System architecture of a fully combined PET/CT scanner using LabPET™ electronics with an upgraded analog front-end optimized for PET and CT counting mode operation

摘要

High light yield lutetium based crystals, such as LYSO, enable new potentials in medium and low energy radiation detection. Such scintillators combined with high quantum efficiency avalanche photodiodes (APD), have shown promising results for fully integrated PET/CT scanners. In such systems, a single detection apparatus is used for the acquisition of both PET and CT signals, allowing reduced hardware and potentially lower effective scanner cost. Using this approach, a prototype PET/CT scanner is developed using the LabPET™ digital electronics and a new upgraded front-end analog board optimized for PET and CT operation. The upgraded analog board has 2 × 64 acquisition channels based on LYSO crystal arrays (pixel size of 1.125 × 1.125 × 12 mm3) coupled 1:1 to pixelated APD photodetectors. The analog signal outputs are amplified by an optimized application-specific integrated circuit (ASIC) that offers dual charge sensitive pre-amplifier (CSP) and shaper gain modes for individual channels. For PET acquisition, the CSP-Shaper gain is adjustable from 8 to 48 mV/fC, while CT acquisition can operate from 65 to 390 mV/fC. Moreover, the LabPET™ firmware was updated and optimized to meet the new hardware requirements. This paper describes the architecture of the prototype PET/CT scanner and focuses on the effect of these updates on the counting performance for both PET and CT acquisition modes. In PET operation, the events processing rate has shown a 15% improvement compared to the previous firmware version. Each channel has reached an average count rate of ~17 500 cps (counts per second). In CT mode, the firmware recorded a maximum average count rate of 400 000 cps per channel, thus allowing a total of ~25 million cps considering all 64 channels of one LabPET™ digital board.