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

Purpose: 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.

Methods: 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.

Results: 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.

Conclusion: 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.