To see the other types of publications on this topic, follow the link: Cone-beam.
Dissertations / Theses on the topic 'Cone-beam'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Cone-beam.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Almada, Levi Rafael Santos. "Cone Beam em endodontia." Master's thesis, [s.n.], 2011. http://hdl.handle.net/10284/2590.
Full textAbstract:
Trabalho apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Medicina DentáriaA imagiologia como uma área de interesse à qual se recorre frequentemente em Medicina Dentária, tem vindo a evoluir muito nos últimos anos apresentando novas tecnologias. A Tomografia Computorizada de Feixe Cónico (CBCT) é uma dessas tecnologias mais recentes, que possibilita a visualização de imagens em três dimensões das estruturas dentárias e das estruturas ósseas adjacentes. Situações como identificação de canais radiculares “anormais” em quantidade e morfologia, detecção de fracturas radiculares verticais, avaliação do processo de recuperação pós tratamento, poderão ser melhor e mais facilmente identificadas e tratadas com esta nova opção imagiológica. O objectivo deste trabalho é analisar o uso da CBCT em Endodontia. Para isso recorreu-se a uma pesquisa na base de dados online PubMed e Scielo, limitando a pesquisa a publicações feitas após o ano 2008 inclusivé, de onde resultou a selecção de 42 artigos. Com a realização deste trabalho foi possível concluir que o uso CBCT em Endodontia é de facto uma mais-valia, constituindo uma excelente ferramenta de diagnóstico. Imaging, as an area of interest which is frequently used by dentistry, has evolved in recent years featuring new technologies. Cone Beam Computed Tomography (CBCT) is one of these newer technologies, which enables the visualization of three-dimensional images of dental structures and adjacent bone tissue. Situations as identification of abnormal number and morphology of root canals, detection of vertical root fractures, evaluation of healing process after treatment, may be better and more easily identified and dealt with this new imaging option. The aim of this study, is to analyze the use of CBCT in Endodontics. Online search was performed on PubMed and Scielo database, limiting the search to publications made after the year 2008 inclusive. This resulted in the selection of 42 articles. With this study, it was concluded that the use of CBCT in Endodontics is indeed a great asset, making it an excellent diagnosis tool.
2
Yang, Xiaochun 1971. "Geometry of cone-beam reconstruction." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8338.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 2002.Includes bibliographical references (p. 89-91).
Geometry is the synthetic tool we use to unify all existing analytical cone-beam reconstruction methods. These reconstructions are based on formulae derived by Tuy [Tuy, 1983], Smith [Smith, 1985] and Grangeat [Grangeat, 1991] which explicitly link the cone-beam data to some intermediate functions in the Radon transform domain. However, the essential step towards final reconstruction, that is, differential-backprojection, has not yet achieved desired efficiency. A new inversion formula is obtained directly from the 3D Radon inverse [Radon, 1917, Helgason, 1999]. It incorporates the cone-beam scanning geometry and allows the theoretical work mentioned above to be reduced to exact and frugal implementations. Extensions can be easily carried out to 2D fan-beam reconstruction as well as other scanning modalities such as parallel scans by allowing more abstract geometric description on the embedding subspace of the Radon manifold. The new approach provides a canonical inverse procedure for computerized tomography in general, with applications ranging from diagnostic medical imaging to industrial testing, such as X-ray CT, Emission CT, Ultrasound CT, etc. It also suggests a principled frame for approaching other 3D reconstruction problems related to the Radon transform. The idea is simple: as was spelled out by Helgason on the opening page of his book, The Radon Transform [Helgason, 1999] - a remarkable duality characterizes the Radon transform and its inverse. Our study shows that the dual space, the so-called Radon space, can be geometrically decomposed according to the specified scanning modality.
(cont.) In cone-beam X-ray reconstruction, for example, each cone-beam projection is seen as a 2D projective subspace embedded in the Radon manifold. Besides the duality in the space relation, the symbiosis played between algebra and geometry, integration and differentiation is another striking feature in the tomographic reconstruction. Simply put, * Geometry and algebra: the two play fundamentally different roles during the inverse. Algebraic transforms carry cone-beam data into the Radon domain, whereas, the geometric decomposition of the dual space determines how the differential-backprojection operator should be systematically performed. The reason that different algorithms in cone-beam X-ray reconstruction share structural similarity is that the dual space decomposition is intrinsic to the specified scanning geometry. The differences in the algorithms lie in the appearance of algebra on the projection submanifold. The algebraic transforms initiate diverse reconstruction methods varying in terms of computational cost and stability. Equipped with this viewpoint, we are able to simplify mathematical analysis and develop algorithms that are easy to implement. Integration and differentiation: forward projection is the integral along straight lines (or planes) in the Euclidean space. During the reconstruction, differentiation is performed over the parallel planes in the projective Radon space, a manifold with clear differential structure. It is important to learn about this differential structure to ensure that correct differentiation can be carried out with respect to the parameters governing the scanning process during the reconstruction ...
by Xiaochun Yang.
Ph.D.
3
Turbell, Henrik. "Cone-Beam Reconstruction Using Filtered Backprojection." Doctoral thesis, Linköping : Univ, 2001. http://www.bibl.liu.se/liupubl/disp/disp2001/tek672s.pdf.
Full text
4
Rathore, Sonali A. Tyndall Donald A. "Cone beam CT in occlusal caries research." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2009. http://dc.lib.unc.edu/u?/etd,2866.
Full textAbstract:
Thesis (M.S.)--University of North Carolina at Chapel Hill, 2009.Title from electronic title page (viewed Jun. 4, 2010). "... in partial fulfillment of the requirements for the degree of Master of Science in the department of Oral and Maxillofacial Radiology." Discipline: Oral and Maxillofacial Radiology; Department/School: Dentistry.
5
Allareddy, Veeratrishul. "Incidental findings on cone beam computed tomography." Thesis, University of Iowa, 2009. https://ir.uiowa.edu/etd/457.
Full text
6
Watson, Peter. "Scatter artifact correction in cone-beam CT images." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=117080.
Full textAbstract:
Cone-beam computed tomography (CBCT) images suffer from poor image quality, in a large part due to scattered x-rays. In this work, a fast and accurate Monte Carlo based scatter correction algorithm was implemented on real CBCT data. A fast Monte Carlo simulation developed in the EGSnrc framework was used to transport photons through an uncorrected CBCT scan. From the simulation output, the contribution from both primary and scattered photons for each projection image was estimated. Using these estimates, a subtractive scatter correction was performed on the CBCT projection data. Implementation of the scatter correction algorithm on CBCT phantom scans was shown to help mitigate scatter-induced artifacts, such as cupping and streaking. The scatter corrected images were also shown to have improved accuracy in reconstructed attenuation coefficient values. These results suggest that the proposed scatter correction algorithm is successful in improving image quality in real CBCT images, and are promising results towards the reliable use of CBCT images in adaptive radiotherapy.Les images de tomodensitométrie à faisceau conique (CBCT) souffrent d'une qualité d'image inférieure en partie due aux rayonnement diffusés. Dans cet ouvrage, un algorithme Monte Carlo rapide et précis fut appliqué sur des images CBCT cliniques. En utilisant un logiciel de transport de particules à base Monte Carlo pour transporter des photons dans un CBCT où les données n'ont pas été corrigés, la contribution des photons diffusés primaires et secondaires pour chaque image fut estimée. En utilisant cet estimé, une correction fut apportée sur les données du CBCT. La méthode de correction CBCT a démontré sa capacité de mitiger les artéfacts introduient par la diffusion des photons. Les images corrigées ont montré une plus grande précision pour la reconstruction des coéfficients d'atténuation. Ces résultats suggèrent que la méthode proposée pour corriger des images CBCT fut un succès pour l'amélioration de la qualité d'images CBCT réelles, et insinuent une utilisation able des images CBCT en radiothérapie adaptative.
7
Doshi, Susan. "Statistical image analysis in cone-beam computed tomography." Thesis, University of Bath, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619218.
Full textAbstract:
Cone-beam computed tomography (CBCT) is used to verify the patient’s position prior to commencing radiotherapy treatment. Soft tissues such as the prostate are hard to distinguish, and so gold markers may be implanted. These markers cause artefacts in the 3D reconstruction. In this thesis, we apply statistical image analysis techniques to CBCT data, with two purposes: we estimate the marker locations (with an assessment of uncertainty), and create reconstructions with fewer artefacts. In our first analysis, we define a Bayesian statistical model for the projection data, encouraging local smoothness in the prior. We use estimates of the true projection images (generated using Markov chain Monte Carlo, MCMC) in a conventional 3D reconstruction. The results are visually superior to those obtained using a frequency-domain smoothing filter. In our second analysis, we model the markers as they appear in the projection images. We restrict our model to regions of interest generated using morphological analysis. We combine the information from many projection images to generate an accurate estimate of the marker locations in 3D space. This produces accurate estimates of marker location, but no accurate measure of uncertainty. Our third analysis uses a template model for the markers in 3D space, with a separate model for the patient tissues. In phantom experiments, we obtain accurate estimates of the tissue properties and marker locations. For practical computational reasons, we can only analyse a small volume of the patient. Artefacts in the reconstruction used to determine the tissue properties outside the volume of interest prevent the successful estimation of both the tissue properties and marker locations in patients, but we accurately estimate the marker locations alone, with estimates of uncertainty. Additionally, we process the projection images, removing the markers. These processed images can be used to generate reconstructions with fewer artefacts.
8
Vilches, Freixas Gloria. "Dual-energy cone-beam CT for proton therapy." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI099/document.
