Assessment of the influence of lung inflation state on the quantitative parameters derived from hyperpolarized gas lung ventilation MRI in healthy volunteers

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 (Hscore)] were evaluated. Increased ventilation heterogeneity, quantified by reduced %VV and increased Hscore, 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 Hscore 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 Hscore. The results suggest that imaging patients at different lung volumes may help to elucidate obstructive disease pathophysiology and progression.