Impact of hybrid iterative reconstruction on unenhanced liver CT

Objective: To clarify the impact of hybrid iterative reconstruction (HIR) and filtered back projection (FBP) on unenhanced liver CT. Methods: 30 patients with hepatocellular carcinoma (HCC) underwent unenhanced CT. The images were reconstructed with FBP and weak (Level 1), mild (Level 4) and strong (Level 7) levels of HIR (iDose4; Philips Medical Systems, Cleveland, OH). Quantitatively, attenuations of the HCC (with the largest lesion in each case), hepatic parenchyma (the average of four segments) and image noise (standard deviation of the attenuations in hepatic parenchyma) were compared between the four kinds of reconstruction using the two-tailed paired ttest. Qualitatively, liver lesion conspicuity and characterization were also compared using the Wilcoxon signed-rank test. Results: Attenuation of the liver lesion with the strong level of HIR was significantly higher than that with FBP (p50.0005). Attenuations of hepatic parenchyma with all three HIR levels were significantly lower than that with FBP (p#0.0002 in all comparisons). Image noisewith each of the three HIR levels was significantly smaller than that with FBP (p,0.0001 in any comparison). There was no significant difference in lesion conspicuity and characterization between FBP and each HIR level (p$0.0819 in all comparisons). Conclusion: Although attenuations of the liver lesion and hepatic parenchyma were significantly different between HIR and FBP, HIR had no significant effect on lesion conspicuity and characterization. Advances in knowledge: Attenuations of liver lesions and hepatic parenchyma differ significantly between HIR and FBP images.