Abstract
Diffusion MRI-based tractography is the most commonly-used technique when inferring the structural brain connectome, i.e., the comprehensive map of the connections in the brain. The utility of graph theory-a powerful mathematical approach for modeling complex network systems-for analyzing tractography-based connectomes brings important opportunities to interrogate connectome data, providing novel insights into the connectivity patterns and topological characteristics of brain structural networks. When applying this framework, however, there are challenges, particularly regarding methodological and biological plausibility. This article describes the challenges surrounding quantitative tractography and potential solutions. In addition, challenges related to the calculation of global network metrics based on graph theory are discussed.Evidence Level: 5Technical Efficacy: Stage 1.
Highlights
Streamline-based tractography from noninvasive diffusion MRI data is the central technique for the study of structural connectivity of the living human brain
Any analyses derived from uncorrected, whole-brain tractography approaches will be subject to biases
The construction of a structural connectome involves a series of steps, and each step entails choices that can have flowthrough effects on the connectivity results
Summary
Mapping Structural Connectivity Using Diffusion MRI: Challenges and Opportunities. Chun-Hung Yeh, PhD,1,2,3,4* Derek K. As the human brain has a dense neural architecture comprising billions of neurons to form one of the most complex network systems in the world, it is an outstanding challenge to obtain its connectivity patterns in vivo with the elements and connections in different levels; for instance, at the microscale (single neurons), mesoscale (a group of neurons), and macroscale (distinct brain gray matter (GM) regions).[3,4,13] Modern noninvasive neuroimaging modalities have enabled both functional and anatomical connectivity information to be measured in the living human brain (Fig. 1) Among those techniques, diffusion magnetic resonance imaging (MRI) is the main in vivo technique for inferring white matter (WM) fiber connectivity due to its noninvasive ability to delineate WM pathways in the brain, using so-called fiber-tracking or tractography.[14] To date, diffusion MRI-based tractography has become an essential component of the field of connectomics, for the investigation of WM connectivity in the healthy brain,[15,16,17] as well as how connectivity is disrupted by brain disorders.[18].
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