Effect of inter-crystal scatter events on coincidence detection in LabPET scanners

Compton scattering of gamma photons can give rise to inter-crystal crosstalk in detector arrays for positron emission tomography (PET). PET systems made of pixelated detectors with individual readout can recover inter-crystal scatter (ICS) events in the list-mode data file, but these events are generally ignored since their inclusion in the image reconstruction process leads to undesirable image noise. For such systems, including lines-of-response (LORs) resulting from triple events increases detection efficiency, but at the expense of degrading image quality. Therefore, it is important to understand the various processes contributing to triple coincidences to underline neglected sources of noise counteracting the benefit of ICS inclusion. It was found that a main source of mispositioned LORs is caused by triple randoms consisting of a true coincidence with a single detection. Limiting the contribution of these triple randoms when recovering ICS events resulted in improvements of image quality.