Abstract
Single-photon-counting (SPC) x-ray imaging has the potential to improve image quality and enable novel energy-dependent imaging methods. Similar to conventional detectors, optimizing image SPC quality will require systems that produce the highest possible detective quantum efficiency (DQE). This paper builds on the cascaded-systems analysis (CSA) framework to develop a comprehensive description of the DQE of SPC detectors that implement adaptive binning. The DQE of SPC systems can be described using the CSA approach by propagating the probability density function (PDF) of the number of image-forming quanta through simple quantum processes. New relationships are developed to describe PDF transfer through serial and parallel cascades to accommodate scatter reabsorption. Results are applied to hypothetical silicon and selenium-based flat-panel SPC detectors including the effects of reabsorption of characteristic/scatter photons from photoelectric and Compton interactions, stochastic conversion of x-ray energy to secondary quanta, depth-dependent charge collection, and electronic noise. Results are compared with a Monte Carlo study. Depth-dependent collection efficiency can result in substantial broadening of photopeaks that in turn may result in reduced DQE at lower x-ray energies (20-45 keV). Double-counting interaction events caused by reabsorption of characteristic/scatter photons may result in falsely inflated image signal-to-noise ratio and potential overestimation of the DQE. The CSA approach is extended to describe signal and noise propagation through photoelectric and Compton interactions in SPC detectors, including the effects of escape and reabsorption of emission/scatter photons. High-performance SPC systems can be achieved but only for certain combinations of secondary conversion gain, depth-dependent collection efficiency, electronic noise, and reabsorption characteristics.
Highlights
Advances in x-ray detector technology have enabled singlephoton-counting (SPC) x-ray detectors with the ability to identify individual photon interactions
Stateof-the-art systems are capable of count rates that may be adequate for some applications including mammography16–20 and breast computed tomography,21–24 but remain restrictive
We show in Appendix C that pNA,B given N0 input quanta is given by p NA, B
Summary
Advances in x-ray detector technology have enabled singlephoton-counting (SPC) x-ray detectors with the ability to identify individual photon interactions. When equipped with multithresholding circuits, these systems enable energyresolving photon-counting (EPC) imaging where the deposited energy from each interacting x-ray photon is estimated.. It is anticipated that the resulting spectral distribution of energy-depositing events will lead to advanced spectroscopic procedures and improve image quality by reducing image noise from random physical processes including Swank and electronic readout noise.. Charge sharing between neighboring detector elements can cause a degradation of image quality and loss of spectral information.. Charge sharing between neighboring detector elements can cause a degradation of image quality and loss of spectral information.4,27–30 This effect is mitigated with techniques that sum charges in neighboring Stateof-the-art systems are capable of count rates that may be adequate for some applications including mammography and breast computed tomography, but remain restrictive. In addition, charge sharing between neighboring detector elements can cause a degradation of image quality and loss of spectral information. This effect is mitigated with techniques that sum charges in neighboring
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