Geometry calibration for a dental cone-beam CT system with an offset detector

In this work, we propose a robust offline geometry calibration method for an offset-detector-based dental cone-beam computed tomography (CBCT) system. Although a host of geometric calibration methods for CT system have been developed, the calibration of dental CBCT systems remains to be one of the challenging cases due to the presence of an offset detector and due to the smaller system dimensions. We highlight the technical difficulties encountered in such dental CBCT geometric calibration, and provide an efficient and robust recipe for the accurate calibration. Through a particular design of the phantom, a heuristic estimation of the isocenter, and an enforcement of smooth change of the extracted geometric parameters, we show that the aforementioned challenges can be overcome. Fabrication errors that may exist in the geometry calibration phantom are also considered. We scanned two physical phantoms with a commercial dental CBCT for evaluating the proposed geometry calibration method. The results confirm that the proposed method can achieve an accurate and efficient geometry calibration in the offset-detector-based CBCT systems.