Timing Resolution Improvements from Cooling in BGO PET Detection with Analog SiPMs

Abstract

Using Bismuth Germanate (BGO) scintillators coupled to general purpose analog Silicon Photomultipliers (SiPM) we have developed methods to improve the coincidence timing resolution of PET detectors with BGO in order to reach a timing resolution that can be used for time of flight (TOF) PET detection. TOF measurements have already been acquired using LYSO crystals, but the low cost of BGO along with its optical properties and favorable energy resolution make BGO an attractive option to reduce the overall cost of PET scanners without sacrificing image quality. Using an analog SiPM with a pre-amplifier at a higher voltage improves energy and timing resolution for BGO coincidence detection, but also introduces a much higher baseline noise level, which can obscure the start of the waveform. We have found this noise level can be significantly reduced by cooling the detectors to values below -30°C, allowing us to perform leading edge discrimination (LED) timing at much lower voltages. On average cooling the detectors to this point improves their timing resolution by around 300ps, and as much as 600ps. Using this setup our values are approaching the values necessary for time of flight PET detection. In this paper we will discuss the experimental setup in further depth and share promising initial timing and energy resolution results from our findings.