Contrast-enhancement, image noise and dual-energy simulations for quantum-counting clinical CT

The spectral sensitivity of quantum-counting detectors promises increased contrast-to-noise ratios and dual-energy capabilities for Computed Tomography (CT). In this article we quantify the benefits as well as the conceptual limitations of this technology under realistic clinical conditions. We present detailed simulations of a CT system with CdZnTe-based quantum-counting detector and compare to a conventional energy-integrating detector with Gd2O2S scintillator. Detector geometries and pixel layouts are adapted to specific requirements of clinical CT and its high-flux environment. The counting detector is realized as a two-threshold counter. An image-based method is used to adapt thresholds and data weights optimizing contrasts and image noise with respect to the typical spectra provided by modern high-power tungsten anode X-ray tubes. We consider the case of moderate X-ray fluxes and compare contrasts and image noise at same patient dose and image sharpness. We find that the spectral sensitivity of such a CT system offers dose reduction potentials of 31.5% (9.2%) maintaining Iodine-water contrast-to-noise ratios at 120kVp (80kVp). The improved contrast-to-noise ratios result mainly from improved contrasts and not from reduced image noise. The presence of fluorescence effects in the sensor material is the reason why image noise levels are not significantly reduced in comparison to energy-integrating systems. Dual-energy performance of quantum-counting single-source CT in terms of bone-Iodine separation is found to be somewhat below the level of today's dual-source CT devices with optimized pre-filtration of the X-ray beams.