PubMed · 14872212
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Marianne Chulay. 2004. Chulay commentary.. https://doi.org/10.1038/sj.jp.7211039
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The DXAS Calibration computer program provides a quantitative and automated solution to the problem of calibrating spectra from dispersive XAS beamlines. Such spectra, obtained in arbitrary energy units, are calibrated with respect to the absorption features of a supplied reference spectrum, which has been obtained under similar conditions on a calibrated beamline. In addition to basic energy coordinate transformation parameters, DXAS Calibration supplies instrument corrections to compensate for mismatches in instrument response functions between the dispersive and reference beamlines.
The aim of this study has been to explore and verify whether the use of a previously designed Analysis-by-Synthesis algorithm is capable to precisely measuring implant wear. The abrasion of polyethylene particles is seen as the main reason for the loosening of prosthetic components in the hip. It lies in the sub-millimeter range, and precision is a crucial point in wear measurement. In the Analysis-by-Synthesis algorithm, the synthetic X-ray image of the implant is matched to its original X-ray projection. This intensity based approach and the use of X-ray images with their inherent high resolution allow principally precise measurements. Wear has been defined based on the estimated implant parameters and under minimization of the impact of the main sources of error. The latter was theoretically studied in a sensitivity analysis. The use of the algorithm was tested in vitro as well as in vivo. In experimental data, the accuracy and the impact of the pelvic position and orientation were studied. The precision was assessed using dual radiographs of 20 patients with total hip replacement. A standard deviation of 49 microm was found.
Magnetic resonance imaging (MRI) has become increasingly important as an imaging technique in cross-sectional imaging of head and neck diseases. To investigate whether MRI examinations can be performed without risk in patients with metal implants even at higher field strengths, we examined different materials in 7 Tesla MRI. Implants near sensory organs like the middle ear or eye are of particular interest here. Using the 7 Tesla research MRI for small animals, we tested implants made of various metals like titanium, gold, gold/platinum, platinum/iridium, gold-plated silver, PTFE and stainless steel for heating, translocation and rotation according to a standardized protocol. A fiber optic temperature probe measured the heating of the implant before, during and after MRI scanning. None of the implants showed significant heating. The gold-plated stainless steel ventilation tube was the only implant to markedly change its position already in the Petri dish. Of the remaining implants, a trachea support ring, a nose dilatator and the wire from the ventilation tubes moved during vibration of the Petri dish. With exception of two implants, all implants changed positions in the water bath. In the swim test, the gold implants showed the least movement of all the implants. In this study, the properties of the non-ferromagnetic implant materials differed in the 7 Tesla MRI. Stainless steel ventilation tubes, the trachea support ring and the nose dilatator were not suited for the 7 Tesla MRI system, because they changed their position during MRI. In the case of ventilation tubes with a steel wire, the wire should be removed before MRI to prevent injury to the external auditory canal. There was a tendency for the pure gold implants to move less in the 7 Tesla MRI than all other tested materials. General statements cannot be made about the MRI suitability of different implants. Every implant should be individually examined to confirm its definitive MRI compatibility. Particularly, middle ear implants warrant special attention here due to their closeness to the oval window.