Full textAbstract:
La proton thérapie est une modalité de traitement du cancer qu’utilise des faisceaux de protons. Les systèmes de planification de traitement actuels se basent sur une image de l’anatomie du patient acquise par tomodensitométrie. Le pouvoir d’arrêt des protons relatif à l’eau (Stopping Power Ratio en Anglais, SPR) est déterminé à partir des unités Hounsfield (Hounsfield Units en Anglais, HU) pour calculer la dose absorbée au patient. Les protons sont plus vulnérables que les photons aux modifications du SPR du tissu dans la direction du faisceau dues au mouvement, désalignement ou changements anatomiques. De plus, les inexactitudes survenues de la CT de planification et intrinsèques à la conversion HU-SPR contribuent énormément à l’incertitude de la portée des protons. Dans la pratique clinique, au volume de traitement s’ajoutent des marges de sécurité pour tenir en compte ces incertitudes en détriment de perdre la capacité d’épargner les tissus autour de la tumeur. L’usage de l’imagerie bi-énergie en proton thérapie a été proposé pour la première fois en 2009 pour mieux estimer le SPR du patient par rapport à l’imagerie mono-énergie. Le but de cette thèse est d’étudier la potentielle amélioration de l’estimation du SPR des protons en utilisant l’imagerie bi-énergie, pour ainsi réduire l’incertitude dans la prédiction de la portée des protons dans le patient. Cette thèse est appliquée à un nouveau système d’imagerie, l’Imaging Ring (IR), un scanner de tomodensitométrie conique (Cone-Beam CT en Anglais, CBCT) développé pour la radiothérapie guidée par l’image. L’IR est équipé d’une source de rayons X avec un système d’alternance rapide du voltage, synchronisé avec une roue contenant des filtres de différents matériaux que permet des acquisitions CBCT multi-énergie. La première contribution est une méthode pour calibrer les modèles de source et la réponse du détecteur pour être utilisés en simulations d’imagerie X. Deuxièmement, les recherches ont évalué les facteurs que peuvent avoir un impact sur les résultats du procès de décomposition bi-énergie, dès paramètres d’acquisition au post-traitement. Les deux domaines, image et basée en la projection, ont été minutieusement étudiés, avec un spéciale accent aux approches basés en la projection. Deux nouvelles bases de décomposition ont été proposées pour estimer le SPR, sans avoir besoin d’une variable intermédiaire comme le nombre atomique effectif. La dernière partie propose une estimation du SPR des fantômes de caractérisation tissulaire et d’un fantôme anthropomorphique à partir d’acquisitions avec l’IR. Il a été implémentée une correction du diffusé, et il a été proposée une routine pour interpoler linéairement les sinogrammes de basse et haute énergie des acquisitions bi-énergie pour pouvoir réaliser des décompositions en matériaux avec données réelles. Les valeurs réconstruits du SPR ont été comparées aux valeurs du SPR expérimentales déterminés avec un faisceau d’ions de carboneProton therapy is a promising radiation treatment modality that uses proton beams to treat cancer. Current treatment planning systems rely on an X-ray computed tomography (CT) image of the patient's anatomy to design the treatment plan. The proton stopping-power ratio relative to water (SPR) is derived from CT numbers (HU) to compute the absorbed dose in the patient. Protons are more vulnerable than photons to changes in tissue SPR in the beam direction caused by movement, misalignment or anatomical changes. In addition, inaccuracies arising from the planning CT and intrinsic to the HU-SPR conversion greatly contribute to the proton range uncertainty. In clinical practice, safety margins are added to the treatment volume to account for these uncertainties at the expense of losing organ-sparing capabilities. The use of dual-energy (DE) in proton therapy was first suggested in 2009 to better estimate the SPR with respect to single-energy X-ray imaging. The aim of this thesis work is to investigate the potential improvement in determining proton SPR using DE to reduce the uncertainty in predicting the proton range in the patient. This PhD work is applied to a new imaging device, the Imaging Ring (IR), which is a cone-beam CT (CBCT) scanner developed for image-guided radiotherapy (IGRT). The IR is equipped with a fast kV switching X-ray source, synchronized with a filter wheel, allowing for multi-energy CBCT imaging. The first contribution of this thesis is a method to calibrate a model for the X-ray source and the detector response to be used in X-ray image simulations. It has been validated experimentally on three CBCT scanners. Secondly, the investigations have evaluated the factors that have an impact on the outcome of the DE decomposition process, from the acquisition parameters to the post-processing. Both image- and projection-based decomposition domains have been thoroughly investigated, with special emphasis on projection-based approaches. Two novel DE decomposition bases have been proposed to estimate proton SPRs, without the need for an intermediate variable such as the effective atomic number. The last part of the thesis proposes an estimation of proton SPR maps of tissue characterization and anthropomorphic phantoms through DE-CBCT acquisitions with the IR. A correction for X-ray scattering has been implemented off-line, and a routine to linearly interpolate low-energy and high-energy sinograms from sequential and fast-switching DE acquisitions has been proposed to perform DE material decomposition in the projection domain with real data. DECT-derived SPR values have been compared with experimentally-determined SPR values in a carbon-ion beam
9
Ashfaq, Awais. "Segmentation of Cone Beam CT in Stereotactic Radiosurgery." Thesis, KTH, Skolan för teknik och hälsa (STH), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193107.
Full textAbstract:
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.
10
Balasundaram, Ashok Mol André. "Cone beam computed tomography imaging of periodontal bone." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2008. http://dc.lib.unc.edu/u?/etd,2063.
Full textAbstract:
Thesis (M.S.)--University of North Carolina at Chapel Hill, 2008.Title from electronic title page (viewed Feb. 17, 2009). "... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Diagnostic Sciences and General Dentistry, School of Dentistry." Discipline: Diagnostic Sciences and General Dentistry; Department/School: Dentistry.
11
Kumar, Vandana Ludlow John B. "Comparison of conventional and Cone Beam CT synthesized cephalograms." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2007. http://dc.lib.unc.edu/u?/etd,955.
Full textAbstract:
Thesis (M.S.)--University of North Carolina at Chapel Hill, 2007.Title from electronic title page (viewed Dec. 18, 2007). "... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Diagnostic Sciences and General Dentistry, School of Dentistry." Discipline: Diagnostic Sciences and General Dentistry; Department/School: Dentistry.
12
Mason, Jonathan Hugh. "Quantitative cone-beam computed tomography reconstruction for radiotherapy planning." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/33193.
Full textAbstract:
Radiotherapy planning involves the calculation of dose deposition throughout the patient, based upon quantitative electron density images from computed tomography (CT) scans taken before treatment. Cone beam CT (CBCT), consisting of a point source and flat panel detector, is often built onto radiotherapy delivery machines and used during a treatment session to ensure alignment of the patient to the plan. If the plan could be recalculated throughout the course of treatment, then margins of uncertainty and toxicity to healthy tissues could be reduced. CBCT reconstructions are normally too poor to be used as the basis of planning however, due to their insufficient sampling, beam hardening and high level of scatter. In this work, we investigate reconstruction techniques to enable dose calculation from CBCT. Firstly, we develop an iterative method for directly inferring electron density from the raw X-ray measurements, which is robust to both low doses and polyenergetic artefacts from hard bone and metallic implants. Secondly, we supplement this with a fast integrated scatter model, also able to take into account the polyenergetic nature of the diagnostic X-ray source. Finally, we demonstrate the ability to provide accurate dose calculation using our methodology from numerical and physical experiments. Not only does this unlock the capability to perform CBCT radiotherapy planning, offering more targeted and less toxic treatment, but the developed techniques are also applicable and beneficial for many other CT applications.
13
Sunnegårdh, Johan. "Iterative Filtered Backprojection Methods for Helical Cone-Beam CT." Doctoral thesis, Linköpings universitet, Bildbehandling, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-20035.
Full textAbstract:
State-of-the-art reconstruction algorithms for medical helical cone-beam Computed Tomography (CT) are of type non-exact Filtered Backprojection (FBP). They are attractive because of their simplicity and low computational cost, but they produce sub-optimal images with respect to artifacts, resolution, and noise. This thesis deals with possibilities to improve the image quality by means of iterative techniques. The first algorithm, Regularized Iterative Weighted Filtered Backprojection (RIWFBP), is an iterative algorithm employing the non-exact Weighted FilteredBackprojection (WFBP) algorithm [Stierstorfer et al., Phys. Med. Biol. 49, 2209-2218, 2004] in the update step. We have measured and compared artifact reduction as well as resolution and noise properties for RIWFBP and WFBP. The results show that artifacts originating in the non-exactness of the WFBP algorithm are suppressed within five iterations without notable degradation in terms of resolution versus noise. Our experiments also indicate that the number of required iterations can be reduced by employing a technique known as ordered subsets. A small modification of RIWFBP leads to a new algorithm, the Weighted Least Squares Iterative Filtered Backprojection (WLS-IFBP). This algorithm has a slightly lower rate of convergence than RIWFBP, but in return it has the attractive property of converging to a solution of a certain least squares minimization problem. Hereby, theory and algorithms from optimization theory become applicable. Besides linear regularization, we have examined edge-preserving non-linear regularization.In this case, resolution becomes contrast dependent, a fact that can be utilized for improving high contrast resolution without degrading the signal-to-noise ratio in low contrast regions. Resolution measurements at different contrast levels and anthropomorphic phantom studies confirm this property. Furthermore, an even morepronounced suppression of artifacts is observed. Iterative reconstruction opens for more realistic modeling of the input data acquisition process than what is possible with FBP. We have examined the possibility to improve the forward projection model by (i) multiple ray models, and (ii) calculating strip integrals instead of line integrals. In both cases, for linearregularization, the experiments indicate a trade off: the resolution is improved atthe price of increased noise levels. With non-linear regularization on the other hand, the degraded signal-to-noise ratio in low contrast regions can be avoided. Huge input data sizes make experiments on real medical CT data very demanding. To alleviate this problem, we have implemented the most time consuming parts of the algorithms on a Graphics Processing Unit (GPU). These implementations are described in some detail, and some specific problems regarding parallelism and memory access are discussed.
