MONTE-CARLO OPTIMIZATION OF DEPTH-OF-INTERACTION RESOLUTION IN PET CRYSTALS

The light distribution along one edge of a PET scintillation crystal was investigated with a Monte Carlo simulation. This position dependent light distribution can be used to measure the 511 keV photon interaction position in the crystal on an event by event basis, thus reducing radial elongation. The predicted full width at half maximum (FWHM) of the light distribution on the 3 x 30 mm surface of a 3 x 10 x 30 mm BGO crystal surrounded by diffuse reflector is 3.0 mm. This light distribution is constant for widths (originally 3 mm) between 1 and 6 mm, but decreases from 3.0 to 1.8 mm FWHM as the height is reduced from 10 to 3 mm. Other geometrical modifications were simulated, including corner reflectors on the opposing 3 x 30 mm surface. A promising geometry is a 2.2 x 5 x 30 mm BGO crystal, for which a 2.2 mm FWHM light distribution is predicted, which should yield a PET detector module with depth of interaction measurement resolution of 3.6 mm FWHM.