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Background Microvascular abnormalities and impaired gas transfer have been observed in patients with COVID-19. The progression of pulmonary changes in these patients remains unclear. Research Question Do patients hospitalized with COVID-19 without evidence of architectural distortion on structural imaging exhibit longitudinal improvements in lung function measured by using 1H and 129Xe MRI between 6 and 52 weeks following hospitalization? Study Design and Methods Patients who were hospitalized with COVID-19 pneumonia underwent a pulmonary 1H and 129Xe MRI protocol at 6, 12, 25, and 51 weeks following hospital admission in a prospective cohort study between November 2020 and February 2022. The imaging protocol was as follows: 1H ultra-short echo time, contrast-enhanced lung perfusion, 129Xe ventilation, 129Xe diffusion-weighted, and 129Xe spectroscopic imaging of gas exchange. Results Nine patients were recruited (age 57 ± 14 [median ± interquartile range] years; six of nine patients were male). Patients underwent MRI at 6 (n = 9), 12 (n = 9), 25 (n = 6), and 51 (n = 8) weeks following hospital admission. Patients with signs of interstitial lung damage were excluded. At 6 weeks, patients exhibited impaired 129Xe gas transfer (RBC to membrane fraction), but lung microstructure was not increased (apparent diffusion coefficient and mean acinar airway dimensions). Minor ventilation abnormalities present in four patients were largely resolved in the 6- to 25-week period. At 12 weeks, all patients with lung perfusion data (n = 6) showed an increase in both pulmonary blood volume and flow compared with 6 weeks, although this was not statistically significant. At 12 weeks, significant improvements in 129Xe gas transfer were observed compared with 6-week examinations; however, 129Xe gas transfer remained abnormally low at weeks 12, 25, and 51. Interpretation 129Xe gas transfer was impaired up to 1 year following hospitalization in patients who were hospitalized with COVID-19 pneumonia, without evidence of architectural distortion on structural imaging, whereas lung ventilation was normal at 52 weeks.

IntroductionMicrovascular abnormalities and impaired 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.MethodsPatients who were hospitalised due to COVID-19 pneumonia underwent a pulmonary1H and129Xe MRI protocol at 6, 12, 25 and 51 weeks after hospital admission. The imaging protocol included: ultra-short echo time, dynamic contrast enhanced lung perfusion,129Xe lung ventilation,129Xe diffusion weighted and129Xe 3D spectroscopic imaging of gas exchange.Results9 patients were recruited and underwent MRI at 6 (n=9), 12 (n=9), 25 (n=6) and 51 (n=8) weeks after hospital admission. Patients with signs of interstitial lung damage at 3 months were excluded from this study. At 6 weeks after hospital admission, patients demonstrated impaired129Xe gas transfer (RBC:M) but normal lung microstructure (ADC, LmD). Minor ventilation abnormalities present in four patients were largely resolved in the 6–25 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 week follow up, significant improvements in129Xe gas transfer were observed compared to 6-week examinations, however129Xe gas transfer remained abnormally low at weeks 12, 25 and 51. Changes in129Xe gas transfer correlated significantly with changes in pulmonary blood volume and TLCOZ-score.ConclusionsThis study demonstrates that multinuclear MRI is sensitive to functional pulmonary changes in the follow up of patients who were hospitalised with COVID-19. Impairment of xenon transfer may indicate damage to the pulmonary microcirculation.

MR imaging of neonates is difficult for many reasons and a major factor is safe transport to the MR facilities. In this article we describe the use of a small, investigational 3-T MR customised for brain imaging and sited on a neonatal unit of a tertiary centre in the UK, which is in contrast to a 300-m journey to the whole-body MR scanner used at present for clinical cases. We describe our methods for preparing babies for safe transport and scanning on an investigational 3-T MR scanner on a neonatal unit and the development of appropriate MR sequences. The MR scanner does not have CE marking at present so this early development work was undertaken on normal neonates whose parents consented to a research examination. Fifty-two babies were scanned and there were no serious adverse events. The MR examinations were considered to be diagnostically evaluable in all 52 cases and in 90% the imaging was considered to be at least as good as the quality obtained on the 1.5-T scanner currently used for clinical cases. We have shown that this investigational 3-T MR scanner can be used safely on a neonatal unit and we have refined the MR sequences to a point that they are clinically usable. • Access to neonatal MR imaging is limited. • We describe an investigational 3-T MR scanner site on a neonatal unit. • The scanner produces images suitable for clinical practice.

Introduction Hyperpolarised 3 He MRI provides high resolution images of lung ventilation and is more sensitive than spirometry to early changes in lung ventilation in cystic fibrosis (CF). Lung clearance index (LCI) is a global measure of ventilation heterogeneity which is also sensitive to early changes in the lungs in CF before spirometry. The aim of this study was to investigate the capability of hyperpolarised 3 He MRI and LCI to detect ventilation changes in children with mild CF. Methods 4 CF patients (FEV 1 78 110% predicted) and 4 healthy volunteers have been assessed so far. 3 He ventilation images were acquired at breath-hold following inhalation of hyperpolarised 3 He, with 2.7x2.7x10mm resolution and full lung coverage using a 1.5T MRI system. The percentage of lung ventilated (VV%) was calculated as 3 He ventilated volume divided by total lung volume segmented from 1 H MR images. LCI was measured using 0.2% SF6 and a modified Innocor gas analyser. LCI was performed sitting and repeated supine to mimic the position adopted for MRI scanning. Spirometry and plethysmography were also performed. Gas trapping was calculated as% difference in plethysmographic versus washout FRC. Results Healthy volunteers had a mean (standard deviation) age of 8.8(1.5) years, FEV 1 % predicted = 97(10) and gas trapping = 4.4(9.1)%. LCI sitting was 6.9,7.3,6.6 and 6.9, LCI supine was 7.3,7.5,6.8 and 6.4. Healthy volunteers had homogeneous ventilation in 3 He ventilation images e.g. Fig1(a), and VV% = 94.5(2.8). CF patients had an age of 11.8(2.9) years, FEV 1 % predicted = 95(13), and gas trapping = 8.7(11.0). LCI sitting was 7.7,6.6,6.6 and 9.1, LCI supine was 7.8,7.3,7.1 and 11.8. Ventilation abnormalities were observed using 3 He MRI in all four CF patients scanned (Fig 1(b-e), with order corresponding to the LCI values given), and VV% = 89.2(2.6). 2 of the 4 CF patients had normal sitting and supine LCI and 2 of 3 had no evidence of gas trapping, but 3 He MRI showed clear focal ventilation defects in all patients (b-d). Conclusions High quality 3 He MRI images can be produced in young children. Preliminary results suggest that hyperpolarised 3 He ventilation MRI may be more sensitive to early ventilation changes in CF than LCI or conventional lung function tests. Acknowledgements CF Trust funding