title: Quantification of metal artifacts on cone beam computed tomography images.
abstract: OBJECTIVE
  To quantify metal artifacts obtained from a wide range of cone beam computed tomography (CBCT) devices and exposure protocols, to compare their tolerance to metals of different densities, and to provide insights regarding the possible implementation of metal artifact analysis into a QC protocol for CBCT.
  
  
  METHODS
  A customized polymethyl methacrylate (PMMA) phantom, containing titanium and lead rods, was fabricated. It was scanned on 13 CBCT devices and one multi-slice computed tomography (MSCT) device, including high-dose and low-dose exposure protocols. Artifacts from the rods were assessed by two observers by measuring the standard deviation of voxel values in the vicinity of the rods, and normalizing this value to the percentage of the theoretical maximum standard deviation.
  
  
  RESULTS
  For CBCT datasets, artifact values ranged between 6.1% and 27.4% for titanium, and between 10.% and 43.7% for lead. Most CBCT devices performed worse than MSCT for titanium artifacts, but all of them performed better for lead artifacts. In general, no clear improvement of metal artifacts was seen for high-dose protocols, although certain devices showed some artifact reduction for large FOV or high exposure protocols.
  
  
  CONCLUSIONS
  Regions in the vicinity of the metal rods were moderately or gravely affected, particularly in the area between the rods. In practice, the CBCT user has very limited possibilities to reduce artifacts. Researchers and manufacturers need to combine their efforts in optimizing exposure factors and implementing metal artifact reduction algorithms.
authors.affiliation: Oral Imaging Center, Faculty of Medicine, Katholieke Universiteit Leuven, Leuven, Belgium. ruben.pauwels@med.kuleuven.be
authors.forename: Ruben
authors.initials: R
authors.lastname: Pauwels
authors.forename: Harry
authors.initials: H
authors.lastname: Stamatakis
authors.forename: Hilde
authors.initials: H
authors.lastname: Bosmans
authors.forename: Ria
authors.initials: R
authors.lastname: Bogaerts
authors.forename: Reinhilde
authors.initials: R
authors.lastname: Jacobs
authors.forename: Keith
authors.initials: K
authors.lastname: Horner
authors.forename: Kostas
authors.initials: K
authors.lastname: Tsiklakis
mesh_terms: D016477:Artifacts; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation*; D021621:Imaging, Three-Dimensional / Q000295:instrumentation; D007854:Lead; D008670:Metals; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted; D014025:Titanium
chemical_list: D008670:Metals; D007854:Lead; D014025:Titanium