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The respiratory consequences of acute COVID-19 infection and related symptoms tend to resolve 4 weeks post-infection. However, for some patients, new, recurrent, or persisting symptoms remain beyond the acute phase and persist for months, post-infection. The symptoms that remain have been referred to as long-COVID. A number of research sites employed 129 Xe magnetic resonance imaging (MRI) during the pandemic and evaluated patients post-infection, months after hospitalization or home-based care as a way to better understand the consequences of infection on 129 Xe MR gas-exchange and ventilation imaging. A systematic review and comprehensive search were employed using MEDLINE via PubMed (April 2023) using the National Library of Medicine's Medical Subject Headings and key words: post-COVID-19, MRI, 129 Xe, long-COVID, COVID pneumonia, and post-acute COVID-19 syndrome. Fifteen peer-reviewed manuscripts were identified including four editorials, a single letter to the editor, one review article, and nine original research manuscripts (2020-2023). MRI and MR spectroscopy results are summarized from these prospective, controlled studies, which involved small sample sizes ranging from 9 to 76 participants. Key findings included: 1) 129 Xe MRI gas-exchange and ventilation abnormalities, 3 months post-COVID-19 infection, and 2) a combination of MRI gas-exchange and ventilation abnormalities alongside persistent symptoms in patients hospitalized and not hospitalized for COVID-19, 1-year post-infection. The persistence of respiratory symptoms and 129 Xe MRI abnormalities in the context of normal or nearly normal pulmonary function test results and chest computed tomography (CT) was consistent. Longitudinal improvements were observed in long-term follow-up of long-COVID patients but mean 129 Xe gas-exchange, ventilation heterogeneity values and symptoms remained abnormal, 1-year post-infection. Pulmonary functional MRI using inhaled hyperpolarized 129 Xe gas has played a role in detecting gas-exchange and ventilation abnormalities providing complementary information that may help develop our understanding of the root causes of long-COVID. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 5., (© 2023 The Authors. Journal of Magnetic Resonance Imaging published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Purpose: To develop and assess ultrashort echo-time (UTE) magnetic resonance imaging (MRI) biomarkers of lung function in asthma patients., Materials and Methods: Thirty participants including 13 healthy volunteers and 17 asthmatics provided written informed consent to UTE and pulmonary function tests in addition to hyperpolarized-noble-gas 3T MRI and computed tomography (CT) for asthmatics only. The difference in MRI signal-intensity (SI) across four lung volumes (full-expiration, functional-residual-capacity [FRC], FRC+1L, and full-inspiration) was determined on a voxel-by-voxel basis to generate dynamic proton-density (DPD) maps. MRI ventilation-defect-percent (VDP), UTE SI, and DPD values as well as CT radiodensity were determined for whole lung and individual lobes., Results: Mean SI at full-expiration (P < 0.01), FRC (P < 0.05), and DPD (P < 0.01) were greater in healthy volunteers compared to asthmatics. In asthmatics, UTE SI at full-expiration and DPD were correlated with FEV 1 /FVC (SI r = 0.73/P = 0.002; DPD r = 0.75/P = 0.003), RV/TLC (SI r = -0.57/P = 0.02), or RV (DPD r = -0.62/P = 0.02), CT radiodensity (SI r = 0.83/P = 0.006; DPD r = 0.71/P = 0.01), and lobar VDP (SI r s  = -0.33/P = 0.02; DPD r s  = -0.47/P = 0.01)., Conclusion: In patients with asthma, UTE SI and dynamic proton-density were related to pulmonary function measurements, whole lung and lobar VDP, as well as CT radiodensity. Thus, UTE MRI biomarkers may reflect ventilation heterogeneity and/or gas-trapping in asthmatics using conventional equipment, making this approach potentially amenable for clinical use., Level of Evidence: 2 J. Magn. Reson. Imaging 2017;45:1204-1215., (© 2016 International Society for Magnetic Resonance in Medicine.)

