title: CT colonography: external clinical validation of an algorithm for computer-assisted prone and supine registration.
abstract: OBJECTIVE
  To perform external validation of a computer-assisted registration algorithm for prone and supine computed tomographic (CT) colonography and to compare the results with those of an existing centerline method.
  
  
  METHODS
  All contributing centers had institutional review board approval; participants provided informed consent. A validation sample of CT colonographic examinations of 51 patients with 68 polyps (6-55 mm) was selected from a publicly available, HIPAA compliant, anonymized archive. No patients were excluded because of poor preparation or inadequate distension. Corresponding prone and supine polyp coordinates were recorded, and endoluminal surfaces were registered automatically by using a computer algorithm. Two observers independently scored three-dimensional endoluminal polyp registration success. Results were compared with those obtained by using the normalized distance along the colonic centerline (NDACC) method. Pairwise Wilcoxon signed rank tests were used to compare gross registration error and McNemar tests were used to compare polyp conspicuity.
  
  
  RESULTS
  Registration was possible in all 51 patients, and 136 paired polyp coordinates were generated (68 polyps) to test the algorithm. Overall mean three-dimensional polyp registration error (mean ± standard deviation, 19.9 mm ± 20.4) was significantly less than that for the NDACC method (mean, 27.4 mm ± 15.1; P = .001). Accuracy was unaffected by colonic segment (P = .76) or luminal collapse (P = .066). During endoluminal review by two observers (272 matching tasks, 68 polyps, prone to supine and supine to prone coordinates), 223 (82%) polyp matches were visible (120° field of view) compared with just 129 (47%) when the NDACC method was used (P < .001). By using multiplanar visualization, 48 (70%) polyps were visible after scrolling ± 15 mm in any multiplanar axis compared with 16 (24%) for NDACC (P < .001).
  
  
  CONCLUSIONS
  Computer-assisted registration is more accurate than the NDACC method for mapping the endoluminal surface and matching the location of polyps in corresponding prone and supine CT colonographic acquisitions.
authors.affiliation: Centre for Medical Imaging and Centre for Medical Image Computing, University College London, Podium Level 2, University College Hospital, 235 Euston Rd, London NW1 2BU, England.
authors.forename: Darren J
authors.initials: DJ
authors.lastname: Boone
authors.forename: Steve
authors.initials: S
authors.lastname: Halligan
authors.forename: Holger R
authors.initials: HR
authors.lastname: Roth
authors.forename: Tom E
authors.initials: TE
authors.lastname: Hampshire
authors.forename: Emma
authors.initials: E
authors.lastname: Helbren
authors.forename: Greg G
authors.initials: GG
authors.lastname: Slabaugh
authors.forename: Justine
authors.initials: J
authors.lastname: McQuillan
authors.forename: Jamie R
authors.initials: JR
authors.lastname: McClelland
authors.forename: Mingxing
authors.initials: M
authors.lastname: Hu
authors.forename: Shonit
authors.initials: S
authors.lastname: Punwani
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Taylor
authors.forename: David J
authors.initials: DJ
authors.lastname: Hawkes
mesh_terms: D000465:Algorithms; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging; D003111:Colonic Polyps / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D023881:Colonography, Computed Tomographic / Q000706:statistics & numerical data*; D006801:Humans; D056888:Patient Positioning / Q000706:statistics & numerical data*; D015995:Prevalence; D016684:Prone Position; D011856:Radiographic Image Enhancement / Q000379:methods*; D013382:Subtraction Technique / Q000706:statistics & numerical data*; D016683:Supine Position; D014481:United States / Q000453:epidemiology