Evaluation of image noise in fan-beam x-ray computed tomography

We investigate the problem of evaluating noise in computed tomography images that are reconstructed from x-ray measurements collected in fan-beam geometry. For reconstruction, we use the classical direct filtered backprojection method, which acts directly on the fan-beam projections without rebinning to the parallel-beam geometry. In this context, we present an accurate and efficient method to evaluate the image noise. This method is first validated using results from Monte-Carlo simulations. Then, we illustrate its advantages through the implementation of a channelized Hotelling observer for a lesion detection task.