Diffusion tensor imaging and fiber tractography
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Diffusion-tensor imaging (DTI) is aan MRI technique technique that uses anisotropic anisotropic diffusion to to estimate the the axonal (white matter) organisation of the brain. Fiber tractography (FT) is a 3D a 3D reconstruction technique technique to access neural neural tracts using using data collected by DTI.
Within cerebral white matter, water molecules tend to diffuse more freely along the direction of axonal fascicles than across them. Such directional dependence of diffusivity is termed anisotropy.
Colour coding
- red for fibres crossing from left to right
- green for fibres traversing in
antero-posterioranteroposterior direction - blue for fibres going from superior to inferior
Quantitative analysis methods
- ROI (region of interest) based
- voxel
based-based - histogram analysis
- tractography/fibre tracking
Physics of DTI
- DTI provides quantitative analysis of the magnitude and directionality of water molecules
- the word tensor indicates a 3 x 3 matrix used here with eigen values and eigen vectors as its constituents
- the two main parameters derived from DTI data are mean diffusivity (MD) or in
otheranother term apparent diffusion coefficient (ADC) and fractional anisotropy (FA) - FA reflects the directionality of molecular displacement by diffusion and vary between 0 (isotropic diffusion) and 1 (infinite
anisotropicdiffusionanisotropic diffusion). FA value of CSF is 0 - MD reflects the average magnitude of molecular displacement by diffusion. The more the MD value, the more the isotropic is the medium
- AD - axial diffusivity represents the longest eigen vector
- RD - radial diffusivity represents the average of two shorter eigen vectors
- DTI data
aquisitionacquisition is done by SE-EPI with application of diffusion gradients in multiple directions
-<p><strong>Diffusion-tensor imaging (DTI) </strong>is a MRI technique that uses anisotropic diffusion to estimate the axonal (white matter) organisation of the brain. <strong>Fiber tractography (FT)</strong> is a 3D reconstruction technique to access neural tracts using data collected by DTI.</p><p>Within cerebral white matter, water molecules tend to diffuse more freely along the direction of axonal fascicles than across them. Such directional dependence of diffusivity is termed anisotropy.</p><h4>Colour coding </h4><ul>- +<p><strong>Diffusion-tensor imaging (DTI) </strong>is an MRI technique that uses anisotropic diffusion to estimate the axonal (white matter) organisation of the brain. <strong>Fiber tractography (FT)</strong> is a 3D reconstruction technique to access neural tracts using data collected by DTI.</p><p>Within cerebral white matter, water molecules tend to diffuse more freely along the direction of axonal fascicles than across them. Such directional dependence of diffusivity is termed anisotropy.</p><h4>Colour coding </h4><ul>
-<li>green for fibres traversing in antero-posterior direction</li>- +<li>green for fibres traversing in anteroposterior direction</li>
-<li>voxel based</li>- +<li>voxel-based</li>
-<li>the two main parameters derived from DTI data are mean diffusivity (MD) or in other term apparent diffusion coefficient (ADC) and fractional anisotropy (FA)</li>-<li>FA reflects the directionality of molecular displacement by diffusion and vary between 0 (isotropic diffusion) and 1 (infinite anisotropicdiffusion). FA value of CSF is 0</li>- +<li>the two main parameters derived from DTI data are mean diffusivity (MD) or in another term apparent diffusion coefficient (ADC) and fractional anisotropy (FA)</li>
- +<li>FA reflects the directionality of molecular displacement by diffusion and vary between 0 (isotropic diffusion) and 1 (infinite anisotropic diffusion). FA value of CSF is 0</li>
-<li>DTI data aquisition is done by SE-EPI with application of diffusion gradients in multiple directions</li>- +<li>DTI data acquisition is done by SE-EPI with application of diffusion gradients in multiple directions</li>
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