Diagnosis of persistent intestinal ischemia in the rabbit using proton magnetic resonance imaging

Noninvasive diagnosis of persistent intestinal ischemia remains an elusive goal. Magnetic resonance imaging (MRI) recognizes changes in tissue water content, and several authors have demonstrated increased intensity within 6 hours of intestinal ischemia. To simulate the clinical situation more closely, we studied the efficacy of MRI in drfferentiating ischemic from viable segments of bowel 24 hours after injury in a rabbit model. A segment of distal ileum was rendered ischemic by vascular isolation and ligation. Controls underwent sham operation without vascular ligation. After 24 hours, multislice transverse scans were done using both T₁ and T₂ weighting. Image intensity was calculated from the isolated loop (absolute intensity), and paraspinal muscle intensity was used as an internal standard to calculate relative intensity (isolated bowel/paraspinal muscle). Animals were killed and bowel necrosis was confirmed histologically. Both absolute and relative intensity were significantly higher in animals undergoing persistent intestinal ischemia. This was true using both T₁ and T₂ weighting. In a further group of rabbits using the same model, intensity was calculated both before and after intravenous gadolinium. No significant difference was seen between sham and ischemic animals. Our data show that (1) MRI can differentiate ischemic from viable bowel 24 hours after ischemic injury, and (2) the use of intravenous contrast does not improve accuracy. We conclude that MRI may represent a useful noninvasive technique for the diagnosis of persistent intestinal ischemia and that clinical studies should be initiated.