Quality control in longitudinal studies with computed tomographic densitometry of the lungs.

To guarantee the reliability of densitometric data in clinical trials on pulmonary emphysema a quality control procedure is presented, to prevent that a measured progression in lung density could be reflected by a gradual change in the maintenance of the computed tomographic scanner. For that purpose, a foam phantom has been developed, which mimicks the densities of emphysematous lung tissue, fixed in a sealed Perspex box. Analysis software was developed to automatically compare the density readings with a baseline reference. It was found that this quality control procedure can pick up subtle changes in the scanner of less than 1 hounsfield unit, due to changes in the X-ray tube, detectors, or reconstruction software, and can detect certain imaging artifacts. Therefore, it is recommended that this type of procedure be used to ensure the integrity of densitometric data in longitudinal studies.