Differentiation of capillary leak and hydrostatic pulmonary edema with a macromolecular MR imaging contrast agent

The ability of a macromolecular contrast agent (polylysine-[gadopentetate dimeglumine]40) to allow distinction of pulmonary capillary leak from hydrostatic pulmonary edema was investigated. Capillary leak edema was induced in 12 rats by means of venous injection of oleic acid; hydrostatic pulmonary edema was induced in 10 rats by means of continuous infusion of 0.9% sodium chloride. In the oleic acid pulmonary edema model, the signal intensity continued to increase for 12 minutes after administration of contrast material, indicating a leak of paramagnetic molecules from the intravascular to the extravascular spaces. Conversely, lung enhancement remained virtually constant after injection of contrast material in the hydrostatic edema model, as would be expected in the absence of endothelial damage. Hydrostatic edema tended to be distributed homogeneously throughout the lung, while capillary leak edema tended to occur predominantly in the peripheral portions of the lung. These findings indicate that macromolecular contrast agents can facilitate differentiation between edema caused by elevated intravascular pressure and edema induced by abnormal capillary permeability.