A slow control system with gain stabilization for a small animal MR-compatible PET insert

Abstract

The Biomedical Imaging Lab at the University of Manitoba is building an MR compatible PET insert system. The detectors include SensL SPM ArraySB-4 SiPMs and dual layer offset LYSO crystal blocks with 409 total crystals. The detectors’ gain varies with temperature and bias voltage. Measurements inside the MR magnet revealed that the equilibrium temperature was around 30°C. The photopeak amplitude, energy resolution and events per crystal were studied at 30°C and also at temperatures from 20°C to 40°C with a fixed overvoltage of 2.5V and with a fixed bias voltage of 27.95V. It was determined that a fixed overvoltage helps stabilize detector output but is not sufficient. A study of detector characteristics versus overvoltage was subsequently conducted and a lookup table was constructed to adjust bias voltage. A distributed network-based control system was developed in this thesis project to monitor the operating parameters of the detectors.