Diffusion Tensor Imaging (DTI)

Diffusion tensor imaging (DTI) is a magnetic resonance imaging (MRI) technique that allow the measurement of the restricted diffusion of water in tissue in order to produce neural tract images instead of using this data specially for the purpose of assigning contrast or colours to pixels in a cross sectional image. It also provides useful structural information about muscle as well as other tissues such as the prostate and heart. In DTI, each voxel has one or more pairs of parameters: a rate of diffusion and a preferred direction of diffusion which is described in terms of three dimensional spaces. The properties of each voxel of a single DTI image is usually calculated by vector or tensor math from six or more different diffusion weighted acquisitions, each obtained with a different orientation of the diffusion sensitizing gradients. The higher information content of a DTI voxel makes it extremely sensitive to subtle pathology in the brain. In addition the directional information can be exploited at a higher level of structure to select and follow neural tracts through the brain. This process is called tractography . A more precise statement of the image acquisition process is that the image-intensities at each position are attenuated, depending on the strength (b-value) and direction of the so-called magnetic diffusion gradient, as well as on the local microstructure in which the water molecules diffuse. The more attenuated the image is at a given position, the greater diffusion there is in the direction of the diffusion gradient. In order to measure the tissue's complete diffusion profile, one needs to repeat the MR scans, applying different directions (and possibly strengths) of the diffusion gradient for each scan.