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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

CHARACTERISATION OF SAMPLES OF ORE PARTICLES USING X-RAY MICRO-TOMOGRAPHY

Murat Cakici Unknown Date (has links)
The degree of mineral liberation is important for the efficiency of subsequent physical separation processes such as froth flotation. Mineral liberation studies involve determining the volumetric abundance or volumetric grade distribution of a specific mineralogical phase in a particular mineral. Currently, methodologies for assessing mineral liberation are laborious regarding sample preparation, analysis time (from weeks to months), and the need for stereological correction. These constraints can be eliminated by using X-ray CT which gives the cross-sections directly from three-dimensional data in shorter time (from ten minutes to hours) with minimal sample preparation. X-ray computed tomography (CT) is a non-destructive technique which allows three-dimensional visualisation of inner structures of an object based on the variations in density and atomic composition. Initially, it was developed as a medical tool for imaging soft tissue and bone. During the last decade, the number of X-ray CT applications in engineering and geology has steadily increased, with the improvements in performance and imaging capabilities. The aim of the present work is to apply X-ray CT technique for finely divided ore samples and to study the relationship between mineral liberation and CT results. Four different ore types were used in this study: Northparkes ore (Australia), Ernest Henry ore (Australia), Keetac ore (USA) and Cannington ore (Australia). Different settings of the desktop X-ray CT technique were applied for each particular ore sample for several ore liberation (particle size distribution) properties. Two dimensional CT images were reconstructed from the three-dimensional X-ray CT data. It was found that the settings for CT technique were a function of the ore type. Particularly in the case of Cannington (high density ore) the best setting conditions split from the rest of the ores tested. The appearance of different artifacts occurring during the analysis were studied and kept to the minimum. A functionality between mineral liberation and CT results was found. The variables affecting the most the results were the Voltage and Minimum Intensity Percentage. Contrary to the expected trends, variables having a negligible effect on the results were found to be exposure time / equivalent Al filter thickness.
12

CHARACTERISATION OF SAMPLES OF ORE PARTICLES USING X-RAY MICRO-TOMOGRAPHY

Murat Cakici Unknown Date (has links)
The degree of mineral liberation is important for the efficiency of subsequent physical separation processes such as froth flotation. Mineral liberation studies involve determining the volumetric abundance or volumetric grade distribution of a specific mineralogical phase in a particular mineral. Currently, methodologies for assessing mineral liberation are laborious regarding sample preparation, analysis time (from weeks to months), and the need for stereological correction. These constraints can be eliminated by using X-ray CT which gives the cross-sections directly from three-dimensional data in shorter time (from ten minutes to hours) with minimal sample preparation. X-ray computed tomography (CT) is a non-destructive technique which allows three-dimensional visualisation of inner structures of an object based on the variations in density and atomic composition. Initially, it was developed as a medical tool for imaging soft tissue and bone. During the last decade, the number of X-ray CT applications in engineering and geology has steadily increased, with the improvements in performance and imaging capabilities. The aim of the present work is to apply X-ray CT technique for finely divided ore samples and to study the relationship between mineral liberation and CT results. Four different ore types were used in this study: Northparkes ore (Australia), Ernest Henry ore (Australia), Keetac ore (USA) and Cannington ore (Australia). Different settings of the desktop X-ray CT technique were applied for each particular ore sample for several ore liberation (particle size distribution) properties. Two dimensional CT images were reconstructed from the three-dimensional X-ray CT data. It was found that the settings for CT technique were a function of the ore type. Particularly in the case of Cannington (high density ore) the best setting conditions split from the rest of the ores tested. The appearance of different artifacts occurring during the analysis were studied and kept to the minimum. A functionality between mineral liberation and CT results was found. The variables affecting the most the results were the Voltage and Minimum Intensity Percentage. Contrary to the expected trends, variables having a negligible effect on the results were found to be exposure time / equivalent Al filter thickness.
13

Análise quantitativa de modelos de prototipagem rápida baseados em dados de tomografia volumétrica, por meio de inspeção de engenharia reversa tridimensional / Quantitative analysis of rapid prototyping models based on datas of cone beam computerized tomography by inspection of three-dimensional reverse engineering

