title: Imaging near metal: The impact of extreme static local field gradients on frequency encoding processes.
abstract: OBJECTIVE
  Magnetic resonance imaging capabilities in the direct vicinity of metallic devices have substantially improved with the recent development of three-dimensional multispectral imaging (3D-MSI) methods. When imaging near metallic hardware, the bulk image distortions in 3D-MSI techniques are reduced to the single-pixel level. However, commonly utilized MSI techniques are ultimately limited by frequency-encoding processes and reveal a class of residual intensity-based susceptibility artifacts that have yet to be formally analyzed.
  
  
  METHODS
  Empirical measurements and simulation techniques are utilized to study the static local magnetic field gradients induced by metal implants and their general impact on frequency-encoding processes. The specific consequences of these gradients on 3D-MSI approaches are also analyzed using empirical and simulated approaches.
  
  
  RESULTS
  Close agreements between empirical and simulated measurements clearly demonstrate the effects of strong local gradients on frequency-encoded imaging capabilities near metallic implants.
  
  
  CONCLUSIONS
  3D-MSI techniques can enable substantially enhanced magnetic resonance imaging capabilities near metallic implants. However, strong local static field gradients generate residual artifacts whose direct mitigation are ultimately limited by frequency encoding processes. Applications of 3D encoding strategies or additional post processing may be required to further reduce residual artifacts in multispectral images near metal implants.
authors.affiliation: GE Healthcare, Magnetic Resonance Division, Waukesha, Wisconsin, USA.
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Koch
authors.forename: Kevin F
authors.initials: KF
authors.lastname: King
authors.forename: Michael
authors.initials: M
authors.lastname: Carl
authors.forename: Brian A
authors.initials: BA
authors.lastname: Hargreaves
mesh_terms: D016477:Artifacts; D006801:Humans; D021621:Imaging, Three-Dimensional; D007720:Knee Prosthesis; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008670:Metals; D019047:Phantoms, Imaging; D059629:Signal-To-Noise Ratio
chemical_list: D008670:Metals
keywords: image artifacts; magnetic resonance imaging of arthroplasty; metal implants