## 3 Results  
N-FBP and N-ASiR/N-ASiR-V maps (with different blending levels of reconstruction) of the CTP486 homogeneous module and CTP404 module with contrast objects are shown in Figures 1 and 2, respectively. Moreover, PDN-ASiR and PDN-ASiR-V maps (with different blending levels of reconstruction) of the CTP486 homogeneous module and CTP404 module with contrast objects are displayed in Figures 3 and 4, respectively. Figure 4: CTP404 phantom module. Maps of the percentage difference (%) between noise of the FBP-reconstructed CT image and noise of both ASiR-V-reconstructed and ASiR-reconstructed CT images with different blending levels (20%, 40%, 60%, 80%, and 100%). Figure 3: CTP486 phantom module. Maps of the percentage difference (%) between noise of the FBP-reconstructed CT image and noise of both ASiR-V-reconstructed and ASiR-reconstructed CT images with different blending levels (20%, 40%, 60%, 80%, and 100%). Figure 2: Noise maps (HU) of a CT image of the CTP404 phantom module reconstructed using FBP and ASiR/ASiR-V with different blending levels (20%, 40%, 60%, 80%, and 100%). The corresponding FBP-reconstructed CT image of the phantom is also displayed. Noise maps of the homogenous CTP486 phantom module (Figure 1) showed only a slight spatial variation of local noise values for the FBP-reconstructed CT image, which seemed less for ASiR-V- and ASiR-reconstructed CT images with higher blending levels. This is corroborated by the _NUI_ values reported in detail in Figure 5. In particular, the _NUI_ value for the FBP-reconstructed CT image was 5.2%, while the _NUI_ values for the ASiR-V- and ASiR-reconstructed CT images with a 100% blending level were 2.7% and 3.4%, respectively. On the other hand, noise maps of the CTP404 phantom module (including various contrast objects) (Figure 2) showed a more appreciable degree of spatial variation of noise, with higher noise values at the boundary between each contrast object and background, especially for ASiR-V- and ASiR-reconstructed CT images. The _NUI_ value for the FBP-reconstructed CT image was 6.7%. The _NUI_ values for the IR-reconstructed CT images increased nonlinearly with the blending level and were 19% and 15% for pure ASiR-V and ASiR, respectively. As shown by PDN-ASiR-V and PDN-ASiR maps of the homogenous CTP486 module (Figure 3), when compared with conventional FBP, both ASiR and ASiR-V allowed a substantial noise reduction in CT imaging. In this regard, noise values in the CT imaging of the homogenous CTP486 phantom module are reported in Table 2 for FBP, ASiR-V, and ASiR. The percentage difference between noise in the FBP-reconstructed CT image and that in both ASiR-V- and ASiR-reconstructed CT images increased with increasing blending level, up to 64% and 53% for ASiR-V and ASiR, respectively (Figure 6). Except for the lowest blending level of 20%, ASiR-V presented greater noise reduction potential than ASiR (Figure 6). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Blending Level** & **FBP** & **ASiR** & **ASiR-V** \\ \hline
0\% & 9.5 (1.3) & & \\
20\% & & 7.9 (1.1) & 8.0 (1.2) \\
40\% & & 6.9 (1.0) & 6.5 (1.0) \\
60\% & & 5.8 (0.8) & 5.4 (0.8) \\
80\% & & 4.9 (0.7) & 4.4 (0.6) \\
100\% & & 4.5 (0.7) & 3.4 (0.5) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Homogeneous CTP486 module. Noise level estimated as the mean (SD) value of N-FBP, N-ASiR, and N-ASiR-V maps within a central circular ROI of 1 cm diameter. Figure 5: Nonuniformity index (_NUI_) values of noise maps of CT reconstructed images (FBP, ASiR-V, and ASiR) of the CTP486 (**a**) and CTP404 (**b**) phantom modules. For _NUI_ estimation, only the inner part of the phantom (diameter, 15 cm) was considered.