Uncovering a third dissolved-phase 129Xe resonance in the human lung: Quantifying spectroscopic features in healthy subjects and patients with idiopathic pulmonary fibrosis

PurposeThe purpose of this work was to accurately characterize the spectral properties of hyperpolarized Xe-129 in patients with idiopathic pulmonary fibrosis (IPF) compared to healthy volunteers. MethodsSubjects underwent hyperpolarized Xe-129 breath-hold spectroscopy, during which 38 dissolved-phase free induction decays (FIDs) were acquired after reaching steady state (echo time/repetition time=0.875/50 ms; bandwidth=8.06 kHz; flip angle approximate to 22 degrees). FIDs were averaged and then decomposed into multiple spectral components using time-domain curve fitting. The resulting amplitudes, frequencies, line widths, and starting phases of each component were compared among groups using a Mann-Whitney-Wilcoxon U test. ResultsThree dissolved-phase resonances, consisting of red blood cells (RBCs) and two barrier compartments, were consistently identified in all subjects. In subjects with IPF relative to healthy volunteers, the RBC frequency was 0.70 parts per million (ppm) more negative (P=0.05), the chemical shift of barrier 2 was 0.6ppm more negative (P=0.009), the line widths of both barrier peaks were approximate to 2ppm narrower (P<0.001), and the starting phase of barrier 1 was 20.3 degrees higher (P= 0.01). Moreover, the ratio RBC:barriers was reduced by 52.9% in IPF (P<0.001). ConclusionsThe accurate decomposition of Xe-129 spectra not only has merit for developing a global metric of pulmonary function, but also provides necessary insights to optimize phase-sensitive methods for imaging Xe-129 gas transfer. Magn Reson Med 78:1306-1315, 2017. (c) 2016 International Society for Magnetic Resonance in Medicine.