gms | German Medical Science

Objective: As maximization of extent of resection with minimized postoperative deficits, especially in case of primary brain tumors, is correlated with improved outcome, precise and reliable information about location and spatial extent of white matter tracts is indispensable. In this way, Diffusion Tensor Imaging (DTI) and fiber tractography had become widespread used methods to visualize major white matter tracts non-invasively in the human brain in-vivo. In order to approve reconstruction results within the post-processing routine with application of different algorithms and visualization strategies, improved data acquisition is needed as a first step. To optimize the acquisition protocol, four different settings are evaluated here.

Method: Four different types of DTI data sets (30 diffusion encoding gradients, transversal data acquisition) of 5 healthy volunteers (mean age: 29.80±5.67, male/female: 2/3) were acquired on a 3T MR-Scanner (Trio, Siemens, Germany) including voxel size of 2x2x2mm³ and voxel size of 1.5x1.5x3mm³ (in coronal direction) orientated parallel to the anterior commissure – posterior commissure (AC-PC) line or parallel to the course of the optic nerve. DTI-based fiber tractography of the visual pathways was performed using the tensor deflection approach, the most commonly used algorithm in clinical practice. Two regions of interest were manually drawn, the first outlining the lateral geniculate nucleus and its close vicinity in the course of the optic radiation and the second determining the visual cortex obtained via functional magnetic resonance imaging.

Results: Resulting fiber tractography showed different results for the used parameter- and planning-settings for MRI data acquisition. Settings with isotropic voxel sizes (2x2x2mm³) showed sparse reconstruction results in 4 out of 5 cases in contrast to more dense reconstructions for anisotropic voxel sizes (1.5x1.5x3mm³) in coronal direction. Orientation parallel to the course of the optic nerve showed more solid fiber reconstructions in contrast to orientation parallel to the AC-PC-line in all cases.

Conclusions: Parameter- and planning-settings of MRI data acquisition influence the results of fiber tractography. In the special case of the visual pathway, anisotropic voxels deliver favorable results compared to isotropic voxel sizes as well as image orientation parallel to the course of the optic nerve, and should therefore be considered for further research and clinical application.