Comparison of Conventional and SDM-Based Read-Out Systems for Gamma-Ray Imaging

One relatively inexpensive way a gamma-ray imaging system can be upgraded is by updating the read-out electronics system and, as a consequence, modernizing the digitization and data-processing methods. The objective of this project is to replace the front-end electronics of modular gamma-ray cameras utilized in multiple small-animal PET and SPECT systems developed at the University of Arizona within the last 20 years. We have previously presented the new front-end board, which utilizes 1-bit sigma-delta modulation (SDM) for energy estimation and a non-uniform 2-bit SDM architecture for timing estimation and triggering. One advantage of this digitization method is that instead of ADC integrated circuits, only a few analog components per channel are utilized, which reduces the complexity and power consumption of the system. The board also includes, among other resources, a Xilinx FPGA combined with an ARM-based processor, DDR3 SDRAM and QSPI flash memory. This project presents the comparison between the original and the new SDM-based front-end electronics board, implemented in a 9-channel modular gamma-ray camera, by obtaining the spectrum of each individual photomultiplier tube (PMT) with both frontend boards. The results show an improvement of 1.5x to 2x in the PMT spectrum resolution with the new approach.