A scintillator element (22) includes scintillator blocks (60) arranged to form an array, and transparent or translucent material (62) disposed between adjacent scintillator blocks of the array. The transparent or translucent material may comprise epoxy or glue disposed between adjacent scintillator blocks of the array and adhering the adjacent scintillator blocks together. In some embodiments the scintillator blocks have a refractive index for scintillation light of at least •=1.8, and the transparent or translucent material has a refractive index for the scintillation light of at least •=1.6. An array of light detectors (24), such as silicon photomultipliers (SiPM) detectors formed monolithically on a silicon substrate, may be disposed on a bottom face of the scintillator element to detect scintillation light generated in the scintillator element. For PET applications, the scintillator element and the array of light detectors define a radiation detector (20) configured to detect 511 keV radiation.