Automatic articulated registration of hand radiographs

In this paper, we propose a methodology to automatically carry out registration of hands out of conventional X-ray images. The registration method we describe here will be referred to as “articulated registration”; the method is a landmark-based elastic registration procedure in which individual bones are affinely registered and soft tissues are elastically registered so that long skeletal structures are maintained straight while a continuous and smooth transformation is obtained all over the image. In order for the method to be fully automatic, the landmarks used for the registration are detected using a number of image processing algorithms. An optimization step for the refinement of the landmarks locations is included within the registration algorithm; the algorithm is based on an iterative procedure to maximize a local similarity measure. A final procedure to correct bone width has also been performed. We show that the articulated registration described here is robust and outperforms alternatives based on the thin-plate splines (TPS) algorithm. The algorithm for automatic landmark position finding has been tested using registered images with landmarks manually selected by an expert.