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Master's Dissertation
DOI
10.11606/D.59.2007.tde-12092007-082142
Document
Author
Full name
Alessandra Tomal
Institute/School/College
Knowledge Area
Date of Defense
Published
Ribeirão Preto, 2007
Supervisor
Committee
Poletti, Martin Eduardo (President)
Caldas, Linda Viola Ehlin
Medeiros, Regina Bitelli
Title in Portuguese
Medidas experimentais dos coeficientes de atenuação de tecidos mamários e sua influência no contraste e dose mamográfica
Keywords in Portuguese
Câncer de mama
Coeficiente de atenuação
contraste objeto
dose
Abstract in Portuguese
O estudo e a determinação das propriedades de atenuação de tecidos mamários são fundamentais para o entendimento e para a quantificação do contraste e da dose absorvida em um exame mamográfico. A proposta deste trabalho é determinar experimentalmente os coeficientes de atenuação de tecidos mamários e, posteriormente, incorporar esses resultados a um modelo teórico-analítico que possibilite o estudo da influência de diversos parâmetros no contraste de objetos e na dose em mamografia. Dentre os fatores de estudo, destacam-se as características da mama (geometria e composição), a técnica radiográfica, a combinação ânodo-filtro e o receptor de imagem. Os coeficientes de atenuação foram medidos usando geometria de feixe estreito, no intervalo de energia entre 8 e 30 keV, utilizando um difratômetro de raios-X 4-círculos P3 Nicolet-Siemens e um monocromador de Si (111). Para essas medidas foram utilizadas 63 amostras de tecidos mamários (classificadas previamente como tecidos normais, fibroadenomas e/ou diferentes tipos de carcinomas). Os coeficientes de atenuação medidos foram comparados com predições teóricas, obtidas usando a regra das misturas, e com dados experimentais previamente publicados. O modelo desenvolvido para o contraste objeto leva em conta as contribuições primária e secundária na radiação transmitida. A dose média absorvida foi estimada através de duas aproximações, que permitem predizer os limites superior e inferior, e de uma aproximação mais completa, que inclui as componentes espalhadas simples e duplas. O modelo desenvolvido neste trabalho permite a obtenção de resultados de forma simples e rápida, com valores similares aos obtidos por simulação Monte Carlo, bem como definir limites de detecção de massas tumorais.
Title in English
Experimental Measurements of the Attenuation Coefficients of Breast Tissues and their Influence on Contrast and Mammographic Dose
Keywords in English
Attenuation Coefficient
Breast Cancer
Dose
Subject Contrast
Abstract in English
The study and determination of attenuation properties of breast tissues are fundamental to understand and quantify contrast and absorbed dose in the mammographic examination. The purpose of this work is to experimentally determine the attenuation coefficient of breast tissues, and then to include these results into a theoretical analytical model, in order to study the influence of several parameters on subject contrast and dose in mammography. Among the parameters studied, one can emphasize the breast characteristics (geometry and composition), the radiographic technique, the target-filter combination and the image receptor. The attenuation coefficients were measured using narrow beam geometry, within the energy range of 8-30 keV, using an x-ray diffractometer 4-circle P3 Nicolet-Siemens and a monocromator of Si (111). For these measurements were analyzed 63 breast tissue samples (previously classified as normal tissues, fibroadenomas and several types of carcinomas). The linear attenuation coefficients measured were compared with theoretical predictions obtained from the mixture rule, and with experimental data previously published. The developed model to the subject contrast takes into account the primary and scattered contribution of the transmitted radiation. The average absorbed dose was estimated considering two simplified approaches, which allowed to predict upper and lower limit values, and a more complete approach, which included the contribution of single and double scattered radiation. The analytical model developed in this work provided results in a fast and simple way, with a good agreement with those reported by others authors who had used Monte Carlo simulation, as well it allowed to define limit values for detection of tumor masses.
 
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Publishing Date
2007-09-14
 
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