The current paper considers the applicability of micro-tomographic methods for the investigation of growth mechanisms of metallic tin whiskers. Tin whiskers are metallic fibers that grow spontaneously from lead-free tin-coated surfaces, causing short circuit related issues in electronic devices, therefore making this phenomenon an interesting topic for in-depth analysis. In order to investigate such minuscule structures by X-rays, a tomographic setup employing a directconverting pixel large area detector based on the Timepix readout ASIC is used. Featuring an extraordinary contrast and high dynamic range, these detectors have proven to be powerful tools in the analysis of samples containing fine features of low radiographic absorption.Initial tomographic results reveal fully 3D morphological information on tin whiskers, albeit at lower spatial resolution than by scanning electron microscope (SEM), which is the commonly used method to investigate this phenomenon. However, the additional morphological information obtained by micro-tomography gives additional means of analysis, likely to help understand the underlying growth mechanisms. K: Inspection with x-rays; Computerized Tomography (CT) and Computed Radiography (CR); Detection of defects; X-ray detectors 1Corresponding author.
In mammography the difficult task to detect microcalcifications (≈ 100 µm) and low contrast structures in the breast has been a topic of interest from its beginnings. The possibility to improve the image quality requires the effort to employ novel X-ray imaging techniques, such as phase-contrast, and high resolution detectors. Phase-contrast techniques are promising tools for medical diagnosis because they provide additional and complementary information to traditional absorption-based X-ray imaging methods. In this work a Hamamatsu microfocus X-ray source with tungsten anode and a photon counting detector (Timepix operated in Medipix mode) was used. A significant improvement in the detection of phase-effects using Medipix detector was observed in comparison to an standard flat-panel detector. An optimization of geometrical parameters reveals the dependency on the X-ray propagation path and the small angle deviation. The quantification of these effects was achieved taking into account the image noise, contrast, spatial resolution of the phase-enhancement, absorbed dose, and energy dependence.
In recent years phase-contrast has become a much investigated modality in radiographic imaging. The radiographic setups employed in phase-contrast imaging are typically rather costly and complex, e.g. high performance Talbot-Laue interferometers operated at synchrotron light sources. In-line phase-contrast imaging states the most pedestrian approach towards phase-contrast enhancement. Utilizing small angle deflection within the imaged sample and the entailed interference of the deflected and un-deflected beam during spatial propagation, in-line phase-contrast imaging only requires a well collimated X-ray source with a high contrast & high resolution detector. Employing high magnification the above conditions are intrinsically fulfilled in cone-beam micro-tomography. As opposed of 2D imaging, where contrast enhancement is generally considered beneficial, in tomographic modalities the in-line phase-contrast effect can be quite a nuisance since it renders the inverse problem posed by tomographic reconstruction inconsistent, thus causing reconstruction artifacts. We present an experimentally enhanced model-based approach to disentangle absorption and in-line phase-contrast. The approach employs comparison of transmission data to a system model computed iteratively on-line. By comparison of the forward model to absorption data acquired in continuous rotation strong local deviations of the data residual are successively identified as likely candidates for in-line phase-contrast. By inducing minimal vibrations (few mrad) to the sample around the peaks of such deviations the transmission signal can be decomposed into a constant absorptive fraction and an oscillating signal caused by phase-contrast which again allows to generate separate maps for absorption and phase-contrast. The contributions of phase-contrast and the corresponding artifacts are subsequently removed from the tomographic dataset. In principle, if a 3D handling of the sample is available, this method also allows to track discontinuities throughout the volume and therefore states a powerful tool in 3D defectoscopy.
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