Theoretical modeling of the performance of x-ray imaging detectors enables understanding relationships between the physics of x-ray detection and x-ray image quality, and enables theoretical optimization of novel x-ray imaging techniques and technologies. We present an overview of a framework for theoretical modeling of the frequency-dependent signal and noise properties of single-photon-counting (SPC) and energy-resolving x-ray imaging detectors. We show that the energy-response function, large-area gain, modulation transfer function (MTF), noise power spectrum (NPS) (including spatio-energetic noise correlations) and detective quantum efficiency (DQE) of SPC and energy-resolving x-ray imaging detectors are related through the probability density function (PDF) describing the number electron-hole (e-h) pairs collected in detector elements following individual x-ray interactions. We demonstrate how a PDF-transfer approach can be used to model analytically the MTF and NPS, including spatio-energetic noise correlations, of SPC and energy-resolving x-ray imaging detectors. Our approach enables modeling the combined effects of stochastic conversion gain, electronic noise, characteristic emission, characteristic reabsorption, coulomb repulsion and diffusion of e-h pairs and energy thresholding on the MTF and NPS. We present applications of this framework to (1) analysis of the frequency-dependent DQE of SPC systems that use cadmium telluride (CdTe) x-ray converters, and (2) analysis of spatio-energetic noise correlations in CdTe energy-resolving x-ray detectors. The developed framework provides a platform for theoretical optimization of next-generation SPC and energy-resolving x-ray imaging detectors.
KEYWORDS: Modulation transfer functions, Sensors, X-rays, X-ray detectors, Signal detection, Systems modeling, Iodine, X-ray imaging, Selenium, Signal to noise ratio, Image quality, Photon counting
Contrast-enhanced digital mammography using spectroscopic x-ray detectors may improve image quality relative to existing contrast-enhanced breast imaging approaches. We present a framework for theoretical modelling of signal and noise in contrast-enhanced spectral mammography (CESM) and apply our framework to systems that use a spectroscopic amorphous selenium (a-Se) field-Shaping multi-Well Avalanche Detector (SWAD) which uses avalanche gain to overcome the low conversion gain of a-Se. We modelled an approach that uses an a-Se SWAD with 100x100 μm2 detector elements, a converter thickness of 300 μm, an avalanche gain of ten, a 10-keV electronic noise floor and two energy bins. We modelled the influence of quantum efficiency, conversion gain, avalanche gain, characteristic emission, electronic noise, energy thresholding and image subtraction on the modulation transfer function (MTF), noise power spectrum (NPS) and iodine contrast. We investigated the choice of energy thresholds for the task of visualizing iodine signals. Our analysis demonstrates that reabsorption of characteristic photons yields energy-bin-dependent MTFs. As a result, spectral subtraction of low-energy and high-energy images enhances high spatial frequencies relative to low spatial frequencies. This effect, combined with better noise performance when using the lowest possible threshold to separate low-energy photons from electronic noise, results in better imaging performance than when reabsorption is suppressed through thresholding. Our theoretical framework enables quantifying trade offs between contrast, spatial resolution and noise for analysis of novel approaches for CESM, and provides a theoretical platform for comparison of CESM with existing approaches.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.