Persistent isolated impairment of gas transfer following COVID-19 pneumonitis relates to perfusion defects on dual-energy computed tomography

Breathlessness is common in patients after COVID-19 [1]. Patients may have an isolated impairment of gas transfer (diffusion of the lung for carbon monoxide, DLCO) at lung function testing, often without obvious interstitial lung disease or classical pulmonary emboli (PE) on imaging. Iodine maps from post-COVID patients undergoing dual energy computed tomography (DECT) demonstrate hypoenhancement in areas of normal lung parenchyma [2] ( figure 1 ). We hypothesized that in breathless patients recovering from COVID-19, low DLCO would correlate with a CT marker of lung perfusion, measured using DECT-derived iodine enhancement, including in patients where parenchymal disease was absent. As an even more specific indicator for the pulmonary vascular compartment, we hypothesized that KCO (DLCO corrected for alveolar volume) would even better correlate with DECT perfusion, and more so than forced vital capacity (FVC) and CT measures of interstitial lung involvement.