Validation of a PET Monte-Carlo simulator with random events and dead time modeling

To perform Monte-Carlo simulations of PET tomographs, we used SimSET (a simulation system for emission tomography). Since we need to estimate performance characteristics of different tomographs, this widely used simulation package had limited properties for our use. We integrated a module to generate random events from a singles simulation and we modeled dead time losses. The count rate model we used is based on the method developed by Moisan et al. (1997) for the Siemens HR+ scanner. We needed a reliable simulation tool, which could provide data such as scatter fraction, sensitivity, count rates or noise equivalent count rate (NEC). So, we carried out a two-steps validation of SimSET in 3-D alone and with additional features. First, we compared results obtained with SimSET and with two other simulators (GePEToS, a PET simulator using Geant4 and a simulator developed by Adam et al. (1998)). We estimated energy spectrum and sensitivity to scattered events. Second, we compared our simulated data with experimental data obtained on two Siemens tomographs : the ECAT HR+ and the ECAT ACCEL. We determined spatial resolution, scatter fraction, sensitivity (global and for each plane) and all the different count rates (true, scattered, and random). We found that SimSET can be used to simulate the physical response of different tomographs with a medium accuracy. This lost of accuracy is mainly due to a too simple modeling of the detector (no block detectors). Further validation is planned concerning 2-D mode.