title: Spatial excitation using variable-density spiral trajectories.
abstract: OBJECTIVE
  To examine the usefulness of variable-density k-space trajectories for the design of multi-dimensional spatially selective RF pulses.
  
  
  METHODS
  Experimental phantom and in vivo studies were performed and confirmed by simulations. Two-dimensional spatially selective magnetization patterns were excited using variable-density spiral trajectories and analyzed with respect to the signal excitation outside the excitation field of view (FOX).
  
  
  RESULTS
  By using variable-density trajectories, signal excitation outside the FOX was drastically reduced compared to trajectories with a uniform density, while maintaining fairly short pulse durations.
  
  
  CONCLUSIONS
  A main advantage of the method is that unwanted signal excitation outside the nominal FOX can be reduced without significantly increasing the duration of the RF excitation pulse. The variable-density approach is useful for all applications that require a well-defined spatial excitation profile, e.g., to perform imaging in a reduced field of view (FOV), for spatial saturation pulses, for curved slice imaging or in MR spectroscopy.
authors.affiliation: Philips Research Laboratories, Sector Technical Systems, Hamburg, Germany. christoph.schroeder@philips.com
authors.forename: Christoph
authors.initials: C
authors.lastname: Schröder
authors.forename: Peter
authors.initials: P
authors.lastname: Börnert
authors.forename: Bernd
authors.initials: B
authors.lastname: Aldefeld
mesh_terms: D003198:Computer Simulation; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D011846:Radio Waves