Diffusion Tensor Imaging (DTI) is a type of magnetic resonance imaging (also called diffusion MRI or dMRI) that enables the visualization of the location, orientation, and anisotropy (direction) of the brain’s white matter (axon) tracts. DTI measures the diffusion of water molecules along the axon in order to produce neural tract images.
Tractography, specifically, is the process of imaging the directional information of neural tracts through the brain. Tractography is possible because myelin sheaths facilitate the diffusion of water molecule preferentially along their main direction. Preferential oriented diffusion is called anisotropic diffusion.
Generally, axons provide communication between brain regions and between the brain and the spinal cord. In these images, the axons are colored based on their orientation and direction. For example, axons running from front to back are blue, from right to left are red, and from interior to exterior are green. In the image above, the red axons of the corpus callosum are connecting the two hemispheres. Cleverly, DTI has been described as a white matter atlas.