Quantification of brain shift effects by MR-imaging

Neuronavigation and frameless stereotactic procedures are based on preoperatively defined coordinates of MRI or CT-scans. However, opening of the dura and surgical manipulations cause brain shift effects which render the accuracy of the predefined trajectories or coordinates of limited value. We developed different approaches to quantify these effects with high accuracy at different positions of the brain. The method is evaluated by a simulation model. The derived results show brain shift effects of at least 2 cm at the surface, and about 6 mm to 7 mm for positions located at the interhemisphere fissure and the lateral ventricles. Comparable evaluations carried out with data sets of a volunteer scanned for different positions of his head showed no significant shift effects. The results encourage us to develop a quantitative method which could be easily applied to correct the primary acquired data to the actual intraoperative situation.