White Matter Tract Atlases of a Century of Human Life

Abstract

The brain’s white matter (WM) evolves at a rapid pace during childhood and adolescence, stabilizes during young and middle adulthood, and degenerates in late adulthood. Here, we introduce a set of white matter tract atlases spanning birth to 100 years of age, covering 215 WM bundles to facilitate quantification of WM changes across the entire human lifespan. To our knowledge, this is to date the most comprehensive set of atlases, covering the largest time span with the largest number of WM bundles.

Methods

In order to build WM tract atlases, we used MRI data from the Lifespan Human Connectome Projects (HCPs): (i) Baby Connectome Project (BCP, 0-5 years; Howell B.R. 2019); (ii) HCP Development (HCP-D, 8-21 years; Somerville L.H. 2018); (iii) HCP Young Adult (HCP, 22-37 years; Essen D.C.V 2013); and (iv) HCP Aging (HCP-A, 36-100 years; Bookheimer S.Y. 2019).

WM tractography was performed using super-resolution asymmetry spectrum imaging (ASI; Wu Y. 2019, 2020a, 2020b). ASI fits a mixture of asymmetric fiber orientation distribution function (FODF) to the diffusion signal. WM tractograms were then generated by successively following local directions determined from the FODFs. ASI-based tractography mitigates the gyral bias problem (Wu Y. 2019, 2020a) common in existing tractography algorithms and improves cortico-cortical connectivity. The fiber streamlines of each subject were warped to the atlas space via affine and nonlinear transforms estimated between the tissue map of the subject and an age-specific atlas. We employed TractDL (Wu Y. 2020c) to identify a total of 215 fiber bundles from the streamlines. The bundles were annotated anatomically following previous studies (Yeh F-C. 2018; Zhang F. 2018), yielding (i) 42 association pathways; (ii) 18 cerebellar pathways; (iii) 13 commissural pathways; (iv) 14 cranial nerve pathways; (v) 14 brainstem pathways; (vi) 98 projection pathways; and (vii) 16 superficial pathways.

We investigated the change of the relative volume of each tract bundle across the entire life span. For each bundle, the volume was computed by (i) counting the number of streamlines traversing each voxel, (ii) normalizing the streamline count for each with respect to the total number of streamlines in the bundle, and (ii) computing the volume sum of the voxels traversed by the tract bundle, with each voxel weighted by the normalized streamline count.

References

  1. Wu, Y., Ahmad, S., Lin, W., Yap, P.-T., 2021. White Matter Tract Atlases of a Century of Human Life, in: OHBM, Virtual Meeting, 21-25 June, 2021.