The past few decades have seen substantial growth in Additive Manufacturing (AM) technologies. However, this growth has mainly been process-driven. The evolution of engineering design to take advantage of the possibilities afforded by AM and to manage the constraints associated with the technology has lagged behind. This paper presents the major opportunities, constraints, and economic considerations for Design for Additive Manufacturing. It explores issues related to design and redesign for direct and indirect AM production. It also highlights key industrial applications, outlines future challenges, and identifies promising directions for research and the exploitation of AM's full potential in industry.Design, Manufacturing, Additive Manufacturing
To explore the future clinical potential of improved soft-tissue visibility with grating-based X-ray phase contrast (PC), we have developed a first preclinical computed tomography (CT) scanner featuring a rotating gantry. The main challenge in the transition from previous bench-top systems to a preclinical scanner are phase artifacts that are caused by minimal changes in the grating alignment during gantry rotation. In this paper, we present the first experimental results from the system together with an adaptive phase recovery method that corrects for these phase artifacts. Using this method, we show that the scanner can recover quantitatively accurate Hounsfield units in attenuation and phase. Moreover, we present a first tomography scan of biological tissue with complementary information in attenuation and phase contrast. The present study hence demonstrates the feasibility of gratingbased phase contrast with a rotating gantry for the first time and paves the way for future in vivo studies on small animal disease models (in the mid-term future) and human diagnostics applications (in the long-term future).differential X-ray phase contrast | grating interferometer | X-ray imaging O ne of the main shortcomings of existing biomedical X-ray imaging systems is their weak contrast in soft tissue. This limitation can be addressed by phase-sensitive imaging methods that rely on the phase shift that X-rays undergo when passing through matter (1). The resultant refraction angle can be utilized as contrast mechanism in a grating-based interferometer in radiographic (2, 3) and tomographic acquisition mode (4, 5). In a computed tomography scan, quantitative information about the sample's composition can be extracted-i.e., the linear attenuation coefficient μ and decrement of the refractive index δ can be reconstructed (6-8). Because the grating-based phase-contrast imaging method is compatible with X-ray tube sources, when operated as Talbot-Lau interferometer (9), a translation to a clinical application scenario is currently discussed with great enthusiasm in the research community. Recent studies with laboratory X-ray sources have shown excellent imaging results with respect to softtissue contrast (10)(11)(12)(13)(14). In order to explore the envisioned clinical potential, we have developed a first preclinical phase-contrast CT scanner. This development represents an important milestone in the translation of phase-contrast imaging to clinical settings, as all grating-based phase-contrast setups, which are reported in the literature so far, use a rotating sample for tomographic scans. Because this mode of operation is obviously not preferable for intended in vivo animal studies, we have explored with this work the step from rotating sample to rotating gantry. The main challenge in this translation process was mechanical stability regarding the required precise alignment of the X-ray optical components (gratings). Even mechanical movements of either grating of only fractions of a micrometer during gantry rotation already c...
Differential phase contrast X-ray imaging (DPCI) has gained a lot of interest in the past years. It is based on X-ray grating interferometry and the image quality is strongly dependant on the grating quality. Periodic line and space structures with periods in the micron range are required for the source and absorption grating. In case of energies > 30 keV their height should be larger than 100 µm resulting in aspect ratios of more than 100. Deep X-ray lithography and gold electroforming (LIGA technology) is used to fabricate these challenging structures. After resist, design and process optimization gratings with 2.4 µm period have been electroformed up to 120 µm, Visibilities of up to 70% for 29 keV and up to 20% for 52 keV have been achieved for monochromatic synchrotron light. Structures with larger periods could be manufactured up to 200 µm; further increase of the height and the gratings quality is possible yielding to high performance gratings also for high energies.
ZusammenfassungHintergrund. Nach interagierenden Modellen der Entwicklung von frühgeborenen Risikokindern kompensiert ein positives soziales Klima nachteilige Entwicklungslangzeitfolgen.Anhand der Daten aus der bayerischen Entwicklungsstudie bezüglich der kognitiven und Verhaltensentwicklung ehemaliger, sehr unreifer Frühgeborenen wurden die Auswirkungen von medizinischen und sozialen Risikofaktoren untersucht.Die kognitive und schulische Entwicklung waren bei sehr unreifen Frühgeborenen (<32 SSW) eher mit medizinischen als sozialen Faktoren korreliert, bei Kindern mit mittlerem bis niedrigem Risiko war das Gegenteil der Fall.Hochrisikokinder wiesen eine geringere Plastizität des Organismus und eine niedrige Aufholtendenz in frühen Entwicklungsphasen auf. Schlussfolgerung. Die aus den Erfahrungen an vor 30 oder 40 Jahren geborenen Hochrisikokindern entwickelten Modelle können nicht ohne Weiteres auf Hochrisikokinder des 21.Jahrhunderts übertragen werden. Auswirkungen der gefundenen Abhängig-keiten auf frühe Interventionsstrategien und die klinische Versorgung von früh geborenen Risikokindern werden diskutiert. SchlüsselwörterFrühgeborene · VLBW (very low birth weight) · Lernbehinderung · Verhaltensprobleme · Entwicklungspsychopathologie · Risiko · Resilienz Das FrühgeboreneMonatsschr Kinderheilkd 2001 · [Suppl 1] 149:S 53-S 61
The concept of grating-based phase-contrast computed tomography (CT) can be implemented into a compact, cone-beam geometry gantry setup. The authors believe that this work represents an important milestone in translating phase-contrast x-ray imaging from previous proof-of-principle experiments to first preclinical biomedical imaging applications on small-animal models.
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