Tract-specific analysis of white matter pathways in healthy subjects: a pilot study using diffusion tensor MRI

To date, very scant data is available regarding normal diffusion properties of white matter (WM) fibers. The present study aimed to initiate the establishment of a database of normal diffusion tensor metrics of cerebral WM fibers, including the uncinate fasciculus (UF), posterior cingulum (PC), fornix, and corticospinal tract (CST) for healthy adults using tract-specific analysis by diffusion tensor tractography (DTT). We also attempted to clarify whether age and laterality exerted any effects on this study group. DTT of WM fibers were generated for 100 healthy subjects, then mean diffusivity (MD) and fractional anisotropy (FA) of the tracts were measured. Pearson correlation analysis was used to evaluate age relationships. Paired t testing was used to compare hemispheric asymmetry. Interobserver correlation tests were also performed. Our results showed FA values for UF (right, 0.42 +/- 0.03; left, 0.40 +/- 0.03), PC (0.51 +/- 0.06, 0.52 +/- 0.06), fornix (0.37 +/- 0.06, 0.38 +/- 0.06), CST (0.70 +/- 0.06, 0.69 +/- 0.07), and MD values for UF (0.81 +/- 0.03, 0.82 +/- 0.04), PC (0.72 +/- 0.03, 0.72 +/- 0.04), fornix (1.86 +/- 0.32, 1.94 +/- 0.37), and CST (0.72 +/- 0.03, 0.74 +/- 0.04). We identified a significant positive correlation between age and MD in the right UF and bilateral fornices, and a negative correlation between age and FA in bilateral fornices. Hemispheric asymmetry was observed in FA of UF (right > left) and MD of CST (left > right). The results constitute a normative dataset for diffusion parameters of four WM tracts that can be used to identify, characterize, and establish the significance of changes in diseases affecting specific tracts.