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TractEM: Evaluation of protocols for deterministic tractography white matter atlas

Posted by on Friday, December 3, 2021 in Diffusion Weighted MRI, Image Segmentation, Labeling, Magnetic resonance imaging, Reproducibility, Tractography.

Rheault, Francois, Roza G. Bayrak, Xuan Wang, Kurt G. Schilling, Jasmine M. Greer, Colin B. Hansen, Cailey Kerley et al. “TractEM: Evaluation of protocols for deterministic tractography white matter atlas.” Magnetic Resonance Imaging 85 (2022): 44-56.

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Purpose: One of the key challenges of the manual delineation of white matter pathways is human-rater’s subjectivity in labeling. Clearly communicating the manual processes to capture this information is cumbersome, yet essential to lay a solid foundation for comprehensive atlases. Segmentation protocols must be designed so the interpretation of the requested tasks as well as locating structural landmarks is anatomically accurate, intuitive and reproducible.

Methods: In this work, we quantified the reproducibility of a first iteration of an open/public multi-bundle segmentation protocol. This allowed us to establish a baseline for its reproducibility as well as to identify the limitations for future iterations. The protocol was tested/evaluated on both typical 3 T research acquisition Baltimore Longitudinal Study of Aging (BLSA) and high-acquisition quality Human Connectome Project (HCP) datasets.

Results: The results show that a rudimentary protocol can produce acceptable intra-rater and inter-rater reproducibility. However, this work highlights the difficulty in generalizing reproducible results and the importance of reaching a consensus on the anatomical description of white matter pathways.

Conclusions: The protocol has been made available in open source to improve generalizability and reliability in collaboration. The goal is to improve upon the first iteration and initiate a discussion on the anatomical validity (or lack thereof) of some bundle definitions and the importance of reproducibility of tractography segmentation.


Average shape and position of all bundles that are part of the TractEM protocol (association and projection pathways are shown only for the left hemisphere). The average was computed using segmentation from 4 raters and 4 datasets (BLSA) using a majority vote. This highlights the general agreement on the shape, but as seen in the lower right vignette the variability of each individual segmentation can be quite extreme.