Fiber tractography of the optic radiations: impact of diffusion model, voxel shape and orientation

BACKGROUND: Reliable visualization of the optic radiations (OR) is of major importance in tumor surgery close to the OR to prevent permanent visual field deficits. Diffusion tensor imaging (DTI) based fiber tractography (FT) has become a standard tool to visualize major white matter tracts and to support the prevention of postoperative deficits. Nevertheless, FT of the OR is notoriously challenging due to its high neuroanatomical complexity. METHODS: To improve FT of the OR we analyzed the effect of a more complex diffusion model and the effect of different voxel shapes and orientations. MRI data of 21 healthy subjects was acquired using isometric and anisometric voxel sizes and standard and adapted slice angulation. FT was performed using the DTI based approach and an orientation distribution function (ODF) based approach. Results were visually inspected, and fiber tract volumes were compared. RESULTS: DTI based FT led to poor results, failing to reconstruct plausible tracts at all in up to 26.11% of all cases. The ODF based approach resulted in more compound and solid tracts showing also significantly larger tract volumes. Voxel shape or orientation did not influence DTI, but ODF based FT. Isometric or anisometric voxels with standard slice orientation revealed highest tract volumes. Adapted orientation in combination with anisometric voxels led to significantly smaller tract volumes. CONCLUSIONS: Plausible tractography of the OR can be achieved using ODF based fiber tracking within a clinically feasible timeframe. Voxel shape and orientation seem to be of minor importance and might be kept to isometric voxel for flexible application of FT.