Early identification of small airways disease on lung cancer screening CT: comparison of current air trapping measures.
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.
Department of Radiology, University Medical Centre Utrecht, Heidelberglaan 100, HP E01.132, Postbus 85500, 3508 GA, Utrecht, The Netherlands. metsonno@gmail.com
Onno M
OM
Mets
Pieter
P
Zanen
Jan-Willem J
JW
Lammers
Ivana
I
Isgum
Hester A
HA
Gietema
Bram
B
van Ginneken
Mathias
M
Prokop
Pim A
PA
de Jong
D000368:Aged; D055088:Early Detection of Cancer; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging*; D008175:Lung Neoplasms / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D011656:Pulmonary Emphysema / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000209:etiology; D012129:Respiratory Function Tests; D012907:Smoking / Q000009:adverse effects; D014057:Tomography, X-Ray Computed