Purpose or Case Report: To describe the normal progression of quantitative CT chest parameters in children
Methods & Materials: All patients with an available normal non-contrast enhanced chest CT from 2008 to 2019 were included. Patients with any abnormality in the lung parenchyma, thoracic cage deformity/malformation, acute/chronic respiratory symptoms, or incomplete field of view were excluded. Lung parenchyma was segmented with a semi-automated technique using an open source software. Percentage of low attenuation areas ≤ -900 HU (LAA), high attenuation areas ≥ -700 HU (HAA), mean lung density (MLD), kurtosis, skewness, lung mass, and volume were obtained. Kurtosis describes the sharpness of a histogram’s peak, whereas skewness shows the degree of asymmetry. Descriptive data were presented as mean ± standard deviation. Linear regression models were used to evaluate the relationship between quantitative CT parameters with age (years). Reference equations were obtained using the intercepts and slopes. P-values < 0.05 were considered significant.
Results: 220 children (111 girls) were included. The mean age was 9.5 ± 5.9 years. The most common CT indication was “staging/restaging lung metastasis” (n = 185), followed by “suspected pulmonary blebs” (n = 9) and “suspected thoracic mass” (n = 8). LAA showed a weak correlation with age (r = 0.26, R² = 0.70, p < 0.001). HAA displayed a strong negative correlation with age (r = -0.84, R² = 0.71, p < 0.001). The MLD had a strong negative correlation with age (r = -0.83, R² = 0.71, p = < 0.001). Kurtosis (r = 0.75, R2 = 0.57, p < 0.001) and skewness (r = 0.82, R² = 0.68, p < 0.001) showed a strong positive correlation with age. Finally, mass (r = 0.92, R² = 0.85, p < 0.001) and volume (r = 0.86, R² = 0.75, p < 0.001) showed a strong positive correlation with age. Reference equations for calculating expected values by age (years) are as follows: LAA (%) = 0.028 – (0.009 x Age), HAA (%) = 84.2 – (4.7 x Age), MLD (HU) = 572 + (14.7 x Age), kurtosis = 4 + (0.9 x Age), skewness = 1.7 + (1.3 x Age), mass (g) = 86.2 + (44.4 x Age), and volume (L) = 0.2 – (0.2 x Age).
Conclusions: Quantitative CT analysis shows that as children grow, the lung parenchyma attenuation decreases linearly and becomes more homogenous. Age is a moderate to strong predictor of the different quantitative CT parameters, except for low attenuation areas.