Automatic orbital computed tomography coordinating method and quantitative error evaluation based on signed distance field

Background Orbital computed tomography (CT) is commonly used for the diagnosis and digital evaluation of orbital diseases. Yet, this approach requires longer scanning time, increased radiation exposure, and, especially, difficult patient positioning that can affect judgment and data processing. According to high-quality research on orbital imaging, computer-assisted surgery, and artificial intelligent diagnostic development, the correction of a coordinate system is a necessary procedure. Nevertheless, existing manual calibration methods are challenging to reproduce and there is no objective evaluation system for errors. Purpose To establish a method for automatic calibration of orbital CT images and implementation of quantitative error evaluation. Material and Methods A standard three-dimensional (3D) orbit model was manually adjusted, and optimized orbital models were reconstructed based on the initial registration of the skull-bound directed bounding box and the registration of the mutual information method. The calibration error was calculated based on the signed distance field. Seventeen cases of orbital CT were quantitatively evaluated. Results A new method for automatic calibration and quantitative error evaluation for orbital CT was established. The calibrated model error with +/- 2 mm accounted for 81.61% +/- 6.91% of the total models, and the error of +/- 1 mm accounted for 53.49% +/- 7.07% of the total models. Conclusion This convenient tool for orbital CT automatic calibration may promote the related quantitative research based on orbital CT. The automated operation and small error are beneficial to the popularization and application of the tool, and the quantitative evaluation facilitates other coordinate systems.