CT Quantification of Emphysema in Young Subjects with No Recognizable Chest Disease

Abstract

The purpose of this prospective study was to evaluate volumetric CT emphysema quantification (CT densitovolumetry) in a young population with no recognizable lung disease. A cohort of 30 nonsmoking patients with no recognizable lung disease (16 men, 14 women; age range, 19-41 years) underwent inspiratory and expiratory CT, after which the data were postprocessed for volumetric quantification of emphysema (threshold, -950 HU). Correlation was tested for age, weight, height, sex, body surface area (BSA), and physical activity. Normal limits were established by mean +/- 1.96 SD. No correlation was found between the measured volumes and age or physical activity. Correlation was found between BSA and normal lung volume in inspiration (r = 0.69, p = 0.000), shrink volume (i.e., difference in total lung volume in inspiration and in expiration) (r = 0.66, p = 0.000), and percentage of shrink volume (r = 0.35, p = 0.05). For an alpha error of 5%, the limits of normality based on this sample are percentage of emphysema in inspiration, 0.35%; percentage of emphysema in expiration, 0.12%; and maximum lung volume in expiration, 3.6 L. The maximum predicted percentage of shrink volume can be calculated as %SV = 29.43% + 16.97% x BSA (+/- 1.96 x 7.61%). Young healthy nonsmokers with no recognizable lung disease can also show a small proportion of emphysematous-like changes on CT densitovolumetry when a threshold of -950 HU is used. Reference values should be considered when applying the technique for early detection or grading of emphysema and when studying aging lungs.