Diagnosis of Intestinal Ischemia in the Rat Using Magnetic Resonance Imaging

Abstract

Noninvasive diagnosis of persistent ischemia after intestinal revascularization has remained an elusive goal. Because magnetic resonance imaging (MRI) can detect changes in tissue water, we studied its efficacy in differentiating ischemic from perfused intestine in an animal model.

Six-week-old rats were subjected to (1) 30-min superior mesenteric artery (SMA) occlusion and reperfusion, (2) permanent SMA ligation, or (3) sham operation, and were then imaged for 90 min using a small-animal MRI scanner with T₁ weighting (T_R= 1000 msec, T_E= 25 msec). In an additional group of rats, the experiment was repeated using a new contrast technique consisting of oral ferrite to decrease luminal signal and intravenous gadolinium to increase bowel wall signal. Mean abdominal intensity over the scanning period was calculated for each animal (n= 5 rats per experimental group).

Definition of individual bowel loops was subjectively improved in animals scanned with intravenous and oral contrast. Mean abdominal intensity was significantly lower in ligated vs sham rats (43.90 ± 8 vs 59.63 ± 6 and 46.19 ± 6 vs 54.26 ± 6, with and without contrast, respectively). There was no significant difference in intensity between reperfused and sham animals.

MRI differentiated persistently ischemic bowel from viable bowel in this model, both with and without the use of contrast. These data suggest that MRI may have a potential role in the noninvasive diagnosis of persistent intestinal ischemia.

Key Words:

• contrast agents
• ferrite
• gadolinium-DTPA
• intestinal ischemia
• ischemia-reperfusion injury
• nuclear magnetic resonance