title: Distributing coil elements in three dimensions enhances parallel transmission multiband RF performance: A simulation study in the human brain at 7 Tesla.
abstract: We explore the advantages of using a double-ring radiofrequency (RF) array and slice orientation to design parallel transmission (pTx) multiband (MB) pulses for simultaneous multislice (SMS) imaging with whole-brain coverage at 7 Tesla (T).
  
  
  
  A double-ring head array with 16 elements split evenly in two rings stacked in the z-direction was modeled and compared with two single-ring arrays consisting of 8 or 16 elements. The array performance was evaluated by designing band-specific pTx MB pulses with local specific absorption rate (SAR) control. The impact of slice orientations was also investigated.
  
  
  
  The double-ring array consistently and significantly outperformed the other two single-ring arrays, with peak local SAR reduced by up to 40% at a fixed excitation error of 0.024. For all three arrays, exciting sagittal or coronal slices yielded better RF performance than exciting axial or oblique slices.
  
  
  
  A double-ring RF array can be used to drastically improve SAR versus excitation fidelity tradeoff for pTx MB pulse design for brain imaging at 7 T; therefore, it is preferable against single-ring RF array designs when pursuing various biomedical applications of pTx SMS imaging. In comparing the stripline arrays, coronal and sagittal slices are more advantageous than axial and oblique slices for pTx MB pulses. Magn Reson Med 75:2464-2472, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN.
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Wu
authors.affiliation: University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN.
authors.forename: Jinfeng
authors.initials: J
authors.lastname: Tian
authors.affiliation: University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schmitter
authors.affiliation: University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN.
authors.forename: J Tommy
authors.initials: JT
authors.lastname: Vaughan
authors.affiliation: University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN.
authors.forename: Kâmil
authors.initials: K
authors.lastname: Uğurbil
authors.affiliation: University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN.
authors.forename: Pierre-François
authors.initials: PF
authors.lastname: Van de Moortele
mesh_terms: D001921:Brain / Q000000981:diagnostic imaging*; D004867:Equipment Design; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D008954:Models, Biological; D019047:Phantoms, Imaging
keywords: high-field MRI; multiring RF array design; parallel transmit multiband pulse design; simultaneous multislice imaging; transmit B1 homogenization