Detecting Subtle Changes in Structure. Chris Rorden Diffusion Tensor Imaging Measuring white matter integrity Tractography and analysis. Diffusion weighted images measures random motion of water molecules. In ventricles, CSF is unconstrained, so high velocity diffusion
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Diffusion weighted images measures random motion of water molecules.
In ventricles, CSF is unconstrained, so high velocity diffusion
In brain tissue, water more constrained, so less diffusion.Diffusion Weighted Imaging
DTI is an extension of DWI that allows us to measure direction of motion.
DTI allows us to measure both the velocity and preferred direction of diffusion
In gray matter, diffusion is isotropic (similar in all directions)
In white matter, diffusion is anisotropic (prefers motion along fibers).Diffusion Tensor Imaging (DTI)
The amount of diffusion occurring in one pixel of a MR image is termed the Apparent Diffusion Coefficient (ADC) or Mean Diffusivity (MD).
The non-uniformity of diffusion with direction is usually described by the term Fractional Anisotropy (FA).DTI
A tensor is composed of three vectors. is termed the Apparent Diffusion Coefficient (ADC) or Mean Diffusivity (MD).
Think of a vector like an arrow in 3D space – it points in a direction and has a length.
The first vector is the longest – it points along the principle axis.
The second and third vectors are orthogonal to the first.What is a tensor?
V3 = V2
MD is termed the Apparent Diffusion Coefficient (ADC) or Mean Diffusivity (MD).DTI
V1 modulated by FA
Color shows principle tensor direction, brightness shows FA
Group mean images based on normalized data.
Rudebeck (2009) JoN