Over the last fifteen years, there has been a rapid growth in the use of high resolution X-ray computed tomography (HRXCT) imaging in material science applications. We use it at nanoscale resolutions up to 50 nm (nano-CT) for key research problems in large scale operation of polymer electrolyte membrane fuel cells (PEMFC) and lithium-ion (Li-ion) batteries in automotive applications. PEMFC are clean energy sources that electrochemically react with hydrogen gas to produce water and electricity. To reduce their costs, capturing their electrode nanostructure has become significant in modeling and optimizing their performance. For Li-ion batteries, a key challenge in increasing their scope for the automotive industry is Li metal dendrite growth. Li dendrites are structures of lithium with 100 nm features of interest that can grow chaotically within a battery and eventually lead to a short-circuit. HRXCT imaging is an effective diagnostics tool for such applications as it is a non-destructive method of capturing the 3D internal X-ray absorption coefficient of materials from a large series of 2D X-ray projections. Despite a recent push to use HRXCT for quantitative information on material samples, there is a relative dearth of computational tools in nano-CT image processing and analysis. Hence, we focus on developing computational methods for nano-CT image analysis of fuel cell and battery materials as required by the limitations in material samples and the imaging environment. The first problem we address is the segmentation of nano-CT Zernike phase contrast images. Nano-CT instruments are equipped with Zernike phase contrast optics to distinguish materials with a low difference in X-ray absorption coefficient by phase shifting the X-ray wave that is not diffracted by the sample. However, it creates image artifacts that hinder the use of traditional image segmentation techniques. To restore such images, we setup an inverse problem by modeling the X-ray phase contrast optics. We solve for the artifact-free images through an optimization function that uses novel edge detection and fast image interpolation methods. We use this optics-based segmentation method in two main research problems - 1) the characterization of a failure mechanism in the internal structure of Li-ion battery electrodes and 2) the measurement of Li metal dendrite morphology for different current and temperature parameters of Li-ion battery cell operation. The second problem we address is the development of a space+time (4D) reconstruction method for in-operando imaging of samples undergoing temporal change, particularly for X-ray sources with low throughput and nanoscale spatial resolutions. The challenge in using such systems is achieving a sufficient temporal resolution despite exposure times of a 2D projection on the order of 1 minute. We develop a 4D dynamic X-ray computed tomography (CT) reconstruction method, capable of reconstructing a temporal 3D image every 2 to 8 projections. Its novel properties are its projection angle sequence and the probabilistic detection of experimental change. We show its accuracy on phantom and experimental datasets to show its promise in temporally resolving Li metal dendrite growth and in elucidating mitigation strategies. Keywords: X-ray computed tomography, 4D X-ray computed tomography, phase contrast optics, fuel cells, Li-ion batteries, signal processing and optimization.

The problem of reconstructing an image from a set of tomographic data is not new, nor is it lacking attention. However there is still a distinct gap between the mathematicians and the experimental scientists working in the computed tomography (CT) imaging community. One of the aims in this thesis is to bridge this gap with mathematical reconstruction algorithms and analysis approaches applied to practical CT problems. The thesis begins with an extensive analysis for assessing the suitability of reconstruction algorithms for a given problem. The paper presented examines the idea of extracting physical information from a reconstructed sample and comparing against the known sample characteristics to determine the accuracy of a reconstructed volume. Various test cases are studied, which are relevant to both mathematicians and experimental scientists. These include the variance in quality of reconstructed volume as the dose is reduced or the implementation of the level set evolution method, used as part of a simultaneous reconstruction and segmentation technique. The work shows that the assessment of physical attributes results in more accurate conclusions. Furthermore, this approach allows for further analysis into interesting questions in CT. This theme is continued throughout the thesis. Recent results in compressive sensing (CS) gained attention in the CT community as they indicate the possibility of obtaining an accurate reconstruction of a sparse image from severely limited or reduced