In surgical removal of a malignant brain tumor, which is close to a pyramidal tract, diffusion tensor images obtained by preoperative magnetic resonance imaging (MRI) can display the spatial relationship between the tumor and the pyramidal tract. This image, however, is not appropriate to navigate the surgery because of brain shift due to surgical manipulation. We developed a navigation system employing intraoperative diffusion weighted imaging (DWI) using open MRI, which is the first trial with a 0.3 T scanner to aim at complete removal of cerebral tumors. A newly developed surgical coil has both functions of head fixation in surgery and a receiver coil in scan. The DWI of volunteers could display nerve fibers such as pyramidal tracts and corpus callosum under the optimized scan parameters. By refining navigation software, a physical position directed by the pointing device could be displayed correctly on three cross-sectional T1 (or T2) weighted images and three-dimensional (3D) DWI. Initial clinical evaluation of this system revealed that the spatial relationship between the tumor, the pyramidal tract, and the treatment position could be displayed correctly. Furthermore, the surgeons could recognize these positions intraoperatively and visually. The navigation system employing intraoperative DWI for a tumor and nerve fibers helped the surgeons remove the tumor and obviated postoperative disturbance such as motor paralysis.
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