QC 351 A7 no. 65 / The significance of signal-dependent noise is discussed. Particular emphasis is placed on the type of multiplicative noise present in the density variations in a photographic emulsion. A theoretical treatment of the effect of multiplicative noise on signal detection and signal discrimination problems is presented. Optimum test statistics are derived for processing a sampled message to detect the presence of a known signal. Multiplicative noise described by Poisson and Gaussian statistics is considered. The expressions are extended to include the two-signal discrimination problem. Two-dimensional signal fields in the presence of multiplicative noise are simulated in a computer and processed for optimum signal detection according to the two derived methods. These results are compared to the results of processing based on the assumption of stationary noise statistics. This comparison reveals that modest improvements (20% to 30% reduction in false alarm rate) are obtained when the signal-dependent nature of the noise statistics is considered. The effects of signal-to-noise ratio, signal structure, and changing background level are also investigated. An example of optimum signal discrimination using circles and squares as signals in multiplicative noise is reported. An improvement in the percentage of correctly identified signals is again observed when the proper test statistic is used. Two examples of signal filtering in the presence of signal-dependent noise are included. The first concerns the processing of a real star field to determine the location of weak stars. The second is an illustration of the signal information contained in the noise spectrum of a message recorded on a common photographic film.

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Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-04-08T12:52:45Z No. of bitstreams: 0 / Made available in DSpace on 2016-04-08T12:52:45Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-04-08T12:52:45Z No. of bitstreams: 0 / Made available in DSpace on 2016-04-08T12:52:45Z (GMT). No. of bitstreams: 0 / A braquiterapia é a modalidade de tratamento radioterápico que utiliza fontes radioativas seladas a uma distância curta do tumor, diminuindo o risco de aplicação de uma dose indesejável em tecidos sadios adjacentes. Para que a braquiterapia seja confiável, é necessário estabelecer um programa de práticas dosimétricas visando a determinação da dose ideal de radiação para esta prática radioterápica. Neste trabalho apresenta a aplicação de duas metodologias destinadas à dosimetria utilizando filmes radiocrômicos. Medidas experimentais foram realizadas com filmes EBT3 em objetos simuladores composto de material homogêneo e heterogêneo (pulmão, osso e tecidos moles) construídos especialmente para medidas de dose em braquiterapia. Os processamentos e analises das imagens resultantes do procedimento experimental foram realizados com o software IMAGEJ e MATLAB. Os resultados foram avaliados a partir de comparações medidas experimentais de dose e obtidas por simulações pelo Método de Monte Carlo. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP