Abstract
In this study, the effect of lung volume on quantitative measures of lung ventilation was investigated using MRI with hyperpolarized (3)He and (129)Xe. Six volunteers were imaged with hyperpolarized (3)He at five different lung volumes [residual volume (RV), RV + 1 liter (1L), functional residual capacity (FRC), FRC + 1L, and total lung capacity (TLC)], and three were also imaged with hyperpolarized (129)Xe. Imaging at each of the lung volumes was repeated twice on the same day with corresponding (1)H lung anatomical images. Percent lung ventilated volume (%VV) and variation of signal intensity [heterogeneity score (H(score))] were evaluated. Increased ventilation heterogeneity, quantified by reduced %VV and increased H(score), was observed at lower lung volumes with the least ventilation heterogeneity observed at TLC. For (3)He MRI data, the coefficient of variation of %VV was <1.5% and <5.5% for H(score) at all lung volumes, while for (129)Xe data the values were 4 and 10%, respectively. Generally, %VV generated from (129)Xe images was lower than that seen from (3)He images. The good repeatability of (3)He %VV found here supports prior publications showing that percent lung-ventilated volume is a robust method for assessing global lung ventilation. The greater ventilation heterogeneity observed at lower lung volumes indicates that there may be partial airway closure in healthy lungs and that lung volume should be carefully considered for reliable longitudinal measurements of %VV and H(score.) The results suggest that imaging patients at different lung volumes may help to elucidate obstructive disease pathophysiology and progression. NEW & NOTEWORTHY We present repeatability data of quantitative metrics of lung function derived from hyperpolarized helium-3, xenon-129, and proton anatomical images acquired at five lung volumes in volunteers. Increased regional ventilation heterogeneity at lower lung inflation levels was observed in the lungs of healthy volunteers.