Figure 1f: Error classification. (a) Observer error: 7-mm adenoma missed at CT colonography in original study. Left: Prone transverse soft-tissue image shows polyp (arrow). Right: 3D endoluminal view of polyp. (b) Observer measurement error: In original study, polyp (arrow) was measured as 7 mm at CT colonography and 15 mm at colonoscopy. Consensus retrospective CT colonographic measurement was 9.5 mm. Left: Supine transverse soft-tissue image. Right: Endoluminal view. (c) Artifact error: Severe respiratory motion caused by breathing during both supine sagittal (left) and prone transverse (right) acquisitions prevents polyp identification. Error classification. (d) Distention error: Arrows highlight limited distention that prevents polyp identification in supine (right) and prone (left) transverse views. (e) Excessive fluid error: 15-mm polyp found at colonoscopy was not visible in cecum at CT colonography owing to excess fluid (arrows) in colon. Left: Supine transverse view. Right: Prone transverse view. (f) Excessive stool error: 100-mm polyp in cecum is indistinguishable from large clumps of stool which appear throughout the colon. Arrow pointing up = stomach, arrow pointing right = small bowel; all other arrows = clumps of stool. Left: Supine coronal view (very small arrow in upper left corner is computer cursor). Right: Supine transverse view.