Coleção de Artigos Acadêmicos
URI permanente para esta coleçãohttps://repositorio.insper.edu.br/handle/11224/3227
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57 resultados
Resultados da Pesquisa
Artigo Científico Gabor filters and phase portraits for the detection of architectural distortion in mammograms(2006) Rangayyan, Rangaraj M.; FABIO JOSE AYRESSegmentation of the tumor in neuroblastoma is complicated by the fact that the mass is almost Always heterogeneous in nature; furthermore, viable Architectural distortion is a subtle abnormality in mammograms, and a source of overlooking errors by radiologists. Computer-aided diagnosis (CAD) techniques can improve the performance of radiologists in detecting masses and calcifications; however, most CAD systems have not been designed to detect architectural distortion. We present a new method to detect and localise architectural distortion by analysing the oriented texture in mammograms. A bank of Gabor filters is used to obtain the orientation field of the given mammogram. The curvilinear structures (CLS) of interest (spicules and fibrous tissue) are separated from confounding structures (pectoral muscle edge, parenchymal tissue edges, breast boundary, and noise). The selected core CLS pixels and the orientation field are filtered and downsampled, to reduce noise and also to reduce the computational effort required by the subsequent methods. The downsampled orientation field is analysed to produce three phase portrait maps: node, saddle, and spiral. The node map is further analysed in order to detect the sites of architectural distortion. The method was tested with 19 mammograms containing architectural distortion. In a preliminary experiment, a sensitivity of 84% was obtained at 7.8 false positives per image.Artigo Científico Three-Dimensional Segmentation of the Tumor in Computed Tomographic Images of Neuroblastoma(2007) Deglint, Hanford J.; Rangayyan, Rangaraj M.; FABIO JOSE AYRES; Boag, Graham S.; Zuffo, Marcelo K.Segmentation of the tumor in neuroblastoma is complicated by the fact that the mass is almost Always heterogeneous in nature; furthermore, viable tumor, necrosis, and normal tissue are often intermixed. Tumor definition and diagnosis require the analysis of the spatial distribution and Hounsfield unit (HU) values of voxels in computed tomography (CT) images, coupled with a knowledge of normal anatomy. Segmentation and analysis of the tissue composition of the tumor can assist in quantitative assessment of the response to therapy and in the planning of delayed surgery for resection of the tumor. We propose methods to achieve 3-dimensional segmentation of the neuroblastic tumor. In our scheme, some of the normal structures expected in abdominal CT images are delineated and removed from further consideration; the remaining parts of the image volume are then examined for the tumor mass. Mathematical morphology, fuzzy connectivity, and other image processing tools are deployed for this purpose. Expert knowledge provided by a radiologist in the form of the expected structures and their shapes, HU values, and radiological characteristics are incorporated into the segmentation algorithm. In this preliminary study, the methods were tested with 10 CT exams of four cases from the Alberta Children’s Hospital. False-negative error rates of less than 12% were obtained in eight of the 10 exams; however, seven of the exams had false-positive error rates of more than 20% with respect to manual segmentation of the tumor by a radiologist.Artigo Científico A review of computer-aided diagnosis of breast cancer: Toward the detection of subtle signs(2007) Rangayyan, Rangaraj M.; FABIO JOSE AYRES; Desautels, J.E. LeoMammography is the best available tool for screening for the early detection of breast cancer. Mammographic screening has been shown to be effective in reducing breast cancer mortality rates: screening programs have reduced mortality rates by 30–70%. Mammograms are difficult to interpret, especially in the screening context. The sensitivity of screening mammography is affected by image quality and the radiologist's level of expertise. Computer-aided diagnosis (CAD) technology can improve the performance of radiologists, by increasing sensitivity to rates comparable to those obtained by double reading, in a cost-effective manner. Current research is directed toward the development of digital imaging and image analysis systems that can detect mammographic features, classify them, and provide visual prompts to the radiologist. Radiologists would like the ability to change the contrast of a mammogram, either manually or with pre-selected settings. Computer techniques for detecting, classifying, and annotating diagnostic features on the images would be desirable. This paper presents an overview of digital image processing and pattern analysis techniques to address several areas in CAD of breast cancer, including: contrast enhancement, detection and analysis of calcifications, detection and analysis of masses and tumors, analysis of bilateral asymmetry, and detection of architectural distortion. Although a few commercial CAD systems have been released, the detection of subtle signs of breast cancer such as global bilateral asymmetry and focal architectural distortion remains a difficult problem. We present some of our recent works on the development of image processing and pattern analysis techniques for these applications.Artigo Científico Detection of architectural distortion in prior screening mammograms using Gabor filters, phase portraits, fractal