Exploring cell biodiversity - Neutron scattering investigation of water diffusion in complex system

Scientists from biophysics, biology and medicine fields are interested in exploring and characterizing topologically cerebral tissue in order to diagnostic different diseases which affect brain in many patients [1-3]. One of the most diffuse diagnostic techniques is dMRI (diffusion magnetic resonance imaging) which extracts information about heterogeneity and asymmetries in brain tissue studying water diffusion dynamics (~80% mass constituent of tissues). The experimental limit of this technique is related to the acquisition time, TA, of the order of milliseconds. Water molecules diffuse within micrometre distance using TA as diffuse time (Eistein equation D~2<x2>TA). Cells have micrometric size and they consist in many organelles surrounded by water molecules essentially, therefore dMRI lose information concerning interaction between water molecules and extra/intra cellular material. Such limit, from physical point of view, means that dMRI gets out information on an average diffusion coefficient, losing information of local motions. Nevertheless, many works show that the diffusion properties of water molecules in brain tissue are not in agreement with classical free-like diffusion (Fick law). Although, several models have been proposed to describe such a discrepancy, an univocal physical interpretation of water dynamics in brain is still not achieved [4-13]. Aims of PhD project Neutron scattering technique gives access to space scale of the order of interatomic distances and dynamics in ps-ns time scale. It is particular sensitive to highly enriched H macromolecules, such as water. Thus, neutron scattering may offer a unique tool to overcome the dMRI experimental limit. Recently studies of quasi-elastic neutron scattering (QENS) on cerebral tissue of bovine and mice have shown that it is possible to distinguish two water pools in cerebral tissues: the first one having a behaviour similar to bulk water (called free-like water) with a diffusion coefficient similar to free water (Dw=2.3*10-5 cm2/s) and a second one showing a reduced diffusion coefficient probably due to interactions with intra and extra cellular material [14-15]. The project aims at addressing the following points: • Joint complementary QENS and dMRI investigation; • Proton dynamics of water at different degrees of confinement. Comparison of dMRI and QENS on phantoms; • Proton dynamics in glioma at different degrees of malignancy.