Fundamentals of a scalable network in SPADnet-based PET systems

Abstract

In SPADnet we have advocated the use of standardized photonic modules for modular assembly of PET systems. In this paper, we tackle the scalability problem, starting from synchronization. Since the photonic modules in a ring must ensure tens of picoseconds in timing accuracy, it is essential that the synchronization of each module be accurate, irrespective of the number of modules in a ring, the ring's size, and the number of rings in the system. We propose a hybrid solution, where a hard-wired clock synchronization network is combined with a network-based clock offset estimator. This combination enables scalability while maintaining high precision. A novel least squares synchronization algorithm is optimized and implemented in hardware equipped with a delay line FPGA TDC, allowing picosecond clock synchronization. The solution is verified in an 8 node system.