Analog signal multiplexing for PSAPD-based PET detectors: simulation and experimental validation

Abstract

A 1 mm3 resolution clinical positron emission tomography (PET) system employing 4608 position-sensitive avalanche photodiodes (PSAPDs) is under development. This paper describes a detector multiplexing technique that simplifies the readout electronics and reduces the density of the circuit board design. The multiplexing scheme was validated using a simulation framework that models the PSAPDs and front-end multiplexing circuits to predict the signal-to-noise ratio and flood histogram performance. Two independent experimental setups measured the energy resolution, time resolution, crystal identification ability and count rate both with and without multiplexing. With multiplexing, there was no significant degradation in energy resolution, time resolution and count rate. There was a relative 6.9 ± .0% and 9.4 ± 1.0% degradation in the figure of merit that characterizes the crystal identification ability observed in the measured and simulated ceramic-mounted PSAPD module flood histograms, respectively.

Optical delay encoding for fast timing and detector signal multiplexing in PET

“…Schemes such as Anger logic or cross strip multiplexing are often used to reduce the number of readout channels in position sensitive or highly pixelated detector arrays. 1,27,32 The pulses output from these analog multiplexing methods could be further multiplexed onto a single fiber using optical pulse train encoding. For example, dozens or hundreds of pixels in a detector array could be electrically connected using Anger logic, resulting in four outputs.…”

“…Typical electronic schemes such as resistive or capacitive multiplexing can compromise timing, energy, and spatial resolution, and may still require complex data acquisition systems. [1][2][3][4] This is not ideal for the development of new high resolution or time-of-flight (ToF) PET scanners.…”

Evaluation of transimpedance amplifiers for readout of a position sensitive avalanche photodiode

“…This 10-20 fold increase in signal suggests better noise performance of the PSAPDs compared to the APDs used by Holl et al and presents the trans impedance amplifier as an attractive solution to test any count rate limitations of the original beta camera [2]. Furthermore, past work with these devices characterize them as an array of photodiodes with an integral array of resistors to encode position [3]. Therefore, the equivalent circuit of the PSAPD appears more like a charge division network loaded by a large semiconductor junction capacitance (-150 pF) than an APD.…”

Relevancies of multiple-interaction events and signal-to-noise ratio for Anger-logic based PET detector designs

“…There have been several published studies focusing on the study of spatial resolution limit of PET systems. On the simulation side, it was reported that for a point source of 18 F in waterequivalent tissues, 750 mm FWHM (full-width-half-maximum) resolution could be attained with 1 mm crystal elements and a 20 cm [11], taking into account the effects of positron range, photon acollinearity and crystal width. Another simulation study focused on the effect of multiple interactions of incoming 511 photons within different detector materials [12].…”