## 3 Results
### Qualitative and Quantitative Experimental Results of Head Data  
The reconstruction results of head CT data from 90\({}^{\circ}\) projection data are shown in Figure 10. The average PNSR, SSIM, and RMSE results for the reconstruction results of the head CT data from 90\({}^{\circ}\) projection data are shown in Table 4.  
Figure 8: The absolute difference between the experimental results of each method and the reference results. The pixel range of the images is \([0,255]\). (Best viewed with zoom-in).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Angle** & **FBP** & **SART-TV** & **SIN** & **Tomo-GAN** & **SIAR-GAN** \\ \hline \([0^{\circ},150^{\circ}]\) & 39.4962 \(\pm\) 5.0869 & 28.2127 \(\pm\) **0.9706** & 13.0721 \(\pm\) 2.1081 & 11.0954 \(\pm\) 2.6180 & **7.3066**\(\pm\) 1.4727 \\ \([0^{\circ},120^{\circ}]\) & 41.6998 \(\pm\) 4.4619 & 31.7996 \(\pm\) 1.6256 & 15.8862 \(\pm\) 2.3972 & 13.7782 \(\pm\) 2.6471 & **7.9773**\(\pm\) **1.4524** \\ \([0^{\circ},90^{\circ}]\) & 57.0615 \(\pm\) 3.5469 & 37.0192 \(\pm\) **1.4280** & 19.5390 \(\pm\) 1.8999 & 15.5744 \(\pm\) 3.0219 & **8.8614**\(\pm\) 1.6025 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Average RMSE results (mean \(\pm\) standard deviation).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Angle** & **FBP** & **SART-TV** & **SIN** & **Tomo-GAN** & **SIAR-GAN** \\ \hline \([0^{\circ},150^{\circ}]\) & 39.4962 \(\pm\) 5.0869 & 28.2127  
Although the reconstruction results of SART-TV are intuitively better than those of FBP, neither of them achieved satisfactory reconstruction results. The main problem of SIN reconstruction results is that there is a certain degree of ambiguity. Both SI-GAN and Tomo-GAN methods obtained reconstruction results similar to the reference, but, from the  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Indicator** & **FBP** & **SART-TV** & **SIN** & **Tomo-GAN** & **SIAR-GAN** \\ \hline PSNR & 10.1629 \(\pm\) 0.6996 & 14.7071 \(\pm\) **0.6204** & 23.1279 \(\pm\) 1.6591 & 25.7152 \(\pm\) 2.4894 & **28.7140**\(\pm\) 1.5467 \\ SSIM & 0.2812 \(\pm\) 0.0339 & 0.2973 \(\pm\) **0.0348** & 0.7249 \(\pm\) 0.0548 & 0.7886 \(\pm\) 0.0597 & **0.8814**\(\pm\) 0.0496 \\ RMSE & 79.3923 \(\pm\) 6.2318 & 47.0200 \(\pm\) 2.3155 & 18.1147 \(\pm\) 3.4723 & 13.8080 \(\pm\) 4.5798 & **9.4966**\(\pm\) **1.9533** \\ \hline \hline \end{tabular}
\end{table}
Table 4: Average PNSR, SSIM, and RMSE results for the reconstruction results of the head CT data from the 90\({}^{\circ}\) projection data (mean \(\pm\) standard deviation).  
Figure 10: Reconstruction results of the head CT data from the 90\({}^{\circ}\) projection data. The first, third, and fifth rows of images are the reconstruction results of each method. The image in the first column in each of these rows is the reference image reconstructed by the standard FBP algorithm using the full scan. The subsequent columns show the images reconstructed by SIAR-GAN (2 nd column), Tomo-GAN (3 rd column), SIN (4 th column), SART-TV (5 th column), and FBP (6 th column) algorithms. Below each reconstruction result, the residual image obtained by subtracting the corresponding reconstructed image from the reference image is shown. The pixel range of the residual images is [0, 255]. (Best viewed with zoom-in).  
residual images, the reconstruction results of SI-GAN have less errors. The data in Table 4 demonstrate the above analysis, with the best performing results given in bold.