Assessing the feasibility of hyperpolarized 129 Xe multiple-breath washout MRI in pediatric cystic fibrosis

Purpose: To assess the feasibility of hyperpolarized 129Xe multiple‐breath washout MRI in pediatric cystic fibrosis (CF) participants with preserved lung function. Fractional ventilation (r), defined as the fractional gas replacement per breath, was mapped using 2 signal models: (1) constant T1 and (2) variable T1 as a function of the hyperpolarized gas washout. Methods: A total of 17 pediatric participants were recruited (mean age 11.7 ± 2.8 years), including 7 children with clinically stable CF and 10 aged‐matched healthy controls. Pulmonary function tests were performed, including spirometry, to measure the forced expiratory volume in 1 second and nitrogen multiple‐breath washout to measure the lung clearance index. Hyperpolarized 129Xe MRI was performed during consecutive breaths of air following a single 129Xe inhalation, and fractional ventilation maps were calculated. Results: The forced expiratory volume in 1 second was similar in both groups (P = .32), but there was a statistically significant difference in lung clearance index between healthy and CF participants (P = .001). With variable T1 modeling, CF participants had a mean r of 0.44 ± 0.08 and healthy participants had a mean r of 0.37 ± 0.12 (P = .20). With constant T1 modeling, CF participants had a mean r′ of 0.48 ± 0.08, and healthy participants had a mean r′ of 0.43 ± 0.12 (P = .32). Therefore, assuming a constant T1 leads to a relative bias in r of 15.1% ± 6.4% and 20.8% ± 7.4% for CF and healthy participants, respectively (P = .12). Conclusion: This study demonstrates that hyperpolarized 129Xe multiple‐breath washout imaging is feasible in pediatric participants with CF, and inclusion of variable T1 modeling reduces bias in the fractional ventilation measurements.Canadian Institutes of Health Research. Grant Numbers: MOP 123431, PJT 153099 Hospital for Sick Children. Grant Number: Cystic Fibrosis Research Catalyst Natural Sciences and Engineering Research Council of Canada. Grant Number: RGPIN 217015‐2013 Mitacs Cystic Fibrosis Canad