Diffusion Tensor imaging (DTI) is an advanced MRI technique that enables examination of brain microstructure. Commonly reported DTI measures are fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD). FA describes the degree of directional coherence of diffusion, which is believed to reflect axonal diameter, axonal density, and myelination. A decrease in FA is generally associated with an increase in RD (associated with demyelination) or a decrease in AD (reflecting axonal injury) (Beaulieu, 2002; Pfefferbaum & Sullivan, 2005). A key advantage of DTI is its ability to detect white matter changes before they become apparent on conventional MR images (Pfefferbaum & Sullivan, 2005; Pfefferbaum et al., 2000).
