Longitudinal 1H and 129Xe lung MRI in patients with post-COVID residual lung abnormalities

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, 129Xe steady state free precession (ventilation), 129Xe 3D spoiled gradient echo multiple b-value (diffusion-weighted), 129Xe 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 129Xe signal in the red blood cells to membrane (RBC:M) was calculated from the dissolved phase 129Xe acquisition. Ventilation defect percentage (VDP) was calculated from the 129Xe ventilation acquisition. Mean diffusive length scale (LmD) was calculated from the 129Xe 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 LmD did not significantly change with time (VDP: p = 0.100; LmD: 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.