least 50-100 mm spatial resolution. The actual resolution needed for a particular application depends X-ray microtomography allows imaging of the on the microstructural features of interest and their interior microstructure of materials nonshapes. destructively and with spatial resolution which can approach that of optical microscopy (typically, no After presenting the author's perspective of the better than 1 mm in samples whose cross-sectional development of microtomography, imaging, X-ray

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... meter is on the order of 1 mm, and 10 mm for attenuation, and the physical concepts underlying 10 mm specimens). First, X-ray computed tomography are reviewed. Data collection microtomography's origin in medical imaging and strategies, radiation sources, and detectors are sumthe physics behind computed tomography are marised in the third section. The fourth section reviewed. Summaries of apparatus, radiation describes how microtomography has been applied to sources, data collection schemes, and of materials several classes of materials problems. Speculation applications follow. To date, most materials concerning future directions concludes the review. applications fall into one of four areas: inorganic matrix composites, transport in porous media, calcified tissue, and fatigue crack closure. Details of studies in each area highlight the advantages Background X-ray microtomography brings, and the final It is hard to know whether the theft of ideas, themes, section focuses on future directions suggested by concepts, etc. is more important in popular culture recent work using imaging modalities other than (or in the fine arts for that matter) or in science and X-ray attenuation. IMR/343 engineering. Because the subject here is how high