Fabrication and replication of high efficiency blazed gratings with grayscale electron beam lithography and UV nanoimprint lithography

In a waveguide-type display for augmented reality, the image is injected in the waveguide and extracted in front of the eye appearing superimposed on the real world scene. An elegant and compact way of coupling these images in and out is by using blazed gratings, which can achieve high diffraction efficiencies, thereby reducing stray light and decreasing the required power levels. This study investigates the fabrication of blazed gratings with grayscale electron beam lithography and the subsequent replication of the realized 3D grating structures in a polymer material with ultraviolet nanoimprint lithography. As such, diffractive elements are realized on a waveguide sheet, with very good control over the dimensions and the profile of the printed features. Blazed gratings are designed for green light (λ= 543 nm) and a diffraction angle of 43°. Making use of a PMMA resist and by carefully optimizing the electron-beam parameters, electron dose distributions and development step, blazed gratings with a pitch of 508 nm and a fill factor of 0.66 are achieved. Finally, a master is realized with two blazed gratings, 3 cm apart, which are replicated using ultraviolet nanoimprint lithography onto a waveguide sheet. The in- and outcoupling of an image through these two blazed gratings is shown, appearing sharp and non-distorted in the environment, and a throughput efficiency of 17.4% is confirmed

Bacteriostasis testing on allograft tissue inoculated in Wilkins-Chalgren broth

Tissue banks culture tissue specimens to confirm the absence of viable micro-organisms after decontamination with antibiotics. It is possible that antibiotic residues attached to decontaminated tissue are introduced into enrichment culture media. These could have an inhibitory effect on the culture results and generate false-negative results. Our aim was to detect bacteriostasis in Wilkins-Chalgren broth inoculated with bone and tendon remnants. These remnants had been soaked in a solution containing gentamicin as part of the tissue-processing procedure. We used the United States Pharmacopeia method for bacteriostasis testing with gentamicin-susceptible Pseudomonas aeruginosa American Type Culture Collection (ATCC) 15442, Staphylococcus aureus ATCC 6538, Bacillus subtilis ATCC 6633 as test strains, and gentamicin-resistant Candida albicans ATCC 90029 as control. The residual gentamicin concentration in the broths was determined and gentamicin-soaked tissue was placed on Mueller-Hinton agar inoculated with a staphylococcal suspension. Bacteriostasis was present in 53-75% of the reference test strains. Tendon remnants had a significantly higher rate of bacteriostasis (85%) than bone remnants (28%). Broths inoculated with tendon remnants had the highest residual gentamicin concentrations.status: publishe

Short- and long-term bacterial inhibiting effect of high concentrations of glycerol used in the preservation of skin allografts

Human skin allografts are important in the treatment of severe burns. Transplantation of skin allografts can cause bacterial transmission. Glycerol in higher concentrations is an appropriate storage medium for allograft cadaver skin and has been attributed an antimicrobial effect. We investigated this effect in more detail. First, the minimal inhibitory concentration of glycerol was determined for 13 bacteria and 1 yeast. This gives an indication about an immediate (20h of incubation) antibacterial effect of glycerol. Second, effect of glycerol in the long-term was studied. Therefore, the survival time was determined for 11 different bacteria suspended in different concentrations of glycerol (50% and 85%) and incubated at three temperatures (4, 24, and 36 degrees C). The minimal inhibitory concentration exceeded 256microg/mL, thus glycerol had no direct inhibitory effect. In contrast, a long-term antimicrobial effect was present and more pronounced at higher concentrations of glycerol and higher temperatures of incubation. The mean survival time of Pseudomonas aeruginosa strains in glycerol 85% at 24 degrees C was 2.6 days, 14.7 days for the tested staphylococci and 29.6 days for three vegetative Bacillus species. In conclusion, microbial safety of glycerol-preserved skin can be increased by preserving skin allografts for some weeks at room temperature.status: publishe

Antimicrobial susceptibility of coagulase-negative staphylococci on tissue allografts and isolates from orthopedic patients

