Characterization of Two Thin Postion-Sensitive Avalanche Photodiodes on a Single Flex Circuit for Use in 3-D Positioning PET Detectors

We are developing 1 mm resolution, 3-D positioning, high sensitivity positron emission tomography imaging systems for small animal and breast-dedicated imaging applications. The system uses detector modules that comprises two adjacent position-sensitive avalanche photodiodes (PSAPDs), each with a segmented lutetium oxyorthosilicate (LSO) scintillation crystal array, mounted on a single flex cable readout circuit. The module is oriented two PSAPDs deep in the depth of interaction direction, which facilitates high photon sensitivity (~2 cm of LSO). In this study, we are testing two PSAPD chips in a single flex-cable module simultaneously to investigate their performance and access the degree of inter-device cross-talk. The inter-device cross-talk was measured by looking at the signal in an un-irradiated PSAPD chip while the adjacent PSAPD chip was irradiated, both chips under bias. The signal was three orders of magnitude lower in the unirradiated PSAPD versus the irradiated PSAPD. Individual crystal energy resolution for an array coupled to a PSAPD was measured to be 10.03 plusmn 4.45%for the 1 mm times 1 mm times 3 mm array. All crystals were resolved in a flood histogram, with an average peak-to valley ratio of ~11, with the lowest PVR being 1.8. The average coincidence time resolution was 3.75 ns FWHM across the devices. These measurements indicate that degradation due to the close proximity of two PSAPDs on the same readout circuit is small.