Correlation of pre-operative MRI and intra-operative 3D ultrasound to measure brain tissue shift

The usefulness of stereotactic neurosurgery performed via a craniotomy is limited because the craniotomy leads to a brain tissue shift of 10 mm on average. We have recently completed an examination of 2D intra-operative ultrasound as a means of visualization and measurement of brain shift. A commercial 3D tracking system was used for real-time registration of the ultrasound video to pre-operative MIt images, and annotation of the images was used to measure the shift. More than 15 surgical cases have been performed thus far with the 2D system. We are now undertaking phantom studies with tracked 3D ultrasound, and have developed sophisticated tools for real-time overlay of ultrasound and MRI volumes. These tools include a virtual-reality view of the ultrasound probe with live ultrasound video superimposed over a 3D-rendered MRI of the brain, as well as 3D ultrasound/MRI transparency overlay views. Algorithms to automatically extract landmarks from MRJ and 3D ultrasound images are under development. We aim to use these landmarks to automatically generate nonlinear warp transformations to correct the pre-operative MRI as well as surgical target coordinates for brain shift. Portions of the C++ code developed for this project have been contributed to the open-source Visualization Toolkit (VTK).