title: Parallel imaging in non-bijective, curvilinear magnetic field gradients: a concept study.
abstract: OBJECTIVE
  The paper presents a novel and more generalized concept for spatial encoding by non-unidirectional, non- bijective spatial encoding magnetic fields (SEMs). In combination with parallel local receiver coils these fields allow one to overcome the current limitations of neuronal nerve stimulation. Additionally the geometry of such fields can be adapted to anatomy.
  
  
  METHODS
  As an example of such a parallel imaging technique using localized gradients (PatLoc)- system, we present a polar gradient system consisting of 2 x 8 rectangular current loops in octagonal arrangement, which generates a radial magnetic field gradient. By inverting the direction of current in alternating loops, a near sinusoidal field variation in the circumferential direction is produced. Ambiguities in spatial assignment are resolved by use of multiple receiver coils and parallel reconstruction. Simulations demonstrate the potential advantages and limitations of this approach.
  
  
  CONCLUSIONS
  The exact behaviour of PatLoc fields with respect to peripheral nerve stimulation needs to be tested in practice. Based on geometrical considerations SEMs of radial geometry allow for about three times faster gradient switching compared to conventional head gradient inserts and even more compared to whole body gradients. The strong nonlinear geometry of the fields needs to be considered for practical applications.
authors.affiliation: Department of Diagnostic Radiology, Medical Physics, University Hospital, Hugstetterstr.55, 79106 Freiburg, Germany. juergen.hennig@uniklinik-freiburg.de
authors.forename: Juergen
authors.initials: J
authors.lastname: Hennig
authors.forename: Anna Masako
authors.initials: AM
authors.lastname: Welz
authors.forename: Gerrit
authors.initials: G
authors.lastname: Schultz
authors.forename: Jan
authors.initials: J
authors.lastname: Korvink
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Liu
authors.forename: Oliver
authors.initials: O
authors.lastname: Speck
authors.forename: Maxim
authors.initials: M
authors.lastname: Zaitsev
mesh_terms: D000465:Algorithms; D001921:Brain / Q000473:pathology; D003198:Computer Simulation; D003952:Diagnostic Imaging / Q000295:instrumentation* / Q000379:methods; D004574:Electromagnetic Fields; D004867:Equipment Design; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D008280:Magnetics; D019047:Phantoms, Imaging