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

Purpose To assess the feasibility of hyperpolarized 129 Xe 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 T 1 and (2) variable T 1 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 129 Xe MRI was performed during consecutive breaths of air following a single 129 Xe 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 T 1 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 T 1 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 T 1 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 129 Xe multiple‐breath washout imaging is feasible in pediatric participants with CF, and inclusion of variable T 1 modeling reduces bias in the fractional ventilation measurements.