Non-Rigid MR/US Registration for Tracking Brain Deformations

During a neurosurgical intervention, the brain tissues shift and warp. In order to keep an accurate positioning of the surgical instruments, one has to estimate this deformation from intraoperative images. 3D ultrasound (US) imaging is an innovative and low-cost modality which appears to be suited for such computer-assisted surgery tools. In this paper, we present an image-based technique to register intra-operative 3D US with pre-operative Magnetic Resonance (MR) data. A first automatic rigid registration is achieved by maximizing a similarity measure that generalizes the correlation ratio. Then, brain deformations are tracked in the 3D US timesequence using a "demon's" like algorithm. Experiments show that a registration accuracy of the MR voxel size is achieved for the rigid part, and a qualitative accuracy of a few millimeters could be obtained for the complete tracking system