Hybrid deterministic-stochastic modeling of x-ray beam bowtie filter scatter on a CT system. 
Knowledge of scatter generated by bowtie filter (i.e. x-ray beam compensator) is crucial for providing artifact free images on the CT scanners.  Our approach is to use a hybrid deterministic-stochastic simulation to estimate the scatter level generated by a bowtie filter made of a material with low atomic number.  First, major components of CT systems, such as source, flat filter, bowtie filter, body phantom, are built into a 3D model.  The scattered photon fluence and the primary transmitted photon fluence are simulated by MCNP - a Monte Carlo simulation toolkit.  The rejection of scattered photon by the post patient collimator (anti-scatter grid) is simulated with an analytical formula.  The biased sinogram is created by superimposing scatter signal generated by the simulation onto the primary x-ray beam signal.  Finally, images with artifacts are reconstructed with the biased signal.  The effect of anti-scatter grid height on scatter rejection are also discussed and demonstrated.