A fast indirect backprojection algorithm

Backprojection (BP) operation is of fundamental importance for image reconstruction from filtered projections in the framework of the computerized tomography (CT). The conventional BP algorithm, based upon the projection element spreading and cumulation along straight lines in the Cartesian coordinate image domain, provides a high quality reconstruction but suffers from being computationally expensive. Seeking a more effective BP algorithm, the authors have developed a new indirect scheme envisaging a two-stage process of reconstruction, in which the image polar coordinate domain is used as an intermediary between the projection and the image Cartesian coordinate domain. The BP scheme assumes a more complicated but more effective spreading of the projection elements. The algorithm developed provides the speedup of factor 3.3 with regard to the conventional BP algorithm. Experimental image reconstruction examples supplied by the indirect BP versus the conventional BP are given