Polycapillary x-ray optics can be used as pre- or post-patient optics to design mammographic imaging systems with higher resolution, greater contrast, and a lower absorbed patient dose. A multi-fiber collimating prototype optic, used as pre-patient beam shaper, provides 39% transmission efficiency at 17.5 keV, good uniformity, and only 3.9 mrad divergence. Experimental optics characterization results are compared with detailed computer simulations including analysis of optical defects such as channel waviness and bending. The collimating optic was used to produce monochromatic radiation by diffracting from a silicon crystal. The monochromatic contrast, measured at 8 keV with a polypropylene phantom, was 5 times greater than the measured polychromatic contrast.
Polycapillary fibers and a prototype collector for high energy x rays with a 2 m focal length have been fabricated and characterized. Measurements of a prototype collector, performed in collimating mode, show that the optic has high transmission, good uniformity, and small exit divergence. The transmission as a function of energy was analyzed using an extended single fiber geometrical optic simulation and the result shows that the simulation fits the data fairly well. Scatter transmission and contrast enhancement were measured in focusing mode using a parallel beam input.
Polycapillary collimating optics collect x rays produced by a point source over a wide solid angle (as large as 10 - 15 degrees cone angle) and a large energy bandwidth, and provide a quasi-parallel beam with a small divergence (a few milliradians). These optics are emerging as important tools in materials analysis, medical imaging, x-ray lithography and protein crystallography. Results of measurements carried out on three multi-fiber polycapillary x-ray collimating optics are described. Parameters influencing efficient employment of these optics, such as transmission versus photon energy, output beam uniformity, and divergence are characterized. Monte Carlo simulations based on ray-tracing geometrical optics are compared with experimental performances to extract additional information.
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