title: Magnetic permeability as a predictor of the artefact size caused by orthodontic appliances at 1.5 T magnetic resonance imaging.
abstract: OBJECTIVE
  Artefacts caused by orthodontic attachments limit the diagnostic value and lead to removal of these appliances before magnetic resonance imaging. Magnetic permeability can predict the artefact size. There is no standardised approach to determine the permeability of such attachments. The aim was to establish a reliable approach to determine artefact size caused by orthodontic attachments at 1.5 T MRI.
  
  
  METHODS
  Artefact radii of 21 attachments were determined applying two prevalent sequences of the head and neck region (turbo spin echo and gradient echo). The instrument Ferromaster (Stefan Mayer Instruments, Dinslaken) is approved for permeability measurements of objects with a minimum size (d = 20 mm, h = 5 mm). Eleven small test specimens of known permeability between 1.003 and 1.431 were produced. They are slightly larger than the orthodontic attachments. Their artefacts were measured and cross tabulated against the permeability. The resulting curve was used to compare the orthodontic attachments with the test bodies.
  
  
  RESULTS
  Steel caused a wide range of artefact size of 10-74 mm subject to their permeability. Titanium, cobalt-chromium and ceramic materials produced artefact radii up to 20 mm. Measurement of artefacts of the test bodies revealed an interrelationship according to a root function. The artefact size of all brackets was below that root function.
  
  
  CONCLUSIONS
  The permeability can be reliably assessed by conventional measurement devices and the artefact size can be predicted. The radiologist is able to decide whether or not the orthodontic attachments should be removed.
  
  
  CONCLUSIONS
  This study clarifies whether an orthodontic appliance must be removed before taking an MRI.
authors.affiliation: Department of Prosthodontics, Geriatric Dentistry and Craniomandibular Disorders, Charité - Universitätsmedizin Berlin, Aßmannshauser Str. 4-6, 14197, Berlin, Germany. felix.blankenstein@charite.de.
authors.forename: Felix H
authors.initials: FH
authors.lastname: Blankenstein
authors.affiliation: Department of Radiology, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117, Berlin, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Asbach
authors.affiliation: Department of Prosthodontics, Geriatric Dentistry and Craniomandibular Disorders, Charité - Universitätsmedizin Berlin, Aßmannshauser Str. 4-6, 14197, Berlin, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Beuer
authors.affiliation: Ingenieurbüro Johannes Glienke, Abendrotweg 19, 12307, Berlin, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Glienke
authors.affiliation: Fa. Stefan Mayer Instruments, Wallstr. 7, 46535, Dinslaken, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mayer
authors.affiliation: Department of Prosthodontics, Geriatric Dentistry and Craniomandibular Disorders, Charité - Universitätsmedizin Berlin, Aßmannshauser Str. 4-6, 14197, Berlin, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Zachriat
mesh_terms: D016477:Artifacts; D002516:Ceramics; D002857:Chromium; D003035:Cobalt; D006801:Humans; D066298:In Vitro Techniques; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009967:Orthodontic Appliances; D019047:Phantoms, Imaging; D013232:Steel; D014025:Titanium
chemical_list: D002857:Chromium; D013232:Steel; D003035:Cobalt; D014025:Titanium
keywords: Artefacts; MR imaging; Orthodontic appliances; Permeability; Phantom