title: Dielectric waveguides for ultrahigh field magnetic resonance imaging.
abstract: The design of RF coils for MRI transmit becomes increasingly challenging at high frequencies required for MRI at 7T and above. Our goal is to show a proof of principle of a new type of transmit coil for higher field strengths.
  
  
  
  We demonstrate an alternative transmit coil design based on dielectric waveguide principles which transfers energy via evanescent wave coupling. The operating principles and conditions are explored by simulations. The waveguide is applied for in vivo imaging at 7T.
  
  
  
  The waveguide can be an efficient transmit coil when four conditions are fulfilled: (1) the waveguide should be operated just above the cutoff frequency of the lowest order transverse electric mode, (2) the waveguide should not operate at a frequency where the wavelength fits an integer number of times in the waveguide length and standing wave patterns become very prominent, (3) for homogeneous excitation, the waveguide should be bent around the object, and (4) there should be an air gap between the waveguide and the object.
  
  
  
  By choosing the dielectric and the dimensions adequately, the dielectric waveguide couples the magnetic field efficiently into the body. The waveguide can be redesigned for higher frequencies by simple adaptations and may be a promising transmit alternative. Magn Reson Med 76:1314-1324, 2016. © 2015 Wiley Periodicals, Inc.
authors.affiliation: UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy, University Medical Center Utrecht, The Netherlands. j.j.bluemink@umcutrecht.nl.
authors.forename: Johanna J
authors.initials: JJ
authors.lastname: Bluemink
authors.affiliation: UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Alexander J E
authors.initials: AJ
authors.lastname: Raaijmakers
authors.affiliation: UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Wouter
authors.initials: W
authors.lastname: Koning
authors.affiliation: UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Anna
authors.initials: A
authors.lastname: Andreychenko
authors.affiliation: UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Debra S
authors.initials: DS
authors.lastname: Rivera
authors.affiliation: UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Luijten
authors.affiliation: UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Dennis W J
authors.initials: DW
authors.lastname: Klomp
authors.affiliation: UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: Cornelis A T
authors.initials: CA
authors.lastname: van den Berg
mesh_terms: D017076:Computer-Aided Design; D017097:Electric Impedance; D004735:Energy Transfer; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007089:Image Enhancement / Q000295:instrumentation*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008280:Magnetics / Q000295:instrumentation*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014159:Transducers
keywords: dielectric; transmit; ultrahigh field; waveguides