Monochromatic x-ray imaging with polycapillary and doubly-curved crystal optics.

摘要

Contrast can be enhanced in radiographic imaging with the use of monochromatic radiation compared to conventional broadband source. Monochromatic beam radiation can be produced with synchrotron sources or with conventional sources by diffraction off of monochromaor crystals, the former is not available for medical applications and the latter gives a low monochromatic intensity for imaging.;With the use of x-ray optics, monochromatic intensities from conventional sources could be increased. Two types of optics were investigated, polycapillary and curved crystal. First, a monochromatic imaging system was designed with a low power source, polycapillary collimating optic and flat monochromatizing crystal. The choice of crystal is a trade-off between intensity and resolution. For all crystals, the subject contrast was a factor of two better than for conventional systems, in agreement with theoretical values.;To predict resolution and intensity for monochromatic imaging, a theoretical 3-dimension resolution calculation was developed. The angular resolutions for in-plane and out-of-plane directions were different and the out-of-plane resolution is not dependent on the energy. The measured resolutions were in agreement with theoretical values, as was the measured intensity.;As an alternative to polycapillary optics, doubly curved crystal (DCC) optics can be used to collect and focus monochromatic x rays from a divergence source. Higher monochromatic intensity can be obtained than with a flat crystal. The choice of the imaging distance to the DCC optics is a trade-off between intensity and resolution. Measurements for image performance were also performed. Contrast enhancement is a factor of about 2.;A refractive index imaging system was also designed with a combination of a source, a collimating optics and double crystal diffraction. The imaging performances of this system were measured. The in-plane resolution was slightly improved. The refractive contrast is much better than the subject contrast.;For both methods, monochromatization occurs before the patient, resulting in a potential dose reduction as well as significant measured contrast enhancement. The doubly curve crystal system is better than polycapillary optics system.