Medical Physics, 2007, nr. 11, vol. 34, pp. 4098 - 4108.
Medical images that are to be registered for clinical application often contain both structures that deform and ones that remain rigid. Nonrigid registration algorithms that do not model properties of different tissue types may result in deformations of rigid structures. In this paper we propose a local rigidity penalty term, which is included in the registration function in order to penalise deformation of rigid objects. This term can be used for any representation of the deformation field capable of modelling locally rigid transformations. By using a B-spline representation of the deformation field, a fast algorithm can be devised. We compare the proposed method with an unconstrained nonrigid registration algorithm. It is evaluated on clinical 3D CT follow-up data of the thorax and on 2D DSA image sequences. The results show that nonrigid registration using the proposed rigidity penalty term is capable of nonrigidly aligning images, while keeping user-defined structures locally rigid.
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