title: Parallel transmit capability of various RF transmit elements and arrays at 7T MRI.
abstract: In this work, 22 configurations for remote radiofrequency (RF) coil arrays consisting of different transmit element designs for 7 Tesla (T) ultrahigh-field MRI are compared by numerical simulations.
  
  
  
  Investigated transmit RF element types are rectangular loops, micro striplines, micro striplines with meanders, 250-mm shielded dipoles with meanders, and lambda over two dipoles with and without shield. These elements are combined in four different configurations of circumferential RF body arrays with four or eight transmit elements each. Comparisons included coupling behavior, degrees of freedom offered by the individual transmit patterns, and metrics like power and specific absorption rate efficiency.
  
  
  
  Coupling between neighboring RF elements is elevated (up to -7 dB) for all arrays with eight elements, whereas it is below -25 dB for arrays with only four elements. The cumulative sum of singular values points out highest degrees of freedom for the central transversal, reduced values in the central coronal, and minimum values in the sagittal slice. Concerning power and SAR efficiency, eight lambda over two dipoles are most advantageous.
  
  
  
  Among the investigated remote arrays and parameters, a combination of eight dipoles appears to be most favorable for potential use in 7T body MRI. Magn Reson Med 79:1116-1126, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.|High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany.
authors.forename: Stefan H G
authors.initials: SHG
authors.lastname: Rietsch
authors.affiliation: Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Orzada
authors.affiliation: Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.|Electromagnetic Theory and Applied Mathematics, Faculty of Electrical Engineering and Information Technology, University of Applied Sciences Aachen, Aachen, Germany.
authors.forename: Andreas K
authors.initials: AK
authors.lastname: Bitz
authors.affiliation: Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.|High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany.
authors.forename: Marcel
authors.initials: M
authors.lastname: Gratz
authors.affiliation: Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.|Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Ladd
authors.affiliation: Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.|High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany.
authors.forename: Harald H
authors.initials: HH
authors.lastname: Quick
mesh_terms: D003198:Computer Simulation; D004867:Equipment Design; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D011846:Radio Waves
keywords: 7 T; RF antenna array; parallel transmit (pTx); radio frequency (RF); ultrahigh field