Acute and repair stage characteristics of magnetic resonance relaxation times in oxygen-induced pulmonary edema.

Proton magnetic relaxation times, T1 and T2, were determined for rat lungs exposed to 80% oxygen for a duration of 2 weeks. The transverse magnetization decay curve of the lung tissue was multiexponential. A linear combination of two decay curves with different T2 values fits the multiexponential decay suggesting that there are at least two different components of tissue water in the lung. Remarkable prolongation of T1 and T2 was demonstrated as lung injuries progressed in the acute stage of pulmonary edema. Both 1/T1 and 1/T2 were significantly correlated with 1/water content of the lung tissue. In the repair stage, T1 and T2 were significantly shortened. Shortening coincided with the spontaneous resolution of pulmonary edema. Relaxation rates showed no significant correlation with 1/water content in this stage. These results indicate that the physical state of water in the tissue is affected not only by the water content but also by the derangement of macromolecules in pulmonary edema. T2 was more sensitive than T1 for detecting pulmonary damage.