Performance characterization of a dual-threshold time-over-threshold APD-based detector front-end module for PET imaging

The LabPET II front-end module is an avalanche photodiode (APD) based pixelated detector designed to achieve submillimetric spatial resolution in pre-clinical Positron Emission Tomography (PET). This technology is also based on Time-over-Threshold (ToT) signal processing and designed to be used as a generic platform for ultra-high resolution PET imaging of small and medium-size animals. The basic building block uses a 4×8 array of 1.12×1.12×12 mm
³
Lu
1.9
Y
0.1
SiO
5
:Ce (LYSO) scintillator pixels with one-to-one coupling to a 4×8 pixelated APD array mounted on a ceramic carrier. Four of these detectors are mounted on a PCB with two 64-channel ASICs interfacing to two detector modules each. Signals from each APD pixel can be individually processed by dedicated dual-threshold ToT channels providing timing and energy data. Energy calibration was performed using gamma ray sources in the range 300–1275 keV to correct the non-linearity of the ToT signal and obtain energy spectra. Energy and timing performance of the complete front-end module was evaluated. Results confirm the functionality of the dual threshold ToT circuit implemented in the 64-channel ASIC, as well as the physical performance of the most recent LabPET II version of APD-based detectors for applications in high-resolution PET imaging.