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

The light distribution along one edge of a PET scintillation crystal w as investigated with a Monte Carlo simulation. This position dependent light distribution can be used to measure the 511 keV photon interact ion 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 BG O crystal surrounded by diffuse reflector is 3.0 mm. This light distri bution is constant for widths (originally 3 mm) between 1 and 6 mm, bu t decreases from 3.0 to 1.8 mm FWHM as the height is reduced from 10 t o 3 mm. Other geometrical modifications were simulated, including corn er 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 distri bution is predicted, which should yield a PET detector module with dep th of interaction measurement resolution of 3.6 mm FWHM.