Development of a Monte Carlo Simulation Code (MCSDI) and Its Test Results for Optimal Design of a Digital Radiographic System Based on CMOS Image Sensor

We have developed a Monte Carlo simulation code, the so-called Monte Carlo Simulation for Digital Imager (MCSDI), using the Visual C programming language for the optimal design of a digital radiographic system. The MCSDI code has emulated a variety of test conditions for X-ray energy distributions (bremsstrahlung and characteristic X-rays) and exposure levels, beam shapes (parallel or cone-shaped), and scintillator types and structures (Gd2O2S : Tb or CsI(Tl), and flat or columnar), and a variety of test phantoms. In this paper, we describe the image characteristics of a digital radiographic system based on a CMOS image sensor using the MCSDI code in terms of the contrast-to-noise ratio (CNR), the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE). This code is expected to be useful in designing the optimal components for a digital radiographic system with respect to the detector pixel size, the scintillator type and thickness, the tube voltage, the exposure level, and so on.