Diffusion tensor imaging (DTI) is a new 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 pixel, 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. Image File history File links Illus_dti. ... Magnetic Resonance Image showing a vertical cross section through a human head. ... Look up anisotropy in Wiktionary, the free dictionary. ... Comparative brain sizes In animals, the brain, or encephalon (Greek for in the head), acts as the control center of the central nervous system. ... White matter is one of the two main solid components of the central nervous system. ... An axon, or nerve fiber, is a long slender projection of a nerve cell, or neuron, which conducts electrical impulses away from the neurons cell body or soma. ... In neuroscience, myelin is an electrically insulating phospholipid layer that surrounds the axons of many neurons. ... Schematic drawing of the effects of diffusion through a semipermeable membrane. ... Diffusion MRI is a specific Magnetic Resonace Imaging (MRI) modality that produces in vivo images of biological tissues weighted with the local microstructural characteristics of water diffusion. ... Current flowing through a wire produces a magnetic field (M) around the wire. ... A pixel (pix, 1932 abbreviation of pictures, coined by Variety headline writers + element) is one of the many tiny dots that make up the representation of a picture in a computers memory. ... In mathematics, a tensor is a generalized quantity or a certain kind of geometrical entity that includes all the ideas of scalars, vectors, matrices and linear operators. ... In linear algebra, the eigenvectors (from the German eigen meaning own) of a linear operator are non-zero vectors which, when operated on by the operator, result in a scalar multiple of themselves. ...

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 corticospinal or pyramidal tract is a massive collection of axons that travel between the cerebral cortex of the brain, and the spinal cord. ... // Early work on motor cortex function Back in the 1940s, Canadian neurosurgeon Wilder Penfield wanted to know which bits of epileptics brains he could suck out without them noticing. ... Cross-section through cervical spinal cord. ... A nerve is an enclosed, cable-like bundle of nerve fibers or axons, which includes the glia that ensheath the axons in myelin. ...

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. A lesion is a non-specific term referring to abnormal tissue in the body. ... Tumor (American English) or tumour (British English) originally means swelling, and is sometimes still used with that meaning. ...

External links

• White Matter Atlas
• Pediatric DTI database
• Thesis on DTI
• Information, with image gallery