Learning-based multi-material CBCT image reconstruction with ultra-slow kV switching

Objective The purpose of this study is to perform multiple ( ≥ 3 ) material decomposition with deep learning method for spectral cone-beam CT (CBCT) imaging based on ultra-slow kV switching. Approach In this work, a novel deep neural network called SkV-Net is developed to reconstruct multiple material density images from the ultra-sparse spectral CBCT projections acquired using the ultra-slow kV switching technique. In particular, the SkV-Net has a backbone structure of U-Net, and a multi-head axial attention module is adopted to enlarge the perceptual field. It takes the CT images reconstructed from each kV as input, and output the basis material images automatically based on their energy-dependent attenuation characteristics. Numerical simulations and experimental studies are carried out to evaluate the performance of this new approach. Main Results It is demonstrated that the SkV-Net is able to generate four different material density images, i.e., fat, muscle, bone and iodine, from five spans of kV switched spectral projections. Physical experiments show that the decomposition errors of iodine and CaCl 2 are less than 6 % , indicating high precision of this novel approach in distinguishing materials. Significance SkV-Net provides a promising multi-material decomposition approach for spectral CBCT imaging systems implemented with the ultra-slow kV switching scheme.