Low- and high-attenuation lung volume in quantitative chest CT in children

<b>Background:</b> In contrast to studies in adults with emphysema, application of fixed thresholds to determine low- and high-attenuation areas (air-trapping and parenchymal lung disease, respectively) in pediatric quantitative chest CT is problematic. <b>Objective:</b> To assess the effects of age on: (i) mean lung attenuation at full inspiration; (ii) low- and high-attenuation thresholds (LAT and HAT) defined as mean and one standard deviation below and above the mean attenuation, respectively. We hypothesized that significant associations exist between age or total lung capacity measured by CT (TLC_CT), and %TLC_CT with low or high attenuation. <b>Methods:</b> Chest CTs from children aged 6-17 years without abnormal findings were retrieved from hospital database and histograms of attenuation coefficients were analyzed. <b>Results:</b> Examinations from 80 children were included. Inverse functions described relationships between age and mean lung attenuation, LAT or HAT (P&lt;.0001). Predicted value for LAT decreased from -846 HU in 6-year-old children to approximately -950 HU in 13- to 17-year-old subjects, which is the cut-off value used to assess emphysema severity in adults. %TLC_CT with low attenuation correlated weakly with age (r_s = -0.31; P =.005) and was &lt;5% for subjects 9-17 years old. Inverse associations were found between: (i) %TLC_CT with low attenuation and TLC_CT (r²=0.47; P&lt;.0001); (ii) %TLC_CT with high attenuation and age (r²=0.49; P&lt;.0001); (iii) %TLC_CT with high attenuation and TLC_CT (r²=0.76; P&lt;.0001). <b>Conclusion:</b> Quantitative analysis of chest CTs from children without lung disease can be applied to define age-specific LAT and HAT for the evaluation of severity of pediatric lung disease.