ABSTRACT
Introduction: Microvascular abnormalities and impaired 129Xe gas transfer have been observed in patients with COVID 19. The progression of pathophysiological pulmonary changes during the post acute period in these patients remains unclear. Methods: Patients who were hospitalised due to COVID 19 pneumonia underwent a pulmonary 1H and 129Xe MRI protocol at 6, 12, 25 and 50 weeks after hospital admission. The imaging protocol included: ultra short echo time, dynamic contrast enhanced lung perfusion, 129Xe lung ventilation, 129Xe diffusion weighted and 129Xe 3D spectroscopic imaging of gas exchange. Results: 9 patients were recruited and underwent MRI at 6 (n=9), 12 (n=9), 25 (n=6) and 50 (n=3) weeks after hospital admission. At 6 weeks after hospital admission, patients demonstrated impaired 129Xe gas transfer (RBC:M) but normal lung microstructure (ADC, LmD). Minor ventilation abnormalities present in four patients were largely resolved in the 6 to 25 week period. At 12 week follow up, all patients with lung perfusion data available (n=6) showed an increase in both pulmonary blood volume and flow when compared to 6 weeks, though this was not statistically significant. At 12 and 25 week follow up, significant improvements in 129Xe gas transfer were observed compared to 6 week examinations, however 129Xe gas transfer remained abnormally low. Conclusions: This study demonstrates that multinuclear MRI is sensitive to functional pulmonary changes in the follow up of patients who were hospitalised with COVID 19. Persistent impairment of xenon transfer may represent a physiological mechanism underlying ongoing symptoms in some patients and may indicate damage to the pulmonary microcirculation.