Geometric measurement using complementary metal oxide semiconductor imaging sensor in the cone beam computed tomography gantry system

The cone beam computed tomography (CBCT) system often suffers from a variety of vibrations of the rotating gantry. In this paper we present a new geometric measurement method for gantry vibration before installing the X-ray source and detector in our developing CBCT system. The gantry geometry could be measured and analyzed by using a high speed complementary metal oxide semiconductor (CMOS) imaging sensor on an X-ray source position and a reflective marker on the detector position. A high speed CMOS imaging sensor was used to acquire projection data more than a flat panel detector with a maximum of 30 fps in order to correctly measure and analyze the gantry geometry in CBCB system. The projection image for gantry geometry in single-circle orbit were acquired from 0° (start point) to 360° (end point). The geometric parameters were calculated using the difference between the start point and each rotation point. The 1,440 (120 fps×12 s) projection images were used for precise analysis of the gantry system with 5 rpm. The fluctuation problem found in experimental results of the CMOS imaging sensor was analyzed by measuring it with an accelerometer sensor. After we solved the geometric problems from these experiment results, the gantry vibration of the U-axis and V -axis in the CBCT system was largely improved.