14
Brozovich, Gimena. "Rol del cone beam en el diagnóstico en endodoncia." Trabajo final de especialización, Universidad Nacional de Cuyo. Facultad de Odontología, 2020. http://bdigital.uncu.edu.ar/15307.
Full textAbstract:
El diagnóstico por imágenes en endodoncia en determinados casos se ve limitado por la superposición de estructuras anatómicas, por una anatomía compleja radicular o la poca definición de la imagen radiografía, es por esto que con el uso de tomografía computarizada de haz cónico podemos obtener una magnificación y con ello mayor precisión para el correcto diagnóstico y planificación del caso clínico.
Por lo tanto, el objetivo de este trabajo es realizar una descripción minuciosa de los usos y aplicaciones del CBCT en el campo de la endodoncia, justificando su uso, mediante la presentación de un caso clínico.
En el presente trabajo se describe el caso clínico de un paciente que concurre a la consulta con sintomatología dolorosa en elemento 37, clínicamente sano, la radiografía periapical no aporto información suficiente para el diagnóstico, motivo por el cual se le solicitó una Tomografía Cone Beam, en la cual se pudo determinar con precisión la presencia de una reabsorción apical, lo cual resultó determinante para el diagnóstico y la planificación del tratamiento El conocimiento y manejo adecuado de esta tecnología resulta indispensable para la correcta prescripción del estudio.Fil: Brozovich, Gimena. Universidad Nacional de Cuyo. Facultad de Odontología.
15
Amor, Zaineb. "Bone segmentation and extrapolation in Cone-Beam Computed Tomography." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-279802.
Full textAbstract:
This work was done within the French R&D center of GE Medical Systems and focused on two main tasks: skull bone segmentation on 3D Cone-Beam Computed Tomography (CBCT) data and skull volumetric shape extrapolation on 3D CBCT data using deep learning approaches. The motivation behind the first task is that it would allow interventional radiologists to visualize only the vessels directly without adding workflow to their procedures and exposing the patients to extra radiations. The motivation behind the second task is that it would help understand and eventually correct some artifacts related to partial volumes. The skull segmentation labels were prepared while taking into ac- count imaging-modality related considerations and anatomy-related considerations. The architecture that was chosen for the segmentation task was chosen after experimenting with three different networks, the hyperparameters were also optimized. The second task explored the feasability of extrapolating the volumetric shape of the skull outside of the field of view with limited data. At first, a simple convolutional autoencoder architecture was explored, then, adversarial training was added. Adversarial training did not improve the performances considerably.I detta arbete undersöktes två huvuduppgifter, skallbenssegmentering på 3D CBCT-data och extrapolering av skallvolumetrisk form på 3D CBCT-data. För båda uppgifterna användes djupinlärningsmetoder. Den första uppgiften är användbar eftersom den skulle göra det möjligt för interventionsradiologer att endast visualisera blodkärlen direkt utan att lägga till arbetsflöde i sina procedurer. För att förbereda uppgifterna tog vi hänsyn till avbildningsmodalitetsrelaterade faktorer och anatomirelaterade faktorer. Arkiekturen för denna uppgift valdes efter experiment med tre olika nätverk, hyperparametrarna optimerades också. Den andra uppgiften undersökte möjligheten att extrapolera den volumetriska formen på skallen utanför synfältet med begränsade data. Denna uppgift är viktig eftersom den möjliggör korrigering av specifika artefakter kopplade till partiella volymer. I början undersöktes en enkel autoencoder-arkitektur, därefter tillkom adversarial training vilket inte avsevärt förbättrade prestandan.
16
Bedford, Mariam. "A cone beam analysis of the maxillary bony canal." University of the Western Cape, 2013. http://hdl.handle.net/11394/4208.
Full textAbstract:
>Magister Scientiae - MScAim: To determine the prevalence and diameter of the maxillary end osseous canal which carries the anastomosis of the infra alveolar artery (a branch of the posterior superior alveolar artery) and the infra- orbital artery. Material and methods: Data was analyzed from one hundred archived cone beam computed tomography (CBCT) images. The presence of the end osseous anastomosis in the lateral sinus wall was identified by utilizing axial views. The vessel diameter was also measured in those images where the canal was identified. Results: The maxillary bony canal was identified in 49 (49%) of 100 maxillary sinus.14 (14%) presented on the right hand side, 10 (10%) presented on the left hand side, 25 (25%) had a bilateral presence with a remaining 51 (51%) which cannot be identified on the imaging. From the 49 canals that were identified, 5 canals had a diameter that was 2-3mm wide,19 canals had a diameter that was 1-2mm wide and the remaining 25 had a diameter that was less than 1mm. Conclusion: A sound knowledge of the maxillary sinus vascularity is essential as severe bleeding can occur due to damage of the intra-osseous branch during sinus augmentation procedures. CBCT analysis is required as a pre-requisite for the pre-planning stages during implant treatment to prevent complications such as haemorrhage, sinus perforations or associated vascular anomalies that may arise
17
Klein, Christopher [Verfasser], and Elmar [Akademischer Betreuer] Kotter. "Die Cone-Beam-Computertomographie in der Diagnostik der Skaphoidfraktur." Freiburg : Universität, 2019. http://d-nb.info/1203066155/34.
Full text
18
Marotta, Serena. "Soluzioni numeriche alla ricostruzione tomografica cone-beam per tessuti molli." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Find full textAbstract:
Lo scopo della tesi, una volta analizzato il modello fisico-matematico del processo di acquisizione dei dati, è stato quello di studiare opportuni modelli matematici e algoritmi di ricostruzione per CBCT che fossero in grado di evidenziare i tessuti molli nei dati ricostruiti. La tesi si è svolta nell'ambito di una collaborazione scientifica con l'azienda Skanray di San Lazzaro.
19
Sunnegårdh, Johan. "Iterative Enhancement of Non-Exact Reconstruction in Cone Beam CT." Thesis, Computer Vision, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-2577.
Full textAbstract:
Contemporary algorithms employed for reconstruction of 3D volumes from helical cone beam projections are so called non-exact algorithms. This means that the reconstructed volumes will contain artifacts irrespective of the detector resolution and number of projections angles employed in the process.
It has been proposed that these artifacts can be suppressed using an iterative scheme which comprises computation of projections from the already reconstructed volume as well as the non-exact reconstruction itself.
The purpose of the present work is to examine if the iterative scheme can be applied to the non-exact reconstruction method PI-original in order to improve the reconstruction result. An important part in this implementation is a careful design of the projection operator, as a poorly designed projection operator may result in aliasing and/or other artifacts in the reconstruction result. Since the projection data is truncated, special care must be taken along the boundaries of the detector. Three different ways of handling this interpolation problem is proposed and examined.
The results show that artifacts caused by the PI-original method can indeed be reduced by the iterative scheme. However, each iteration requires at least three times more processing time than the initial reconstruction, which may call for certain compromises, smartness and/or parallelization in the innermost loops. Furthermore, at higher cone angles certain types of artifacts seem to grow by each iteration instead of being suppressed.
20
Sunnegårdh, Johan. "Combining analytical and iterative reconstruction in helical cone-beam CT." Licentiate thesis, Computer Vision, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8286.
Full textAbstract:
Contemporary algorithms employed for reconstruction of 3D volumes from helical cone beam projections are so called non-exact algorithms. This means that the reconstructed volumes contain artifacts irrespective of the detector resolution and number of projection angles employed in the process. In this thesis, three iterative schemes for suppression of these so called cone artifacts are investigated.
The first scheme, iterative weighted filtered backprojection (IWFBP), is based on iterative application of a non-exact algorithm. For this method, artifact reduction, as well as spatial resolution and noise properties are measured. During the first five iterations, cone artifacts are clearly reduced. As a side effect, spatial resolution and noise are increased. To avoid this side effect and improve the convergence properties, a regularization procedure is proposed and evaluated.
In order to reduce the cost of the IWBP scheme, a second scheme is created by combining IWFBP with the so called ordered subsets technique, which we call OSIWFBP. This method divides the projection data set into subsets, and operates sequentially on each of these in a certain order, hence the name “ordered subsets”. We investigate two different ordering schemes and number of subsets, as well as the possibility to accelerate cone artifact suppression. The main conclusion is that the ordered subsets technique indeed reduces the number of iterations needed, but that it suffers from the drawback of noise amplification.
The third scheme starts by dividing input data into high- and low-frequency data, followed by non-iterative reconstruction of the high-frequency part and IWFBP reconstruction of the low-frequency part. This could open for acceleration by reduction of data in the iterative part. The results show that a suppression of artifacts similar to that of the IWFBP method can be obtained, even if a significant part of high-frequency data is non-iteratively reconstructed.
21
Sunnegårdh, Johan. "Combining analytical and iterative reconstruction in helical cone-beam CT /." Linköping : Department of Electrical Engineering, Linköpings universitet, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8286.
Full text
22
Adler, Jonas. "GPU Monte Carlo scatter calculations for Cone Beam Computed Tomography." Thesis, KTH, Numerisk analys, NA, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-140221.
