Implementation of Fiber Tract Navigation

Objective: To implement fiber tracking in a common neuronavigation environment for routine clinical use to visualize major white matter tracts intraoperatively.

Methods: A single-shot, spin-echo diffusion weighted echo planar imaging sequence with six diffusion directions on a 1.5 T magnetic resonance scanner was used for diffusion tensor imaging. For three-dimensional (3-D) tractography, we applied a knowledge-based multiple volume of interest approach. Tracking was initiated in each voxel of the initial seed volume in retrograde and orthograde directions according to the direction of the major eigenvector by applying a tensor deflection algorithm. Tractography results were displayed as streamlines assigned direction encoding color. After selecting the fiber tract bundle of interest by defining inclusion and exclusion volumes, a 3-D object was generated automatically by wrapping the whole fiber tract bundle. This 3-D object was displayed along with other contours representing tumor outline and further functional data with the microscope heads-up display.

Results: In 16 patients (three cavernomas, 13 gliomas), major white matter tracts (pyramidal tract, n = 14; optic radiation, n = 2) were visualized intraoperatively with a standard navigation system. Three patients developed a postoperative paresis, which resolved in two in the postoperative course. Additional planning time for tractography amounted to up to 10 minutes. Comparing the tractography results with a fiber bundle generated on a different platform by applying a distortion-free sequence revealed a good congruency of the defined 3-D outlines in the area of interest.

Conclusion: Fiber tract data can be reliably integrated into a standard neuronavigation system, allowing for intraoperative visualization and localization of major white matter tracts such as the pyramidal tract or optic radiation.