amount of measured data. Literature produced so far has not shown that CS directly guarantees a successful recovery in X-ray CT, and it is still unclear under which conditions a successful sparsity regularized reconstruction can be achieved. The work presented in the thesis aims to answer this question in a practical setting, and seeks to establish a direct connection between the success of sparsity regularization methods and the sparsity level of the image, which is similar to CS. Using this connection, one can determine the sufficient amount of measurements to collect from just the sparsity of an image. A link was found in a previous study using simulated data, and the work is repeated here with experimental data, where the sparsity level of the scanned object varies. The preliminary work presented here verifies the results from simulated data, showing an "almost-linear" relationship between the sparsity of the image and the sufficient amount of data for a successful sparsity regularized reconstruction. Several unexplained artefacts are noted in the literature as the `partial volume', the 'exponential edge gradient' or the 'penumbra' effect, with no clear explanation for their cause, or established techniques to remove them. The work presented in this paper shows that these artefacts are due to a non-linearity in the measured data, which comes from either the set up of the system, the scattering of rays or the dependency of linear attenuation on wavelength in the polychromatic case. However, even in monochromatic CT systems, the non-linearity effect can be detected. The paper shows that in some cases, the non-linearity effect is too large to ignore, and the reconstruction problem should be adapted to solve a non-linear problem. We derive this non-linear problem and solve it using a numerical optimization technique for both simulatedand real, gamma-ray data. When compared to reconstructions obtained using the standard linear model, the non-linear reconstructed images show clear improvements in that the non-linear effect is largely eliminated. The thesis is finished with a highlight article in the special issue of Solid Earth, named "Pore-scale tomography & imaging - applications, techniques and recommended practice". The paper presents a major technical advancement in a dynamic 3D CT data acquisition, where the latest hardware and optimal data acquisition plan are applied and as a result, ultra fast 3D volume acquisition was made possible. The experiment comprised of fast, free-falling water-saline drops traveling through a pack of rock grains with varying porosities. The imaging work was enhanced by the use of iterative methods and physical quantification analysis performed. The data acquisition and imaging work is the first in the field to capture a free falling drop and the imaging work clearly shows the fluid interaction with speed, gravity and more importantly, the inter- and intra-grain fluid transfers.

X-ray scatter in cone-beam computed tomography (CBCT) is known to reduce image quality by introducing image artifacts, reducing contrast, and limiting computed tomography (CT) number accuracy. The extent of the effect of x-ray scatter on CBCT image quality is determined by the shape and magnitude of the scatter distribution in the projections. A method to allay the effects of scatter is imperative to enable application of CBCT to solve a wider domain of clinical problems. The work contained herein proposes such a method. A characterization of the scatter distribution through the use of a validated Monte Carlo (MC) model is carried out. The effects of imaging parameters and compensators on the scatter distribution are investigated. The spectral frequency components of the scatter distribution in CBCT projection sets are analyzed using Fourier analysis and found to reside predominately in the low frequency domain. The exact frequency extents of the scatter distribution are explored for different imaging configurations and patient geometries. Based on the Fourier analysis it is hypothesized the scatter distribution can be represented by a finite sum of sine and cosine functions. The fitting of MC scatter distribution estimates enables the reduction of the MC computation time by diminishing the number of photon tracks required by over three orders of magnitude. The fitting method is incorporated into a novel scatter correction method using an algorithm that simultaneously combines multiple MC scatter simulations. Running concurrent MC simulations while simultaneously fitting the results allows for the physical accuracy and flexibility of MC methods to be maintained while enhancing the overall efficiency. CBCT projection set scatter estimates, using the algorithm, are computed on the order of 1-2 minutes instead of hours or days. Resulting scatter corrected reconstructions show a reduction in artifacts and improvement in tissue contrast and voxel value accuracy.

