluated and compared for different phase sorting methods such as internal markers, external markers and image-based methods (LIFT and IFDR). Also, a method for generating additional projections to be used in 4D-CBCT reconstruction is proposed to reduce the artifacts that result when reconstructing from an insufficient number of projections. Experimental results showed that the feasibility of the proposed method in recovering the edges and reducing the streak artifacts.

The purpose of this study was to use existing Cone Beam Computer Tomography images to determine the vertical and horizontal location of the mental foramen in relation to the mandibular first and second premolars, as well as the distance in millimeters from the apex of each. The distance from the inferior border of the foramen to the inferior border of the mandible was also recorded. The average distance from the apices of the mandibular first and second premolars to the mental foramen was 7.43mm (SD= 1.97) and 5.30mm (SD=1.65) respectively. The foramen was located 11.44mm (SD=1.49) from the inferior border of the mandible. The foramen was in line with the apex of the mandibular second premolar 41% of the time. The mental foramen was further away from the inferior border of the mandible in males and older patients. Mental foramina seemed to be positioned more apically and distally in older patients.

The purpose of this study was to assess the changes in size of periapical lesions 3-12 months following root canal treatment using CBCT. Patients who had non-surgical root canal therapy (NSRCT) or non-surgical retreatment (ReTx) from July 30,2014 to August 19, 2015 with a periapical lesion of endodontic origin and received NSRCT or ReTx and had a pre-treatment or intra-treatment CBCT were invited to participate. Volumetric and linear measurements of periapical lesions on initial and post- treatment CBCT images were performed. A total of 20 patients with 23 treated teeth with 30 separate periapical radiolucent lesions returned for follow up 91-390 days after the initiation of endodontic treatment. Lesions showed an overall reduction in volume (p=0.0096), maximum coronal diameter (p=0.0117), maximum sagittal diameter (p=0.0071), and maximum axial diameter (p=0.0006). Lesions show a significant reduction in size 3-12 months following non-surgical endodontic treatment using CBCT.

OBJECTIVES: This retrospective cohort study tested the effect of Rapid Maxillary Expansion (RME) on symmetrical volumetric changes in the nasal cavity. Volumetric changes in overall nasal cavity, nasopharynx, and oropharynx were also assessed as well as minimum cross-sectional width changes and molar angulation in association with RME. METHODS: CBCT scans of before and after RME treatment for 28 subjects (17 females, 11 males, average age 9.85 ± 2.42 years) were collected from a previously de-identified database. All subjects were treated for maxillary constriction using banded hyrax expanders. Mimics software was utilized to segment the nasal and pharyngeal airways and create various compartments (left and right nasal cavity, nasopharynx, and oropharynx) for volumetric analysis. Minimum cross-sectional width measurements and maxillary first molar angulation were also assessed. Paired T-test was used to quantify the changes brought about by expansion. Statistical significance was set at the 0.05 level. RESULTS: Posterior expansion as measured between right and left greater palatine foramen (GPF) averaged 2.41 mm (SD = 1.03 mm). There were statistically significant differences in overall nasal cavity (2249.6 ± 2102.5 mm3), right nasal cavity (968.8 ± 1082.7), left nasal cavity (1197.3 ± 1587.0), nasopharyngeal (1000.6 ± 917.7), and oropharyngeal (2349.2 ± 2520.8) volumes. In comparing the right to left nasal cavity, no significant changes were noted for initial volume, post-expansion volume, or pre to post-expansion changes (T2-T1). For cross-sectional analysis, the right nasal cavity (0.13 ± 0.07 mm) and left nasal cavity (0.11 ± 0.06 mm) showed significant increases in minimum crosssectional width measurements. Initial maxillary molar angulation had no significant correlation to initial nasal cavity volume on either side. CONCLUSIONS: RME has significant benefits to increasing nasal and pharyngeal airway cavity volumes in all segments of the airway. Nasal cavity expands symmetrically. Minimum cross-sectional width of the left and right nasal cavities showed highly symmetrical improvements. Initial maxillary molar angulation has no relationship to initial nasal cavity volume.

