Inter-crystal scatter in a dual layer, high resolution LSO-APD positron emission tomograph
Abstract
Improving system efficiency without jeopardizing spatial resolution is one of the main problems of small animal PET scanners. In pursuit of this goal, the future LSO-APD-PET prototype MADPET-II will combine highly granulated detector modules with a dual layer structure. The individual readout of the LSO crystals allows separately handling multiple signals related to those photons scattering between different crystal units (inter-crystal scatter, ICS). The contribution of ICS events can significantly increase the system efficiency. Such coincidences are not characterized by a unique LOR. However, in order to minimize resolution degradation, it would be desirable to identify the primary path of the ICS events. Since ICS is geometry dependent, this work was aimed at investigating the effects of ICS in the performance of the dual layer prototype. Different recovery algorithms to select the primary crystal were implemented and developed, and applied to Monte Carlo simulated data. Some of these algorithms were based on the properties of Compton kinematics. For a centred point source and a 100 keV lower energy threshold, the absolute system efficiency was found to increase by 35% when including ICS events: from 1.8% without ICS events to 2.8% with ICS. Similarly, for a threshold of 200 keV, the contribution of ICS coincidences still represented approximately 20% of the total detected coincidences, leading to an absolute system efficiency of almost 2%. The mispositioning introduced…
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