Quantitative CT image-based structural and functional changes during asthma acute exacerbations

Asthma acute exacerbations (AE) have been investigated using quantitative computed tomography (QCT)-based imaging metrics, but QCT has not yet been used to investigate a comprehensive set of imaging metrics during AE. This study aims to explore imaging features, captured both at segmental and parenchymal scales, during asthma AE compared with those in stable asthma (SA). Two sets of the QCT images at total lung capacity (TLC) and functional residual capacity (FRC) were captured for 14 subjects during asthma AE and in SA phase, respectively. We calculated airway wall thickness (WT), hydraulic diameter (Dh), and airway circularity (Cr) of the 36 segmental airways; percentage of functional small airway disease (fSAD%); percentage of emphysema; tissue fraction (βtiss); and coefficient of variation of βtiss (CV of βtiss). We performed Spearman correlation tests for changes in QCT metrics and pulmonary function tests, measured in AE and SA. During asthma AE, structural metrics, that is, WT, Dh, and Cr, were not changed significantly. In functional metrics, CV of βtiss at FRC indicating the heterogeneity of lung tissue distribution was significantly increased, whereas the mean of βtiss at FRC did not change during AE. An increase of fSAD% during AE was most correlated with a decrease of forced expiratory volume in 1 s and forced vital capacity, especially in the lower lobes. This study demonstrates that the heterogeneous feature of βtiss measured at lower lobes is more noticeable during asthma AE, compared with other traditional imaging metrics. This metric could be utilized to identify unique features during asthma AE.