Design studies of a high resolution PET detector using APD arrays

We evaluated a compact, high resolution PET detector module using avalanche photodiode (APD) arrays to replace bulky position sensitive PMTs. The newly developed APD array is a planar processed 4x4 array which has a 2x2 mm(2) pixel size with 0.4 mm gaps between pixels, about 60% quantum efficiency at 420 nm wavelength, and uniform high gain (> 1000) across all channels. A 4x4 array of 2x2x10 mm(3) LSO crystals was coupled to an APD array. Different readout electronics and signal multiplexing schemes were explored. All crystals in the detector array were clearly identified in the flood source histogram, with average peak-to-valley ratios of about 12:1 using a charge sharing resistor network. The energy resolution was measured to be similar to 14% at 511 keV in the detector array. The measured timing resolution was 2.6 ns in coincidence with a LSO/PMT detector. By optimizing the readout electronics currently being used, it is likely that detector performance can be further improved. We have also determined depth-of-interaction (DOI) by reading out two APD arrays connected to the ends of a 2x2x22 mm(3) LSO crystal. Preliminary measurements show good DOI measurement capability with DOT positioning uncertainty between 4 and 6.5 mm.