Comparison of T1-weighted landmark placement and ROI transfer onto
diffusion-weighted EPI sequences for targeted tractography tasks in the
optic nerve
Abstract
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.