Ultrasound/MRI Overlay with Image Warping for Neurosurgery

Performing a craniotomy will cause brain tissue to shift. As a result of the craniotomy, the accuracy of stereotactic localization techniques is reduced unless the brain shift can be accurately measured. If an ultrasound probe is tracked by a 3D optical tracking system, intraoperative ultrasound images acquired through the craniotomy can be compared to pre-operative MRI images to quantify the shift. We have developed 2D and 3D image overlay tools which allow interactive, realtime visualization of the shift as well as software that uses homologous landmarks between the ultrasound and MRI image volumes to create a thin-plate-spline warp transformation that provides a mapping between pre-operative imaging coordinates and the shifted intra-operative coordinages. Our techniques have been demonstrated on poly vinyl alcohol cryogel phantoms which exhibit mechanical and imaging properties similar to those of the human brain.