title: Detectability of small and flat polyps in MDCT colonography using 2D and 3D imaging tools: results from a phantom study.
abstract: OBJECTIVE
  The objective of this phantom study was to determine the performance of MDCT colonography for the detection of small polyps under ideal imaging conditions and to determine the added value of 3D imaging when used as an adjunct to 2D imaging.
  
  
  METHODS
  Thirty-six polypoid and 39 flat polyps (44 lesions, 2-5 mm; 31 lesions, 6-8 mm) were placed in three explanted segments of a thoroughly cleaned porcine colon (overall length, 4.5 m) that was distended with air and submerged in a water phantom. MDCT data sets with 4 x 1 mm collimation and 6-mm table feed were reconstructed every 0.7 mm with 1.25-mm effective slice width. The data were reviewed by three radiologists using 2D images in all three projections and with 3D volume-rendered images available as an adjunct to the 2D images.
  
  
  RESULTS
  Additional 3D as a problem-solving tool significantly increased the overall sensitivity (96% vs 90%), decreased the total number of false-positive calls (n = 9 vs n = 5), and increased the diagnostic confidence level (p < 0.03) compared with 2D images alone. Small polyps less than or equal to 5 mm (89% vs 95%, p = 0.004) and flat polyps (82% vs 94%, p = 0.001) especially benefited from 3D. Sensitivity was generally higher for polypoid than for flat polyps (99% vs 94%, p = 0.041).
  
  
  CONCLUSIONS
  Under phantom conditions, simulating an ideal clinical setup, MDCT colonography is not limited by spatial resolution and detects polyps less than or equal to 5 mm in size with high sensitivity and specificity. Additional 3D image tools improve diagnostic accuracy and reviewer confidence, especially for the detection of flat and small polyps.
authors.affiliation: Department of Radiology, Medical University of Vienna, Waehringer Guertel 18-20, A-1090, Vienna, Austria. thomas.mang@akhwien.at
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Mang
authors.forename: Cornelia
authors.initials: C
authors.lastname: Schaefer-Prokop
authors.forename: Andrea
authors.initials: A
authors.lastname: Maier
authors.forename: Ewald
authors.initials: E
authors.lastname: Schober
authors.forename: Gerhard
authors.initials: G
authors.lastname: Lechner
authors.forename: Mathias
authors.initials: M
authors.lastname: Prokop
mesh_terms: D000818:Animals; D003111:Colonic Polyps / Q000000981:diagnostic imaging*; D023881:Colonography, Computed Tomographic; D005188:False Negative Reactions; D005189:False Positive Reactions; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D066298:In Vitro Techniques; D019047:Phantoms, Imaging; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric; D013552:Swine