Local models for artefact reduction in iterative CT reconstruction

Metal artefact reduction (MAR) in computed tomography remains a challenging problem. Projection completion (PC) and iterative reconstruction with an advanced projection model are the two most important MAR methods. PC often results in strong artefact reduction, but by the interpolation step information about the metal and its surrounding is lost. This information can be important in e.g. orthopaedic surgery for implant follow-up. Iterative methods use all available information and are more suitable in such cases. Unfortunately, these methods are slow, especially when using a more adequate, more complex model. We present a local model reconstruction scheme which uses iterative reconstruction but only increases the complexity of the model in the vicinity of metals. Hereby we can limit the computation time while keeping a similar image quality. Moreover, when using a sequential update of several image parts, one obtains a better convergence of the metals, leading to an improved artefact reduction.