Early identification of small airways disease on lung cancer screening CT: comparison of current air trapping measures

Lung. 2012 Dec;190(6):629-33. doi: 10.1007/s00408-012-9422-8. Epub 2012 Oct 12.


Background: 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.

Methods: 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-ratio(MLD)) 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.

Results: Functionally relevant air trapping was present in 38 (8.9 %) participants. E/I-ratio(MLD) 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-ratio(MLD) yielded an accuracy of 81.5 %.

Conclusions: The expiratory to inspiratory ratio of mean lung density (E/I-ratio(MLD)) is most suitable for detecting air trapping on low-dose screening CT and performs significantly better than other suggested quantitative measures.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Early Detection of Cancer*
  • Humans
  • Lung / diagnostic imaging*
  • Lung Neoplasms / diagnosis*
  • Male
  • Middle Aged
  • Pulmonary Emphysema / diagnosis
  • Pulmonary Emphysema / diagnostic imaging
  • Pulmonary Emphysema / etiology
  • Respiratory Function Tests
  • Smoking / adverse effects
  • Tomography, X-Ray Computed*