Experimental determination of PET modulation transfer functions incorporating positron range effects using an oversampled cylindrical source

Background Spatial resolution is a fundamental performance parameter of positron emission tomography (PET) systems and is commonly assessed using standardized point‐source‐in‐air procedures. While this configuration minimizes scattering and attenuation effects, it does not account for positron transport in tissue‐equivalent media, whose contribution may become increasingly relevant as PET system resolution improves. Purpose To develop and validate a direct experimental methodology for PET spatial resolution assessment that incorporates positron‐range effects without relying on Monte Carlo simulations or parametric modeling of the system response. Methods A modular polymethyl methacrylate (PMMA) phantom containing a thin linear radioactive source ( or ) was used to ensure full positron absorption. By slightly inclining the source relative to the scanner axis, an oversampling strategy was implemented. The reconstructed volume was projected onto a one‐dimensional profile to obtain a sub‐pixel sampled point spread function (PSF), from which the modulation transfer function (MTF) was derived by Fourier transformation. Finite source‐size correction and uncertainty propagation from PSF to MTF were performed. Radial and tangential MTFs were also determined at off‐center positions. Results The oversampling strategy yielded very small statistical uncertainties in both PSF and MTF estimates. Measurements performed on two PET/CT systems of different technological generations showed negligible differences between and in the older scanner, whereas measurable radionuclide‐dependent effects were observed in the newer system. In the latter, exhibited a broader PSF and lower MTF than , with values of 0.085 and 0.112 , respectively. Conclusions The proposed methodology provides a statistically efficient framework for experimental PET spatial‐resolution characterization under realistic conditions. It enables quantitative assessment of positron‐range effects and complements standardized resolution measurements, particularly in modern high‐resolution PET systems.