Biological samples are frequently stained with heavy metals in preparation for examining the macro, micro and ultra-structure using X-ray microtomography and electron microscopy. A single X-ray microtomography scan reveals detailed 3D structure based on staining density, yet it lacks both material composition and functional information. Using a commercially available polychromatic X-ray source, energy integrating detectors and a two-scan configuration labelled by their energy- “High” and “Low”, we demonstrate how a specific element, here shown with iron, can be detected from a mixture with other heavy metals. With proper selection of scan configuration, achieving strong overlap of source characteristic emission lines and iron K-edge absorption, iron absorption was enhanced enabling K-edge imaging. Specifically, iron images were obtained by scatter plot material analysis, after selecting specific regions within scatter plots generated from the “High” and “Low” scans. Using this method, we identified iron rich regions associated with an iron staining reaction that marks the nodes of Ranvier along nerve axons within mouse spinal roots, also stained with osmium metal commonly used for electron microscopy.
Micro Computed Tomography (micro-CT) of cores is an emerging technology that yields vital information about key rock and fluid properties at pore-scale resolution. Micro-CT imaging results presented to date are encouraging and indicate that this technology has the potential to revolutionize petrophysical analysis and reservoir engineering. The application of micro-CT in petroleum engineering requires reconstructed scan data to be of high and uniform image quality to enable reliable analysis during subsequent segmentation and numerical modeling. This is achievable in existing micro-CT systems using standard circular scan trajectories with non-exact filtered backprojection (FBP) reconstruction, but requires small cone angles to keep cone beam artifacts below detectable limits. We describe the implementation and results of adapting an exact helical FBP reconstruction algorithm (the so-called “Katsevich Algorithm” or KFBP) and data acquisition scheme on a high-performance micro-CT system normally running in circular scan trajectory mode. Side-by-side comparisons of stitched circular scan trajectories with continuous helical scan trajectories on simulated and real rock core data show the throughput advantage of this modality for applications relevant for the petroleum industry keeping equivalent image quality to low cone angle circular scans. The analytical exact helical reconstruction can be performed in quasi-real time leading to instantaneous results. Simulated and experimental results indicate that an imaging throughput improvement of 2-5 times can be achieved employing KFBP-based exact helical reconstruction compared to the standard circle scan trajectory when imaging whole rock cores/plugs that are significantly longer than their diameter.
Purpose: To understand the propagation of electrons through the acceleration gradient of the Xoft micro‐miniature x‐ray source via electrostatic modeling of the fields and x‐ray pinhole camera imaging. Materials and Methods: 1) A 3D model of the source was built using OmniTrak3, and electron trajectories were traced from the hot cathode to the x‐ray producing anode. A finite element model of the filament temperature profile was input to a Richardson‐Dushman thermionic emission/extraction model to determine the electron emission density distribution. Assumptions made were that the field was graded linearly along the length, and that electrical connection between conductive and resistive components was ideal. 2) A ShadoCam4 x‐ray sensitive camera was used to acquire images of sources through a 30 μm pinhole mounted 15 mm from the source. The camera was 105 mm from the pinhole, providing a magnification of 7×. The camera was read out through a USB computer interface. Images were typically acquired over ten second integration times. Results: The actual images showed distinct patterns that were identifiable with model predictions. Structures associated with particular emission locations and launch angles on the filament were clearly observed. Conversely, patterns in the images were explainable in terms of parameters such as the absolute location of the filament. Image patterns which were relatively similar to the nominal had no correlation with measured spatial distribution patterns of the sources, but where there were notable variations in the image patterns it was possible to infer correlations with polar and/or azimuthal measurements. Conclusions: Electron trajectories within the accelerating structure were explored through pinhole imaging and computer modeling, and sensitivities to mechanical tolerances were established that were valuable in setting manufacturing tolerances. This study was funded by Xoft, Inc. 3 Field Precision LLC, Albuquerque, NM. 4 Rad‐icon Imaging Corp, Santa Clara, CA.
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