title: Induced magnetic moment in stainless steel components of orthodontic appliances in 1.5 T MRI scanners.
abstract: OBJECTIVE
  Most orthodontic appliances are made of stainless steel materials and induce severe magnetic susceptibility artifacts in brain MRI. In an effort for correcting these artifacts, it is important to know the value of induced magnetic moments in all parts of orthodontic appliances. In this study, the induced magnetic moment of stainless steel orthodontic brackets, molar bands, and arch-wires from several vendors is measured.
  
  
  METHODS
  Individual stainless steel brackets, molar bands, and short segments of arch-wire were positioned in the center of spherical flask filled with water through a thin plastic rod. The induced magnetic moment at 1.5 T was determined by fitting the B0 map to the z-component of the magnetic dipole field using a computer routine.
  
  
  RESULTS
  The induced magnetic moment at 1.5 T was dominated by the longitudinal component mz, with a small contribution from the transverse components. The mz was insensitive to the orientation of the metal parts. The orthodontic brackets collectively dominated the magnetic dipole moment in orthodontic appliances. In brackets from six vendors, the total induced mz from 20 brackets for nonmolar teeth ranged from 0.108 to 0.158 (median 0.122) A ⋅ m(2). The mz in eight molar bands with bracket attachment from two vendors ranged from 0.0004 to 0.0166 (median 0.0035) A ⋅ m(2). Several full length arch wires had induced magnetic moment in the range of 0.006-0.025 (median 0.015) A ⋅ m(2).
  
  
  CONCLUSIONS
  Orthodontic brackets collectively contributed most to the total magnetic moment. Different types of brackets, molar bands, and arch wires all exhibit substantial variability in the induced magnetic moment.
authors.affiliation: Department of Radiology, Children's Medical Center, Dallas, Texas 75235 and Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390.
authors.forename: Zhiyue J
authors.initials: ZJ
authors.lastname: Wang
authors.affiliation: Department of Radiology, Children's Medical Center, Dallas, Texas 75235 and Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390.
authors.forename: Nancy K
authors.initials: NK
authors.lastname: Rollins
authors.affiliation: Baylor College of Dentistry, Texas A&M University, Dallas, Texas 75246.
authors.forename: Hui
authors.initials: H
authors.lastname: Liang
authors.affiliation: Division of Orthodontics, Children's Medical Center, Dallas, Texas 75235.
authors.forename: Yong Jong
authors.initials: YJ
authors.lastname: Park
mesh_terms: D016477:Artifacts; D060328:Magnetic Phenomena; D008279:Magnetic Resonance Imaging; D009967:Orthodontic Appliances; D013193:Stainless Steel
chemical_list: D013193:Stainless Steel