Small-Animal PET of Rat Lung Perfusion in Supine and Prone Position

Emerging experimental data indicate that the pulmonary blood flow remained directed toward the dorsal regions after turning animals from a supine to a prone position. This finding supported the hypothesis that the distribution of perfusion throughout the lung was not primarily dictated by the gravity but by the fractal behavior of the pulmonary vasculature. However there are only limited data about the spatial distribution of lung perfusion in rats in prone and supine position. The purpose of the study was to quantify the relative perfusion (Q) distribution in rat lungs in both positions using [68Ga]Ga-DOTA-microspheres with small-animal PET, -CT, and -MRI to obtain reference data for further investigations on injured rat lungs. Methods: Regional pulmonary perfusion was investigated after injection of [68Ga]Ga-DOTA-microsphers (20 micrometer diameter) of albumin in both prone and supine positions in normal breathing rats, anesthetized with desflurane. The heart rate was continuously recorded. The right femoral artery and vein were cannulated, arterial blood pressure, blood gases, and pH were measured. The microspheres were intravenously applied. Emission data were collected for 30 min. Before and after the PET measurement the animals were studied with CT to investigate the lungs and to calculate their volumes. Randomly selected animals were studied also with smallanimal MRI. The [68Ga]-activity 3D distributions were analyzed from the coregistered volume data reconstructed with 3D OSEM MAP algorithm (resolution in the center of field of view 1.8 mm). Results: There were no significant differences of mean Q in the ventral and dorsal elements of normal rat lungs. Conclusion: The body position (prone and supine) of normal breathing rats does not influence the mean Q btained with small-animal PET and the lung volumes measured with small-animal CT. The histogram of the regional blood flow in supine position reflects a more heterogeneous blood flow distribution.