La radiothérapie est une modalité importante dans le traitement de néoplasie telle que le cancer pulmonaire. Cependant, les poumons sont susceptibles à des toxicités radio-induites comme la pneumonie radique et la fibrose pulmonaire radique. Plusieurs patients souffrant du cancer pulmonaire ont aussi des comorbidités tel la maladie obstructive pulmonaire chronique, qui affecte déjà leur fonction respiratoire. Actuellement, la planification de la radiothérapie tient compte de l’anatomie mais non de la fonction différentielle des poumons. La planification de la radiothérapie guidée par la fonction aurait pour but d’inclure cette fonction différentielle dans le processus de planification, évitant l’irradiation du parenchyme sain et améliorant le profil de toxicités du traitement. Différentes techniques d’imagerie fonctionnelle sont présentement à l’étude. La tomodensitométrie à double-énergie (DECT, dual-energy computed tomography) est une technique qui utilises des rayons-X d’énergie différente, permettant une meilleure différentiation du matériel. L’article présenté dans ce mémoire étudie une technique préalablement décrite de décomposition de matériaux qui utilise des cartographies d’iodine dérivées des images de DECT avec contraste. Nous avons réalisé une étude longitudinale de la perfusion pulmonaire, un indicateur de la fonction respiratoire. Des patients avec un cancer pulmonaire traités avec radiothérapie stéréotaxique ou conventionnelle ont été recrutés de façon prospective et ont eu un DECT avec contraste avant le début des traitements et 6 et 12 mois post-traitement. Des réponses fonctionnelles normalisées ont été calculées à 6 et 12 mois pour 3 catégories de dose d’irradiation : moins de 5 Gray, 5-20 Gray et plus de 20 Gray. Aux analyses statistiques, nous avons observé une corrélation de cette réponse avec la dose de radiation reçue. Les régions qui ont reçu le plus de dose ont démontré une plus grande baisse de fonction. La réponse fonctionnelle normalisée est également corrélée avec le temps écoulé post-radiothérapie. Nous avons conclu que la cartographie d’iodine dérivée du DECT permet d’évaluer l’effet de la dose de radiation sur les changements fonctionnels du parenchyme pulmonaire post-radiothérapie. Ainsi, le DECT permet d'évaluer les changements de fonction pulmonaire post-radiothérapie et pourrait être utilisé pour évaluer les dommages post-radiques. / Radiotherapy is an important modality in the treatment of malignancies such as lung cancer. However, the lungs are susceptible to radiation-induced lung injury such as radiation pneumonitis and radiation fibrosis. In addition, many lung cancer patients also suffer from comorbidities such as chronic obstructive lung disease, which affect their baseline respiratory function. Current standard of care for radiotherapy planning considers the anatomy but not the differential function of the lungs. Function-guided radiotherapy planning would seek to include the differential function of the lungs, avoiding the irradiation of healthy parenchyma, therefore improving the toxicity profile of the treatment. Currently, different functional imaging techniques are being studied for this purpose. Dual-energy computed tomography (DECT) is a technique which uses two X-rays of different energy, allowing improved material differentiation. The article presented in this thesis studies the use of a previously described 2-material decomposition technique using iodine maps derived from contrast-enhanced DECT images. This allows for the longitudinal evaluation of lung perfusion, a surrogate for respiratory function. Lung cancer patients who were treated with stereotactic radiotherapy or conventional radiotherapy were prospectively enrolled and underwent a contrast-enhanced DECT before the treatment and at 6 and 12 months post-treatment. Normalized functional responses were calculated at 6 and 12 months for three dose ranges: less than 5 Gray, 5-20 Gray and more than 20 Gray. This normalized functional response was found to correlate with the dose received. The regions receiving the most radiation dose demonstrate the greatest decrease in function. It was also found be correlated with the time elapsed after radiotherapy. We concluded that DECT-derived iodine maps can be used to evaluate the dose-response effect of radiation on lungs. DECT can therefore be an interesting technique to study post-treatment pulmonary parenchymal changes and can be used to assess post-radiation damage.

