Pulmonary edema: an MR study of permeability and hydrostatic types in animals.

Permeability pulmonary edema was induced in ten rats by intravenous injection of oleic acid. Hydrostatic pulmonary edema was induced in another ten rats by continuous infusion of saline. Permeability pulmonary edema was detected as increased signal intensity in all animals on images obtained with repetition times (TR) of 2.0 sec and echo times (TE) of 28 and 56 msec. Hydrostatic pulmonary edema was perceivable only in seven of ten rats. It was best seen on spin-echo TR = 2.0 sec, TE = 28 msec images as increased intensity either throughout the whole lung or in a predominant central distribution. The slopes of the relationships between the mean signal intensity and water content of both lungs were lower for hydrostatic pulmonary edema than for permeability pulmonary edema. Hydrostatic pulmonary edema demonstrated similar T1 but markedly shorter T2 relaxation times than permeability edema. Magnetic resonance imaging can be used to estimate severity of hydrostatic and permeability pulmonary edemas.