A precise knowledge of the geometry is always pivotal to a x-ray imaging system, such as computed tomography, digital x-ray tomosynthesis and computed laminography. A typical tomosynthesis system is referred to as the relative positions between the focal spots of the x-ray source and the detector, the object remains in a fixed position above the detector and the x-ray tube emits x-ray beams in the direction of the detector. While moving along the trajectory, these x-ray beams are detected by the detector with a fixed position and then sent to the tomosynthesis system to be reconstructed. In order to get an accurate image, exact knowledge of the system geometry is required. We have carried on research in x-ray intra-oral digital tomosynthesis(IDT) for some time and have already made some progress. In order to get a better medical image, we make effort to solving the problem of determining system geometry and propose a new calibration method, which only needs two fiducial markers arbitrarily locating on the detector plan. Then dealing with an arbitrary projected image together with some prior information, we can determine all the focal spot positions. Thus, our method can well determine the system geometry and is suitable for clinical applications. It is worth mentioning that this method can satisfy not only our IDT system but also other tomosynthesis systems. Numerical simulation and experiments have been done and the results confirmed the validity of our work.
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