Tuning of avalanche photodiode PET camera

The ability of a PET (positron emission tomography) system to reproduce the source distribution accurately depends, in the first place, on proper calibration and efficient quality control of the detectors and processing electronics. These procedures are simplified with individual detectors such as BGO (bismuth germanate)/avalanche photodiode detectors, but the large number of channels and the several interdependent parameters that must be adjusted make the process delicate and lengthy. The authors describe the procedures and algorithms being developed to adjust and verify the detector bias, the noise and energy thresholds, the signal references, and the timing delays for the Sherbrooke PET tomograph. All settings are adjusted using a sequence of iterative tuning algorithms whose convergence is optimized for each parameter. Preliminary results show that the complete calibration can be carried out automatically and reliably overnight and that specific checks can be performed in a few tens of seconds as needed