Comparison of He and Xe MRI for evaluation of lung microstructure and ventilation at 1.5T.

BACKGROUND

To support translational lung MRI research with hyperpolarized Xe gas, comprehensive evaluation of derived quantitative lung function measures against established measures from He MRI is required. Few comparative studies have been performed to date, only at 3T, and multisession repeatability of Xe functional metrics have not been reported.

PURPOSE/HYPOTHESIS: To compare hyperpolarized Xe and He MRI-derived quantitative metrics of lung ventilation and microstructure, and their repeatability, at 1.5T.

STUDY TYPE

Retrospective.

POPULATION

Fourteen healthy nonsmokers (HN), five exsmokers (ES), five patients with chronic obstructive pulmonary disease (COPD), and 16 patients with nonsmall-cell lung cancer (NSCLC).

FIELD STRENGTH/SEQUENCE: 1.5T. NSCLC, COPD patients and selected HN subjects underwent 3D balanced steady-state free-precession lung ventilation MRI using both He and Xe. Selected HN, all ES, and COPD patients underwent 2D multislice spoiled gradient-echo diffusion-weighted lung MRI using both hyperpolarized gas nuclei.

ASSESSMENT

Ventilated volume percentages (VV%) and mean apparent diffusion coefficients (ADC) were derived from imaging. COPD patients performed the whole MR protocol in four separate scan sessions to assess repeatability. Same-day pulmonary function tests were performed.

STATISTICAL TESTS

Intermetric correlations: Spearman's coefficient. Intergroup/internuclei differences: analysis of variance / Wilcoxon's signed rank. Repeatability: coefficient of variation (CV), intraclass correlation (ICC) coefficient.

RESULTS

A significant positive correlation between He and Xe VV% was observed (r = 0.860, P < 0.001). VV% was larger for He than Xe (P = 0.001); average bias, 8.79%. A strong correlation between mean He and Xe ADC was obtained (r = 0.922, P < 0.001). MR parameters exhibited good correlations with pulmonary function tests. In COPD patients, mean CV of He and Xe VV% was 4.08% and 13.01%, respectively, with ICC coefficients of 0.541 (P = 0.061) and 0.458 (P = 0.095). Mean He and Xe ADC values were highly repeatable (mean CV: 2.98%, 2.77%, respectively; ICC: 0.995, P < 0.001; 0.936, P < 0.001). DATA CONCLUSION: Xe lung MRI provides near-equivalent information to He for quantitative lung ventilation and microstructural MRI at 1.5T.

LEVEL OF EVIDENCE

3 Technical Efficacy Stage 2 J. Magn. Reson. Imaging 2018.