An Attenuated Projector for Iterative Reconstruction Algorithm of a High Sensitivity Tomographic Gamma Scanner

Tomographic Gamma Scanners are tools for nondestructive assay and characterization of nuclear waste drums. In these scanners, a three dimensional image of the activity distribution of every radioisotope stored in the drum is obtained by performing a single-photon emission tomography. AR-TGS is a novel architecture of tomographic gamma scanners that combines an HPGe detector with six NaI(Tl) detectors in order to achieve high-sensitivity. In this work, a projector for a 2D MLEM reconstruction algorithm of AR-TGS is presented. This projector models the geometry of the system, the collimator´s response and the attenuation in the field of view by performing a ray-tracing with several lines of response per detector. The projector was evaluated with Monte Carlo simulations of different phantoms and with experimental measurements. The algorithm proved to be an accurate model of the acquisition process and was used to reconstruct data sets with different strategies, such as utilising matched and unmatched projector/backprojector pairs. The results showed that the use of this projector in image reconstruction considerably improved spatial resolution and image quality compared with an attenuated Siddon projector. The quantification properties of the algorithm for homogeneous and heterogeneous drums matrices were also analyzed.