A Modular Low Dead-time Coincidence System for High Resolution PET Cameras

A high-resolution-oncologic-transformable PET (HOTPET) is currently under development. The detector ring of the camera consists of 12 detector modules. Because the High-Yield-Pile-Up-Event-Recovery (HYPER) front-end electronics is applied in this new generation PET camera, a low dead-time coincidence circuitry is needed to take advantage of the efficiency improvement from this new technology. The coincidence matching of events coming from different detector modules is performed by an AND-logic on the arriving edges of the module output timing-pulses. A flexible modular architecture has been adopted to facilitate the use of the coincidence circuitry for different detector module configurations as well as different electronic and mechanical implementation. The application of backplane/plug-in architecture and programmable devices (EPLD/FPGA) and DSP (Digital Signal Processor) provide enough reprogrammable flexibility and expandability, ranging from animal and breast PET to whole-body PET. There are 42 possible pair combinations of modules derived from maximum 12 detector modules in coincidence with 7 opposite modules. Both the total (true + accidental) and accidental coincidences are simultaneously collected in real time; the accidental timing shift is ≥200ns relative to true events. The timing-gate window for the coincidence AND-logic can be dynamically digitally adjusted during data acquisition between 6.5-16ns to optimize signal/noise in the data. The prototype circuit showed that the timing accuracy is far better than 0.5 ns and the coincidence dead-time is less than 21ns.