Direct plain radiographic methods versus EBRA-Digital for measuring implant migration after total hip arthroplasty.

We aimed to determine whether the precision and sensitivity of migration measurements after total hip arthroplasty (THA) using direct plain radiographic techniques could be made comparable to those of digital methods (EBRA-Digital; University of Innsbruck, Innsbruck, Austria) by careful control of radiographic technique and use of modern measuring tools. Precision was examined by analysis of consecutive radiographs taken after repositioning in 20 patients after hybrid THA. The precision (95% confidence interval) of measurements for cup migration using direct methods was +/-1.11 to 3.07 mm (x-axis) and +/-1.28 to 1.92 mm (y-axis). The precision of EBRA for cup measurements was +/-1.00 mm (x-axis) and +/-0.82 mm (y-axis). The precision of stem y-axis migration measurements was +/-1.12 to 6.91 mm using direct methods and +/-0.80 mm using EBRA. Migration of the stem (1.53 mm subsidence; P<.01) and the cup (0.53 mm cranial migration, P<.05) was detected using EBRA in 10 patients followed for 6 months after hybrid THA, but significant migration was not detectable using the most precise of the direct methods. Careful measures to standardize plain radiographs improve precision of direct radiographic measurements; however, their long-term sensitivity remains inferior to methods that employ quality control and measurement algorithms to measure migration from digitized radiographs.

Holographic optical elements recorded in silver halide sensitized gelatin emulsions. Part 2. Reflection holographic optical elements.

Silver halide sensitized gelatin (SHSG) holograms are similar to holograms recorded in dichromated gelatin (DCG), the main recording material for holographic optical elements (HOEs). The drawback of DCG is its low energetic sensitivity and limited spectral response. Silver halide materials can be processed in such away that the final hologram will have properties like a DCG hologram. Recently this technique has become more interesting since the introduction of new ultra-fine-grain silver halide (AgHal) emulsions. In particular, high spatial-frequency fringes associated with HOEs of the reflection type are difficult to construct when SHSG processing methods are employed. Therefore an optimized processing technique for reflection HOEs recorded in the new AgHal materials is introduced. Diffraction efficiencies over 90% can be obtained repeatably for reflection diffraction gratings. Understanding the importance of a selective hardening process has made it possible to obtain results similar to conventional DCG processing. The main advantage of the SHSG process is that high-sensitivity recording can be performed with laser wavelengths anywhere within the visible spectrum. This simplifies the manufacturing of high-quality, large-format HOEs, also including high-quality display holograms of the reflection type in both monochrome and full color.