A patchwork (back)projector to accelerate artifact reduction in CT reconstruction

Artifacts in computed tomography (CT) reconstruction are often caused by an inaccurate modeling of the acquisition during reconstruction. These artifacts can be severe when metals are in the field of view. A better modeling of the acquisition during reconstruction reduces artifacts but often leads to a substantial increase in computation time. Because metals are the most prominent source of the artifacts, we hypothesize it would be sufficient to limit the more complex model to regions close to metals and use less complex, faster models for the other parts. For this purpose we present a patchwork (back)projector, embedded in an iterative reconstruction algorithm, which is able to change reconstruction properties for a particular area in the object. We combined reconstruction models with different complexity for the reduction of non-linear partial volume effects and beam hardening. In this way we reduced the computation time while keeping the same image quality. Moreover, an improved convergence is achieved by dividing the image into subareas, patches. The presented results are for a two dimensional geometry, in the future we will extend this to three dimensions.