Coleção de Artigos Acadêmicos
URI permanente para esta coleçãohttps://repositorio.insper.edu.br/handle/11224/3227
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59 resultados
Resultados da Pesquisa
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 The Lysyl Oxidase Inhibitor, b-Aminopropionitrile, Diminishes the Metastatic Colonization Potential of Circulating Breast Cancer Cells(2009) Bondareva, Alla; Downey, Charlene M.; FABIO JOSE AYRES; Liu, Wei; Boyd, Steven K.; Hallgrimsson, Benedikt; Jirik, Frank R.Lysyl oxidase (LOX), an extracellular matrix remodeling enzyme, appears to have a role in promoting breast cancer cell motility and invasiveness. In addition, increased LOX expression has been correlated with decreases in both metastases-free, and overall survival in breast cancer patients. With this background, we studied the ability of b-aminopropionitrile (BAPN), an irreversible inhibitor of LOX, to regulate the metastatic colonization potential of the human breast cancer cell line, MDA MB-231. BAPN was administered daily to mice starting either 1 day prior, on the same day as, or 7 days after intracardiac injection of luciferase expressing MDA-MB-231-Luc2 cells. Development of metastases was monitored by in vivo bioluminescence imaging, and tumor-induced osteolysis was assessed by micro-computed tomography (mCT). We found that BAPN administration was able to reduce the frequency of metastases. Thus, when BAPN treatment was initiated the day before, or on the same day as the intra-cardiac injection of tumor cells, the number of metastases was decreased by 44%, and 27%, and whole-body photon emission rates (reflective of total tumor burden) were diminished by 78%, and 45%, respectively. In contrast, BAPN had no effect on the growth of established metastases. Our findings suggest that LOX activity is required during extravasation and/or initial tissue colonization by circulating MDA-MB-231 cells, lending support to the idea that LOX inhibition might be useful in metastasis prevention.Artigo Científico Ambiguity through confidence functions(2009) Chateauneuf, Alain; JOSÉ HELENO FAROWe characterize preference relations over bounded below Anscombe and Aumann’s acts and give necessary and sufficient conditions that guarantee the existence of a utility function u on consequences, a confidence function ϕ on the set of all probabilities over states of nature, and a positive threshold level of confidence ˛0 such that our preference relation has a functional representation J, where given an act f J(f) = min p ∈ L˛0 ϕ 1 ϕ(p) S u(f) dp. The level set L˛0ϕ := {p : ϕ(p) ≥ ˛0} reflects the priors held by the decision maker and the valueϕ(p) captures the relevance of prior p for his decision. The combination ofϕ and˛0 may describe the decision maker’s subjective assessment of available information. An important feature of our representation is the characterization of the maximal confidence function which allows us to obtain results on comparative ambiguity aversion and on special cases, namely the subjective expected utility, the Choquet expected utility with convex capacity, and the maxmin expected utilitArtigo 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 Sales managers’ performance and social capital: the impact of an advice network(2009) DANNY PIMENTEL CLARO; Laban Neto, Sílvio AbrahãoArtigo Científico A economia da caprinocultura em Pernambuco: problemas e perspectivas(2009) Sampaio, Breno; Sampaio, Yony; Lima, Ricardo Chaves; Aires, Amanda; GUSTAVO RAMOS SAMPAIOA caprinocultura é uma das atividades mais indicadas para regiões semi áridas, sendo bastante explorada no nordeste brasileiro. São estimadas as produções de carne, leite e pele, o valor dessa produção e a participação no emprego em Per nambuco e analisados os mercados nacional e internacional. Enumeram-se os prin cipais problemas para a expansão da cadeia, como manejo inadequado, problemas sanitários, limitações das instalações e das tecnologias. Com manejo melhorado, pode ser praticada por pequenos e médios produtores, sendo sustentável no semiárido, do ponto de vista ambiental, econômico e social, preservando a cobertura vegetal e mantendo a biodiversidade. O mercado de carne apresenta crescimento da demanda tanto nacional como internacional e déficit de oferta. O mercado de peles é outro mercado em expansão, com grandes perspectivas internas e para exportação.Artigo Científico Rank tests for instrumental variables regression with weak instruments(2007) Andrews, Donald W.K.; GUSTAVO BARBOSA SOARESArtigo Científico A crise cambial brasileira de 1999, a literatura de seus protagonistas e a compreensão do fato(2009) CARLOS ALBERTO FURTADO DE MELO: Este trabalho trata da crise cambial ocorrida no Brasil em final de 1998 e início de 1999. Foi um importante momento da história econômica e política do país, pois mudando o regime cambial, no longo prazo, transformou a economia. E, despertando uma série de conflitos no interior do governo e na coalizão de Fernando Henrique Cardoso, deu ao país, ao fim e ao cabo do processo, dinâmica política que faria ruir o bloco político tucano-peflista. Esse processo resultou na vitória da oposição, três anos mais tarde, 2002, com a vitória do Partido dos Trabalhadores e seu candidato, Luiz Inácio Lula da Silva. Na sintética bibliografia, estão apresentadas quatro obras que são, basicamente, memorialísticas, analistas parciais, ou “documento de combate político”, feitos à época ou em relação àquele momento. Foram escritas por atores que viveram os fatos, mas que não tiveram a intenção de buscar sínteses. São narrativas parciais do processo, feitas como memória ou jornalismo. Todavia, obras que permitem ao analista, ao cientista político, ao historiador recompor o processo agregando detalhes e dando sentido explicativo para além dessas obras, transformando os acontecimentos em fato político, cientificamente analisado e compreendido.