Polymethylmethacrylate (PMMA) removal during septic total joint arthroplasty revision is associated with a high fracture and perforation risk. Ultrasonic cement removal is considered a bone-preserving technique. Currently, there is still a lack of sound data on efficacy as it is difficult to detect smaller residues with reasonable technical effort. However, incomplete removal is associated with the risk of biofilm coverage of the residue. Therefore, the study aimed to investigate the efficiency of ultrasonic-based PMMA removal in a human cadaver model. The femoral components of a total hip and a total knee prosthesis were implanted in two cadaver femoral canals by 3rd generation cement fixation technique. Implants were then removed. Cement mantle extraction was performed with the OSCAR-3-System ultrasonic system (Orthofix®). Quantitative analysis of cement residues was carried out with dual-energy and microcomputer tomography. With a 20 µm resolution, in vitro microcomputer tomography visualized tiniest PMMA residues. For clinical use, dual-energy computer tomography tissue decomposition with 0.75 mm resolution is suitable. With ultrasound, more than 99% of PMMA was removed. Seven hundred thirty-four residues with a mean volume of 0.40 ± 4.95 mm3 were identified with only 4 exceeding 1 cm in length in at least one axis. Ultrasonic cement removal of PMMA was almost complete and can therefore be considered a highly effective technique. For the first time, PMMA residues in the sub-millimetre range were detected by computer tomography. Clinical implications of the small remaining PMMA fraction on the eradication rate of periprosthetic joint infection warrants further investigations.

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Dual energy X-ray absorptiometry (DXA) has been well established in both clinical and research settings for measurement of bone mineral density (BMD), and is becoming more widely utilized for assessment of body composition. Reliability and validity are essential factors in both applications of this technique; however, neither have been confirmed for the QDR-4500A DXA at Virginia Tech. Therefore, measurements of the whole body (WB), lumbar spine (LS), total proximal femur (TPF) and total forearm (TF) were made in a group of young-adult males and females at two time-points, 5-7 days apart. Significant differences were not found in BMD (g/cm2) at these body sites with repeated measurements by DXA. Furthermore, measures of percent body fat (%BF), lean body mass (LBM), and fat mass (FM) by DXA were reliable. Validity of %BF by DXA was assessed from comparison to single-frequency bioelectrical impedance analysis (BIA). Significant differences were not found in measures of %BF by DXA and BIA. A second study investigated the reliability and validity of the QDR-4500A DXA in measurements of distal tibia (DT) BMD. Significant differences were not found between repeated measurements. Validity was established by a significant correlation between WB BMD and DT BMD. A third study examined the influence of navel jewelry on the accuracy of LS DXA measurements. Repeated measurements with a spine phantom revealed that both a navel ring and a barbell produced significantly greater measures of LS BMD compared to the spine phantom alone. Manual correction of navel jewelry did not eliminate BMD inaccuracies. Data from these studies confirmed that the QDR-4500A DXA at Virginia Tech was a reliable and valid device in measurement of WB, LS, TPF, TF and DT BMD, as well as %BF, LBM, and FM. In addition, effects of navel jewelry on LS BMD have been recognized. Further studies investigating the reliability and validity of DT BMD measures as well as effects of different types, gauges, and shapes of body jewelry on BMD measures in human subjects are warranted. / Master of Science