Purpose: To evaluate cystic fibrosis (CF) subjects over 4 years using (3) He magnetic resonance imaging (MRI), pulmonary function tests, and track hospitalization and physician visits., Materials and Methods: Five CF adults provided written informed consent to an approved protocol and underwent MRI, spirometry, and plethysmography at baseline, 7 days, and 4 ± 1 years later. (3) He MRI ventilation defect percent (VDP) was generated for all subjects and timepoints., Results: After 4 years, mean forced expiratory volume in 1 second / forced vital capacity (FEV1 /FVC) was lower (P = 0.01) in all subjects and there were no other pulmonary function test changes. Two CF adults showed significantly elevated (worse) (3) He VDP at baseline and after 4 years they had significantly greater (worsened) VDP (P = 0.02), without a significant FEV1 decline (P = 0.06) but with a greater number of exacerbations (P < 0.05). Baseline VDP strongly correlated with FEV1 (r(2)  = 0.98, P = 0.0007) at 4-year follow-up., Conclusion: For two CF subjects, VDP was significantly worse at baseline and worsened over 4 years, which was in agreement with a greater number of hospitalizations and clinic visits. These results are limited by the very small sample size, but the strong VDP correlation with longitudinal changes in FEV1 generates the hypothesis that abnormal VDP may temporally precede FEV1 decline in CF subjects; this must be tested in a larger CF study., (© 2014 Wiley Periodicals, Inc.)

Background: To evaluate ultra-short-echo-time (UTE) MRI pulmonary signal-intensity measurements and reproducibility in chronic obstructive pulmonary disease (COPD)., Methods: A two-dimensional sequence (echo-time = 0.05 ms; acquisition-time = 13 s) with interleaved half-pulse excitation and radial ramp-sampling was used with compressed-sensing to reconstruct UTE images from under-sampled data. Five healthy volunteers and 15 subjects with COPD provided written informed consent to imaging and pulmonary-function-tests. Healthy volunteers underwent MRI at four lung volumes: full-expiration, functional-residual-capacity (FRC), FRC+1L, and full-inhalation; COPD patients underwent computed-tomography (CT) and MRI at FRC+1L. Three-week reproducibility was evaluated and the relative area of the density histogram ≤ -950 HU (RA950 ) was compared with mean MRI signal-intensity. The 15th percentile of signal-intensity-histogram (SI15 ) was compared with the 15th percentile of the CT-density-histogram (HU15 )., Results: In healthy subjects, signal-intensity correlated with the inverse of lung volume (r = 0.99; P = 0.007). Contrast-to-noise and signal-to-noise ratios were significantly improved for 32-channel UTE (P < 0.01). The coefficient of variation for 3-week repeated measurements was 4%. There were significant correlations for signal-intensity with RA950 (r = -0.71; P = 0.005), FEV1 /FVC (r = 0.59; P = 0.02), and for SI15 with HU15 (r = 0.62; P = 0.01)., Conclusion: Pulmonary signal-intensity is reproducible and related to tissue density. In COPD subjects with and without bronchiectasis, signal-intensity was also related to pulmonary function and CT measurements., (© 2014 Wiley Periodicals, Inc.)

Purpose: To compare hyperpolarized helium-3 ((3) He) and xenon-129 ((129) Xe) MRI in asthmatics before and after salbutamol inhalation., Materials and Methods: Seven asthmatics provided written informed consent and underwent spirometry, plethysmography, and MRI before and after salbutamol inhalation. (3) He and (129) Xe ventilation defect percent (VDP) and ventilation coefficient of variation (COV) were measured. To characterize the airways spatially related to ventilation defects, wall area percent (WA%) and lumen area (LA) were evaluated for two subjects who had thoracic x-ray computed tomography (CT) acquired 1 year before MRI., Results: Before salbutamol inhalation, (129) Xe VDP (8 ± 5%) was significantly greater than (3) He VDP (6 ± 5%, P = 0.003). Post-salbutamol, there was a significant improvement in both (129) Xe (5 ± 4%, P < 0.0001) and (3) He (4 ± 3%, P = 0.001) VDP, and the improvement in (129) Xe VDP was significantly greater (P = 0.008). (129) Xe MRI COV (Pre: 0.309 ± 0.028, Post: 0.296 ± 0.036) was significantly greater than (3) He MRI COV (Pre: 0.282 ± 0.018, Post: 0.269 ± 0.024), pre- (P < 0.0001) and post-salbutamol (P < 0.0001) and the decrease in COV post-salbutamol was significant ((129) Xe, P = 0.002; (3) He, P < 0.0001). For a single asthmatic, a sub-segmental (129) Xe MRI ventilation defect that was visible only before salbutamol inhalation but not visible using (3) He MRI was spatially related to a remodeled fourth generation sub-segmental airway (WA% = 78%, LA = 2.9 mm(2) )., Conclusion: In asthma, hyperpolarized (129) Xe MRI may help reveal ventilation abnormalities before bronchodilation that are not observed using hyperpolarized (3) He MRI., (Copyright © 2013 Wiley Periodicals, Inc.)