Estimating 3D Local Noise Power Spectrum from a Few FDK-reconstructed Cone-Beam CT Scans

For CT whose noise is nonstationary, a local NPS is often needed to characterize the system's noise property. A good estimation of the local NPS for CT usually requires many repeated scans. To overcome this data demand, we have previously developed a radial NPS method to estimate the 2D local NPS for FBP-reconstructed fan-beam CT from a few repeats utilizing the polar separability of CT NPS in polar coordinates [1]. In this work we extend the 2D approach to estimate the 3D local NPS for FDK-reconstructed cone-beam CT (CBCT) scans, since the CBCT NPS has similar separability in cylindrical coordinates. We evaluate the accuracy of the 3D local radial NPS method by comparing it to the traditional local NPS estimates using simulated CBCT data. The results show that the 3D radial local NPS method with only 2 to 6 scans yields mean squared error less than 5%) relative to the reference local NPS and can predict signal detectability accurately for evaluating system performance.