A method and a system for preparing a radiation image of a target are provided. The radiation imaging method includes the steps of collecting radiation emission data from a target, classifying the data into at least one energy range, separating the data in each energy range into N independent radiation distributions, 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. The system includes at least one radiation detector module and at least one computerized component configured to perform the steps of the method.
