# Safety Assessment of Microwave Breast Imaging: Heating Analysis on Digital Breast Phantoms
## 4 Discussion  
Testing the safety of microwave mammography through virtual experiments was the aim of this work, with a focus directly on the biological effect, namely the induced temperature increase. The highest temperature increase observed in this analysis is 58.5 \(\mu\)K. Such a small temperature increase is related to the low incident power level at which the MammoWave system operates (1 mW). Other MI devices could operate at different power \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{2}{c}{**Model \#5**} & \multicolumn{4}{c}{**Horn Antenna Position**} \\ \hline \multirow{3}{*}{8} & Fat & 4.97 & 2.12 & 2.41 & 2.60 & 2.36 \\ \cline{2-6}  & Gland & 14.1 & 8.28 & 6.63 & 11.6 & **12.3** \\ \cline{2-6}  & Skin & **15.9** & **12.6** & **12.7** & **13.3** & 12.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: _Cont._ \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Model \#1**} & \multicolumn{2}{c}{**Horn Antenna Position**} \\ \hline \multirow{3}{*}{f [GHz]} & \multirow{3}{*}{Breast tissue} & \multirow{3}{*}{\(\circ\)} & \multirow{3}{*}{\(\circ\)} \\  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \cline{1-1} \cline{5-5}  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Peak of temperature increase (\(\mu\)K) varying breast tissue, horn, and Vivaldi antenna position. Bolded values identify, for each antenna’s position, the tissue with the highest temperature increase. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Model \#1**} & \multicolumn{2}{c}{**Horn Antenna Position**} \\ \hline \multirow{3}{*}{f [GHz]} & \multirow{3}{*}{Breast tissue} & \multirow{3}{*}{\(\circ\)} \\  & & & \\ \cline{1-1} \cline{5-5}  & & & \\ \cline{1-1} \cline{5-5}  & & & \\ \cline{1-1} \cline{5-5}  & & & \\ \hline \hline \multirow{3}{*}{6} & Fat & 7.80 & 6.25 \\ \cline{1-1} \cline{5-5}  & Gland & **43.7** & **33.7** \\ \cline{1-1} \cline{5-5}  & Skin & 11.7 & 11.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Peak of temperature increase (\(\mu\)K) varying breast tissue, horn, and Vivaldi antenna position. Bolded values identify, for each antenna’s position, the tissue with the highest temperature increase. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Model \#1**} & \multicolumn{2}{c}{**Horn Antenna Position**} \\ \hline \multirow{3}{*}{f [GHz]} & \multirow{3}{*}{Breast tissue} & \multirow{3}{*}{\(\circ\)} \\  & & & \\ \cline{1-1} \cline{5-5}  & & & \\ \cline{1-1} \cline{5-5}  & & & \\ \cline{1-1} \cline{5-5}  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Peak of temperature increase (\(\mu\)K) varying breast tissue, horn, and Vivaldi antenna position. Bolded values identify, for each antenna’s position, the tissue with the highest temperature increase. levels; however, the linear relationship between temperature and power ensures that the temperature increase at these frequencies remains very low even at much higher powers, such as up to 1 W. In this case, linearity assures that the temperature peak will increase by three orders of magnitude, with a maximum temperature increase lower than 60 mK. Simulations showed that the breast absorbs energy from the EM waves, whose intensity becomes attenuated as the radiation penetrates the biological tissue. In most cases, the temperature peak occurs in fibroglandular tissue. Specifically, this happens throughout the range of frequencies analyzed in models #1, #2, and #3 up to 6 GHz, except for model #1 with the horn antenna in position 5 transmitting at 4 GHz and for model #3 with the horn antenna in position 1 transmitting at 4 GHz, where the temperature peak was found in the skin. At 8 GHz, temperature peaks tend to move from the fibroglandular tissue to the skin for all models. Precisely, this happens for model #1 with the horn antenna in positions 4 and 5, for model #2 with all horn positions except number 2, and for model #3 with all the considered antenna positions.