Impact of bowtie filter and detector collimation on multislice CT scatter profiles: A simulation study

Area of Science:

• Medical Physics
• Radiological Imaging
• Computational Science

Background:

• Scatter radiation in diagnostic computed tomography (CT) affects image quality and quantitative accuracy.
• Understanding scatter distribution is crucial for optimizing CT scanner design and reconstruction algorithms.

Purpose of the Study:

• To investigate the impact of scan subject size, antiscatter grid (ASG), collimator size, and bowtie filter on scatter radiation distribution in a 16-slice CT scanner using Monte Carlo simulations.
• To analyze the effects of scatter on reconstructed attenuation coefficients and the influence of tissue heterogeneities.

Main Methods:

• Simulated full radiation transport using Geant4 in a realistic CT scanner model.
• Quantified antiscatter grid (ASG) transmission and simulated normalized scatter profiles (NSP) and scatter-to-primary-ratio (SPR) profiles for different beam energies and phantom sizes.
• Assessed the impact of scatter on attenuation coefficients and developed a method to characterize spatial frequency content of sinogram signals.

Main Results:

• Scatter radiation (NSP and SPR) increased linearly with collimator opening and monotonically with phantom size.
• The antiscatter grid (ASG) reduced central axis NSP threefold and detector scatter by factors of 25-500.
• Scatter profiles were dominated by low spatial frequencies, but SPR contributed to high-frequency artifacts near dense structures.

Conclusions:

• Geant4 Monte Carlo simulations are effective for characterizing CT detector response to scatter radiation.
• The ASG significantly reduces scatter but affects narrow-beam attenuation measurements, requiring incorporation into iterative reconstruction models.
• Tissue heterogeneities have a modest influence on scatter profiles but do not significantly add high spatial frequency content.