Os molares superiores são um dos grupos dentários que mais recebem tratamentos endodônticos e apresentam grande complexidade anatômica nos seus sistemas de canais radiculares. A presença de um canal mesiopalatino (MP) na raiz mesiovestibular é um achado bastante comum e a sua não detecção está relacionada com um alto índice de insucessos na terapia endodôntica. Recentemente, a tomografia computadorizada de feixe cônico (TCFC) vem ganhando destaque na avaliação do canal MP pela sua capacidade de fornecer informações detalhadas e em três dimensões, sendo considerada o melhor método de imagem para essa investigação in vivo. Desta forma, o objetivo desta tese foi pesquisar a prevalência e simetria do número de canais da raiz mesiovestibular em primeiros molares superiores homólogos, por meio da TCFC, assim como, analisar o uso dos filtros de refinamento de imagem para esta investigação. Para o primeiro objetivo, desenvolveu-se uma pesquisa com 264 pacientes possuindo o primeiro molar superior bilateralmente. Foi encontrada simetria em 78,79% dos pacientes, sendo que o canal MP esteve presente bilateralmente em 67,42%. Do total de 528 dentes avaliados, 78% apresentaram o canal MP não havendo correlação da sua presença com sexo e faixa etária (p > 0,05). Para o segundo objetivo, 30 exames de TCFC foram avaliados com cinco diferentes filtros (Original, Smooth, Sharpen, Sharpen Mild, Angio Sharpen Low e Angio Sharpen High) além das imagens originais (sem filtro). Todos os filtros apresentaram altos índices de acurácia (> 83,3%), sensibilidade (> 90%) e especificidade (> 62%), sem diferença estatística (p > 0,05). Entretanto, quando o nível de certeza foi avaliado, os filtros Angio Sharpen High e Sharpen apresentaram os piores resultados, com diferença significativa para as imagens Originais (p <0,05). Os resultados das pesquisas conduzidas permitem concluir que o canal MP é uma condição altamente prevalente e a sua simetria bilateral é frequente. O emprego de filtros de imagem da TCFC não influenciou a detecção do canal MP, entretanto os filtros de maior realce devem ser evitados pois reduzem a certeza do diagnóstico. / The upper molars are the dental group that most receives endodontic treatments and presents great anatomical complexity of their root canal systems. The presence of a second mesiobuccal canal (MB2) is a common finding and its non-detection is related to a high failure rate in endodontic therapy. Recently, cone-beam computed tomography (CBCT) has been highlighted in the MB2 evaluation for its ability to provide detailed and three-dimensional information, and is considered the best imaging method for such investigation in vivo. Thus, the aim of this thesis was to investigate the prevalence and symmetry of the root canal numbers from the mesiobuccal root of first homologous upper molars, as well as to evaluate the use of CBCT image filters for that purpose. For the first objective, a research was developed with 264 patients having the first upper molar bilaterally. Symmetry was found in 78.79% patients, and the MB2 was bilaterally present in 67.42%. Out the total of 528 teeth evaluated, 78% presented the MB2, with no correlation with sex and age group (p > 0.05). For the second objective, 30 CBCT scans were evaluated with five different filters (Original, Smooth, Sharpen, Sharpen Mild, Angio Sharpen Low and Angio Sharpen High) in addition to the original images (none filter). All filters presented high levels of accuracy (> 83.3%), sensitivity (> 90%) and specificity (> 62%), with no statistical difference (p > 0.05). However, when the level of certainty was evaluated, Angio Sharpen High and Sharpen filters presented the worst results, with significant difference for Original images (p < 0.05). The results of the conducted studies allow us to conclude that the MB2 is a highly prevalent condition and its bilateral simmetry is frequent. The use of CBCT image filters did not influence the MB2 detection, however higher enhancement filters should be avoided because they reduce the certainty of the diagnosis.

INTRODUCTION: Utilization of rapid maxillary expansion (RME) is common for the correction of sagittal discrepancies in orthodontic treatment. RME appliances will transmit a compressive force to the periodontal support structures. This resultant force can lead to resorption of the dento-alveolar structures leading to unwanted dental movements. The purpose of this retrospective study was to compare changes from a periodontal and root resorption perspective by means of computer tomography with tooth-borne and bonded expanders. METHODS: The sample comprised of cone beam computed tomography and spiral CT images of 41 subjects, 12 to 17 years old, with unilateral or bilateral posterior crossbites. 20 subjects treated previously with a bonded expander and 21 with a banded expander. Pre and post-treatment images were digitized and landmarks were identified to measure buccal and lingual cortex thickness, alveolar height, root length and angulation by means of a computerized method. RESULTS: RME with banded and bonded expanders have similar effects from periodontal and root resorption perspectives. Changes include increasing thickness of lingual alveolar bone 0.2 to 0.7 mm, decreases in buccal bone width 0.1 to 0.5 mm; and decreases in alveolar height 0.1 to 0.9 mm and root length 0.3 to 1.0mm of each support teeth. CONCLUSIONS: RME with banded and bonded expanders exhibited similar changes post-expansion and these variables should not play a role in selection of the type of device.

