Methylcellulose as a rectal contrast agent for MR imaging of rectal carcinoma.

Abstract

available; and easy to prepare, administer, and store safely. We also needed an endorectal contrast material that had high enough viscosity to ensure adequate distention of the bowel and had signal characteristics that would maximize the contrast between the bowel wall and the contrast agent itself on T1- and T2-weighted images. We considered the use of water as a rectal contrast agent, but no formal evaluation was performed. The images of three patients who had water instilled as a rectal contrast agent clearly showed insufficient distention attributable to the low viscosity of water. Methylcellulose is a compound familiar to radiologists because of its use for double-contrast barium studies of the small bowel. A search through MEDLINE [7] revealed the first report of its usage in MR imaging in 1992, albeit as an upper gastrointestinal contrast agent [8]. The compound we used was a pharmaceutical-grade sodium salt of carboxymethylcellulose (BDH Laboratory Supplies, Poole, England). The compound comes in the form of granules, so adjusting the viscosity of the solution for optimal distention was easily done. We conducted a preliminary study to determine the optimal volume and concentration of methylcellulose. Exact viscosity measurements were not performed. Instead, concentrations by weight and volume were titrated using the guidelines given by the methylcellulose manufacturer. We found that the normal concentrations of 0.5‐1.0% used in small-bowel enteroclysis provided inadequate viscosity. We decided that solutions of 2.5%, 5%, and 7.5% were most likely to be suitable for our purpose. Solutions over 7.5%, such as 10%, were found to be too viscous to be easily delivered via a syringe; solutions with higher concentrations also resulted in severe clumping and inadequate distention. Therefore, we did not evaluate them. The carboxymethylcellulose was mixed in a ster