Full textAbstract:
A GPU Monte Carlo code for x-ray photon transport has been implemented and extensively tested. The code is intended for scatter compensation of cone beam computed tomography images. The code was tested to agree with other well known codes within 5% for a set of simple scenarios. The scatter compensation was also tested using an artificial head phantom. The errors in the reconstructed Hounsfield values were reduced by approximately 70%. Several variance reduction methods have been tested, although most were found infeasible on GPUs. The code is nonetheless fast, and can simulate approximately 3 ·109 photons per minute on a NVIDIA Quadro 4000 graphics card. With the use of appropriate filtering methods, the code can be used to calculate patient specific scatter distributions for a full CBCT scan in approximately one minute, allowing scatter reduction in clinical applications.En GPU Monte Carlo kod för transport av röntgenfotoner har implementerats och utförligt testats. Koden är avsed för spridningskorrektion av CBCT-bilder. Koden har testats mot PENELOPE och resultaten överenstämmer inom 5% för ett antal enklare geometrier. Koden testades också i en verklig uppställning med ett artificiellt huvud. De resulterande felen i de beräknade Hounsfieldvärdena minbskade med ca 70%. Ett antal variansreduktionstekniker har också testats, men de flesta gav ingen förbättring på GPU. Koden är trots detta avsevärt snabb och kan simulera ca 3 · 109 photoner per minut med ett Quadro 4000 grafik-kort. Med hjälp av väl valda filtreringsmetoder kan koden användas för att beräkna patientspecifika spridningsfördelningar för ett fullständigt CBCT-scan på under en minut. Detta är tillräkligt för spridningskorrektion i kliniska tillämpningar.
23
Patel, Shanon. "The clinical applications of cone beam computed tomography in endodontics." Thesis, King's College London (University of London), 2012. https://kclpure.kcl.ac.uk/portal/en/theses/the-clinical-applications-of-cone-beam-computed-tomography-in-endodontics(28daff53-0941-4b36-b8ea-beeb7dc2a8e6).html.
Full textAbstract:
A series of 5 investigations assessed the application of cone beam computed tomography (CBCT) for the management of endodontic problems. Cone beam computed tomography improved the detection of the presence and absence of simulated periapical lesions in human dry mandibles. The overall sensitivity was 0.248 and 1.0 for periapical radiography and CBCT respectively. The receiver operating characteristics (ROC) area under the curve (AUC) values were 0.791 and 1.000 for intraoral radiography and CBCT, respectively. There was no improvement in the detection of artificially created vertical root fractures (VRF) in root treated teeth using CBCT compared with periapical radiographs. The overall AUC value of incomplete and complete VRF was 0.53 for periapical radiography and 0.45 for CBCT (p=0.034). The overall sensitivity of periapical radiography (0.05) was lower than CBCT (0.57) regardless of the extent of the VRF (p=0.027). Periapical radiographs (0.98) had a higher overall specificity than CBCT (0.34), (p=0.027). The prevalence of periapical radiolucencies of 273 individual roots in 151 teeth viewed with CBCT (48%) of teeth treatment planned for endodontic treatment was significantly higher when compared with periapical radiographs (20%). Periapical radiographs and CBCT scans of 123 of the teeth in 99 patients assessed 1 year after completion of primary root canal treatment were compared to their respective pre-treatment periapical radiographs and CBCT scans. Analysis by tooth revealed that the ’healed’ rate (absence of periapical radiolucency) was 87% using periapical radiographs and 62.5% using CBCT (p<0.001). This increased to 95.1% and 84.7% respectively when the ’healing’group (reduced size of periapical radioiUcency) was included (p<0.002). Outcome diagnosis of teeth showed a statistically significant difference between systems (p<0.001). The influence of periapical radiography and CBCT for the detection and management of in-vivo root resorption lesions was assessed. Periapical radiography ROC ADC values were 0.780 and 0.830 for diagnostic accuracy of internal and external cervical resorption respectively. The CBCT ROC AUC values were 1.000 for both internal and external cervical resorption. There was a significantly higher prevalence (p=0.028) for the correct treatment option being chosen with CBCT compared with intraoral radiographs. These investigations demonstrated that CBCT is more effective in diagnosis ex vivo and in vivo periapical radiolucencies, and for the diagnosis and management of root resorption. However, CBCT did not improve the detection of VRF in this experimental model.
24
Petrie, Tracy. "Motion binning in cone-beam CT without a prior model." Thesis, University of Leeds, 2010. http://etheses.whiterose.ac.uk/1684/.
Full textAbstract:
Cone-beam CT (CBCT), used to reduce setup error in radiotherapy, takes a sequence of about 670 two-dimensional X-rays acquired in a circular arc around the patient over two minutes and reconstructs a three-dimensional volume from these projections. Consequently, when tissues move significantly during the acquisition the resulting volume is blurry or contains streaks. The projections themselves, though, are sharp. One of the main areas of research with CBCT has been to attempt to reconstruct the motion from these projections by collecting them into respiratory-phase or amplitude bins and using these to reconstruct bin-specific volumes. A variety of mechanisms are employed to identify and record respiratory motion so that it can be correlated with the projections. Not all motion that occurs in the body can be correlated with respiration. The research question pursued in this thesis is whether motion can be identified in a binning process without prior knowledge or models of the motion. Nomenclature describing motion classes and a specific type of artefact are introduced. The distinctiveness of this artefact class is demonstrated and methods to mitigate it are proposed and evaluated. Several techniques are then used to reduce an intractable search space to a computationally feasible one. A unique application of PCA to the reconstruction process allows new kinds of search approaches to be considered including an exhaustive search which requires a protocol change and a multiple-restart hill-climbing search that can be used with existing protocols. Experiments with three classes of phantoms, including a novel animated physical phantom, show the effectiveness of the two search methods which are finally compared with each other.
25
Bevilacqua, Francesca. "Projection and reconstruction-based noise filtering methods in cone beam CT." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Find full textAbstract:
This thesis has been motivated and developed within a collaboration project between the Department of
Mathematics of the University of Bologna and the company Skanray Europe Srl. In detail, this work focuses
on Cone Beam CT reconstruction of the human head, with particular interest in detecting small soft tissue
elements within white and grey brain matter. This problem is expecially difficult due to the small contrast in
the X-ray attenuation coefficient between the two substances to be discriminated.
After accurately modelling the data acquisition process (also according to the requirements of the
company), we propose a novel reconstruction algorithm based on two subsequent steps. First, the
measured and degraded projections are restored, namely the blur and the noise are removed. Second, the
restored projections are feeded as input to a variational reconstruction method named TV3D-L2, so as to
get an accurate final reconstruciton of the head.
Several experimental tests are presented which provide evidence for the proposed approach
outperforming classical ones expecially for low-dose CT.
26
Schöndube, Harald [Verfasser]. "Helical Cone-Beam Computed Tomography using the Differentiated Backprojection / Harald Schöndube." Aachen : Shaker, 2010. http://d-nb.info/1106838726/34.
Full text
27
Klintström, Eva. "Image Analysis for Trabecular Bone Properties on Cone-Beam CT Data." Doctoral thesis, Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-142066.
Full textAbstract:
Trabecular bone structure as well as bone mineral density (BMD) have impact on the biomechanical competence of bone. In osteoporosis-related fractures, there have been shown to exist disconnections in the trabecular network as well as low bone mineral density. Imaging of bone parameters is therefore of importance in detecting osteoporosis. One available imaging device is cone-beam computed tomography (CBCT). This device is often used in pre-operative imaging of dental implants, for which the trabecular network also has great importance. Fourteen or 15 trabecular bone specimens from the radius were imaged for conducting this in vitro project. The imaging data from one dual-energy X-ray absorptiometry (DXA), two multi-slice computed tomography (MSCT), one high-resolution peripheral quantitative computed tomography (HR-pQCT) and four CBCT devices were segmented using an in-house developed code based on homogeneity thresholding. Seven trabecular microarchitecture parameters, as well as two trabecular bone stiffness parameters, were computed from the segmented data. Measurements from micro-computed tomography (micro-CT) data of the same bone specimens were regarded as gold standard. Correlations between MSCT and micro-CT data showed great variations, depending on device, imaging parameters and between the bone parameters. Only the bone-volume fraction (BV/TV) parameter was stable with strong correlations. Regarding both HR-pQCT and CBCT, the correlations to micro-CT were strong for bone structure parameters as well as bone stiffness parameters. The CBCT device 3D Accuitomo showed the strongest correlations, but overestimated BV/TV more than three times compared to micro-CT. The imaging protocol most often used in clinical imaging practice at our clinic demonstrated strong correlations as well as low radiation dose. CBCT data of trabecular bone can be used for analysing trabecular bone properties, like bone microstructure and bone biomechanics, showing strong correlations to the reference method of micro-CT. The results depend on choice of CBCT device as well as segmentation method used. The in-house developed code based on homogeneity thresholding is appropriate for CBCT data. The overestimations of BV/TV must be considered when estimating bone properties in future clinical dental implant and osteoporosis research.
28
Cropp, Robert James. "Implementation of respiratory-correlated cone-beam CT on Varian linac systems." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/37220.
Full textAbstract:
Respiratory-correlated (4D) X-ray CT scans produce a set of images corresponding to different phases of a patient's breathing cycle. In external beam radiotherapy, information about a tumor's motion due to respiration can be used to optimize a treatment plan, provided the patient can be accurately aligned for treatment. Cone-beam CT (CBCT) systems are becoming widespread on treatment linac units and are used to aid in alignment.