Fatima Maria de Angelis Kang 18 September 2009 (has links)
O objetivo neste estudo foi avaliar a reprodutibilidade quantitativa dos modelos tridimensionais gerados por meio de imagens de tomografia volumétrica de feixe cônico, obtidos por dois tomógrafos volumétricos NEWTOM 9000 DVT (i- (Quantitative Radiology, Verona, Itália) e i-CAT (Imaging Sciencies Int. Hatfield, Pensilvânia. Estados Unidos da América), submetidos à inspeção de engenharia reversa. Uma mandíbula macerada foi digitalizada por meio do SCANNER 3D VIVID 910, com precisão de 0,01 mm, associado à fotometria digital, sendo utilizado o software GEOMAGIC STUDIO, e assim obteve-se um modelo considerado padrão ouro. Posteriormente realizamos o exame de tomografia volumétrica de feixe cônico, na mesma mandíbula nos dois tomógrafos volumétricos, obtendo-se assim os modelos virtuais tridimensionais. Por meio de um alinhamento das geometrias do padrão ouro com os modelos virtuais resultantes da tomografia do aparelho NEWTOM 9000 DVT e do i-CAT, foram observadas as possíveis discrepâncias. Concluímos que estas alterações encontradas após a análise quantitativa das diversas regiões foram menores nas imagens adquiridas pelo tomógrafo volumétrico de feixe cônico modelo i-CAT, e portanto possibilitam a geração de modelos de prototipagem rápida de melhor qualidade. / The purpose of this study was to evaluate the quantitative reproductability of the 3d models created using CT images. The images used were obtained from two different cone beam tomographs: NEWTOM 9000 DVT (Quantitative Radiology, Verona, Italy) and i-CAT ( Imaging Sciences Int., Hatfield, EUA) and then inspected through reverse engineering processing software. A dry mandible was digitalized using a 3D Scanner VIVID 910 and the GEOMAGIC STUDIO software to obtain a 0,01mm precision model considered to be our gold standard. Two distinct 3D virtual models were then created after submitting the same dry mandible to a cone beam exam on both tomographs (NEWTOM and i-Cat). Possible discrepancies between the 3D models and the gold standard were analyzed through and alignment of their geometries. After evaluating the discrepancies at the different sites of the models, we concluded that the virtual model obtained using the i-Cat tomograph images was more accurate and therefore of greater quality.
14

3D Image Reconstruction Using Optical Phase Retrieval And Cone-Beam Tomography

Hemanth, T 02 1900 (has links) (PDF)
No description available.
15

Impacto da tomografia de feixe cônico e da experiência profissional no planejamento do tratamento com implantes dentários / Impact of cone beam tomography and professional experience in dental implant treatment planning

