Imaging con tensore di diffusione: differenze tra le versioni

Versione delle 18:20, 25 ott 2010

Versione delle 22:22, 25 ott 2010

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{{s|neuroscienze|biotecnologie}}

{{T|Lingua=inglese|Argomento=Neuroscienze|Data=Ottobre 2010}}

'''DTI''', acronimo di '''Diffusion Tensor Imaging''', è un termine con il quale di intende una tecnica di visualizzazione cerebrale.

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This demonstrates a cubic dependence of transverse magnetization on time. Anisotropic diffusion will have a similar solution method, but with a more complex diffusion tensor.

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===Applicazioni===

Le principali applicazioni sono quelle nella visualizzazione della [[sostanza bianca]], per determinare la localizzazione, orientamento, e [[anisotropia]] dei tratti e fasci di fibre nervose. L'architettura dei gruppi di [[Assone|assoni]] in fasci paralleli, e le loro guaine di [[mielina]], facilitano la [[diffusione]] delle molecole d'acqua preferenzialmente lungo la loro principale direttrice. Questa diffusione orientata si denomina ''diffuzione anisotropica'' (dall'inglese: ''anisotropic diffusion'').

[[Image:DTI-sagittal-fibers.jpg|thumb|240px|Tractographic reconstruction of neural connections via DTI]]

The imaging of this property is an extension of diffusion MRI. If a series of diffusion gradients (i.e. [[magnetic field]] variations in the MRI magnet) are applied that can determine at least 3 directional vectors (use of 6 different gradients is the minimum and additional gradients improve the accuracy for "off-diagonal" information), it is possible to calculate, for each [[voxel]], a [[tensor]] (i.e. a symmetric positive definite 3×3 [[matrix (mathematics)|matrix]]) that describes the 3-dimensional shape of diffusion. 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.

Some clinical applications of DTI are in the tract-specific localization of white matter [[lesion]]s such as trauma and in defining the severity of [[Traumatic brain injury#Focal vs. diffused|diffuse traumatic brain injury]]. The localization of [[tumor]]s in relation to the white matter tracts (infiltration, deflection), has been one of the most important initial applications. In surgical planning for some types of [[brain tumors]], surgery is aided by knowing the proximity and relative position of the [[corticospinal tract]] and a tumor.

The use of DTI for the assessment of white matter in development, pathology and degeneration has been the focus of over 2,500 research publications since 2005. It promises to be very helpful in distinguishing [[Alzheimer's disease]] from other types of [[dementia]]. Applications in brain research cover e.g. connectionistic investigation of [[neural network]]s [[in vivo]].<ref>L. Minati, D. Aquino, ''Probing neural connectivity through Diffusion Tensor Imaging (DTI)'', In: R. Trappl (Ed.) ''Cybernetics and Systems 2006'':263-68, 2006</ref>

DTI also has applications in the characterization of [[skeletal muscle|skeletal]] and [[cardiac muscle]]. The sensitivity to fiber orientation also appears to be helpful in the arena of [[sports medicine]] where it greatly aids imaging of structure and injury in [[muscle]]s and [[tendon]]s.

A recent study at [[Barnes-Jewish Hospital]] and [[Washington University School of Medicine]] of healthy persons and both newly affected and chronically-afflicted individuals with [[optic neuritis]] caused by [[multiple sclerosis]] (MS) showed that DTI can be used to assess the course of the condition's effects on the eye's [[optic nerve]] and the vision because it can assess [[Diffusion MRI#Measures of anisotropy and diffusivity|axial diffusivity]] of water flow in the area. {{Citation needed|date=June 2009}}

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Nell'ottobre del 2009 venne pubblicata una ricerca che documentava un incremento localizzato della anisotropia frazionale in seguito all'addestramento a un complesso compito visivo-motorio ([[:en:juggling]]). Nel lavoro si sosteneva che si trattasse della prima evidenza di cambiamenti dovuti all'esperienza nella microstruttura della [[sostanza bianca]] in esseri umani adulti sani.<ref>Nature Neuroscience doi:10.1038/nn.2412</ref>

==Voci correlate==