Implementation and Assessment of Dynamic Fluence Field Modulation with Multiple Aperture Devices

Area of Science:

• Medical Imaging
• Physics
• Engineering

Background:

• Cone-beam CT (CBCT) imaging is crucial for medical diagnostics.
• Controlling X-ray beam characteristics is vital for image quality and dose reduction.
• Existing methods for beam modulation have limitations in artifact correction and noise control.

Purpose of the Study:

• To experimentally demonstrate dynamic fluence field modulation (FFM) using a dual multiple aperture device (MAD) system for CBCT.
• To design and implement FFM profiles optimizing for image flatness and minimum mean variance.
• To develop and validate a novel correction algorithm for MAD-based FFM in CBCT.

Main Methods:

• A dual MAD system with tungsten bars was integrated into a CBCT bench.
• FFM profiles were created using MAD translations and pulse width modulation.
• A specialized correction algorithm was developed to address focal spot shifts and spectral effects.
• Reconstructions of an elliptical phantom were analyzed for variance and noise power spectrum (NPS).

Main Results:

• The proposed correction algorithm successfully removed high-frequency ring artifacts, unlike conventional methods.
• Measured beam profiles closely matched theoretically computed FFM target profiles.
• FFM optimized for flatness resulted in nearly isotropic NPS and homogeneous variance.
• FFM optimized for minimum mean variance achieved lower noise levels compared to unmodulated scans.

Conclusions:

• Dual-MAD CT enables effective dynamic fluence field modulation for CBCT.
• The developed correction algorithm significantly improves image reconstruction quality by removing artifacts.
• This approach offers robust control over fluence and image quality for diverse phantom applications.