Lookup table-based simulation of directly-converting counting X-ray detectors for computed tomography

Medical computed tomography (CT) can benefit from directly-converting counting detectors. As yet there is little expertise with this type of detectors in commercially available clinical CT systems, a precise detector model is required for developing such a system. We introduce a lookup table-based simulation of counting detectors on X-ray photon level that allows studying the influence of detector parameters and efficiently evaluating proposed designs. It uses energy-resolved sinograms of incoming X-ray photons as input data and generates photon counts for each channel and reading. The effects of Poisson noise, photon interactions, pulse generation, read-out electronics and electrode signal processing are covered. The photon interaction data as well as signal characteristics are provided in the form of detector-specific lookup tables. This approach offers the precision of Monte-Carlo simulations and the efficiency of model-based descriptions. Unlike standard Monte-Carlo simulations, it is capable of simulating whole CT-scans in a reasonable amount of time on a standard workstation. Due to this efficiency, the influence of detector parameters on image quality in the reconstructed image domain can be evaluated. The simulation is verified against measured data.