DescriptionComputed Tomography (CT) image reconstruction is an important technique used in a wide range of applications. Among reconstruction methods, Model-Based Iterative Reconstruction (MBIR) generally produces higher quality images. However, the irregular data access pattern, the difficulty of effective parallelization and slow algorithmic convergence have made MBIR impractical for many applications. This paper presents a new algorithm for MBIR, Non-Uniform Parallel Super-Voxel (NU-PSV), that regularizes the data access pattern, enables massive parallelism and ensures fast convergence. We compare the NU-PSV algorithm with two state-of-the-art implementations on a 69632-core distributed system. Results indicate that the NU-PSV algorithm has an average speedup of 1665 compared to the fastest state-of-the-art implementations.