This thesis describes the implementation of respiratory-correlated cone-beam CT scans on two types of Varian units: iX and TrueBeam. Procedures for 4D CBCT scans on each type have been developed and used to image a moving phantom. The respiratory phase of the motion is recorded with the Varian Real-time Position Management (RPM) system, which uses optical tracking. To improve image quality, the gantry rotation speed is reduced below the default value of 6°/s: this reduces streak artifacts. Each projection image from the scan is assigned to one of ten phase bins according to its respiratory phase value. A 3D image is reconstructed for each phase bin with software developed for this project, which uses conventional Feldkamp-Davis-Kress filtered backprojection. Four 4D scans of a periodically moving phantom have been taken, with different gantry speeds and mAs values. To evaluate the effect of these scan parameters on image quality, and demonstrate a potential application of 4D CBCT, a procedure for automated tumor trajectory measurement has been developed. The
measurement uses image registration between phase images, with either a rigid translation or a B-spline deformation algorithm. In the highest-quality images, the displacements of an insert in the phantom are measured within 1 mm of the correct values by both algorithms. In lower-quality images the translation algorithm is more robust. The two algorithms give similar results when applied to 4D CT images of actual lung cancer patients.
29
Scheidgen, Moritz [Verfasser]. "Entwicklung eines Phantomkopfes zur Validierung eines Cone-Beam-Systems / Moritz Scheidgen." Köln : Deutsche Zentralbibliothek für Medizin, 2013. http://d-nb.info/1033318515/34.
Full text
30
Konate, Souleymane. "EFFICIENT CONE BEAM RECONSTRUCTION FOR THE DISTORTED CIRCLE AND LINE TRAJECTORY." Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2971.
Full textAbstract:
We propose an exact filtered backprojection algorithm for inversion of the cone beam data in the case when the trajectory is composed of a distorted circle and a line segment. The length of the scan is determined by the region of interest , and it is independent of the size of the object. With few geometric restrictions on the curve, we show that we have an exact reconstruction. Numerical experiments demonstrate good image quality.Ph.D.
Department of Mathematics
Sciences
Mathematics PhD
31
Barros, Renata Quirino de Almeida. "Radiografia panorâmica e tomografia cone beam: Análise de tumores dos maxilares." Universidade Estadual da Paraíba, 2011. http://tede.bc.uepb.edu.br/tede/jspui/handle/tede/1681.
Full textAbstract:
Made available in DSpace on 2015-09-25T12:18:24Z (GMT). No. of bitstreams: 1
Renata Quirino de Almeida Barros.pdf: 651574 bytes, checksum: 691f9ca6ac269e365c41d390ddf57550 (MD5)
Previous issue date: 2011-07-20The diagnosis through image of neoplastic lesions that affect the maxillomandibular complex has been worthful for dentists in the elaboration of the surgical planning. This work aims to evaluate and correlationate the accuracy of panoramic radiography compared to the cone beam computed tomography, regarding the delineation of odontogenic and non-odontogenic tumors, diagnosed at the city of Campina Grande, Paraíba, Brazil, in the period between November 2009 and March 2011. There were 23 tumors diagnosed in various regions of the maxillomandibular complex, whose panoramic radiographies and computed tomographies were analyzed by 2 radiologists, in terms of the following radiographic aspects: radiolucency, presence or absence of mineralizations, definition of the lesions edges, expansion and breaking of bone cortical, as well as the relation to the anatomic structures and dental elements. The results were: 73,9% of patients with odontogenic tumors and 26,1% non-odontogenic, having histopathological standard for diagnosis, 65,2% of female patients and 34,8% of male patients, 56,5% of tumors located at the mandible, 34,8% at the maxilla and 8,7% at both arcs. It was observed the limitation of panoramic radiography in the analysis of the radiographic aspects. The cone beam tomography offered results more focused and statistically meaningful for the evaluation of bone destruction, as well as for the expansion of vestibular and palatine/lingual cortical. It was concluded that despite of panoramic radiography being the chosen examination to visualize lesions in maxilla, cone beam computed tomography provides better accuracy in terms of delineation, expansion and breaking of cortical bones, helping in the surgical planning and patient s follow up.
O diagnóstico por imagem das lesões tumorais que acometem o complexo maxilo-mandibular tem sido de grande valia para o cirurgião-dentista na elaboração de um planejamento cirúrgico. Este trabalho teve como objetivo avaliar e correlacionar a acurácia da radiografia panorâmica frente à tomografia computadorizada cone beam no delineamento dos tumores odontogênicos e não odontogênicos dos maxilares, diagnosticados no município de Campina Grande PB, no período de novembro de 2009 a março de 2011. Foram diagnosticados 23 tumores em várias regiões do complexo maxilo-mandibular, cujas radiografias panorâmicas e tomografias computadorizadas foram analisadas por 2 radiologistas, quanto aos seguintes aspectos imaginológicos: forma de radioluscência, presença ou não de mineralizações, definição das margens da lesão, expansão e rompimento de cortical óssea, bem como relação com estruturas anatômicas e dentes. Os resultados nos mostraram que 65,2% dos pacientes eram do sexo feminino e 34,8% do masculino, 56,5% dos tumores estavam localizados na mandíbula, 34,8% na maxila e 8,7% em ambos os arcos, 73,9% dos pacientes apresentaram tumores odontogênicos e 26,1% não odontogênicos, tendo como padrão de diagnóstico o histopatológico. Observou-se a limitação da radiografia panorâmica na análise dos aspectos radiográficos observados. A tomografia cone beam ofereceu resultados mais direcionados e estatisticamente significativos para avaliação do rompimento das corticais vestibular e palatina/lingual, bem como para a expansão óssea. Concluiu-se que apesar da radiografia panorâmica ser o exame de escolha para visualizar as lesões que acometem os maxilares, a tomografia computadorizada de feixe cônico proporcionou uma melhor acurácia no delineamento, expansão e rompimento das corticais ósseas, auxiliando no planejamento cirúrgico e na proservação do paciente.
32
Weissheimer, André. "Métodos de avaliação tridimensional do complexo craniofacial em tomografia cone beam." Pontifícia Universidade Católica do Rio Grande do Sul, 2013. http://hdl.handle.net/10923/5583.
Full textAbstract:
Made available in DSpace on 2013-12-13T01:01:21Z (GMT). No. of bitstreams: 1
000452798-Texto+Completo-0.pdf: 11258762 bytes, checksum: 1779e23c337cdf8d461b246e5a82e0c5 (MD5)
Previous issue date: 2013Introduction : this thesis aimed to evaluate the software accuracy for 3D analysis of craniofacial complex in cone beam computed tomography (CBCT). With this purpose, two studies were performed. The first study evaluated the precision and accuracy of 6 imaging software programs for measuring the upper airway volume in CBCT. The second study aimed to validate a fast method for 3D superimposition of CBCT. Methods : in study 1, the sample consisted of 33 growing patients and 1 oropharynx acrylic phantom (OAP), scanned with iCAT scanner. The known OAP volume was used as gold standard (GS). Semi-automatic segmentations of the patients´ oropharynx (OP) and OAP was performed using Mimics, ITK-Snap, OsiriX, Dolphin3D, InVivo Dental and Ondemand3D software programs. In study 2, the sample consisted of CBCT scans of 18 patients. For 10 patients as a gold standard, the spatial position of the pretreatment CBCT volume was reoriented, saved as a reoriented volume, and then superimposed to the original image. For 8 patients, 4 non-growing and 4 growing patients, pre and post-treatment scans were superimposed. Superimposition accuracy was assessed by visual inspection and measured by using the CMF application and expressed via color maps. Results : in study 1, the OAP segmentations with Mimics, Dolphin3D, OsiriX and ITK-Snap showed less than 2% error in volume compared to the GS. Ondemand3D and InVivo Dental showed more than 5% error compared to the GS. In the OP segmentation, ITK-Snap, Mimics, OsiriX and Dolphin3D were statistically significantly different (P<. 05) from InVivo Dental. No statistical difference (P>. 05) was found between InVivo Dental and OnDemand3D. In study 2, Superimposition error of the spatial reorientation as measured by the color-coded surface distances was less than 0. 5mm. Superimposition error of pre and post treatment scans for both growing and non-growing patients at the cranial base were smaller than 0. 5 mm, which was considered acceptable and clinically insignificant. Conclusion : in study 1, all 6 imaging software programs were reliable but showed errors in the volume segmentation of OP. Mimics, Dolphin3D, ITK-Snap and OsiriX were similar and more accurate than InVivo Dental and Ondemand3D. In study 2, the voxel-based superimposition method evaluated was reproducible in different clinical conditions, time-efficient and potentially applicable for both research and clinical practice.
