Defining the Optimal Beam Hardening Correction Parameters for CT Dimensional Metrology Applications

Because of its unique ability of revealing an object’s internal structures, Computed Tomography (CT) has gained interest in many industrial fields for e.g. defect detection and reverse engineering. With the fast development of better X-ray sources, smaller X-ray detector pixel resolutions, and faster image reconstruction and analysis tools, the performance of industrial CT has been significantly improved. Recently, X-ray CT technology has entered the application field of dimensional metrology, as an alternative to tactile and optical 3D coordinate measuring technique. Nevertheless, the measurement quality of industrial CT machines is affected by many parameters, among which beam hardening plays a crucial role. It has been proven that the accuracy and uncertainty of CT dimensional measurements is largely influenced by the applied beam hardening correction method. As a routine procedure in industry, the beam hardening effect is corrected by applying hardware pre-filtration complemented with a software correction that implies linearization using predefined polynomial fitting curves. This correction method can largely eliminate beam hardening artifacts e.g. cupping effect and streaks. However, measurement results reveal that the effectiveness of such method is closely related to the selected X-ray power and hardware filter. Overcorrection often occurs with inappropriate machine settings, which results in dimensional errors. This paper investigates the correlation between X-ray power, filter and beam hardening correction algorithm, and aims at establishing a procedure for defining the optimal parameters for CT metrology applications. Keywords Computed tomography, Metrology, Beam hardening correction