Differentiation of alveolitis and pulmonary fibrosis in rabbits with magnetic resonance imaging after intrabronchial administration of bleomycin

RATIONALE AND OBJECTIVES. The authors investigate the ability of magnetic r esonance imaging to differentiate alveolitis and pulmonary fibrosis by corr elating magnetic resonance and pathologic Endings. METHODS. Lung damage was induced in 52 rabbits by instillation of 5 mL bleo mycin sulfate (10 mg/kg) into a lower-lobe bronchus using a balloon cathete r, Magnetic resonance examinations were performed in a group of 7 animals 3 hours after the initial damage, and in groups of 8 animals 24 hours and 8, 14, 30, and 80 days after the initial damage. Control animals were examine d 3 hours (n = 5), 24 hours, and 8 days (n = 3 for each), respectively, aft er the instillation of 5 mL 0.9% sodium chloride. Magnetic resonance imagin g at 1.5 T included conventional T1-weighted sequences before and after inj ection of gadolinium-DTPA (0.1 mmol/kg), and T2-weighted fast spin echo seq uences. The signal intensity and contrast enhancement of injured lung were evaluated and compared with the contralateral healthy lung and with the lun gs of control animals. All animals were killed immediately after the magnet ic resonance examination, and the lungs were removed and fixed before secti oning and staining. RESULTS There was good correlation between signal intensity and contrast en hancement with magnetic resonance imaging and histologic examination, The e arly phase of acute alveolitis showed lesions with high signal intensity on both T1- and T2-weighted images and marked contrast enhancement after gado linium-DTPA administration, whereas in the late fibrotic stage the lesions displayed significantly lower signal intensity and contrast enhancement. CONCLUSION. Magnetic resonance imaging can differentiate between alveolitis and fibrosis by means of signal intensity and contrast enhancement after g adolinium-DTPA administration.