Fortes, João Henrique Parise 19 January 2017 (has links)
O objetivo deste estudo foi investigar variações no planejamento pré-cirúrgico para tratamento com implantes dentários entre cirurgiões dentistas com diferentes níveis de experiência profissional utilizando-se apenas a radiografia panorâmica (PAN), ou associando-a a tomografia computadorizada de feixe cônico (PAN+TCFC). Materiais e métodos: seis cirurgiões-dentistas, de dois diferentes níveis de experiência (sênior: Sr e júnior: Jr) executaram planejamentos pré-cirúrgicos simulados em PANs e após um mês em PAN+TCFCs, considerando os parâmetros: comprimento do implante (CI); largura do implante (LI); necessidade de enxerto ósseo (EO); necessidade de outros procedimentos cirúrgicos (PC). Para observar a concordância entre os planejamentos usando PAN e PAN+TCFC em relação a CI e LI, foi utilizado o teste estatístico de Bland-Altman. O coeficiente de kappa foi usado para observar a concordância entre os examinadores em relação a indicação de EO e PC. Os dados foram analisados por meio do software GraphPad Prism, versão 6.0. Resultados: O teste de Bland-Altman mostrou boa concordância nos planejamentos para os valores de CI e LI interexaminadores (Srs x Jrs) e intraexaminadores (PAN x TCFC). A estatística descritiva mostrou que examinadores Jrs indicam implantes dentários de maior largura quando planejam a partir da PAN em comparação com a TCFC. O teste de kappa mostrou forte (k>0,75) concordância entre examinadores Jrs e Srs nos planejamentos para tratamento com implantes em relação a indicação de outros procedimentos (PAN e TCFC). Na indicação de enxertos ósseos o nível de concordância entre os examinadores foi forte (k>0,75) quando o planejamento foi feito com PAN e regular quando o planejamento foi feito com TCFC. Conclusão: de acordo com a interpretação de nossos dados, há variações no planejamento pré-cirúrgico para tratamento com implantes dentários relacionadas a experiência profissional e o tipo de exame de imagem utilizado para o planejamento. / The purpose of this study was to investigate variations in pre-surgical planning for dental implant treatment among dental surgeons with different levels of professional experience using panoramic radiography (PAN) or associating it with computed cone beam tomography (PAN + TCFC). Materials and methods: Six dentists, from two different levels of experience (Senior: Sr and Junior: Jr) performed simulated pre-surgical planning in PANs and after one month in PANs + TCFCs, considering the parameters: implant length (CI); Implant width (LI); Need for bone graft (EO); Need for other surgical procedures (PC). In order to observe the agreement between the planning using PAN and PAN + TCFC in relation to IC and LI, the Bland-Altman test was used. The kappa coefficient was used to observe agreement between the examiners regarding the indication of OE and PC. Data were analyzed using GraphPad Prism software, version 6.0. Results: The Bland-Altman test showed good agreement in the plans for inter-examiner (Sr x Jr) and intra-examiner (PAN x TCFC) values. Descriptive statistics have shown that Jr examiners indicate larger dental implants when planning from PAN compared to TCFC. The kappa test showed strong (k> 0.75) agreement between Jr and Sr examiners in the plans for treatment with implants in relation to the indication of other procedures (PAN and TCFC). In the indication of bone grafts the level of concordance between the examiners was strong (k> 0.75) when planning was done with PAN and regular when planning was done with TCFC. Conclusion: according to the interpretation of our data, there are variations in the pre-surgical planning for treatment with dental implants related to professional experience and the type of imaging test used for the planning.
16

Periodontite apical induzida em cães: efeito do tratamento endodôntico. Estudo microbiológico, tomográfico e de microscopia confocal

