Quantitative analysis of hyperpolarized ¹²⁹Xe ventilation imaging in healthy volunteers and subjects with chronic obstructive pulmonary disease

In this study, hyperpolarized ¹²⁹Xe MR ventilation and ¹H anatomical images were obtained from three subject groups: young healthy volunteers (HVs), subjects with chronic obstructive pulmonary disease (COPD) and age-matched controls (AMCs). Ventilation images were quantified by two methods: an expert reader-based ventilation defect score percentage (VDS%) and a semi-automated segmentation-based ventilation defect percentage (VDP). Reader-based values were assigned by two experienced radiologists and resolved by consensus. In the semi-automated analysis, ¹H anatomical images and ¹²⁹Xe ventilation images were both segmented following registration to obtain the thoracic cavity volume and ventilated volume, respectively, which were then expressed as a ratio to obtain the VDP. Ventilation images were also characterized by generating signal intensity histograms from voxels within the thoracic cavity volume, and heterogeneity was analyzed using the coefficient of variation (CV). The reader-based VDS% correlated strongly with the semi-automatically generated VDP (r=0.97, p<0.0001) and with CV (r=0.82, p<0.0001). Both ¹²⁹Xe ventilation defect scoring metrics readily separated the three groups from one another and correlated significantly with the forced expiratory volume in 1s (FEV₁) (VDS%: r=-0.78, p=0.0002; VDP: r=-0.79, p=0.0003; CV: r=-0.66, p=0.0059) and other pulmonary function tests. In the healthy subject groups (HVs and AMCs), the prevalence of ventilation defects also increased with age (VDS%: r=0.61, p=0.0002; VDP: r=0.63, p=0.0002). Moreover, ventilation histograms and their associated CVs distinguished between subjects with COPD with similar ventilation defect scores, but visibly different ventilation patterns.