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Abstract: In this paper, we present a constrained version of Kaczmarz extended algorithm for improving image reconstruction from projections in computerized tomography. We prove convergence of our algorithm in the general inconsistent case to a “constrained” least squares solution of the reconstruction problem, under weaker hypothesis than those proposed in a previous paper by Koltracht and Lancaster for classical Kaczmarz’s projection method. Numerical experiments and comparisons are also presented on some model problems from the field of electromagnetic geotomography. [Copyright &y& Elsevier]

Abstract: The goal of intensity-modulated radiation therapy (IMRT) is to deliver sufficient doses to tumors to kill them, but without causing irreparable damage to critical organs. This requirement can be formulated as a linear feasibility problem. The sequential (i.e., iteratively treating the constraints one after another in a cyclic fashion) algorithm ART3 is known to find a solution to such problems in a finite number of steps, provided that the feasible region is full dimensional. We present a faster algorithm called ART3+. The idea of ART3+ is to avoid unnecessary checks on constraints that are likely to be satisfied. The superior performance of the new algorithm is demonstrated by mathematical experiments inspired by the IMRT application. [Copyright &y& Elsevier]