Comparison of Filtered Back Projection, Hybrid Iterative Reconstruction, Model-Based Iterative Reconstruction, and Virtual Monoenergetic Reconstruction Images at Both Low- and Standard-Dose Settings in Measurement of Emphysema Volume and Airway Wall Thickness: A CT Phantom Study.

Objective: To evaluate the accuracy of emphysema volume (EV) and airway measurements (AMs) produced by various iterative reconstruction (IR) algorithms and virtual monoenergetic images (VME) at both low- and standard-dose settings.

Materials and Methods: Computed tomography (CT) images were obtained on phantom at both low- (30 mAs at 120 kVp) and standard-doses (100 mAs at 120 kVp). Each CT scan was reconstructed using filtered back projection, hybrid IR (iDose4 ; Philips Healthcare), model-based IR (IMR-R1, IMR-ST1, IMR-SP1; Philips Healthcare), and VME at 70 keV (VME70). The EV of each air column and wall area percentage (WA%) of each airway tube were measured in all algorithms. Absolute percentage measurement errors of EV (APEvol ) and AM (APEWA% ) were then calculated.

Results: Emphysema volume was most accurately measured in IMR-R1 (APEvol in low-dose, 0.053 ± 0.002; APEvol in standard-dose, 0.047 ± 0.003; all p < 0.001) and AM was the most accurate in IMR-SP1 on both low- and standard-doses CT (APEWA% in low-dose, 0.067 ± 0.002; APEWA% in standard-dose, 0.06 ± 0.003; all p < 0.001). There were no significant differences in the APEvol of IMR-R1 between low- and standard-doses (all p > 0.05). VME70 showed a significantly higher APEvol than iDose4 , IMR-R1, and IMR-ST1 (all p < 0.004). VME70 also showed a significantly higher APEWA% compared with the other algorithms (all p < 0.001).

Conclusion: IMR was the most accurate technique for measurement of both EV and airway wall thickness. However, VME70 did not show a significantly better accuracy compared with other algorithms.