title: Development of a cathartic-free colorectal cancer screening test using virtual colonoscopy: a feasibility study.
abstract: OBJECTIVE
  The purpose of our study was to develop a method to subtract barium-labeled stool from the colon using a phantom and to evaluate the performance of the technique in a pilot human population.
  
  
  METHODS
  A phantom containing 6-mm flat polyps and three types of simulated stool (homogeneous, moderately heterogeneous, and severely heterogeneous) mixed with barium was created, scanned, and tested using three stool subtraction algorithms but no cathartic. Thirty patients with suspected colorectal polyps were studied using stool tagging to determine which was the most effective stool subtraction algorithm. Colonoscopy was the reference standard. Examinations were evaluated blindly using the unsubtracted and 6 weeks later both the unsubtracted and subtracted data sets.
  
  
  RESULTS
  A threshold of 200 H and expansion and convolution techniques were the most effective tools for subtracting stool and minimizing artifacts. When applied to the human population, sensitivities using the unsubtracted data sets were 90% (18/20) and 68% (26/38) for polyps > or = 1 cm and > or = 5 mm, respectively. Specificities were 100% (4/4) and 75% (3/4) for polyps > or = 1 cm and > or = 5 mm. For the stool-subtracted data sets, sensitivities were 90% (18/20) and 71% (27/38) for polyps > or = 1 cm and > or = 5 mm. Per patient sensitivities were 88% (15/17) and 77% (20/26) for > or = 1 cm and > or = 5 mm polyps. Specificities were 100% (4/4) for large polyps and 25% (1/4) for smaller polyps.
  
  
  CONCLUSIONS
  Image processing tools combining thresholding, expansion, and convolution were the most useful for stool subtraction. Laxative-free colon examinations using barium for stool labeling can be performed at CT colonography with or without stool subtraction with high accuracy. Further study is warranted.
authors.affiliation: Department of Radiology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA.
authors.forename: Kristina T
authors.initials: KT
authors.lastname: Johnson
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Carston
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Wentz
authors.forename: Armando
authors.initials: A
authors.lastname: Manduca
authors.forename: Steven M
authors.initials: SM
authors.lastname: Anderson
authors.forename: C Daniel
authors.initials: CD
authors.lastname: Johnson
mesh_terms: D000465:Algorithms; D001466:Barium Sulfate; D002399:Catharsis; D023881:Colonography, Computed Tomographic / Q000295:instrumentation / Q000379:methods*; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging*; D003287:Contrast Media; D004733:Enema; D005240:Feasibility Studies; D005243:Feces; D005260:Female; D006801:Humans; D008297:Male; D008403:Mass Screening / Q000379:methods; D008875:Middle Aged; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique
chemical_list: D003287:Contrast Media; D001466:Barium Sulfate