Lung Volume Dependence and Repeatability of Hyperpolarized ¹²⁹Xe MRI Gas Uptake Metrics in Healthy Volunteers and Participants with COPD

Purpose: To assess the effect of lung volume on measured values and repeatability of xenon 129 (Xe-129) gas uptake metrics in healthy volunteers and participants with chronic obstructive pulmonary disease (COPD).Materials and Methods: This Health Insurance Portability and Accountability Act-compliant prospective study included data (March 2014-December 2015) from 49 participants (19 with COPD [mean age, 67 years & PLUSMN; 9 (SD)]; nine women]; 25 older healthy volunteers [mean age, 59 years & PLUSMN; 10; 20 women]; and five young healthy women [mean age, 23 years & PLUSMN; 3]). Thirty-two participants underwent repeated Xe-129 and same-breath-hold proton MRI at residual volume plus one-third forced vital capacity (RV+FVC/3), with 29 also undergoing one examination at total lung capacity (TLC). The remaining 17 participants underwent imaging at TLC, RV+FVC/3, and residual volume (RV). Signal ratios between membrane, red blood cell (RBC), and gas-phase compartments were calculated using hierarchical iterative decomposition of water and fat with echo asymmetry and least-squares estimation (ie, IDEAL). Repeatability was assessed using coefficient of variation and intraclass correlation coefficient, and volume relationships were assessed using Spearman correlation and Wilcoxon rank sum tests. Results: Gas uptake metrics were repeatable at RV+FVC/3 (intraclass correlation coefficient = 0.88 for membrane/gas; 0.71 for RBC/ gas, and 0.88 for RBC/membrane). Relative ratio changes were highly correlated with relative volume changes for membrane/gas (r = -0.97) and RBC/gas (r = -0.93). Membrane/gas and RBC/gas measured at RV+FVC/3 were significantly lower in the COPD group than the corresponding healthy group (P & LE; .001). However, these differences lessened upon correction for individual volume differences (P = .23 for membrane/gas; P = .09 for RBC/gas). Conclusion: Dissolved-phase Xe-129 MRI-derived gas uptake metrics were repeatable but highly dependent on lung volume during measurement.