Dark Lumen Magnetic Resonance Colonography in a Rodent Polyp Model: Initial Experience and Demonstration of Feasibility

Purpose:We sought to assess dark lumen magnetic resonance (MR) colonography for the detection of colon polyps in a rodent model with histology as the gold standard. Material and Methods:Fourteen male Wistar rats were subjected to carcinogenic N-methyl-N′-nitro-N-nitrosoguanidine at the age of 4 months to induce colon neoplasms. MR imaging was performed after a time interval of 1 year. Preparation and data acquisition was performed with the animals under full anesthesia. After a body-warm saline enema images were acquired on a clinical 1.5-T whole-body MR system using a standard extremity coil. Plain and contrast-enhanced (0.3 mmol/kg; Gd-DOTA; Dotarem, Guerbet, France) 3-dimensional T1-weighted gradient recall echo images were acquired. Two radiologists analyzed the MR data sets in consensus for lesion depiction. Contrast uptake in colonic wall and polyps was quantitatively assessed by signal-to-noise ratio and contrast-to-noise ratio measurements and compared using a Wilcoxon–Mann–Whitney U test with statistical significance at a P value < 0.05. Finally, all animals were killed, and the MR imaging results were compared with pathologic findings. Sensitivity and specificity were calculated. Results:By pathology, a total of 15 polyps were found in 9 of 14 rats. MR colonography detected 13 of 15 polyps measuring between 4 and 11 mm (mean 7 ± 0.6 mm) in 8 of 9 animals, resulting in a sensitivity and specificity of 0.87 and 1.0, respectively. Compared with the precontrast data, all polyps showed a statistically significant increase in signal-to-noise ratio (78.2 ± 6.3 to 167.4 ± 17.7) and contrast-to-noise ratio (45.4 ± 5.2 to 124.6 ± 11.2). Conclusion:MR colonography with a dark colon lumen and a bright, contrast-enhanced colon wall appears well suited for the detection of colonic lesions in a rodent model.