TISSUE CHARACTERIZATION OF PNEUMONIA AND IRRADIATED RAT LUNGS WITH MAGNETIC-RESONANCE RELAXATION-TIMES

To interpret the MRI signal intensities, the T-1 and T-2 values were determined in vitro for rat lungs with radiation pneumonitis, fibrosis or pneumonia, and also for muscle and fat tissues. The transverse magnetization decays mentioned above exhibited two components, a T-2 fast (T-2f) and a T-2 slow (T-2s) component. Lungs from rats with pneumonia had significantly longer T-2f and T-2s, values than lungs from rats with radiation pneumonitis and fibrosis. The T-2f and T-2s values for a ''pneumonia lung'' were not significantly different from those of muscle. The measured values of T-2f and T-2s suggested that radiation pneumonitis and fibrosis likely exhibit lower signal intensities than do muscle and that a ''pneumonia lung'' likely exhibits a similar signal intensity to that of muscle on T-2-weighted MR images.