In-vivo Evaluation of Bleomycin-induced Lung Fibrosis Model Mouse Using Ultra High-field 7 T-MRI and Micro-CT

Abstract

Purpose: This study aimed to perform longitudinal observation using 4D-computed tomography (CT) and compare images acquired by 3D-CT and 3D-ultrashort echo time (UTE) for evaluation of bleomycin-induced lung fibrosis model. Method: The pulmonary fibrosis model was induced by instilling intratracheally with 50 μl of bleomycin. 4D-CT images were classified into four phases after acquisition and analyzed. To study the effects of respiratory gating, we aquired 3D-CT and 3D-UTE images with and without respiratory gating. For comparison between CT and UTE images, we performed no-triggerd 3D-CT and 3D-UTE under free-breathing. MR signal intensity ratio and CT values were measured in three regions of the upper, middle, and lower lung. Results: At 4DCT, total lung volume at maximum inspiration (4th phase) decreased significantly compared with control mouse and the ratio of lung volume at inspiration to expiration also showed a significant decrease. In comparison of the images between with and without respiratory gating, clearer images were obtained by respiratory gating. However, there was no significant difference between both. In comparison between CT and UTE images, magnetic resonance (MR) signal intensity ratio and CT value were significantly correlated, but 3D-UTE images showed poor delineation of the lower lung and that near the diaphragm compared with 3D-CT images. Conclusion: 4D micro-CT and nontriggered 3D UTE-magnetic resonance imaging (MRI) under free breathing can be useful to evaluate bleomycininduced lung fibrosis model mouse.