In subjects with chronic obstructive pulmonary disease (COPD), hyperpolarized xenon-129 ((129)Xe) magnetic resonance imaging (MRI) reveals significantly greater ventilation defects than hyperpolarized helium-3 ((3)He) MRI. The physiological and/or morphological determinants of ventilation defects and the differences observed between hyperpolarized (3)He and (129)Xe MRI are not yet understood. Here we aimed to determine the structural basis for the differences in ventilation observed between (3)He and (129)Xe MRI in subjects with COPD using apparent diffusion coefficients (ADC) and computed tomography (CT). Ten COPD ex-smokers provided written, informed consent and underwent MRI, CT, spirometry, and plethysmography. (3)He and (129)Xe MRI ventilation volume was generated using semiautomated segmentation, and ADC maps were registered to generate ADC values for lung regions of interest ventilated by both gases (ADCHX) and by (3)He gas only (ADCHO). CT wall area percentage and the lowest 15th percentile point of the CT lung density histogram (HU15%) were also evaluated. For lung regions accessed by (3)He gas only, mean (3)He ADCHO was significantly greater than for regions accessed by both gases (ADCHO = 0.503 ± 0.119 cm(2)/s, ADCHX = 0.470 ± 0.125 cm(2)/s, P < 0.0001). The difference between (3)He and (129)Xe ventilation volume was significantly correlated with CT HU15% (r = -65, P = 0.04) and (3)He ADCHO (r = 0.70, P = 0.02), but not CT wall area percentage (r = -0.34, P = 0.33). In conclusion, in this small study in COPD subjects, we observed significantly decreased (129)Xe MRI ventilation compared with (3)He MRI, and these regions of decreased (129)Xe ventilation were spatially and significantly correlated with regions of increased pulmonary emphysema, but not airway wall thickness.

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Pulmonary magnetic resonance imaging using hyperpolarised 129Xe gas (XeMRI) can quantify ventilation inhomogeneity by measuring the percentage of unventilated lung volume (ventilation defect per cent (VDP)). While previous studies have demonstrated its sensitivity for detecting early cystic fibrosis (CF) lung disease, the utility of XeMRI to monitor response to therapy in CF is unknown. The aim of this study was to assess the ability of XeMRI to capture treatment response in paediatric CF patients undergoing inpatient antibiotic treatment for a pulmonary exacerbation.15 CF patients aged 8–18 years underwent XeMRI, spirometry, plethysmography and multiple-breath nitrogen washout at the beginning and end of inpatient treatment of a pulmonary exacerbation. VDP was calculated from XeMRI images obtained during a static breath hold using semi-automated k-means clustering and linear binning approaches.XeMRI was well tolerated. VDP, lung clearance index and the forced expiratory volume in 1 s all improved with treatment; however, response was not uniform in individual patients. Of all outcome measures, VDP showed the largest relative improvement (−42.1%, 95% CI −52.1–−31.9%, p<0.0001).These data support further investigation of XeMRI as a tool to capture treatment response in CF lung disease.

Background: The ventilation defect percent (VDP), measured from hyperpolarized (HP) 129 Xe magnetic resonance imaging (MRI), is sensitive to functional changes in cystic fibrosis (CF) lung disease. The purpose of this study was to measure and compare VDP from HP 129 Xe MRI acquired at two institutions in stable pediatric CF subjects with preserved lung function. Methods: This retrospective analysis included 26 participants from two institutions (18 CF, 8 healthy, age range 10-17). Pulmonary function tests, N 2 multiple breath washout (to measure lung clearance index, LCI), and HP 129 Xe MRI were performed. VDP measurements were compared between two trained analysts using meananchored linear binning. Correlations were investigated for VDP compared to the forced expiratory volume in one second (FEV 1 ) and LCI. Results: VDP measurements agreed for the two analysts with an intraclass correlation coefficient of 0.99. In the combined dataset, VDP measured by Analyst 1 was 5.96 ± 1.82% and 15.96 ± 6.76% for the healthy and CF groups, respectively (p = .0004). Analyst 2 showed similar differences between healthy and CF (p = .0003). VDP measured by either analyst was shown to correlate with FEV 1 (R 2 = 0.33, p = .003; and R 2 = 0.26, p = .009 for Analysts 1 and 2, respectively) and LCI (R 2 = 0.76, p b .0001; and R 2 = 0.77, p b .0001 for Analysts 1 and 2, respectively). Conclusion: HP 129 Xe MRI provides a robust measurement of ventilation heterogeneity in stable pediatric CF subjects at two sites. Since measurements performed at two sites yielded similar VDP values with near-identical values between different analysts, implementation of the technique in multi-center trials in CF appears feasible.