CHEST Variation in quantitative CT air trapping in heavy smokers on repeat CT examinations

Objectives To determine the variation in quantitative com-puted tomography (CT) measures of air trapping in low-dose chest CTs of heavy smokers. Methods We analysed 45 subjects from a lung cancer screening trial, examined by CT twice within 3 months. Inspiratory and expiratory low-dose CT was obtained using breath hold instructions. CT air trapping was defined as the percentage of voxels in expiratory CT with an attenuation below −856 HU (EXP−856) and the expiratory to inspiratory ratio of mean lung density (E/I-ratioMLD). Variation was determined using limits of agreement, defined as 1.96 times the standard deviation of the mean difference. The effect of both lung volume correction and breath hold reproducibility was determined. Results The limits of agreement for uncorrected CT air trap-ping measurements were −15.0 to 11.7 % (EXP−856) and −9.8 to 8.0 % (E/I-ratioMLD). Good breath hold reproducibility significantly narrowed the limits for EXP−856 (−10.7 to 7.5 %, P00.002), but not for E/I-ratioMLD (−9.2 to 7.9 %, P00.75). Statistical lung volume correction did not improve the limits for EXP−856 (−12.5 to 8.8 %, P00.12) and E/I-ratioMLD (−7.5 to 5.8 %, P00.17). Conclusions Quantitative air trapping measures on low-dose CT of heavy smokers show considerable variation on repeat CT examinations, regardless of lung volume correc-tion or reproducible breath holds. Key Points • Computed tomography quantitatively measures small air-ways disease in heavy smokers. • Measurements of air trapping vary considerably on repeat CT examinations. • Variation remains substantial even with reproducible breath holds and lung volume correction