Effects of energy threshold and dead time on Compton camera performance

Abstract

We study the effects of energy threshold and dead time on the sensitivity and image resolution of the Compton camera. The simulation model includes the decay times, detection time jitters, energy threshold and detector dead time as well as basic detector parameters such as Doppler broadening, energy resolution and finite detector resolution. The GEANT4 toolkit was used to model the camera geometry and performance for two common nuclear medicine energies that correspond to 99mTc (140.5 keV) and 18F (511 keV) radiotracers. Results without the energy threshold and time effects show good agreement with previous studies. For 140.5 keV, the inclusion of energy threshold improved image resolution from 10.7 to 9.5 mm with a source-to-detector distance of 5 cm, while the inclusion of time effects made no further difference on resolution. The energy threshold reduced the sensitivity by 48%, and subsequent inclusion of time effects further reduced the sensitivity by 17%. At 511 keV, the application of energy threshold reduced the sensitivity by 6%, while the time effects dominated count rate losses with further reduction of 13%. However, the inclusion of the two effects had negligible impact on the resolution.