Orientador: Guilherme de Paula Nogueira / Banca: Yuri Tani Utsunomiya / Banca: Marco Antonio Rodrigues Fernandes / Resumo: O objetivo desse estudo foi inferir a Densidade Mineral óssea (DMO) a partir da imagem radiográfica (Raios-X) usando como referência a DMO de uma escada de alumínio mensurada por Absorciometria por de Duas-Energias (DXA). Para isso foram utilizadas 30 amostras de tecido ósseo cortical e 30 amostras de tecido ósseo trabecular de osso bovino "in vitro". Foram mensurados neste estudo a Densidade Mineral Óssea (DMO), o Conteúdo Mineral Ósseo (CMO) ambos obtidos pelo densitômetro LUNAR®-DPX ALPHA; a Quantidade Mineral Óssea (QMO) massa das cinzas após a calcinação das amostras; a densidade real das amostras (dReal=massa/volume). Foram feitas 10 tomadas de RX com as 60 amostras, entremeadas pela escada de alumínio (referencial densitométrico). A correlação entre as técnicas (DR-tons de cinza e DXA g/cm2) gerou equações de regressão para cada uma das dez radiografias e permitiu inferir a densidade mineral óssea (DMODR), obtida através da conversão dos tons de cinza em densidade radiográfica pelo software ImageJ® para cada uma das 10 tomadas radiográficas; calculou-se então a média da densidade mineral óssea calculada pela densitometria radiográfica (XDMODR) de todas as dez radiografias. Foi observado que a média da densidade real das amostras foi de 2,2±0,23g/cm2 e 1,05±0,09g/cm2 enquanto que a média da densidade mensurada pelo DXA foi de 0,73±0,11g/cm2 e 0,22±0,11g/cm2, observou que a media da DMODR ficou em 0,93±0,11g/cm2 e 0,34±0,14 g/cm2 para o osso cortical e trabecular respect... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The aim of this study was to infer the bone mineral density (BMD) from the radiographic image (X-X) with reference to the BMD of an aluminum step wedge measured by absorptiometry Dual-energy (DXA). For this we used 30 samples of cortical bone 30 and cancellous bone tissue samples of bovine bone "in vitro". Were measured in this study Bone Mineral Density (BMD), bone mineral content (BMC) both obtained by densitometer LUNAR® DPX-ALPHA; Volume Bone Mineral (QMO) mass of ash after calcination of the samples; the real density of the samples (dReal = mass / volume). 10 taken RX were made with the samples 60, interspersed by aluminum step wedge (densitometric reference). The correlation between the techniques (gray DR-tones and DXA g / cm 2) generated regression equations for each of the ten X-rays and allowed to infer bone mineral density (DMODR) obtained by converting grayscale radiographic density by ImageJ® for each of the 10 radiographic taken. It was then calculated average bone mineral density calculated by X-ray densitometry (XDMODR) radiographs of all ten. Was observed that the average true density of the samples was 2.2±0.23g/cm2 and 1.05±0.09g/cm2 while the average density measured by DXA was 0.73±0.11g/cm2 and 0.22±0.11g/cm2 interesting that the average DMODR was 0.93±0.11g/cm2 and 0.34±0.14g/cm2 for cortical and cancellous bone respectively. The average of the BMC was 0.19±0.08g and 0.9±0.02g, and the average QMO 0.14±0.04g and 0.05±0 03g for cortical and cancellous bo... (Complete abstract click electronic access below) / Mestre

Objectifs : L’objectif a été de d’optimiser les protocoles d’acquisition des examens d’angiomammographie double-énergie, d’étudier la faisabilité de l’angiotomosynthèse pour la détection et la caractérisation des tumeurs mammaires, et d’étudier la faisabilité des biopsies stéréotaxiques sous guidage de l’angiomammographie. Méthodes : Une étude d’optimisation des paramètres d’acquisition de l’angiomammographie a été réalisée dans 4 situations cliniques pour lesquelles la qualité diagnostique requise des images de basse énergie et la dose totale délivrée à la patiente ne sont pas identiques. L’optimisation des paramètres d'exposition (anode/filtre, kVp, mAs) des images de basse énergie (BE) et haute énergie (HE) a été réalisée à partir d’une modélisation théorique de la chaîne d’acquisition. Une validation a été effectuée par mesures expérimentales sur des images de fantôme d’inserts d’iode. Nous avons ensuite étudié la technique d’angiotomosynthèse mammaire basée sur une approche double-énergie. Un nouveau fantôme anthropomorphique numérique du sein et de ses lésions, basé sur l’utilisation de primitives géométriques complexes et d’une technique de maillage surfacique, a été amélioré et utilisé pour évaluer les performances de l’angiomammographie optimisée, puis de l’angiotomosynthèse en comparaison à l’angiomammographie. Enfin, nous avons proposé un scénario pour la réalisation d’un examen de stéréotaxie avec injection d’un agent de contraste iodé et étudié la faisabilité de recombinaison d’image de haute et de basse énergie acquises à des temps différents de l’injection.Résultats et