title: Use of gray values in CBCT and MSCT images for determination of density: influence of variation of FOV size.
abstract: OBJECTIVE
  To determine the effect of field of view (FOV) size on gray values in cone beam computed tomography (CBCT) and multislice computed tomography (MSCT) images.
  
  
  METHODS
  A phantom made up of 3 cylinders containing distilled water, plaster, and motor oil was constructed and inserted into an acrylic cylinder filled with distilled water. The phantom was scanned with a CBCT and MSCT device using 3 FOV sizes. Gray value of each material was evaluated in 40 axial slices, and the comparison between the results obtained with the same FOV size was made.
  
  
  RESULTS
  In CBCT examinations, there was significant difference between the gray values of different FOVs for the 3 materials. In the MSCT, there was significant difference for the oil. Gray values showed significant difference between the CBCT and MSCT examinations for the 3 materials in the 3 different FOV sizes.
  
  
  CONCLUSIONS
  Gray values determined in CBCT images are significantly influenced by the FOV size. Although the gray values obtained in MSCT have shown statistically significant differences between some acquisitions, the analysis of those differences seems to indicate low clinical relevance.
authors.affiliation: *Postgraduate Student, Department of Orthodontics, Juiz de Fora Federal University, Juiz de Fora, Brazil. †Professor, Department of Orthodontics, Juiz de Fora Federal University, Juiz de Fora, Brazil. ‡Professor, Department of Statistics, Juiz de Fora Federal University, Juiz de Fora, Brazil. §Associate Professor and Chair, Department of Orthodontics, Juiz de Fora Federal University, Juiz de Fora, Brazil.
authors.forename: Andreia Fialho
authors.initials: AF
authors.lastname: Rodrigues
authors.forename: Marcio José da Silva
authors.initials: MJ
authors.lastname: Campos
authors.forename: Alfredo
authors.initials: A
authors.lastname: Chaoubah
authors.forename: Marcelo Reis
authors.initials: MR
authors.lastname: Fraga
authors.forename: Robert Willer
authors.initials: RW
authors.lastname: Farinazzo Vitral
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000592:standards; D061330:Multidetector Computed Tomography / Q000592:standards; D019047:Phantoms, Imaging; D011861:Radiography, Dental / Q000592:standards