Recirculation of Inhaled Xenon Does Not Alter Lung CT Density

Abstract

Xenon-enhanced computed tomography (Xe-CT) measures regional ventilation from changes in lung parenchymal CT density during the multibreath washin/washout of inhaled Xe gas. Because Xe is moderately soluble, vascular uptake and redistribution has been proposed as a confounding phenomenon. We propose that the redistribution of Xe via the circulation is negligible, and correction is unwarranted. Unilateral ventilation with 60% Xe was performed in intubated canines. Whole-lung CT images were obtained at baseline and after 1 and 5 minutes of unilateral Xe ventilation. Comparisons between blocked (B) and Xe ventilated (V) whole lung densities were made. Density of paraspinous muscle and blood (aorta, inferior vena cava) were also compared. The density of lung tissue in the V lungs increased significantly compared to B lungs after 1 minute (B -688.5 +/- 54.3 Hounsfield units [HU] vs. V -535.4 +/- 55.6 HU, P < .05) and 5 minutes (B -689.1 +/- 52.2 HU vs. V -492.9 +/- 89.1 HU, P < .05) of Xe ventilation. The density in the blocked lungs did not significantly change after either 1 or 5 minutes of ventilation with Xe. Although density tended to increase with time in the blood and muscle, the change only reached significance in muscle at 5 minutes. Five minutes of ventilation with a high concentration of Xe does not cause measurable density changes in the contralateral, unventilated lung. Xe accumulation in muscle tissue limits redistribution. Correction of Xe-CT time series density data may be unnecessary.