A fast and hardware mimicking analytic CT simulator

Different algorithms have been utilized for x-ray computed tomography (CT) simulation based on Monte Carlo technique, analytic calculation, or combination of them. Software packages based on Monte Carlo algorithm provide sophisticated calculations but the time consuming nature of them limits its applicability. Analytic calculation for CT simulation has been also evaluated in recent years. Due to ignoring basic physical processes, analytic methods have limited applications. In this study, a hardware mimicking algorithm has been developed to accurately model the CT imaging chain using analytic calculation. The model includes x-ray spectrum generation according to the pre-defined scanning protocol. The detector is designed to acquire the data either in integral or spectral modes. CT geometry can be used as parallel or fan beam with different sizes. Poisson noise model was applied to the acquired projection data. Varieties of projection-based computerized phantoms have been designed and implemented in the simulator. CT number and background noise of the simulated images have been compared with experimental data. On average, the relative difference between simulated and experimental HUs are 8.3%, 7.5%, and 8.0% for bone; 12.1%, 10.3%, and 7.8% for contrast agent; and 16.6%, 3.6%, and 5.2% for the background at 80 kVp/500 mAs, 120 kVp/250 mAs, and 140 kVp/125 mAs, respectively. The relative difference between simulated and experimental noise values vary between 2% to slightly less than 26%. For scanning and image generation with a computer equipped with Intel Core2 Quad CPU and 2.0 GB of RAM, the simulator takes about 32 seconds for generating a 512×512 single slice image when it is adjusted to acquire 900 projection angles with 20 mm slice thickness and 140kVp/200 mAs scanning protocol. The simulation time is independent of photon intensity.