Three-Dimensional Visualization of Motor Cortex and Pyramidal Tracts Employing Functional and Diffusion Weighted MRI Methods, Applications and Limitations

Background: Functional MRI (fMRI) combines anatomic with functional information and has, therefore, been widely used for preoperative planning of patients with mass lesions affecting functionally important brain regions. However, the course of functionally important fiber tracts is not visualized. We therefore propose to combine fMRI with diffusion weighted MRI (DWI) that allows visualization of large fiber tracts and to implement these data in a neuronavigation system. Methods: DWI was successfully performed at a field strength of 1.5 T, employing a spin-echo sequence with gradient sensitivity in six non-colinear directions to visualize the course of the pyramidal tracts and combined with echo-planar T2*fMRI during a hand motor task in 15 patients and 30 healthy controls. Results: Fusion of both data sets allowed visualization of the displacement of both primary sensorimotor area (M1) and corresponding large descending fiber tracts in patients. Intraoperatively, these data were present in a neuronavigation environment. Conclusion: The combination of fMRI with DWI allows for assessment of functionally important cortical areas and additional visualization of large fiber tracts. Information about orientation of fiber tracts in normal appearing white matter in patients with tumors within the cortical motor system cannot be obtained by other functional or conventional imaging methods and is as vital for reducing operative morbidity as the information about functional cortex. This technique might, therefore, have the prospect of guiding neurosurgical interventions, especially when being linked to a neuronavigation system.