The effects of scatter on the performance of the PETRRA positron camera

The PETRRA positron camera consists of two 60 cm × 40 cm detectors mounted on a rotating gantry. Each detector contains a layer of 1 cm thick barium fluoride (BaF₂) crystals interfaced to a multiwire proportional chamber (MWPC) filled with 4.2 mbar of the photosensitive vapor tetrakis dimethylamino ethylene (TMAE). The camera acquires data in list mode and produces 3D images which can contain high levels of scatter and random coincidences. Scatter comes from the patient and the detector support structure whereas randoms rates depend on the detector count rates and coincidence timing resolution. The camera has little energy resolution but low energy scattered photons produce a smaller range of pulse sizes and can be discriminated against using signal thresholding.