Abstract
ObjectivesTo determine the variation in quantitative computed tomography (CT) measures of air trapping in low-dose chest CTs of heavy smokers.MethodsWe 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.ResultsThe limits of agreement for uncorrected CT air trapping 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 %, P = 0.002), but not for E/I-ratioMLD (−9.2 to 7.9 %, P = 0.75). Statistical lung volume correction did not improve the limits for EXP−856 (−12.5 to 8.8 %, P = 0.12) and E/I-ratioMLD (−7.5 to 5.8 %, P = 0.17).ConclusionsQuantitative air trapping measures on low-dose CT of heavy smokers show considerable variation on repeat CT examinations, regardless of lung volume correction or reproducible breath holds.Key Points• Computed tomography quantitatively measures small airways 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.
Highlights
Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality worldwide, and is projected to become one of the leading causes of death in the world in the coming decades [1, 2]
Reproducibility of computed tomography (CT) air trapping measures between the two visits was assessed by the concordance correlation coefficient, which takes into account both the correlation and the distance to the line of identity [19]
We report the limits of agreement in quantitative assessment of CT air trapping in current and former heavy smokers
Summary
Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality worldwide, and is projected to become one of the leading causes of death in the world in the coming decades [1, 2]. It is thought that the disease starts long before obstruction is measurable on spirometry by narrowing and disappearance of small airways, before the onset of emphysematous destruction which eventually results in deterioration of lung function [3]. This sequence of events makes the evaluation of small airways disease highly interesting for measuring disease progression in the early stages of smoking-induced lung disease. Air trapping can be automatically quantified by CT, which makes it suitable to study disease progression in large cohort studies [4, 5], lung cancer screening examinations [6, 7] and drug trials. The objective of this study was to determine the variation in two commonly used quantitative CT air trapping measures in current and former heavy smokers
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