A computing system (116) includes a reconstruction processor (114) configured to execute computer readable instructions, which cause the reconstruction processor to: receive, in electronic format, non-spectral projection data, reconstruct the non-spectral projection data to generate a non-spectral image, retrieve a non-spectral to spectral voxel value map for a basis material of interest from a set of non-spectral to spectral voxel value maps, generate a spectral iterative reconstruction start image based on the non-spectral image and the non-spectral to spectral voxel value map, and reconstruct a spectral image, in electronic format, for the material basis of interest from the non-spectral projection data with a spectral iterative reconstruction algorithm and the spectral iterative reconstruction start image.