title: Urinary bladder segmentation in CT urography (CTU) using CLASS.
abstract: OBJECTIVE
  The authors are developing a computerized system for bladder segmentation on CTU, as a critical component for computer aided diagnosis of bladder cancer.
  
  
  METHODS
  A challenge for bladder segmentation is the presence of regions without contrast (NC) and filled with intravenous contrast (C). The authors have designed a Conjoint Level set Analysis and Segmentation System (CLASS) specifically for this application. CLASS performs a series of image processing tasks: preprocessing, initial segmentation, 3D and 2D level set segmentation, and postprocessing, designed according to the characteristics of the bladder in CTU. The NC and the C regions of the bladder were segmented separately in CLASS. The final contour is obtained in the postprocessing stage by the union of the NC and C contours. With Institutional Review Board (IRB) approval, the authors retrospectively collected 81 CTU scans, in which 40 bladders contained lesions, 26 contained diffuse wall thickening, and 15 were considered to be normal. The bladders were segmented by CLASS and the performance was assessed by rating the quality of the contours on a 10-point scale (1 = "very poor," 5 = "fair," 10 = "perfect"). For 30 bladders, 3D hand-segmented contours were obtained and the segmentation accuracy of CLASS was evaluated and compared to that of a single level set method in terms of the average minimum distance, average volume intersection ratio, average volume error and Jaccard index.
  
  
  RESULTS
  Of the 81 bladders, the average quality rating for CLASS was 6.5 ± 1.3. Thirty nine bladders were given quality ratings of 7 or above. Only five bladders had ratings under 5. The average minimum distance, average volume intersection ratio, average volume error, and average Jaccard index for CLASS were 3.5 ± 1.3 mm, (79.0 ± 8.2)%, (16.1 ± 16.3)%, and (75.7 ± 8.4)%, respectively, and for the single level set method were 5.2 ± 2.6 mm, (78.8 ± 16.3)%, (8.3 ± 33.1)%, (71.0 ± 15.4)%, respectively.
  
  
  CONCLUSIONS
  The results demonstrate the potential of CLASS for segmentation of the bladder.
authors: Department of Radiology, the University of Michigan, Ann Arbor, Michigan 48109-0904.
authors: Lubomir
authors: L
authors: Hadjiiski
authors: Heang-Ping
authors: HP
authors: Chan
authors: Richard H
authors: RH
authors: Cohan
authors: Elaine M
authors: EM
authors: Caoili
authors: Yuen
authors: Y
authors: Law
authors: Kenny
authors: K
authors: Cha
authors: Chuan
authors: C
authors: Zhou
authors: Jun
authors: J
authors: Wei
mesh_terms: D000465:Algorithms; D006801:Humans; D021621:Imaging, Three-Dimensional; D010363:Pattern Recognition, Automated; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D012015:Reference Standards; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012984:Software; D014057:Tomography, X-Ray Computed; D001743:Urinary Bladder / Q000000981:diagnostic imaging* / Q000473:pathology; D014567:Urography / Q000379:methods*