Diffusion-based tractography in the optic nerve requires sampling strategies assisted by anatomical landmark information (regions of interest, ROIs). We aimed to investigate the feasibility of expert-placed, high resolution T1-weighted ROI-data transfer onto lower spatial resolution diffusion-weighted images. Slab volumes from twenty volunteers were acquired and preprocessed including distortion bias correction and artifact reduction. Constrained spherical deconvolution was used to generate a directional diffusion information grid (FOD-model (fibre orientation distribution)). Three neuroradiologists marked landmarks on both diffusion imaging variants and structural datasets. Structural ROI information (volumetric interpolated breath-hold sequence (VIBE)) was respectively registered (linear with 6/12 degrees of freedom (DOF)) onto single-shot (ss-EPI) and readout-segmented (rs-EPI) volumes respectively. All eight ROI/FOD combinations were compared in a targeted tractography task of the optic nerve pathway. Inter-rater reliability for placed ROIs among experts was highest in VIBE images (lower confidence interval 0.84 to 0.97, mean 0.91) and lower in both ss-EPI (0.61 to 0.95, mean 0.79) and rs-EPI (0.59 to 0.86, mean 0.70). Tractography success rate was highest in VIBE-drawn ROIs registered (6-DOF) onto rs-EPI FOD (70.0% over 5%-threshold, capped to failed ratio 39/16) followed by both 12-DOF registered (67.5%; 41/16) and non-registered VIBE (67.5%; 40/23). On ss-EPI FOD, VIBE ROI-datasets obtained fewer streamlines overall with each at 55.0% above 5%-threshold and with lower capped to failed ratio (6-DOF: 35/36; 12-DOF: 34/34, non-registered 33/36). The combination of VIBE-placed ROIs (highest inter-rater reliability) with 6-DOF registration onto rs-EPI targets (best streamline selection performance) is most suitable for white matter template generation required in group-studies.

Purpose Successful utilization of anatomical templates in the evaluation of diffusion-weighted neuroimaging-studies requires accurate registration of intra-individual datasets. We investigated the feasibility of structural MRI image registration onto single-shot and read-out segmented echo-planar diffusion-weighted imaging variants for use in tractographic samplings of the visual system, in particular the optic nerve. Methods Slab volumes of the optic nerve pathway from thirteen volunteers were acquired and preprocessed. Three neuroradiologists marked landmarks (ROIs, regions of interest) on two diffusion-weighted and one structural dataset. Structural ROIs were respectively registered (6/12 degrees of freedom, DOF) onto single-shot (ss-EPI) and readout-segmented (rs-EPI) volumes. All six ROI/FOD (fibre orientation distribution) combinations underwent a targeted tractography task (MRtrix3: iFOD2). Results Inter-rater reliability for ROI-placement was highest in VIBE images (0.66 to 0.95, mean 0.85) and lower in both ss-EPI (mean 0.77) and rs-EPI (0.46 to 0.84, mean 0.64). Sufficient FOD generation in the optic nerve was successful in 12/26 of all cases for ss-EPI volumes (46.2% of cases) and in 18/26 for rs-EPI volumes (69.2%). Spatial shift of VIBE-drawn ROI-coordinates after 6-DOF registration was highest for ss-EPI-targets (medians: 1.15 to 1.4 mm; rs-EPI 0.82 to 0.93 mm), whereas 12-DOF registration caused less spatial shifts (ss-EPI: 0.64 to 1.03 mm; rs-EPI: 0.58 mm to 0.79 mm). Tractography results revealed no significant differences between ss-EPI and rs-EPI sequences on cases with mutual generation of sufficient FODs (n=10). Conclusion Structurally-placed ROIs (highest inter-rater reliability) with 6-DOF registration onto rs-EPI targets (highest FOD-generation rate) seems most suitable for white matter template generation.