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

Abstract

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 I124, then with I131. It is shown that with I124 PET, results with an optimized window improve upon those with the standard window but achieve less than half of the ideal improvement. Nevertheless, I124 PET shows improved resolution compared to I131 SPECT with triple-energy-window scatter correction. © 2009 American Association of Physicists in Medicine.