## 3 Result
### Temperature Field Variation at Different Vessel Radii  
We used \(\Omega=1\) as the ablation zone boundary [33] and analyzed the ablation of vessels with a radius of 0.1-1.0 mm at the end (at the red line), as shown in the thermal damage location map of the vessel in Figure 5, with blood flowing from A to B and flow rate varying with the vessel diameter. Figure 6a-j shows the thermal damage of the end section of the vessel at a distance of 1 mm between the fiber and the vessel, at a maximum temperature of 90 \({}^{\circ}\)C and 400 s of ablation, and the green line indicates the range of loss. As can be seen \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{2}{c}{**Brain**} & \multirow{2}{*}{**Blood**} \\  & **Native** & & **Denatured** \\ \hline Absorption coefficient, \(\mu_{\text{a}}\) (1/m) & 50 & 62 & 883 \\ Scattering coefficient, \(\mu_{\text{s}}\) (1/m) & 6700 & 7890 & 14.201 \\ Anisotropy factor, g & 0.96 & 0.93 & 0.98 \\ Density, \(\rho\) (kg/m\({}^{3}\)) & 1040 & 1050 \\ Specific heat capacity, c (J/(kg\(\cdot\)K)) & 3590 & 4180 \\ Thermal conductivity, k & 0.503 & 0.517 \\ (W/(m\(\cdot\)K)) & \multicolumn{2}{c}{} \\ Dynamic viscosity, \(\mu\) (Pa-s) & \multicolumn{2}{c}{} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Optical properties and thermal physical parameters of tissues and blood vessels [30,31]. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Parameter**} & \multicolumn{1}{c}{**Fiber Core**} & \multicolumn{1}{c}{**Thin Layer**} \\ \hline Absorption coefficient, \(\mu_{\text{a}}\) (1/m) & - & 266 \\ Scattering coefficient, \(\mu_{\text{s}}\) (1/m) & - & 3000 \\ Anisotropy factor, g & - & 0.98 \\ Density, \(\rho\) (kg/m\({}^{3}\)) & 2203 & 2203 \\ Specific heat capacity, c (J/(kg\(\cdot\)K)) & 703 & 703 \\ Thermal conductivity, k (W/(m\(\cdot\)K)) & 1.38 & 1.38 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristic parameters of optical fibers [32]. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**No.**} & \multicolumn{1}{c}{**Radius, r (mm)**} & \multicolumn{1}{c}{**No.**} & \multicolumn{1}{c}{**Radius, r (mm)**} \\ \hline
1 & 0.1 & 6 & 0.6 \\
2 & 0.2 & 7 & 0.7 \\
3 & 0.3 & 8 & 0.8 \\
4 & 0.4 & 9 & 0.9 \\
5 & 0.5 & 10 & 1.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Radius parameters of blood vessels [13]. from the Figure 6, the end cross-section of the 0.1-0.3 mm radius vessel was completely coagulated; the 0.4 mm vessel had 90% coagulation, the 0.5-0.6 mm vessel continued to decrease in the coagulation range and suffered partial thermal damage, but not enough to cause blood flow blockage; and the 0.7-1.0 mm vessel blood was not affected in any way. The temperature field had a coagulation effect on the vessels; at a constant distance from the fiber, the vessel coagulation decreased with increasing radius, indicating that the vessels carried more heat from the temperature field. When performing precise intracranial thermal ablation, the target temperature of LITT was set at 45-90 \({}^{\circ}\)C [5] to achieve the ablation temperature without causing vaporization due to high temperature and adhesion of residual tissue in fiber retraction. The maximum temperature was controlled by PID not to exceed 90 \({}^{\circ}\)C, and \(\Omega\) = 1 was used as the ablation boundary for 400 s. Figure 7a-j shows the effect of different vessel radii 0.1-1.0 mm on the ablation temperature field, and Figure 7k shows the actual ablation temperature plot without the influence of vessels. The Figure 7 show that small vessels' effect on the temperature field is also worthy of attention, which will produce obvious directional effects.