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

Abstract

AbstractDiffusion‐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 20 volunteers were acquired and preprocessed including distortion bias correction and artifact reduction. Constrained spherical deconvolution was used to generate a directional diffusion information grid (fibre orientation distribution‐model [FOD]). 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 EPI (ss‐EPI) and readout‐segmented EPI (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 based on streamline selection performance 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 nonregistered 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, nonregistered 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.