## 4 Discussion  
The comparison of the \(Q_{\text{max}}\) values for the various considered variants revealed that, with the same dose for the patient, the image quality using the W-Rh combination was about 3.5% higher than that of the Mo-Mo system for breasts with a thickness of 32 mm, about 83% higher for 45 mm-thick breasts, and over 2.4 times greater for 90 mm-thick breasts. The tungsten X-ray tube lost its superiority in performance only for the smallest considered breast thickness. In this case, better image quality was obtained with the combination of Rh-Rh and Mo-Rh. However, rhodium X-ray tubes are not used in mammography systems with the type of image detector considered in this study. The advantage of X-ray tubes with a tungsten anode over other solutions was confirmed in the published results of previous experimental studies [12; 13] and those using Monte Carlo methods [14; 17]. The conclusions regarding the Rh-Rh combination derived from [PERSON] et al. [17] are partially different from those presented in this paper. The authors of this previous study concluded that such a combination is never optimal, which contradicts the results shown in this paper for breasts with a thickness of 32 mm. The significant differences in the used methodology are most likely responsible for the discrepancy between the conclusions of the two studies. [PERSON] et al. performed simulations for breast phantoms with thicknesses of 2 cm, 4 cm, and 6 cm  
Figure 6: \(Q\) parameter as a function of high voltage for the 75 mm-thick breast and various anode–filter combinations. The points from the simulation are connected with a line. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{6}{c}{**Thickness of Phantom**} \\ \hline  & & 32 mm & 45 mm & 53 mm & 60 mm & 75 mm & 90 mm \\ \hline  & & & \multicolumn{6}{c}{Phantom glandularity} \\ \hline  & & 67\% & 41\% & 29\% & 20\% & 9\% & 4\% \\ \hline \multirow{2}{*}{Mo-Mo} & **voltage** & **24 kV** & **25 kV** & **25 kV** & **28 kV** & **27 kV** & **29 kV** \\  & **Qmax** & 0.991 & 1.959 & 2.029 & 1.171 & 1.312 & 1.313 \\ \hline \multirow{2}{*}{Mo-Rh} & **voltage** & **24 kV** & **25 kV** & **26 kV** & **27 kV** & **28 kV** & **28 kV** \\  & **Qmax** & 1.278 & 2.084 & 2.103 & 2.131 & 1.503 & 1.889 \\ \hline \multirow{2}{*}{Rh-Rh} & **voltage** & **25 kV** & **25 kV** & **26 kV** & **26 kV** & **27 kV** & **28 kV** \\  & **Qmax** & 1.957 & 2.273 & 2.471 & 2.476 & 1.832 & 2.150 \\ \hline \multirow{2}{*}{W-Rh} & **voltage** & **24 kV** & **25 kV** & **26 kV** & **28 kV** & **28 kV** & **30 kV** \\  & **Qmax** & 1.026 & 3.589 & 5.374 & 2.965 & 2.109 & 3.200 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Optimal voltages on the X-ray tube in kV for breasts of various structures and the corresponding \(Q_{\text{max}}\) (maximum values of parameter \(Q\)) for the selenium image detector. and a granularity of 50%, as well as thicknesses of 8 cm and 10 cm with a granularity of 10%, which, in the light of subsequent reports on the typical structure of the breast [17], is a far-reaching simplification. Moreover, their simulations were performed for a contrasting object of the 5 mm glandular tissue, only for four voltages, but also considered the contrast with microcalcifications. In the present study, the highest values of the \(Q_{\text{max}}\) parameter were observed for breasts with thicknesses ranging from 53 mm to 60 mm (25-28 kV). Lower image quality for breasts with smaller dimensions is due to their high glandularity, resulting in a deterioration of the physical contrast. For large breasts (over 60 mm after compression), the increase in tissue volume is not sufficiently compensated by the decreasing content of glandular tissue, and therefore the image quality in this case also decreases. This observed tendency is different from that presented by [PERSON] et al. [14], who revealed that the highest quality of imaging was associated with small breasts with thicknesses of 2 cm to 3 cm. This discrepancy is because [PERSON] et al.