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 4×4 array which has a 2×2 mm1 pi×el size with 0.4 mm gaps between pi×els, about 60% quantum efficiency at 420 nm wavelength, and uniform high gain (> 1000) across all channels. A 4×4 array of 2×2×10 mm3 LSO crystals was coupled to an APD array. Different readout electronics and signal multiple×ing schemes were e×plored. All crystals in the detector array were clearly identified in the flood source histogram, with average peak-lo-valley ratios of about 12:1 using a charge sharing resistor network. The energy resolution was measured to be -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 2×2×22 mm3 LSO crystal. Preliminary measurements show good DOI measurement capability with DOI positioning uncertainty between 4 and 6.5 mm.