conclusion : Les optima des paramètres d’exposition trouvés par simulation avec les valeurs de SDNRpixel et SDNR2pixel /Dosetotale qui en résultent, ont été confirmés expérimentalement. Les valeurs de SDNR par pixel dans les images recombinées sont augmentées pour toutes les indications cliniques en comparaison à celle obtenues avec SenoBright ® (produit commercial de référence). L'impact sur la qualité de l’image de BE, évalué par des expérimentations sur fantôme CDMAM, a montré que les paramètres optimisés fournissent une détection similaire ou acceptable par rapport à la mammographie standard, à l’exception de l'indication de dépistage lorsque l’on considère les objets de très petits diamètres.L’étude de lecture humaine d’images simulées d’un fantôme anthropomorphique du sein incluant le rehaussement glandulaire physiologique et différents modèle tumoraux n’a pas montré d’augmentation significative de sensibilité de détection des acquisition 3D d’angiotomosynthèse comparativement aux acquisitions 2D d’angiomammographie. Les deux paramètres qui influençaient le plus la sensibilité était la concentration en iode des tumeurs et la densité du sein. L’angiomammographie était par ailleurs significativement plus spécifique que l’angiotomosynthèse. Une perspective d’amélioration pour l’angiotomosynthèse pourrait donc être l’utilisation d’algorithmes de reconstruction 3D spécifiques de cette modalité qui minimiseraient le bruit de reconstruction. Le scénario proposé pour la réalisation de biopsies sous guidage de l’angiomammographie, a mis en évidence deux contraintes techniques que sont l’échauffement du tube à rayons X et le surcroit de dose dû à la répétition des paires d’acquisitions en haute et basse énergies. Une des solutions envisagées a été de limiter le nombre d’acquisitions de BE. Notre étude a montré que la recombinaison d’une image HE avec une image BE acquise antérieurement modifiait le SDNR des lésions simulées comparativement à une recombinaison appariée d’images BE et HE acquises au même temps de l’injection. Ces modifications dépendaient du temps du pic de rehaussement maximal et du washout de la lésion. / Objectives: The purpose was to optimize the exposure parameters of CESM examinations, to assess the feasibility of contrast-enhanced DBT (CE-DBT) for the detection and the characterization of breast tumors, and to assess CESM-guided stereotactic biopsies. Methods: At first, we optimized the CESM exposure parameters in four different clinical applications for which different levels of average glandular dose and different low energy image quality are required. The optimization of exposure parameters (anode/filter, kVp, mAs) for low energy (LE) and high energy (HE) images at different levels of average glandular dose and different ratios between LE and total doses has been conducted using a simulator of the x-ray mammographic image chain. An experimental validation was then performed through phantom experiments. Secondly, we assessed the potential of CE-DBT based on a dual-energy approach. A new mesh-based anthropomorphic breast phantom was improved and used to evaluate the performance of CESM and then to compare CESM and CE-DBT. Finally, we evaluated the technical feasibility of CESM-guided biopsy. After identifying some technical constraints, we assessed the performance of the recombination of LE and HE images acquired at different times after injection, using simulated images of a geometric phantom with uniform texture, and simulated images of an anthropomorphic textured phantom with and without motion artifacts.Results and conclusion : For the four different clinical indications, optima found by simulation, with resulting SDNRpixel and SDNR2pixel/Dosetotal, were confirmed through real acquisition of images on phantoms. Our results indicate that the SDNR per pixel in recombined CESM images increased in all of the four clinical indications compared to recombined images obtained using SenoBright ® (commercial product used as reference). This result suggests the possibility to detect more subtle contrast enhancements and to decrease the number of false negatives found in clinical CESM examinations. The impact of a new dose allocation between LE and HE exposures was also evaluated on LE image quality. Results from CDMAM phantom experiments indicate that optimized