1. A data acquisition method for microtomographic analysis of a specimen, the specimen comprising varying phase fractions of first and second types of material, the method including the steps of: a. making a plurality of sets of projections of the specimen, each projection of the specimen being a measure of the incident energy (I) of a conebeam x-ray transmitted from an x-ray source through the specimen to a detector, said detector having a plurality of x-ray sensitive pixels and each set of projections including a first projection of the specimen of a selected view, wherein said x-rays used to make said first projection have a first energy spectra, and a second projection of the specimen of a selected view, wherein said x-rays used to make said second projection have a second energy spectra different from said first energy spectra, and wherein each set of projections are made of different selected views of the specimen; b. quantifying the phase fraction of the material forming the specimen for each said selected view of the specimen by evaluating the differences in said incident x-ray energy transmitted through the specimen between said first and second projections of said specimen at each of the detector pixels for each set of projections, wherein said quantifying process for each set of projections of the specimen produces a first processed projection representative of the phase fraction of a first type of material forming the specimen and a second processed projection representative of the second type of material forming the specimen; and c. calculating the phase fraction of the material forming the specimen at a selected point in the specimen by performing backplane analyses of said processed projections, wherein a first backplane analysis is performed of said first processed projections to obtain an indication of the phase fraction of the first type of material forming the specimen at said selected point and a second backplane analysis is performed of said second processed projections to obtain an indication of the phase fraction of said second type of material forming the specimen at said selected point.