MR evaluation of pulmonary interstitial and intravascular fluids

Serial dilutions of sheep plasma and red blood cells were made yielding blood samples of various hematocrits (Hcts). These samples were studied at bore temperature (34 degrees C) in a 0.25 T pulsed NMR analyzer for differences in T1 and T2. An inverse relationship between Hct and T1 was demonstrated (P less than .001); no change was detected in T2 with Hcts from 0% to 88%. Plasma and lung lymph samples were also obtained from chronically instrumented, unanesthetized sheep to determine the effects on T1 and T2 of increasing hydrostatic pressure and altering capillary permeability in the lungs. Normal baseline lung lymph T1 was longer than the concurrent plasma T1. T1 of lung lymph was inversely proportional to the lymph/plasma protein ratio. Edema induced by elevation of hydrostatic pressure lengthens T1, whereas increased capillary permeability shortens T1. T2s were unchanged in plasma and lymph in the baseline state with hydrostatic edema, and with increased capillary permeability.