A geometric calibration method for an open cone-beam CT system

The image quality of cone-beam CT systems depends directly on the precise knowledge of position and orientation of the X-ray source and the detector. The current methods to determine this geometric information are mainly focused on conventional cone-beam CTs with planar or near-planar scanning trajectories. Due to the fixed alignment of X-ray source and detector, such systems have disadvantages in intraoperative use. Therefore, we develop a first prototype for cone-beam CT characterized by a free alignment of X-ray source and detector. This results in an open system allowing an intraoperative access to the patient and the implementation of non-planar scanning trajectories in the operating room. In this paper, we present a geometric calibration method to determine the position and orientation of X-ray source and detector for any arbitrary projection. Enhancing the theoretical method proposed in Mennessier et al. [1] by introducing an asymmetrical marker arrangement, we realized a calibration method suitable for practical use. We analyzed the resulting accuracy and applied our approach to the open cone-beam CT prototype.