WFU Physics Colloquium

TITLE: X-Ray Scatter Computation and Simulation in Cone Beam Computed Tomography

SPEAKER: Jie Liu

TIME: Wednesday July 29, 2015 at 10:00 AM

PLACE: Room 107 Olin Physical Laboratory

In cone beam computed tomography (CBCT) with large object volume within the x-ray field, the measured signal can be contaminated by a large amount of scatter photons due to x-ray interactions with the irradiated object. Scatter can severely degrade the quality of the reconstructed CT images by creating artifacts and quantification errors. Thus scatter correction has become an important processing step for improving image fidelity in CBCT. Algorithm-based methods proposed in the literature include analytical calculations, Monte Carlo (MC) simulations and superposition calculations. Analytical and MC methods apply well-established physical models describing scattering interactions to accurately calculate or simulate scatter profiles. The prevailing challenge is the expensive computation cost inherently required. Superposition methods use simplified object model and are computationally efficient. But the detailed object information is not considered and inferior accuracy can occur. Therefore, an optimal method with balanced performance in computation speed and accuracy is of the investigation interest.

An analytical model was first proposed to efficiently calculate the dominant Compton single scatter component. Dimensional reduction technique was applied to reduce the computation complexity. Electron binding effect, etc. were also investigated and accommodated in a more general form. To validate the model, MC simulations as the reference results were performed in various scenarios. A comprehensive frame was later developed to cover all scatter components including Compton, Rayleigh single and multiple scatter. A long series of MC simulations were performed to create databases pertaining to scatter parameters for implementation in calculations that were based on both detector measurement and object information.

A compact form for the line integration of Compton single scatter was obtained. The proposed model for Compton single scatter showed highly improved computation efficiency compared to conventional analytical method. Databases for beam scatter kernel were obtained and a general form was parameterized. The comprehensive scatter calculation method was evaluated in both accuracy and computation speed and showed balanced performance in both aspects for potentially practical applications.