Reconstrução tomográfica de imagens utilizando técnicas POCS seqüenciais e paralelas.

Abstract

In this dissertation four algorithms are presented for the tomographic reconstruction of images using methods denominated POCS - Projections onto Convex Sets, which are the ART - Algebraic Reconstruction Technique, the SIRT - Simultaneous Iterative Reconstructive Technique, the sequencial POCS and parallel POCS. A comparison is made between the reconstruction methods named above, in the presence of noise and in the reconstruction from limited view. In each reconstruction, the result of each iteration is compared with the desired image, also showing the convergence curve for each method. For the tomographic reconstructions, projections from test bodies obtained throught simulation were used and also experimental projections obtained by the mini-tomograph scanner of CNPDIA-EMBRAPA. Although were considered only the reconstruction based an projections obtained with parallel beams, the methods here described can also reconstruct images that are independent of the source-detector geometry used by the tomograph scanner. The use of restrictions over the solutions, as in the case of serial and parallel POCS, demonstrated efficiency in reducing the variability due to the ill-conditioning of the problem.