Sources of error in lung densitometry with CT

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, phys iologic changes, and image segmentation errors on lung densitometry. Among others, spatial dependency and long-term reproducibility of the density mea surements of blood and air were examined over a period of 4 years in a grou p of 28 patients with pulmonary emphysema, These results were related to th e 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 r eplacement 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 postpro cessing technique can correct for these changes.