Zapata, Ronald Ordinola 05 November 2009 (has links)
Este trabalho teve o objetivo de avaliar a capacidade da bactéria Enterococcus faecalis em induzir periodontite apical no modelo experimental canino; verificar se o preparo químico-mecânico afeta a sobrevivência dessa bactéria no sistema de canais radiculares e avaliar o reparo desses dentes por meio de radiografia periapical e tomografia computadorizada cone beam. Dentes com e sem tratamento endodôntico foram avaliados por meio de microscopia confocal de varredura a laser. Para tal, foram utilizados 2 cães. A bactéria Enterococcus faecalis foi inoculada nos canais de 4 pré-molares superiores, 11 prémolares inferiores e 9 incisivos superiores. As câmaras pulpares foram seladas e, após 60 dias, os canais das raízes distais dos pré-molares e de 7 incisivos superiores foram submetidos a tratamento endodôntico em sessão única e os canais das raízes mesiais dos pré-molares e 2 incisivos superiores foram deixados sem tratamento (controle). Amostras microbiológicas foram feitas antes e após o preparo químico-mecânico. O reparo foi avaliado após 6 meses do tratamento mediante radiografias periapicais e por tomografia computadorizada cone beam. A comparação entre as imagens obtidas após o período experimental pelos 2 métodos foi feita por medições da área em mm2 de cada lesão encontrada, utilizando o software ImageTool Os resultados mostraram que a presença de periodontite apical crônica foi verificada em todos os dentes inoculados, independentemente da colonização pela bactéria Enterococcus faecalis ou pela flora mista. O preparo químico-mecânico reduziu significativamente o número de bactérias no interior dos canais radiculares (p<0.05). Os resultados radiográficos e tomográficos demonstraram lesões de menor diâmetro nos dentes tratados endodonticamente em comparação ao grupo controle (p<0.05). A comparação entre os métodos demonstrou diferença estatística entre eles sendo evidenciada áreas radiolúcidas maiores utilizando a tomografia cone beam em comparação com a radiografia periapical (p<0.05). Concluiu-se que a bactéria Enterococcus faecalis induziu periodontite apical crônica similarmente à flora mista; o tratamento endodôntico reduziu o número de bactérias cultiváveis significativamente embora sem relação com o reparo radiográfico. Os dentes tratados em sessão única apresentavam lesões menores em comparação aos não-tratados e as áreas das lesões observadas na TC cone beam foram maiores do que as áreas encontradas nas radiografias periapicais. A microscopia confocal e o método proposto neste estudo se mostraram eficazes para determinar, qualitativamente, a viabilidade bacteriana e a distribuição de ácidos nucléicos bacterianos dentro dos túbulos dentinários. Houve diferença entre a dentina infectada in vitro com o padrão de infecção in vivo, caracterizada pela presença de biofilmes aderidos à parede do canal radicular. / The aims of this study were to evaluate the Enterococcus faecalis ability to induce apical periodontitis in dogs root canals, to verify the bacterias ability to survive to the cleaning and shaping procedures and to assess the healing of the induced apical periodontitis by periapical radiograph and cone beam computed tomography. Also, endodontically treated and non-treated teeth were evaluated by confocal laser scanning microscope. Two mongrel dogs were used in the experiment. Enterococcus faecalis strain was inoculated into the root canals of 4 maxillary premolars, 11 mandibular premolars and 9 maxillary incisors. After 60 days the root canals of the distal roots of the mandibular and maxillary pre-molars and 7 maxillary incisors were endodontically treated. The premolars mesial root canal and 2 maxillary incisors were used as control (no treatment). Microbiologic samples were done after and before the cleaning and shaping procedure. The healing was evaluated after 6 months by periapical radiographs and cone beam computed tomography. The comparison between obtained images after the experimental period by the two methods was done using measures of the lesion area in mm2 with ImageTool software. The results showed the presence of chronic apical periodontitis in every inoculated teeth, with Enterococcus faecalis or mixed infection. The cleaning and shaping procedures reduced the number of bacteria of the root canals (p<0.05). The radiographic and tomographic results showed the lower diameter lesion in endodontically treated teeth than in the control group (p<0.05). The comparison between the methods showed statistical difference and greater radiolucent areas were evident in cone beam computed tomography images (p<0.05). It is possible to conclude that the bacteria Enterococcus faecalis induced chronic apical periodontitis as well as the mixed microflora; the endodontic treatment reduced the number of cultivable bacteria in a significant way, but with no relation to the radiographic healing. The treated teeth in only one session presented smaller lesions in comparison to the non-treated teeth and the lesions area in cone beam computed tomography were bigger than the areas found in periapical radiograph. The confocal microscopy and the proposed method of this study showed to be efficient to determine the bacterial ability and the distribution of bacterial nucleic acids inside the dentin tubules. There was difference between in vitro infected dentin with the in vivo infection pattern, which presents biofilm attached to the root canal walls.
17

Impacto da tomografia de feixe cônico e da experiência profissional no planejamento do tratamento com implantes dentários / Impact of cone beam tomography and professional experience in dental implant treatment planning

