English: CT colonography of a rectal mass. Left image is a volume rendering and right image is a thin slice. It also shows the rectal tube used for insufflation of gas to distend the colon.

Original caption: Differentiation from stool and colonic neoplasia by dual-energy CT. Male, 88 years of age. (A,B) denote colonography and CT axial plane image revealed irregular upheaval masses in the posterior wall of the rectum (white arrow). It is difficult to differentiate tumors from stool.

Dual-energy contrast-enhanced CT (axial plane) revealed no enhancement of masses, iodine value = −1.4 mg/ml (white arrow), suggesting no blood supply to the masses, which was validated as stool by colonography.