Diffusion MRI fiber tractography of the brain

Abstract

The ability of fiber tractography to delineate non-invasively the white matter fiber pathways of the brain raises possibilities for clinical applications and offers enormous potential for neuroscience. In the last decade, fiber tracking has become the method of choice to investigate quantitative MRI parameters in specific bundles of white matter. For neurosurgeons, it is quickly becoming an invaluable tool for the planning of surgery, allowing for visualization and localization of important white matter pathways before and even during surgery. Fiber tracking has also claimed a central role in the field of "connectomics," a technique that builds and studies comprehensive maps of the complex network of connections within the brain, and to which significant resources have been allocated worldwide. Despite its unique abilities and exciting applications, fiber tracking is not without controversy, in particular when it comes to its interpretation. As neuroscientists are eager to study the brain's connectivity, the quantification of tractography-derived "connection strengths" between distant brain regions is becoming increasingly popular. However, this practice is often frowned upon by fiber-tracking experts. In light of this controversy, this paper provides an overview of the key concepts of tractography, the technical considerations at play, and the different types of tractography algorithm, as well as the common misconceptions and mistakes that surround them. We also highlight the ongoing challenges related to fiber tracking. While recent methodological developments have vastly increased the biological accuracy of fiber tractograms, one should be aware that, even with state-of-the-art techniques, many issues that severely bias the resulting structural "connectomes" remain unresolved.

Modeling Brain Dynamics in Brain Tumor Patients Using the Virtual Brain

“…This limited variability in individual SC matrices could be due to the quality of current individual SC matrices. Although great advances have been made in diffusion-weighted imaging acquisitions and tractography algorithms, it is known that DWI tractography underestimates the number of short-distance streamlines in favor of long fiber tracks (Jeurissen et al, 2017). Although in the current study we have used a relatively new multi-shell DWI sequence with b-values of up to 2800 s/mm 2 and a state-of-the-art processing pipeline, future studies could investigate whether prediction accuracies of individual SC matrices improve when using data of even better quality (using for example 7T MRI scanners, with multiband sequences and/or longer acquisition times).…”

“…In addition, a distance matrix was constructed by calculating the average length of all streamlines connecting any two nodes (MRtrix3 tck2connectome). By using a proper high-order model and taking into account the full fiber orientation distribution function (through CSD), by taking into account the presence of non–white matter tissue (through multi-tissue CSD), by applying realistic individual anatomic priors (through ACT), and by ensuring fidelity of the tractograms to the data (through SIFT), it has been shown that the biological accuracy of tractograms can be vastly increased compared with those obtained with unfiltered unconstrained diffusion tensor tracking (Jeurissen et al, 2017). …”

The role of diffusion MRI in neuroscience

“…However, although empirical or simulation studies can clearly demonstrate that variation in these tissue properties modulates diffusion parameters, we are still faced with an inverse problem when trying to interpret an observed difference in diffusion parameters (e.g. reduced FA), as there is no one‐to‐one relationship between a given diffusion parameter and the underlying tissue structure . Nevertheless, diffusion parameters provide useful non‐invasive measures of local tissue microstructure, with sensitivity to features including membrane integrity, myelin thickness, axon diameter and packing density.…”

Mapping connectomes with diffusion MRI: deterministic or probabilistic tractography?

“…The connectome refers to a comprehensive network description of the brain, often represented as a graph, where nodes denote brain regions and edges represent white matter pathways . Tractography can be used to reconstruct white matter pathways in vivo using diffusion‐weighted MRI (dMRI) . Tractography was originally developed to reconstruct and virtually dissect individual or small groups of white matter fascicles, whereas connectomics requires high‐throughput, whole‐brain reconstruction of thousands of connections.…”