João Henrique Parise Fortes 19 January 2017 (has links)
O objetivo deste estudo foi investigar variações no planejamento pré-cirúrgico para tratamento com implantes dentários entre cirurgiões dentistas com diferentes níveis de experiência profissional utilizando-se apenas a radiografia panorâmica (PAN), ou associando-a a tomografia computadorizada de feixe cônico (PAN+TCFC). Materiais e métodos: seis cirurgiões-dentistas, de dois diferentes níveis de experiência (sênior: Sr e júnior: Jr) executaram planejamentos pré-cirúrgicos simulados em PANs e após um mês em PAN+TCFCs, considerando os parâmetros: comprimento do implante (CI); largura do implante (LI); necessidade de enxerto ósseo (EO); necessidade de outros procedimentos cirúrgicos (PC). Para observar a concordância entre os planejamentos usando PAN e PAN+TCFC em relação a CI e LI, foi utilizado o teste estatístico de Bland-Altman. O coeficiente de kappa foi usado para observar a concordância entre os examinadores em relação a indicação de EO e PC. Os dados foram analisados por meio do software GraphPad Prism, versão 6.0. Resultados: O teste de Bland-Altman mostrou boa concordância nos planejamentos para os valores de CI e LI interexaminadores (Srs x Jrs) e intraexaminadores (PAN x TCFC). A estatística descritiva mostrou que examinadores Jrs indicam implantes dentários de maior largura quando planejam a partir da PAN em comparação com a TCFC. O teste de kappa mostrou forte (k>0,75) concordância entre examinadores Jrs e Srs nos planejamentos para tratamento com implantes em relação a indicação de outros procedimentos (PAN e TCFC). Na indicação de enxertos ósseos o nível de concordância entre os examinadores foi forte (k>0,75) quando o planejamento foi feito com PAN e regular quando o planejamento foi feito com TCFC. Conclusão: de acordo com a interpretação de nossos dados, há variações no planejamento pré-cirúrgico para tratamento com implantes dentários relacionadas a experiência profissional e o tipo de exame de imagem utilizado para o planejamento. / The purpose of this study was to investigate variations in pre-surgical planning for dental implant treatment among dental surgeons with different levels of professional experience using panoramic radiography (PAN) or associating it with computed cone beam tomography (PAN + TCFC). Materials and methods: Six dentists, from two different levels of experience (Senior: Sr and Junior: Jr) performed simulated pre-surgical planning in PANs and after one month in PANs + TCFCs, considering the parameters: implant length (CI); Implant width (LI); Need for bone graft (EO); Need for other surgical procedures (PC). In order to observe the agreement between the planning using PAN and PAN + TCFC in relation to IC and LI, the Bland-Altman test was used. The kappa coefficient was used to observe agreement between the examiners regarding the indication of OE and PC. Data were analyzed using GraphPad Prism software, version 6.0. Results: The Bland-Altman test showed good agreement in the plans for inter-examiner (Sr x Jr) and intra-examiner (PAN x TCFC) values. Descriptive statistics have shown that Jr examiners indicate larger dental implants when planning from PAN compared to TCFC. The kappa test showed strong (k> 0.75) agreement between Jr and Sr examiners in the plans for treatment with implants in relation to the indication of other procedures (PAN and TCFC). In the indication of bone grafts the level of concordance between the examiners was strong (k> 0.75) when planning was done with PAN and regular when planning was done with TCFC. Conclusion: according to the interpretation of our data, there are variations in the pre-surgical planning for treatment with dental implants related to professional experience and the type of imaging test used for the planning.
18

Periodontite apical induzida em cães: efeito do tratamento endodôntico. Estudo microbiológico, tomográfico e de microscopia confocal

