Imaging con tensore di diffusione: differenze tra le versioni

Versione delle 22:29, 25 ott 2010

Versione delle 22:33, 25 ott 2010

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[[Image:DTI-sagittal-fibers.jpg|thumb|250px|Ricostruzione Trattografica delle connessioni neurali via DTI]]

La visualizzazione (imaging) di questa proprietà della materia bianca è una estensione della [[Risonanza magnetica|RM]] a diffusione. Se vengono applicate una serie di gradienti di diffusione (ad.es. variazioni del [[campo magnetico]] nel magnete della RMI) in maniera che possano fornire almento 3 vettori direzionali (usel'utilizzo ofdi 6 differentdiversi gradientsgradienti isè theil minimumminimo andindispensabile additionale gradienti gradientsaddizionali improvemigliorano thel'accuratezza accuracyper forl'informazione "off-diagonaldiagonale" information), ite isdunque possibleè topossibile calculatecalcolare, forper eachogni [[voxel]], aun [[tensortensore]] (iad.ees. adefinire symmetric positive definite 3×3una [[matrixMatrice (mathematicsmatematica)|matrixmatrice]] simmetrica positiva) thatche descrive la forma describestridimensionale thedella 3-dimensionaldiffusione shapedelle ofmolecole diffusiond'acqua. 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 fractional anisotropy which is a scalar measure of the degree of anisotropy in a given voxel. Mean diffusivity (MD) or trace is a scalar measure of the total diffusion within a voxel. These measures are commonly used clinically to localize white matter lesions that do not show up on other forms of clinical MRI.

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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 [[nerve]]s). Tractography is a useful tool for measuring deficits in white matter, such as in aging. Its estimation of fiber orientation and strength is increasingly accurate, and it has widespread potential implications in the fields of cognitive neuroscience and neurobiology.