Longitudinal 1 H and 129 Xe Lung MRI in Patients With Post‐COVID Residual Lung Abnormalities

ABSTRACT Background It is unclear how lung function may recover in patients with residual lung abnormalities (RLAs) following COVID‐19 pneumonia. Purpose To evaluate lung function trends over time in patients with RLAs following hospitalization due to COVID‐19. Study Type Prospective, multicenter longitudinal cohort study. Population Twenty‐four participants hospitalized due to COVID‐19 with RLAs identified on CT ≥ 3 months postdischarge (median IQR age 69 (15) years; 3 female) underwent at least one MRI at 6 months ( n = 16), 1 year ( n = 19), or 2 years ( n = 14). Field Strength/Sequence 1.5 T. Dynamic contrast enhanced (DCE) 3D spoiled gradient echo, 129 Xe steady state free precession (ventilation), 129 Xe 3D spoiled gradient echo multiple b ‐value (diffusion‐weighted), 129 Xe 4‐echo flyback 3D radial (dissolved phase). Assessment Pulmonary blood flow, volume, and mean transit time (MTT) were calculated from DCE MRI. The fraction of 129 Xe signal in the red blood cells to membrane (RBC:M) was calculated from the dissolved phase 129 Xe acquisition. Ventilation defect percentage (VDP) was calculated from the 129 Xe ventilation acquisition. Mean diffusive length scale (Lm D ) was calculated from the 129 Xe diffusion‐weighted acquisition. Statistical Tests Changes in metrics with time and associations between metrics were assessed using mixed‐effect linear regression. Correlations were tested using Spearman's correlation coefficient. Regional differences were assessed using a Friedman's test with a Bonferroni adjustment. p < 0.05 was considered significant. Results Pulmonary blood flow and MTT improved significantly over time (MTT: 6 months, 15.3 (IQR, 2.0); 1 year, 15.6 (1.4); 2 years, 15.0 (5.3); pulmonary blood flow: 6 months, 75.4 (IQR, 22.0); 1 year, 83.2 (47.4); 2 years, 107.3 (51.1)). RBC:M z ‐score was low at all three visits (6 months, −2.85 (0.98); 1 year, −2.44 (1.34); 2 years, −2.60 (1.39)), with no improvement with time ( p = 0.993). VDP and Lm D did not significantly change with time (VDP: p = 0.100; Lm D : p = 0.166). Data Conclusion Improvements in lung perfusion were measured; however, there was no corresponding enhancement in RBC:M. Evidence Level Level 2. Technical Efficacy Stage 3.