Evaluation of the effects of titanium induced CT artifacts on biomechanical models generation

X-ray CT is capable of providing detailed information about the geometry and material properties of musculoskeletal structures. Such accurate data would be of great interest in studying the effect of orthopaedic implants on bone adaptive behaviour. Metallic implants, however, generate artifacts, typically seen as starburst streaking, which can seriously degrade the accuracy of CT data. The aim of this study was to measure the artifactual errors produced in the CT images of a cortical bone and water equivalent materials phantom by a titanium alloy hip joint prosthetic stem. The image data have been analyzed and the average error over the 10 mm thick cortical bone surrounding the implant evaluated. Subsequently the mean error on each pixel crown surrounding the implant was assessed. The effect of this local error on the material properties assessment of a biomechanical model of the bone-implant complex was estimated. An apparent increase in bone density of approximately 3% was observed in the cortical bone region. The effect of the titanium implant, however, is confined within a 4-8 pixels (1.2-2.4 mm) distance from the prosthetic implant. Even if the local perturbation is very difficult to correct, some possibilities to reduce the effect of the artifactual errors on the material properties assignment to a biomechanical model are proposed.