gms | German Medical Science

Objective: To reconstruct speech-related major white matter tracts connecting Broca and Wernicke areas and to integrate this information into a standard microscope-based navigation system for surgery of lesions close to these tract systems in order to prevent postoperative speech deficits.

Methods: A single-shot spin-echo diffusion weighted echo planar sequence (with 6 diffusion gradients) was used for diffusion tensor imaging (DTI) based fiber tracking in 28 patients. Motor and sensory speech areas identified by functional MRI applying silent reading and naming paradigms were used as seed regions for a tensor defection algorithm, tracking both in retro- and orthograde directions according to the direction of the principal eigenvector in each voxel. Rigid registration of the b0 diffusion images with 3-D T1-weighted anatomical datasets allowed integration of the data in the navigation setup where also the functional data were co-registered. Reconstructed fiber tracts applying an alternative tracking algorithm implementing a probabilistic approach (A*) were registered via an import in an analyze data format. To visualize the data in the surgical field the fiber tracts were wrapped by hulls, the generated 3-D objects were dispalyed by the microscope heads-up display.

Results: In all patients speech-related fiber tracts connecting Broca and Wernicke areas could be visualized successfully. The registration error of DTI with standard 3-D anatomical data was less than 2 mm in the area of interest, i.e. adjacent to the lesion. The additional implementation of a probabilistic tracking algorithm made it possible to confirm the results of the standard DTI evaluation. In 14% there was a new temporary postoperative speech deficit, which vanished in about a week. Only in one patient (3.6%) was there a permanent speech deterioration.

Conclusions: Speech related fiber tracts can be reliably visualized by DTI-based fiber tracking. Application of different tracking algorithms increases the reliability of the reconstructed fiber bundles. Integration of speech related tract systems in a multimodal navigation setup helps avoiding postoperative speech deficits.