Influence factors of two dimensional position map on photomultiplier detector block designed by quadrant sharing technique

The position decoding accuracy and the spatial resolution of positron emission tomography detectors are greatly influenced by the performance of the two-dimensional position map, including the gain uniformity of photomultiplier tube （PMT）, the baseline offset of the PMT signals and the accuracy of analogue to digital converter （ADC）. In this work, a PMT-quadrant sharing detector was designed. Two data acquisition platforms are employed to conduct the influence factors on the two-dimensional position map performances, one was that the waveforms of the PMT signals were scanned by the sequence acquisition mode based on the oscilloscope of LeCroy waveRunner 204MXi-A, and another was a self-developed high speed ADC data acquisition module. Results show that the event decoding positions were concentrated on the PMT with higher gain, the position map was distorted at the baseline offset of signal, and the cross-line artifacts were caused by the insufficient ADC sampling bit for a larger size position map. All the parameters need be adjusted properly to stabilize a real system, and the flexible oscilloscope platform can be used to design the detector block and the other platform with high ADC accuracy. Likely, the electrical circuit with a proper ADC accuracy adjusts the PMT gains and baseline offsets.