Analog processing board for the MiCES small animal PET scanner

The analog signal summing board for the micro crystal element scanner (MiCES) small animal positron emission tomograph is described. The MiCES scanner uses a detector module with a position sensitive photomultiplier tube (PSPMT) providing 12 output signals. To reduce the number of electronic channels, the signals are summed to produce four output signals (X+, X-, Y+, Y-). Our current analog summing board uses a simple resistor network to provide weighting of the summed input signals. A weakness of this implementation is the decoding performance of crystals near the edges of the PSPMT. Because the MiCES scanner incorporates a very compact crystal array (22×22 crystals, each 0.8×0.8×10mm), that uses all of the PSPMT photocathode, improving the edge decoding is an important goal. The analog summing board described in this paper uses a threshold amplifier, weighted resistor network, and a low voltage differential signal (LVDS) converter. Thresholds are set on each of the 12 PSPMT signals to block those signals that inject more noise than information into the summing network. The result is an improvement in edge decoding. Output signals are converted to LVDS levels to minimize noise during signal transfer to the system analog processing boards.