Threshold optimization for efficient contrast imaging with quantum counting CT detectors

Photon counting detectors are expected to bring along various clinical benefits in CT imaging. Among the benefits of these detectors is their intrinsic spectral sensitivity that allows to resolve the incident X-ray spectrum. Their capability for multi-energy imaging enables material segmentation, but it is also possible to use the spectral information to create fused gray-scale CT images with improved imaging properties. We have developed and investigated an optimization method that maximizes the image contrast-to-noise ratio, making use of the spectral information in data recorded with a counting detector with up to six energy thresholds. The resulting merged gray-scale CT images exhibit significantly improved CNR 2 for a number of clinically established, potentially novel and hypothetical contrast agents in the thin absorber approximation. In this work we motivate and describe the optimization method, provide the deduced optimal sets of threshold energies and mixing weights, and summarize the maximally achievable gain in CNR 2 for each contrast agent under study.