Abstract
Rationale. In healthy individuals, the density of pulmonary parenchyma at computed tomography (CT) in the dependent lung is higher than the density in the nondependent lung, reflecting a gravity-dependent density gradient. Abnormal pulmonary perfusion is known to result in regional differences in CT density. We evaluated possible disturbances in the normal CT density gradient in patients with idiopathic pulmonary arterial hypertension (IPAH).
Methods. We analyzed non-contrast enhanced thin section CTs of 7 patients with IPAH - established on right heart catheterisation - and 8 healthy controls. Regions of interest (ROI) were selected in the most dependent and nondependent areas at two levels: aortic arch and pulmonary venous confluence. The mean densities in Hounsfield Units (HU) for the ROIs in each lung region were obtained and their average was taken as the mean density for that region. Average densities were calculated for the dependent and non-dependent ROIs in each level and zonal and global density gradients were derived.
Results. Patients with IPAH were characterized by a decreased density gradient compared to the healthy individuals, at the level of aortic arch (median, 15.3 versus 35.6, p = .04), the level of pulmonary venous confluence (median, 29.1 versus 46.3, p = .02) and globally (median, 24.6 versus 42.9, p = .03).
Conclusion. Patients with IPAH have a significantly reduced gravity-dependent density gradient compared to healthy individuals. This observation suggests that the normal gradient is largely dependent on the structural integrity and compliance of the pulmonary vasculature.
- © 2014 ERS