title: Optimization of dental CBCT exposures through mAs reduction.
abstract: OBJECTIVE
  To investigate the effect of tube current-exposure time (mAs) reduction on clinical and technical image quality for different CBCT scanners, and to determine preliminary minimally acceptable values for the mAs and contrast-to-noise ratio (CNR) in CBCT.
  
  
  METHODS
  A polymethyl methacrylate (PMMA) phantom and an anthropomorphic skull phantom, containing a human skeleton embedded in polyurethane, were scanned using four CBCT devices, including seven exposure protocols. For all protocols, the mAs was varied within the selectable range. Using the PMMA phantom, the CNRAIR was measured and corrected for voxel size. Eight axial slices and one coronal slice showing various anatomical landmarks were selected for each CBCT scan of the skull phantom. The slices were presented to six dentomaxillofacial radiologists, providing scores for various anatomical and diagnostic parameters.
  
  
  RESULTS
  A hyperbolic relationship was seen between CNRAIR and mAs. Similarly, a gradual reduction in clinical image quality was seen at lower mAs values; however, for several protocols, image quality remained acceptable for a moderate or large mAs reduction compared with the standard exposure setting, depending on the clinical application. The relationship between mAs, CNRAIR and observer scores was different for each CBCT device. Minimally acceptable values for mAs were between 9 and 70, depending on the criterion and clinical application.
  
  
  CONCLUSIONS
  Although noise increased at a lower mAs, clinical image quality often remained acceptable at exposure levels below the manufacturer's recommended setting, for certain patient groups. Currently, it is not possible to determine minimally acceptable values for image quality that are applicable to multiple CBCT models.
authors.affiliation: 1 Department of Radiology, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand.|2 OMFS-IMPATH Research Group, Oral Imaging Center, Department of Imaging and Pathology, Biomedical Sciences Group, University of Leuven, Leuven, Belgium.
authors.forename: R
authors.initials: R
authors.lastname: Pauwels
authors.affiliation: 2 OMFS-IMPATH Research Group, Oral Imaging Center, Department of Imaging and Pathology, Biomedical Sciences Group, University of Leuven, Leuven, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Seynaeve
authors.affiliation: 2 OMFS-IMPATH Research Group, Oral Imaging Center, Department of Imaging and Pathology, Biomedical Sciences Group, University of Leuven, Leuven, Belgium.
authors.forename: J C G
authors.initials: JC
authors.lastname: Henriques
authors.affiliation: 3 Department of Stomatology, Public Health and Forensic Dentistry, University of São Paulo, School of Dentistry of Ribeirão Preto of Dentistry, São Paulo, Brazil.
authors.forename: C
authors.initials: C
authors.lastname: de Oliveira-Santos
authors.affiliation: 4 School of Dentistry, Pontifical Catholic University of Paraná, Curitiba, Brazil.
authors.forename: P C
authors.initials: PC
authors.lastname: Souza
authors.affiliation: 4 School of Dentistry, Pontifical Catholic University of Paraná, Curitiba, Brazil.
authors.forename: F H
authors.initials: FH
authors.lastname: Westphalen
authors.affiliation: 5 Stomatology Department, Bauru School of Dentistry, University of São Paulo, São Paulo, Brazil.
authors.forename: I R F
authors.initials: IR
authors.lastname: Rubira-Bullen
authors.affiliation: 6 Department of Oral Medicine, School of Dentistry, Federal University of Goiás, Goiás, Brazil.
authors.forename: R F
authors.initials: RF
authors.lastname: Ribeiro-Rotta
authors.affiliation: 7 Department of Surgery, Faculty of Dentistry, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil.
authors.forename: M I B
authors.initials: MI
authors.lastname: Rockenbach
authors.affiliation: 8 Department of Oral Diagnosis, Piracicaba Dental School, University of Campinas, Piracicaba, Brazil.
authors.forename: F
authors.initials: F
authors.lastname: Haiter-Neto
authors.affiliation: 1 Department of Radiology, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand.|2 OMFS-IMPATH Research Group, Oral Imaging Center, Department of Imaging and Pathology, Biomedical Sciences Group, University of Leuven, Leuven, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Pittayapat
authors.affiliation: 9 Department of Radiology, University Hospitals Leuven, Leuven, Belgium.
authors.forename: H
authors.initials: H
authors.lastname: Bosmans
authors.affiliation: 10 Department of Experimental Radiotherapy, University Hospitals Leuven, Leuven, Belgium.
authors.forename: R
authors.initials: R
authors.lastname: Bogaerts
authors.affiliation: 1 Department of Radiology, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand.
authors.forename: R
authors.initials: R
authors.lastname: Jacobs
mesh_terms: D000328:Adult; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging; D016477:Artifacts; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008297:Male; D008334:Mandible / Q000000981:diagnostic imaging; D008437:Maxilla / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D019904:Polymethyl Methacrylate / Q000737:chemistry; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000379:methods*; D019252:Radiography, Dental, Digital / Q000295:instrumentation / Q000379:methods*; D012886:Skull / Q000000981:diagnostic imaging; D013997:Time Factors
chemical_list: D019904:Polymethyl Methacrylate
keywords: computer-assisted image processing; computer-assisted radiographic image interpretation; cone-beam computed tomography; quality control