Differentiation of alveolitis and pulmonary fibrosis with a macromolecular MR imaging contrast agent.

The ability of macromolecular contrast agent (polylysine-[gadopentetate dimeglumine]) to allow differentiation of pulmonary fibrosis and alveolitis at magnetic resonance imaging was investigated. Lung damage was induced by means of left bronchial instillation of 200 micrograms of cadmium chloride. Rats were imaged 3 hours (early alveolitic stage, n = 5), 24 hours (late alveolitic stage, n = 5), and 8 days (fibrotic stage, n = 5) later. Rats imaged 3 hours after cadmium chloride instillation demonstrated a gradually increasing contrast enhancement over 45 minutes (from 314% +/- 110 to 476% +/- 69 over baseline [P less than .01]), indicating a leak of paramagnetic macromolecules from the intravascular into the extravascular spaces. Conversely, lung enhancement remained virtually constant after injection of contrast material in contralateral control lungs and in damaged lungs imaged 24 hours and 8 days after cadmium chloride instillation. Furthermore, the enhancement in the fibrotic lung was lower (170% +/- 50) than that in the alveolitic and control lungs (320% +/- 65 and 298% +/- 61, respectively), indicating a decrease in plasma volume in the fibrotic lung. A macromolecular contrast agent can facilitate the differentiation between the exudative and fibrotic phases of interstitial lung disease.