Rationale and objectives: To determine and analyze the most important error sources in lung CT densitometry in vivo.
Methods: The authors examined the influences of CT acquisition errors, physiologic changes, and image segmentation errors on lung densitometry. Among others, spatial dependency and long-term reproducibility of the density measurements of blood and air were examined over a period of 4 years in a group of 28 patients with pulmonary emphysema. These results were related to the measured lung densities in this group.
Results: The density measurement of blood and air is strongly dependent on the position in the thorax. Despite full-scanner calibrations, x-ray tube replacement can induce a significant increase in measured blood density.
Conclusions: A change in a lung density parameter over time can actually be the result of tube replacement or changing blood density. A simple postprocessing technique can correct for these changes.