Framework for evaluating photon-counting detectors under pile-up conditions.

Area of Science:

• Medical Imaging Physics
• Detector Science

Background:

• X-ray photon-counting detectors (PCDs) offer advanced capabilities for medical imaging.
• Existing theoretical frameworks often assume linear detector response, which is invalid under typical clinical operating conditions with significant pile-up.

Purpose of the Study:

• To develop a framework for evaluating PCDs that accounts for their non-linear behavior caused by pile-up.
• To enable accurate assessment of PCD performance under clinically relevant conditions.

Main Methods:

• Utilized small-signal analysis to study PCD behavior under pile-up.
• Introduced the perturbation point spread function (pPSF) to describe detector response.
• Employed Monte-Carlo simulations for idealized direct- and indirect-conversion PCDs.

Main Results:

• Calculated pPSFs for two PCDs, demonstrating their utility in assessing signal sensitivity to lesions.
• Illustrated detrimental pile-up effects, including contrast inversion and bin cancellation.
• Quantified spectral and spatial performance under realistic operating conditions.

Conclusions:

• The proposed framework accurately quantifies PCD performance under clinical conditions, highlighting non-linear effects.
• PCDs should not be analyzed as linear systems; this framework adapts existing measures like the modulation transfer function.
• The framework aids in developing better PCDs and imaging systems.