Three-dimensional image reconstruction from exponential parallel-beam projections

In this paper, we present a filtered-backprojection (FBP) algorithm suitabl e for image reconstruction from exponential X-ray (parallel-beam) projectio ns sampled on any subset of the sphere that includes great circles. This al gorithm is similar to the true three-dimensional reconstruction algorithm o f Ra et al (1982) for nonattenuated projections. It is derived by combining all reconstructions that can be obtained from subsets of measurements corr esponding to great circles. Our results generalize those published by Hazou (1988) and Weng et al. (1996) for reconstruction from projections sampled on the unit sphere. However, they remain modest, as they only apply to spec ific sets of measurements.