Nuclear magnetic resonance as a noninvasive method of diagnosing intestinal ischemia: Technique and preliminary results

Despite the long-standing effort to identify a noninvasive method of diagnosing intestinal ischemia, no reliable biochemical or radiographic technique has evolved. We explored the use of phosphorus nuclear magnetic resonance (PNMR) as a method of detecting surgically induced intestinal ischemia. Using Lewis strain rats (250 to 300 g), small intestine ischemia was produced by ligation in succession from the ligament of Treitz to the ileocecal valve 1 of 2 (group I), 2 of 3 (group II), 3 of 4 (group III), and 4 of 5 (group IV) mesenteric terminal vessels. A sham-operated group was used as a control. Following the surgical procedure, the abdomen was closed and the rat positioned under the PNMR apparatus. Using phosphorus spectroscopy, data were analyzed using a computer program and plotted on a graph indicating relative peaks for the phosphate-based compounds. As a means of comparing groups, we devised an inorganic phosphate to phosphocreatine ratio (“ischemia index”), a qualitative measurement indicating trends used to evaluate ischemia. At the completion of the PNMR study, the abdomen was reopened and proximal, mid, and distal small intestine segments were harvested for histological evaluation using a previously established grading system for intestinal ischemia. Preoperatively, immediately postoperatively, and approximately 2 hours postoperatively, blood samples were obtained for hexosaminidase levels. With increasing vascular ligation, there was an upward trend in both the histological appearance of ischemia and the PNMR ischemia index indicative of increasing tissue ischemia. A similar trend was identified when the histological ischemia grade was directly correlated with the PNMR ischemia index. Hexosaminidase levels did not correlate with ischemia in this study. This study describes a new application of PNMR and demonstrates its potential feasibility as a noninvasive method of evaluating intestinal ischemia in vivo.