title: Subject- and resource-specific monitoring and proactive management of parallel radiofrequency transmission.
abstract: Develop a practical comprehensive package for proactive management of parallel radiofrequency (RF) transmission.
  
  
  
  With a constrained optimization framework and predictive models from a prescan based multichannel calibration, we presented a method supporting design and optimization of parallel RF excitation pulses that accurately obey the forward/reflected peak and average power limits of the RF power amplifiers in parallel transmit imaging experiments and Bloch simulations. Moreover, local SAR limits were incorporated into the parallel RF excitation pulses using electromagnetic field simulations. Virtual transmit coils concept for minimization of reflected power (effecting subject-specific matching) was additionally demonstrated by leveraging experimentally calibrated power models.
  
  
  
  Incorporation of experimentally calibrated power prediction models resulted in accurate compliance with prescribed hardware and global specific absorption rate (SAR) limits. Incorporation of spatial average 10 g SAR models, facilitated by simplifying numerical approximations, provided assurance of patient safety. RF pulses designed with various constraints demonstrated excellent excitation fidelity-the normalized root-mean-square error of the simulated excitation profiles was 2.6% for the fully constrained pulses, comparable to that of the unconstrained pulses. An RF shimming example showed a reduction of the reflected-to-forward power ratio to 1.7% from a conventional approach's 8.1%.
  
  
  
  Using the presented RF pulse design method, effective proactive management of the multifaceted power and SAR limits was demonstrated in experimental and simulation studies. Magn Reson Med 76:20-31, 2016. © 2015 Wiley Periodicals, Inc.
authors.affiliation: Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.|The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA.|NYU WIRELESS, New York University Polytechnic School of Engineering, Brooklyn, New York, USA.|RF Test Labs, Inc., New York, New York, USA.
authors.forename: Cem M
authors.initials: CM
authors.lastname: Deniz
authors.affiliation: Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.|The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA.|NYU WIRELESS, New York University Polytechnic School of Engineering, Brooklyn, New York, USA.|RF Test Labs, Inc., New York, New York, USA.
authors.forename: Leeor
authors.initials: L
authors.lastname: Alon
authors.affiliation: Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.|NYU WIRELESS, New York University Polytechnic School of Engineering, Brooklyn, New York, USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: Brown
authors.affiliation: Zhu Consulting, Scarsdale, New York, USA.
authors.forename: Yudong
authors.initials: Y
authors.lastname: Zhu
mesh_terms: D003198:Computer Simulation; D017076:Computer-Aided Design; D004574:Electromagnetic Fields; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D000069079:Radiation Exposure / Q000032:analysis* / Q000517:prevention & control; D011834:Radiation Monitoring / Q000295:instrumentation / Q000379:methods*; D011835:Radiation Protection / Q000379:methods*; D011846:Radio Waves; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: RF safety; high field MRI; parallel transmission; pulse design; specific absorption rate