Direct imaging of pulmonary gas exchange with hyperpolarized xenon MRI

Chronic respiratory diseases, including chronic obstructive pulmonary disease (COPD), interstitial lung disease (ILD), and asthma, are among the leading causes of morbidity and mortality worldwide. Recent estimates indicate that chronic respiratory diseases affect over 540 million people in the world in 2017 and account for an estimated 3.9 million deaths.1 Medical imaging plays a pivotal role in the diagnosis, progression monitoring, treatment planning, and outcome evaluation of respiratory diseases. Despite the tremendous developments in medical imaging technology, currently no tools are available that can directly depict, quantify, and localize the gas exchange of oxygen from the alveoli to the lung parenchyma and blood.

Gas exchange is a critical function of the lung, yet it is not possible to non-invasively visualize this process with current clinical methods. Magnetic resonance imaging (MRI) using hyperpolarized noble gases 3He and 129Xe has facilitated the development of unique strategies for evaluating lung structure and gas exchange function.2 In particular, the solubility of 129Xe in biological tissues, combined with its sensitivity to the surrounding environment, makes hyperpolarized 129Xe MRI uniquely capable of characterizing regional gas exchange,3 which is not accessible with the use of hyperpolarized 3He. Hyperpolarized 129Xe gas MRI has shown significant promise in detecting and evaluating abnormalities in pulmonary small airways, parenchyma, and vasculature by quantifying ventilation, gas diffusion, and regional gas exchange. This technique has been widely used to assess the microstructure and functional changes caused by lung diseases, such as COPD, ILD, and COVID-19. Additionally, it has received clinical approval in both China and the United States.