Final PhD Seminar

Quantitative X-ray computed tomography? - Three perspectives and an epilogue

Mr Carl (Qiheng) Yang
Materials Physics, ANU

Almost exactly 50 years after its invention, X-ray computed tomography (XCT) has become an indispensable tool across a wide range of disciplines in medicine, science and engineering. Its strengths lie not only in its ability to probe the interior of objects in a non-destructive manner, but also its extraordinary versatility and consequent ubiquity. So far the information provided by XCT scans have been mainly morphological; structures and patterns could be discerned but questions of composition and physical properties can be answered only with difficulty, if at all. This is partly due to its reliance on algorithm reconstruction, as the raw data for XCT is not immediately useful. Integrating all the complexities of the physical process of x-ray interaction into the reconstruction algorithms has proved to be a formidable challenge.

One major feature of the x-ray interaction with matter is its energy dependence; this is responsible for a large class of artefacts in the reconstructed results grouped under the term "beam hardening". Even with a simple two component model of the x-ray energy dependence, much can be done to address these artefacts, and this in turn helps to make possible the direct measurement of physical properties from XCT. I will try and approach this problem from three distinct angles which are nevertheless grouped together by the same model: 1) Simple calibration and analysis of existing XCT tomograms; 2) modified single energy iterative reconstruction; and 3) dual energy iterative reconstruction using novel variance data. I hope to demonstrate that for existing XCT reconstruction algorithms, a little physics goes a long way.

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