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Abstract #0078

Activation Energies for Water Diffusion in ex-vivo White Matter

Bibek Dhital1, Christian Labadie1,2, Harald E. Mller1, Robert Turner1

1Max Planck Institute for Human Cognitive & Brain Sciences, Leipzig, Germany; 2Laboratoire de Spectromtrie Ionique et Molculaire, Universit Claude Bernard Lyon 1, Lyon, France

We made MR measurements of diffusion up to very high b-factor in excised human corpus callosum, over a wide temperature range. Above a freezing phase transition at -20 C, data showed a robust bi-exponential dependence on b-factor. Below this temperature only half of the slow component remained, suggesting two water pools within this component. An Arrhenius plot revealed significantly different activation energies for the fast and slow components. The lower of these corresponds well to breaking a hydrogen bond in a locally ordered region. This suggests that unfrozen water consists of hydration layers close to the membranes.