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

For the energy-subtraction Compton scatter camera, 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 will pass all the criteria. In this study, we attempt to identify major sources of false preferred events and their fraction among preferred events. Results from this analysis can be used to develop a weighting scheme indicative of the likelihood that an event, which 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 false preferred events - source volume scatters, and chance coincidences - are identified. For a sample geometric model, the fractions of false preferred events are calculated for various system energy and timing resolutions. Recommendations on optimal source energy and preferred event weighting function are given.