title: Influence of exposure factors on the variability of CBCT voxel values: a phantom study.
abstract: OBJECTIVE
  To assess the influence of milliamperage and kilovolt peak (kVp) on the variability of cone beam CT (CBCT) voxel values.
  
  
  METHODS
  CBCT scans were obtained from radiographic phantoms in varying concentrations of dipotassium hydrogen phosphate solutions (200-1200 mg ml(-1)) under different protocols of milliamperage and kVp. In addition, scans were performed with and without a dental implant and exo-mass. The variability of CBCT voxel values was measured on each scan, and factorial analysis of variance and the post hoc Tukey test were performed (α = 0.05). Linear regression was performed to assess the relationship between voxel value variability and dipotassium hydrogen phosphate concentration.
  
  
  RESULTS
  milliamperage and the presence of a dental implant did not produce significant interference (p = 0.28 and 0.87, respectively) in voxel value variability. Scans at the highest kVp value presented a significant reduction (p ≤ 0.0001) in voxel value variability when only exo-mass was not present. Voxel value variability was not influenced by exo-mass in scans at the highest levels of milliamperage and kVp. The presence of exo-mass produced a significant reduction (p ≤ 0.0001) in voxel value variability in most of the scans. Higher concentrations yielded greater variations in voxel values in all scans, except for those operating at the highest levels of mAs and kVp.
  
  
  CONCLUSIONS
  mAs did not influence the variability of CBCT voxel values; higher kVp reduced such variability when only the object was smaller than the field of view.
authors.affiliation: Department of Oral Diagnosis, Division of Oral Radiology, State University of Campinas, Piracicaba Dental School, Piracicaba, Sao Paulo, Brazil.
authors.forename: M L
authors.initials: ML
authors.lastname: Oliveira
authors.forename: D Q
authors.initials: DQ
authors.lastname: Freitas
authors.forename: G M B
authors.initials: GM
authors.lastname: Ambrosano
authors.forename: F
authors.initials: F
authors.lastname: Haiter-Neto
mesh_terms: D019412:Anatomy, Cross-Sectional; D016477:Artifacts; D002021:Buffers; D054893:Cone-Beam Computed Tomography / Q000379:methods* / Q000706:statistics & numerical data; D015921:Dental Implants; D004560:Electricity; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D019047:Phantoms, Imaging; D010710:Phosphates / Q000737:chemistry; D017680:Potassium Compounds / Q000737:chemistry; D011829:Radiation Dosage
chemical_list: D002021:Buffers; D015921:Dental Implants; D010710:Phosphates; D017680:Potassium Compounds; C013216:potassium phosphate
keywords: cone beam computed tomography; densitometry; photon absorptiometry