Spectral CT imaging with hybrid detectors in integrating and dynamic-threshold counting modes

Abstract

In recent years, spectral CT with photon counting detectors (PCDs) has exhibited more advantages compared to conventional CT systems. Spectral CT has the potential to substantially advance CT imaging by reducing image noise and dose, improving contrast and target specificity, and enabling functional imaging with special molecular markers (e.g. Gold nanoparticles). The current PCDs, however, is difficult to balance the amount of energy bins and the data noise of statistical fluctuation at each bins. More energy bins mean higher energy discriminating ability, but lower photon number at each bin. Moreover, in order to obtain enough energy bins, the current PCD is made up by small spectral detector subelements which have different thresholds. However, the more energy bins it has, the more complicated circuitry is. Hence, the PCD element becomes complex and large if we want many energy bins. Both spatial and energy resolutions are compromised. The state-of-the-art PCD has eight energy bins. It is difficult to make more energy bins. The overall goal of our research is to develop a hybrid detector which combines the integrating and dynamic-threshold counting modes. Its energy thresholds, or energy bins, can be flexibly arranged and dynamically changed during the spectral CT scanning. In each energy bin, current-integrating readouts are used. Thus, we can get many energy bins with very limited amount of PCD subelements. We develop a smart algorithm to reconstruct the true-color CT images by the data from this hybrid detector with adjustable energy thresholds (e.g. randomly changing). This paper will introduce this new spectral CT system with hybrid detector, its image reconstruction algorithm, and the simulation results.