Image registration with sliding motion constraints for 4D CT motion correction

A common assumption in medical image registration is that the estimation of a globally continuous deformation field is plausible in reality. However, a sliding behavior of adjacent organ boundaries (e.g. lung and ribcage) cannot be described in a plausible way by a continuous deformation field. In this paper, we address this issue with a novel registration framework that explicitly models sliding of interfaces and can preserve discontinuities in the deformation field along predefined organ boundaries. Incorporated methods involve constrained nonlinear registration and a finite element discretization on unstructured tetrahedral meshes. Evaluation is based on the freely available DIR-Lab datasets.