Characterization of a PET detector head based on continuous LYSO crystals and monolithic, 64-pixel silicon photomultiplier matrices

The characterization of a PET detector head based on continuous LYSO crystals and silicon photomultiplier (SiPM) arrays as photodetectors has been carried out for its use in the development of a small animal PET prototype. The detector heads are composed of a continuous crystal and a SiPM matrix with 64 pixels in a common substrate, fabricated specifically for this project. Three crystals of 12 mm x 12 mm x 5 mm size with different types of painting have been tested: white, black and black on the sides but white on the back of the crystal. The best energy resolution, obtained with the white crystal, is 16% FWHM. The detector response is linear up to 1275 keV. Tests with different position determination algorithms have been carried out with the three crystals. The spatial resolution obtained with the center of gravity algorithm is around 0.9 mm FWHM for the three crystals. As expected, the use of this algorithm results in the displacement of the reconstructed position toward the center of the crystal, more pronounced in the case of the white crystal. A maximum likelihood algorithm has been tested that can reconstruct correctly the interaction position of the photons also in the case of the white crystal.