Origin of unassigned sub-bundle clusters

Determine whether sub-bundles that cannot be assigned across all subjects arise from segmentation inaccuracies, tractography failures, registration errors, or genuine inter-individual anatomical variability.

Background

The atlas-based tractometry framework assigns subject streamlines to geometrically defined sub-bundles. Some sub-bundles were not represented in every participant and were therefore excluded from statistical analyses to maintain balanced comparisons.

The paper notes that excluding these incomplete sub-bundles may introduce selection bias because potentially informative anatomical regions are removed. The unresolved issue is whether the missing associations reflect methodological failures—such as inaccurate segmentation, unsuccessful tractography, or registration errors—or genuine variability in the anatomy of the white-matter pathways across individuals. Resolving this issue is important for improving the reliability and interpretability of sub-bundle tractometry.