About DTI

Diffusion Tensor Imaging (DTI), is an application of diffusion imaging where several sets of diffusion-weighted images are acquired with the diffusion gradients applied in different directions. This technique enables the detection of diffusion anisotropy in various mediums such as brain white matter.

The diffusive properties of an anisotropic medium can be described with a 3 X 3 symmetric tensor. The eigenvalues of the diffusion tensor are the diffusion coefficients in the three principal directions of diffusivity, and the eigenvector corresponding to the largest eigenvalue is the main diffusivity direction in the medium. It is then possible to construct image maps from the main diffusivity direction, and for various anisotropy indices calculated from the eigenvalues. The anisotropy indices range from 0, in the case of completely isotropic diffusion, to 1, in the case of completely anisotropic diffusion.

Age Differences In The Normal Pediatric Population Measured With Diffusion MRI

As an additional segment of the fMRI study mapping language development in normal pediatric subjects, we have been acquiring diffusion tensor data in some of the subjects. We have correlated the results for fractional anisotropy (FA) and trace of the apparent diffusion coefficient (TADC) with age using a voxelwise analysis (PPT 1.1MB). The complete results are available in our Radiology manuscript and are summarized below.

We investigated a healthy sample of male and female subjects 5-18 years old. The subjects in our study were healthy and were specifically recruited for the investigation of normal brain development. Therefore, we are able to avoid the potential problem of transferability of results from a non-normal population.

Areas in which the TADC negatively correlated with subject age were found throughout the white matter (Figure 1). The changes in TADC involve mainly association and commissural fibers, which connect different areas of the cortex with each other. This hints at an ongoing process of modification in these fiber tracts, which has been observed in association cortex in postmortem studies.

The positive correlation of FA with age was strongest in the internal capsule (Figure 2), and the corresponding projective fiber tracts descending to or ascending from it. These correspond to corticospinal, corticonuclear, and possibly thalamocortical tracts. The correlation seems to be most pronounced in fibers passing to primary and supplementary motor areas (Brodmann areas 4 and 6), which is consistent with ongoing maturation and refinement of fine motor control, especially finger movements. Correlation of FA with subject age was also seen in the right inferior longitudinal fasciculus and the left arcuate fasciculus. The findings in the left arcuate fasciculus lend support to a hypothesis of a continued refinement and strengthening of connections between classical (Broca's and Wernicke's) language areas, compatible with the ongoing refinement of language function during normal development.