X-ray scatter in cone-beam computed tomography (CBCT) is known to reduce image quality by introducing image artifacts, reducing contrast, and limiting computed tomography (CT) number accuracy. The extent of the effect of x-ray scatter on CBCT image quality is determined by the shape and magnitude of the scatter distribution in the projections. A method to allay the effects of scatter is imperative to enable application of CBCT to solve a wider domain of clinical problems. The work contained herein proposes such a method. A characterization of the scatter distribution through the use of a validated Monte Carlo (MC) model is carried out. The effects of imaging parameters and compensators on the scatter distribution are investigated. The spectral frequency components of the scatter distribution in CBCT projection sets are analyzed using Fourier analysis and found to reside predominately in the low frequency domain. The exact frequency extents of the scatter distribution are explored for different imaging configurations and patient geometries. Based on the Fourier analysis it is hypothesized the scatter distribution can be represented by a finite sum of sine and cosine functions. The fitting of MC scatter distribution estimates enables the reduction of the MC computation time by diminishing the number of photon tracks required by over three orders of magnitude. The fitting method is incorporated into a novel scatter correction method using an algorithm that simultaneously combines multiple MC scatter simulations. Running concurrent MC simulations while simultaneously fitting the results allows for the physical accuracy and flexibility of MC methods to be maintained while enhancing the overall efficiency. CBCT projection set scatter estimates, using the algorithm, are computed on the order of 1-2 minutes instead of hours or days. Resulting scatter corrected reconstructions show a reduction in artifacts and improvement in tissue contrast and voxel value accuracy.

Made available in DSpace on 2014-10-09T12:34:55Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:59Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP:09/07417-9

Submitted by Renata Lopes (renatasil82@gmail.com) on 2015-12-02T16:29:15Z No. of bitstreams: 1 marianarochanadaes.pdf: 1380064 bytes, checksum: f78140bd2137599acdd476c8c0e433a7 (MD5) / Rejected by Adriana Oliveira (adriana.oliveira@ufjf.edu.br), reason: Coreeção letras maiúsculas título on 2015-12-03T11:30:57Z (GMT) / Submitted by Renata Lopes (renatasil82@gmail.com) on 2015-12-03T11:36:28Z No. of bitstreams: 1 marianarochanadaes.pdf: 1380064 bytes, checksum: f78140bd2137599acdd476c8c0e433a7 (MD5) / Rejected by Adriana Oliveira (adriana.oliveira@ufjf.edu.br), reason: Título: somente primeira letra da primeira palavra em maiúsculo e nomes próprios também. Palavras-chave: primeira letra de cada palavra em maiúsculo. Acrescentar uma em cada linha (não precisa colocar ponto e nem vírgula no final) on 2015-12-03T11:59:32Z (GMT) / Submitted by Renata Lopes (renatasil82@gmail.com) on 2015-12-03T13:42:04Z No. of bitstreams: 1 marianarochanadaes.pdf: 1380064 bytes, checksum: f78140bd2137599acdd476c8c0e433a7 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2015-12-03T13:59:10Z (GMT) No. of bitstreams: 1 marianarochanadaes.pdf: 1380064 bytes, checksum: f78140bd2137599acdd476c8c0e433a7 (MD5) / Made available in DSpace on 2015-12-03T13:59:10Z (GMT). No. of bitstreams: 1 marianarochanadaes.pdf: 1380064 bytes, checksum: f78140bd2137599acdd476c8c0e433a7 (MD5) Previous issue date: 2015-02-06 / FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais / Apesar das muitas indicações da tomografia computadorizada de feixe cônico (TCFC) na Odontologia, a avaliação da qualidade óssea, por meio das Unidades Hounsfield (HU), não apresenta um consenso sobre sua precisão e confiabilidade. O objetivo neste estudo foi avaliar, por meio de uma revisão sistemática da literatura, os principais