title: Effect of slice thickness and primary 2D versus 3D virtual dissection on colorectal lesion detection at CT colonography in 452 asymptomatic adults.
abstract: OBJECTIVE
  The objective of our study was to compare the performance of primary 3D search using 360 degree virtual dissection with primary 2D search using a 2.5- versus a 1.25-mm slice thickness.
  
  
  METHODS
  Four hundred fifty-two asymptomatic patients underwent CT colonography (CTC) and colonoscopy. Examinations were reconstructed to 1.25- and 2.5-mm slice thicknesses and interpreted using primary 3D search (360 degree virtual dissection) and primary 2D search. Two of three experienced reviewers were randomly assigned to each case; 1,808 interpretations were performed.
  
  
  RESULTS
  There were 64 adenomas > or = 6 mm, 26 of which were large adenomas > or = 1 cm. For adenomas 6-9 mm in diameter, the area under the receiver operating characteristic curve (AUC) using 2.5-mm data sets was 0.66, 0.62, 0.90 and 0.78, 0.69, 0.67 for reviewers 1, 2, and 3, respectively, using primary 3D versus 2D search (p = not significant [NS]). For neoplasms > or = 10 mm, the AUC using 2.5-mm data sets was 0.74, 0.85, 0.89 and 0.66, 0.86, 0.92 for reviewers 1, 2, and 3 using primary 3D versus 2D search (p = NS). There was no significant difference using 1.25-mm collimation. Double review using both primary 3D and 2D search yielded sensitivities of 84% (16/19) and 95% (18/19) for large neoplasms (> or = 1 cm) using 2.5- and 1.25-mm data sets, respectively. Five of five (100%) adenocarcinomas were identified. The sensitivity of colonoscopy for large neoplasms was 77% (20/26) (20% [1/5] for adenocarcinoma).
  
  
  CONCLUSIONS
  No advantage exists for 1.25- or 2.5-mm slice thickness or for primary 3D versus 2D search at CTC. Double review using primary 3D (virtual dissection) and 2D search reduces interobserver variability and competes with colonoscopy for the detection of large lesions.
authors: Department of Radiology, Mayo Clinic, 200 First St., SW, Rochester, MN 55905, USA.
authors: C Daniel
authors: CD
authors: Johnson
authors: Joel G
authors: JG
authors: Fletcher
authors: Robert L
authors: RL
authors: MacCarty
authors: Jay N
authors: JN
authors: Mandrekar
authors: William S
authors: WS
authors: Harmsen
authors: Paul J
authors: PJ
authors: Limburg
authors: Lynn A
authors: LA
authors: Wilson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019412:Anatomy, Cross-Sectional / Q000379:methods*; D023881:Colonography, Computed Tomographic / Q000379:methods*; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011856:Radiographic Image Enhancement / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity