|—||Albert Einstein, July 2, 1945|
Diffusion Tensor Imaging (DTI): a magnetic resonance imaging technique that uses single-shot echo-planar MRI pulse sequences which have been optimized to detect the diffusivity of water molecules in tissue. By inducing magnetic gradients in different non-colinear directions while a subject is in the scanner, a series of diffusion weighted images (DWIs) can be acquired. For each given gradient, the echo attenuation values (ie “intensities”) at each voxel can then be used to calculate the apparent diffusion coefficient (ADC). The set of ADCs for each voxel can be used in turn to calculate the diffusion tensor for that voxel, an ellipsoid which models the diffusion profile of water within that voxel. The eccentricity of the ellipsoid is known as the Fractional Anisotropy (FA); the mean of the three principle eigenvectors is known as the mean diffusivity (MD).