A Volumetric Optical Flow Method for Measurement of Brain Deformation from Intraoperative Magnetic Resonance Images

A method to measure spatial and temporal brain deformation from sequential intraoperative Magnetic Resonance Images (MRI) and its preliminary clinical results are reported. Deformation is estimated with a volumetric optical flow measurement based on local intensity differences. A multi-resolution approach was used to efficiently estimate the deformation. We applied the method to five different cases and the method is highlighted by illustrative features accompanied by five sets of intraoperative MRI scanned before and after dura opening, twice during tumor resection and immediately after dura closure. The maximum cortical surface shift measured was 11 mm and subsurface shift was 4 mm. Volume change was measured by aligning the sequence of intraoperative MR images immediately after the opening of the dura to the images during the tumor resection. The amount of deformation present at each stage of the surgery was visualized. The computed deformation field was most satisfactory when the skin was first segmented and removed from the images prior to the optical flow computation. Magnetic field inhomegeneities as well as administration of contrast agent (Gadolinium-DTPA) were observed to modify the deformation field. The method demonstrated a good capability of intra-operative surface, subsurface and midline shift measurement.