# Performance Evaluation of the Current Birmingham PEPT Cameras
## 6 Discussion  
The key parameters of the three positron cameras are compared in Table 1.  
Figure 8 compares the data rates of the three systems as a function of source activity for a central source. For both SuperPEPT and MicroPEPT, the value plotted is the true coincidence rate, obtained as the difference between the rates of prompt and delayed coincidences. The curve for the ADAC Forte shows the total prompt coincidence rate, so overestimates the trues rate.  
Both SuperPEPT and MicroPEPT have much higher sensitivity than the Forte and are capable of delivering much higher data rates, enabling much more precise tracking of fast-moving tracers.  
The sensitivity of MicroPEPT is approximately four times lower than that of SuperPEPT. This lower sensitivity is balanced by improved spatial resolution (\(w\approx 3\) mm for MicroPEPT, \(w\approx 6\) mm for SuperPEPT) so that for the same source activity, the precision of tracking achieved by the two systems is very similar. However, the data rate of SuperPEPT falls off above an activity of approximately 13 MBq due to the limited bandwidth of the data acquisition system, whereas that of MicroPEPT continues to increase up to 50 MBq activity, so that if tracer activity is not a limitation, MicroPEPT is able to achieve better tracking than SuperPEPT (over its much more limited FOV). In future, SuperPEPT might benefit from employing a data acquisition system with higher bandwidth, but it already represents a dramatic improvement on previous PEPT systems.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Camera** & **FOV** & **Sensitivity at Centre** & **Effective \(w\) Value** &
\begin{tabular}{c} **Maximum True** \\ **Coincidence Rate** \\ \end{tabular} \\ \hline ADAC Forte & 51 cm \(\times\) 38 cm \(\times\) 50 cm \({}^{*}\) & 1.4\% & 8.5 mm & 0.12 MHz \\ \hline SuperPEPT & 40 cm diameter 54 cm axially & 22\% & 6 mm & 2.3 MHz \\ \hline MicroPEPT & 13 cm diameter 16.5 cm axially & 5.4\% & 3 mm & 2 MHz \\ \hline \hline \end{tabular} \({}^{*}\) Separation adjustable from 25–80 cm: data reported here are for a separation of 50 cm.  
\end{table}
Table 1: Comparison of the three positron cameras.  
Figure 7: Data rates measured from MicroPEPT for a central \({}^{11}\)C source of varying activity. The upper set of points shows the total coincidence rate, the lower set the delayed coincidence rate, and the middle set the rate of true coincidences given by the difference prompt delayed. The dotted line corresponds to a sensitivity of 5.4%.  
For simplicity, all the results presented here are for a single tracer particle mounted at the centre of the FOV. For an off-centre source, the absolute data rates will be lower, but the comparison between the three systems remains broadly similar. SuperPEPT and MicroPEPT also offer great potential for simultaneous tracking of multiple tracer particles.  
Funding acquisition, D.J.P.; Investigation, D.J.P. and D.M.H.; Methodology, D.J.P.; Software, D.M.H.; Supervision, T.K.W.; Writing--original draft, D.J.P.; Writing--review & editing, D.J.P., D.M.H. and T.K.W. All authors have read and agreed to the published version of the manuscript.  
Financial support for construction of SuperPEPT and MicroPEPT was provided by EPSRC, UK under Programme Grant EP/R045046/1.  
Not applicable.  
The authors declare no conflict of interest.