Technical note: comparing coherent and incoherent scatter effects for cone-beam CT

Area of Science:

• Medical Physics
• Radiological Imaging
• Computational Modeling

Background:

• Scatter radiation in flat-detector CT (FD-CT) impacts image quality and is crucial for accurate dose calculations.
• Current assumptions often overemphasize incoherent (Compton) scatter, potentially underestimating the role of coherent scatter.

Purpose of the Study:

• To compute and analyze coherent and incoherent scatter contributions in FD-CT systems.
• To investigate the impact of scatter on 2D projections using realistic voxel phantoms.
• To evaluate scatter characteristics across varying phantom sizes, energies, and acquisition parameters.

Main Methods:

• A hybrid simulation approach combining analytical single-scatter calculation with Monte Carlo (MC) multiple-scatter estimation.
• Separation and quantification of coherent and incoherent scatter components.
• Simulations performed on cylindrical water phantoms and clinical voxel phantoms (head, thorax).

Main Results:

• Single scatter constitutes a significant portion of total scatter, even in large phantoms.
• Coherent scatter was found to dominate the total scatter distribution in most simulated scenarios, including at 120 keV.
• Incoherent (Compton) scatter, while less spatially distributed, contributed more to the overall scatter magnitude.

Conclusions:

• Coherent scatter plays a more dominant role in FD-CT scatter distributions than previously assumed.
• Accurate scatter modeling in FD-CT requires explicit consideration of both coherent and incoherent scatter.
• The developed simulation method provides a valuable tool for understanding and mitigating scatter artifacts in FD-CT.