MR colonography: how does air compare to water for colonic distention?

To prove the feasibility of air-distended magnetic resonance colonography (MRC) and compare it with water-based distention.

In five volunteers, the colon was imaged twice: once after distending the colon with air and a second time after distending the colon with water. A total of 50 patients, who had been referred to colonoscopy for a suspected colorectal pathology were randomized into water-distention (N = 25) and air-distention (N = 25) groups. A contrast-enhanced T1-weighted three-dimensional volume interpolated breath-hold (VIBE) sequence was collected. Comparative analysis was based on qualitative ratings of image quality and bowel distention, as well as contrast-to-noise ratio (CNR) measurements for the colonic wall with respect to the colonic lumen. In addition, patient acceptance was evaluated.

Inflammatory changes and colorectal masses were correctly identified on MRC in eight patients each. One 4-mm polyp identified at colonoscopy was missed on water-distended MRC. There were no false positive findings. No significant differences were found between air- and water-distention regarding discomfort levels and image quality. The presence of air in the colonic lumen was not associated with susceptibility artifacts. CNR of the contrast-enhanced colonic wall, as well as bowel distention, were superior on air-distended three-dimensional data sets.

MRC can be performed using either water or air for colonic distention. Both techniques permit assessment of the colonic wall and identification of colorectal masses. While discomfort levels are similar for both agents, MRC with air provides higher CNR and better colonic distention.