1. A method for reconstructing an image from a sinogram, comprising: (a) generating in image space an artifact-reduced reconstructed image of a current sinogram residue; (b) minimizing in Radon space a difference between the current sinogram residue and a Radon transform of the artifact-reduced reconstructed image of the current sinogram residue to calculate a next sinogram residue; and (c) generating a final reconstruction result from at least one artifact-reduced reconstructed image generated at step (a) when the next sonogram residue converges.