Augmented reality based on fast deformable 2D-3D registration for image guided surgery

Augmented reality systems (ARS) allow the transparent projection of preoperative CT images onto the physicians view. A significant problem in this context is the registration between the patient, and the tomographic images, especially in the case of soft tissue deformation. The basis of our ARS is a volume rendering component on standard PC platform, which allows interactive volumetric deformation as a supplement to the 3D-texture based approaches. The volume is adaptively subdivided into a hierarchy of sub-cubes, each of which is deformed linearly. In order to approximate the Phong illumination model, our system allows pre-calculated gradients to be deformed efficiently. The registration is realized by the introduction of a two-stage procedure. Firstly, we compute a rigid pre-registration by the use of fiducial markers in combination with an electro-magnetic navigation system. The second step accounts for the non-linear deformation. For this purpose, several views of an object are captured and compared with its corresponding synthetic renderings hi an optimization method using mutual information as metric. Throughout the experiments with our approach, several tests of the rigid registration has been carried out in a real laparoscopic intervention setup as a supplement to the actual clinical routine. In order to evaluate the non-linear part of the registration, up until now several dummy objects (synthetically deformed datasets) have been successfully examined.