Performance Characterization of MPPC Modules for TOF-PET Applications

PET detectors commonly feature large numbers of multipixel photon counters (MPPCs), requiring data acquisition systems with significant signal multiplexing or using application specific integrated circuits (ASICs) for independent MPPC readout. We evaluate here two Hamamatsu C13500-4075LC-12 detector modules designed for time-of-flight (TOF) PET. Each module has a 12 × 12 lutetium fine silicate crystal array (4.2 χ 4.2 × 20 mm
³
) one-to-one coupled to a 12 × 12 array of 4 mm MPPCs. Each detector has 8 18-channel ASICs utilizing time-over-threshold (ToT) readout. At low event rates, the detectors have full-width at half-maximum (FWHM) energy resolution of 11.8%±0.4%, measured in linearized energy spectra, and 275 ps FWHM coincidence timing resolution (CTR) using energy window of ±1 photopeak FWHM. The 511 keV photopeak amplitude in the ToT spectrum changed 0.24%/°C. There was <;10% event loss up to 1450 kcps/detector. From count rates of 35-1450 kcps the 511 keV photopeak position varied by 1.2%, while photopeak FWHM in the ToT spectra increased by 54%, from 5.8% to 9.0%, corresponding to energy resolution changing from 11.8% to approximately 18.0%. Over this count rate range the CTR varied from 285 to 435 ps FWHM. The TOFPET module performance suggests they are well suited to use in whole-body PET applications.