Variability in densitometric assessment of pulmonary emphysema with computed tomography

Objectives: The objectives of this Study were to investigate whether computed tomography (CT) densitometry can be applied consistently in different centers; and to evaluate the reproducibility of densitometric quantification of emphysema by assessment of different sources of variation, ie, intersite, interscan and inter- and intraobserver variability, in comparison with intersubject variability. Materials and Methods: In 5 different hospitals, 119 patients with emphysema were scanned Using standardized protocols. In each site, an observer performed a quantitative densitometric analysis; (including blood recalibration) on the corresponding patient group (n = 23-25) and one observer analyzed the entire group of 119 patients. After several months, the latter observer analyzed all data for a second time. Subsequently, different sources of variation were assessed by variance component analysis with and without volume correction of the data. Results: Inter- and intraobserver variability marginally contributes to the total variability (< 0.001%). The interscan variability was 0.02% of the total variation after application of volume correction. The intersite variability was 48% as a result of one deviating CT scanner. Air recalibration normalized deviating air densities in CT scanners. Within sites, the intersubject variability ranged between 93% and 99% based on the analysis of 2 subsequent CT scans of the patients.