title: 2D Pulses using spatially dependent frequency sweeping.
abstract: To introduce a method of designing two-dimensional (2D) frequency-modulated pulses that produce phase coherence in a spatiotemporal manner. Uniquely, this class of pulses provides the ability to compensate for field inhomogeneity using a spatiotemporally dependent trajectory of maximum coherence in a single-shot.
  
  
  
  A pulse design method based on a k-space description is developed. Bloch simulations and phantom experiments are used to demonstrate sequential spatiotemporal phase coherence and compensation for B1+ and B0inhomogeneity.
  
  
  
  In the presence of modulated gradients, the 2D frequency-modulated pulses were shown to excite a cylinder in a selective manner. With a surface coil transmitter, compensation of the effect of B1+ inhomogeneity was experimentally verified, in agreement with simulation results. In addition, simulations were used to demonstrate partial compensation for B0inhomogeneity.
  
  
  
  The 2D frequency-modulated pulses are a new class of pulses that generate phase coherence sequentially along a spatial trajectory determined by gradient- and frequency-modulated functions. By exploiting their spatiotemporal nature, 2D frequency-modulated pulses can compensate for spatial variation of the radiofrequency field in a single-shot excitation. Preliminary results shown suggest extensions might also be used to compensate for static field inhomogeneity. Magn Reson Med 76:1364-1374, 2016. © 2015 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minnesota, USA.|Department of Electrical and Computer Engineering, University of Minnesota, Minnesota, USA.|Department of Medicine, Cardiovascular Division, University of Minnesota, Minnesota, USA.
authors.forename: Albert
authors.initials: A
authors.lastname: Jang
authors.affiliation: Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minnesota, USA.
authors.forename: Naoharu
authors.initials: N
authors.lastname: Kobayashi
authors.affiliation: Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minnesota, USA.
authors.forename: Steen
authors.initials: S
authors.lastname: Moeller
authors.affiliation: Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minnesota, USA.|Department of Electrical and Computer Engineering, University of Minnesota, Minnesota, USA.
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Vaughan
authors.affiliation: Department of Electrical and Computer Engineering, University of Minnesota, Minnesota, USA.|Department of Medicine, Cardiovascular Division, University of Minnesota, Minnesota, USA.
authors.forename: Jianyi
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minnesota, USA. gar@cmrr.umn.edu.
authors.forename: Michael
authors.initials: M
authors.lastname: Garwood
mesh_terms: D000465:Algorithms; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D062211:Spatio-Temporal Analysis
keywords: MRI; chirp; frequency-modulated pulse; hyperbolic secant; magnetic field inhomogeneity; spatiotemporal encoding