Introdução : o objetivo desta tese foi avaliar a acurácia de programas para análises 3D do complexo maxilofacial em tomografia computadorizada cone beam (TCCB). Com esse propósito, dois estudos foram realizados. O primeiro estudo avaliou a precisão e acurácia de 6 programas para avaliação do volume da via aérea superior em TCCB. O segundo estudo objetivou validar um método rápido de superposição 3D de TCCB.Método : no estudo 1, a amostra consistiu de 33 pacientes e 1 Phantom de acrílico da orofaringe (PAO), escaneados com o tomógrafo iCAT. O volume conhecido do PAO foi utilizado com “padrão ouro”. Segmentação semiautomática da orofaringe dos pacientes (OP) e do PAO foi realizada com os programas Mimics, ITK-Snap, OsiriX, Dolphin3D, InVivo Dental e Ondemand3D. No estudo 2, a amostra consistiu de TCCB de 18 pacientes. Em 10 pacientes, como padrão de comparação, a TCCB pré-tratamento foi reorientada espacialmente, salva como TCCB reorientada, e então superposta na imagem original. Em 8 pacientes, sendo 4 sem crescimento e 4 em crescimento, foram superpostas as TCCB e pós-tratamento. A acurácia da superposição foi avaliada através de inspeção visual e mensurada através do programa CFM com mapas coloridos. Resultados : no estudo 1, as segmentações com o Mimics, Dolphin3D, OsiriX e ITK-Snap mostraram menos de 2% de erro no volume do PAO em comparação ao “padrão ouro”. O Ondemand3D e o InVivo Dental apresentaram mais de 5% de erro no volume do PAO em comparação ao “padrão ouro”. As segmentações da OP com o ITK-Snap, Mimics, OsiriX e Dolphin3D foram estatisticamente diferentes (P<. 05) em comparação ao InVivo Dental. Não houve diferença estatisticamente significante (P>. 05) entre os programas InVivo Dental e o OnDemand3D. No estudo 2, o erro da superposição das TCCB reorientadas, medidas através dos mapas coloridos foi menor que 0,5mm. O erro da superposição das TCCB pré-tratamento e pós-tratamento para pacientes com e sem crescimento, na região da base do crânio, foi menor que 0,5 mm e considerado aceitável e clinicamente insignificante. Conclusão : no estudo 1, todos os 6 programas foram precisos, mas apresentaram erros no volume da segmentação da OP. Mimics, Dolphin3D, ITK-Snap e OsiriX foram considerados similares e mais acurados em comparação ao InVivo Dental e Ondemand3D. No estudo 2, o método de superposição baseado em voxel avaliado foi reproduzível em diferentes condições clínicas, rápido e potencialmente aplicável para pesquisa e prática clínica.
33
Bhatia, Navnina. "Scattering correction in cone beam tomography using continuously thickness-adapted kernels." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI092.
Full textAbstract:
La tomodensitométrie intégrant une source de rayons X à faisceau divergent et un détecteur grand champ est une technique bien connue dans le domaine de la tomographie industrielle. La nature des matériaux et les épaisseurs traversées conduisent inévitablement à la génération de rayonnement diffusé. Ce dernier est généré par l’objet mais également par le détecteur. La présence de rayonnement parasite conduit à ne plus respecter l’hypothèse de la loi de Beer-Lambert. Par conséquent, on voit apparaitre sur les coupes tomographiques des artefacts de reconstruction comme des streaks, des effets ventouses ou des valeurs d’atténuation linéaire erronée. Par conséquence, on retrouve dans la littérature de nombreuses méthodes de correction du diffusé. Ce travail vise à mettre en point et tester une méthode originale de correction du diffusé. Le premier chapitre de cette étude, dresse un état de l’art de la plupart des méthodes de corrections existantes. Nous proposons, dans le deuxième chapitre, une évolution de la méthode de superposition des noyaux de convolution (Scatter Kernel Superposition). Notre méthode repose sur une description continue des noyaux en fonction de l’épaisseur traversée. Dans cette méthode, les noyaux de diffusion sont paramétrés analytiquement sur toute la plage d'épaisseur. Le procédé a été testé pour des objets à la fois mono-matériaux et poly-matériaux, ainsi que sur des données expérimentales et simulées. Nous montrons dans le troisième chapitre l’importance de la contribution du diffusé détecteur dans la qualité de l’image reconstruite. Mais également l’importance de décrire les noyaux de convolution à l'aide d'un modèle à quatre gaussienne. Les résultats obtenus à partir de données expérimentales prouvent que la correction du diffusé de l'objet seul ne suffit pas pour obtenir une image de reconstruite sans artefacts. Afin de disposer d’une meilleur modélisation du diffusé du détecteur, nous décrivons, dans le dernier chapitre, une méthode basée sur la combinaison de données expérimentales et simulées permettant d’améliorer l’estimation des noyaux de diffuséAdvanced Cone Beam Computed Tomography (CBCT) typically uses a divergent conebeam source and a large area detector. As a result, there an inevitable increase in the size area of illumination causing an increase in the intensity of X-ray scatter signal, both from the object and the detector. This leads to the violation of prime assumption of reconstruction process which is based on straight line integrals path followed by the photons. Consequently scatter artifacts appear in the reconstruction images as steaks, cupping effect and thus produce wrong reconstruction values. Due to the severity of the reconstruction artifact caused by scatter, many scatter corrections methods have been adopted in literature. The first part of this study, reviews most of the existing scatter correction methods. The effect of scattering becomes more prominent and challenging in case of X-ray source of high energy which is used in industrial Non Destructive Testing (NDT), due to higher scatter to primary ratio (SPR). Therefore, in this study, we propose a continuously thickness-adapted deconvolution approach based on improvements in the Scatter Kernel Superposition (SKS) method. In this method, the scatter kernels are analytically parameterized over the whole thickness range of the object under study to better sample the amplitude and shape of kernels with respect to the thickness. The method is tested for both homogeneous and heterogeneous objects as well as simulated and experimental data. Another important aspect of this study is the comprehensive evaluation of contribution of the detector scatter performed using continuous method by separating the contribution of scatter due to the object and the detector. This is performed by modeling the scatter kernels using a four-Gaussian model. In the first approach, we performed this evaluation based on simulation of kernels from Monte Carlo simulations and the corrections are performed on typical industrial experimental data. The results obtained prove that the scatter correction only due to the object is not sufficient to obtain reconstruction image, free from artifacts, as the detector also scatters considerably. In order to prove this point experimentally and to have a better modeling of the detector, we describe a method based on combination of experiments and simulations to calculate the scatter kernels. The results obtained also prove, the contribution of the detector scattering becomes important and the PSF of the detector is not constant as considered in the studies so far, but it varies to a great extend with the energy spectrum
34
England, Gregory Miles. "Effect of Scanning Conditions on Cone Beam Computed Tomography Gray Value." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1458951153.
Full text
35
Zhu, Lei. "Circular reconstruction and scatter correction in X-ray cone-beam CT /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
Full text
36
Markwell, Timothy S. "MegaVoltage Cone Beam Computed Tomography with a standard medical linear accelerator." Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/87438/1/Timothy_Markwell_Thesis.pdf.
Full textAbstract:
Accurate patient positioning is vital for improved clinical outcomes for cancer treatments using radiotherapy. This project has developed Mega Voltage Cone Beam CT using a standard medical linear accelerator to allow 3D imaging of the patient position at treatment time with no additional hardware required. Providing 3D imaging functionality at no further cost allows enhanced patient position verification on older linear accelerators and in developing countries where access to new technology is limited.
37
Mauro, Rodrigo Antonio Pereira. "Dosimetria em tomografia computadorizada de feixe cônico odontológica." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-21112017-193930/.
Full textAbstract:
Os objetivos deste trabalho foram caracterizar os níveis de referência de radiodiagnóstico para a tomografia computadorizada de feixe cônico odontológica e as características de desempenho dos equipamentos como quilovoltaqgem de pico, rendimento, camada semirredutora, etc., com o intuito de conhecer os níveis dosimétricos em que os pacientes estão expostos, permitindo assim identificar protocolos de aquisição de imagem mais adequados, levando-se em consideração os princípios de radioproteção, e também testar a capacidade de tais equipamentos em alcançar uma imagem de qualidade. A Cone Beam Computed Tomography tem se tornado ferramenta extremamente útil na utilização em procedimentos radiológicos na área odontológica, pois, a riqueza de informações que a imagem 3D trás para o planejamento cirúrgico ou em qualquer procedimento, minimiza as possibilidades de erros, possibilita diagnósticos mais confiáveis e claros, tendo influência direta no resultado final esperado pelo paciente. Por se tratar de uma técnica de imagem que utiliza radiação ionizante, deve-se ter uma atenção criteriosa voltada para os níveis de radiação, além de implementar uma rotina de controle de qualidade. O parâmetro dosimétrico mais utilizado em tomografia computadorizada é o Computed Tomography Dose Index, porém, quando aplicado à tomografia odontológica, a geometria cônica do feixe e ainda a extensão do campo de visão tornam essa grandeza inviável e enganosa, assim, faz-se necessária a padronização de uma grandeza dosimétrica mais otimizada, para evitar a subestimação dos níveis de dose em feixes de ampla abrangência. O PKA tem sido utilizado como uma possível grandeza dosimétrica em tomografia odontológica, uma vez que em sua metodologia de medida, todo o feixe é englobado pelo medidor, não depende da distância fonte - detector, além de ser sensível aos parâmetros de exposição. Diante disso, propõe-se o PKA ser utilizado para estabelecimento dos níveis de dose de referência em diagnóstico odontológico. Os valores PKA obtidos para este estudo estão em uma faixa entre 34,6 mGy.cm^2 e 2901,6 mGy.cm^2, com valor médio de 980,7 mGy.cm^2. Os valores encontrados para os níveis de referência de radiodiagnóstico calculados a partir do 3º quartil estão divididos em três classes referentes ao tamanho do campo de visão, onde para campos pequenos, médios e grandes os valores são 1241 mGy.cm^2, 1521 mGy.cm^2 e 1408 mGy.cm^2 respectivamente, e 1446 mGy.cm^2 é o valor global independente do campo de visão. Os testes de controle de qualidade foram todos positivos, com uma atenção para o i-CAT FLX, que excedeu levemente o limite aceitável para a exatidão do kVp. Uma comparação entre CTDI100 e CTDI300, reportou que o CTDI300 é em média 49% maior em relação ao CTI100. Os níveis de referência de radiodiagnóstico são representativos dos níveis de dose otimizados, e servem como base para adequação e otimização dos parâmetros de exposição do equipamento. Os testes de controle de qualidade alertam para possíveis irregularidades no funcionamento do tomógrafo, e deve complementar obrigatoriamente a rotina dos procedimentos clínicos.The objectives of this study are to characterize the radiodiagnostic reference levels for computed tomography of dental cones and as performance characteristics of equipment such as peak kyvoltage, yield, semi-reducing layer, etc., in order to know the levels of the values in that users are exposed, thus allowing to identify more adequate image acquisition protocols, taking in basic concepts of radioprotection, and also to test the capacity of such equipment in a quality image. The Cone Beam CT scan has become active, useful in medical, medical, dental, on the Internet, in any situation, minimizes as possibilities of errors, allows for more reliable and clear diagnoses, having a direct influence on the final result expected by the patient. Because it is an imaging technique that uses ionizing radiation, careful attention should be given to radiation levels, in addition to implementing a quality control routine. The dosimetric parameter most commonly used in computed tomography is the Computed tomography dose index, however, when applied to dental tomography, the conic geometry of the beam and still the extension of the field of view make this greatness unfeasible and deceptive, so it is done The. standardization of a more optimized dosimetric quantity, to avoid an underestimation of the dose levels in beams of wide range. The PKA has been used as a possible dosimetric magnitude in dental tomography, since in its measurement methodology, the whole beam is encompassed by the meter, it does not depend on the source - detector distance, besides being sensitive to the exposure parameters. Therefore, it is proposed that PKA be used for the establishment of reference dose levels in dental diagnosis. The PKA values obtained for this study ranged from 34.6 mGy.cm^2 to 2901.6 mGy.cm^2, with a mean value of 980.7 mGy.cm^2. The values found for the levels of radiodiagnostic reference values calculated from the 3rd quartile are divided into three classes referring to the size of the field of vision, where for small, medium and large fields are the values are 1241 mGy.cm^2, 1521 mGy.cm^2 and 1408 mGy.cm^2 respectively, and 1446 mGy.cm^2 is the global independent value of the field of view. The quality control tests were all positive, with an attention to the i-CAT FLX, which slightly exceeded the acceptable limit for kVp accuracy. A face between CTDI100 and CTDI300, reported that the CTDI300 is on average 49% higher than the CTI100. Radiodiagnostic reference levels are representative of optimized dose levels and serve as a basis for adequacy and optimization of the exposure parameters of the equipment. The quality control tests alert to possible irregularities in the operation of the tomograph, and develop properly from the clinical process.
