WATER SELF-DIFFUSION MEASUREMENTS IN EXCISED RAT LUNGS

Water self diffusion in excised rat lungs has been measured using puls ed-held-gradient (PFG) techniques. The apparent diffusion coefficient, D-app, was measured from a plot of the magnetization M vs g(a)(2) to be 4.0 x 10(-6) cm(2)/s in the limit of small gamma delta g(a), where gamma is the gyromagnetic ratio, delta is the duration of the applied gradient pulses, and g(a) is the applied gradient strength. D-app is i ndependent of the diffusion time, t, for values of t between 18 and 10 6 ms. For larger values of gamma delta g(a), an additional smaller val ue of the slope of M vs g(a)(2) was observed, indicating the existence of other, more slowly dephasing spins. Variation of t revealed that t he relative magnetization associated with the more slowly dephasing sp ins decreases as t is increased. In addition, the relative magnetizati on of the slowly dephasing spins decreases as the temperature, T, of t he excised rat lung is increased. Slow exchange from the compartment o f the more rapidly to that of the more slowly dephasing spins may expl ain some of the observed dependence of the relative magnetizations on t and T, Measurements of water self diffusion in rat lung at various l evels of water content indicate a correlation between T-2 components a nd diffusion components. A new technique that combines the PFG with th e Carr-Purcell-Meiboom-Gill technique is presented. The application of this technique to excised rat lung confirms the correlation between T -2 and diffusion components. (C) 1996 Academic Press, Inc.