22 September 2008 Development of polarized and monochromatic x-ray beams from tube sources
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Abstract
The development of sources and optics has allowed the migration of techniques originally developed for synchrotron beam lines to field, industrial and clinical applications. For example, monochromatic beams produced with synchrotron sources are known to give higher contrast for mammography than clinical broadband sources. However, clinical sources with very narrow energy bandwidth, produced for example with flat monochromator crystals, tend to have limited intensity and field of view. Doubly curved crystal x-ray optics can provide intense focused monochromatic fan beams from laboratory x-ray tube sources. These optics are routinely employed in crystallography and x-ray fluorescence, however, careful analysis is required to assess whether the focused beam creates unacceptable divergence and hence poor spatial resolution in imaging. The intensity and resolution of the focused beam were measured and compared to simulation results. The measurements and simulations were in good agreement, allowing for system design to provide the required resolution. High efficiency collimating optics coupled with diffracting crystals also can produce relatively high intensity and resolution. For both methods, monochromatization occurs before the patient, resulting in a potential dose reduction as well as significant measured contrast enhancement. If the diffraction angle is chosen at 90 degrees, a polarized monochromatic beam is produced. While synchrotron sources are naturally polarized, polarized beams have been less accessible for field and clinical applications. Development has begun of polarized beam sources using very low power x-ray tubes coupled to polycapillary optics. The choice of the polarizing and analyzing crystals is a tradeoff between intensity and sensitivity to depolarization effects. Intensity and rocking curve measurements have been performed with matched silicon crystals and graphite crystals.
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Robert Schmitz, Ayhan Bingölbali, Abrar Hussain, C. A. MacDonald, "Development of polarized and monochromatic x-ray beams from tube sources", Proc. SPIE 7077, Advances in X-Ray/EUV Optics and Components III, 70770Y (22 September 2008); doi: 10.1117/12.797278; https://doi.org/10.1117/12.797278
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