Optimising XCT acquisition speed for image quality and dimensional measurements

Acquisition speed is an important consideration for the use of XCT in industry and research applications. A literature review to examine the acquisition parameters with the greatest impact on the speed showed that authors typically use a lower number of projections in faster XCT. The operator and their acquisition parameter selection have a significant impact on the resulting image quality. Different image quality metrics have been used to access acquisition parameters among which, for the first time, anisotropy. For CFRPs a low voltage and a long SDD provided the best contrast between the polymer and the resin, which have very similar absorption coefficients. The effect of acquisition parameters on image quality metrics and dimensional measurements was investigated; anisotropy and SNR showed a better correlation to the dimensional measurements than the other investigated parameters. There is no significant measurement improvement when increasing the number of projections or the averages and reducing the projections or binning minimally affected the measurement accuracy. The current standard of measurement obtained with XCT and scanning practices were investigated by a round robin studies on metrology systems and a comparison between a metrology and non-metrology XCT system was made. For the first time systems have been compared using the same objects. The results showed that all tested metrology XCT systems were capable to achieve sub-voxel measurements but their MPE statements were too tight. The comparison between the metrology and non-metrology XCT systems showed applying voxel scaling makes the results comparable to metrology graded systems especially for larger magnifications (<0.3 voxel). Finally early results are presented that show first time use of improved micromanufacturing techniques (PFIB, two-photon polymerisation and electro chemical deposition) for 3D objects to measure spatial resolution with equally spaced features down to 5 _m in both plastic and metal. Where current objects are usually 2D or 3D with rather large features, these objects can be used to measure the resolution in the reconstructed volume on the required magnitude

Relationship between bullet diameter and bullet defect diameter in human calvariums

Existing literature on the relationship between bullet diameter and bullet defect diameter in the human calvarium is summarized and discussed. The hypothesis, derived from the literature, that bullet deformation influences bullet defect diameter was studied in a small controlled experiment. The mean defect size caused by non-deforming projectiles was found to be smaller than the mean defect size caused by deforming projectiles of equal original mass and size. The p value of the difference between the two means, measured in two different ways, was found to be 0.002 for both in a Mann-Whitney U test and was significant if the confidence level is set at 5%

Performance testing of dimensional X-ray computed tomography systems

X-ray Computed Tomography (XCT) has become a common tool for dimensional analysis as it allows for non-destructive internal and external measurements. Manufacturers often specify the accuracy of dedicated metrology XCT systems as a maximum permissible error (MPE) statement determined using workpieces, test lengths and positions that are significantly different between manufacturers. The VDI/VDE 2630-1.3:2011 guideline provides specification and respective test methods to verify performance against these MPE statements and has been applied in this study to evaluate four different commercial XCT systems in a uniform way. For this examination a multi-sphere test object was developed that explicitly complies with these guidelines and maximises the use of the whole measurement volume, which has then been scaled to test both high and low magnifications. The study consisted of two parts: scans according to a protocol to allow for a fair comparison between all the systems and free scans where manufacturers could show the best capabilities of their system. With these particular objects no system complied with its own MPE statement, however sub voxel accuracies were found. The maximum error in terms of voxels ranged between 0.16 voxel to 0.43 voxel for low magnification (voxel size of 100 μm) and 0.49 voxel to 0.82 voxel for high magnification (voxel size of 14 μm) between systems. This indicates the need for greater standardisation and transparency on how accuracy statements are determined, and more directed protocols for testing the performance of a system. In particular due to the extreme range of measurement volumes and voxel sizes/resolutions XCT are capable of, it is demonstrated that it maybe reasonable to consider an MPE dependent on voxel size

Review of high-speed imaging with lab-based x-ray computed tomography

X-ray computed tomography (CT) is frequently used for non-destructive testing with many applications in a wide range of scientific research areas. The difference in imaging speeds between synchrotron and lab-based scanning has reduced as the capabilities of commercially available CT systems have improved, but there is still a need for faster lab-based CT both in industry and academia. In industry high-speed CT is desirable for inline high-throughput CT at a higher resolution than currently possible which would save both time and money. In academia it would allow for the imaging of faster phenomena, particularly dynamic in-situ testing, in a lab-based setting that is more accessible than synchrotron facilities. This review will specifically highlight what steps can be taken by general users to optimise scan speed with current equipment and the challenges to still overcome. A critical evaluation of acquisition parameters across recent high-speed studies by commercial machine users is presented, indicating some areas that could benefit from the methodology described. The greatest impacts can be achieved by maximising spot size without notably increasing unsharpness, and using a lower number of projections than suggested by the Nyquist criterion where the anecdotal evidence presented suggests usable results are still achievable

Strong spin-orbit interaction and gg-factor renormalization of hole spins in Ge/Si nanowire quantum dots

The spin-orbit interaction lies at the heart of quantum computation with spin qubits, research on topologically non-trivial states, and various applications in spintronics. Hole spins in Ge/Si core/shell nanowires experience a spin-orbit interaction that has been predicted to be both strong and electrically tunable, making them a particularly promising platform for research in these fields. We experimentally determine the strength of spin-orbit interaction of hole spins confined to a double quantum dot in a Ge/Si nanowire by measuring spin-mixing transitions inside a regime of spin-blockaded transport. We find a remarkably short spin-orbit length of $\sim$65 nm, comparable to the quantum dot length and the interdot distance. We additionally observe a large orbital effect of the applied magnetic field on the hole states, resulting in a large magnetic field dependence of the spin-mixing transition energies. Strikingly, together with these orbital effects, the strong spin-orbit interaction causes a significant enhancement of the $g$-factor with magnetic field.The large spin-orbit interaction strength demonstrated is consistent with the predicted direct Rashba spin-orbit interaction in this material system and is expected to enable ultrafast Rabi oscillations of spin qubits and efficient qubit-qubit interactions, as well as provide a platform suitable for studying Majorana zero modes

Effective X-ray micro computed tomography imaging of carbon fibre composites

Compression moulding of carbon fibre sheet moulding compounds is an attractive manufacturing method for composite structures. Investigating fibre orientation, defects and voids in these components is important for quality control. X-ray computed tomography is a non-destructive imaging method used on different kind of sheet moulded compound to identify such issues, but it is still a challenge on carbon fibre sheet moulding compound due to the similarities in density of the carbon fibres and polymer matrix. This study aims to determine the best-practice for optimising acquisition parameters for imaging carbon fibre composites. The first experiment assessed the effect of excess material on a region of interest scans was investigated, a common acquisition approach to maintain resolution to resolve fibres. This showed in this specific case the scan quality decreases when surrounding material reaches approximately 75% of the field of view indicating region of interest scanning is feasible. In the second experiment seven X-ray computed tomography parameters were systematically evaluated to optimise image quality for observing the structures and defects, resulting in 168 scans. The results indicate that the source–detector distance and the source voltage have the most significant impact, where users should always consider maximising this distance and minimising voltage for the best image quality

Adhesion formation after surgery for locally advanced colonic cancer in the COLOPEC trial

This study investigated the impact of laparoscopic or open resection of locally advanced colonic cancer on the incidence and severity of adhesions evaluated by laparoscopy at 18 months, primarily intended to evaluate peritoneal recurrence. Open surgery was identified as an independent risk factor for adhesions, but not intraperitoneal chemotherapy.</p