Purpose: To assess dark lumen MR colonography (MRC), a technique based on a rectal enema with water in combination with the intravenous injection of Gd-DOTA for the detection of polyps in a rodent model.

Methods and Materials: 14 male Wistar rats were subjected to carcinogenic N-methyl-N-nitro-N-nitrosoguanidine (MNNG) at the age of 4 months in order 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. Following a body-warm saline enema MR imaging was performed on a clinical 1.5-T whole-body MR system using a standard extremity coil. Plain and contrast-enhanced (0.1 mmol/kg; Gd-DOTA; Dotarem, Guerbet, France) 3D T1-w GRE (VIBE) images were acquired. Two radiologists analysed the MR data sets in consensus for lesion depiction. Contrast uptake in colonic wall and polyps was quantitatively assessed by signal-to-noise (SNR), and contrast-to-noise ratio (CNR) measurements. Finally, all animals were euthanized and the imaging results were compared with histology.

Results: By histology, a total of 15 polyps were found in 9 of 14 rats. MRC detected 8/9 polyps resulting in a sensitivity/specifity of 0.89/1.0. Compared to the pre-contrast data, all polyps showed a statistically significant increase in SNR (78.2 ± 6.3 to 167.4 ± 17.7) and CNR (45.4 ± 5.2 to 124.6 ± 11.2), respectively.

Conclusion: Contrast-enhanced MRC based on a dark colonic lumen and a bright, contrast-enhanced colonic wall appears well suited for the detection of colonic polyps. Marked contrast uptake in polyps facilitates their detection. (P.R., J.B., C.L., X.V., C.C. are employees of Guerbet.)