Performance of the Moving Voxel Image Reconstruction (MVIR) Method in the Fixed Site Detection System (FSDS) Prototype

We have developed a dynamic gamma-ray emission image reconstruction method called MVIR (Moving Voxel Image Reconstruction) for lane detection in multilane portal monitor systems. MVIR was evaluated for use in the Fixed Site Detection System (FSDS), a prototype three-lane gamma-ray portal monitor system for EZ-pass toll plazas. As a baseline, we compared MVIR with a static emission image reconstruction method in analyzing the same real and simulated data sets. Performance was judged by the distributions of image intensities for source and no-source vehicles over many trials as a function of source strength. We found that MVIR produced significantly better results in all cases. The performance difference was greatest at low count rates, where source/no-source distributions were well separated with the MVIR method, allowing reliable source vehicle identification with a low probability of false positive identifications. Static emission image reconstruction of the same data produced overlapping distributions that made source vehicle identification unreliable. The performance of the static method was acceptable at high count rates. Both algorithms reliably identified two strong sources passing through at nearly the same time.