1. A radiation imaging method, comprising the steps of: collecting radiation emission data from a target including at least one radiation source, wherein the data includes measurements from at least two projections; classifying the data into at least one energy range; separating the data in each energy range into N independent radiation distributions, wherein N is a number of the radiation sources, and each of the N independent radiation distributions corresponds to each of the radiation sources; processing the data in each of the N independent radiation distributions to estimate its true distribution; and reconstructing a radiation distribution image of the target using the processed data.