Hyperpolarized ¹²⁹Xe MRI and spectroscopy of gas exchange abnormalities in chronic hypersensitivity pneumonitis

To evaluate 3D gas-exchange functional imaging characteristics using ¹²⁹Xe MRI in a group of study participants with chronic hypersensitivity pneumonitis (CHP) as compared with healthy control participants.

In this prospective study, 11 participants with clinical and CT findings of CHP (4M 7F, mean age 67 ± 6.1 years) as well as 41 healthy subjects (25M 16F, mean age 44 ± 18 years) were enrolled between 2017 and 2022 and underwent ¹²⁹Xe MRI. Three-dimensional images of ventilation, interstitial membrane uptake, and RBC transfer were rendered into quantitative 3D maps relative to a healthy reference cohort. In addition, ¹²⁹Xe spectroscopy was used to assess the RBC:membrane ratio (RBC:M), the oxygen-dependent RBC chemical shift, and cardiogenically-driven RBC oscillation amplitude. Differences between the CHP participants and healthy subjects were assessed using the two-sample t-test or Wilcoxon rank-sum test as appropriate.

CHP participants demonstrated significant differences in 6 parameters (p < 0.001) including regions of reduced ventilation, increased membrane uptake, and reduced RBC transfer as compared to healthy subjects. Gas exchange abnormalities measured on spectroscopy included a reduced RBC:M, reduced RBC chemical shift, and increased RBC oscillation amplitude.

In participants with CHP, ¹²⁹Xe MRI demonstrated gas exchange abnormalities common to other fibrotic lung diseases including increased membrane uptake, deficits in RBC transfer, and reduced RBC:M. However, CHP participants also exhibited prominent ventilation abnormalities, which may be reflective of the airway-centric nature of the disease. Further, the high variability observed in the membrane uptake could suggest varying degrees of disease progression or activity.