Serial intraoperative magnetic resonance imaging of brain shift

OBJECTIVE: A major shortcoming of image-guided navigational systems is the use of preoperatively acquired image data, which does not account for intra operative changes in brain morphology. The occurrence of these surgically i nduced volumetric deformations ("brain shift") has been well established. M aximal measurements for surface and midline shifts have been reported. Ther e has been no detailed analysis, however, of the changes that occur during surgery. The use of intraoperative magnetic resonance imaging provides a un ique opportunity to obtain serial image data and characterize the time cour se of brain deformations during surgery. METHODS: The vertically open intraoperative magnetic resonance imaging syst em (SignaSP, 0.5 T; CE Medical Systems, Milwaukee, WI) permits access to th e surgical field and allows multiple intraoperative image updates without t he need to move the patient. We developed volumetric display software (the 3D Slicer) that allows quantitative analysis of the degree and direction of brain shift. For 25 patients, four or more intraoperative volumetric image acquisitions were extensively evaluated. RESULTS: Serial acquisitions allow comprehensive sequential descriptions of the direction and magnitude of intraoperative deformations. Brain shift oc curs at various surgical stages and in different regions. Surface shift occ urs throughout surgery and is mainly attributable to gravity. Subsurface sh ift occurs during resection and involves collapse of the resection cavity a nd intraparenchymal changes that are difficult to model. CONCLUSION: Brain shift is a continuous dynamic process that evolves differ ently in distinct brain regions. Therefore, only serial imaging or continuo us data acquisition can provide consistently accurate image guidance. Furth ermore, only serial intraoperative magnetic resonance imaging provides an a ccurate basis for the computational analysis of brain deformations, which m ight lead to an understanding and eventual simulation of brain shift for in traoperative guidance.