Positron range effects in high resolution 3D PET imaging

Positron range limits the spatial resolution of PET images. It has a different effect for different isotopes and propagation materials, therefore it is important to consider it during image reconstruction, in order to obtain the best image quality. Positron range distribution was computed using Monte Carlo simulations with PeneloPET. The simulation models positron trajectories and computes the spatial distribution of the annihilation coordinates for the most common isotopes used in PET: ¹⁸F, ¹¹C, ¹³N, ¹⁵O, ⁶⁸Ga and ⁸²Rb. Range profiles are computed for different positron propagation materials, obtaining one kernel profile for each isotope-material combination. These range kernels were introduced in FIRST, a 3D-OSEM image reconstruction software, and employed to blur the object during forward projection. The blurring introduced takes into account the material in which the positron is annihilated, obtained for instance from a CT image. In this way, different positron range corrections for each material in the phantom are considered. We compare resolution and noise properties of the images reconstructed with and without positron range modelling. For this purpose, acquisitions of an Image Quality phantom filled with different isotopes have been simulated for the ARGUS small animal PET scanner.