The feasibility of on-axis synthetic near-field amplitude holograms for three-dimensional display applications is demonstrated. An iterative optimization algorithm is used that generates an object-dependent diffuser that utilizes the phase and, to some extent, amplitude freedoms in the reconstruction plane. The discrimination between twin images and undiffracted terms is thus improved. The on-axis approach presents important advantages: a low coherence requirement for the illuminating source, a lower spacebandwidth and higher viewing angle than with the off-axis alternatives. Defocusing and parallax are experimentally attained with an extended white-light source and a lensless setup.
27 cemented stems were implanted in fresh-frozen human cadaver femora with third generation antegrade cementing technique and with prechilled vacuum-mixed and pre-pressurized Palacos R bone cement. 3 groups with different implantation techniques were compared according to the achieved cement mantle thickness distribution. Group 1 (modified stem fixation): 7 canulated stems inserted over guidetubes that were fixed in distal synthetic plugs (3 Willert CF-30 and 4 flanged Charnley stems). The guidetubes served simultaneously for stem centralization and evacuation of the intramedullary cavity. Group 2: 12 stems with distal centralizers with fins (4 flanged Charnley, 8 anatomic cemented AC), and Group 3: 8 stems without centralizer (4 Willert CF-30 and 4 flanged Charnley). For analysis, each femur was cut into mean 25 cross-sections (range, 22 -31). Contact radiographs were taken and digitized with a sampling distance of 0.12mm (204.8 dpi). Using a custommade computer program (FemStat 1.001), the cement mantle thickness was determined at mean 650 implant surface points per cross section. Results: The percentage of critical cement mantle thickness was lower for the canulated stems with guidetube. Here 14.1 % of the measurements were smaller than 2mm. For the stems with distal centralizer and without centralizer this was 28.3 % and 28.2 % (p = 0.003 and p = 0.002, U-test). Cement mantles smaller than 1mm were also reduced for group 1 (2.8 % compared with 4.7 % and 7.5 %) but this was not significant (p = 0.384 and p = 0.094). The stems without centralizers had only slightly inferior cement mantles if compared to stems with distal centralizers with fins (for < 2mm p = 0.571, for < 1mm p = 0.305). Comparing different cementing techniques for one constant type of prosthesis (Charnley) the canulated stems with guide tubes provided a significantly better cement mantle thickness than the stems with distal centralizers (for < 2mm 10.3 % compared with 26.6 %, p = 0.029; for < 1mm 1.5 % compared with 3.4 %, p = 0.343). Distal centralizers failed, as the intramedullary cavity is elliptic in cross section and the gaps between the wings caused malposition. For all stems in group 3 improvement of the cement mantle thickness was predominantly achieved in the distal and middle third of the femur. Conclusion: The implantation technique with canulated stems inserted over a guidetube allows superior stem positioning leading to a more favourable cement mantle.Keywords: Hip arthroplasty, centralizer, cement, computer analysis 27 zementierte Hüftendoprothesen wurden in humane Autopsiefemora mit einer antegraden Zementiertechnik der dritten Generation implantiert. Vorgekühlter und vorkomprimierter Palacos-RKnochenzement wurde verwendet. Drei Gruppen mit verschiedenen Implantationstechniken wurden hinsichtlich der erreichten Zementmanteldicken-Verteilung untersucht. Der prozentuale Anteil der Messungen mit kritischem Zementmantel war bei den kanülierten Schäften (Gruppe 1) signifikant kleiner als bei den anderen Gruppen. Hier ergaben nur insg...
The familiar optically recorded rainbow hologram is frequently used to produce color holograms. It is simple to compute the corresponding synthetic hologram structures, which would require no recording process and would be capable of displaying virtual three-dimensional objects. It is difficult, however, to materialize the computed structures because of the high space-bandwidth product required. To find a way around this problem we used a set of three computer-generated holograms as master holograms for an optical recording process in which each master hologram contains information about a different color. This reduces the space-bandwidth product requirements for the synthetic structures to convenient values.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.