US 5,402,460 AGranted

Three-dimensional microtomographic analysis system

AssigneeUniversity of Washington

InventorsRoger H. Johnson, Alan C. Nelson, Robert M. Fisher

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Abstract

A microtomographic system (10) for generating high-resolution, three dimensional images of a specimen (16) is disclosed. The microtomograph system includes an x-ray generator (12) that produces an x-ray beam (14), a specimen holder (18) that holds the specimen in the beam, and an x-ray detector (20) that measures the attenuation of the beam through the specimen. Two projections of each view of the specimen are made with this microtomographic system. Each projection is made with a different intensity x-ray beam. After the projections of one view of the specimen are made, the specimen is rotated on the specimen holder and another set of projections are made. The projections of each view of the specimen are analyzed together to provide a quantitative indication of the phase fraction of the material comprising the specimen. The projections of the different views are combined to provide a three-dimensional image of the specimen.

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.

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Abstract

Claims12