Development and performances of a dental digital radiographic system using a high resolution CCD image sensor

Dental digital radiographic (DDR) system using a high resolution charge-coupled device (CCD) imaging sensor was developed and the performances of this system for dental clinic imaging was evaluated. In order to determine the performances of the system, the modulation transfer function (MTF), the signal to noise ratio according to X-ray exposure, the dose reduction effects and imaging quality of the system were investigated. This system consists of a CCD imaging sensor (pixel size: 22 mum) to detect X-ray, an electrical signal processing circuit and a graphical user interface software to display the images and diagnosis. The MTF was obtained from a Fourier transform of the line spread function (LSF), which was itself derived from the edge spread function (ESF) of a sharp edge image acquired. The spatial resolution of the system was measured at a 10% contrast in terms of the corresponding MTF value and the distance between the X-ray source and the CCD image sensor was fixed at 20 cm. The best image quality obtained at the exposure conditions of 60 kVp, 7 mA and 0.05 sec. At this time, the signal to noise ratio and X-ray dose were 23 and 41% (194 muGy) of a film-based method (468 muGy). The spatial resolution of this system, the result of MTF, was approximately 12 line pairs per mm at the 0.05 exposure time. Based on the results, the developed DDR system using a CCD imaging sensor could be suitably applied for intra-oral radiographic imaging because of its low dose, real time acquisition, no chemical processing, image storage and retrieval etc.