Evaluation and Optimization of an Image Acquisition System for Dual-Energy Cargo Inspections

An optimization study on an image acquisition system was conducted to improve the performance of a dual-energy cargo inspection system that enables material decomposition. The image acquisition system in this paper used a line scan method that acquired images while moving cargo vehicles by the moving system. Also, dual-energy X-ray images were obtained by controlling the X-ray source and detector simultaneously with an external signal generator. The image acquisition system was optimized through gain and offset corrections, signal sensitivity optimization, and beam filtration optimization. In order to evaluate the performance of the cargo inspection system, a penetration test was conducted based on the American National Standards Institute, ANSI 42.46, and the contrast-to-noise ratio (CNR) was measured to analyze the acquired images more quantitatively. As a result of the signal sensitivity optimization, the CNR was improved by 28.5%. We also measured the attenuation coefficient of dual-energy X-rays based on the thickness of the filter for beam filtration optimization. As the thickness of the lead filter was increased, the difference in the attenuation coefficient of dual-energy X-rays increased, and the attenuation coefficient difference was saturated in the 4-mm lead filter. Therefore, the lead filter with a thickness of 4 mm was selected as a filter that can sufficiently broaden the average energy difference of the dual-energy X-rays without impairing the image quality, which ultimately improves the material decomposition ability.