Monolithic 64-channel SiPM matrices for small animal PET

The University of Pisa and INFN Pisa are developing a small animal PET prototype scanner employing continuous LYSO crystals and the silicon photomultiplier (SiPM) matrices fabricated at FBK-irst. The SiPM matrices have 64 SiPM pixel elements in a common substrate. The SiPM elements are 1.4 mm×1.5 mm size, in a 1.5 mm×1.5 mm pitch. The test of the first detector heads is taking place in collaboration with IFIC, Valencia. The detectors consist of a LYSO crystal of 12 mm×12 mm coupled to a SiPM matrix. Characterization and position determination tests have been carried out. The energy resolution obtained is 14.5% FWHM at 511 keV. The spatial resolution with center-of-gravity algorithms is 0.9 mm FWHM. A Maximum likelihood method is also being tested. This method allows to separate points at 1 mm distance, and to reconstruct correctly the interaction position also at the edges of the detector.