Establishing an accurate gas phase reference frequency to quantify super(129)Xe chemical shifts in vivo

• Published in: Magnetic resonance in medicine 2017-04, Vol.77 (4), p.1438-1445
• Main Authors: Virgincar, Rohan S, Robertson, Scott H, Nouls, John, Degan, Simone, Schrank, Geoffry M, He, Mu, Driehuys, Bastiaan
• Format: Article
• Language: English
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.26229

Purpose super(129)Xe 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-N sub(2), Xe-Xe, and Xe-O sub(2) interactions. In this study, we addressed this by introducing a robust method to determine the 0 ppm super(129)Xe reference from in vivo data. Methods Respiratory-gated hyperpolarized super(129)Xe 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. Results Gas-phase super(129)Xe exhibited two distinct resonances corresponding to super(129)Xe in conducting airways (varying from -0.6 plus or minus 0.2 to 1.3 plus or minus 0.3 ppm) and alveoli (relatively stable, at -2.2 plus or minus 0.1 ppm). Dissolved-phase super(129)Xe exhibited five reproducible resonances in the thorax at 198.4 plus or minus 0.4, 195.5 plus or minus 0.4, 193.9 plus or minus 0.2, 191.3 plus or minus 0.2, and 190.7 plus or minus 0.3 ppm. Conclusion The alveolar super(129)Xe 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.