title: Computer assisted detection software for CT colonography: effect of sphericity filter on performance characteristics for patients with and without fecal tagging.
abstract: The aim of this study is to investigate the effect of changing sphericity filter values on performance of a computer assisted detection (CAD) system for CT colonography for data with and without fecal tagging. Colonography data from 138 patients with 317 validated polyps were divided into those with (86) and without (52) fecal tagging. Polyp coordinates were established by three observers and datasets analysed subsequently by a proprietary CAD system used at four discrete sphericity filter settings. Prompts were compared with the known coordinates in order to determine sensitivity and specificity. Sensitivity was highest at low sphericity; of 164 polyps 6 mm or more, 144 (87.8%) were detected at sphericity 0.3, and 132 (80.1%) at sphericity 0.9. Of 42 polyps measuring 10 mm or more, 40 (95.2%) were detected at sphericity 0.3, and 36 (85.7%) at sphericity 0.9. There was no significant difference in sensitivity for tagged and un-tagged data but specificity was reduced in tagged data at low sphericity and significantly reduced in untagged data at high sphericity. CAD had a sensitivity of 95.2% for polyps measuring 1 cm or more and 87.8% for polyps 6 mm or more when used at a sphericity setting of 0.3. Higher sphericity settings increased specificity while reducing sensitivity. The bowel preparation used significantly impacts on specificity.
authors.affiliation: Medicsight PLC, Berkeley Sq, London, UK.
authors.forename: Jamshid
authors.initials: J
authors.lastname: Dehmeshki
authors.forename: Steve
authors.initials: S
authors.lastname: Halligan
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Taylor
authors.forename: Mary E
authors.initials: ME
authors.lastname: Roddie
authors.forename: Justine
authors.initials: J
authors.lastname: McQuillan
authors.forename: Lesley
authors.initials: L
authors.lastname: Honeyfield
authors.forename: Hamdan
authors.initials: H
authors.lastname: Amin
mesh_terms: D001466:Barium Sulfate; D003111:Colonic Polyps / Q000000981:diagnostic imaging* / Q000473:pathology; D023881:Colonography, Computed Tomographic; D003287:Contrast Media; D003974:Diatrizoate Meglumine; D005243:Feces; D006801:Humans; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D012680:Sensitivity and Specificity
chemical_list: D003287:Contrast Media; D001466:Barium Sulfate; D003974:Diatrizoate Meglumine