Analysis of Water Diffusion in White Matter Using a Hydration Layer Model

Elena Olariu¹, Ian Cameron^1,2

Diffusion measurements have been made with MRI for many years but an explanation for the observed behavior, in terms of the underlying mechanisms is still illusive. Diffusion decays have frequently been interpreted in terms of a two compartment model with the fast and slow diffusion coefficients associated with extra- and intracellular water, respectively. Unfortunately, the observed signal fractions are not consistent with the true ratio of intra- to extracellular water. Recently, LeBihan has suggested that the two observed components may be associated with free water and hydration water rather than with intra- and extracellular water. It is reasonable to expect that intra- and extracellular hydration water will diffuse more slowly than the rest of the tissue water. The purpose of the research reported here was to investigate this suggestion to see if the predictions of this model are consistent with measured diffusion decay data.