title: Dual optimization method of radiofrequency and quasistatic field simulations for reduction of eddy currents generated on 7T radiofrequency coil shielding.
abstract: OBJECTIVE
  To optimize the design of radiofrequency (RF) shielding of transmit coils at 7T and reduce eddy currents generated on the RF shielding when imaging with rapid gradient waveforms.
  
  
  METHODS
  One set of a four-element, 2 × 2 Tic-Tac-Toe head coil structure was selected and constructed to study eddy currents on the RF coil shielding. The generated eddy currents were quantitatively studied in the time and frequency domains. The RF characteristics were studied using the finite difference time domain method. Five different kinds of RF shielding were tested on a 7T MRI scanner with phantoms and in vivo human subjects.
  
  
  RESULTS
  The eddy current simulation method was verified by the measurement results. Eddy currents induced by solid/intact and simple-structured slotted RF shielding significantly distorted the gradient fields. Echo-planar images, B1+ maps, and S matrix measurements verified that the proposed slot pattern suppressed the eddy currents while maintaining the RF characteristics of the transmit coil.
  
  
  CONCLUSIONS
  The presented dual-optimization method could be used to design RF shielding and reduce the gradient field-induced eddy currents while maintaining the RF characteristics of the transmit coil.
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Yujuan
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Siemens Medical Solutions, Pittsburgh, Pennsylvania, USA.
authors.forename: Tiejun
authors.initials: T
authors.lastname: Zhao
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.|Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Shailesh B
authors.initials: SB
authors.lastname: Raval
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Narayanan
authors.initials: N
authors.lastname: Krishnamurthy
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Hai
authors.initials: H
authors.lastname: Zheng
authors.affiliation: Department of Physics and Astronomy, University of Western Ontario, London, Canada.
authors.forename: Chad T
authors.initials: CT
authors.lastname: Harris
authors.affiliation: Department of Physics and Astronomy, University of Western Ontario, London, Canada.
authors.forename: William B
authors.initials: WB
authors.lastname: Handler
authors.affiliation: Department of Physics and Astronomy, University of Western Ontario, London, Canada.
authors.forename: Blaine A
authors.initials: BA
authors.lastname: Chronik
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.|Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Tamer S
authors.initials: TS
authors.lastname: Ibrahim
mesh_terms: D001921:Brain / Q000033:anatomy & histology; D003198:Computer Simulation; D003300:Copper; D004574:Electromagnetic Fields; D004867:Equipment Design; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D019047:Phantoms, Imaging; D011846:Radio Waves
chemical_list: D003300:Copper
keywords: 7T MRI; RF shielding; Tic-Tac-Toe RF coil; echo-planar imaging; eddy current simulation; full wave RF simulation; gradient coil model