Study demonstrates multinuclear MRI is sensitive to functional pulmonary changes in the follow up of patients hospitalized with COVID-19

By Dr. Priyom Bose, Ph.D.Apr 11 2022Reviewed by Danielle Ellis, B.Sc.

Several studies reported similarities in clinical presentations between patients hospitalized due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and those with typical pneumonia and acute respiratory distress syndrome (ARDS). Some of the common symptoms experienced by all patients are hyperinflammation and progressive hypoxemia.

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources

In addition, some patients with SARS-CoV-2 infection experience inflammatory and thrombotic vasculopathy with endothelial dysfunction and excessive blood flow to collapsed lung tissue. Researchers have also observed anomalies in pulmonary vasoregulation in patients with severe coronavirus disease 2019 (COVID-19).

Background

Very limited information about the medium- and long-term outcomes of microvascular abnormalities alongside pulmonary damages in patients requiring hospitalization due to SARS-CoV-2 infection is available. Scientists revealed that a lung MRI with hyperpolarised ¹²⁹Xe gas offers regionally sensitive estimations of lung ventilation and gas diffusion within the lung airspace. Diffusion-weighted MRI (DW-MRI) and mathematical models of hyperpolarised gas diffusion offer a quantitative assessment of acinar airway dimensions. Additionally, the apparent diffusion coefficient (ADC) offers 3D in vivo information on the underlying microstructure of the lung tissues.

It is not clear if lung perfusion abnormalities or alveolar/interstitial endothelial changes, or a combination of the two, are controlling the reduced xenon gas transfer and breathlessness seen in patients post COVID-19. Scientists stated that ¹²⁹Xe is soluble in the lung tissue membrane (M) and the red blood cells (RBC). Therefore, researchers have used a specific ratio of the ¹²⁹Xe signal in the RBC:M, RBC:gas, and M:gas to probe the transfer of gas between airspace, membrane, and blood.

Using ¹²⁹Xe MRI, researchers reported that reduced gas transfer to the RBC was found in thirteen patients who were acutely infected with COVID-19 and required hospitalization. Additionally, they found considerable enhancement in lung ventilation defects in these patients.

A new study

A new study published in medRxiv* preprint server has focussed on determining the lung function of severely infected COVID-19 patients who required hospitalization. In this study, researchers subjected patients to a pulmonary 1H and ¹²⁹Xe MRI protocol at 6, 12, 25, and 50 weeks after hospitalization.

The multinuclear MRI protocol combined various approaches that include hyperpolarised ¹²⁹Xe imaging methods (which are sensitive to ventilation), lung microstructure (DW-MRI), gas exchange (dissolved xenon spectroscopic imaging), 1H DCE perfusion, and UTE lung structural imaging. Following these protocols, researchers were able to evaluate pathophysiological changes in patients who had been hospitalized with COVID-19 pneumonia during the post-acute period.

Findings

The current study used hyperpolarised ¹²⁹Xe imaging methods to reveal that hospitalized patients with COVID-19 were sensitive to ventilation. DW-MRI analysis helped elucidate lung microstructure and gas exchange via dissolved xenon spectroscopic imaging along with 1H DCE perfusion and UTE lung structural imaging. These tools helped researchers determine the pathophysiological changes in patients hospitalized with COVID-19 pneumonia during the post-acute period. The initial results showed that although these patients suffered impaired gas transfer (RBC:M), the lung microstructure (ADC and LmD) measures were normal.

Researchers observed that four of nine patients exhibited small ventilation defects at six weeks, which were mostly fixed by the 25th week. The current study revealed that some patients exhibited continued abnormalities in ¹²⁹Xe gas transfer at 25-50 weeks after hospitalization. However, others showed steady improvement across the same time frame with RBC:M within 25-50 weeks.

The findings of this study are in line with previous studies that reported low RBC:M values between hospital discharge and 24 weeks post-discharge. The current study further revealed that RBC:gas and M:gas did not exhibit significant longitudinal change, which indicates that the change in RBC:M was a collective effect of changes in both M and RBC.

Scientists analyzed covariance between RBC:M and pulmonary blood volume, which revealed that an increase in RBC:M in patients was positively correlated with an increase in pulmonary blood volume. This result implies that microvascular recovery could cause changes in RBC:M in such patients.

Conclusion

One of the key limitations of this study is that not all patients had dynamic contrast-enhanced (DCE) 1H lung MRI. However, patients with DCE data revealed an increase in regional pulmonary blood flow. Another limitation of the study is its small sample size, which is predominantly due to difficulties in recruiting participants for scanning after being discharged from hospitals.

However, the findings of this study indicate that impaired lung ventilation is not a likely cause for prolonged symptoms after the acute stage of COVID-19. In the future, more research is required to establish the link between dissolved phase ¹²⁹Xe imaging metrics and personal characteristics, such as age and sex.

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources