## 3 Results and Discussion  
Each observer scored the images such as the one shown in Figure 3 to determine the IQF for an individual hole in the phantom for all the observers. The IQF average was then calculated for each image of the barely observable hole recorded by each observer. Table 1 shows the data of one observer for holes with various diameters and different contrast. Each observer scored three images obtained under similar conditions. For each hole-diameter, the limit of concentration of contrast media making the image of the hole barely observable is indicated in Table 1. The limit of the lowest concentration in the hole of a specific diameter is multiplied and used as indicated in Equation (1) to determine the IQF value. The average value of the IQF for each of the ten observers was obtained, as displayed in Table 2. Detecting the smallest diameter hole (1 mm) was difficult for most participants. This evidently defines the particular resolution detection limits for the used CT system. IQF value improved with increasing diameter, as shown in Figure 2.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Image**} & \multicolumn{4}{c}{**Image**} & \multicolumn{4}{c}{**Image**} \\ \hline
**D** & **IC** & \(\mathbf{D\times IC}\) & **D** & **IC** & \(\mathbf{D\times IC}\) & **D** & **IC** & \(\mathbf{D\times IC}\) \\ \hline
1.00 & No detectable hole & 0.0000 & 1.00 & No detectable hole & 0.0000 & 1.00 & No detectable hole & 0.0000 \\
2.50 & 0.0400 & 0.1000 & 2.50 & 0.0400 & 0.1000 & 2.50 & 0.0400 & 0.1000 \\
5.00 & 0.0370 & 0.1850 & 5.00 & 0.0320 & 0.1600 & 5.00 & 0.0370 & 0.1850 \\
6.00 & 0.0280 & 0.1680 & 6.00 & 0.0320 & 0.1920 & 6.00 & 0.0290 & 0.1740 \\
7.50 & 0.0280 & 0.2100 & 7.50 & 0.0290 & 0.2180 & 7.50 & 0.0290 & 0.2180 \\
9.00 & 0.0260 & 0.2340 & 9.00 & 0.0280 & 0.2520 & 9.00 & 0.0280 & 0.2520 \\
10.00 & 0.0260 & 0.2600 & 10.00 & 0.0240 & 0.2400 & 10.00 & 0.0260 & 0.2600 \\
11.00 & 0.0230 & 0.2530 & 11.00 & 0.0240 & 0.2640 & 11.00 & 0.0230 & 0.2530 \\
12.50 & 0.0230 & 0.2880 & 12.50 & 0.0230 & 0.2880 & 12.50 & 0.0230 & 0.2880 \\ \multicolumn{2}{c}{Image quality factor} & 1.6980 & Image quality factor & 1.7130 & Image quality factor & 1.7290 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The derived image quality factor from the mean values of the image scores verified by single assessors for iodine concentrations (IC, mM) and diameters (D, mm).  
This was a clear expression of the subject contrast influence, according to the CT images. The iodine concentration had little influence on the detectability of the holes instead of the diameter size, as indicated in Table 1. As can be seen, the image quality factor for the 9 mm width hole was lower compared the image quality factor for the 10 mm width hole, even though the identical concentration of iodine was used. Table 2 shows the average image quality factor of the ten assessors diverse from 11.610 to 1.750 and illustrates excellent contrast distribution values with slight standard deviation (SD).  
These results demonstrate that this modified phantom can pose a valuable means of assessing the low contrast detectability for CT scanners beyond the few points of measurements offered by current phantoms such as Catphan. Additionally, this phantom brings the advantages of using contrast detail phantoms which are typically used in projection radiography into the area of computed tomography.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Assessors** & **Mean IQF** \\ \hline
1 & 01.61 \(\pm\) 0.01 \\
2 & 01.65 \(\pm\) 0.09 \\
3 & 01.62 \(\pm\) 0.03 \\
4 & 01.63 \(\pm\) 0.05 \\
5 & 01.69 \(\pm\) 0.04 \\
6 & 01.73 \(\pm\) 0.01 \\
7 & 01.71 \(\pm\) 0.06 \\
8 & 01.71 \(\pm\) 0.02 \\
9 & 01.73 \(\pm\) 0.01 \\
10 & 01.75 \(\pm\) 0.00 \\ Overall average & 01.69 \(\pm\) 0.05 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The mean values of image quality factor (IQF) for the ten assessors and overall mean IQF value.  
Figure 3: It displays a typical slice from the phantom scan used in the process of scoring.