dimension, and texture analysis(2008) Rangayyan, Rangaraj M.; Prajna, Shormistha; FABIO JOSE AYRES; Desautels, J. E. LeoObjective Mammography is a widely used screening tool for the early detection of breast cancer. One of the commonly missed signs of breast cancer is architectural distortion. The purpose of this study is to explore the application of fractal analysis and texture measures for the detection of architectural distortion in screening mammograms taken prior to the detection of breast cancer. Materials and methods A method based on Gabor filters and phase portrait analysis was used to detect initial candidates for sites of architectural distortion. A total of 386 regions of interest (ROIs) were automatically obtained from 14 “prior mammograms”, including 21 ROIs related to architectural distortion. From the corresponding set of 14 “detection mammograms”, 398 ROIs were obtained, including 18 related to breast cancer. For each ROI, the fractal dimension and Haralick’s texture features were computed. The fractal dimension of the ROIs was calculated using the circular average power spectrum technique. Results The average fractal dimension of the normal (false-positive) ROIs was significantly higher than that of the ROIs with architectural distortion (p = 0.006). For the “prior mammograms”, the best receiver operating characteristics (ROC) performance achieved, in terms of the area under the ROC curve, was 0.80 with a Bayesian classifier using four features including fractal dimension, entropy, sum entropy, and inverse difference moment. Analysis of the performance of the methods with free-response receiver operating characteristics indicated a sensitivity of 0.79 at 8.4 false positives per image in the detection of sites of architectural distortion in the “prior mammograms”. Conclusion Fractal dimension offers a promising way to detect the presence of architectural distortion in prior mammograms.Artigo Científico A influência da qualidade na atratividade de instituições de ensino superior com capital aberto(2008) Gramani, Maria Cristina NogueiraQuando a rentabilidade está aliada à qualidade de uma Instituição de Ensino Superior (IES) com capital aberto, sua atratividade por parte de futuros investidores é maior. Em geral, a rentabilidade das IES´s é divulgada por meio de prospectos, resultados trimestrais e relação com investidores (RI), entretanto esforços bem menores são alocados às demonstrações de indicadores de qualidade. Desta forma, este artigo propõe identificar fatores que refletem a qualidade de IES´s, apontando doze indicadores, dentre os quais, alguns que levam a benefícios à qualidade e outros que podem acusar riscos de diminuição da qualidade. Também foi construído um mapa de posicionamento com estes doze indicadores alocando-os nas variáveis rentabilidade e qualidade, de forma a identificar o nível de atratividade de uma IES.Artigo Científico Coordinating collaborative joint efforts with suppliers: the effects of trust, transaction specific investment and information network in the Dutch flower industry(2006) DANNY PIMENTEL CLARO; PRISCILA BORIN DE OLIVEIRA CLARO; Hagelaar, GeoffreyArtigo Científico Rank tests for instrumental variables regression with weak instruments(2007) Andrews, Donald W.K.; GUSTAVO BARBOSA SOARESArtigo Científico An analysis of income differentials by marital status(2008) Madalozzo, Regina CarlaO casamento não oficializado, coabitação, tem se tornado cada vez mais freqüente nas últimas décadas. O objetivo deste trabalho é examinar a relação entre os salários das mulheres casadas e das solteiras ou coabitantes. A literatura a este respeito mostra que, enquanto o prêmio financeiro para o casamento é verificado em diversos estudos e países quando o objeto de estudo são os homens, o resultado para mulheres não é conclusivo. A principal inovação do presente estudo é a existência de controles para seleção, tanto na escolha em participar da força de trabalho como de alterar seu estado civil. Regressões "switching" e decomposição de Oaxaca mostram a existência de uma penalização financeira para mulheres casadas. Corrigindo para ambos os tipos de seleção, a diferença nos salários das mulheres casadas com relação às coabitantes varia entre 49% e 53%, favorecendo as coabitantes. Este resultado aponta para a existência de uma penalidade ao casamento.Artigo Científico Gender wage gaps: comparing the 80s, 90s and 00s in Brazil(2007) Madalozzo, Regina Carla; Martins, Sérgio RicardoUsando microdados para o Brasil nos anos de 1981, 1992 e 2004, o presente estudo emprega a técnica de regressão quantílica na estimação do hiato de salários entre gêneros, fazendo uso de componentes explicados e não explicados. A regressão quantílica é uma técnica mais apropriada a este problema do que o método de mínimos quadrados ordinários (OLS) porque ajuda a entender não apenas o efeito médio de características individuais sobre o salário de uma pessoa, como também o efeito de pertencer a uma parte específica da distribuição, a saber, o quantil. Concluímos que, na verdade, as diferenças salariais se reduziram. Também concluímos que o declínio da diferença salarial assume um padrão não linear (suficientemente semelhante nos três anos analisados), o que também leva à conclusão de que nem todas as mulheres estão conseguindo igualdade de renda em comparação com os salários dos membros correspondentes do sexo masculino..Artigo Científico The structure of worker compensation in Brazil, with a comparison to France and the United States(2008) NAERCIO AQUINO MENEZES FILHO; Muendler, Marc-Andreas; Ramey, Garey