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Scientific Lectures //

Interpretation of Diffusion Imaging Measures

Arvind Caprihan, Ph.D.- Associate Professor of Translational Neuroscience, Mind Research Network

February 17, 2015

ABSTRACT: Diffusion imaging makes macroscopic measurements in voxels of the order of 8 mm3 and infers properties about tissue microstructure. This inverse problem of determining micro-scale properties of tissue architecture, intracellular and extracellular spaces, cell membranes, and cell swelling from macroscopic diffusion data is an ill-posed problem. In other words, a wide variety of models can explain the observed measurements and over fitting is easily possible. New methods of collecting diffusion data with greater diffusion sensitivity and larger number of diffusion probing directions in a reasonable experiment time are now available. This has renewed the interest in models for interpreting diffusion data. We review the connection between the diffusion experiment and the inferences it can make about the microstructure. Interpretation of commonly used diffusion parameters, such as fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) with respect to brain disorders and brain injury will be discussed. Finally the current thinking in fitting the diffusion data with more complex tissue architecture models will be examined.

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