Note that the FA is extreme in regions of white matter (e.g. The figure below shows the fractional anistropy and mean diffisuity of a group of healthy individuals. The other is to use the data for tractography to illustrate the shape and direction of fiber tracts (comparing C versus D). One is to describe it as having normal or abnormal ADC values per pixel (e.g. Therefore, are two ways to describe and analyze diffusion data. For example, in figure C below the water is moving isotropically, while in D the water is moving anisotropically. the brain's white matter) the diffusion properties are anisotropic - water will move in the direction of the fibers much more rapidly than orthogonal to the fibers. On the other hand, in some areas such as along the fiber bundles of neurons (e.g. For example, in the figure below, water is diffusing faster in A than B. inside cells) water is constrained, and the mean diffusion (apparent diffusion coefficient, or ADC) is slow, while in regions such as the ventricles the motion of the cerebral spinal fluid is unconstrained and relatively fast. Consider the drawing A below, where the red line shows the typical diffusion of a water molecule, randomly moving around - the black ball shows this molecules diffusion speed and direction. However, in practice different sequences can give dramatically different results (especially in terms of regional variability) so you probably want to use existing databases primarily as a starting point for developing a set of templates based on your own population, scanner and protocol.įurthermore, analysis methods for DTI remain primitive. This means that one can compare results to different atlases from other centers, for example the Hokkaido University Fractional Anisotropy Database. Furthermore, in theory DTI values should be relatively calibrated - healthy adults should show similar values regardless of which scanner is used. DTI appears to be a tremendously important tool, as it is sensitive to acute brain injury (you can see strokes that can not be detected by conventional MRI) and it correlates with white matter integrity. Diffusion imaging measures the random motion of water (and other liquids with hydrogen). This page describes Diffusion Tensor Imaging was written by Leigh Morrow, Paul Morgan and Chris Rorden.
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