Impact of the light detection chain on the NEC in a full-body PET scanner

In an ideal PET scanner, the count rate behavior depends on the true sensitivity, the scatter fraction, the singles rate and the coincidence timing window. However, a detailed system analysis shows that due to signal pile-up, the design of the light detection chain (light output, light spread, light detection) also has a strong impact on the resolution and performance of the system. In this paper, the dependence between the light detector size and the count rate behavior is analyzed, and the results are illustrated in terms of the noise equivalent count rate (NEC). Using a suite of system simulation tools, the performance of a PET scanner is modeled down to the level of single optical photons and photo electrons, allowing the count rate behavior to be derived from first principles. Hereby, scintillator materials with different decay times (LYSO, LaBr₃) are considered. The results show that for activity levels encountered with short half-life tracers like ¹¹C and ¹⁵O, the system NEC can differ by a factor of more than two for systems with identical scintillator geometries, but different light detector sizes