Method for measuring the focal distance of 3D-CT imaging system with high accuracy using image auto-correlation

In the three dimensional computed tomography imaging system, it is impossible to measure the X-ray focus to object-rotating-axis distance (FOD) by direct means, so how to obtain the value of FOD with simple and feasible method is an involved engineering problem. Through acquiring the digital radiography (DR) images of the double-circled object at two imaging positions, the auto-correlation operation was executed, so as to get distance of the two circles' projection center. Then through solving equations, the value of FOD was finally obtained. Experiment results prove that the accuracy of this method can satisfy the requirements of the practical scanning system. This testing method is also easy to realize and of high anti-noise ability. Furthermore, it can be realized automatically by software.