title: Establishing an accurate gas phase reference frequency to quantify129Xe chemical shifts in vivo.
abstract: 129Xe interacts with biological media to exhibit chemical shifts exceeding 200 ppm that report on physiology and pathology. Extracting this functional information requires shifts to be measured precisely. Historically, shifts have been reported relative to the gas-phase resonance originating from pulmonary airspaces. However, this frequency is not fixed-it is affected by bulk magnetic susceptibility, as well as Xe-N2, Xe-Xe, and Xe-O2interactions. In this study, we addressed this by introducing a robust method to determine the 0 ppm129Xe reference from in vivo data.
  
  
  
  Respiratory-gated hyperpolarized129Xe spectra from the gas- and dissolved-phases were acquired in four mice at 2T from multiple axial slices within the thoracic cavity. Complex spectra were then fitted in the time domain to identify peaks.
  
  
  
  Gas-phase129Xe exhibited two distinct resonances corresponding to129Xe in conducting airways (varying from -0.6 ± 0.2 to 1.3 ± 0.3 ppm) and alveoli (relatively stable, at -2.2 ± 0.1 ppm). Dissolved-phase129Xe exhibited five reproducible resonances in the thorax at 198.4 ± 0.4, 195.5 ± 0.4, 193.9 ± 0.2, 191.3 ± 0.2, and 190.7 ± 0.3 ppm.
  
  
  
  The alveolar129Xe resonance exhibits a stable frequency across all mice. Therefore, it can provide a reliable in vivo reference frequency by which to characterize other spectroscopic shifts. Magn Reson Med 77:1438-1445, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, North Carolina, USA.|Biomedical Engineering, Duke University, Durham, North Carolina, USA.
authors.forename: Rohan S
authors.initials: RS
authors.lastname: Virgincar
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, North Carolina, USA.|Medical Physics Graduate Program, Duke University, Durham, North Carolina, USA.
authors.forename: Scott H
authors.initials: SH
authors.lastname: Robertson
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, North Carolina, USA.|Radiology, Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: John
authors.initials: J
authors.lastname: Nouls
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, North Carolina, USA.|Center for Molecular and Biomolecular Imaging, Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: Simone
authors.initials: S
authors.lastname: Degan
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, North Carolina, USA.|Radiology, Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: Geoffry M
authors.initials: GM
authors.lastname: Schrank
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, North Carolina, USA.|Electrical and Computer Engineering, Duke University, Durham North Carolina, USA.
authors.forename: Mu
authors.initials: M
authors.lastname: He
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, North Carolina, USA.|Biomedical Engineering, Duke University, Durham, North Carolina, USA.|Medical Physics Graduate Program, Duke University, Durham, North Carolina, USA.|Radiology, Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: Bastiaan
authors.initials: B
authors.lastname: Driehuys
mesh_terms: D000818:Animals; D009682:Magnetic Resonance Spectroscopy / Q000379:methods* / Q000592:standards*; D051379:Mice; D008807:Mice, Inbred BALB C; D011650:Pulmonary Alveoli / Q000737:chemistry*; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014979:Xenon Isotopes / Q000008:administration & dosage / Q000032:analysis* / Q000592:standards*
chemical_list: D014979:Xenon Isotopes
keywords: bulk magnetic susceptibility; chemical shift; hyperpolarized 129Xe spectroscopy