## 4 Discussion  
In this study, a primary objective was to optimize the parameters chosen during tracking of point sources in awake rat PET imaging using a motion detection and correction system. We have achieved significant insights that shed light on the factors influencing detectability and image quality in this motion correction strategy.  
Initially, we investigated the effects of injected activity on the detectability of point sources attached to the animal. Through extensive simulations, we demonstrated the importance of random correction in ensuring the detection of all point sources. It was also found that that, to obtain image deviations below \(RMS_{e}\) of 0.05 of the reference, requires keeping the activity of the sources below 8 uCi. Additionally, the point sources require a minimum activity when the brain's activity exceeds 90 uCi. While this study was performed using FDG as the tracer, we acknowledge that the activity levels in other organs may vary depending on the tracer used, potentially affecting random coincidences. Therefore, future studies using different tracers should take this into account when optimizing tracking systems.  
Next, we addressed the trade off of subtracting coincidences associated with quick-movement and non-precise point source tracking. Through our observations of the four rats within the scanner, as shown in Figure 7, we identified a tendency for these animals to display increased movement during the initial stages of the acquisition. This initial movement could be attributed to the novelty of the environment. However, it became evident that, as the rats acclimated to the scanner, movement reduced.  
By optimizing our motion detection and correction parameters, we achieved low noise and excellent image resolution, with the best images obtained when retaining 73% of coincidences for our rat. Remarkably, even with a loss of 27% of coincidences, the impact on image resolution was only 8% and on SNR was 6%, as demonstrated in Figure 10. While our current experiments were conducted with a 10 min acquisition time, future research will explore the potential advantages of longer acquisition durations. Extending the acquisition time may provide an opportunity to capture additional information and enhance imaging sensitivity. However, it is important to recognize that longer acquisition times can introduce challenges related to increased subject movement, necessitating further investigation into the associated motion correction techniques and potential limitations.  
We note that the position of the animal's head near the end of the FOV of the scanner may have contributed to the loss of resolution observed. The non-homogeneous resolution across the FOV of the scanner, which exhibits a poorer resolution at the edges of the FOV and could have worsened the image quality. For future studies, it would be beneficial to consider this non-uniform resolution when placing the animal and optimizing motion detection and correction systems for awake rat PET imaging. Additionally, exploring methods to improve the resolution near the edges of the FOV could further enhance image quality in awake rat PET studies [27].  
Another important aspect is that, recently, [PERSON] et al. [28] have proposed adding corrections for cases where point sources shift on the animal's skin. In our approach, instead of trying to correct for these, we remove them from the acquisition by introducing the \(\chi^{2}\) parameter. This way, whether the sources have shifted on the animal or an incorrect transformation has been computed, these counts will not introduce erroneous information into the reconstruction. The loss of counts introduced this way is moderate and can be compensated by a modest increase in acquisition time.