| Summary: | In contrast to studies of adults with emphysema, application of fixed thresholds to determine low- and high-attenuation areas (air-trapping and parenchymal lung disease) in pediatric quantitative chest CT is problematic. We aimed to assess age effects on: (i) mean lung attenuation (full inspiration); and (ii) low and high attenuation thresholds (LAT and HAT) defined as mean attenuation and 1 SD below and above mean, respectively. Chest CTs from children aged 6–17 years without abnormalities were retrieved, and histograms of attenuation coefficients were analyzed. Eighty examinations were included. Inverse functions described relationships between age and mean lung attenuation, LAT or HAT (<i>p</i> < 0.0001). Predicted value for LAT decreased from −846 HU in 6-year-old to −950 HU in 13- to 17-year-old subjects (cut-off value for assessing emphysema in adults). %TLC<sub>CT</sub> with low attenuation correlated with age (r<sub>s</sub> = −0.31; <i>p</i> = <i>0</i>.005) and was <5% for 9–17-year-old subjects. Inverse associations were demonstrated between: (i) %TLC<sub>CT</sub> with high attenuation and age (r<sup>2</sup> = 0.49; <i>p</i> < 0.0001); (ii) %TLC<sub>CT</sub> with low attenuation and TLC<sub>CT</sub> (r<sup>2</sup> = 0.47; <i>p</i> < 0.0001); (iii) %TLC<sub>CT</sub> with high attenuation and TLC<sub>CT</sub> (r<sup>2</sup> = 0.76; <i>p</i> < 0.0001). In conclusion, quantitative analysis of chest CTs from children without lung disease can be used to define age-specific LAT and HAT for evaluation of pediatric lung disease severity.
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