A method to achieve spatial linearity and uniform resolution at the edges of monolithic scintillation crystal detectors for PET

We have performed Monte Carlo simulations of the scintillation light transport between two adjacent 27.2 mm × 26.7 mm × 20 mm LYSO crystals, optically coupled together using MeItmount coupling medium with a refractive index of 1.7. Each crystal was read out by 4 Hamamatsu S118283344M monolithic SiPM arrays from one crystal side. Event positioning reconstruction results show that this optical coupling technique can substantially reduce the edge-artifacts in these crystals. With realistic values for the multiplication noise of the SiPMs and electronic readout noise, we obtain intrinsic spatial resolutions of ~3.1 mm FWHM at the center and ~3.0 mm FWHM at 0.6 mm from the optical coupling edge of the 20 mm thick monolithic crystals. When reducing the number of readout channels by applying a 4 : 1 multiplexing ratio, a ~4.1 and ~4.3 mm FWHM resolution, respectively, at the center and 0.6 mm from the optical coupling edge was obtained. The simulations further show that a coincidence timing resolution of 350 ps FWHM can be obtained with this crystal geometry, with a 30% SiPM photon detection efficiency (PDE).