Spatial resolution studies for a prototype proton CT scanner

A GEANT4 simulation of the phase II proton CT (pCT) scanner built by the pCT collaboration was used in order to study the spatial resolution of the imaging system. A digital edge phantom composed of water-equivalent polymer with 6 body-equivalent material inserts was created. A modified version of the oversampling method was used in order to construct edge spread functions and modulation transfer functions for materials of varying relative stopping power located at several radial displacements from the center of the phantom. It was determined that for a binning size of 1mm×2.5mm and image pixel size of 1 mm2, the limiting resolution observed was 50-75% of the Nyquist frequency. This result could be improved to 60-85% of the Nyquist frequency by reducing the binning size for the filtered back projection to 0.5mm×2.5 mm.