SiPM side detectors for performance enhancements of an EMCCD-based gamma camera

To achieve ultra-high spatial resolution gamma ray imaging, the use of charge-coupled devices (CCDs) has become of great interest. However, these detectors still suffer from performances degradations due to their high intrinsic noise level. In our developped electron-multiplying CCD based gamma camera, we have introduced the use of solid state photomultipliers in side detection of a continuous crystal to improve the signal-to-background ratio and energy resolution. The so-called silicon photomultipliers (SiPMs) are individually read-out to measure the previously lost optical photons escaping through the crystal sides to give an a-priori evaluation of the energy and position of the γ-rays interactions to a statistical algorithm for EM-CCD image analysis. In this work, we show the results obtained using 12 SiPMs optically coupled to a 3 mm thick CsI:Tl crystal where the prelocated events are reconstructed using a maximum likelihood algorithm. This algorithm uses Look-Up Tables (LUTs) evaluated by Monte-Carlo simulations to retrieve the interaction positions via the individual SiPMs signals. The spatial resolution obtained with this process is evaluated at 0.8 mm using a 200 μm pinhole collimator with a ^99mTc source. The energy resolution is then measured at 19% for the 140 keV γ-rays emission.