title: Accuracy and reliability of cone-beam computed tomography measurements: Influence of head orientation.
abstract: BACKGROUND
  The purpose of this research is to determine the accuracy and reliability of measurements obtained from 3-dimensional (3D) cone-beam computed tomography (CBCT) for different head orientations.
  
  
  METHODS
  Stainless steel wires were fixed to a dry skull at different places. The skull was scanned by using CBCT in the centered and 5 other positions. Intraobserver and interobserver reliability tests were performed by using 6 landmarks identified on the virtual 3D skulls by 2 operators. Two methods were used to determine the accuracy of measurements on the virtual 3D skull scanned in different positions. In the first method, 12 linear distances were compared on the physical skull and the 3D virtual skull in the centered and the other scanning positions. In the second method, registration of each of the 5 positions on the centered position was done separately, and coordinates of 11 landmarks were identified in each position and compared with the centered position. Data gathered from the 2 methods were compared statistically.
  
  
  RESULTS
  Concordance correlation and Pearson correlation coefficients values were almost 0.9999 in all the comparisons denoting: (1) high intraobserver and interobserver reliability; (2) very high concordance between the physical skull and the CBCT centered-position measurements; (3) very high concordance between measurements of the centered position in relation to those obtained from the different skull positions; and (4) registration of the skulls in the different positions showed high concordance, with the highest values between the centered and off-centered positions, and the lowest with the complex position.
  
  
  CONCLUSIONS
  Accuracy and reliability of CBCT measurements are not affected by changing the skull orientation. Thus, the upper-lip and chin rests should not be considered absolute requirements during CBCT imaging if a stable head position is ensured.
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Faculty of Oral and Dental Medicine, Cairo University, Cairo, Egypt.
authors.forename: Amr Ragab
authors.initials: AR
authors.lastname: El-Beialy
authors.forename: Mona Salah
authors.initials: MS
authors.lastname: Fayed
authors.forename: Ahmed Mohammed
authors.initials: AM
authors.lastname: El-Bialy
authors.forename: Yehya A
authors.initials: YA
authors.lastname: Mostafa
mesh_terms: D000465:Algorithms; D002102:Cadaver; D002508:Cephalometry / Q000379:methods; D054893:Cone-Beam Computed Tomography; D006257:Head / Q000502:physiology; D006801:Humans; D015588:Observer Variation; D056888:Patient Positioning; D015203:Reproducibility of Results; D012886:Skull / Q000000981:diagnostic imaging*; D018709:Statistics, Nonparametric