Electronics design for a low-cost high-sensitivity rodent-research PET (RRPET)

We designed and implemented electronics for a low-cost high-sensitivity positron emission tomography camera for research involving rodents. To reduce cost and increase sensitivity, we used continuous full-ring photomultiplier tube (PMT) with quadrant sharing (PQS) detector design. In this prototype camera, 168 PMTs decode 144 scintillation detector blocks consisting of 9216 crystal elements. An Anger position matrix board weight sums the 144 detector blocks as eight individual gamma camera zones. The full-ring detector decoding is performed by eight fixed local zones. However, in the PMT-quadrant-sharing design, every two adjacent zones share seven axial PMTs. A boundary processing technique has been developed for the PMT-quadrant-sharing detector blocks so that the decoding of the full-ring detector can be performed by individual zones. A high-yield-pileup-event-recovery decoding board, a module-based coincidence processing system and a data acquisition computer, which were originally developed for a whole-body PET, can still be used by this rodent PET camera. The camera needs only eight decoding boards, and each board decodes 18 detector blocks of one detector zone. The entire decoding electronics need only 24 ADCs and can handle about six million events/second of single-rate. A motherboard decodes the control commands from the data acquisition computer, performs the real-time boundary processing and distributes DC power signals to all the eight decoding boards. To further reduce the cost and size of the camera, we have developed a new compact PMT voltage divider with adjustable PMT gain that can be controlled by programming the dynode high voltages directly. The very front-end preamplifier is also integrated into this divider board to increase the signal-to-noise ratio. A new instantaneous light-emitting diode automatic PMT gain calibration method is also used in this camera for better quality control; the gains of 168 PMTs can be equalized within 1 minute.