Methods for characterization and optimisation of measuring performance of stereoscopic x-ray systems with image intensifiers

The use of biplanar high-speed x-ray fluoroscopy to study fast, 3D movements that are inaccessible from external views has grown significantly in the past decade. Owing to the development of specialised software for calibration, distortion correction, and automated tracking of radio-opaque marker implants, this technique will soon become the standard to analyse skeletal kinematics of vertebrate animals. However, tests of important characteristics of biplanar x-ray systems, such as resolution and precision, remain scarce and incomplete. We present methods to determine imaging resolution and 3D stereoscopic and dynamic resolutions to follow moving markers in 3D, and demonstrate them on a newly installed stereoscopic x-ray system with image intensifiers. Using four-megapixel cameras, image resolution slightly surpasses previous reports. The spatial resolution appears to be optimal at magnification factors (ratio of source-to-detector to source-to-subject distance) between 1.33 and 2.20. This new information will allow biplanar x-ray system users to optimise the relative position of tube, subject, and image intensifiers.