parameters provide similar or acceptable detection compared to standard mammography, except for screening indication when considering the very small diameter objects.The human observer study on anthropomorphic phantom images, taking into account tumor and breast parenchyma enhancement, revealed that detection and characterization sensitivity of iodine-enhanced lesions are not statistically different between 2D CESM and 3D CE-DBT. The most influencing parameters for the detectability and the lesion size assessment were the lesion iodine concentration and the breast density. CESM was significantly more specific than CE-DBT. One of the assumptions to explain this result is the presence of higher noise in CE-DBT than in CESM images. A future improvement for CE-DBT could therefore be the design of a specific reconstruction algorithm minimizing reconstructed noise.With respect to CESM-guided biopsy the proposed scenario pointed out two major constraints, one related to the thermal load of the x-ray tube, the second related to the increased dose due to the repetition of LE and HE images. One proposed solution was to limit the number of LE exposures, requiring the possibility to recombined LE and HE images acquired at different injection time points. Our study showed that the recombination of a HE image with a LE image acquired earlier leads to SDNR changes compared to paired recombination. These changes are function of the enhancement time to peak and the washout of the lesion, and had a limited impact on the lesion detectability.

Nesta tese, buscou-se avaliar se a tomografia computadorizada de duplaenergia pós-contraste (TCDE) é capaz de detectar diferenças regionais da perfusão pulmonar em um modelo animal suíno incluindo variações de decúbito, lesão alveolar e oclusão da artéria pulmonar com balão, comparando estes resultados com os obtidos pela perfusão de primeira passagem com a tomografia computadorizada dinâmica (TCD). Dez suínos landrace foram divididos em Grupos A (N = 5, controle) e B (N = 5). Animais do Grupo B foram submetidos ao protocolo de lesão alveolar induzida por ventilação mecânica (LPIV). O volume sanguíneo perfundido e o fluxo sanguíneo pulmonar foram, respectivamente, estimados pela TCDE (%VSPTCDE) e pela TCD (FSPTCD), em diversas condições experimentais: posição supina versus prona, presença versus ausência de LPIV, presença ou ausência de oclusão da artéria pulmonar. A correlação entre %VSPTCDE e FSPTCD foi moderada (R = 0,60) com ampla variabilidade (intervalo 0,35-0,91) entre animais. %VSPTCDE e FSPTCD demonstraram padrões similares de heterogeneidade da perfusão pulmonar nas diferentes condições experimentais. Entretanto, reduções do %VSPTCDE causadas pela oclusão com balão foram em média -29,32 %, enquanto reduções do FSPTCD foram em média -86,78 % (p < 0,001). Estimativas quantitativas do VSPTCDE tiveram um erro médio de +4.3 ml/100g em comparação com o FSPTCD, com limites de concordância de 95 % entre -16,6 ml/100g e 25,1 ml/100g. A TCDE póscontraste é capaz de prover estimativas semiquantitativas que refletem a heterogeneidade regional da perfusão pulmonar causada por mudanças de decúbito, lesão alveolar e oclusão da artéria pulmonar com balão, apresentando moderada correlação com a perfusão de primeira passagem pela TCD / We aimed to evaluate whether contrast-enhanced dual-energy CT (DECT) detects regional pulmonary perfusion changes in a swine model of acute lung injury, with variations in decubitus and transient occlusion of the pulmonary artery, comparing these results with those obtained with dynamic CT perfusion (DynCT). Ten landrace swine were assigned to Groups A (N = 5, control) and B (N = 5). Group B was subjected to ventilator-induced lung injury (VILI). Perfused blood volume and pulmonary blood flow were quantified by DECT (PBVDECT) and DynCT (PBFDynCT), respectively, under different settings: supine versus prone, and with/without balloon occlusion of a pulmonary artery (PA) branch. Correlation of regional PBVDECT versus PBFDynCT was moderate (R = 0.60) with high variability (range 0.35-0.91) among the animals. Regional pulmonary perfusion changes assessed by %PBVDECT agreed with PBFDynCT in response to decubitus changes, lung injury and balloon occlusion in the multivariate analysis. However, reductions in %PBVDECT caused by balloon occlusion were in average -29.32 %, whereas reductions in PBFDynCT were in average -86.78 % (p < 0.001). Quantitative estimates of PBVDECT had a mean bias of +4.3 ml/100g in comparison with PBVDynCT, with 95 % confidence intervals between -16.6 ml/100g and 25.1 ml/100g. Semiquantitative contrastenhanced DECT reflects regional changes in perfusion caused decubitus changes, acute lung injury, and balloon occlusion of the PA, with moderate correlation in comparison with DynCT

