# Training:Glossary

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**Diffusion Weighted Imaging (DWI)**is a technique based on sensitizing the MR signal to the diffusive motion of water molecules in tissue. The variation of the diffusion along different spatial directions provides information about diffusion anisotropy and ultimately about tissue structure.**b factor**: Sensitivity of a pulse sequence to the diffusion process. The higher the value b, the stronger the diffusion weighting.**Diffusion Tensor Imaging (DTI)**is a non invasive in-vivo imaging technique that enables the measurement of the diffusion of water molecules in tissue.**Diffusion Tensor**: 3x3 symmetric matrix. It can be visualized using an ellipsoid where the principal axes correspond to the directions of the eigenvector system.**Diffusion Anisotropy**describes the direction preference of the diffusion process.**Fractional Anisotropy (FA)**describes the degree of anisotropy, from 0 to isotropic to 1 for fully anisotropic.**Mean Diffusivity (MD)**describes the average degree of diffusion.**Apparent Diffusion Coefficient (ADC)**is a measure of the freedom of water molecules diffusion in the tissue environment.**Fibers, tracts**: open-curves representing diffusion paths of water molecules.**Fiber Clustering**methods analyze a collection of tractographic paths in 3D, and separate them into bundles, or clusters, that contain paths with similar shape and spatial position. The resulting bundles are expected to contain fiber paths with similar anatomy and function.