Evaluation of scintillator afterglow for use in a combined optical and PET imaging tomograph

The design of a dual modality imaging system for small animal optical and positron emission tomography imaging (OPET) is underway. Its detector must be capable of imaging high energy γ-rays from PET while also resolving optical wavelength photons from bioluminescence. GSO, high purity GSO, BGO, LSO, LYSO, and LaBr scintillators were investigated for their use in the OPET detector. Of specific interest were scintillators with low afterglow, since afterglow photons in the decay of the larger γ-ray events are indistinguishable from the photons generated by bioluminescence. Samples from these crystals were coupled to a photomultiplier tube (PMT) and produced scintillation light from γ-ray events originating from a positron source. The PMT output was directed to a special signal processing circuit that allowed measurement of single photons at different times in the decay of the scintillation. GSO and BGO exhibited optimal performance for use in the OPET system due to their low afterglow. LSO, LYSO, and LaBr were determined unsuitable for use with the current OPET design due to their significant afterglow components. The effect of the afterglow of GSO on the detection of the bioluminescence signal-to-noise ratio (SNR) was evaluated for the OPET system.