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Extracting displacement data from coregistered ultrasound for brain modeling

Image guided neurosurgery systems rely on rigid registration of the brain to preoperative images, not taking into account the displacement of brain tissue during surgery. Co-registered ultrasound appears to be a promising means of detecting tissue shift in the operating room. Although the use of ultrasound images alone may be insufficient for adequately describing intraoperative brain deformation, they could be used in conjunction with a computational model to predict full volume deformation. We rigorously test the assumption that co-registered ultrasound is an accurate source of sparse displacement data. Our co-registered ultrasound system is studied in both clinical applications as well as in a series of porcine experiments. Qualitative analysis of patient data indicates that ultrasound correctly depicts displaced tissue. The porcine studies demonstrate that features from co-registered ultrasound and CT or MR images are properly aligned to within approximately 1.7 mm. Tissue tracking in pigs suggests that the magnitude of displaced tissue may be more accurately predicted than the actual location of features. We conclude that co-registered ultrasound is capable of detecting brain tissue shift, and that incorporating displacement data into computational model appears feasible.