Impact of radiation dose level on CT number accuracy in photon counting CT

It is well known that when radiation dose is reduced in x-ray computed tomography, image noise increases and noise induced streaks may appear. However, to quantify the accuracy of the image reconstruction, another source of error, known as the statistical bias, also needs to be considered. In the projection domain, signal bias originates in the quantum nature of the x-ray photon fluctuations as well as the nonlinear nature of the logarithmic transform used to generate line integral data. The bias in the projection domain is then propagated into the image domain through the image reconstruction process to generate CT number biases. The purpose of this work is to experimentally study the dependence of CT number bias on the radiation dose.