A high performance detector head with matrices of silicon photomultipliers (SiPMs) is under development at the University of Pisa. The detector head will be employed in the construction of a high spatial resolution, MR compatible small animal PET scanner. Silicon photomultipliers from FBKirst (Trento, Italy) are being evaluated for this purpose. SiPM elements of 1 mm × 1 mm size and SiPM matrices composed of four (2×2) pixel elements have been tested. An intrinsic timing resolution of 60 ps sigma has been measured. The results with LSO crystals show an energy resolution of 20% FWHM at 511 keV, and a coincidence timing resolution of 600 ps rms. New devices with improved characteristics and active area, as well as SiPM matrices with 16 (4×4) SiPM elements have been produced, and will be evaluated