A Comparison between Half-fan and Full-fan Geometry Calibration in Dental Cone-beam CT

Abstract

Flat-panel-detector based cone-beam CT (CBCT) is in active uses for various medical applications. Depending on the application purposes, the x-ray source and the detector are mounted on a specific gantry such as ring-type or arm-type structures. Systematic errors of a scanning trajectory can occur from mechanical causes in such CBCT systems, and they must be appropriately corrected for securing high spatial resolution. We have noticed an arm-type CBCT with an offset detector, which is often the stereotype of a dental CT system, is particularly challenging in terms of geometry calibration. Because of the offset region of the detector, information of geometry calibration phantom is lost in projection data domain and it leads to discontinuity of geometry parameters. In this study, we compare two geometry parameters. One is calculated in the half-fan geometry and the other is calculated in the full-fan geometry. Also we analyze those calculated parameter and accordingly qualify those geometry parameters with resolution phantom in real dental CBCT system.