38
Riblett, Matthew J. "Motion-Induced Artifact Mitigation and Image Enhancement Strategies for Four-Dimensional Fan-Beam and Cone-Beam Computed Tomography." VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5542.
Full textAbstract:
Four dimensional imaging has become part of the standard of care for diagnosing and treating non-small cell lung cancer. In radiotherapy applications 4D fan-beam computed tomography (4D-CT) and 4D cone-beam computed tomography (4D-CBCT) are two advanced imaging modalities that afford clinical practitioners knowledge of the underlying kinematics and structural dynamics of diseased tissues and provide insight into the effects of regular organ motion and the nature of tissue deformation over time. While these imaging techniques can facilitate the use of more targeted radiotherapies, issues surrounding image quality and accuracy currently limit the utility of these images clinically.
The purpose of this project is to develop methods that retrospectively compensate for anatomical motion in 4D-CBCT and correct motion artifacts present in 4D-CT to improve the image quality of reconstructed volume and assist in localizing respiration-influenced, diseased tissue and mobile structures of interest. In the first half of the project, a series of motion compensation (MoCo) workflow methods incorporating groupwise deformable image registration and projection-warped reconstruction were developed for use with 4D-CBCT imaging. In the latter half of the project, novel motion artifact observation and artifact- weighted groupwise registration-based image correction algorithms were designed and tested. Both deliverable components of this project were evaluated for their ability to enhance image quality when applied to clinical patient datasets and demonstrated qualitative and quantitative improvements over current state-of-the-art.
39
Grauer, Dan Proffit William R. "Airway volume and shape from cone-beam CT relationship to facial morphology /." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2007. http://dc.lib.unc.edu/u?/etd,1197.
Full textAbstract:
Thesis (M.S.)--University of North Carolina at Chapel Hill, 2007.Title from electronic title page (viewed Mar. 26, 2008). "... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Orthodontics of the School of Dentistry." Discipline: Orthodontics; Department/School: Dentistry.
40
Malusek, Alexandr. "Calculation of scatter in cone beam CT : Steps towards a virtual tomograph." Doctoral thesis, Linköping : Department of Medical and Health Sciences, Linköping University, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11275.
Full text
41
Abolaban, Fouad Abdulaziz. "On board cone beam CT for treatment planning in image guided radiotherapy." Thesis, University of Surrey, 2011. http://epubs.surrey.ac.uk/745996/.
Full textAbstract:
Background: Movement of tumours between or during radiotherapy treatment fractions poses a risk to surrounding healthy tissues and potentially lowers the treatment dose to the intended area. To increase the efficacy of radiotherapy, radiation oncologists utilise image-guided radiotherapy (IGRT) to enhance the delivery of radiation to cancerous tumours. Concern about concomitant radiation doses and poor quality images have previously limited the use of such technology when developing treatment plans for adaptive radiotherapy. Recent improvements to the On-board Imager (OBI; Varian version 1.4) including expansion of the number of acquiring modes from four to six, have rejuvenated efforts to use Cone Beam Computed Tomography (CBCT) with OBI as a radiotherapy treatment planning tool. Aim: This research aimed to investigate the possibility of using the new version of the Varian On-Board CBCT imager Vl.4, for adaptive radiotherapy. This work has led to the development of a methodology on how to initiate and implement CBCT scans for - - - - - -- -. -- - -- .- -- the purpose of increasing the accuracy of radiotherapy treatments using adaptive radiotherapy. Methods: The adaptation of radiotherapy plans using CBCT scan images involved three stages. CBCT concommitant doses were determined in the first stage by measuring the dose received by three types of phantom; the RANDO anthropomorphic phantom, the computer-imaging reference system phantom (CIRS) and cylindrical water phantoms of varying diameter. Two- and three-dimensional simulations were also obtained for CBCT using EXCEL, and Monte Carlo codes (BEAMnrc and DOSXYZnrc). The manufacturer's schematic diagram of the head was used to simulate a detailed CBCT dose simulation with the effect of beam output and bow-tie filter included as dose-modifiers. Based on these dose measurements, relationships between CBCT concomitant dose and patient size were found. In addition, estimations of secondary induced cancer were modelled based on these doses. In the second stage, CBCT scan calibrations were conducted. The relationship IV Abstract between the Hounsfield Unit (HU) and electron density (ED) of CBCT scans were described mathematically for each CIRS-062A phantom configuration. Later, these CBCT HU-to-ED calibrations were benchmarked against the CT RU-to-ED relationship of GE lightspeed CT employed in treatment planning. Finally, in the third stage, the obtained HU-to-ED calibrations were applied to treatment plans calculated on CIRS and RANDO phantoms using single-beam and IMRT configurations. Dose calculations derived from the OBI CBCT were compared with those from the GE Lightspeed CT. Results:Using a female RANDO phantom, doses were lowered by factors of36, 8,22 and 16, at the eyes, oesophagus, thyroid and brain, respectively, when using the new version ofVarian CBCT vl.4. In both the standard dose head mode and pelvis mode, the concomitant dose at all positions decreases as the phantom size increases. The concomitant dose measured on the smallest cylindrical water phantoms (10cm in diameter) resulted in a theoretical risk of secondary skin cancer of 0.005% in the standard dose mode and 0.05% in the pelvis mode, assuming a 30-fraction course of ---- -treatmentwith CBCT images acquired on a daily basis. Importantly, these-doses are - approximately 10 times greater than those measured for the largest phantom. The risk of secondary cancer for this phantom size at the oesophagus, thyroid, and brain sites are 0.0443, 0.0106 and 0.0439 % respectively for 30 daily images of head and neck treatment. Dose calculations on both the CIRS and RANDO phantoms showed that for the single beam treatment, only 1 % difference in the mean dose values are delivered to the majority of insertions when using the original CT or CBCT images and respective calibration curves. The only exception was for dense bone, which exhibited a 2% difference. For the IMRT treatment plan results showed that when the CT scan image is used the mean doses were less than 1.1 %. Conclusion: CBCT doses from the OBI version 1.4 are significantly lower than doses from version 1.3, making it possible to use CBCT to assist with adaptive radiotherapy on a daily basis, without a significantly increased secondary cancer risk. This technology is a useful tool to aid patient positioning for radiotherapy and to allow v Abstract VI daily adaptive IGRT. Radiation dose varies significantly with both patient size and tumour position in relation to scanning mode. It is therefore recommended that patient-specific imaging protocols be considered, especially with regard to paediatric patients who can be expected to receive a higher dose. The single beam and the WRT comparisons showed that the CBCT images and calibration curves can be used in treatment planning.
42
Salas, de los Santos Marly Dorothy. "Dimorfismo sexual a través del foramen magno mediante tomografía computarizada Cone Beam." Bachelor's thesis, Universidad Nacional Mayor de San Marcos, 2019. https://hdl.handle.net/20.500.12672/9388.
Full textAbstract:
Determina el dimorfismo sexual a través de las dimensiones del foramen magno en adultos. La muestra estuvo constituida por tomografías cone beam de 272 pacientes (170 mujeres y 102 varones) en las cuales se midió dos parámetros (diámetro anteroposterior máximo, diámetro transversal máximo) mediante imágenes en corte axial. El área basada según Routal y Teixeira fueron obtenidas a partir de las mediciones. La información fue recolectada mediante un instrumento de recolección de datos. Para el análisis de datos se utilizó la prueba estadística de la t de Student para muestras independientes, correlación de Pearson y análisis de función discriminante. Se obtuvo diferencias significativas entre las dimensiones del foramen magno y el dimorfismo sexual (p<0.05). También se precisó el sexo mediante una ecuación de regresión lineal que incluía a los parámetros diámetro anteroposterior máximo, diámetro transversal máximo, área del foramen basada en fórmulas de Routal y Teixeira que predice el dimorfismo sexual en un 76.83%. Concluye que la estructura anatómica del foramen magno permite determinar el dimorfismo sexual en pacientes adultos.Tesis
43
Joshi, Jimish Dilip. "Characterization and Improvement of a Cone-Beam CT Scanner for Quantitative Imaging." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1284997522.
