Figure 6a. Retained barium mimicking active bleeding in a hemodynamically stable 77-year-old man who presented with bright red blood from the rectum. Transverse (a) and sagittal (b) CT angiograms show retained colonic barium from a prior examination (arrow). No contrast material jet is seen, and the barium is hyperattenuating relative to extravasated contrast material. Results from subsequent catheter angiography were also negative. Retained contrast material can mimic active bleeding or limit the CT angiographic evaluation of lower gastrointestinal bleeding.