X-ray Local Micro-CT Algorithm Pseudo-global Tomography And Its Applications

The structure of specific material determines the material’s property. Currently, kinds ofmethods are used for materials’ testing. In these methods, X-ray micro-CT (μCT) as anon-destructive imaging technique providing maps of the interior structure of the sample has aunique advantage. X-ray μCT has been widely used in material science, specifically the study ofdeformation, fatigue and fracture, of processing and of the interactions between corrosion andenvironment. The third-generation synchrotron radiation (SR) further promotes the wide use ofμCT. The SR light source has the advantages of high-flux, high monochromatic and highcoherence, which makes SR-μCT has incomparable advantages compare with the traditionalμCT.With high speed development of material science, the microstructures of material becomemore and more care about, and higher resolution been required in μCT. Under the condition ofexisting technology, the detector has a limited size. With the limited size of detector, higherresolution means smaller detector field of view (FOV). For some reasons (for example, thesample is fragile, the inner microstructure may broken when the sample is made too small), thesample can’t be made so small. In this case, the resolution of μCT can’t high enough to see somefine structures in the sample because of the limitation of FOV. The appearance of local CTbecomes the key to solve the problem. Because the local property, the sample can be bigger thanthe FOV of detector, and the resolution can be high enough to see the fine structure.Because of this advantage, some local algorithms appeared in recent decades. Thesealgorithms alleviate the people’s demand for local CT in certain degree. But these algorithms orbelong qualitative local algorithm, or can’t be widely used in the material science for somerestricted condition. In order to solve these problems in the local CT, this paper aims at practicalapplication, dedicated to carry out the research and application of quantitative local CT. Andcombine with data-constrained modeling (DCM) to perform materials’ quantitative analysis. Themain contributions are summarized as follows:1. A local algorithm pseudo-global tomography was proposed. The algorithm uses an effectivestrategy to collect and compensate the lost part of projections in the local CT according theFBP algorithm Filter’s quick attenuation and the affection of lost projections, which caneffectively reduce the artifacts caused by projection truncation. Using a known material tocalibrate the reconstruction, this local CT method can be used for quantitative X-ray imaging. The pseudo-global tomography is radically based on the conventional FBP algorithm, so it isconvenient to be transplanted into the extensively used programs and equipments based onFBP algorithm.2. Developed a program for local CT reconstruction based on pseudo-global tomography. Andthe program had been used to process the local CT data of standard sample, coal sample andrabbit femur. The program compiled by matlab. The correct inner structure of the sampleamong all the region of interest (ROI) can be reconstructed using local projections by thisprogram.3. Combined pseudo-global tomography with DCM to perform local quantitative analysis ofcoal sample, and get the3D distribution of composition in the coal sample. And comparedwith the result of low resolution global CT based DCM. It indicates that the3D distributionsof compositions in the ROI of the sample can be obtained nondestructively with localCT-based DCM. Compared with global-CT based DCM, the new approach can display finerstructures of compositions in the sample ROI. Elevated spatial resolution can reduce theover-estimation of void caused by broadened distribution of the CT reconstructed values,which is common in CT. Quantitative characterization of materials microstructures willenable quantitative prediction of their bulk properties. It can be foreseen that the newapproach has a vast application prospective in materials science. And it also has a greatpotential application in unconventional oil and gas resources evaluation and exploitation.4. Apply pseudo-global tomography to biological sample rabbit femur for local quantitativereconstruction. And have a compare with traditional global reconstruction. The result showsthat this local CT algorithm not only performs well in quantitative local reconstruction of thesample’s local region, but also shows great advantage in resolution. This provides researchreference for applying the local algorithm to the similar sample, and has a significantmeaning for biomedical research.