A Multiplexer Design for Position-Sensitive Avalanche Photodiode Detectors in a PET Scanner

A small-animal positron emission tomography (PET) scanner using PS-APD (position-sensitive avalanche photodiode) detectors has been developed for simultaneous PET/MRI imaging. In this scanner, up to 16 detector modules (one PS-APD per module) are used, and each detector module produces 4 signals to be digitized with their peak values. This leads to as many as 64 analog outputs to the data acquisition (DAQ) system, requiring 64 DAQ channels. In the future, the system will be extended to 32 modules, resulting in 128 channels. It is possible to sample all channels simultaneously, but most of them do not contain useful data, since only one coincidence event (producing data on 8 channels) is identified each time. The purpose of this work was to develop a general-purpose method for reducing the number of analog inputs to the data acquisition for the sparse fast analog signals produced in a PET scanner. To achieve this, a multiplexer board was designed to sample coincidence events from the PET scanner. The effect of the multiplexer on signal quality was evaluated and the average peak-to-valley ratios in detector flood histograms with and without multiplexer were 2.97 and 3.02 respectively. On-board coincidence, pile-up rejection and multiple coincidence rejection functions were implemented and worked as expected. The dead time performance was also characterized.