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Previous issue date: 2008-05-13 / Although it has been suggested that retinal vasculature is a diffusion-limited aggregation (DLA) fractal, no study has been dedicated to standardizing its fractal analysis . The aims of
this project was to standardize a method to estimate the fractal dimensions of retinal vasculature and to characterize their normal values; to determine if this estimation is
dependent on skeletization and on segmentation and calculation methods; to assess the suitability of the DLA model and to determine the usefulness of log-log graphs in characterizing vasculature fractality . To achieve these aims, the information, mass-radius and box counting dimensions of 20 eyes vasculatures were compared when the vessels were
manually or computationally segmented; the fractal dimensions of the vasculatures of 60 eyes of healthy volunteers were compared with those of 40 DLA models and the log-log graphs
obtained were compared with those of known fractals and those of non-fractals. The main results were: the fractal dimensions of vascular trees were dependent on segmentation
methods and dimension calculation methods, but there was no difference between manual segmentation and scale-space, multithreshold and wavelet computational methods; the means
of the information and box dimensions for arteriolar trees were 1.29. against 1.34 and 1.35 for the venular trees; the dimension for the DLA models were higher than that for vessels; the
log-log graphs were straight, but with varying local slopes, both for vascular trees and for fractals and non-fractals. This results leads to the following conclusions: the estimation of the
fractal dimensions for retinal vasculature is dependent on its skeletization and on the segmentation and calculation methods; log-log graphs are not suitable as a fractality test; the
means of the information and box counting dimensions for the normal eyes were 1.47 and 1.43, respectively, and the DLA model with optic disc seeding is not sufficient for retinal
vascularization modeling / Embora artigos recentes sugiram que a vasculatura ret?nica seja um fractal de agrega??o limitada por difus?o (DLA) e que a an?lise fractal ser? uma ferramenta ?til para o diagn?stico
automatizado das doen?as vasculares da retina, nenhuma padroniza??o dos m?todos foi adotada nesses estudos. Assim, esta tese objetivou: padronizar um m?todo para a estima??o
das dimens?es fractais da vasculatura arteriolar e venular da retina e caracterizar os seus valores normais; determinar se essa estima??o ? dependente da esqueletiza??o e dos m?todos
de segmenta??o e de c?lculo de dimens?o; avaliar a sufici?ncia do modelo DLA e determinar a utilidade dos gr?ficos log-log na caracteriza??o da fractalidade da vasculatura. Para isso,
compararam-se as dimens?es de informa??o, de massa-raio e "por contagem de caixas" das vasculaturas de 20 olhos, quando os vasos foram segmentados manual ou computacionalmente. A seguir, as dimens?es fractais das vasculaturas de 60 olhos de
volunt?rios sadios foram comparadas com as de quarenta modelos DLA e os gr?ficos log-log obtidos foram comparados com os de fractais conhecidos e os de n?o-fractais.Os principais resultados obtidos foram: as dimens?es fractais das ?rvores vasculares foram dependentes dos m?todos de segmenta??o e de c?lculo de dimens?o, por?m n?o houve diferen?a entre a segmenta??o manual e os m?todos computacionais scale-space e wavelet; a m?dia das
dimens?es de informa??o e por caixas para as ?rvores arteriolares foi 1,29, contra 1,34 e 1,35 para as ?rvores venulares e esses valores foram inferiores aos obtidos para os modelos DLA; os gr?ficos log-log se ajustaram ? reta, mas com inclina??es locais vari?veis, tanto para as ?rvores vasculares, quanto para fractais e n?o-fractais. A an?lise dos resultados permitiu concluir que: a estima??o das dimens?es fractais da vasculatura ret?nica foi dependente da sua esqueletiza??o e dos m?todos de segmenta??o e de c?lculo de dimens?o; os gr?ficos log-log n?o tiveram utilidade como teste de fractalidade; as m?dias das dimens?es de informa??o e por contagem de caixas para os olhos normais foram, respectivamente, 1,47 e 1,43 e o modelo DLA com "semente" no disco ?ptico n?o foi suficiente para a modelagem da vasculariza??o ret?nica
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/13126 |
| Date | 13 May 2008 |
| Creators | Mendon?a, Marcelo Bezerra de Melo de |
| Contributors | CPF:00190403691, http://lattes.cnpq.br/8841547160023098, Medeiros, Aldo da Cunha, CPF:07117701404, http://lattes.cnpq.br/9873289951810864, Lucena, Liacir dos Santos, CPF:00405663404, http://lattes.cnpq.br/7151949476055522, Nogueira, Romildo Albuquerque, CPF:03394425491, Costa, Rog?rio Alves, CPF:77454480934, http://lattes.cnpq.br/6725307551799082, Or?fice, Fernando |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em Ci?ncias da Sa?de, UFRN, BR, Ci?ncias da Sa?de |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/embargoedAccess |
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