  In computed tomography (CT) reconstruction, scattering causes server quality
degradation of the reconstructed CT images by introducing streaks and cupping
artifacts which reduce the detectability of low contrast objects. Monte Carlo
(MC) simulation is considered as the most accurate approach for scatter
estimation. However, the existing MC estimators are computationally expensive
especially for the considered high-resolution flat-panel CT. In this paper, we
propose a fast and accurate photon transport model which describes the physics
within the 1 keV to 1 MeV range using multiple controllable key parameters.
Based on this model, scatter computation for a single projection can be
completed within a range of few seconds under well-defined model parameters.
Smoothing and interpolation are performed on the estimated scatter to
accelerate the scatter calculation without compromising accuracy too much
compared to measured near scatter-free projection images. Combining the scatter
estimation with the filtered backprojection (FBP), scatter correction is
performed effectively in an iterative manner. In order to evaluate the proposed
MC model, we have conducted extensive experiments on the simulated data and
real-world high-resolution flat-panel CT. Comparing to the state-of-the-art MC
simulators, our photon transport model achieved a 202$\times$ speed-up on a
four GPU system comparing to the multi-threaded state-of-the-art EGSnrc MC
simulator. Besides, it is shown that for real-world high-resolution flat-panel
CT, scatter correction with sufficient accuracy is accomplished within one to
three iterations using a FBP and a forward projection computed with the
proposed fast MC photon transport model.
