In multi-lens microscopic cone-beam CT system, different resolutions can be achieved by tuning different objective lens with different magnifications, following the scan field of view (FOV) changed. By this multi-FOV/resolution acquisition strategy, many applications like truncation problem can be solved successfully. However, in order to achieve high-resolution image, the microscopic cone-beam CT system should comply with its geometrical restrictions accordingly, which are not only for that of conventional cone-beam system but also for that of multiple objective lens. Hence, compared with the existed cone-beam system calibration, a specific united calibration method is proposed in this paper. A set of geometrical parameters is presented, which can fully describe whole geometry of conventional cone-beam system as well as multi-lens. By taking use of projective data of circular trajectory of one single ball phantom, a cost function with the described arguments based on the projective lines of the phantom is built up. After solving the cost function, the calibration parameters can be determined optimally. The simulated and experimental results demonstrate that the proposed method shows significant improvements in robustness, precision and implementation.
A geometric calibration method for cone beam CT systems
