title: Polyp measurement with CT colonography: multiple-reader, multiple-workstation comparison.
abstract: OBJECTIVE
  The risk of invasive colorectal cancer in colorectal polyps correlates with lesion size. Our purpose was to define the most accurate methods for measuring polyp size at CT colonography (CTC) using three models of workstations and multiple observers.
  
  
  METHODS
  Six reviewers measured 24 unique polyps of known size (5, 7, 10, and 12 mm), shape (sessile, flat, and pedunculated), and location (straight or curved bowel segment) using CTC data sets obtained at two doses (5 mAs and 65 mAs) and a previously described colonic phantom model. Reviewers measured the largest diameter of polyps on three proprietary workstations. Each polyp was measured with lung and soft-tissue windows on axial, 2D multiplanar reconstruction (MPR), and 3D images.
  
  
  RESULTS
  There were significant differences among measurements obtained at various settings within each workstation (p < 0.0001). Measurements on 2D images were more accurate with lung window than with soft-tissue window settings (p < 0.0001). For the 65-mAs data set, the most accurate measurements were obtained in analysis of axial images with lung window, 2D MPR images with lung window, and 3D tissue cube images for Wizard, Advantage, and Vitrea workstations, respectively, without significant differences in accuracy among techniques (0.11 < p < 0.59). The mean absolute error values for these optimal settings were 0.48 mm, 0.61 mm, and 0.76 mm, respectively, for the three workstations. Within the ultralow-dose 5-mAs data set the best methods for Wizard, Advantage, and Vitrea were axial with lung window, 2D MPR with lung window, and 2D MPR with lung window, respectively. Use of nearly all measurement methods, except for the Vitrea 3D tissue cube and the Wizard 2D MPR with lung window, resulted in undermeasurement of the true size of the polyps.
  
  
  CONCLUSIONS
  Use of CTC computer workstations facilitates accurate polyp measurement. For routine CTC examinations, polyps should be measured with lung window settings on 2D axial or MPR images (Wizard and Advantage) or 3D images (Vitrea). When these optimal methods are used, these three commercial workstations do not differ significantly in acquisition of accurate polyp measurements at routine dose settings.
authors.affiliation: Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
authors.forename: Brett M
authors.initials: BM
authors.lastname: Young
authors.forename: J G
authors.initials: JG
authors.lastname: Fletcher
authors.forename: Scott R
authors.initials: SR
authors.lastname: Paulsen
authors.forename: Fargol
authors.initials: F
authors.lastname: Booya
authors.forename: C Daniel
authors.initials: CD
authors.lastname: Johnson
authors.forename: Kristina T
authors.initials: KT
authors.lastname: Johnson
authors.forename: Zackary
authors.initials: Z
authors.lastname: Melton
authors.forename: Drew
authors.initials: D
authors.lastname: Rodysill
authors.forename: Jay
authors.initials: J
authors.lastname: Mandrekar
mesh_terms: D000465:Algorithms; D003111:Colonic Polyps / Q000000981:diagnostic imaging*; D023881:Colonography, Computed Tomographic / Q000295:instrumentation / Q000379:methods*; D003626:Data Display; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation* / Q000379:methods; D008297:Male; D015588:Observer Variation; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement / Q000295:instrumentation* / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted