Detection with polychromatic x-ray pencil beam illumination: information-theoretic bounds

Area of Science:

• Physics
• Information Theory
• Materials Science

Background:

• Non-destructive testing (NDT) using x-ray imaging is crucial for defect detection, cargo inspection, and security screening.
• These applications involve detection problems where target presence must be determined.
• Task-specific information (TSI) bounds provide an information-theoretic metric for evaluating detection performance.

Purpose of the Study:

• To present task-specific information (TSI) bounds for a threat detection task.
• To evaluate the performance of an x-ray imaging system using polychromatic pencil beam illumination and energy-resolving detectors.
• To determine the minimum threat thickness required for detection under various object configurations.

Main Methods:

• Utilized a system with polychromatic x-ray pencil beam illumination and energy-resolving detectors.
• Performed both absorption and diffraction measurements for object analysis.
• Examined three threat class configurations: homogeneous fixed thickness, homogeneous stochastic thickness, and dual-material stochastic thickness.

Main Results:

• Investigated threat detection using water (non-threat) and diesel (threat) as model materials.
• For a dual-material object with stochastic thickness, a minimum threat thickness of 4.5 cm was identified.
• This minimum thickness is necessary to achieve a task-specific information (TSI) of at least 0.7.

Conclusions:

• Joint absorption and diffraction measurements are effective for threat detection in complex scenarios.
• The study quantifies the minimum detectable threat thickness for specific object compositions and configurations.
• TSI bounds offer a valuable metric for optimizing x-ray imaging systems for security applications.