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

¹ Department of Radiology, Liverpool Heart and Chest Hospital, NHS Trust, Thomas Dr., Liverpool L143PE, United Kingdom.
² Department of Radiology, Universidade Federal Fluminense, Centro de Ciências Médicas, Niteroi, RJ, Brazil.
³ Department of Radiology, Complexo Hospitalar Santa Casa de Porto Alegre, Rua João Alfredo, 558/301, Cidade Baixa CEP 90050-230, Porto Alegre, RS, Brazil.
⁴ Post Graduation Program in Pulmonary Sciences of the Federal University of Rio Grande do Sul (UFRGS), Department of Chest Medicine, Complexo Hospitalar Santa Casa de Porto Alegre, Porto Alegre, RS, Brazil.
⁵ Department of Nuclear Medicine, Complexo Hospitalar Santa Casa de Porto Alegre, Porto Alegre, RS, Brazil.
⁶ Irion Radiologia, Porto Alegre, RS, Brazil.

OBJECTIVE. The purpose of this prospective study was to evaluate volumetric CT emphysema quantification (CT densitovolumetry) in a young population with no recognizable lung disease.

SUBJECTS AND METHODS. 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.

RESULTS. 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%).

CONCLUSION. 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.

Keywords: CT • density • densitometry • emphysema • lung • lung function • volume

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