Monochromatic imaging can provide better contrast and resolution than conventional broadband radiography. In broadband systems, low energy photons do not contribute to the image, but are merely absorbed, while high energy photons produce scattering that degrades the image. By tuning to the optimal energy, one can eliminate undesirable lower and higher energies. Monochromatization is achieved by diffraction from a single crystal. A crystal oriented to diffract at a particular energy, in this case the characteristic line energy, diffracts only those photons within a narrow range of angles. The resultant beam from a divergent source is nearly parallel, but not very intense. To increase the intensity, collimation was performed with polycapillary x-ray optics, which can collect radiation from a divergent source and redirect it into a quasi parallel beam. Contrast and resolution measurements were performed with diffracting crystals with both high and low angular acceptance. Testing was first done at 8 keV with an intense copper rotating anode x-ray source, then 17.5 keV measurements were made with a low power molybdenum source. At 8 keV, subject contrast was a factor of five higher than for the polychromatic case. At 17.5 keV, monochromatic contrast was two times greater than the conventional polychromatic contrast. The subject contrasts measured at both energies were in good agreement with theory. An additional factor of two increase in contrast, for a total gain of four, is expected at 17.5 keV from the removal of scatter. Scatter might be simply removed using an air gap, which does not degrade resolution with a parallel beam.

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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.In addition, post-patient optics, monolithic linearly tapered optics used for "scatter-rejection," were characterized. Measurements included a detailed analysis of optic defects which had been causing poor transmission, only 5 % at 20 keV due to localized glass inclusions. Manufacturing improvements resulted in repeatable transmissions near 50%. These optics result in improved contrast because of scatter transmission of less than 1%.Pre-and/or post-patient polycapillary x-ray optics technology could greatly improve imaging in mammography.

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