A read-out strategy for high-resolution large-area SiPM-based modular gamma-ray cameras

Ongoing developments in the field of molecular imaging have increased the need for gamma-ray detectors with better spatial resolution, while maintaining a large detection area. One approach to improve spatial resolution is to utilize smaller light sensors for finer sampling of scintillation light distribution. However, the number of required sensors per camera must increase significantly, which in turn increases the complexity of the imaging system. Examples of challenges that arise are the analog-to-digital conversion of large numbers of channels, and a bottleneck effect that results from transferring large amounts of raw list-mode data to an acquisition computer. Here we present the design of a read-out electronics system that addresses these challenges. The read-out system, which is designed for a 10"× 10"SiPM-based scintillation gamma-ray camera, can process up to 162 light-sensor signals per event. This is achieved by implementing 1-bit and non-uniform 2-bit sigma-delta modulation analogto-digital conversion, and an on-board processing system with a large number of input/output user pins and relatively high processing power. The processor is a system-on-a-module that also has SDRAM, which allows us to buffer raw list-mode data on board. The bottleneck effect is avoided by buffering event data on the camera module, and only transferring it when the main acquisition computer requests it. This design can be adapted for other crystal/sensor configurations, and can be scaled for a different number of channels.