title: Localized, gradient-reversed ultrafast z-spectroscopy in vivo at 7T.
abstract: To collect ultrafast z-spectra in vivo in situations where voxel homogeneity cannot be assured.
  
  
  
  Saturating in the presence of a gradient encodes the frequency offset spatially across a voxel. This encoding can be resolved by applying a similar gradient during readout. Acquiring additional scans with the gradient polarity reversed effectively mirrors the spatial locations of the frequency offsets so that the same physical location of a positive offset in the original scan will contribute a negative offset in the gradient-reversed scan.
  
  
  
  Gradient-reversed ultrafast z-spectroscopy (GRUFZS) was implemented and tested in a modified, localized PRESS sequence at 7T. Lysine phantoms were scanned at various concentrations and compared with coventionally-acquired z-spectra. Scans were acquired in vivo in human brain from homogeneous and inhomogeneous voxels with the ultrafast direction cycled between read, phase, and slice. Results were compared to those from a similar conventional z-spectroscopy PRESS-based sequence.
  
  
  
  Asymmetry spectra from GRUFZS are more consistent and reliable than those without gradient reversal and are comparable to those from conventional z-spectroscopy. GRUFZS offers significant acceleration in data acquisition compared to traditional chemical exchange saturation transfer methods with high spectral resolution and showed higher relative SNR effficiency.
  
  
  
  GRUFZS offers a method of collecting ultrafast z-spectra in voxels with the inhomogeneity often found in vivo. Magn Reson Med 76:1039-1046, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Center for Magnetic Resonance and Optical Imaging, Department of Radiology, University of Pennsylvania, Phildelphia PA.
authors.forename: Neil E
authors.initials: NE
authors.lastname: Wilson
authors.affiliation: Center for Magnetic Resonance and Optical Imaging, Department of Radiology, University of Pennsylvania, Phildelphia PA.
authors.forename: Kevin
authors.initials: K
authors.lastname: D'Aquilla
authors.affiliation: Center for Magnetic Resonance and Optical Imaging, Department of Radiology, University of Pennsylvania, Phildelphia PA.
authors.forename: Catherine
authors.initials: C
authors.lastname: Debrosse
authors.affiliation: Center for Magnetic Resonance and Optical Imaging, Department of Radiology, University of Pennsylvania, Phildelphia PA.
authors.forename: Hari
authors.initials: H
authors.lastname: Hariharan
authors.affiliation: Center for Magnetic Resonance and Optical Imaging, Department of Radiology, University of Pennsylvania, Phildelphia PA.
authors.forename: Ravinder
authors.initials: R
authors.lastname: Reddy
mesh_terms: D000465:Algorithms; D001921:Brain / Q000378:metabolism*; D006801:Humans; D008239:Lysine / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D014018:Tissue Distribution
chemical_list: D008239:Lysine
keywords: CEST; GRUFZS; brain; glutamate; high field; ultrafast z-spectroscopy