Geometrical Calibration of a 2.5D Periapical Radiography System

Abstract

The objective of this study was to develop a geometrical calibration method applicable to the 2.5D prototype Periapical Radiography System and estimate component position errors. A two-steel-ball phantom with a precisely known position was placed in front of a digital X-ray sensor for two-stage calibration. In the first stage, the following three parameters were estimated: (1) r, the distance between the focal spot and the rotation axis of the X-ray tube; (2) ψ, the included angle between the straight line formed by the X-ray tube’s focal spot and rotation axis and the straight line of the orthogonal sensor; and (3) L4, the distance between the rotation axis and the plane where the two steel balls were positioned. In the second stage, the steel balls’ positions were determined to calculate the positions of the X-ray tube on the x, y, and z axes. Computer simulation was used to verify the accuracy of the calibration method. The results indicate that for the calibration approach proposed in this study, the differences between the estimated errors and setting errors were smaller than 0.15% in the first and second stages, which is highly accurate, verifying its applicability to accurate calibration of the 2.5D Periapical Radiography System.