Ronald Ordinola Zapata 05 November 2009 (has links)
Este trabalho teve o objetivo de avaliar a capacidade da bactéria Enterococcus faecalis em induzir periodontite apical no modelo experimental canino; verificar se o preparo químico-mecânico afeta a sobrevivência dessa bactéria no sistema de canais radiculares e avaliar o reparo desses dentes por meio de radiografia periapical e tomografia computadorizada cone beam. Dentes com e sem tratamento endodôntico foram avaliados por meio de microscopia confocal de varredura a laser. Para tal, foram utilizados 2 cães. A bactéria Enterococcus faecalis foi inoculada nos canais de 4 pré-molares superiores, 11 prémolares inferiores e 9 incisivos superiores. As câmaras pulpares foram seladas e, após 60 dias, os canais das raízes distais dos pré-molares e de 7 incisivos superiores foram submetidos a tratamento endodôntico em sessão única e os canais das raízes mesiais dos pré-molares e 2 incisivos superiores foram deixados sem tratamento (controle). Amostras microbiológicas foram feitas antes e após o preparo químico-mecânico. O reparo foi avaliado após 6 meses do tratamento mediante radiografias periapicais e por tomografia computadorizada cone beam. A comparação entre as imagens obtidas após o período experimental pelos 2 métodos foi feita por medições da área em mm2 de cada lesão encontrada, utilizando o software ImageTool Os resultados mostraram que a presença de periodontite apical crônica foi verificada em todos os dentes inoculados, independentemente da colonização pela bactéria Enterococcus faecalis ou pela flora mista. O preparo químico-mecânico reduziu significativamente o número de bactérias no interior dos canais radiculares (p<0.05). Os resultados radiográficos e tomográficos demonstraram lesões de menor diâmetro nos dentes tratados endodonticamente em comparação ao grupo controle (p<0.05). A comparação entre os métodos demonstrou diferença estatística entre eles sendo evidenciada áreas radiolúcidas maiores utilizando a tomografia cone beam em comparação com a radiografia periapical (p<0.05). Concluiu-se que a bactéria Enterococcus faecalis induziu periodontite apical crônica similarmente à flora mista; o tratamento endodôntico reduziu o número de bactérias cultiváveis significativamente embora sem relação com o reparo radiográfico. Os dentes tratados em sessão única apresentavam lesões menores em comparação aos não-tratados e as áreas das lesões observadas na TC cone beam foram maiores do que as áreas encontradas nas radiografias periapicais. A microscopia confocal e o método proposto neste estudo se mostraram eficazes para determinar, qualitativamente, a viabilidade bacteriana e a distribuição de ácidos nucléicos bacterianos dentro dos túbulos dentinários. Houve diferença entre a dentina infectada in vitro com o padrão de infecção in vivo, caracterizada pela presença de biofilmes aderidos à parede do canal radicular. / The aims of this study were to evaluate the Enterococcus faecalis ability to induce apical periodontitis in dogs root canals, to verify the bacterias ability to survive to the cleaning and shaping procedures and to assess the healing of the induced apical periodontitis by periapical radiograph and cone beam computed tomography. Also, endodontically treated and non-treated teeth were evaluated by confocal laser scanning microscope. Two mongrel dogs were used in the experiment. Enterococcus faecalis strain was inoculated into the root canals of 4 maxillary premolars, 11 mandibular premolars and 9 maxillary incisors. After 60 days the root canals of the distal roots of the mandibular and maxillary pre-molars and 7 maxillary incisors were endodontically treated. The premolars mesial root canal and 2 maxillary incisors were used as control (no treatment). Microbiologic samples were done after and before the cleaning and shaping procedure. The healing was evaluated after 6 months by periapical radiographs and cone beam computed tomography. The comparison between obtained images after the experimental period by the two methods was done using measures of the lesion area in mm2 with ImageTool software. The results showed the presence of chronic apical periodontitis in every inoculated teeth, with Enterococcus faecalis or mixed infection. The cleaning and shaping procedures reduced the number of bacteria of the root canals (p<0.05). The radiographic and tomographic results showed the lower diameter lesion in endodontically treated teeth than in the control group (p<0.05). The comparison between the methods showed statistical difference and greater radiolucent areas were evident in cone beam computed tomography images (p<0.05). It is possible to conclude that the bacteria Enterococcus faecalis induced chronic apical periodontitis as well as the mixed microflora; the endodontic treatment reduced the number of cultivable bacteria in a significant way, but with no relation to the radiographic healing. The treated teeth in only one session presented smaller lesions in comparison to the non-treated teeth and the lesions area in cone beam computed tomography were bigger than the areas found in periapical radiograph. The confocal microscopy and the proposed method of this study showed to be efficient to determine the bacterial ability and the distribution of bacterial nucleic acids inside the dentin tubules. There was difference between in vitro infected dentin with the in vivo infection pattern, which presents biofilm attached to the root canal walls.
19

