title: 3D gradient system for two B0 field directions in earth's field MRI.
abstract: OBJECTIVE
  A new gradient system for earth's field magnetic resonance imaging (EFMRI) is presented that can be rotated relatively to the earth's field direction while maintaining the ability to encode images. Orthogonal components of the gradient field are exploited to reduce the number of gradient coils.
  
  
  METHODS
  Two favorable orientations of the gradient system relative to the earth's magnetic field (parallel and perpendicular) are discussed. We introduce the theory for the magnetic fields of the new gradient system and illustrate the design of the coil geometries which were worked out with the help of simulations and a numerical optimization algorithm. Field mapping measurements and imaging experiments in the two different orientations of the gradient system were carried out.
  
  
  RESULTS
  Orthogonal components of the gradient field take over the role of the additionally needed gradient fields when the gradient system is rotated relative to the earth's magnetic field. The results from the field mapping and imaging experiments verify the presented theory and show the functionality of the new gradient system.
  
  
  CONCLUSIONS
  The presented system demonstrates that gradient coils can be used for image encoding in multiple directions. This fact can be exploited to realize an EFMRI setup for parallel and perpendicular prepolarization with a single set of gradient coils.
authors.affiliation: Research Center Magnetic-Resonance-Bavaria (MRB), Würzburg, Germany, lother@mr-bavaria.de.
authors.forename: Steffen
authors.initials: S
authors.lastname: Lother
authors.forename: Uvo
authors.initials: U
authors.lastname: Hoelscher
authors.forename: Thomas
authors.initials: T
authors.lastname: Kampf
authors.forename: Peter
authors.initials: P
authors.lastname: Jakob
authors.forename: Florian
authors.initials: F
authors.lastname: Fidler
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004574:Electromagnetic Fields; D004867:Equipment Design; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging