Quantification of emphysema using low-dose chest CT: Effect of iterative reconstruction

Abstract

Background: Iterative reconstruction (IR) is widely used in low-dose CT examinations for reducing image noise and saving radiation dose. Lung density profile has been reported to be significantly influenced by IR. The aim of this study was to evaluate the changes of emphysema quantification according to variation of low-density thresholds, percentile of lung density, and volume of low-attenuation clusters in low-dose chest CT using IR comparing with those using filtered back projection (FBP). Methods: 50 patients (39 men and 11 women; mean age 56.7 years) who underwent low dose (20 mA, dose modulation) chest CT scans for lung cancer screening were included in the study. CT images were reconstructed using both FBP and IR (iDose; Philips Healthcare, Netherlands). Lung volume, mean lung density, low density volumes with the threshold of -950 HU (LDV-950) and -910 HU (LDV-910), 15th percentile of lung density, and volume of low attenuation clusters (cluster sizes 2–8,8–65, 66–186, >186 mm2) were measured in each set of low-dose CT images. The measurement results of two reconstruction methods were compared using concordance correlation coefficient (ρc) and a Bland-Altman plot. Findings: Although total lung volume and mean lung density showed almost perfect agreement (ρc=0.99), all other measurements showed poor agreement between IR and FBP (0.090–0.855). LDV-910 showed relatively better agreement (ρc=0.842) compared with LDV-950 (ρc=0.648) and 15th percentile (ρc=0.527). Mean differences of LDV-950, LDV-910, and 15th percentile measured in two algorithms were 3.9%, 3.3%, and 28.7 HU. Mean differences of volume of low attenuation clusters were 2.1%, 3.0%, 0.6%, and 1.9%, respectively. Interpretation: Measurement of emphysema quantification with low-dose CT using IR showed significantly different results than with those using FBP. Low-density volume using higher threshold showed better agreement. Funding: None. Conflicts of interest: We declare that we have no conflicts of interest.