Measuring the Accuracy of CT Bone Geometry for Orthopedic Implants
High resolution Computed Tomography imaged a cylindrical bone/soft tissue phantom on three different CT scanners at two different techniques (low kVp/mAs and high kVp/mAs). Simulated bone annuli in the images were subjected to image processing and edge detection based on radial image intensity profiles. The measured bone diameters and thicknesses were compared with the known dimensions of the bone rings in the cylindrical phantom. Bone measurement error decreased with increasing radius of the bone step and increased as the bone thickened. Analysis of Variance failed to show any significant differences in the errors across three scanners and two x-ray techniques suggesting that CT for bone 3-D can safely use lower dose techniques. The error in measuring the diameter of the bone showed a significant decrease as the diameter of the bone increased, however, bone thickness failed to show a similar trend and the measurements remained relatively accurate. Overall the accuracy of the CT bone diameter measurements ranged from −11.0% to −1.0% and thickness error from −3.7% to 5.7%.
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