A method is described for adapting 3D image datasets so that they can be registered and combined with 2D images of the same subject, wherein deformation or movement of parts of the subject has occurred between obtaining the 3D image and the 2D image. 2D-3D registrations of the images with respect to multiple features visible in both images are used to provide point correspondences between the images in order to provide an interpolation function that can be used to determine the position of a feature visible in the first image but not the second image and thus mark the location of the feature on the second image. Also described is apparatus for carrying out this method.