A 1-year time course study of the relaxation times and histology for irradiated rat lungs.

To investigate the NMR relaxation times for irradiated rat lung tissue, we measured T1 and T2 at 11 different times during the injury's 1-year time course. A biexponential analysis of T2 was used to determine T2 fast (T2f) and T2 slow (T2s). In addition, we measured water content and correlated changes in the relaxation times with pathological changes. The correlation indicates the following: (1) Shortly after irradiation, the biexponential T2 decay for 1/3 of the samples became monoexponential and there were no noticeable pathological changes observed using light microscopy. (2) During radiation pneumonitis, T2f and T2s were prolonged. This accompanied acute edematous changes and inflammatory cell infiltration. (3) Finally, during radiation fibrosis T1 shortened and collagen increased. We observed no significant correlation between relaxation time changes and water content changes throughout the 1-year time course.