title: Multiband accelerated spin-echo echo planar imaging with reduced peak RF power using time-shifted RF pulses.
abstract: OBJECTIVE
  To evaluate an alternative method for generating multibanded radiofrequency (RF) pulses for use in multiband slice-accelerated imaging with slice-GRAPPA unaliasing, substantially reducing the required peak power without bandwidth compromises. This allows much higher accelerations for spin-echo methods such as SE-fMRI and diffusion-weighted MRI where multibanded slice acceleration has been limited by available peak power.
  
  
  METHODS
  Multibanded "time-shifted" RF pulses were generated by inserting temporal shifts between the applications of RF energy for individual bands, avoiding worst-case constructive interferences. Slice profiles and images in phantoms and human subjects were acquired at 3 T.
  
  
  RESULTS
  For typical sinc pulses, time-shifted multibanded RF pulses were generated with little increase in required peak power compared to single-banded pulses. Slice profile quality was improved by allowing for higher pulse bandwidths, and image quality was improved by allowing for optimum flip angles to be achieved.
  
  
  CONCLUSIONS
  A simple approach has been demonstrated that significantly alleviates the restrictions imposed on achievable slice acceleration factors in multiband spin-echo imaging due to the power requirements of multibanded RF pulses. This solution will allow for increased accelerations in diffusion-weighted MRI applications where data acquisition times are normally very long and the ability to accelerate is extremely valuable.
authors.affiliation: Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota 55455, USA. eja@umn.edu
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Auerbach
authors.forename: Junqian
authors.initials: J
authors.lastname: Xu
authors.forename: Essa
authors.initials: E
authors.lastname: Yacoub
authors.forename: Steen
authors.initials: S
authors.lastname: Moeller
authors.forename: Kâmil
authors.initials: K
authors.lastname: Uğurbil
mesh_terms: D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology*; D017352:Echo-Planar Imaging / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013113:Spin Labels
chemical_list: D013113:Spin Labels