Quality Control in Longitudinal Studies with Computed Tomographic Densitometry of the Lungs

Abstract

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.

Differences in CT Perfusion Summary Maps for Patients with Acute Ischemic Stroke Generated by 2 Software Packages

“…Because these scanner systems are regularly calibrated, we expect that this variation is smaller than the variation due to using different software-analysis packages. 25 However, this was not investigated in this study. Such a comparison would require additional CT scanning of patients with stroke and is, therefore, unethical because of an increase of radiation and contrast material and a delayed treatment.…”

Retinoid treatment of Emphysema in Patients on the Alpha-1 International Registry. The REPAIR study: study design, methodology and quality control of study assessments

“…In the absence of established international guidelines to guarantee the reliability of CT densitometry data in this study, a quality assurance procedure based on the current experience within this field was implemented [Stoel et al 2008]. The results showed that CT is a reliable endpoint for disease progression with higher sensitivity than conventional or other functional and symptomatic measures [Bakker et al 2005].…”

“…Therefore, lung density was adjusted for volume to determine lung density progression independently, thereby estimating any treatment effect on tissue loss alone. The theory and methodology are described in detail elsewhere [Stoel et al 2008]. In brief, the algorithm for the volume adjustment assumes that, for a given individual, there is a unique linear relationship between lung density and volume at each visit.…”

Low-dose lung cancer screening with photon-counting CT: a feasibility study

“…The detection of GGNs and emphysema are important and challenging tasks, however, the next step after detection is to provide quantitative metrics that can be used to evaluate and assess disease progression; this task is complicated by the HU variability between systems. In certain diseases, even a 1 HU change may be clinically significant to demonstrate disease progression, as with alpha1-antitrypsin deficiency (Stoel et al 2008). Thus efforts at improved accuracy for lung density ascertainment is necessary to provide quantitative biomarkers for the further development of treatments for diseases such as emphysema and idiopathic pulmonary fibrosis (IPF) that are currently characterized by HU changes.…”