We are designing a 1mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> resolution PET (Positron Emission Tomography) system with over twenty-thousand readout channels. Multiplexing of the PSAPD (position sensitive avalanche photodiode) detectors would simplify the readout electronics and reduce the density of the circuit board design. We used simulations and experiments to study the performance of three front-end circuit configurations, 1) no multiplexing, 2) multiplexing with single-ended preamplifiers, and 3) multiplexing with differential preamplifiers, by evaluating their energy resolution and crystal identification ability. With single-ended multiplexing, there is no degradation in energy resolution but there is some degradation in crystal identification. With the novel differential multiplexing scheme presented in this paper, in simulation, there is less than 0.1dB degradation in energy resolution and no significant degradation in crystal identification. We also present a pseudo-differential technique which can be used when differential preamplifiers are not available, which we found gives a slight improvement over single-ended multiplexing.
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