Full text
44
Allen, Jessica. "Evaluation of Maxillary Molar Furcations, Clinical Measurements versus Cone Beam Computed Tomography." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3407.
Full textAbstract:
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.
45
Chen, Shufei. "Markerless Lung Tumor Trajectory Estimation from Rotating Cone Beam Computed Tomography Projections." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4439.
Full textAbstract:
Respiration introduces large tumor motion in the thoracic region which influences treatment outcome for lung cancer patients. Tumor motion management techniques require characterization of temporal tumor motions because tumor motion varies patient to patient, day to day and cycle to cycle. This work develops a markerless algorithm to estimate 3 dimensional (3D) lung-tumor trajectories on free breathing cone beam computed tomography (CBCT) projections, which are 2 dimensional (2D) sequential images rotating about an axis and are used to reconstruct 3D CBCT images.
A gold standard tumor trajectory is required to guide the algorithm development and estimate the tumor detection accuracy for markerless tracking algorithms. However, a sufficient strategy to validate markerless tracking algorithms is lacking. A validation framework is developed based on fiducial markers. Markers are segmented and marker trajectories are xiv obtained. The displacement of the tumor to the marker is calculated and added to the segmented marker trajectory to generate reference tumor trajectory. Markerless tumor trajectory estimation (MLTM) algorithm is developed and improved to acquire tumor trajectory with clinical acceptable accuracy for locally advanced lung tumors. The development is separate into two parts. The first part considers none tumor deformation. It investigates shape and appearance of the template, moreover, a constraint method is introduced to narrow down the template matching searching region for more precise matching results. The second part is to accommodate tumor deformation near the end of the treatment. The accuracy of MLTM is calculated and compared against 4D CBCT, which is the current standard of care.
In summary, a validation framework based on fiducial markers is successfully built. MLTM is successfully developed with or without the consideration of tumor deformation with promising accuracy. MLTM outperforms 4D CBCT in temporal tumor trajectory estimation.
46
Hidalgo, Rivas Jose Alejandro. "Aspects of dental cone-beam computed tomography in children and young people." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/aspects-of-dental-conebeam-computed-tomography-in-children-and-young-people(6656111c-8b79-4ad2-b35c-e02d1f47d211).html.
Full textAbstract:
Cone-beam computed tomography (CBCT) has become increasingly popular in dentistry. It is usually associated with radiation doses that are lower than those seen with conventional computed tomography (CT) but greater than those seen with dental radiography. Because exposure to ionising radiation is associated with risks, the radiation protection principles of justification and optimisation should be applied. These are especially important in children and young people due to their greater risk of developing stochastic effects. Justification requires a balancing of the radiation risk with the potential benefits and the latter is dependent on diagnostic efficacy. There has been a proliferation of articles published on dental CBCT and there is a need to review this systematically so that diagnostic efficacy can be judged. In terms of optimisation, radiation dose reduction can be achieved in various ways, but the use of barrier materials to protect younger patients in CBCT has not been adequately tested. Reduction in exposure parameters in CBCT will lower doses but at the expense of a loss of image quality. While some efforts have been made to relate radiation exposure and image quality in CBCT, there is a need to develop low-dose CBCT protocols specifically for children and young people. The first aim of this thesis was to survey current uses of CBCT in children and young people in three United Kingdom dental hospitals. The second aim was to determine the efficacy of thyroid shielding in a child phantom testing several different designs, materials and thickness of thyroid shields. The third aim was to evaluate the evidence on diagnostic efficacy of dental CBCT for root fractures in permanent, non-endodontically treated, anterior teeth by conducting a systematic review. The fourth aim was to evaluate objective and subjective image quality in a laboratory study to determine a low-dose CBCT protocol which maintains adequate diagnostic image quality for a clinical indication in children. Finally, the aim was to evaluate this low-dose protocol in terms of image quality in real clinical situations. A high adherence to the European guidelines No 172 on radiation protection in dental CBCT was found amongst the surveyed hospitals. Thyroid shielding was found to be effective in dose reduction when performing a large field of view CBCT scan in a child phantom, but design influenced efficacy. The systematic review showed that research articles investigating CBCT diagnostic accuracy for vertical and horizontal root fractures had deficiencies in methodology, while only one study was identified addressing higher levels of diagnostic efficacy. A low-dose imaging protocol was identified in a laboratory study, which has been shown to be an effective tool in dose reduction providing an adequate diagnostic image quality and reducing radiation doses considerably for clinical indications in the anterior maxilla in children and young people.
47
Laurent, Caroline A. "An evaluation of facial asymmetry using three-dimensional cone-beam computed tomography." Diss., Search in ProQuest Dissertations & Theses. UC Only, 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1465485.
Full text
48
Kapralov, Mikhail. "EFFICIENT INVERSION OF THE CONE BEAM TRANSFORM FOR A GENERAL CLASS OF CURVES." Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2975.
Full textAbstract:
We extend an efficient cone beam transform inversion formula, proposed earlier for helices, to a general class of curves. The conditions that describe the class are very natural. Curves C are smooth, without self-intersections, have positive curvature and torsion, do not bend too much in a certain sense, and do not admit lines which are tangent to C at one point and intersect C at another point. A domain U is found where reconstruction is possible with a filtered backprojection type algorithm. Results of numerical experiments demonstrate very good image quality. The algorithm developed is useful for image reconstruction in computerized tomography.M.S.
Department of Mathematics
Sciences
Mathematical Science MS
49
Karimi, Davood. "Sparsity-based methods for image reconstruction and processing in cone-beam computed tomography." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/58483.
Full textAbstract:
X-ray computed tomography (CT) is an essential tool in modern medicine. As the scale and diversity of the medical applications of CT continue to increase, the quest for reducing the radiation dose becomes of extreme importance. However, producing high-quality images from low-dose scans has proven to be a serious challenge. Therefore, further research in developing more effective image reconstruction and processing algorithms for CT is necessary.
This dissertation explores the potential of patch-based image models and total variation (TV) regularization for improving the quality of low-dose CT images. It proposes novel algorithms for 1) denoising and interpolation of CT projection measurements (known as the sinogram), 2) denoising and restoration of reconstructed CT images, and 3) iterative CT image reconstruction.
For sinogram denoising, patch-based and TV-based algorithms are proposed. For interpolation of undersampled projections, an algorithm based on both patch-based and TV-based image models is proposed. Experiments show that the proposed algorithms substantially improve the quality of CT images reconstructed from low-dose scans and achieve state-of-the-art results in sinogram denoising and interpolation.
To suppress streak artifacts in CT images reconstructed from low-dose scans, an algorithm based on sparse representation in coupled learned dictionaries is proposed. Moreover, a structured dictionary is proposed for denoising and restoration of reconstructed CT images. These algorithms significantly improve the image quality and prove that highly effective CT post-processing algorithms can be devised with the help of learned overcomplete dictionaries.
This dissertation also proposes two iterative reconstruction algorithms that are based on variance-reduced stochastic gradient descent. One algorithm employs TV regularization only and proposes a stochastic-deterministic approach for image recovery. The other obtains better results by using both TV and patch-based regularizations. Both algorithms achieve convergence behavior and reconstruction results that are better than widely used iterative reconstruction algorithms compared to. Our results show that variance-reduced stochastic gradient descent algorithms can form the basis of very efficient iterative CT reconstruction algorithms.
This dissertation shows that sparsity-based methods, especially patch-based methods, have a great potential in improving the image quality in low-dose CT. Therefore, these methods can play a key role in the future success of CT.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
50
Dong, Xue. "Novel methods for scatter correction and dual energy imaging in cone-beam CT." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51903.
Full textAbstract:
Excessive imaging doses from repeated scans and poor image quality mainly due to scatter contamination are the two bottlenecks of cone-beam CT (CBCT) imaging. This study investigates a method that combines measurement-based scatter correction and a compressed sensing (CS)-based iterative reconstruction algorithm to generate scatter-free images from low-dose data. Scatter distribution is estimated by interpolating/extrapolating measured scatter samples inside blocked areas. CS-based iterative reconstruction is finally carried out on the under-sampled data to obtain scatter-free and low-dose CBCT images. In the tabletop phantom studies, with only 25% dose of a conventional CBCT scan, our method reduces the overall CT number error from over 220 HU to less than 25 HU, and increases the image contrast by a factor of 2.1 in the selected ROIs. Dual-energy CT (DECT) is another important application of CBCT. DECT shows promise in differentiating materials that are indistinguishable in single-energy CT and facilitates accurate diagnosis. A general problem of DECT is that decomposition is sensitive to noise in the two sets of projection data, resulting in severely degraded qualities of decomposed images. The first study of DECT is focused on the linear decomposition method. In this study, a combined method of iterative reconstruction and decomposition is proposed. The noise on the two initial CT images from separate scans becomes well correlated, which avoids noise accumulation during the decomposition process. To fully explore the benefits of DECT on beam-hardening correction and to reduce the computation cost, the second study is focused on an iterative decomposition method with a non-linear decomposition model for noise suppression in DECT. Phantom results show that our methods achieve superior performance on DECT imaging, with respect to noise reduction and spatial resolution.