Diffusion-tensor MRI imaging and fiber tractography

Diffusion-tensor imaging (DTI) is an MRI technique that uses anisotropic diffusion to estimate the axonal (white matter) organisation of the brain. Fiber tractography (FT) is a 3D reconstruction technique to access neural tracts 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.

  • red for fibres crossing from left to right
  • green for fibres traversing in anteroposterior direction
  • blue for fibres going from superior to inferior
  • ROI (region of interest) based
  • voxel-based
  • histogram analysis
  • tractography/fibre tracking 
  • 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 another 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 anisotropic 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 acquisition is done by SE-EPI with application of diffusion gradients in multiple directions
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Article Information

rID: 22702
Section: Physics
Tag: spine
Synonyms or Alternate Spellings:
  • Tractography
  • Diffusion-tensor imaging
  • Fiber tractography
  • MRI tractography

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