title: Characterizing the limits of MRI near metallic prostheses.
abstract: OBJECTIVE
  To characterize the fundamental limits of MRI near metallic implants on RF excitation, frequency encoding, and chemical shift-encoding water-fat separation.
  
  
  METHODS
  Multicomponent three-dimensional (3D) digital models of a total hip and a total knee replacement were used to construct material-specific susceptibility maps. The fundamental limits and spatial relationship of imaging near metallic prostheses were investigated as a function of distance from the prosthetic surface by calculating 3D field map perturbations using a well-validated k-space based dipole kernel.
  
  
  RESULTS
  Regions limited by the bandwidth of RF excitation overlap substantially with those fundamentally limited by frequency encoding. Rapid breakdown of water-fat separation occurs once the intravoxel off-resonance exceeds ∼6 ppm over a full range of fat fractions (0%-100%) and SNR (5-100).
  
  
  CONCLUSIONS
  Current 3D multispectral imaging methods would not benefit greatly from exciting spins beyond ±12 kHz despite the presence of signal that lies outside of this range from tissue directly adjacent to the metallic implants. Methods such as phase encoding in all three spatial dimensions are necessary to spatially resolve spins beyond an excitation bandwidth of ±12 kHz. The approach described in this study provides a benchmark for the capabilities of current imaging techniques to guide development of new MRI methods for imaging near metal.
authors.affiliation: Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Smith
authors.affiliation: Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Artz
authors.affiliation: Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Curtis
authors.initials: C
authors.lastname: Wiens
authors.affiliation: Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Diego
authors.initials: D
authors.lastname: Hernando
authors.affiliation: Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.|Department of Medical Physics, University of Wisconsin, Madison, Wisconsin, USA.|Department of Biomedical Engineering, University of Wisconsin, Madison, Wisconsin, USA.|Department of Medicine, University of Wisconsin, Madison, Wisconsin, USA.|Department of Emergency Medicine, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Scott B
authors.initials: SB
authors.lastname: Reeder
mesh_terms: D016477:Artifacts; D003198:Computer Simulation; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007595:Joint Prosthesis; D007596:Joints / Q000473:pathology* / Q000601:surgery; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008670:Metals; D008954:Models, Biological; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D008670:Metals
keywords: B0 inhomogeneity; magnetic resonance imaging; metallic implants; off-resonance; prostheses; water-fat separation