Nuclear magnetic resonance Hahn spin-echo decay (T2) in live rats with endotoxin lung injury

To determine the possibility of using nuclear magnetic resonance imaging to study experimentally induced lung injury, we measured in the lungs of spontaneously breathing living rats the time course of both the Hahn spin-echo decay (T2) and the proton density after endotoxin injury. In order to minimize artifacts arising from motions of the nearby chest wall and heart, we used a motion-insensitive technique (the interleaved line scan). A typical Hahn T2 measurement was obtained over a region of interest from a series of images each with a different echo time, which ranged from 16 to 110 ms. Lung water content was determined by integrating the proton density over the region of interest. The Hahn T2 and proton density were measured before and at 1, 3, 6, and 9 h after intravenous injection of endotoxin. The effects of the treatment administered before and after endotoxin injection were also evaluated. Endotoxin treatment caused lengthening of both fast (T2f) and slow (T2s) Hahn T2 components but had no significant effect on the proton density, consistent with the notion that endotoxin causes lung injury without significant lung water accumulation in rats. However, the methylprednisolone treatment prevented the lengthening of T2s but did not seem to have a significant effect on T2f. Our results suggest that NMR imaging can be used to detect and monitor experimental lung injury in intact living animals, even in the absence of variations of lung water content.