NMR spectroscopy of heterogeneous solid-liquid mixtures. Spin grouping and exchange analysis of proton spin relaxation in a tissue.

An attempt to resolve the complicated proton NMR signal of a heterogeneous material is presented. Lung tissue is used to illustrate the approach to this problem, which is based on resolving the total proton magnetization into components according to their relaxation times. This procedure is utilized at both low and high magnetic fields. These results are then correlated and analyzed for the effect of exchange between spin groups. For example, the total proton NMR signal of lung tissue is shown to arise from three interacting proton groups: protons on solid macromolecules, bound water protons, and bulk water protons. The dynamics of water is modeled to satisfy the dispersivity and the values of the relaxation parameters obtained considering the effect of exchange. It is proposed that this approach is generally applicable.