A Tomografia Computadorizada de Energia Dupla (DECT em inglês) é um dos campos das imagens tomográficas que mais evoluiu nos últimos anos. O DECT usa dois espectros para irradiar pacientes e é capaz de diferenciar tecidos com base na sua composição elementar. Apesar de serem semelhantes aos dispositivos padrão de tomografia, para essa modalidade é necessário o desenvolvimento de ferramentas específicas que permitam o estudo de suas propriedades de imagem. O objetivo deste trabalho era construir um sistema simulado de Tomografia Computadorizada (TC) com a capacidade de produzir imagens semelhantes às obtidas em dispositivos DECT reais. O TC simulado também permitiria explorar as propriedades das imagens de materiais de teste antes de sua construção física. Este trabalho presenta a simulação do processo de aquisição de imagens de um dispositivo DECT que funciona a partir da troca rápida de kV, o GE Discovery CT 750 HD. A geometria simulada foi baseada num dispositivo atualmente disponível no InRad (Instituto de Radiologia da Faculdade de Medicina da Universidade de São Paulo). As simulações foram realizadas usando o código Monte Carlo PENELOPE/penEasy para simular o transporte de radiação através dos materiais e detectores. Também é apresentada uma comparação entre as imagens obtidas no dispositivo real e nas simulações. Para isso, foi preparado um objeto simulador cilíndrico contendo concentrações de materiais equivalentes a iodo e cálcio. As imagens de tal objeto simulador foram adquiridas no equipamento GE Discovery CT 750 HD. Um objeto simulador equivalente foi modelado e as suas imagens foram simuladas com o código PENELOPE/penEasy. As imagens foram adquiridas e reconstruídas de acordo com as possibilidades do equipamento clínico de tomografia. Imagens de concentração de material e imagens monoenergéticas foram obtidas a partir do dispositivo CT clínico e das simulações. O algoritmo BMD (Basis Material Decomposition em Inglês) baseado nas projeções foi implementado usando os coeficientes de atenuação mássicos da água e do iodo. Consequentemente, imagens de concentração dos materiais água e iodo foram obtidas. A concentração medida nos cilindros de iodo foi equivalente às esperadas tanto no dispositivo real quanto nas imagens simuladas. Foram observados artefatos de endurecimento de feixe nas imagens de concentração de material. Imagens monoenergéticas foram obtidas para diferentes energias. Tais imagens foram obtidas a partir da superposição das imagens de concentração de água e iodo, que foram ponderadas pelos seus respectivos coeficientes de atenuação mássicos. Verificou-se que para as imagens monoenergéticas simuladas e reais em altas energias a imagem de concentração da água é a componente dominante, produzindo imagens que apresentaram as cavidades de iodo como menos atenuantes do que a água. Por outro lado, para energias baixas, a componente dominante nas imagens monoenergéticas foi a imagem de concentração do iodo. O CNR foi analisado nas imagens monoenergéticas como função da energia. As curvas do CNR dos dispositivos simulado e real exibiram semelhanças em sua forma, mas com escala diferente devido à diferença no ruído. Foi possível concluir que o modelo DECT simulado apresenta resultados qualitativos semelhantes aos obtidos no dispositivo real. O sistema de TC simulado permite explorar as características das imagens com diferentes materiais e composições. Ele também pode ser usado como uma ferramenta didática para melhorar a compreensão da diferenciação de materiais em tomografia espectral e DECT. / Dual Energy (DE) Computed Tomography (CT) is one of the fields of tomographic images that has evolved rapidly during the last years. DECT uses two X-ray spectra to irradiate patients It is capable to differentiate materials based on its elementary composition. Despite being similar to standard CT