Physiological gas exchange mapping of hyperpolarized 129 Xe using spiral-IDEAL and MOXE in a model of regional radiation-induced lung injury.

Abstract

To map physiological gas exchange parameters using dissolved hyperpolarized (HP) 129 Xe in a rat model of regional radiation-induced lung injury (RILI) with spiral-IDEAL and the model of xenon exchange (MOXE). Results are compared to quantitative histology of pulmonary tissue and red blood cell (RBC) distribution. Two cohorts (n=6 each) of age-matched rats were used. One was irradiated in the right-medial lung, producing regional injury. Gas exchange was mapped 4weeks postirradiation by imaging dissolved-phase HP 129 Xe using spiral-IDEAL at five gas exchange timepoints using a clinical 1.5T scanner. Physiological lung parameters were extracted regionally on a voxel-wise basis using MOXE. Mean gas exchange parameters, specifically air-capillary barrier thickness (δ) and hematocrit (HCT) in the right-medial lung were compared to the contralateral lung as well as nonirradiated control animals. Whole-lung spectroscopic analysis of gas exchange was also performed. δ was significantly increased (1.43±0.12μm from 1.07±0.09μm) and HCT was significantly decreased (17.2±1.2% from 23.6±1.9%) in the right-medial lung (i.e., irradiated region) compared to the contralateral lung of the irradiated rats. These changes were not observed in healthy controls. δ and HCT correlated with histologically measured increases in pulmonary tissue heterogeneity (r=0.77) and decreases in RBC distribution (r=0.91), respectively. No changes were observed using whole-lung analysis. This work demonstrates the feasibility of mapping gas exchange using HP 129 Xe in an animal model of RILI 4weeks postirradiation. Spatially resolved gas exchange mapping is sensitive to regional injury between cohorts that was undetected with whole-lung gas exchange analysis, in agreement with histology. Gas exchange mapping holds promise for assessing regional lung function in RILI and other pulmonary diseases.