resultados de pesquisas que compararam diversos materiais em exames de tomografia computadorizada multislice (TCMS) e TCFC, utilizando HU como unidade de medida. Para isso, foi realizada uma busca na base de dados Medline (PubMed) utilizando as palavras chaves “cone beam computed tomography”, “cone beam tomography”, “cbct”, “Hounsfield unit” e “Hounsfield”. A exclusão dos artigos foi realizada, inicialmente, por meio da leitura do título e resumo e, posteriormente, após a leitura do texto completo. Os dados da amostra selecionada (n=8) foram distribuídos em tabelas, possibilitando sua comparação. Os resultados obtidos em relação à aplicação de HU em TCFC foram divergentes, com alguns autores aplicando diretamente HU nesse exame, outros desenvolvendo fatores de correção para essa comparação e outros ainda, invalidando a utilização dessa unidade em exames de TCFC. Apenas um estudo concluiu que se pode aplicar diretamente HU em TCFC, sem prejuízo para avaliação das densidades dos tecidos. Assim, pode-se concluir que uma nova abordagem é necessária para o desenvolvimento de futuros trabalhos nessa linha e que a tentativa de aplicar HU em TCFC deveria ser abandonada. / Despite the many indications of cone beam computed tomography (CBCT) in dentistry, there is no consensus regarding the accuracy and reliability of bone quality assessment, through Hounsfield Units (HU). The aim of this study was to evaluate, through a systematic review of the literature, the main results of studies comparing various tissues in multislice CT (MSCT) and CBCT scans, using the HU as the unit of measurement. To this end, a search was conducted in the Medline (PubMed) database using the keywords "cone beam computed tomography", "cone beam tomography", "CBCT", "Hounsfield unit", and "Hounsfield". Articles were initially excluded by reading the title and abstract, and were later excluded after reading the full text. The data from the selected sample (n = 8) were tabulated and compared. The results obtained regarding the application of HU in CBCT were divergent, with some authors directly applying HU in CBCT, others developing correction factors for this comparison, and still others invalidating the use of this unit in CBCT. Only one study concluded that is possible to directly apply HU in CBCT, without damaging the evaluation of tissue densities. In this way, it’s possible to affirm that a new approach is necessary for the development of future work in this line and that the attempt to apply HU in CBCT should be abandoned.

The objective of this study is to determine the diagnostic performance of computed tomography perfusion (CTP) with and without computed tomography angiography (CTA) in assessment of hemodynamically significant coronary artery lesions in comparison to invasive fractional flow reserve (FFR). Materials and Methods PubMed and Cochrane Center Register of Controlled Trials from January 2010 searched through December 2014. Nine original studies were selected evaluating the diagnostic performance of CTP with and without CTA to invasive coronary angiography in evaluation of hemodynamic significance of coronary lesions (n = 951). Results The sensitivity, specificity, LR+ and LR- and DOR of CTA+CTP were 0.85 [95% confidence interval (CI: 0.79-0.89)] 0.94 (CI: 0.91-0.97), 15.8 (CI: 7.99-31.39), 0.146 (CI: 0.08-0.26), and 147.2 (CI: 69.77-310.66). Summary Receiver Operating Characteristics (SROC) results showed area under the curve (AUC) of 0.97 indicating that CTA+CTP may detect hemodynamically significant coronary artery lesions with high accuracy. The sensitivity, specificity, LR+ and LR- and DOR of CTP were 0.83 (CI: 0.78-0.87), 0.84 (CI: 0.80-0.87) 5.26 (CI: 2.93-9.43), 0.209 (CI: 0.12-0.36), and 31.97 (CI: 11.59-88.20). Conclusions This result suggests that CTP with CTA significantly improves diagnostic performance of coronary artery lesions compared to CTA alone and closely comparable with invasive FFR.

