Oxygen-17 compounds as potential NMR T2 contrast agents: enrichment effects of H2(17)O on protein solutions and living tissues.

The isotopic enrichment of solutions, living tissues, and organisms with oxygen-17 in the form of H2(17)O shortens their proton NMR transverse relaxation times (T2) and produces changes in NMR image intensity. The transverse relaxation rate (1/T2) was found to be linearly dependent on the H2(17)O concentration in biological solutions up to 5% enrichment. The longitudinal relaxation time (T1) is not affected by enrichment. Equal concentrations of H2(17)O do not produce the same magnitude of T2 change in all physiological environments. The reasons for these differences are discussed. The results suggest that certain oxygen-17 compounds should be explored as "contrast agents" in magnetic resonance imaging.