devices, DECT devices require the development of specific tools that allow the study of their image properties. The objective of this work was to build a modelled CT system capable of producing images similar to those obtained in real DECT devices. The modelled CT would also allow exploring the image properties of test materials before their physical construction. This work presents the simulation of the acquisition process of a DECT device that works with rapid kV switching, the GE Discovery CT 750 HD. The simulated geometry was based on a device currently available at the InRad (Institute of Radiology of the Faculty of Medicine of the University of São Paulo). The simulations were carried out using the PENELOPE/penEasy Monte Carlo code, which simulates radiation transport through the materials and detectors. A comparison between the images obtained in the real device and from simulations is also presented. To do so, a real phantom was prepared to be imaged and an equivalent system was simulated. The phantom contained inserts with concentrations of iodine and calcium. The images were acquired and reconstructed according to the possibilities of the real CT device. Standard, material concentration and virtual monoenergetic images were acquired[L1] from both, the real CT device and simulations. The Projection-Based BMD method was implemented using the mass attenuation coefficients of water and iodine. Then, material concentration images of water and iodine were obtained. The iodine concentrations estimated from the images agreed with the expected values in both real device and simulated images. Beam hardening artefacts were observed in the simulated material concentration images. Monoenergetic images were obtained for different energies. Such images were obtained as a superposition of the concentration images of water and iodine, weighed by their respective mass attenuation coefficient. It was verified that in the simulated and real device images, at high energies, the water concentration image predominated in the monoenergetic images, producing images that presented the iodine cavities as less attenuating than water. In contrast, at low energies, the predominant component of the monoenergetic images was the iodine concentration image. Contrast Noise Ratio (CNR) was analysed in the monochromatic images as a function of energy. Simulated and real device CNR curves exhibited similarities in their shape but with a different scale due to their difference in noise. It was possible to conclude that the simulated DECT model presented qualitative results similar to the obtained in the real device. The modelled CT system permits exploring the image features with different materials and compositions. It could also be used as a didactic tool to improve the understanding of material differentiation in spectral or DECT.

O envelhecimento traz modificações na composição corporal habitualmente não acompanhadas por mudança concomitante no índice de massa corporal (IMC). Assim, o IMC tem baixa acurácia para estimar risco de morte atribuído às mudanças de composição corporal em idosos. Entretanto, a maioria dos estudos de composição corporal nesta população utilizou medidas antropométricas ou métodos de alta acurácia mas de elevados custo e complexidade operacional (tomografia computadorizada e ressonância magnética). Atualmente, o melhor método na prática clínica para análise da composição corporal é a absorciometria por dupla emissão de raios-X (DXA). Porém, os poucos estudos que utilizaram DXA apresentam limitações, como análise não estratificada por sexo e avaliação global da gordura corporal, não separando gordura subcutânea e visceral. O objetivo do presente estudo foi avaliar a associação da composição corporal por DXA (incluindo o tecido adiposo visceral) e mortalidade geral (por todas as causas) e cardiovascular em uma população de idosos brasileiros da comunidade. Oitocentos e trinta e nove (839) indivíduos da comunidade (516 mulheres, 323 homens), com 65 anos ou mais, foram avaliados por questionário clínico, exames laboratoriais e composição corporal por DXA na visita inicial. A gordura corporal foi avaliada por índices de massa gorda total e pelo tecido adiposo visceral (VAT), sendo utilizado o scan de corpo total do DXA (HOLOGIC, QDR 4500, software APEX). Baixa massa muscular (BMM) foi