# Dosimetric Evaluation in Micro-CT Studies Used in Preclinical Molecular Imaging
## 3 Results
### Dosimetric Results  
Figure 5 shows the calibration curve (\(D_{w}\) vs. TLS) used to evaluate the absorbed dose measured with the TLD-100. This curve was obtained from the average TL signal of the TLD-100 dosimeters after the surfaces' irradiation with \({}^{60}\)Co at different doses (0 to 500 mGy); the result indicated that the absorbed dose was linear with TL-signal (TLS) (\(R^{2}=0.9999\)). The energy dependence correction factors used with this curve were F\({}_{\xi}\)(35 kV) = 0.91 \(\pm\) 0.10 and F\({}_{\xi}\)(45 kV) = 0.86 \(\pm\) 0.06. \begin{table}
\begin{tabular}{c c c c c} \hline  & \multicolumn{2}{c}{**35 kV**} & \multicolumn{2}{c}{**45 kV**} \\ \cline{2-5}  & **0.2 mA** & **0.4 mA** & **0.2 mA** & **0.4 mA** \\ \hline
**Modality** & \(\mathbf{IDS_{T}}\pm\delta_{\mathbf{IDS_{z}}}\) **(mGy)** & & \(\mathbf{IDS_{T}}\pm\delta_{\mathbf{IDS_{z}}}\) **(mGy)** \\ \hline _Standard_ & 33 \(\pm\) 1 & 66 \(\pm\) 3 & 50 \(\pm\) 2 & 101 \(\pm\) 4 \\ _Good_ & 52 \(\pm\) 2 & 103 \(\pm\) 5 & 78 \(\pm\) 3 & 156 \(\pm\) 6 \\ _Best_ & 74 \(\pm\) 3 & 148 \(\pm\) 6 & 112 \(\pm\) 4 & 223 \(\pm\) 9 \\ \hline \end{tabular}
\end{table} 
Table 4: Imparted Dose at Surface theoretically calculated (IDS\({}_{T}\)) for a cylindrical water phantom (24 mm diameter) for the different microCT parameters of imaging acquisition. \begin{table}
\begin{tabular}{c c c} \hline \hline
**kV** & \(\varGamma\pm\delta_{\mathbf{T}}\) & \(\varGamma^{D}\pm\delta_{D}\) \\
**kV** & **(mGy/mAs)** & **(mGy/mAs)** \\ \hline
35 & 0.76 \(\pm\) 0.03 & 0.52 \(\pm\) 0.01 \\
45 & 1.27 \(\pm\) 0.05 & 0.79 \(\pm\) 0.01 \\ \hline \end{tabular}
\end{table} 
Table 2: Total air kerma per mAs (\(\varGamma\)) and total air dose per mAs (\(\varGamma^{D}\)) performances of the Apogee X-ray tube at isocenter. \begin{table}
\begin{tabular}{c c} \hline \hline
**kV** & \(\varGamma\pm\delta_{\mathbf{\tau}}\) \\ \hline
35 & 1.07 \(\pm\) 0.04 \\
45 & 1.06 \(\pm\) 0.04 \\ \hline \end{tabular}
\end{table} 
Table 3: The air-to-water dose conversion factor (\(\tau\)). Half-value layers (HVL), effective linear attenuation coefficients (\(\mu_{Al}\)), and effective energies (\(E_{\textit{ff}}\)) values for the different combinations of voltage and filament current in the X-ray tube are presented in Table 5; no statistical differences between values with the same kV were observed. The average value of the effective energy of the X-ray beam was calculated from these data as 14.5 \(\pm\) 0.9 keV for 35 kV and 16.6 \(\pm\) 0.6 keV for 45 kV. Table 6 shows the IDS measured in the lucite block for X-rays generated at 35 and 45 kV, each combined with currents of 0.2 and 0.4 mA in the _Standard_, _Good_, and _Best_ acquisition modalities. Results were corrected using the inverse-square effect on the distance (from 290 mm to 278 mm) to make them compatible with the measurements from the surface of the mice. As was expected, IDS was proportional to the mAs value. The IDS of mice at the highest tube potential of the X-ray beam (i.e., at 45 kV) is presented in Table 7, and the IDS reference values provided by the equipment manufacturer are in Table 8. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**35 kV**} & \multicolumn{2}{c}{**45 kV**} \\ \cline{2-5}  & **0.2 mA** & **0.4 mA** & **0.2 mA** & **0.4 mA** \\ \hline
**Modality** & \(\mathbf{IDS_{TL}}\) \(\mathbf{\leq\delta_{IDSTL}}\) **(mGy)** & \(\mathbf{IDS_{TL}}\) \(\mathbf{\pm\delta_{IDSTL}}\) **(mGy)** \\ \hline _Standard_ & 42 \(\pm\) 1 & 86 \(\pm\) 7 & 67 \(\pm\) 4 & 125 \(\pm\) 3 \\ _Good_ & 74 \(\pm\) 4 & 141 \(\pm\) 2 & 106 \(\pm\) 3 & 223 \(\pm\) 7 \\ _Best_ & 111 \(\pm\) 5 & 219 \(\pm\) 12 & 167 \(\pm\)1 & 332 \(\pm\) 8 \\ \hline \hline \end{tabular} Values are corrected by the corresponding energy dependence correction factor.  
\end{table} 
Table 6: Imparted Dose at Surface measured in the lucite block (\(\mathrm{IDS_{TL}}\)) under CPE for the different kV and mAs settings and modalities of image acquisition.