Truncated Data Problems In Helical Cone-Beam Tomography

Anoop, K P 06 1900 (has links)
This report delves into two of the major truncated data problems in helical cone-beam tomography: Axial truncation and Lateral truncation. The problem of axial truncation, also classically known as the Long Object problem, was a major challenge in the development of helical scan tomography. Generalization of the Feldkamp method (FDK) for circular scan to the helical scan trajectory was known to give reasonable solutions to the problem. The FDK methods are approximate in nature and hence provide only approximate solution to the long object problem. Recently, many methods which provide exact solution to this problem have been developed the major breakthrough being the Katsevich’s algorithm which is exact, efficient and also requires lesser detector area compared to Feldkamp methods. The first part of the report deals with the implementation strategies for methods capable of handling axial truncation. Here, we specifically look at the exact and efficient Katsevich’s solution to long object problem and the class of approximate solutions provided by the generalized FDK formulae. The later half of the report looks at the lateral truncation problem and suggests new methods to handle such truncation in helical scan CT. Simulation results for reconstruction with laterally truncated projection data, assuming it to be complete, gives severe artifacts which even penetrates into the field of view (FOV). A row-by-row data completion approach using Linear Prediction is introduced for helical scan truncated data. An extension/improvement of this technique known as Windowed Linear Prediction approach is introduced. Efficacy of both these techniques are shown using simulation with standard phantoms. Various image quality measures for the resulting reconstructed images are used to evaluate the performance of the proposed methods against an already existing technique. Motivated by a study of the autocorrelation and partial autocorrelation functions of the projection data the use of a non-stationary linear model, the ARIMA model, is proposed for data completion. The new model is first validated in the 2D truncated data situation. Also a method of incorporating the parallel beam data consistency condition into this new method is considered. Performance evaluation of the new method with consistency condition shows that it can outperform the existing techniques. Simulation experiments show the efficacy of the ARIMA model for data completion in 2D as well as 3D truncated data scenario. The model is shown to work well for the laterally truncated helical cone-beam case.
20

Die dentale Volumentomographie in Diagnostik und Nachsorge fibro-ossärer Läsionen

Düerkop, Andrea Katharina 20 January 2012 (has links) (PDF)
Die Radiologie fungiert als wesentliches Instrument in der Diagnostik und Nachsorge fibro-ossärer Läsionen (FOL). Hierbei gewinnen überlagerungsfreie, dreidimensionale Aufnahmen aufgrund der im Kopf-Halsbereich vorhandenen hohen Dichte und Vielfalt anatomischer Strukturen und der damit einhergehenden Fülle von Differentialdiagnosen an Bedeutung. Anhand der Studie wurden die röntgenologischen Charakteristika von ossären Dysplasien (OD) und ossifizierenden Fibromen (OF) im dentalen Volumentomogramm herausgestellt, sowie diagnostische und therapeutische Vorteile der dentalen Volumentomographie (DVT) im Vergleich zur Orthopantomographie (OPG) und Computertomographie (CT) ermittelt und gegenübergestellt. Zu diesem Zwecke wurden anhand eines Fragebogens 18 Röntgenbildpaare (OPG-DVT) von FOL durch zehn Betrachter auf (A) deren röntgenologische Eigenschaften sowie Metallartefakte befundet und (B) deren Abbildungsqualität von sehr gut (1) bis schlecht (5) bzw. nicht beurteilbar bewertet. Insgesamt wurden 360 Analysebögen ausgewertet. Entitäts- und röntgentechnikspezifische Unterschiede wurden statistisch ermittelt. Die Abbildungsqualitäten der DVT und CT wurden auf Grundlage einer intensiven Literaturrecherche verglichen. Die Ergebnisse dieser Studie stellten signifikante Unterschiede in den röntgenologischen Eigenschaften von OD und OF heraus. Acht von zehn Strukturen zeigten in den DVT-Aufnahmen eine signifikant bessere Abbildungsqualität im Vergleich zu den OPG-Aufnahmen. Die teilweise gravierenderen Befunde in den DVT-Aufnahmen deuteten auf eine Unterinterpretation dieser Befunde im OPG hin. Die Literaturrecherche zu Gegenüberstellungen der Abbildungsqualitäten in CT und DVT wies nahezu ausnahmslos auf eine Überlegenheit der DVT hin.

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