DETECTION OF EDGES FROM PROJECTIONS

In a number of applications of computerized tomography, the ultimate g oal is to detect and characterize objects within a cross section. Dete ction of edges of different contrast regions yields the required infor mation. This paper addresses the problem of detecting edges from proje ction data. It has been shown that the class of linear edge detection operators used on images can be used for detection of edges directly f rom projection data. This not only reduces the computational burden bu t also avoids getting into difficulties of postprocessing a reconstruc ted image. This is accomplished by a convolution backprojection operat ion. For example, with the Marr-Hildreth edge detection operator, the filtering function that is to be used on the projection data is the Ra don transform of the Laplacian of the 2-D Gaussian function which is c ombined with the reconstruction filter. Simulation results showing the efficacy of the proposed method and a comparison with edges detected from the reconstructed image are presented.