title: Effects of exposure parameters and slice thickness on detecting clear and unclear mandibular canals using cone beam CT.
abstract: OBJECTIVE
  The purpose of this study was to clarify the effects of exposure parameters and image-processing methods when using CBCT to detect clear and unclear mandibular canals (MCs).
  
  
  METHODS
  24 dry half mandibles were divided into 2 groups with clear and unclear MCs based on a previous CBCT study. Mandibles were scanned using a CBCT system with varying exposure parameters (tube voltages 60 kV, 70 kV and 90 kV; and tube currents 2 mA, 5 mA, 10 mA and 15 mA) to obtain a total of 144 scans. The images were processed with different slice thicknesses using ImageJ software (National Institutes of Health, Bethesda, MD). Five radiologists evaluated the cross-sectional images of the first molar region to detect the MCs. The diagnostic accuracy of varying exposure parameters and image-processing conditions was compared with the area under the curve (Az) in receiver-operating characteristic analysis.
  
  
  RESULTS
  The Az values for clear MCs were higher than those for unclear MCs (p < 0.0001). With increasing exposure voltages and currents, Az values increased, but no significant differences were found with high voltages and currents in clear MCs (p = 1.0000 and p = 0.9340). The Az values of serial images were higher than those of overlaid images (p < 0.0001), and those for thicker slices were higher than those for thinner slices (p < 0.0001).
  
  
  CONCLUSIONS
  Our findings indicate that detection of unclear MCs requires either higher exposure parameters or processing of the images with thicker slices. To detect clear MCs, lower exposure parameters can be used.
authors.affiliation: 1 Oral Radiology Division, University of the Republic, Montevideo, Uruguay.
authors.forename: Gainer R
authors.initials: GR
authors.lastname: Jasa
authors.affiliation: 2 Department of Oral and Maxillofacial Radiology, Kyushu University Hospital, Fukuoka, Japan.
authors.forename: Mayumi
authors.initials: M
authors.lastname: Shimizu
authors.affiliation: 3 Department of Oral and Maxillofacial Radiology, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Okamura
authors.affiliation: 4 Department of Radiological Technology, Faculty of Fukuoka Medical Technology, Teikyo University, Fukuoka, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Tokumori
authors.affiliation: 2 Department of Oral and Maxillofacial Radiology, Kyushu University Hospital, Fukuoka, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Takeshita
authors.affiliation: 3 Department of Oral and Maxillofacial Radiology, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
authors.forename: Warangkana
authors.initials: W
authors.lastname: Weerawanich
authors.affiliation: 3 Department of Oral and Maxillofacial Radiology, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Yoshiura
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D066298:In Vitro Techniques; D008334:Mandible / Q000000981:diagnostic imaging*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D014583:Uruguay
keywords: CBCT; computer-assisted image processing; image quality; mandible