Serial Intraoperative MR Imaging of Brain Shift

Introduction: The major shortcoming of image-guided navigational systems is the use of presurgically acquired image data, which does not account for intraoperative changes in brain morphology. The occurrence of these surgically induced volumetric deformations, or "brain shift", has been well established. Maximum measurements for surface and midline shifts were reported. There is no detailed analysis, however, of the changes occurring throughout the entire surgery. Intraoperative MRI provides a unique opportunity to obtain serial imaging data and characterize the time course of brain deformations during surgery. Methods: The vertically open-configuration (0.5 Tesla SignaSP, GE Medical Systems) intraoperative MRI system permits access to the operative field and allows multiple intraoperative image updates without the need of moving the patient. We developed volumetric display software, the "3D Slicer", which allows quantitative analysis of degree and direction of brain shift. On twenty-five patients, four or more volumetric intraoperative image acquisitions were extensively evaluated. Results: Serial acquisitions allow a comprehensive sequential description of the direction and magnitude of intraoperative deformations. Brain shift occurs at various surgical stages and at different regions. Surface shift occurs throughout surgery and is mainly due to gravity. Subsurface shift occurs during resection involving collapse of the resection cavity and intraparenchymal changes that are difficult to model. Conclusions: Brain shift is a continuous dynamic process, which evolves differently in distinct brain regions. Therefore only serial imaging or continuous data acquisition provide consistently accurate image guidance. Furthermore only serial intraoperative MRI provides an accurate basis for the computational analysis of brain deformations, which might lead to an understanding, and eventually simulation of "brain shift" for intraoperative guidance. Running Title: Intraoperative Brain shift