Positron Range Effects on the Spatial Resolution of RPC-PET

This work studies, by simulation, the influence of the positron range into the sub-millimeter spatial resolution of an experimental prototype of Resistive Plate Chamber (RPC) to be applied to small animal Positron Emission Tomography (PET) - a system able to see directly a reasonable region of the positron distribution tail. Employing a Monte Carlo simulation code (Geant4) the positron range distributions, for eight radioisotopes of interest to PET: ²²Na, ¹⁸F, ¹¹C, ¹³N, ¹⁵O, ⁶⁸Ga and ⁸²Rb was modeled. It was found that, owing to the non-Gaussian nature of the positron range distribution, which partially remains in the Point Spread Function (PSF) of the system, a direct image spatial resolution enhancement is achieved. It was experimentally verified that this enhancement is around 10% FWHM for a ²²Na point-like source achieving an image spatial resolution of 470 mum FWHM. The simulated positron distributions compare reasonably well with the experimental measurements from the RPC-PET prototype and with values reported by other authors.