A new tool to monitor the development of acute lung injury in mice; X-ray dark-field imaging
Acute lung injury (ALI), a severe form of acute respiratory distress syndrome (ARDS), is characterized by an increase of vascular permeability that leads to alveolar and interstitial edema followed by hypoxemia. Diagnosis of ARDS is based on the visualization of pulmonary infiltrates by chest radiography or computed tomography (CT), however, any of these tools appear to be sufficiently efficient since 50% of ALI patients are misdiagnosed. Therefore, our aim is to evaluate dark-field imaging as a new tool to diagnostic in vivo early stages of ALI in a comparative study with conventional transmission imaging using an elastase-induced emphysema murine model.
Orotracheal application of porcine pancreatic elastase (80 U/kg BW) (n = 11) or PBS (n = 10) was performed in 8 – 10 week old C57Bl/6N female mice. Mice were imaged immediately before and after (1, 7, 14 and 21 days) the application of elastase or PBS. At day 1 (n = 6) bronchoalveolar lavage (BAL) was collected for differential cell counting and lungs were paraffin-embedded for histological analysis and mean chord length quantification. The remaining mice were sacrificed at day 21 (n = 4 – 5) to perform same histological analysis. All images were acquired with a prototype grating-based small-animal scanner to generate dark-field and transmission radiographs.
At day 1, elastase-treated mice showed a pronounced elevation of neutrophil recruitment into the lung accompanied by pulmonary emphysema. Acute lung injury was visually apparent as a striking decrease in signal intensity of the pulmonary parenchyma on dark-field images at day 1. This was confirmed by dark-field signal intensity quantification, which shows a significantly lower signal compared to the remaining time points. No significant alteration in median transmission signal intensity was noted.
To conclude, our study suggests that dark-field radiography allows for significantly more sensitive detection of acute lung injury in mice compared to conventional transmission imaging.