DTI Flashcards
What is the role of DTI?
1) In-vivo quantification of tissue microstructure integrity
2) Virtual reconstruction of white matter pathways
What is Einstein’s equation?
This governs the displacement of water molecules:
r^2 = 6Dt, where D is the co-efficient of of free water and t is temperature.
How far does water diffuse?
1 micrometer in all directions per millisecond if the movement of water is isotropic
What is ADC?
Apparent diffusion coefficient is the diffusion of water in the brain in a specific direction i.e. ADC along a WM fiber tract > perpendicular to a WM fiber tract
What is the diffusion tensor?
A mathematically derived description of the overall displacement of water molecules in 3D space that is visualised as the diffusion ellipsoid
What factors make up the diffusion tensor?
Eigenvalues along the 3 principle eigenvectors
How is the mean diffusivity calculated?
Average of the 3 eigenvalues
What is a normal mean diffusivity in the brain?
0.5-2 micro mm^2 per second
What is FA?
Fractional isotropy
How is FA calculated?
Compares the diffusion tensor as a ratio of the mean diffusivity for that voxel i.e. the degree of anistropy between 0 = isotropic to 1 = anisotropy
What is axial diffusivity?
The diffusivity along the principle direction of the diffusion tensor (orientation of maximal diffusivity)
What is radial diffusivity?
The diffusivity perpendicular to the principle direction of the diffusion tensor
What is the main assumption when using DTI to reconstruct WM fiber tracts?
That the principle axis of the diffusion tensor is the same as the predominant fibre orientation within each voxel
How are streamline generated?
By reconstructing continuity between voxels using the principle axis of the diffusion tensor
What does the number of streamlines tell you?
This acts as a surrogate measure of tract volume but is not a measure of the number of axonal fibres
