Investigating the Impact of Lso on the Count Rate of Wholebody Pet Tomographs

We investigated the impact of using detectors made of lutetium oxyorthosilicate (LSO) on the count rate performances of wholebody PET tomographs. To that end, we used a simple computational model that predicts the prompt and random contributions to the total event rate in septaless PET tomographs. Dead time factors at all stages of a typical event acquisition stream are calculated from speciied values of their respective processing clock cycle. We validated our approach by tting the true, random and multiple count rates measured with the ECAT{953B and the EXACT HR PLUS scanners for a standard 2020 cm cylindrical phantom. We then investigated the implications of using position encoding detectors made of LSO in the EXACT HR PLUS scanner geometry. The results indicate that only replacing BGO by the faster LSO incurs no appreciable change in the maximumnoise-equivalent-count (NEC) rate of that scanner. However, one could realistically increase the NEC by a factor 2.5 using a 4 nsec coincidence window width with the detector processing front-end operating on a 128 nsec clock cycle. Further reducing the coincidence window width to 600 psec and the front-end clock cycle to 64 nsec leads to an increase of the NEC by a factor 7.5. To sustain the operation of an HR PLUS with these speciications, the saturation bandwidth of the data acquisition system would have to be increased to no more than 4.5 MHz.