What does a high diffusivity mean?
DTI provides a measure of the directions of diffusion of molecules, mainly water, within the brain. An increase in overall diffusion (mean diffusivity (MD)) is typically consistent with increased water content (i.e., edema and inflammation) and thus relatively less resistance, and therefore, higher diffusion rates.
What does mean diffusivity measure?
diffusion
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. Tractography is a useful tool for measuring deficits in white matter, such as in aging.
What is diffusivity in the brain?
Fractional anisotropy in brain measures the total magnitude of water directional movement along the axonal fibers (16), while mean diffusivity is a measure of mean diffusion of each direction. In principle, diffusion along the fibers should be faster than in the perpendicular direction.
Which is the best description of axial diffusivity?
Axial Diffusivity. Axial diffusivity (AD) is a measure of water diffusion along the principal axis of diffusion, and radial diffusivity (RD) comprises the two vectors of diffusion perpendicular to the primary direction of diffusion. From: Handbook of Clinical Neurology, 2014.
What is the meaning of radial diffusivity?
Radial diffusivity refers to the magnitude of diffusion perpendicular to fiber tracts. RD may be relatively more sensitive to myelin, but higher RD might reflect myelin loss, or loss of axons and/or reduced axonal packing density. Two-dimensional Three-dimensional Apparent diffusion coefficient Axial diffusivity Blood–brain barrier Choline
Which is the best description of Mean diffusivity?
Mean diffusivity is the overall directionally averaged magnitude of diffusion, and its increase reflects reduced white matter integrity due to either axonal or myelin degradation. Radial diffusivity refers to the magnitude of diffusion perpendicular to fiber tracts.
What does mean diffusivity and fractional anisotropy represent?
Mean diffusivity, which is made up of radial and axial diffusivity, represents the overall magnitude of water diffusion independent of anisotropy, whereas fractional anisotropy describes the degree of water diffusion independent of the overall water diffusion coefficient (Basser & Pierpaoli, 1996 ).