Water self-diffusion measurements in excised rat lungs.

Water self diffusion in excised rat lungs has been measured using pulsed-field-gradient (PFG) techniques. The apparent diffusion coefficient, Dapp, was measured from a plot of the magnetization M vs ga2 to be 4.0 x 10(-6) cm2/s in the limit of small gamma delta ga, where gamma is the gyromagnetic ratio, delta is the duration of the applied gradient pulses, and ga is the applied gradient strength. Dapp is independent of the diffusion time, t, for values of t between 18 and 106 ms. For larger values of gamma delta ga, an additional smaller value of the slope of M vs ga2 was observed, indicating the existence of other, more slowly dephasing spins. Variation of t revealed that the relative magnetization associated with the more slowly dephasing spins decreases as t is increased. In addition, the relative magnetization of the slowly dephasing spins decreases as the temperature, T, of the excised rat lung is increased. Slow exchange from the compartment of the more rapidly to that of the more slowly dephasing spins may explain some of the observed dependence of the relative magnetizations on t and T. Measurements of water self diffusion in rat lung at various levels of water content indicate a correlation between T2 components and diffusion components. A new technique that combines the PFG with the Carr-Purcell-Meiboom-Gill technique is presented. The application of this technique to excised rat lung confirms the correlation between T2 and diffusion components.