definida como baixa massa muscular apendicular ajustada para gordura corporal, segundo método previamente descrito na literatura (NEWMAN, 2003). A mortalidade foi registrada durante o seguimento médio de aproximadamente 4 anos da avaliação inicial. Modelos de regressão logística, para homens e mulheres, foram utilizados para avaliar a associação entre composição corporal e mortalidade. Após 4,06 ± 1,07 anos de seguimento, houve 132 (15,7%) óbitos, sendo 57 (43,2%) por causas cardiovasculares. Em homens, após ajustes para múltiplas variáveis pertinentes, a presença de BMM (OR 11,36 IC95%: 2,21-58,37, p=0,004) e o VAT (OR 1,99 IC95%: 1,38-2,87, p < 0,001) aumentaram significativamente o risco de mortalidade geral enquanto a gordura corporal total foi associada com menor risco de morte (OR 0,48 IC95%: 0,33-0,71, p < 0,001). Resultados semelhantes foram encontrados para a mortalidade cardiovascular. Em mulheres, apenas a BMM foi preditor de mortalidade geral (OR 62,88 IC95%:22,59-175,0, p < 0,001) e mortalidade cardiovascular (OR 74,54 IC95%: 9,72-571,46, p < 0,001), não havendo associação entre massa gorda total ou visceral com mortalidade. Após os resultados encontrados, percebemos que os riscos associados às mudanças da composição corporal em idosos são diferentes de acordo com o sexo, e contrariam o que a literatura mostra para populações mais jovens em relação ao papel da gordura. Estes resultados sugerem que a composição corporal por DXA parece ser uma ferramenta promissora para avaliação da massa muscular, gordura corporal e risco de mortalidade em idosos, uma vez que consiste em metodologia precisa e de fácil aplicabilidade na prática clínica / Body composition changes resulting from ageing (decreased muscle mass and increased fat tissue) are frequently not accompanied by concomitant changes in body mass index (BMI). Thus, BMI has low accuracy to estimate death risk attributed to changes in body composition in older adults. Currently, the best method for body composition analysis in routine clinical practice is dual energy X-ray absorptiometry (DXA). However, the few studies on body composition by DXA and mortality risk in elderly have some limitations, such as analysis not compartmentalized (subcutaneous and visceral tissues) of body fat and appendicular muscle mass not adjusted for fat mass. Thus, we sought to investigate the association between body composition by DXA (including visceral adipose tissue [VAT]) and mortality in a longitudinal, prospective, population-based cohort of elderly subjects. Eight hundred and thirty nine (839) community-dwelling subjects (516 women, 323 men), 65 years or older, were assessed by questionnaire on clinical data, laboratory exams and body composition by DXA using Hologic QDR 4500A equipment. All analyses were performed at baseline. Both total fat and its compartments (eg. visceral adipose tissue [VAT]) were estimated. Low muscle mass (LMM) was defined as the presence of low appendicular muscle mass adjusted for fat. Mortality was recorded during 4 year-follow-up. Multivariate logistic regression models, for men and women, were used to compute odds ratios for all-cause and cardiovascular mortality. Over a mean follow-up of 4.06 ± 1.07 years, there were 132 (15.7%) deaths. In men, after adjustment for relevant variables, the presence of LMM (OR 11.36, 95% CI: 2.21-58.37, p=0.004) and VAT (OR 1.99 95%CI: 1.38-2.87, p < 0.001, for each 100g-increase) significantly increased all-cause mortality risk, while total body fat, measured by Fat Mass Index (FMI), was associated with decreased mortality risk (OR 0.48, 95% CI: 0.33-0.71, p < 0.001). Similar results were observed for cardiovascular mortality in men. In women, only the presence of LMM was a predictor of all-cause (OR 62.88, 95% CI: 22.59-175.0, p < 0.001) and cardiovascular death (OR 74.54, 95% CI: 9.72-571.46, p < 0.001). Both muscle mass and fat mass, including its compartments, impacts on all-cause and cardiovascular mortality risk in elderly. Moreover, their effects are different according to sex. Visceral fat and subcutaneous fat have opposite roles on mortality risk in elderly men, and this is distinct from what is observed in young adults. Thus, DXA seems to be a promising tool for evaluation risk of mortality in elderly, since it is easily applicable in clinical practice