Unsicherheiten in der Reichweitevorhersage limitieren wesentlich das Ausnutzen der Vorteile von Protonentherapie gegenüber konventioneller Strahlentherapie. Die Verwendung von Zwei-Spektren-Computertomographie (DECT) zur direkten Vorhersage des Bremsvermögen (DirectSPR) ermöglicht eine relevante Verbesserung der Reichweitevorhersage gegenüber der üblicherweise verwendeten Ein-Spektren-Computertomographie (SECT). Im Rahmen dieser Dissertation wurde die Variation in der Reichweitevorhersage zwischen 17 europäischen Partikeltherapiezentren experimentell verglichen. Die Genauigkeit der Reichweitevorhersage bei Verwendung einer DirectSPR-Implementierung wurde umfassend quantifiziert und die Implementierung in die klinische Routine integriert. Dies führte zu einer Reduzierung des klinischen Sicherheitssaum um ca. 35% für die Behandlung von quasistatischen Tumoren in Kopf und Becken und damit einer Schonung des Normalgewebes sowie der das Zielgebiet umgebenden Risikoorgane. Darüber hinaus wurde die DirectSPR-Implementierung zur Bestimmung von Gewebeparametern sowie deren Variabilität für zehn Organe im Kopf und Becken in einer Patienkohorte genutzt. Die vorgestellten Ergebnisse etablieren DECT weiter als zukünftiges Standard-Bildgebungsverfahren in der Partikeltherapie.:1. Introduction 2. Proton therapy 2.1. Physical principles of proton therapy 2.2. Treatment with protons 2.3. Accuracy in proton therapy 3. CT Imaging for proton therapy 3.1. Principles of CT imaging 3.2. CT-based range prediction 3.3. Investigated phantoms and materials 3.4. DECT scan acquisition 3.5. Determination of proton stopping power for reference materials 4. Accuracy of stopping-power prediction in European proton centres 4.1. Study design 4.2. Experimental setup and analysis 4.3. Results 4.4. Discussion of determined deviations 4.5. Conclusion and outlook 4.6. Establishment of guidelines for HLUT calibration 5. Range uncertainties in DirectSPR-based treatment planning 5.1. Clinical implementation of DirectSPR 5.2. Uncertainty quantification 5.3. Resulting uncertainties in SPR prediction 5.4. Experimental validation 5.5. Dosimetric effect of range uncertainty reduction 5.6. Discussion 6. In-vivo tissue characterisation using DirectSPR 6.1. Tissue parameter determination by Woodard and White 6.2. Data preparation and analysis 6.3. Determined tissue parameters and variations 6.4. Discussion 7. The future of image-based range prediction 7.1. Particle imaging 7.2. Creation of synthetic CT images 7.3. Photon-counting computed tomography 8. Summary 9. Zusammenfassung A. Supplement A.1. Investigated materials A.2. EPTN study: Individual results A.3. DirectSPR validation results / Imaging-related range uncertainties effectively limit the full exploitation of the benefits proton therapy offers with respect to conventional photon radiotherapy. The use of dual-energy computed tomography (DECT) for direct stopping-power prediction (DirectSPR) was determined to provide relevant improvements in range prediction over commonly used singleenergy CT (SECT). Within this thesis, the variation in range prediction accuracy between 17 European particle treatment centres were experimentally quantified to determine the current status quo in the community. The overall range uncertainty when using a DirectSPR implementation in treatment planning was comprehensively quantified and the implementation integrated into the clinical workflow. This led to a reduction of clinical safety margins by about 35% for the treatment of quasi-static tumours in the head and pelvis, effectively reducing the dose to surrounding healthy tissue and organs at risk. The DirectSPR implementation was furthermore utilised to assess tissue parameters and their inter- and intra-patient variability for ten organs in the head and pelvis from a cohort of patients. The presented results further establish DirectSPR as the future standard imaging modality in particle therapy.:1. Introduction 2. Proton therapy 2.1. Physical principles of proton therapy 2.2. Treatment with protons 2.3. Accuracy in proton therapy 3. CT Imaging for proton therapy 3.1. Principles of CT imaging 3.2. CT-based range prediction 3.3. Investigated phantoms and materials 3.4. DECT scan acquisition 3.5. Determination of proton stopping power for reference materials 4. Accuracy of stopping-power prediction in European proton centres 4.1. Study design 4.2. Experimental setup and analysis 4.3. Results 4.4. Discussion of determined deviations 4.5. Conclusion and outlook 4.6. Establishment of guidelines for HLUT calibration 5. Range uncertainties in DirectSPR-based treatment planning 5.1. Clinical implementation of DirectSPR 5.2. Uncertainty quantification 5.3. Resulting uncertainties in SPR prediction 5.4. Experimental validation 5.5. Dosimetric effect of range uncertainty reduction 5.6. Discussion 6. In-vivo tissue characterisation using DirectSPR 6.1. Tissue parameter determination by Woodard and White 6.2. Data preparation and analysis 6.3. Determined tissue parameters and variations 6.4. Discussion 7. The future of image-based range prediction 7.1. Particle imaging 7.2. Creation of synthetic CT images 7.3. Photon-counting computed tomography 8. Summary 9. Zusammenfassung A. Supplement A.1. Investigated materials A.2. EPTN study: Individual results A.3. DirectSPR validation results

