Assessment of severity of experimental pulmonary edema with magnetic resonance imaging. Effect of relaxation enhancement by Gd-DTPA.

This study was done to demonstrate the capability of magnetic resonance imaging (MRI), using a spin-echo technique to detect permeability pulmonary edema in vivo, to correlate the signal intensity to the water content of the lung, and to assess the influence of administration of gadolinium-DTPA upon this relationship. Pulmonary edema was induced in 28 rats by intravenous injection of oleic acid (0.05-0.1 cc/kg). This was detected in all animals on images obtained with a repetition time (TR) of 2.0 seconds and echo times (TE) of 28 or 56 msec as increased signal intensity. Compared with control animals, the intensity was increased primarily in the dependent and peripheral portions of the lung. There was a significant linear relationship between the mean signal intensity, obtained from the area of both lungs within one slice, and the water content of both lungs (r = .94). Intravenous administration of gadolinium (Gd)-DTPA, 5 minutes prior to imaging, produced an easily observable increase in signal intensity on images of short TR (0.5 second) in the edematous lung tissue. However, these values did not exceed the intensities obtained without Gd-DTPA, if a long TR (2.0 seconds) was used for imaging. Thus, MRI has the capability for quantitating the severity of oleic acid-induced pulmonary edema. Gd-DTPA distributes rapidly into permeability pulmonary edema. It allows improved sensitivity at shorter pulse sequence repetition times and thus may diminish imaging time.