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

Abstract

Purpose: The purpose of this work was to accurately characterize the spectral properties of hyperpolarized 129 Xe in patients with idiopathic pulmonary fibrosis (IPF) compared to healthy volunteers.

Methods: Subjects underwent hyperpolarized 129 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 129 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 129 Xe gas transfer. Magn Reson Med 78:1306-1315, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Keywords: IPF; hyperpolarized 129Xe; idiopathic pulmonary fibrosis; spectroscopy.

© 2016 International Society for Magnetic Resonance in Medicine.

Figures

Figure 1

Decomposing the dissolved-phase 129Xe spectrum of a representative IPF subject. (a) Using 2 peaks resulted in non-negligible and patterned error in both the time and spectral domains. (b) The error was largely eliminated when decomposed into 3 peaks consisting of one RBC and two barrier resonances.

Figure 2

Decomposing the dissolved-phase 129Xe spectrum in a representative healthy subject. a) Using 2 peaks resulted in residual error that was small, but patterned in the time and spectral domains. b) The error was reduced to the noise floor by decomposing the spectrum into 3 peaks.

Figure 3

For both 2- and 3-peak fits, the RBC:barrier ratio is statistically reduced in IPF subjects relative to healthy subjects. * indicates a statistical difference between groups (P

Figure 4

Comparing 2- vs 3-peak fits among healthy subjects (green) and subjects with IPF (red). * indicates a statistical difference between groups (P

Figure 5

3-peak RBC:barriers ratio correlated strongly with DLCO and FVC. Green crosses represent healthy volunteers, red circles represent subjects with IPF, and black line represents the linear fit.