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

In this study, the effect of lung volume on quantitative measures of lung ventilation was investigated using MRI with hyperpolarized 3He and 129Xe. Six volunteers were imaged with hyperpolarized 3He at five different lung volumes (residual volume (RV), RV+1L, functional residual capacity (FRC), FRC+1L and total lung capacity (TLC)), and three were also imaged with hyperpolarized 129Xe. Imaging at each of the lung volumes was repeated twice on the same day with corresponding 1H lung anatomical images. Percentage 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 3He MRI data, the coefficient of variation of %VV was less than 1.5% and less than 5.5% for Hscore at all lung volumes, whilst for 129Xe data the values were 4% and 10% respectively. Generally, %VV generated from 129Xe images was lower than that seen from 3He images. The good repeatability of 3He %VV found here supports prior publications showing that percentage 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.