Allograft infection occurs at a rate not different from that of similar procedures with large allografts or sterilized prosthetic devices and is usually caused by coagulase-negative staphylococci (CNS). CNS are feared for their limited antimicrobial susceptibility. We aimed at investigating this risk. CNS were isolated from 260 of 1461 allograft tissue grafts and compared with 384 consecutive clinical isolates from a general orthopedic population (258 patients). The CNS were identified and examined for their susceptibility to nine antibiotics used in routine practice. Staphylococcus epidermidis was the most commonly identified (35%) and the most resistant species of the allograft isolates. Comparing the overall antibiotic susceptibility patterns, clinical pathogens were significantly more resistant to six of the nine antibiotics (p < 0.01), namely penicillin, oxacillin, erythromycin, clindamycin, ofloxacin, and gentamicin. In conclusion, massive allograft infection is a well-known life-threatening surgical risk. However, we did demonstrate that allograft-related in contrast to orthopedic clinics-related CNS, are susceptible to commonly used first and second line antibiotics. (c) 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 2007.status: publishe

Claw sign in fetal thymic masses

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Reliability of MR-based posterior fossa and brain stem measurements in open spinal dysraphism in the era of fetal surgery

BACKGROUND AND PURPOSE: Fetal MR imaging is part of the comprehensive prenatal assessment of fetuses with open spinal dysraphism. We aimed to assess the reliability of brain stem and posterior fossa measurements; use the reliable measurements to characterize fetuses with open spinal dysraphism versus what can be observed in healthy age-matched controls; and document changes in those within 1 week after prenatal repair. MATERIALS AND METHODS: Retrospective evaluation of 349 MR imaging examinations took place, including 274 in controls and 52 in fetuses with open spinal dysraphism, of whom 23 underwent prenatal repair and had additional early postoperative MR images. We evaluated measurements of the brain stem and the posterior fossa and the ventricular width in all populations for their reliability and differences between the groups. RESULTS: The transverse cerebellar diameter, cerebellar herniation level, clivus-supraocciput angle, transverse diameter of the posterior fossa, posterior fossa area, and ventricular width showed an acceptable intra- and interobserver reliability (intraclass correlation coefficient > 0.5). In fetuses with open spinal dysraphism, these measurements were significantly different from those of healthy fetuses (all with P < .0001). Furthermore, they also changed significantly (P value range = .01 to < .0001) within 1 week after the fetal operation with an evolution toward normal, most evident for the clivus-supraocciput angle (65.9 ± 12.5°; 76.6 ± 10.9; P < .0001) and cerebellar herniation level (-9.9 ± 4.2 mm; -0.7 ± 5.2; P < .0001). CONCLUSIONS: In fetuses with open spinal dysraphism, brain stem measurements varied substantially between observers. However, measurements characterizing the posterior fossa could be reliably assessed and were significantly different from normal. Following a fetal operation, these deviations from normal values changed significantly within 1 week.status: publishe

Incidental finding of developmental venous anomaly on fetal MRI

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Abstracts 40th Post Graduate Course & 54th Annual Meeting of the European Society of Paediatric Radiology (ESPR)

status: Published onlin

11C-labelled PIB analogues as potential tracer agents for in vivo imaging of amyloid beta in Alzheimer's disease

Pittsburgh Compound-B (PIB) is currently being evaluated clinically for in vivo visualization of amyloid plaques in patients with Alzheimer's disease (AD). We have synthesized three structural isomers of 6-hydroxy-2-(4'-aminophenyl)-1,3-benzothiazole, performed radiolabelling with carbon-11 and investigated their in vivo and in vitro properties. Specific binding to amyloid plaques was demonstrated in vitro using post-mortem brain homogenates of AD patients, transgenic AD mice brain sections and postmortem human AD brain sections. In normal mice, initial brain uptake (at 2 min p.i.) was high and was followed by a fast wash-out. The three structural analogues have a high potential as tracer agents for in vivo visualization of amyloid plaques in AD patients. (C) 2008 Elsevier Masson SAS. All rights reserved.status: publishe