L'objectif de cette thèse était de quantifier le réseau lacuno-canaliculaire du tissu osseux à partir d’images 3D acquises en nano CT synchrotron de phase. Ceci a nécessité d’optimiser les processus d’acquisition et de reconstruction de phase, ainsi que de développer des méthodes efficaces de traitement d'images pour la segmentation et l’analyse 3D. Dans un premier temps, nous avons étudié et évalué différents algorithmes de reconstruction de phase. Nous avons étendu la méthode de Paganin pour plusieurs distances de propagation et l’avons évaluée et comparée à d’autres méthodes, théoriquement puis sur nos données expérimentales Nous avons développé une chaine d’analyse, incluant la segmentation des images et prenant en compte les gros volumes de données à traiter. Pour la segmentation des lacunes, nous avons choisi des méthodes telles que le filtre médian, le seuillage par hystérésis et l'analyse par composantes connexes. La segmentation des canalicules repose sur une méthode de croissance de région après rehaussement des structures tubulaires. Nous avons calculé des paramètres de porosité, des descripteurs morphologiques des lacunes ainsi que des nombres de canalicules par lacune. Par ailleurs, nous avons introduit des notions de paramètres locaux calculés dans le voisinage des lacunes. Nous avons obtenu des résultats sur des images acquises à différentes tailles de voxel (120nm, 50nm, 30nm) et avons également pu étudier l’impact de la taille de voxel sur les résultats. Finalement ces méthodes ont été utilisées pour analyser un ensemble de 27 échantillons acquis à 100 nm dans le cadre du projet ANR MULTIPS. Nous avons pu réaliser une analyse statistique pour étudier les différences liées au sexe et à l'âge. Nos travaux apportent de nouvelles données quantitatives sur le tissu osseux qui devraient contribuer à la recherche sur les mécanismes de fragilité osseuse en relation avec des maladies comme l’ostéoporose. / Osteoporosis is a bone fragility disease resulting in abnormalities in bone mass and density. In order to prevent osteoporotic fractures, it is important to have a better understanding of the processes involved in fracture at various scales. As the most abundant bone cells, osteocytes may act as orchestrators of bone remodeling which regulate the activities of both osteoclasts and osteoblasts. The osteocyte system is deeply embedded inside the bone matrix and also called lacuno-canalicular network (LCN). Although several imaging techniques have recently been proposed, the 3D observation and analysis of the LCN at high spatial resolution is still challenging. The aim of this work was to investigate and analyze the LCN in human cortical bone in three dimensions with an isotropic spatial resolution using magnified X-ray phase nano-CT. We performed image acquisition at different voxel sizes of 120 nm, 100 nm, 50 nm and 30 nm in the beamlines ID16A and ID16B of the European Synchrotron Radiation Facility (ESRF - European Synchrotron Radiation Facility - Grenoble). Our first study concerned phase retrieval, which is the first step of data processing and consists in solving a non-linear inverse problem. We proposed an extension of Paganin’s method suited to multi-distance acquisitions, which has been used to retrieve phase maps in our experiments. The method was compared theoretically and experimentally to the contrast transfer function (CTF) approach for homogeneous object. The analysis of the 3D reconstructed images requires first to segment the LCN, including both the segmentation of lacunae and of canaliculi. We developed a workflow based on median filter, hysteresis thresholding and morphology filters to segment lacunae. Concerning the segmentation of canaliculi, we made use of the vesselness enhancement to improve the visibility of line structures, the variational region growing to extract canaliculi and connected components analysis to remove residual noise. For the quantitative assessment of the LCN, we calculated morphological descriptors based on an automatic and efficient 3D analysis method developed in our group. For the lacunae, we calculated some parameters like the number of lacunae, the bone volume, the total volume of all lacunae, the lacunar volume density, the average lacunae volume, the average lacunae surface, the average length, width and depth of lacunae. For the canaliculi, we first computed the total volume of all the canaliculi and canalicular volume density. Moreover, we counted the number of canaliculi at different distances from the surface of each lacuna by an automatic method, which could be used to evaluate the ramification of canaliculi. We reported the statistical results obtained on the different groups and at different spatial resolutions, providing unique information about the organization of the LCN in human bone in three dimensions.

