1. An x-ray imaging system, comprising: an x-ray source system for generating a high energy x-ray beam and a low energy x-ray beam; a sample holder for rotating a sample in the high energy x-ray beam and the low energy x-ray beam from the x-ray source system to perform a low-energy scan and a high-energy scan of the sample; a detector system for detecting the high energy x-ray beam and the low energy x-ray beam after transmission through the sample to generate projection data; a computer system generating a low-energy reconstructed tomographic volume data set from the low-energy scan and generating a high-energy reconstructed tomographic volume data set from the high-energy scan in the computer system from the projection data, and rendering simultaneous slice views from the low-energy and high-energy reconstructed tomographic volume data sets and presenting a mathematically combined synthetic slice.