X-ray projection simulation based on physical imaging model

In the X-ray CT research area, the linear integral projections of mathematical phantoms were extensively used to evaluate the proposed algorithms with a hypothesis of monochromatic model. However, X-ray tube emits a spectrum of energies and hence it becomes difficult to study some important aspects, such as the reconstructed density accuracy of special reconstruction algorithm and beam hardening effects of polychromatic imaging. If the energy spectrum of X-ray tube, geometry of phantom, and material compositions of all sub-regions are known, the actual projections can be simulated with more accuracy. Motivated by this fact, we propose an improved three-step discrete scheme to simulate the X-ray projections based on physical model. First, CT-numbers of all sub-regions of a phantom are determined in advance. Next, CT-numbers are decomposed into different material compositions under the constraint that sub-regions correspond to different human tissues. Finally, the projections are measured according to the energy spectrum distribution of X-ray tube, using the knowledge of X-ray imaging physics and our strategy to simulate the projecting process. Our scheme requires significantly less storage and computation to achieve a higher accuracy and precision. To demonstrate the feasibility of our scheme, we use the well-known FORBILD head phantom to generate projections and the Feldkamp algorithm for image reconstruction. The anticipated beam hardening effects are clearly seen in images reconstructed from projections simulated using our scheme. This scheme can be utilized in many medical X-ray imaging research aspects, such as algorithm design, performance analysis, distortion calibrations, artifact reduction, etc.