Low Dead-Time Coincidence Electronics
A high-resolution oncologic-transformable PET (HOTPET) has been designed and is 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 modular architecture has been adopted to facilitate the use of the coincidence circuitry for different detector module configurations as well as the electronic and mechanical implementation. The application of backplane/plug-in architecture and programmable EPLD/FPGA devices 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 module-pairs of combination derived from each of 12 detector modules with seven opposite modules. Both the total (true + accidental) and accidental coincidences are collected in real time; the accidental timing shift is ≥200ns relative to true events. The timing-gate window for coincidence AND logic can be digitally adjusted during data acquisition between 6.5 and 16 ns to optimize signal/noise in the data. The prototype circuit showed a timing accuracy of 0.5 ns. Our preliminary test result shows that this new coincidence system has 22 ns dead-time for coincident events and is able to operate up to 10 million coincident events per second.