Relative colon wall attenuation - distinguishing ischemia from other colon wall changes.

BACKGROUND: Differentiation of bowel wall changes between ischemia and other causes in CT imaging can prove challenging, particularly in colon wall. Therefore, measurement of relative colon wall attenuation and contrast uptake were evaluated for aiding in diagnosis of colon ischemia. METHODS: CTs with inquiry for bowel ischemia were retrospectively identified. Cases involving colon ischemia or colon wall changes of other etiologies were included. Three regions of interest (ROIs) were placed in representative areas of colon wall with and without evident changes, in arterial and venous phase images, respectively. Means of the ROIs were used to calculate the relative bowel enhancement between affected and unaffected wall in each contrast phase, as well as the contrast uptake of the wall between phases. Relative enhancement and contrast uptake were compared between patients with and without ischemia. A subset of cases was reanalyzed for intra- and inter-reader comparison. RESULTS: 31 patients with and 56 patients without ischemia were included. Relative enhancement of affected to unaffected colon wall was  -51.2% in arterial phase and  -44.6% in venous phase images for patients with ischemia. Relative enhancement was significantly higher in patients without ischemia at -0.5% in both phases (p < 0.001). There was no significant difference in contrast uptake of affected bowel (40.6% vs. 39.8% respectively, p = 0.67). ROC curves revealed a maximum Youden-Index at a cut-off of -37.4% (AUC: 0.818) in arterial phase to differentiate between groups. Intra-reader comparison showed a good, and inter-reader a moderate, correlation in a subset. CONCLUSIONS: Objective measurement of relative colon wall attenuation between affected and unaffected areas can be an additional imaging feature to aid in identifying ischemic colon.