Characterization of continuously distributed cortical water diffusion rates with a stretched-exponential model

Kevin M. Bennett, Kathleen M. Schmainda, Raoqiong Bennett (Tong), Daniel B. Rowe, Hanbing Lu, James S. Hyde
2003 Magnetic Resonance in Medicine  
Experience with diffusion-weighted imaging (DWI) shows that signal attenuation is consistent with a multicompartmental theory of water diffusion in the brain. The source of this so-called nonexponential behavior is a topic of debate, because the cerebral cortex contains considerable microscopic heterogeneity and is therefore difficult to model. To account for this heterogeneity and understand its implications for current models of diffusion, a stretched-exponential function was developed to
more » ... ribe diffusion-related signal decay as a continuous distribution of sources decaying at different rates, with no assumptions made about the number of participating sources. DWI experiments were performed using a spin-echo diffusionweighted pulse sequence with b-values of 500 -6500 s/mm 2 in six rats. Signal attenuation curves were fit to a stretched-exponential function, and 20% of the voxels were better fit to the stretched-exponential model than to a biexponential model, even though the latter model had one more adjustable parameter. Based on the calculated intravoxel heterogeneity measure, the cerebral cortex contains considerable heterogeneity in diffusion. The use of a distributed diffusion coefficient (DDC) is suggested to measure mean intravoxel diffusion rates in the presence of such heterogeneity. Magn Reson Med 50: 727-734, 2003.
doi:10.1002/mrm.10581 pmid:14523958 fatcat:fwzwwylnjrbahcwrkxyif7fn5q