title: Performance evaluation of matrix gradient coils.
abstract: OBJECTIVE
  In this paper, we present a new performance measure of a matrix coil (also known as multi-coil) from the perspective of efficient, local, non-linear encoding without explicitly considering target encoding fields.
  
  
  METHODS
  An optimization problem based on a joint optimization for the non-linear encoding fields is formulated. Based on the derived objective function, a figure of merit of a matrix coil is defined, which is a generalization of a previously known resistive figure of merit for traditional gradient coils.
  
  
  RESULTS
  A cylindrical matrix coil design with a high number of elements is used to illustrate the proposed performance measure. The results are analyzed to reveal novel features of matrix coil designs, which allowed us to optimize coil parameters, such as number of coil elements. A comparison to a scaled, existing multi-coil is also provided to demonstrate the use of the proposed performance parameter.
  
  
  CONCLUSIONS
  The assessment of a matrix gradient coil profits from using a single performance parameter that takes the local encoding performance of the coil into account in relation to the dissipated power.
authors.affiliation: Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany. feng.jia@uniklinik-freiburg.de.
authors.forename: Feng
authors.initials: F
authors.lastname: Jia
authors.affiliation: Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany.
authors.forename: Gerrit
authors.initials: G
authors.lastname: Schultz
authors.affiliation: Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany.
authors.forename: Frederik
authors.initials: F
authors.lastname: Testud
authors.affiliation: Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany.
authors.forename: Anna Masako
authors.initials: AM
authors.lastname: Welz
authors.affiliation: Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany.
authors.forename: Hans
authors.initials: H
authors.lastname: Weber
authors.affiliation: Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Littin
authors.affiliation: Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany.
authors.forename: Huijun
authors.initials: H
authors.lastname: Yu
authors.affiliation: Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hennig
authors.affiliation: Medical Physics, Department of Radiology, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany.
authors.forename: Maxim
authors.initials: M
authors.lastname: Zaitsev
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004574:Electromagnetic Fields; D004867:Equipment Design; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D015233:Models, Statistical; D015203:Reproducibility of Results; D012984:Software
keywords: Gradient coil; Magnetic resonance imaging (MRI); Matrix coil; Non-linear encoding fields; PatLoc; Spatial encoding