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,D_app, was measured from a plot of the magnetizationMvsg²_ato be 4.0 × 10⁻⁶cm²/s in the limit of small γδg_a, where γ is the gyromagnetic ratio, δ is the duration of the applied gradient pulses, andg_ais the applied gradient strength.D_appis independent of the diffusion time,t, for values oftbetween 18 and 106 ms. For larger values of γδg_a, an additional smaller value of the slope ofMvsg²_awas observed, indicating the existence of other, more slowly dephasing spins. Variation oftrevealed that the relative magnetization associated with the more slowly dephasing spins decreases astis 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 ontandT. Measurements of water self diffusion in rat lung at various levels of water content indicate a correlation betweenT₂components 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 betweenT₂and diffusion components.