The impact of positron range on PET image reconstruction has often been
investigated as a blurring effect that can be partly corrected by adding an element to
the PET system matrix in the reconstruction, usually based on a Gaussian kernel
constructed from the attenuation values. However, the physics involved in PET is
more complex. In regions where density does not vary, positron range indeed involves
mainly blurring. However, in more heterogeneous media it can cause other effects. This
work focuses on positron range in the lungs and its impact on quantification, especially
in the case of pathologies such as cancer or pulmonary fibrosis, for which the lungs have
localised varying density. Using Monte Carlo simulations, we evaluate the effects of
positron range for multiple radionuclides (18F, 15O, 68Ga, 89Zr, 82Rb, 64Cu and 124I) as,
for novel radiotracers, the choice of the labelling radionuclide is important. The results
demonstrate quantification biases in highly heterogeneous media, where the measured
uptake of high-density regions can be increased by the neighbouring radioactivity from
regions of lower density, with the effect more noticeable for radionuclides with highenergy positron emission. When the low-density regions are considered to have less
radioactive uptake (e.g. due to the presence of air), the effect is less severe