title: Knee implant imaging at 3 Tesla using high-bandwidth radiofrequency pulses.
abstract: BACKGROUND
  To investigate the impact of high-bandwidth radiofrequency (RF) pulses used in turbo spin echo (TSE) sequences or combined with slice encoding for metal artifact correction (SEMAC) on artifact reduction at 3 Tesla in the knee in the presence of metal.
  
  
  METHODS
  Local transmit/receive coils feature increased maximum B1 amplitude, reduced SAR exposition and thus enable the application of high-bandwidth RF pulses. Susceptibility-induced through-plane distortion scales inversely with the RF bandwidth and the view angle, hence blurring, increases for higher RF bandwidths, when SEMAC is used. These effects were assessed for a phantom containing a total knee arthroplasty. TSE and SEMAC sequences with conventional and high RF bandwidths and different contrasts were tested on eight patients with different types of implants. To realize scan times of 7 to 9 min, SEMAC was always applied with eight slice-encoding steps and distortion was rated by two radiologists.
  
  
  RESULTS
  A local transmit/receive knee coil enables the use of an RF bandwidth of 4 kHz compared with 850 Hz in conventional sequences. Phantom scans confirm the relation of RF bandwidth and through-plane distortion, which can be reduced up to 79%, and demonstrate the increased blurring for high-bandwidth RF pulses. In average, artifacts in this RF mode are rated hardly visible for patients with joint arthroplasties, when eight SEMAC slice-encoding steps are applied, and for patients with titanium fixtures, when TSE is used.
  
  
  CONCLUSIONS
  The application of high-bandwidth RF pulses by local transmit coils substantially reduces through-plane distortion artifacts at 3 Tesla.
authors.affiliation: Department of Experimental Physics 5, University of Wuerzburg, Wuerzburg, Germany.|Magnetic Resonance, Siemens AG, Erlangen, Germany.
authors.forename: Theresa J
authors.initials: TJ
authors.lastname: Bachschmidt
authors.affiliation: Department of Radiology, Orthopedic University Hospital Balgrist, Zurich, Switzerland.|University of Zurich, Faculty of Medicine, Zurich, Switzerland.
authors.forename: Reto
authors.initials: R
authors.lastname: Sutter
authors.affiliation: Department of Experimental Physics 5, University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Jakob
authors.affiliation: Department of Radiology, Orthopedic University Hospital Balgrist, Zurich, Switzerland.|University of Zurich, Faculty of Medicine, Zurich, Switzerland.
authors.forename: Christian W A
authors.initials: CW
authors.lastname: Pfirrmann
authors.affiliation: Magnetic Resonance, Siemens AG, Erlangen, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Nittka
mesh_terms: D019645:Arthroplasty, Replacement, Knee; D016477:Artifacts; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007720:Knee Prosthesis; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008670:Metals; D019047:Phantoms, Imaging
chemical_list: D008670:Metals
keywords: 3.0 Tesla; magnetic resonance imaging; metal artifact; total knee arthroplasty