Detector modeling techniques for pre-clinical 3D PET reconstruction on the GPU

This paper presents methods to the efficient handling of gamma interaction within the detector crystal matrix in ML-EM-based 3D reconstruction algorithms for positron emission tomography (PET). Geometric calculations as well as the approximation of inter-crystal scattering are executed on the GPU. The main characteristics of the scattering effect are captured by factorized models incorporating both on-the-fly simulation and the use of pre-computed data. The discussed methods involve the modification of the detector radius in the geometric model; applying 4D shifting of the LORs regarding the precalculated crystal-transport probability distributions; replacing the simulated detector response function by an approximated one; or full Monte Carlo simulation of the detector. Results of these different approaches are reported using phantom simulations as well as reconstructing real measurements performed on the NanoPET trademark /CT small animal PET scanner. (orig.)