# New-Generation ASiR-V for Dose Reduction While Maintaining Image Quality in CT: A Phantom Study
## 3 Results  
### Quantitative Analysis  
Image noise decreased with an increase in the blending percentage of ASiR and ASiR-V (Figure 2). Image noise was less than 12 HU (Hounsfield unit) in the majority of ASiR- and ASiR-V-blended images, and the worst result was found for the low blending percentages of ASiR-V with NI30. The closest blending percentage to the FBP reference value was 70% for ASiR NI18, 50% for ASiR-V with NI22, 30% for ASiR-V with NI24, and 90% for ASiR-V with NI30.  
For all the reconstructed images, the average CNR increased with blending (Figure 3a). The CNR (0.5%, 1%, and the average CNR) was higher in ASiR-V with NI24 images than the standard ASiR images currently adopted in our institute, as well as other ASiR-V images (with NI22 or NI30). For CNR of 0.5%, ASiR-V NI22 and NI24 with \(\geq\)50% blending gave a similar or higher value than that for FBP. However, the use of ASiR NI18 did not provide the same/similar encouraging result in regard to the CNR, with values similar to FBP only for very high blending (100%). Similar observations were also made for CNR 1% and the average CNR. Furthermore, the worst result in terms of the CNR was observed in the ASiR-V NI30 images.  
\begin{table}
\begin{tabular}{l l} \hline \hline \multicolumn{2}{l}{**Subjective Overall Image Quality (per Dataset)**} \\ \hline
1 & Bad, no diagnosis possible \\
2 & Insufficient, significantly reduced diagnostic confidence. \\
3 & Moderate, but sufficient for diagnosis \\
4 & Good \\
5 & Excellent \\ \hline \hline \multicolumn{2}{l}{**Subjective Image Artifacts (per Dataset)**} \\ \hline
1 & No artifacts \\
2 & Minor artifacts that do not affect the diagnosis \\
3 & Major artifacts impairing the visualization of important structures but allowing for diagnosis \\
4 & Artifacts affecting diagnostic information \\ \hline \hline \end{tabular}
\end{table}
Table 1: _Cont._  
Figure 2: Image noise as a function of various reconstruction methods measured from the Catphan 600 phantom.  
The SNR increased with the blending percentage for all the reconstructed images (Figure 4). Compared with the scans reconstructed with the standard FBP, the best results were obtained using ASiR-V NI24 and ASiR-V 22, with a blending >60%. ASiR NI18 with high blending (>70%) provided reasonably good performance (SNR) although slightly lower in comparison to ASiR-V NI22 and ASiR-V NI24. Furthermore, the worst result for the SNR was observed in the ASiR-V NI30 images.  
The optimal combination of the algorithm and blending percentage comparable/identical to FBP at a 50% MTF value of 0.32 was found to be ASiR-V NI22 with a 10% blending percentage (Figures 5 and 6). In general, ASiR-V NI22 and NI24 were comparable/identical to FBP using a lower blending percentage (10-40%).  
The highest value of 50% MTF (0.36) was obtained using ASiR-V NI30, independent of blending percentage. However, a number of image artifacts were observed in such images.  
In comparison, ASiR NI18 images acquired with a 10% blending percentage had a 50% MTF value of 0.34, close to the FBP value of 0.32.  
Figure 4: SNR as a function of several reconstruction algorithms measured with the Catphan 600 phantom.  
Figure 3: Average CNR (**a**), CNR 0.5% (**b**), and CNR 1% (**c**) as a function of various reconstruction methods measured using the Catphan 600 phantom.