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Diffusion tensor imaging (DTI) is a new (mid- to late-1990s) magnetic resonance imaging (MRI)-based technique that allows us to visualize the location, the orientation, and the anisotropy of the brain's white matter tracts. The architecture of the axons in parallel bundles and their myelin shield facilitate the diffusion of the water molecules along their main direction. This diffusion which is preferentially oriented in one direction is called "anisotropic diffusion". The imaging of this white matter property is an extension of diffusion MRI. If we apply diffusion gradients (i.e. magnetic field variations in the MRI magnet) in at least 6 directions, it is possible to calculate, for each voxel, a tensor (i.e. a 3*3 matrix) that describes this diffusion anisotropy. The fiber direction is indicated by the tensor’s main eigenvector. This vector can be color-coded, yielding a cartography of the tracts’ position and direction (red for left-right, blue for superior-inferior, and green for anterior-posterior). The brightness is weighted by the tracts’ anisotropy.
Diffusion tensor imaging data can be used to perform tractography within white matter. Fiber tracking algorithms can be used to track a fiber along its whole length (e.g. the corticospinal tract, through which the motor information transit from the motor cortex to the spinal cord and the peripheral nerves).
The clinical applications of DTI are the tract-specific localization of white matter lesions, the localization of tumors in relation to the white matter tracts (infiltration, deflection), the localization of the main white matter tracts for neurosurgical planning, and the assessment of the white matter maturation in children.
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"Diffusion tensor imaging"