Early Identification of Small Airways Disease on Lung Cancer Screening CT: Comparison of Current Air Trapping Measures
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Lung cancer screening CT scans might provide valuable information about air trapping as an early indicator of smoking-related lung disease. We studied which of the currently suggested measures is most suitable for detecting functionally relevant air trapping on low-dose computed tomography (CT) in a population of subjects with early-stage disease.
This study was ethically approved and informed consent was obtained. Three quantitative CT air trapping measures were compared against a functional reference standard in 427 male lung cancer screening participants. This reference standard for air trapping was derived from the residual volume over total lung capacity ratio (RV/TLC) beyond the 95th percentile of predicted. The following CT air trapping measures were compared: expiratory to inspiratory relative volume change of voxels with attenuation values between −860 and −950 Hounsfield Units (RVC−860 to −950), expiratory to inspiratory ratio of mean lung density (E/I-ratioMLD) and percentage of voxels below −856 HU in expiration (EXP−856). Receiver operating characteristic (ROC) analysis was performed and area under the ROC curve compared.
Functionally relevant air trapping was present in 38 (8.9 %) participants. E/I-ratioMLD showed the largest area under the curve (0.85, 95 % CI 0.813–0.883), which was significantly larger than RVC−860 to −950 (0.703, 0.657–0.746; p < 0.001) and EXP−856 (0.798, 0.757–0.835; p = 0.002). At the optimum for sensitivity and specificity, E/I-ratioMLD yielded an accuracy of 81.5 %.
The expiratory to inspiratory ratio of mean lung density (E/I-ratioMLD) is most suitable for detecting air trapping on low-dose screening CT and performs significantly better than other suggested quantitative measures.
KeywordsAir trapping Small airways disease Computed tomography Quantitative analysis
Outside the submitted work, MP declared to have received research Grants from Philips Medical Systems and Toshiba Medical Systems, as well as payments and travel expenses for various lectures on CT and CTA.
Conflict of interest
The authors declared no conflicts for the work under consideration.
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