Tracking neuronal fiber pathways in the living human brain

Abstract

Detailed connectivities have been studied in animals through invasive tracer techniques, but these invasive studies cannot be done in humans, and animal results cannot always be extrapolated to human systems. We have developed noninvasive neuronal fiber tracking for use in living humans, utilizing the unique ability of MRI to characterize water diffusion. We reconstructed fiber trajectories throughout the brain by tracking the direction of fastest diffusion (the fiber direction) from a grid of seed points, and then selected tracks that join anatomically or functionally (functional MRI) defined regions. We demonstrate diffusion tracking of fiber bundles in a variety of white matter classes with examples in the corpus callosum, geniculo-calcarine, and subcortical association pathways. Tracks covered long distances, navigated through divergences and tight curves, and manifested topological separations in the geniculo-calcarine tract consistent with tracer studies in animals and retinotopy studies in humans. Additionally, previously undescribed topologies were revealed in the other pathways. This approach enhances the power of modern imaging by enabling study of fiber connections among anatomically and functionally defined brain regions in individual human subjects.

MR connectomics: Principles and challenges

“…Deterministic line propagation Local path integration along principal diffusion directions Wedeen (1996), Conturo et al (1999), Mori et al (1999), Basser et al (2000).…”

“…The very first tractography algorithms published were of that kind (Conturo et al, 1999;Mori et al, 1999;Wedeen, 1996), but very quickly as people started to understand the intrinsic limitation of DTI, they realized that such a simple solution was the source of very obvious artifacts. Researchers began to be aware of the "fibercrossing problem".…”

“…Past and current state of the art Diffusion-weighted magnetic resonance imaging (MRI), received strong attention for the first time in the early 90s as it proved to be a sensitive biomarker for acute stroke (Moseley et al, 1990). The second reason diffusion imaging came to attention, was because it was observed that not only does white matter exhibit reliable anisotropic properties (Basser et al, 1994;Douek et al, 1991) but that it is indeed possible to infer fiber tract trajectories on the basis of these patterns (Conturo et al, 1999;Mori et al, 1999;Wedeen, 1996). Diffusion Tensor Imaging and tractography was born.…”

Tract probability maps in stereotaxic spaces: Analyses of white matter anatomy and tract-specific quantification

“…The fiber tracking based on FACT was performed by DtiStudio (Jiang et al, 2006). A multi-ROI approach was used to reconstruct tracts of interest (Conturo et al, 1999;Huang et al, 2004), exploiting existing anatomical knowledge of tract trajectories. Tracking was performed from all pixels inside the brain (the so-called brute-force approach), and fibers penetrating manually defined ROIs were assigned to the specific tracts associated with those ROIs.…”

“…By comparing this information with conventional MR parameter maps, we can identify specific white matter tracts that are affected by the lesions. We can extend this approach in a more systematic way by identifying the 3D trajectories of individual white matter tracts using 3D tract reconstruction, or tractography (Conturo et al, 1999;Mori et al, 1999;Basser et al, 2000;Poupon et al, 2000;Parker et al, 2002). Once a tract of interest is defined in three dimensions, we can superimpose its coordinates on MR parameter maps to perform quantitative tract-specific monitoring of pathological conditions (Virta et al, 1999;Xue et al, 1999;Stieltjes et al, 2001;Glenn et al, 2003;Wilson et al, 2003;Partridge et al, 2004;Pagani et al, 2005).…”