Quantitative assessment of lung microstructure and functional changes of smoke-inhalation-induced acute lung injury with hyperpolarized ¹²⁹Xe magnetic resonance.

Abstract

Accurate assessment of smoke-inhalation-induced acute lung injury (SI-ALI) is essential for clinical diagnosis and effective management. Hyperpolarized ¹²⁹Xe magnetic resonance (MR), an emerging imaging modality, has shown broad utility across various pulmonary conditions. This study aimed to evaluate the feasibility and potential of hyperpolarized ¹²⁹Xe MR for assessing gas exchange impairment and microstructural alterations in the lungs following SI-ALI. Two groups of rats (n = 5 per group) were studied. The smoke inhalation injury (SII) group was subjected to three 2-minute exposures to pine sawdust smoke under general anesthesia with endotracheal intubation. The sham group underwent identical procedures but was exposed to clean air. Twenty-four hours after exposure, pulmonary function tests, micro-computed tomography (micro-CT), and ¹²⁹Xe MR examinations were conducted to obtain quantitative physiological parameters. Subsequently, lung tissues were harvested for histological analysis of alveolar septal wall thickness. Rats exposed to smoke (SII group) showed significant decreases in lung volume, as indicated by reduced total lung capacity (TLC, p = 0.036) and forced vital capacity (FVC, p = 0.020). They also had signs of airway obstruction, with lower forced expiratory volume in 100 ms (FEV₁₀₀, p = 0.041) and maximal mid-expiratory flow (MMEF, p = 0.014). Hyperpolarized ¹²⁹Xe MR spectroscopy showed a lower red blood cell to tissue/plasma (RBC/TP) signal ratio in the SII group (0.45 ± 0.04) compared to the sham group (0.51 ± 0.04, p = 0.035), suggesting impaired gas exchange. The gas exchange time constant increased from 21.22 ms to 28.86 ms (p = 0.013), and the septal wall thickness measured by MR also increased (from 8.28 µm to 9.68 µm, p = 0.013). These MR results matched well with histological measurements, which also showed thickened alveolar walls (from 6.99 µm to 7.70 µm). Ventilation imaging revealed clear areas of reduced airflow, which corresponded to regions of lung consolidation seen on micro-CT scans. Hyperpolarized ¹²⁹Xe MR enables quantitative evaluation of both functional and microstructural lung changes in a rat model of SI-ALI. These findings highlight its potential as a powerful noninvasive tool for assessing smoke-inhalation-induced acute lung injury.