Dynamic CT measurement of pulmonary enhancement in piglets with experimental acute respiratory distress syndrome

Purpose: To investigate whether analysis of a washout curve of contrast material obtained with serial computed tomography (CT) enables differentiation between hydrostatic pulmonary edema and pulmonary edema caused by increased capillary permeability. Materials and Methods: The institutional committee on animal experiments approved this study, which was performed in accordance with designated guidelines. Chest CT was performed in 12 piglets after induction of anesthesia and start of mechanical ventilation. Dynamic CT was performed before and after induction of hydrostatic edema (n = 5) or oleic acid-induced increased vascular permeability edema (n = 7). Scans were obtained over 240 seconds during inspiratory breath holding at a single representative subcarinal level in the lungs. This anatomic level was kept constant and included areas of normal ventilation before and after induction of pulmonary edema and areas of ground-glass opacity and consolidation after induction of pulmonary edema. Measured lung attenuation in the regions of interest was normalized to that before contrast material injection and plotted as a function of time. Statistical analysis was performed by using two-way analysis of variance with repeated measures. Results: In general, before induction of pulmonary edema, attenuation of normally aerated lung areas did not increase after the initial peak of enhancement during the first pass of contrast material. In animals with hydrostatic edema, no attenuation changes in areas of ground-glass opacity were observed after the initial peak. Conversely, lung attenuation increased continuously in animals with oleic acid-induced high-permeability pulmonary edema (P = .002). After induction of lung edema, pulmonary enhancement measured in lung regions with normal ventilation or consolidation did not change in either group. Pulmonary fluid accumulation 90 minutes after induction of edema did not significantly differ between groups. Conclusion: Dynamic contrast-material enhanced CT can help differentiate between permeability and hydrostatic lung edema in an animal model.