False-preferred event analysis for the energy-subtraction Compton scatter camera

For the energy-subtraction Compton scatter camera (ESCSC) for medical imaging, a critical requirement is the efficient selection of true preferred events, which will directly affect image contrast. To be able to distinguish preferred events, a set of selection criteria, based on different physical restrictions for different scenarios, is used. However, due to finite energy and timing resolution of the detector systems, some false preferred events (FPEs) will pass all of the criteria. In this study, we attempt to identify major sources of FPEs and their fraction among preferred events. Results from this analysis would be useful in designing the ESCSC as well as other Compton cameras. In addition, these results can be used in development of a weighting scheme indicative of the likelihood that an event that passes all of the criteria is actually a preferred event. This extension is purely analytical and based on the solution of the photon transport problem prescribed by the ESCSC. Two major contributors to FPEs, source volume scatters and chance coincidences, are identified. For a potential ESCSC geometry, the fractions of FPEs are calculated for various system energy and timing resolutions. Recommendations for optimal source energy and preferred event weighting function are provided.