Digitization and visibility issues in flat detector CT: A simulation study

Flat detector CT suffers from a limited visibility of low-contrast objects. On the one hand this is due to increased image noise and x-ray scatter, on the other hand this can be attributed to a limited dynamic range of current flat detectors. Compared to clinical CT detectors with their energy absorption efficiency of 90% or more and their dynamic range of 20 bits or more, flat detectors with their energy absorption efficiency around 50 or 60% and their dynamic range of 10 to 12 bits above the noise floor are significantly inferior. Further on, often intended or unintended over-or underexposure occurs in flat detector CT systems, resulting in undesired effects on image quality. To explore the situation we conduct a simulation study that systematically analyzes the effects of limited dynamic range and of over-or underexposure on CT image quality in general and on low-contrast visibility in particular. We applied our study both to "conventional" attenuation based CT imaging as well as to grating-based differential phase-contrast CT imaging.