Bone registration with 3D CT and ultrasound datasets

Abstract For many navigated surgical procedures, the precise registration of preoperative data sets with bones of the patient is an important requisite. Conventional navigation systems use paired point registration based on anatomical landmarks or fiducial markers. This approach increases the invasiveness, since landmarks must be exposed and fiducial markers must be connected to the bone. Intraoperative imaging modalities can overcome this disadvantage. Ultrasound seems to be ideal because of the easy data acquisition. The problem, however, is the low imaging quality regarding bones. The proposed algorithm for the registration of CT and ultrasound data sets considers the ultrasound imaging properties. That part of the bone surface, which should be visible in the ultrasound data is estimated from the CT data. The ultrasound data is preprocessed to emphasize bone surfaces. Thus, the ultrasound data contains a bright shape that is formed like the surface estimated from the CT data. A surface–volume registration tries to correlate the estimated surface with this bright shape. The algorithm was validated using an ex vivo preparation of a human lumbar spine. The algorithm was shown to cope with initial misalignments of about 30 mm and 15°. Successful registration of in vivo data of lumbar spine, tibia and shoulder indicate the feasibility of the approach.