Assessment of Global and Regional Lung Compliance in Pulmonary Fibrosis With Hyperpolarized Gas MRI

Background: Lung compliance, a biomarker of pulmonary fibrosis, is generally measured globally. Hyperpolarized 129Xegas MRI offers the potential to evaluate lung compliance regionally, allowing for visualization of changes in lung compliance associated with fibrosis.
Purpose: To assess global and regional lung compliance in a rat model of pulmonary fibrosis using hyperpolarized 129Xe gas MRI.
Study Type: Prospective.
Animal Model: Twenty Sprague–Dawley male rats with bleomycin-induced fibrosis model (N = 10) and saline-treated controls (N = 10).
Field Strength/Sequence: 7-T, fast low-angle shot (FLASH) sequence.
Assessment: Lung compliance was determined by fitting lung volumes derived from segmented 129Xe MRI with an iterative selection method, to corresponding airway pressures. Similarly, lung compliance was obtained with computed tomography for cross-validation. Direction-dependencies of lung compliance were characterized by regional lung compliance ratios (R) in different directions. Pulmonary function tests (PFTs) and histological analysis were used to validate the pulmonary fibrosis model and assess its correlation with 129Xe lung compliance.
Statistical Tests: Shapiro–Wilk tests, unpaired and paired t-tests, Mann–Whitney U and Wilcoxon signed-rank tests, and Pearson correlation coefficients. P < 0.05 was considered statistically significant.
Results: For the entire lung, the global and regional lung compliance measured with 129Xe gas MRI showed significant differences between the groups, and correlated with the global lung compliance measured using PFTs (global: r = 0.891; regional: r = 0.873). Additionally, for the control group, significant difference was found in mean regional compliance between areas, eg, 0.37 (0.32, 0.39)
104 mL/cm H2O and 0.47 (0.41, 0.56)
104 mL/cm H2O for apical and basal lung, respectively. The apical-basal direction R was 1.12  0.09 and 1.35  0.13 for fibrosis and control groups, respectively, indicating a significant difference.
Data Conclusion: Our findings demonstrate the feasibility of using hyperpolarized gas MRI to assess regional lung compliance.