Influence of scattering on material quantification using multi-energy x-ray imaging

New horizons in x-ray radiography and computed tomography (CT) have been opened up with the emergence of energy resolved x-ray imaging. This includes the ability to differentiate material components and estimate their equivalent thickness or relative ratio by processing a single shot acquisition image. However, such techniques require highly accurate images, especially for materials close in terms of attenuation. The presence of scattered radiation leads to a loss of contrast and, more importantly, a bias in radiographic material imaging and artefacts in CT. The aim of the present study was to evaluate the disturbance caused by scatter on multi-energy imaging, more precisely, on a material decomposition approach commonly used in radiography or CT. This evaluation was based on numerical simulations using Sindbad-SFFD. Results showed a significant impact of scattered radiation on quantification accuracy for a simplified thorax-sized numerical phantom with an average error of 157.1% and 74.1% for cortical bone and water thickness, respectively. When only 10% of scatter was considered the error still remained significant: 35.1% and 17.5% for cortical bone and water thickness, respectively. The study concludes that a scatter correction method should be performed prior to any material decomposition, if one aims to benefit from energy resolved data in an uncollimated geometry.