Figure 14b. Rectal catheters. (a) Endoluminal CT image shows a large-caliber plastic catheter (diameter, 16 mm) (arrow). (b) Endoluminal CT image shows a small-caliber rubber catheter (diameter, 5 mm) (arrow). Both catheters allow good colonic distention, with less discomfort for the patient when the thin catheter is used.