Redistribution of inhaled hyperpolarized He3 gas during breath-hold differs by asthma severity.

The purpose of this work was to quantify the redistribution of ventilation-weighted signal in the lungs of asthmatic subjects during a breath-hold using high temporal-spatial resolution hyperpolarized (HP) He-3 MRI. HP He-3 MRI was used to obtain time-resolved, volumetric images of lung ventilation during breath-hold in 39 human subjects classified as either healthy/nondiseased (n = 14), mild-tomoderate asthmatic (n = 17), or severely asthmatic (n = 8). Signals were normalized to a standard lung volume, so that voxels within the lung from all 39 subjects could be analyzed as a group to increase statistical power and enable semiautomated classification of voxels into 1 of 5 ventilation level categories (ranging from defect to hyperintense). End-inspiratory ventilation distribution and temporal rates of mean signal change for each of the five ventilation categories were compared using ANOVA. Time rates of signal change were hypothesized to represent underlying gas redistribution processes, potentially influenced by disease. We found that mild-to-moderate asthmatic subjects showed the greatest rate of signal change, even though those with severe asthma had the greatest end-inspiration ventilation heterogeneity. The observed results support the existence of local differences in airway resistances associated with the different obstructive patterns in the lungs for severe vs. mild-to-moderate asthmatic subjects.