Both in radiographic and tomographic mode, conventional X-ray imaging provides information about the examined object which is not sufficient to characterize it precisely. Dual-energy X-ray technique, which consists in combining two radiographs acquired at two distinct energies, allows to obtain both density and atomic number, thus to provide information about material composition, or at least to improve image contrast. Available systems usually perform energetic separation at source level, but separation at detector level is also possible for linear detectors, especially those devoted to translating objects control. Dual-energy equations can be easily written and solved for monochromatic energy spectra and perfect detectors, but become complex when considering realistic spectra, detector sensitivity, and system non-linearity. A decomposition into material basis, using experimental dual-material calibration, allows to solve an approximated system, while getting free of beam hardening and other disturbances. More generally, we analyze the various problems to be solved before benefiting from dual-energy approach, and propose available solutions. We evaluate influence of noise on results accuracy, that strongly influences materials distinguishability. We review the aspects to optimize when considering a specific industrial problem: choice of energy spectra, of materials basis, method design. Numerical simulation is an efficient tool for that optimal system design. Various industrial applications will be considered.

A new gamma-camera architecture named HiSens is presented and evaluated. It consists of a parallel hole collimator, a pixelated CdZnTe (CZT) detector associated with specific electronics for 3D localization and dedicated reconstruction algorithms. To gain in efficiency, a high aperture collimator is used. The spatial resolution is preserved thanks to accurate 3D localization of the interactions inside the detector based on a fine sampling of the CZT detector and on the depth of interaction information. The performance of this architecture is characterized using Monte Carlo simulations in both planar and tomographic modes. Detective quantum efficiency (DQE) computations are then used to optimize the collimator aperture. In planar mode, the simulations show that the fine CZT detector pixelization increases the system sensitivity by 2 compared to a standard Anger camera without loss in spatial resolution. These results are then validated against experimental data. In SPECT, Monte Carlo simulations confirm the merits of the HiSens architecture observed in planar imaging.