Investigating Silicon Photomultipliers for Use in a Gamma Camera

We have investigated the use of a tileable $4 {\times}4$ array of SiPM pixels coupled with a CsI(TI) crystal for use in a gamma camera. We have performed simulations of a number of geometries using both pixelated and monolithic scintillation crystals. Event positioning algorithms were also investigated as an alternative to conventional Anger logic positioning. Simulations have shown that by using multi-channel parallel electronics, we can adequately resolve intrinsic spatial resolution down to 1 mm, even in the presence of noise. Based on the results of these simulations, we have built a prototype SiPM system comprising of 16 detection channels coupled to either 2 mm $(6\times 6)$ or 3 mm $(4\times 4)$ discrete crystals. A charge sensitive preamplifier, pulse height detection circuit and a digital acquisition system make up our pulse processing components in our gamma camera system. With this system, we can adequately distinguish each crystal element in the array and have obtained an energy resolution of $30\pm 1\%$ (FWHM) with Tc-99m (140 keV). In the presence of a magnetic field, we have seen no spatial distortion of the resultant image and have obtained an energy resolution of $31 \pm 3\%$. Subsequent work will expand this prototype system to a larger array ($16 {\times}16$ SiPM pixels) and will include implementing a novel signal multiplexing scheme (256 to 32 channels).