Experimental Evaluation of a SiPM-Based Scintillation Detector for MR-Compatible SPECT Systems

Abstract

In the present work we briefly describe the architecture of a photo-detection module, designed in the framework of the INSERT (INtegrated SPECT/MRI for Enhanced Stratification in Radio-chemoTherapy) project, supported by the European Community. We focus on two main elements of the module: the SiPM photo-detector unit and the multi-channel ASIC. These two components have been investigated with dedicated and independent setups to assess preliminary performance of INSERT architecture. In details, we designed a $ 25.30~\hbox{mm} \times 25.85~\hbox{mm} $ tile, comprising 9 pixels, each one with an $8~\hbox{mm} \times 8~\hbox{mm}$ active area. We developed an Anger camera to characterize the tile coupled to a CsI:Tl scintillator (6 mm thick). We measured an average spatial resolution (FWHM) of 2 mm in the central region of the Field of View and a 15.3% energy resolution using a $^{57}{\rm Co}$ source (122 keV), when the tile is cooled down to 0 $^ \circ {\rm C }$ to reduce the impact of the dark count rate. Furthermore, we developed ANGUS, a 36-channels $0.35 ~\mu \hbox{m}$ CMOS technology ASIC designed to cope with input capacitance up to 5 nF, typical of large area SiPM pixels. The spectroscopic capability of single readout channels were evaluated by coupling an $8~\hbox{mm} \times 8~\hbox{mm} $ pixel with a cylindrical CsI:Tl scintillator (8 mm diameter, 10 mm thickness). Energy resolution at room temperature provided values between 13% and 13.5% (FWHM) at the 122 keV line for the nine pixels.