Ventilation-perfusion mismatch in COPD with or without emphysema: Comparison of structural CT and functional OE-MRI

Single-slice conoral oxygen-enhanced MRI (OE-MRI) images were acquired in 24 patients with chronic obstructive pulmonary disease (COPD) and 12 healthy subjects, from which color-coded V/Q maps were extracted by pixelwise model fitting. COPD were structurally classified by percentage of low attenuation areas under -950 HU (LAA%) in matched single-slice CT images: LAA%≤1%–non-emphysema (n=8), >1%–emphysema (n=16). V/Q maps in COPD were much more heterogeneous than those in healthy subjects, while they showed similar or mildly lower heterogeneity in non-emphysematous COPD than in emphysematous COPD, which demonstrates that comparative V/Q mismatch exists in COPD even if there is no emphysema. To explore potentially different structure-function relationship in two COPD types, correlation between CT and OE-MRI parameters was measured. Median V/Q did not correlate with LLA% in COPD. However, inter-quartile range of V/Q, representing the extent of heterogeneity, was fairly correlated with LLA% in emphysematous COPD (r=0.449, p=0.017), indicating V/Q mismatch in COPD gets worse as emphysema increases. However, the correlation was not found in non-emphysematous COPD. This study elucidates that distinction between emphysematous COPD and non-emphysematous COPD does not affect the presence of V/Q imbalance substantially but that the relationship between V/Q and CT measures does vary between these two types.