Purpose: To develop an analytical cascaded systems analysis (CSA) model for investigating the limits of signal and noise performance [noise‐power spectrum (NPS), modulation transfer function (MTF), and detective quantum efficiency (DQE)] of photon‐counting detectors (PCDs). Methods: Previously developed models for signal and noise propagation in flat‐panel detectors were extended to include physical effects in the imaging chain specific to the performance of PCDs, including the effect of Compton scatter in the detector, time and energy dependent effects of pulse pileup, and signal threshold. A CT imaging bench incorporating a Si‐strip PCD was constructed to test and validate the theoretical model and provide a plaform for evaluation of image quality in photon counting CT. The linearity of detector response was measured across a range of techniques (80 kVp, 0.03– 0.15 mAs), and a phantom consisting of simulated bone and soft tissue was used to evaluate the contrast to noise ratio (CNR) in CT reconstructions. The model was used to investigate limits in DQE as a function of imaging conditions and detector characteristics. Results: The signal response of the imaging system was highly linear with exposure (mR) across the operating range of the x‐ray source as predicted by the model, suggesting a lack of pulse pileup effects under conditions of interest. The soft‐tissue CNR ranged from 1.3 (at 2 mA) to 2.7 (at 10 mA), suggesting quantum‐limited performance and the potential advantage of zero electronic noise for low‐dose imaging. The model predicts zero‐frequency DQE ∼0.2–0.6 over the range 40–90 kVp and demonstrates an optimal range of signal threshold above the electronic noise but below the level of true counts. Conclusion: CSA modeling can be extended to include characteristics unique to PCDs and provide a basis for understanding the limits of imaging performance in photon counting CT. National Institutes of Health Grant No. 2R01‐CA‐112163‐02. Some authors affiliated with Phillips Healthcare.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging