[Serial changes of atelectasis in acute bronchial obstruction: MR imaging pathologic correlation in experimental animal model study].
OBJECTIVE: To evaluate MR imaging (MRI) of atelectatic lungs caused by acute bronchial obstruction. SUBJECTS AND METHODS: In 12 Japanese white rabbits, sudden obstruction of one main bronchus was induced with compressed polyvinyl-alcohol sponge plugs, and three rabbits each were sacrificed at 3, 7, 14, and 21 days. Unilateral complete airway obstruction persisted in 8 of the 12 rabbits. After T1: [500/20/2 (TR/TE/excitations), 5 mm thickness, 12cm FOV] and T2: [2500/80/4,5mm thickness, 12cm FOV] weighted imaging, both lungs and heart were inflated, fixed (Heitzman's method) and embedded en bloc in collodion. MR images of the atelectatic portion were evaluated, and MRI findings of the atelectatic portion were correlated with pathologic findings. RESULTS: MRI, especially T2 weighted images showed some characteristic signal patterns in each period. Correlations of these MRI features were performed with the pathologic findings: 1) The peripheral pulmonary parenchyma, on T2 weighted images showed signal increase with time which was attributed to edematous fluid retention in pulmonary alveoli. 2) The difference between inhomogeneous and homogeneous signal intensities on T2 weighted images on the 7th day was attributed to the patchy and even distribution of inflammatory process in pulmonary parenchyma. 3) On the 21st day, hypointensity bands were observed on T1 and T2 weighted images. These hypointensity bands were attributed to fibrotic changes in bronchial walls and nearby alveolar walls. CONCLUSION: MR images well demonstrated pathological changes in atelectatic lungs caused by acute bronchial obstruction with time, suggesting the clinical usefulness of this approach.