Physics process level discrimination of detections for GATE: Assessment of contamination in SPECT and spurious activity in PET

The GEANT4 application for tomographic emission (GATE) is one of the most detailed Monte Carlo simulation tools for SPECT and PET. It allows for realistic phantoms, complex decay schemes, and a large variety of detector geometries. However, only a fraction of the information in each particle history is available for postprocessing. In order to extend the analysis capabilities of GATE, a flexible framework was developed. This framework allows all detected events to be subdivided according to their type: In PET, true coincidences from others, and in SPECT, geometrically collimated photons from others. The framework of the authors can be applied to any isotope, phantom, and detector geometry available in GATE. It is designed to enhance the usability of GATE for the study of contamination and for the investigation of the properties of current and future prototype detectors. The authors apply the framework to a case study of Bexxar, first assuming labeling with {sup 124}I, then with {sup 131}I. It is shown that with {sup 124}I PET, results with an optimized window improve upon those with the standard window but achieve less than half of the ideal improvement. Nevertheless, {sup 124}I PET shows improved resolution compared to {sup 131}I SPECT withmore » triple-energy-window scatter correction.« less