L'un des objectifs de l'optimisation de la planification du traitement du cancer de la prostate en radiothérapie est de maintenir les marges ajoutées au volume cible clinique (CTV) aussi réduites que possible pour diminuer les volumes de tissus normaux irradiés. Plusieurs méthodes ont été proposées pour définir ces marges : 1) Les méthodes basées sur l'observation des mouvements obtenue par différents systèmes d'imagerie, 2) Des méthodes prédictives des mouvements des organes: à partir d'un modèle représentant les mouvements des organes pelviens, un calcul d'une marge personnalisée peut être réalisé. Nous avons ainsi développé et optimisé un modèle biomécanique par éléments finis de la prostate, de la vessie et du rectum. Ce modèle décrit le mouvement et la déformation des organes pelviens lors du remplissage de certains organes comme la vessie et le rectum. Une évaluation de ce modèle permettant de prédire les mouvements de la prostate au cours des différentes séances de radiothérapie, est montrée en utilisant une série d'images CBCT (Cone Beam Computerized Tomography).

<p>Cone beam computed tomography (CBCT) is a 3D x-ray imaging technique in which the x-ray beam is transmitted to an object with wide beam geometry producing a 2D image per projection. Due to its faster image acquisition time, wide coverage length per scan, and fewer motion artifacts, the CBCT system is rapidly replacing the conventional CT system and becoming popular in diagnostic and therapeutic radiology. However, there are few studies performed in CBCT dosimetry because of the absence of a standard dosimetric protocol for CBCT. Computed tomography dose index (CTDI), a standardized metric in conventional CT dosimetry, or direct organ dose measurements have been limitedly used in the CBCT dosimetry.</p> <p>This dissertation investigated the CBCT dosimetry from the CTDI method to the organ, effective dose, risk estimations with physical measurements and Monte Carlo (MC) simulations.</p> <p>An On-Board Imager (OBI, Varian Medical Systems, Palo Alto, CA) was used to perform old and new CBCT scan protocols. The new CBCT protocols introduced both partial and full angle scan modes while the old CBCT protocols only used the full angle mode. A metal-oxide-semiconductor-field-effect transistor (MOSFET) and an ion chamber were employed to measure the cone beam CTDI (CTDI_CB) in CT phantoms and organ dose in a 5-year-old pediatric anthropomorphic phantom. Radiochromic film was also employed to measure the axial dose profiles. A point dose method was used in the CTDI estimation.</p> <p>The BEAMnrc/EGSnrc MC system was used to simulate the CBCT scans; the MC model of the OBI x-ray tube was built into the system and validated by measurements characterizing the cone beam quality in the aspects of the x-ray spectrum, half value layer (HVL) and dose profiles for both full-fan and half-fan modes. Using the validated MC model, CTDI_CB, dose profile integral (DPI), cone beam dose length product (DLP_CB), and organ doses were calculated with voxelized MC CT phantoms or anthropomorphic phantoms. Effective dose and radiation risks were estimated from the organ dose results.</p> <p>The CTDI_CB of the old protocols were found to be 84 and 45 mGy for standard dose, head and body protocols. The CTDI_CB of the new protocols were found to be 6.0, 3.2, 29.0, 25.4, 23.8, and 7.7 mGy for the standard dose head, low dose head, high quality head, pelvis, pelvis spotlight, and low dose thorax protocols respectively. The new scan protocols were found to be advantageous in reducing the patient dose while offering acceptable image quality.</p> <p>The mean effective dose (ED) was found to be 37.8 ±0.7 mSv for the standard head and 8.1±0.2 mSv for the low dose head protocols (old) in the 5-year-old phantom. The lifetime attributable risk (LAR) of cancer incidence ranged from 23 to 144 cases per 100,000 exposed persons for the standard-dose mode and from five to 31 cases per 100,000 exposed persons for the low-dose mode. The relative risk (RR) of cancer incidence ranged from 1.003 to 1.054 for the standard-dose mode and from 1.001 to 1.012 for the low-dose mode.</p> <p>The MC method successfully estimated the CTDI_CB, organ and effective dose despite the heavy calculation time. The point dose method was found to be capable of estimating the CBCT dose with reasonable accuracy in the clinical environment.</p> / Dissertation

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