title: Slice profile effects on nCPMG SS-FSE.
abstract: OBJECTIVE
  To determine the effects of the RF refocusing pulse profile on the magnitude of the transverse signal smoothness throughout the echo train in non-Carr-Purcell-Meiboom-Gill (nCPMG) single-shot fast spin echo (SS-FSE) imaging and to design an RF refocusing pulse that provides improved signal stability. THEORY AND METHODS: nCPMG SS-FSE quadratic phase modulation requires sufficiently high and uniform refocusing flip angle to achieve a stable signal. Typically, refocusing pulses used in SS-FSE sequences are designed for minimum duration to minimize echo spacing and as a consequence have poor selectivity. However, delay-insensitive variable rate excitation Shinnar-Le Roux (DV-SLR) refocusing pulses can achieve both improved selectivity as well as a short duration. This class of RF pulse is compared against a traditional low time-bandwidth refocusing pulse in a nCPMG SS-FSE in simulation, phantom, and in vivo.
  
  
  RESULTS
  DV-SLR pulses achieve a more stable signal in simulation, phantom, and in vivo cases while maintaining an appropriately short duration as well as not dramatically increasing specific absorption rate (SAR) accumulation.
  
  
  CONCLUSIONS
  The nCPMG SS-FSE method demonstrates improved robustness when a more selective refocusing pulse is used. Refocusing pulses that use a time-varying excitation gradient can achieve this selectivity while maintaining short echo spacing. Magn Reson Med 79:430-438, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, California, USA.|Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
authors.forename: Eric K
authors.initials: EK
authors.lastname: Gibbons
authors.affiliation: Praecedentia Libra, Palaiseau, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Le Roux
authors.affiliation: Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Pauly
authors.affiliation: Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA.
authors.forename: Adam B
authors.initials: AB
authors.lastname: Kerr
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D017352:Echo-Planar Imaging; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D015233:Models, Statistical; D019047:Phantoms, Imaging; D011846:Radio Waves; D012984:Software
keywords: RF pulse; SS-FSE; nCPMG