Design of a dual-modality, digital positron emission tomography/computed tomography (PET/CT) scanner for small animal imaging

Contemporary PET scanners are commonly implemented with VLSI analog front-end electronics to reduce power consumption, space, noise and cost. Analog processing yields excellent results in dedicated applications, but offers little flexibility for sophisticated signal processing. One design goal of the new Sherbrooke PET/CT scanner is to achieve 1 mm resolution in both emission (PET) and transmission (CT) imaging using the same detection system. One further goal is to be able to use PET detectors and electronics to count and discriminate individual X-ray photons in CT mode. These requirements can be better met by sampling and digitizing the analog signal from each individual channel as early as possible. To meet these requirements, we developed an open digital architecture allowing new technology developments to be incorporated. A specific charge-sensitive amplifier (CSP) satisfying PET and CT needs, a low noise data acquisition system and advanced digital signal processing methods are joined together in order to meet requirements. The hardware is based on standard off-the-shelf 8- bit 100-MHz high-speed analog converters (ADC) and high-performance field programmable gate arrays (FPGA). By implementing 64 channels per board, a 1024-channel PET/CT camera can be created by disposing 16 such modular boards on a ring.