Just pretty pictures? What diffusion tractography can add in clinical neuroscience

Abstract

Purpose of review: Diffusion tractography uses non-invasive brain imaging data to trace fibre bundles in the human brain in vivo. This raises immediate possibilities for clinical application but responsible use of this approach requires careful consideration of the scope and limitations of the technique.

Recent findings: To illustrate the potential for tractography to provide new information in clinical neuroscience we review recent studies in three broad areas: use of tractography for quantitative comparisons of specific white matter pathways in disease; evidence from tractography for the presence of qualitatively different pathways in congenital disorders or following recovery; use of tractography to gain insights into normal brain anatomy that can aid our understanding of the consequences of localised pathology, or guide interventions.

Summary: Diffusion tractography opens exciting new possibilities for exploring features of brain anatomy that previously were not visible to us in vivo.

Figure 1

Routes between Broca’s and Wernicke’s Areas in the human brain: A direct path (red), corresponding to the arcuate fasciculus, and an indirect path via the inferior parietal cortex (‘Geschwind’s territory), consisting of an anterior segment (green), and a posterior segment (yellow) (from ref. 64).

Figure 2

Left: Tracing of motor (red) and sensory (green) pathways in a premature infant. Right: Quantitative measurements from along these pathways show increasing FA with age, probably reflecting a combination of increasing packing density and myelination (from ref. 28).

Figure 3

Left: Tracing the superior longitudinal fasciculus (red) around a tumor (yellow) using functional landmarks (blue). Bottom two images show that tracing is much less successful when based on anatomical landmarks. Right: Quantitative measurements show that the displaced tract has elevated FA. This probably reflects increased packing density with tract compression, as there is decreased diffusion perpendicular to the tract, and increased diffusion along it (from ref. 29).