Figure 4b. Respiratory artifact in the lower abdomen in a 71-year-old asymptomatic man. (a) Three-dimensional endoluminal CT image shows abrupt wall defects or polypoid structures (arrows) on opposite luminal walls of the colon. (b) Supine coronal CT scan shows linear artifacts of the colonic wall (straight arrows) and wavelike irregularities of the outer abdominal wall (wavy arrow) caused by respiratory motion.