Photon counting x-ray detectors as scatter probes

Area of Science:

• Medical Imaging Physics
• Detector Technology
• Image Reconstruction

Background:

• Direct conversion Photon Counting Detectors (PCD) are crucial for future Computed Tomography (CT) scanners, offering improvements in resolution, dose efficiency, and spectral performance.
• However, PCDs are not inherently designed to mitigate object scatter, a primary source of artifacts in CT imaging.

Purpose of the Study:

• To explore a novel method for in-situ object scatter estimation using the existing PCD array in CT systems.
• To leverage PCDs for improved scatter estimation, enhancing image quality through better input for reconstruction algorithms.

Main Methods:

• Investigated the use of anti-scatter grids (ASG) with PCDs, introducing a small air gap to promote charge sharing events.
• Utilized the spectral signature of split charge events as a proxy for coincidence counting in PCDs lacking this capability.
• Performed tabletop experiments to assess ASG misalignment impact and measure scatter from a water column using PCDs' low-noise capabilities.

Main Results:

• Quantified high sensitivity of spectral response to ASG alignment, with a threefold increase in 60 keV photon misregistration probability due to misalignment.
• Observed an increase in coincidence counts proportional to the scatter-to-primary ratio (SPR), matching geometric modeling predictions.
• Measured real-space scatter signals from water, revealing energy-dependent, ring-shaped patterns consistent with calculations.

Conclusions:

• PCD detectors offer unexpected capabilities beyond their primary functions, enabling in-situ scatter estimation via charge sharing.
• Demonstrated PCDs' potential for highly sensitive measurements in benchtop setups, comparable to synchrotron-based investigations.