O propósito deste estudo foi avaliar a acurácia do exame de tomografia computadorizada multislice (TCM) e tomografia computadorizada por feixe cônico (TCFC) na identificação de lesões simuladas em mandíbula, em situações com e sem a presença de artefatos metálicos, em diversos protocolos de observação. Foram realizados exames de TCM e TCFC de mandíbulas secas, nas quais foram executadas perfurações simulando lesões. As imagens foram realizadas em dois momentos: na presença e na ausência de restaurações dentárias metálicas. Dois observadores, previamente calibrados, observaram as imagens avaliando-as quanto à presença ou ausência de lesão, número de lojas das lesões e a existência ou não de invasão medular. Os mesmos utilizaram programas de manipulação de imagens instalados em estações de trabalho independentes, para reconstruir as imagens nos seguintes protocolos de avaliação: axial, sagital + coronal, 3D, conjunto (axial+sagital+coronal+3D) e parassagital. A sensibilidade e especificidade (validade) da tomografia computadorizada multislice (64 cortes) (TCM) e da tomografia computadorizada por feixe cônico (TCFC) para diagnóstico de lesões ósseas (simuladas) em mandíbula, utilizando estação de trabalho independente foram demonstradas à medida que os valores encontrados foram superiores a 95% desde que com o protocolo de observação adequado. A influência de artefatos dentários metálicos foi pouco significativa na interpretação de lesões ósseas mandibulares, já que os valores de acurácia nas análises com e sem artefato foram bastante próximas. Os protocolos com aquisição por TCM sofreram mais influência dos artefatos do que os adquiridos por TCFC (valores sutilmente menores), exceto nas reconstruções em 3D, em que as originadas de aquisição por TCFC, apresentaram valores menores de acurácia. O melhor protocolo de pós processamento para interpretação de lesões ósseas simuladas foi o denominado RMP+3D. O protocolo que apresentou os piores resultados foi o que utilizou as reconstruções parassagitais. / The purpose of this study was to evaluate the accuracy of multislice computed tomography (MSCT) and cone-beam computed tomography (CBCT) in identification of simulated mandibular lesions in situations with and without metallic artifacts in several observation protocols. MSCT and CBCT examinations were performed in dry mandibles, in which holes were performed simulating lesions. The images were taken in two stages: in the presence and absence of metal dental restorations. Two observers, previously calibrated, observed the images by evaluating the images for the presence or absence of lesion, loci number and whether there were medullary invasion. Observers used image manipulation softwares, installed on independent workstations, to reconstruct the images in the following evaluation protocols: axial, sagittal + coronal, 3D, sets (axial+ coronal + sagittal + 3 D) and parasagittal. The sensitivity and specificity of MSCT (64 slices) and CBCT for diagnosis of simulated bone lesions in the mandible, using independent workstation were demonstrated as the values obtained were greater than 95% using the appropriate observation protocol. The influence of dental metallic artifacts was negligible in the interpretation of mandibular bone lesions, since the values of accuracy in the analysis with and without artifact were quite close. The images acquired with MCT suffered more influence of artifacts than the protocols acquired by TCFC, although the values were all high and quite close. Except for 3D reconstructions, which originated from the CBCT, showed the lowest accuracy. The best protocol for post-processing and interpretation of simulated bone lesions was called RMP +3 D. The protocol that showed the worst results was parasagital.