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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 resonance imaging to differentiate alveolitis and pulmonary fibrosis by correlating magnetic resonance and pathologic findings.


METHODS
Lung damage was induced in 52 rabbits by instillation of 5 mL bleomycin sulfate (10 mg/kg) into a lower-lobe bronchus using a balloon catheter. 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 examined 3 hours (n = 5), 24 hours, and 8 days (n = 3 for each), respectively, after the instillation of 5 mL 0.9% sodium chloride. Magnetic resonance imaging at 1.5 T included conventional T1-weighted sequences before and after injection of gadolinium-DTPA (0.1 mmol/kg), and T2-weighted fast spin echo sequences. The signal intensity and contrast enhancement of injured lung were evaluated and compared with the contralateral healthy lung and with the lungs of control animals. All animals were killed immediately after the magnetic resonance examination, and the lungs were removed and fixed before sectioning and staining.


RESULTS
There was good correlation between signal intensity and contrast enhancement with magnetic resonance imaging and histologic examination. The early phase of acute alveolitis showed lesions with high signal intensity on both T1- and T2-weighted images and marked contrast enhancement after gadolinium-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 gadolinium-DTPA administration.