title: A generalized slab-wise framework for parallel transmit multiband RF pulse design.
abstract: OBJECTIVE
  We propose a new slab-wise framework to design parallel transmit multiband pulses for volumetric simultaneous multislice imaging with a large field of view along the slice direction (FOVs).
  
  
  METHODS
  The slab-wise framework divides FOVs into a few contiguous slabs and optimizes pulses for each slab. Effects of relevant design parameters including slab number and transmit B1 (B1+) mapping slice placement were investigated for human brain imaging by designing pulses with global or local SAR control based on electromagnetic simulations of a 7T head RF array. Pulse design using in vivo B1+ maps was demonstrated and evaluated with Bloch simulations.
  
  
  RESULTS
  RF performance with respect to SAR reduction or B1+ homogenization across the entire human brain improved with increasing slabs; however, this improvement was nonlinear and leveled off at ∼12 slabs when the slab thickness reduced to ∼12 mm. The impact of using different slice placements for B1+ mapping was small.
  
  
  CONCLUSIONS
  Compared with slice-wise approaches where each of the many imaging slices requires both B1+ mapping and pulse optimization, the proposed slab-wise design framework attained comparable RF performance while drastically reducing the number of required pulses; therefore, it can be used to increase time efficiency for B1+ mapping, pulse calculation, and sequence preparation.
authors.affiliation: University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA.
authors.forename: Xiaoping
authors.identifier: http://orcid.org/0000-0001-6021-9088
authors.initials: X
authors.lastname: Wu
authors.affiliation: University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schmitter
authors.affiliation: University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Auerbach
authors.affiliation: University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA.
authors.forename: Kâmil
authors.initials: K
authors.lastname: Uğurbil
authors.affiliation: University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA.
authors.forename: Pierre-François
authors.initials: PF
authors.lastname: Van de Moortele
mesh_terms: D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D059906:Neuroimaging / Q000379:methods*
keywords: high-field MRI; multiband RF pulse design; parallel excitation; simultaneous multislice imaging; transmit B1 homogenization