A fast algorithm for backprojection

In the filtered backprojection (FBP) procedure for image reconstruction from projections, backprojection dominates the computation time. The authors propose a simple algorithm which reduces the number of multiplications in the linear interpolation and backprojection stage by 50%, with a small increase in the number of additions. The algorithm performs the interpolation and backprojection of four views together. The resulting image is virtually identical to that obtained by classical FBP. The authors have also generalized the algorithm to backproject more than four view together. This generalized version, however, may increase the number of additions disproportionately, and requires nonuniformly spaced angular sampling