Applications of nuclear magnetic cross-relaxation spectroscopy to tissues.

Magnetic cross-relaxation in aqueous heterogeneous systems is a long established phenomenon that makes the observable decay constants for the system mixtures of more fundamental relaxation times which characterize the relaxation of the coupled components. By exploiting the magnetic relaxation coupling between the water spins and the immobilized spins in a tissue, the water-proton-signal intensity may be used to map indirectly a frequency response that is directly related to the 1H NMR spectrum of the immobilized components of the tissue. This method is applied to a number of rat tissues to determine whether there are significant differences among tissues that might be exploited in applications of this experiment to diagnostic magnetic imaging. Significant differences are found among nine rat tissues studied, which suggests that the experimental approach may be used to super-impose fundamentally new information, the dynamic character of the usually unobservable immobilized macromolecular components of the tissue, on a magnetic image.