Anisotropy of transverse spin relaxation in H₂O-D₂O liquid entrapped in Nanocavities: application to studies of connective tissues

The spin-spin relaxation in connective tissues is simulated using a model in which the tissue is represented by a set of nanocavities containing H₂O-D₂O liquid. Collagen fibrils in connective tissues form ordered hierarchical long structures of hydrated nano-cavities with characteristic diameter from 1 nm to several tens of nanometers and length of about 100 nm. We consider influence of the restricted Brownian motion of molecules inside a nano-cavity on spin-spin relaxation. The analytical expression for the transverse time T₂ for H₂O-D₂O the liquid in contained a nanocavity was obtained. We show that the angular dependence of the transverse relaxation rate does not depend on the concentration of D₂O. The theoretical results could explain the experimentally observed dependence of the degree of deuteration on the relaxation time T₂. Accounting the orientation distribution of the nanocavities well agreement with the experimental dependence of the relaxation for articular cartilage on the deuteration degree was obtained.