Front end electronics for a variable field PET camera using the PMT-quadrant-sharing detector array design

This is an electronic design for a PET camera with 8 arrays of position sensitive detectors. Each array has 16 BGO blocks (each block is composed of 49 crystals). The design goals are component and space reduction. Each PMT has its fast amplifier and triggered integrator. Nine flash ADC serve an array of 27 PMT and 784 crystals. The fast signals from one or more PMT clusters are summed. The fast summed signals are thresholded and sent to a programmable logic to determines the probable scintillation zone (4 blocks) and to turn on the associated 9 PMT integrators. After integration, the logic also drives a set of ultra-fast analog switches to connect the flash ADC set to the PMT integration channels in the scintillation zone. The 9 ADC output (integrated pulses with good photon statistics) are latched and compared. The comparator result determines which block in the zone is firing and the appropriate 4 ADC are selected and bused into a position decoder. The decoder outputs the image-slice address and the crystal address. The circuit is pipelined and driven by a 250 MHz master clock. The maximum event-processing rate for the circuit and a random radiation source is 2×10⁶/sec (with 10:1 randomness allowance)