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

PURPOSE

The purpose of this work was to accurately characterize the spectral properties of hyperpolarized Xe in patients with idiopathic pulmonary fibrosis (IPF) compared to healthy volunteers.

METHODS

Subjects underwent hyperpolarized Xe 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≈22 °). 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.

RESULTS

Three 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 0.6 ppm more negative (P = 0.009), the line widths of both barrier peaks were ∼2 ppm narrower (P < 0.001), and the starting phase of barrier 1 was 20.3 ° higher (P =  0.01). Moreover, the ratio RBC:barriers was reduced by 52.9% in IPF (P < 0.001).

CONCLUSIONS

The accurate decomposition of Xe 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 gas transfer. Magn Reson Med 78:1306-1315, 2017. © 2016 International Society for Magnetic Resonance in Medicine.