Quantitative evaluation of hyperpolarized helium-3 magnetic resonance imaging of lung function variability in cystic fibrosis

Abstract

Rationale and objectives: To better understand imaging measurement precision and reproducibility and to provide guidance for measurements in individual cystic fibrosis (CF) subjects, we evaluated CF adults on two occasions 7 ± 2 days apart using spirometry, plethysmography, and hyperpolarized helium-3 ((3)He) magnetic resonance imaging (MRI).

Materials and methods: Twelve CF subjects underwent spirometry, plethysmography, and (3)He MRI twice within 7 ± 2 days, reporting (3)He ventilation defect volume (VDV) and ventilation defect percent (VDP).

Results: Based on measurement variability, the smallest detectable difference (SDD) for (3)He VDV and VDP was determined to be 120 mL and 2%, respectively. Although no significant difference in spirometry or plethysmography was detected after 7 days, there was a significant difference in mean (3)He VDV (130 mL ± 250 mL, P < .0001) and VDP (3% ± 4%, P < .0001), although baseline and 7-day measurements were highly correlated (VDV: r = .85, P = .001; VDP: r = .94, P < .0001). We estimated the sample sizes required to detect a 5%/7%/10% change in (3)He VDP as 60/15/5 subjects per group.

Conclusion: Hyperpolarized (3)He MRI VDP measurement precision resulted in an SDD for individual CF subjects of 2%, indicating that changes greater than this can be attributed to lung functional changes and not measurement error. After 7 days, significant changes in mean (3)He VDV and VDP were detected and these changes were not reflected by changes in pulmonary function measurements. These findings demonstrate the high sensitivity and reproducibility of (3)He MRI functional imaging that permits the use of relatively small samples sizes in CF interventional studies.