Providing visual information to validate 2-D to 3-D registration

This paper addresses a key issue of providing clinicians with visual information to validate the accuracy of 2-D/3-D registration for robot-assisted total hip replacement (THR) surgery. Although numerous registration approaches have been presented, the topic of registration validation has scarcely been addressed in the literature. In practice, clinicians rely on post-operative X-rays to assess the accuracy of implant placement. Motivated by this, we simulate a set of post-operative X-ray images by superimposing the implant positioned pre-operatively onto the intra-operatively collected and calibrated images of the femur, through a transformation computed by the 2-D/3-D registration. With these images, a judgment on the registration accuracy can be made. In addition, this paper introduces methods for superimposing pre-operative data on intra-operative X-ray images that were not corrected for distortion, by applying the same image distortion to the data. This paper also introduces a new framework for incorporating surface normals in the objective function for registration. A comparison between marker-based and image-based registration is conducted. The advantage of our approach is that the simulated post-operative X-ray images are very familiar to clinicians and, therefore, easy for them to interpret. As an added benefit, this technique provides new means for comparing the marker-based and image-based registration for robot-assisted THR surgery. This approach can be extended to other interventions where intra-operative images are used for registration.