Development of a 64-channel APD detector module with individual pixel readout for submillimetre spatial resolution in PET

Visualization and quantification of biological processes by molecular imaging in small animals such as rats and especially mice require the best possible spatial resolution in positron emission tomography (PET). A new avalanche photodiode (APD) detector module, the LabPET II, was developed to achieve submillimetre spatial resolution for this purpose. The module consists of two monolithic APD arrays of 4×8 pixels, each with an active area of 1.1×1.1 mm2 at a 1.2 mm pitch. The two APD arrays mounted in a custom ceramic PGA holder are coupled to an 8×8 tapered LYSO scintillator array designed to accommodate one-to-one coupling between individual APDs and crystal pixels. To investigate the module performance, an analog test board with four 16-channel preamplifier ASICs was designed to be interfaced with the LabPET™ digital processing electronics. At a standard APD operating bias, a mean energy resolution of 27.5±2.1% was typically obtained with a relative standard deviation of 13.8% in signal amplitude for the 64 individual pixels when irradiated with 511 keV photons. With two modules in coincidence, a mean timing resolution of 5.0±0.2 ns FWHM was measured. Finally, an intrinsic spatial resolution of 0.82 mm FWHM was measured by sweeping a 22Na point source between the two detector arrays. The LabPET II detector module demonstrates promising characteristics for dedicated small animal PET imaging at submillimetre resolution and, with some further optimization, would be suitable as the building block for a dual-modality combined PET/CT system.