Structure sensitivity internal diffusion

Diffusion is defined as the random translational motion of molecules or ions that is driven by internal thermal energy - the so-called Brownian motion. The mean movement of a water molecule due to diffusion amounts to several tenth of micrometres during 100 ms. Magnetic resonance is capable of monitoring the diffusion processes of molecules and therefore reveals information about microscopic tissue compartments and structural anisotropy. Especially in stroke patients diffusion sensitive imaging has been reported to be a powerful tool for an improved characterization of ischemic tissue. 

Two experiments have been presented which allow to measure the effective T2 decay rate of individual amide proton and the magnetisation build-up rates for a selective transfer from H2O to using spin diffusion as a mixing element. " The experiments were demonstrated for a uniformly H, N labelled sample of a microcrystalline SH3 domain in which exchangeable deuterons were back-substituted with protons. The NMR experimental data was correlated with the dipolar couplings calculated from H20-H distances which were extracted from the X-ray structure of the protein. It was shown that the T2 decay rates and H20-H build-up rates are sensitive to distance and dynamics of the detected water molecules with respect to the protein, and that qualitative information about localisation and dynamics of internal water molecules can be obtained in the solid state by interpretation of the spin dynamics of a reporter amide proton. 

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