In vitro synchrotron-based radiography of micro-gap formation at the implant–abutment interface of two-piece dental implants

Micro-radiography using hard X-ray synchrotron radiation is the first potential tool to allow an evaluation of the mechanical behavior of the dental implant–abutment complex during force application, thus enabling the enhancement of the design of dental implants which has been based on theoretical analysis to date

Modeling of negative Poisson’s ratio (auxetic) crystalline cellulose Iβ

Energy minimizations for unstretched and stretched cellulose models using an all-atom empirical force field (Molecular Mechanics) have been performed to investigate the mechanism for auxetic (negative Poisson’s ratio) response in crystalline cellulose Iβ from kraft cooked Norway spruce. An initial investigation to identify an appropriate force field led to a study of the structure and elastic constants from models employing the CVFF force field. Negative values of on-axis Poisson’s ratios nu31 and nu13 in the x1-x3 plane containing the chain direction (x3) were realized in energy minimizations employing a stress perpendicular to the hydrogen-bonded cellobiose sheets to simulate swelling in this direction due to the kraft cooking process. Energy minimizations of structural evolution due to stretching along the x3 chain direction of the ‘swollen’ (kraft cooked) model identified chain rotation about the chain axis combined with inextensible secondary bonds as the most likely mechanism for auxetic response

Fresnel propagated submicrometer x ray imaging of water immersed tooth dentin

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Optimization Based Evaluation of Grating Interferometric Phase Stepping Series and Analysis of Mechanical Setup Instabilities

The diffraction contrast modalities accessible by X-ray grating interferometers are not imaged directly but have to be inferred from sine-like signal variations occurring in a series of images acquired at varying relative positions of the interferometer’s gratings. The absolute spatial translations involved in the acquisition of these phase stepping series usually lie in the range of only a few hundred nanometers, wherefore positioning errors as small as 10 nm will already translate into signal uncertainties of 1–10% in the final images if not accounted for. Classically, the relative grating positions in the phase stepping series are considered input parameters to the analysis and are, for the Fast Fourier Transform that is typically employed, required to be equidistantly distributed over multiples of the gratings’ period. In the following, a fast converging optimization scheme is presented simultaneously determining the phase stepping curves’ parameters as well as the actually performed motions of the stepped grating, including also erroneous rotational motions which are commonly neglected. While the correction of solely the translational errors along the stepping direction is found to be sufficient with regard to the reduction of image artifacts, the possibility to also detect minute rotations about all axes proves to be a valuable tool for system calibration and monitoring. The simplicity of the provided algorithm, in particular when only considering translational errors, makes it well suitable as a standard evaluation procedure also for large image series

Using measurements of the spatial SNR to optimize phase contrast X-ray imaging

X-ray phase contrast imaging is a measurement task which is challenging to optimize, because many physical effects determine signal and noise. If we describe the detail visibility by the spatial signal to noise ratio, SNR(u), we can optimize an imaging setup by maximizing its SNR(u). We propose a measurement method for the spatial SNR which is suitable for this purpose. It consists of measuring a series of images from which the spatial SNR is calculated. This allows a convenient and exact optimization of the SNR that does not rely on theoretical simplifications and is not specific to X-ray imaging. We demonstrate the measurement method for the example of choosing the optimal geometrical magnification for cone-beam inline X-ray phase contrast. Additionally, we propose the use of a known signal reconstruction method - the Wiener Deconvolution - to improve the detail visibility by post-processing images within the limits given by the measured SNR(u). As the SNR(u) give s the degree of this improvement, we derive a measure for the effective spatial resolution from the SNR(u)

Fresnel propagated imaging for the study of human tooth dentin by partially coherent x ray tomography

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