MR Imaging-based Evaluation of Mesenteric Ischemia Caused by Strangulated Small Bowel Obstruction and Mesenteric Venous Occlusion: An Experimental Study Using Rabbits

Abstract

Purpose: This study assessed the MRI findings of strangulated small bowel obstruction (SBO) and mesenteric venous occlusion (MVO) in a rabbit model using 3T MRI. Materials and Methods:Twenty rabbits were included in this study. The strangulated SBO and MVO models were generated via surgical procedures in nine rabbits, and sham surgery was performed in two rabbits. The success of generating the models was confirmed via angiographic, macroscopic, and microscopic findings after the surgical procedure. MRI was performed before and 30 min after inducing mesenteric ischemia. T 1 -weighted images (T 1 WIs), T 2 -weighted images (T 2 WIs), and fat-suppressed T 2 WIs (FS-T 2 WIs) were obtained using the BLADE technique, and fat-suppressed T 1 WIs (FS-T 1 WIs) were obtained. The signal intensities of the affected bowel before and after the surgical procedures were visually categorized as high, iso, and low intense compared with the findings for the normal bowel wall on all sequences. Bowel wall thickness was measured, and the signal intensity ratio (SI ratio) was calculated using the signal intensities of the bowel wall and psoas muscle.Results: Angiographic, macroscopic, and microscopic findings confirmed that all surgical procedures were successful. The ischemic bowel wall was thicker than the normal bowel. The bowel wall was thicker in the MVO model (3.17 ± 0.55 mm) than in the strangulated SBO model (2.26 ± 0.46 mm). The signal intensity and SI ratio of the bowel wall were significantly higher after the procedure than before the procedure on all sequences in both models. The mesentery adjacent to the ischemic bowel loop exhibited a high signal intensity in all animals on FS-T 2 WIs. Conclusion:Non-contrast MRI can be used to evaluate mesenteric ischemia caused by strangulated SBO and MVO. FS-T 2 WIs represented the best modality for depicting the high signal intensity in the bowel wall and mesentery caused by ischemia.

MRI for the Detection of Small Bowel Ischemic Injury in Arterial Acute Mesenteric Ischemia: Preclinical Study in a Porcine Model

“…Previous preclinical studies found an increase in necrotic bowel wall signal intensity on T2-WI. [21][22][23] However, higher MRI field-strength (3.0 or 7.0 T) and smaller animals (rats, rabbits, cats) were used, thus making it difficult to extrapolate the results.…”

“…To remain consistent with the study by Bruhn et al, 24 we used the contrast between the ischemic and nonischemic bowels normalized to the spinal muscle. Such normalization has been used previously 23 and was necessary since pigs were moved to and from the operating room to assess bowel viability during the experiment, thus modifying the background noise and limiting signal reproducibility.…”

“…Although significant quantitative changes were observed on TSE T2‐WI and True‐FISP images, the ischemic bowel signals were lower than those of the nonischemic bowel with no pathophysiological explanation. Previous preclinical studies found an increase in necrotic bowel wall signal intensity on T2‐WI 21–23 . However, higher MRI field‐strength (3.0 or 7.0 T) and smaller animals (rats, rabbits, cats) were used, thus making it difficult to extrapolate the results.…”

“…Several studies have found increased signal intensity of the bowel wall on T2‐weighted imaging (T2‐WI) following occlusion of the superior or inferior mesenteric artery in the rat or cat model 20–22 . Similar changes have been reported in rabbits with induced mesenteric venous occlusion 23 . In a larger animal model, Bruhn et al 24 assessed early ischemic changes in a porcine model with percutaneous embolization of the superior mesenteric artery (SMA).…”

“…[20][21][22] Similar changes have been reported in rabbits with induced mesenteric venous occlusion. 23 In a larger animal model, Bruhn et al 24 assessed early ischemic changes in a porcine model with percutaneous embolization of the superior mesenteric artery (SMA). Increased bowel wall intensity was noted on DWI sequences as early as 30 minutes and maintained up to 90 minutes after SMA occlusion.…”