Validation of PET-SORTEO Monte Carlo simulations for the geometries of the MicroPET R4 and Focus 220 PET scanners

PET-SORTEO is a Monte Carlo-based simulator that enables the fast generation of realistic PET data for the geometry of the ECAT EXACT HR+ scanner. In order to address the increasing need for simulation models of animal PET imaging systems, our aim is to adapt and configure this simulation tool for small animal PET scanners, especially for the widely distributed microPET R4 and Focus 220 systems manufactured by Siemens Preclinical Solutions. We propose a simulation model that can produce realistic rodent images in order to evaluate and optimize acquisition and reconstruction protocols. The first part of this study presents the validation of SORTEO against the geometries of the R4 and the Focus 220 systems. This validation is carried out against actual measurements performed on the R4 scanner at the Montreal Neurological Institute in Canada and on the Focus 220 system of the department of radiopharmaceuticals of the Austrian Research Center in Seibersdorf. The comparison of simulated and experimental performance measurements includes spatial resolution, energy spectra, scatter fraction and count rates. In the second part of the study, we demonstrate the ability to rapidly generate realistic whole-body radioactive distributions using the MOBY phantom and give comparative example case studies of the same rodent model simulated with PET-SORTEO for the R4 and Focus 220 systems.