1. A method of processing x-ray images, the method comprising: training an artificial neural network to process multi-spectral x-ray projections to determine composition information in terms of equivalent thickness of at least one basis material; providing a multi-spectral x-ray projection of an object, wherein the multi-spectral x-ray projection of the object contains energy content information describing energy content of the multi-spectral x-ray projection; processing the multi-spectral x-ray projection with the artificial neural network to determine composition information about the object; and providing the composition information about the object.