title: Radiofrequency pulse design for the selective excitation of dissolved 129Xe.
abstract: OBJECTIVE
  To optimize radiofrequency (RF) pulses for the selective excitation of dissolved phase (129)Xe that take into account the very short T2*, while simultaneously, minimally exciting the much larger gas signal.
  
  
  METHODS
  Numerical simulations of Shinnar le-Roux pulses and binomial coefficient composite-element pulses were performed and experimentally implemented on a 1.5 Tesla (T) clinical scanner. These were compared with pulses commonly used for short T2* imaging from the literature. The pulses were then experimentally tested in vivo with healthy volunteers inhaling hyperpolarized (129)Xe using nuclear MR spectroscopy on a 1.5T clinical scanner.
  
  
  RESULTS
  Standard RF excitation pulses inadvertently excite the gas compartment, or are long enough that the T2* of the dissolved compartment deteriorates the received signal. Amplitude modulated binomial composite pulses perform well being short and having high selectivity, however, deteriorate at high amplifier gain setting. Composite pulses using pulse width modulation provide the desired frequency response even in these nonlinear, high gain regimes.
  
  
  CONCLUSIONS
  Composite pulses provide a means of very narrow band frequency selectivity in a short duration pulse that is well suited to dissolved (129)Xe imaging. Pulse width modulation maintains the desired frequency response even in the presence of amplitude distortion.
authors.affiliation: Unit of Academic Radiology, University of Sheffield, Sheffield, United Kingdom.
authors.forename: General
authors.initials: G
authors.lastname: Leung
authors.affiliation: Unit of Academic Radiology, University of Sheffield, Sheffield, United Kingdom.
authors.forename: Graham
authors.initials: G
authors.lastname: Norquay
authors.affiliation: GE Global Research, Munich, Germany.
authors.forename: Rolf F
authors.initials: RF
authors.lastname: Schulte
authors.affiliation: Unit of Academic Radiology, University of Sheffield, Sheffield, United Kingdom.
authors.forename: Jim M
authors.initials: JM
authors.lastname: Wild
mesh_terms: D000465:Algorithms; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008168:Lung / Q000033:anatomy & histology / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D011846:Radio Waves; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012996:Solutions; D014979:Xenon Isotopes / Q000493:pharmacokinetics*
chemical_list: D019275:Radiopharmaceuticals; D012996:Solutions; D014979:Xenon Isotopes
keywords: composite pulse; dissolved xenon; hyperpolarized; lung; selective excitation