The effect of iterative reconstruction on computed tomography assessment of emphysema, air trapping and airway dimensions

OBJECTIVES: To determine the influence of iterative reconstruction (IR) on quantitative computed tomography (CT) measurements of emphysema, air trapping, and airway wall and lumen dimensions, compared to filtered back-projection (FBP). METHODS: Inspiratory and expiratory chest CTs of 75 patients (37 male, 38 female; mean age 64.0 ± 5.7 years) were reconstructed using FBP and IR. CT emphysema, CT air trapping and airway dimensions of a segmental bronchus were quantified using several commonly used quantification methods. The two algorithms were compared using the concordance correlation coefficient (p (c)) and Wilcoxon signed rank test. RESULTS: Only the E/I-ratio(MLD) as a measure of CT air trapping and airway dimensions showed no significant differences between the algorithms, whereas all CT emphysema and the other CT air trapping measures were significantly different at IR when compared to FBP (P < 0.001). CONCLUSION: The evaluated IR algorithm significantly influences quantitative CT measures in the assessment of emphysema and air trapping. However, the E/I-ratio(MLD) as a measure of CT air trapping, as well as the airway measurements, is unaffected by this reconstruction method. Quantitative CT of the lungs should be performed with careful attention to the CT protocol, especially when iterative reconstruction is introduced. KEY POINTS: • New techniques in CT allow numerous quantitative measurements of lung function. • Iterative reconstruction influences quantitative CT measurements of emphysema and air trapping. • Expiratory-to-inspiratory ratio of mean lung density and airway measurements are unaffected by iterative reconstruction. • Quantitative lung-CT should be performed with careful attention to the CT protocol.