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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Filtragem de sinograma tomográfico afetado por ruído Poisson utilizando wavelets anisotrópicas

Pinheiro, Arthur Melo 07 February 2017 (has links)
Submitted by Aelson Maciera (aelsoncm@terra.com.br) on 2017-05-25T18:35:31Z No. of bitstreams: 1 DissAMP.pdf: 2894495 bytes, checksum: 735a85fb9a045d24dcf0e59e0292a147 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-06-01T13:41:45Z (GMT) No. of bitstreams: 1 DissAMP.pdf: 2894495 bytes, checksum: 735a85fb9a045d24dcf0e59e0292a147 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-06-01T13:41:52Z (GMT) No. of bitstreams: 1 DissAMP.pdf: 2894495 bytes, checksum: 735a85fb9a045d24dcf0e59e0292a147 (MD5) / Made available in DSpace on 2017-06-01T13:48:47Z (GMT). No. of bitstreams: 1 DissAMP.pdf: 2894495 bytes, checksum: 735a85fb9a045d24dcf0e59e0292a147 (MD5) Previous issue date: 2017-02-07 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / The diagnostic imaging by computed tomography has become popular in recent decades. As the image acquisition method is effected by exposing the human body to X-ray dose (ionizing radiation), the frequent realization of diagnoses results in the accumulation of radiation, and may be a significant factor in the emergence of cancer diseases. This problem has motivated researchers to develop methods to reduce the dose of X-rays so that the image quality can be maintained. A common methodology involves applying algorithms for filtering noisy tomographic images that can be acquired under low dose of X-rays. This process may occur in the reconstructed image domain or tomographic projections domain. This work proposes a methodology for applying filtering Poisson noise present in tomographic sinogram, which uses the main anisotropic wavelets studied by the scientific community, which are: Curvelet, Contourlet, Shearlet. These wavelets apply the concept of multiscale and multidirectional analysis in a multidimensional signal, and may be advantageous in two-dimensional analysis of sinogram, preserving better image details in a noise reduction process compared to orthogonal wavelets. / Os diagnósticos por imagens através da tomografia computadorizada se popularizaram nas últimas décadas. Como o método de aquisiçao das imagens é efetuado pela exposto do corpo humano a uma dose de raios-X (radiacao ionizante), a frequente realizacão desse exame implica no acumulo de radiaçao, podendo ser um fator significativo para o surgimento de varios tipos de cancer. Essa problematica tem motivado pesquisadores a desenvolverem metodos para reduçao da dose de raios-X de forma que a qualidade da imagem possa ser mantida. Uma metodologia comumente abordada consiste na aplicacão de algoritmos de filtragem sobre imagens tomograficas ruidosas que podem ser adquiridas em condiçães de baixa dose de raios-X. Esse processo pode ocorrer no espaco da imagem reconstruída ou no espaço das projecoes tomograficas. Esse trabalho propoe aplicar uma metodologia para filtragem do ruído Poisson presente no sinograma tomo-grafico, a qual utiliza as principais wavelets anisotropicas estudadas pela comunidade científica, que sao: Curvelet, Contourlet e Shearlet. Essas wavelets aplicam o conceito de analise multiescala e multidirecional em um sinal multidimensional, e podem ser vantajosas na anúlise bidimensional do sinograma, preservando melhor detalhes da imagem em um processo de atenuacao do ruído se comparadas as wavelets ortogonais.

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