Hyperpolarized 129Xenon Magnetic Resonance Imaging to Quantify Regional Ventilation Differences in Mild to Moderate Asthma: A Prospective Comparison between Semiautomated Ventilation Defect Percentage Calculation and Pulmonary Function Tests

Objectives The aim of this study was to investigate ventilation in mild to moderate asthmatic patients and age-matched controls using hyperpolarized (HP) ¹²⁹Xenon magnetic resonance imaging (MRI) and correlate findings with pulmonary function tests (PFTs). Materials and Methods This single-center, Health Insurance Portability and Accountability Act-compliant prospective study was approved by our institutional review board. Thirty subjects (10 young asthmatic patients, 26 ± 6 years; 3 males, 7 females; 10 older asthmatic patients, 64 ± 6 years; 3 males, 7 females; 10 healthy controls) were enrolled. After repeated PFTs 1 week apart, the subjects underwent 2 MRI scans within 10 minutes, inhaling 1-L volumes containing 0.5 to 1 L of ¹²⁹Xe. ¹²⁹Xe ventilation signal was quantified by linear binning, from which the ventilation defect percentage (VDP) was derived. Differences in VDP among subgroups and variability with age were evaluated using 1-tailed t tests. Correlation of VDP with PFTs was tested using Pearson correlation coefficient. Reproducibility of VDP was assessed using Bland-Altman plots, linear regression (R²), intraclass correlation coefficient, and concordance correlation coefficient. Results Ventilation defect percentage was significantly higher in young asthmatic patients versus young healthy subjects (8.4% ± 3.2% vs 5.6% ± 1.7%, P = 0.031), but not in older asthmatic patients versus age-matched controls (16.8% ± 10.3% vs 11.6% ± 6.6%, P = 0.13). Ventilation defect percentage was found to increase significantly with age (healthy, P = 0.05; asthmatic patients, P = 0.033). Ventilation defect percentage was highly reproducible (R² = 0.976; intraclass correlation coefficient, 0.977; concordance correlation coefficient, 0.976) and significantly correlated with FEV_1% (r = -0.42, P = 0.025), FEF_25%-75% (r = -0.45, P = 0.019), FEV1/FVC (r = -0.71, P < 0.0001), FeNO (r = 0.69, P < 0.0001), and RV/TLC (r = 0.51, P = 0.0067). Bland-Altman analysis showed a bias for VDP of -0.88 ± 1.52 (FEV1%, -0.33 ± 7.18). Conclusions ¹²⁹Xenon MRI is able to depict airway obstructions in mild to moderate asthma and significantly correlates with PFTs.