Our group has previously developed a PET insert for simultaneous PET/MRI imaging. The insert consists of silicon photomultipliers (SiPMs) with a resistor-based charge division multiplexing readout circuit. Some limitations include a 2.5ns coincidence time resolution (CTR), a relatively long signal duration of >1.5us, and a 1.3us paralyzable dead time. This thesis focuses on characterizing these limitations and demonstrating a second-generation detector module for improved timing and count rate performance. First, optical coupling optimization using acrylic polymer tapes versus conventional silicone optical grease was investigated. Second, CTR and signal duration was reduced by using an enhanced readout board equipped with three new SiPM-type detectors. Last, dead time of the system was reduced by minimizing the sampling number of the OpenPET acquisition system. Future work includes design modification to accommodate the first-generation scintillator footprint and potentially to adapt the OpenPET acquisition system to read in SiPM `fast' outputs.