1. A computing system comprising: a reconstruction processor 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.