Assessment of pulmonary microstructural changes by hyperpolarized 129Xe diffusion-weighted imaging in an elastase-instilled rat model of emphysema

Background: The purpose of this study was to explore the feasibility of hyperpolarized Xe-129 diffusion-weighted imaging (DWI) for the evaluation of pulmonary microstructural changes in the presence of pancreatic porcine elastase (PPE)-induced pulmonary emphysema rat model. Methods: Sixteen male Sprague-Dawley (SD) rats were randomly divided into two groups, the emphysema model group and control group. Experimental emphysematous models were made by instilling elastase into rat lungs of model group, the control group were instilled with isodose saline. Hyperpolarized Xe-129 magnetic resonance imaging (MRI) and histology were performed in all 16 rats after 30 days. DWIs were performed on a Bruker 7.0 T micro MRI, and the apparent diffusion coefficients (ADCs) were measured in all rats. Mean linear intercepts (MLIs) of pulmonary alveoli were measured on histology. The statistical analyses were performed about the correlation between the mean ADC of hyperpolarized Xe-129 in the whole lung and MLI of pulmonary histology metric. Results: The pulmonary emphysematous model was successfully confirmed by the histology and all scans were also successful. The ADC value of Xe-129 in the model group (0.0313 +/- 0.0005 cm(2)/s) was significantly increased compared with that of the control group (0.0288 +/- 0.0007 cm(2)/s, P<0.0001). Morphological differences such as MLI of pulmonary alveoli were observed between the two groups, the MLI of pulmonary alveoli in model group significantly increased (91 +/- 5 mu m) than that of control group (50 +/- 3 mu m, P<0.0001). Furthermore, the ADCs was moderately correlated with MLIs (r=0.724, P<0.01). Conclusions: These results indicate that Xe-129 ADC value can quantitatively reflect the alveolar space enlargement and it is a promising biomarker for the detection of pulmonary emphysema.